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U S Bepasment of Camrnerce 5285 Part Royal Raaa, Springfield, Virginia 22151 Price Printed Copy $3 00.Microfiche $0.95 This report was prepared as an account of w o r k sponsored by the U n i t e d States Goverlment. Neither the United States nor the United States Aromic Energy Commrssion, nor any of their employees, nor any of their contractors, subcontractors, or their emp'eyees, makes any warranty. express or implied. or assumes any legal Irabdity or respansibrlity far the accuracy, completeness OF usefulness of any ivforrnatmn, apparatus. product OF process disclosed, or represents that i t s use w o u l d net infringe privately owned rights

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ORNL-4812 UC-80 - R e a c t o r Technology

MOLTEM-SALT REACTOR P R O G U N

THE DEVELOPMENT STATUS OF MQLTEM-SALT BREEDER REACTORS

XiI. W. Rosenthal, Program D i r e c t o r P. N. Haubenreich, Associate D i r e c t o r R. B. Briggs, A s s o c i a t e D i r e c t o r

August: 1972

OAK RIDGE KATIQNAL LABOMTOKY Oak R i d g e , Tennessee 37830 o p e r a t e d by U N I O N CARBIDE CORPORATION

f o r the E . S . ATOMIC

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ABSTRACT Molten-salt reactor technology, under development since 1947, has led t o a concept of a high-temperature, thermal-neutron breeder reactor that operates on the t h o ~ i u m - ~fuel ~ ~ Ucycle. A connected processing plant that continuously removes protactinium and fission products from the fuel salt is a b a s i c feature of the system. The success of the Molten-Salt Reactor Experiment that was operated between 1965 and 1969, the development of a new processing method that allowed simplification of the breeder design, and the potential breeding performance, economfcs, and safety of the concept, are cited i - n this report as arguments for the continued development of MSBR's. The report reviews the status of the technology, identifies further development needs f o r an MSBR, and gives the program staff's assessments of the uncertainties and the likelihood of success. Separate. chapters are devoted t o reactor physics, chemistry, graphite, reactor metals, reactor eomponents and systems, c e l l s and building, control and instrumentation, fuel processing, maintenance, design studies, and environmental effects and safety. Keywords: review, molten salts, reactors, breeding, development, design, maintenance, safety, chemistry, processing, a l l o y s , graphite.

CONTENTS Chapter 1.

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. .. . ......................... . . . . . .. and the Alternatives . . - . . .. ... . ~eactor~ h y s f c sana F ~ cycles ~ I . . F u e l and Cookant Chemistry . .. . Graphite .. -. . . . Materials f o r Salt-Containing Vessels and Piping .. Reactor Components and Systems . . . . C e l l s , B u i l d i n g s , and Containment . Instrumentation and Controls . . ... . . Fuel Processing . . . . . . Maintenance .. .. . . . Design Studies and Capital Cost Estimates . . Environmental Effects and Safety . . Future Development Program . ... . The Incentives for MSBR Development .. . Fuel Utilization . . . .

INTRODUCTION, S W R Y , A m CONCLUSIONS * Backgroun$ Features of t h e S i n g l e - P l u i d Breeder Reactor The Processing P l a n t FOP the Single-Fluid Breeder Nuclear and Economic Performance of t h e Breeder The Status of Development, the f i j o r Uncertainties, a

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DESIGK CONCEPT OF THE SINGLE-FLUID MSBR omh, Reference Design * * * Objectives * O r e Csnservatisn * * PswerCost. * * * S a f e t y and Environmental C o n s i d e r a t i o n s Technical F e a s i b i l i t y * s General e ~ ~ ~ s~f et h p e st i n g i e - n u i a weeder Features of the Referenee Design Alternatives t o t h e Reference Design Ebasco V a r i a t i o n s f r o m QRXL Design Low-Power-Density Core References f o r Chapter 3 D

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.. .. . . . . . - . . . . .. .. - . . . SaltSamples.. ... .. - . Deposition . .. . . . . . GasSamples . . ~ . . . ~ . . . . . . . f . . . . . .. . NobleMetals Salt-Borne .. . . .. . Niobium . - . . * . . . - Gas-Borne . . ... .. . . Deposition on Graphite and Hastelloy N . . . Iodine EvaLrnation . . . . . .. . . . . . . Futurework Coolant Salts ... .. .. . Basis f o r Choice of Composition . .. - . Present Status of FHuoroborate Chemistry . . Phase Behavior - . . . . Behavior w i t h Hydroxide Ion . . . Physical Properties . . . . . Compatibility w i t h Hastelloy N . . .. Interactions with Steam . . . .... . Interactions with Fuel S a l t . . .Purification of Fluoroborate Mixtures . .. Radiation and Stability .. .... . Evaluation and Summary of Needed Work .. . Analytical Chemistry .. . . . Requirements . . . . . . . . . . ... . Experience . .

Fission Product. Behavior General.. . Major Groups and Y i e l d s Stable Salt-Soluble P l u o r ~ i d e s . e

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Pump Experience Short-Shaft Bump Long-Shaft Pump I n d u s t r i a l Experience and I n t e r e s t S t a t u s of Pump Technology = S c a l i n g up Pump C a p a c i t y , Desi Fabrication Long-Shaft Pump P o t e n t i a l Improvements I n d u s t r i a l Involvement E f f e c t s of U n c e r t a i n t i e s S a l t Pump Development Requirements Evaluation Coolant System Descriptisn E x p e r i e n c e w i t h Coolant S a l t s S t a t u s s f F l u s r o b o r a t e Coolant Technology U n c e r t a i n t i e s i n Use of F l u o r o b o r a t e F u r t h e r Development Work Cover G a s A d d i t i o n t o and Removal from thePumpBowl.. * * * * C o r r o s i o n Product D e p o s i t i o n Mist C o n t r o l on-Line Analysis CoolantLeah Evaluation Heat Exchangers Requirements and C r i t e r i a f o r t h e Brimary Heat Exchangers and S t e a m Generator e

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.. ... PLANT CONTROL AND ENSTKUMENTATXON .. Requirements and Current Concepts . . . . . Systems f o r N o r m a l Operation . .. . Emergency S y s t e m s . . ...- . . InยงtrUlTl@lltatiQn . . . . .. Features Peculiar to XSBR .. .. Experience with the MSRE: and Other Facilities Control Analyses .. . .. .. Computer Models . . .. ... A n a l y s i s of Steady-State Conditions . . . A n a l y s i s of Transient Behavior ... Accident Analyses . ..... .. ... Reactivity Control . . . ... .. . Instrumentation . . . ... . . .. High-Temperature Flux Sensors . .. . Process Instrumentation ..... ... Rod Drives . . . * . . * . . Salt Throttling Valves . . . ... Digital Computer Application f o r Control and BataHandling . .. .. . Chemical P l a n t Instrumentation and Control . . Uncertainties and Alternatives . . . Evaluation . . . . . . . .... .... References f o r Chapter 16 . . . .... . . Status and Uncertainties Evaluation

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ENVIRONPENTAL EFFECTS AND SAFETY General C o n s i d e r a t i o n s C h a r a c t e r i s t i c s o f Reference-Design MSBR Environmental E f f e c t s of Normal Operation Nuclear S a f e t y Radionuclide Decay H e a t i n g I n t e r a c t i o n o f Materials COrrQSiOn Coolant S a l t H n t e r a c t i o n s Engineered S a f e t y F e a t u r e s S i t i n g Considerations T r a n s p o r t a t i o n During C o n s t r u c t i ~ n T r a n s p o r t a t i o n During O p e r a t i o n Effluents * . * Radionuclide I n v e n t o r y Design-Basis Accident e Decommissioning Summary Experience and Knowledge Containment I n s t r u m e n t a t i o n and C o n t r o l S a l t Handling Uranium Behavior + Fission-Product Behavior K i n e t i c Behavior Furtherwork. Evaluation.... * . . . References f o r Chapter 1 4 a

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Introduction Primary Systems Layout and S t r u c t u r a l Design Background and S t a t u s S e n s i t i v i t y t o Uncertainties F u t u r e Work Evaluation Design Methods - Cudes and S t a n d a r d s Background = Status r Sensitivity t o Uncertainties F u t u r s Work * Evaluation + C a p i t a l Costs Background and S t a t u s Sensitivity t o Uncertainties Evaluatiun = Conclusions References f o r Chapter 2.3

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1. INTRODUCTION, StJNMAKY, AND CONCLUSIOKS I n t h e a u t h o r i z a t i o n r e p o r t [I] on t h e Atomic Energy Commission's programs f o r FU-1973, t h e J o i n t Committee on Atomic Energy e x p r e s s e d PI a word of c a u t i o n " w i t h r e g a r d t o t h e EIoIten-Salt Reactor Program. It s a i d : !I

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For t h e f o u r t h s u c c e s s i v e y e a r , t h e Commission has r e q u e s t e d a u t h o r i z a t i o n of a b o u t $5 m i l l i o n for development of t h e m o l t e n s a l t r e a c t o r . The committee recornends a u t h o r i z a t i o n of t h e $5 m i l l i o n r e q u e s t e d f o r f i s c a l year 1 9 7 3 , a l t h o u g h i n so d o i n g i t w i s h e s t o v o i c e a word of c a u t i o n w i t h r e s p e c t t o t h i s program.

This concept , b o r n under t h e A i m r a f t Nuclear P r o p u l s i o n Program, has been under development for about twenty Over $130 m i l l i o n h a s been expended QII i t to d a t e . years. En light of t h i s l o n g p e r i o d of r e s e a r c h and development and i n r e c o g n i t i o n of p r o g r e s s r e a l i z e d on a l t e r n a t e conc e p t s d u r i n g t h i s p e r i o d , t h e committee recommends t h a t t h e AEC make a thorough r e e v a l u a t i o n o f t h e t e c h n i c a l c h a r a c t e r i s t i c s and p o t e n t i a l of t h e molten s a l t r e a c t o r w i t h a view t o d e c i d i n g whether t h i s work should b e cont i n u e d and, i f S Q , t h e a p p r o p r i a t e l e v e l of f u n d i n g req u i r e d t o a c h i e v e a d e f i n i t e program o b j e c t i v e . S u f f i c i e n t i n f o r m a t i o n should now b e a v a i l a b l e to make a c o n s u m a t e judgment on whether a d d i t i o n a l e f f o r t i s j u s t i f i e d OR t h i s program. The i n t e r e s t i n and p o t e n t i a l s u p p o r t â‚Ź o r t h i s program by the u t i l i t y - i n d u s t r i a l group which h a s been a s s e s s i n g this tecimology should b e c o n s i d e r e d by t h e Commission as a p a r t of i t s e v a l u a t i o n . It is clear t h a t i f t h e m o l t e n s a l t r e a c t o r i s t o achieve fruition i n a time frame d u r i n g w h i c h i t c o u l d

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make a s i g n i f i c a n t c o n t r i b u t i o n t o t h e c i v i l i a n n u c l e a r power program, s i g n i f i c a n t l y more f i n a n c i a l investment w i l l be r e q u i r e d f o r d e t a i l e d d e s i g n and c o n s t r u c t i o n of i m p o r t a n t component test f a c i l i t i e s and an e n g i n e e r i n g p ~ o t s t y p er e a c t o r t o d e m o n s t r a t e commercial a p p l i c a t i o n . I n a d d i t i o n , the u s e of h ~ ~ n o g e n emolten ~ u ~ salt f u e l , with t h e a t t e n d a n t r e q u i r e m e n t of o n - l i n e p r o c e s s i n g , r e q u i r e s i ~ e u n t o i t s e l f i n terms of materials, a n e ~ ~ t technology f u e l c y c l e and equipment. T h e r e f o r e , the committee views a thorough a p p r a i s a l a t t h i s t i m e as i m p e r a t i v e f o r the Commission and t h e i n d u s t r y t o d e t e r m i n e a p p r o p r i a t e p r i o r i t i e s f o r optimum a l l o c a t i o n of a v a i l a b l e f i n a n c i a l and t e c h n i c a l r e s ~ u r c e s

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A n t i c i p a t i n g t h a t the SCAE s t a t e m e n t w i l l lead t o a thorough review t h e mOlten-Sa%t B P e a C t O r cOnC@pfZ, We put t 0 g e t h e r t h i s r e p o r t t o p r o v i d e up-to-date informatien f o r t h e review. The r e p o r t brrbefly des c r i b e s the f e a t u r e s of t h e m o l t e n - s a l t b r e e d e r r e a c t o r as w e v i s u a l i z e i w e s o u r estimate of i t s performance p o t e n t i a l , and a t t e m p t s t o state t h e p r e s e n t s t a t u s of t h e technology t h a t i s r e q u i r e d f o r t h e co~-iceptand t h e l i k c e k i h ~ o dthat any d e v e % o p ~ ~ ~ eneeded nts can be accomplished. success f U u y Although i n w r i t i n g t h e report w e have a t t e m p t e d to d i s c u s s all matters that a r e o f s i g n i f i c a n c e to t h e f e a s i b i l i t y o f the c o n c e p t , we have n o t by any means a t t e m p t e d t o summarize a l l of t h e i n f o r m a t i o n that exists on m o l t e n - s a l t r e a c t o r s . However, t h e r e p o r t d o e s c o n t a i n r e f e r e n c e s t o a number of p e r t i n e n t topical and p r o g r e s s r e p o r t s , i n c l u d i n g many of tire $5 t o p i c a l r e p o r t s t h a t have been w r i t t e n ta r e c o r d what w a s l e a r n e d f r o m c o n s t r u c t i o n and o p e r a t i o n of t h e Efolten-Salt Reactor E x p ~ ~ i ~ e nThese t. and o t h e r r e p o r t s and p a p e r s are a l s o l i s t e d , a l o n g with a b s t r a c t s , i n r e f e r e n c e 2 , and the r e a d e r i s r e f e r r e d t o i t f o r a d d i t i o n a l ineraformtiono Of

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Background

A s n o t e d i n t h e a u t h o r i z a t i o n r e p o r t , t h e o r i g i n of m ~ l t e n - s a l t reactors was i n t h e A i r c r a f t Nuclear P r o p u l s i o n Program. I n P94T9 some p a r t i c i p a n t s in t h a t program ~sncludedt h a t w ~ l t e n - f l ~ o r i d e s d t s had. u s e f u l a t t r i b u t e s f o r the f u e l of a n aircraft p r o p u l s i o n r e a c t o r - n i g h uranium s o l u b i l i t y , e x c e l l e n t chemical s t a b i l i t y , and good p h y s i c a l p r o p e r t i e s - and work was s t a r t e d on a moltern-salt aircraft power p l a n t . Easky i n t h e a i r c r a f t development program came the r e c o g n i t i o n that the molten-salt technology o f f e r e d additional a d v a n t a g e s f o r civilian power u s e : avoidance of f u e l element f a b r i c a t i o n , r a p i d and i n e x p e n s i v e rep r o c e s s i n g , on-line r e f u e l i n g , good n e u t r o n econom)7 , and h i g h temperature Q p e % a t i Q nat bow preSsU%e. b n S @ q U e n t P y , in 1956 a y%OgPaEl begun at ORE% to hVes%igZite RlO%ten-§alt KeaCtGrs f o r Central s t a t i o n g e n e r a t i o n of e l e c t r i c i t y . Three years l a t e r , enough p r o g r e s s had been made i n defining t h e csncept that a n &C task f o r c e on f l u i d - f u e l react o r s could s a y that, w h i l e l i m i t e d i n b r e e d i n g s a t i s , t h e m o l t e n - s a l t approach had t h e g r e a t e s t chance o f t e c h n i c a l success 5f any f l u i d - f u e l system [ a ] . A result of t h i s o p i n i o n w a s that i n 1960 csnstructian of the PlsltenSalt R e a c t o r &:periment w a s a u t h o r i z e d . The 7 . 4 MWCt) MSlRE became critical at Oak Ridge in P 65 and, after a v e r y s u c e e s s f u % o p e r a t i n g h i s t o r y , w a s s h u t down in l a t e 1 9 6 9 S O that its budget c o u l d b e used f o r developments aimed a t m o l t e n - s a l t b r e e d e r r e a c t o r s T h e MSRE experience w a s of major importance to the molten-salt c5ncept. Up until t h e PISRE begail t5 s p e r a t e w e l l , i n s p i t e o f t h e Task Force e a n c l u s i o n , f e w p e o p l e b e s i d e s t h o s e a c t i v e l y involved i n t h e developmen% program considered molten-salt r e a c t o r s t o b e really p r a c t i c a l The rirajor P€?ZiBObi Was t h a t O p e % a t i O l l ZXld 'i@.aiTJt63X3blCe O f a s y s t e l 3 COntaining a highby- r a d i o a c ~ i v ef l u i d f u e l t h a t melted a t over 800°F seemed extremely 0

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difficult. I n 1966, however, t h e F E E began t o p r o v i d e e v i d e n c e t o o f f set t h a t v i e w . When power o p e r a t i o n began, t h e u s u a l s t a r t - u p p r ~ b l e m s w e r e e n c o u n t e r e d ; b u t s u s t a i n e d power o p e r a t i o n provided a remarkable d e m m s t r a t i o n of O p e r a b i l i t y . S t a r t i n g i n l a t e 1966, a n u n i n t e r r u p t e d one-month r u n w a s made, t h e n a t h r e e - r n ~ n t h r u n , and f i n a l l y a six-month run. Next, u s i n g a s m a l l f l u o r i d e v o l a t i l i t y p l a n t connected t o t h e r e a c t o r , t h e OKiginalb p a r t i a l l y e n r i c h e d 235U f u e l was removed from t h e s a l t and was r e p l a c e d by 233U t h a t had been made i n a p r o d u c t i o n r e a c t o r . T I I ~MSRE t h e n o p e r a t e d a f i n a l y e a r on the 23%, which made i t tlie o n l y r e a c t o r t o ever have b e e n o p e r a t e d on t h i s f u e l , and f o r a p e r i o d plutonium w a s used as t h e makeup f u e l . When s h u t down, t h e MSPEE had c i r c u l a t e d f u e l s a l t a t around 1 2 8 0 ° F f o r a t ~ t a ol f 2-112 y e a r s . Busing t h e y e a r s i n which t h e MSW was b e i n g b u i l t and b r o u g h t i n t o o p e r a t i o n , most o f t h e development work on m o l t e n - s a l t r e a c t o r s w a s i n s u p p o r t of i t . A s a r e s u l t s f t h e M S E ' s s u c c e s s , however, t h e budget w a s i n c r e a s e d t o permit work aimed a t m o l t e n - s a l t b r e e d e r r e a c t o r s , and t h e shutdown of t h e MSRE f r e e d a d d i t i o n a l funds f o r t h i s purpose. The most s i g n i f i c a n t p r o d u c t of t h i s e f f o r t h a s b e e n a new chemical p r o c e s s i n g method. Brought f o r t h i n 1968, t h i s development p e r m i t t e d a n i m p o r t a n t change i n o u r concept of an MSBW. (Like many f e a t u r e s of m o l t e n - s a l t r e a c t o r s , t h i s processing concept grew o u t of b a s i c work on t h e ~ h e n i s t ~ - g of f l u o r i d e salts t h a t h a s been c a r r i e d o u t ~ Q Ka number of y e a r s as p a r t of t h e A E C ' s P h y s i c a l Research Program.) \hen molten-salt r e a c t o r s w e r e f i r s t considered f o r c e n t r a l - s t a t i o n u s e , i t w a s n o t clear whether t h e y wsbnld serve b e s t as c o n v e r t e r s o r as t h e r m a l b r e e d e r s . A good c o n v e r t e r could b e o b t a i n e d by p u t t i n g uranium and thorium i n a s i n g l e s a l t , b u t it appeared that t h e y would have t o b e i n s e p a r a t e salts to o b t a i n a good b r e e d e r . T h i s w a s b e c a u s e t h e chemical p r o c e s s i n g methods t h e n a v a i l a b l e w e r e o n l y s u i t a b l e for s e p a r a t e uranium and thorium s a l t s , a f e r t i l e thorium b l a n k e t w a s r e q u i r e d , and m o s t of t h e f e r t i l e material wsuhd have t o b e k e p t o u t o f t h e c ~ r et o l i m i t n e u t r o n captures i n protactinium. The concHusion a t t h a t t i m e was t h a t e i t h e r t h e c o n v e r t e r o r t h e b r e e d e r c o u l d Bead t o low-cost power, and the MSRE ended u p h a v i n g a s i n g l e s a l t s o t h a t i t s e n g i n e e r i n g f e a t u r e s resembled a converter, b u t t h e s a l t did not. c o n t a i n thorium, which made i t s i m i l a r t o the f u e l salt of a two-fluid b r e e d e r . As emphasis i n t h e USAEC r e a c t o r development program s h i f t e d more and more t o b r e e d e r s , t h e d e s i g n and development e f f o r t at O W L w a s conc e n t r a t e d i n c r e a s i n g l y on t h e two-fluid s y s t e m i n s p i t e of t h e g r e a t e r technical d i f f i c u l t y of t h e r e a c t o r c o r e . This d i f f i c u l t y a r o s e c h i e f l y because g r a p h i t e t u b e s w e r e r e q u i r e d t o s e p a r a t e t h e t w o salts i n t h e c o r e , and b u i l d i n g a r e l i a b l e g r a p h i t e p i p i n g s y s t e m t h a t would w i t h s t a n d t h e r i d i a t i o n daraage of the h i g h n e u t r o n f l u x appeared v e r y d i f f i c u l t . %he p r o c e s s i n g advance of 1968 e l i m i n a t e d t h i s problem. This advance w a s the d e m o n s t r a t i o n of the chemical f e a s i b i l i t y of u s i n g P i q u i d bismuth to extract p r o t a c t i n i u m and rare e a r t h s from f u e l s a t t h a t c o n t a i n s b o t h ~ K ~ ~ ~ U and I I thorium. I Protactinium, t h e intermediate i n t h e breeding c h a i n between thorium and 233U9 has a s i g n i f i c a n t n e u t r o n c a p t u r e c r o s s s e c t i o n and must b e k e p t out Q â‚Ź t h e c o r e of a t h e r m a l b r e e d e r t o o b t a i n a good b r e e d i n g ratis. The rare earths are i m p o r t a n t neutPsn p s i s o n s and m u s t also b e removed r a p i d l y f o r good b r e e d i n g . The new process

4

A c o n c e p t u a l design sf a 1860 " ( e ) KSB w a s p r e p a r e d a t ORNL and in l 3 S b a report [ 4 ] w a s i s s u e d d e s c r i b i n g t concept Ebasco Services, I n c a , and a number of i n d u s t r i a l firms and utilities associated with them i n the p r i v a t e l y - f u n d e d Molten-Salt r o u p , have reviewed the moltensalt technology [SI and the OQX d e s i g n [ 3 , and Ebasco and i t s i n d u s t r i a l pagtnelPS have

a%SQ$egla'Ll a SC?pZi%Eite COIICepsUEd d e s i g n S t u d y Q f MSBRqS mder an O L t T s u b c o n t r a c t [SI These e f f o r t s have produced useful sugg e s t i o n s , and s o m e have been incorporated i n t o our concept of an MSER. We v i s u a l i z e the b a s i c concept as shown in P i g . 1.1. Tine core i s f o r m e d from an array of bare g r a p h i t e bars, S Q d e s i g n e d t h a t they can b e r e p l a c e d f r o m above, and having open channels t h a t provide f o r t h e passage o f s a l t . Die volume f r a c t i o n l e f t for s a l t i s d i f f e r e n t in d i f f e r e n t regions sf the core, and i n an a n n u l a r s p a c e i t has been m a d e 13igh enough thag: t h i s volume is undermoderatea and X E S l i k e a b l a n k e t where most of the escaping n e u t r o n s are absorbeeh in t h e thorium. n e fuel s a l t i s a mixture of l i t h i u m - 7 , b e r y l l i u m , thorium, and uranium fEaaorides t h a t m e % t s a t 93B"F, A t reactor o p e r it has a v i s c o s i t y a b o u t like t h a t of k e r o s e n e and a r e vapor p r e s s u r e . A s s h o r n Fa t h e f F re9 this s a l t flu2 t h e $Ore W'rtet-e it iS h e a t e d %O l 3 0 0 " F , and i% t h e n iS PUDIped thKoUgh a heat exchanger w h e r e the h e a t i s t r a n s f e r r e d t o a s d i m f l u o r o b o r a t e intermediate c o o l a n t , T h e c o o l a n t t r a n s p o r t s t h e heat t o a steam s y s t e m where s u p e r c r i t i c a l steam a t l088"F i s generated, l e a d i n g to an o v e r a l l therm1 e f f i c i e n c y 0% 4 4 % . A l l of t h e s a l t - c o n t a i n i n g equipment i s made out ~ a s t e i i o yN, a n i c k e l - b a s e developed e s p e c i a n y f o r with moPten f l u s r i d e s a l t s i n t h e a i r c r a f t p r o p u l s i o n program. A l l of t h e s a l t - c o n t a i n i n g equipment i s l o c a t e d i n s t e e l - l i n e d conc r e t e c e l l s t h a t can b e h e a t e d t o raise t h e equipment above the melting p o i n t of t h e s a l t . a d r a i n tank l o c a t e d below t h e reactor has a n a t u r a l c o n v e c t i o n c o o l i n g s y s t e m that i s always in u s e and t h a t serves as an extreme1~7r e ~ i ~ ileat-a-ej i e e c t i o n system %issisn-proauct decay t ~ ~ Fuel is drained i n t o this t a n k d u r i n g shutdowns, and the c e l l s are designed so that i n the event of a s a l t s p i l l , it would a l s o reach this t a n k and b e c o o l e d . 0

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~ u b b l e sof helium a r e i n j e c t e d i n t o a b y p a s s stream Qf f u e l salt and s w e p t back. obit i n a C y c l Q n e Seg%aPaton^ to purge XelIon-)i3%, t h e major neutron poisons and oqhet- n o b l e gases o u t of t h e r e a s t o r . another and much smaller side stream of f u e l salt i s passed through t h e chemical proc e s s i n g p l a n t ts remove t h e p r o t a e t i n i ~ r nand the s a l t - s o l u b l e f i s s i o n pPBdU6 ts E n c l o s i n g t h e r e a c t s r and t h e chemical plant c e l l s i s a c o n v e n t i o n a l l i n & - c ~ n c ~ e t containment e b u i l d i n g , which backs up t h e c e l l s t h e to p r o v i d e an additional barrier t o t h e e s c a p e of ~ a d i o a ~ t i ~ i t yme . arrangement of the c e l l s and t h e b u i l d i n g l a y o u t p r o v i d e access from above through removable s h i e l d i n g t o all t h e r a d i o a c t i v e p a r t s s f t h e p l a n t t h a t might require maintenance. e

The Prscessiang P l a n t f o r t h e S i n g l e - F l u i d Breeder

t eaters the p r o c e s s i n g plant a t 0.9 gpm, a r a t e which c o n t e n t s of t h e r e a c t o r s y s t e m through the plant every t e n days. It goes f i r s t ts a f l u o r i ~ ~ a t column i~n where t h e uranium i s removed 88 v o l a t i l e UF6. Newt it flows to 8n eXt%a6%8% where it is tacted with l i q u i d bismuth c o n t a i n i n g some diasskwed Eitliiutn, and here i n a r e d u c t i v e - e x t r a c t i o n p r o c e s s , t h e lithium enters t h e f u e l salt in exchange f o r p r o t a c t i n i u m which e n t e r s t h e bismuth An a d d i t i s n a l s t e p transfers t h e p r o t a s t i n i m into a separate salt where i t i s held u n t i l i t decays t o uranium and i s r e t u r n e d t o t h e r e a c t o r . The f u e l s a l t , now free of uranium and protactinium, goes t o t h e 1. ' m e t a l - t r a n s f e r prsceSsF:where i t i s c o n t a c t e d with a c a p t i v e v s l m e s f bismuth into which t h e r a r e earths and some o t h e r fission p r o d u c t s p a s s . From t h i s bismuth the fission p r o d u c t s are in t u r n t r a n s f e r r e d i n t o lithium chloride. I n t h e m e t a l - t r a n s f e r process9 the bismuth a c t s somewhat as a s e l e c t i v e membrane which permits the passage of the f i s s i o n p r o d u c t s between t h e f u e l salt and t h e lithium c h l o r i d e w i t h o u t t h e passage O f thQriUm. F i n a l l y , t h e UFE removed i n t h e i n i t i a l s t e p i s c o n t a c t e d with t h e p u r i f i e d f u e l salt and reduced bask to UF4 f o r r e t u r n t~ t h e r e a c t o r . Waste p r s d u e t s i n t h e plant are atcuaulated, g i v e n a f i n a l f b u s r i n a t i s n t r e a t m e n t to recover any uranium t h a t might have passed that f a r , and put i n s t o r a g e i n t h e reactor b u i l d i n g where they a r e h e l d as long as desired before transfer t o a c e n t r a l waste-disposal f a c i l i t y S p e c i a l ~ a t e l t i a b sw i l l b e r e q u i r e d i n the p r o c e s s i n g plamt. The wall of t h e f l u ~ r i n a t o r ill b e p r o t e c t e d f r ~ msarrssicsn by a f r o z e n layer of salt, The t r a n s f e r l i _ r a e s will p ~ o b a b l ~ gbe r made o u t of molybdenum t u b i n g s and some of t h e large vessels may b e b u i l t o u t o f e

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Using t h e s e v a l u e s , w e have e s t i m a t e d that t h e f u e l - c y c l e c o s t f o r t h e 1800 >G?(e) MSBW w i l l b e a b o u t 1 . 0 m i l P / k w h , as S ~ Q W I I i n t h e f o l l o w i n g b reakdown : m i l l s /kwh

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Fixed c h a r g e s on f i s s i l e i n v e n t o r y a t ib3.2%/yr 0 -36 Fixed c h a r g e s on thorium and c a r r i e r s a l t a t 1 3 . 2 % / y r 8 .O% Thorfum and c a r r i e r s a l t makeup 0 -04 0 4 9 -0 6 9 Fixed c h a r g e s on p r o c e s s i n g p l a n $ a t % 3 . $ % / y r 0 -05 Processing plant operating costs ~ u e pl r o d u c t i o n c r e d i t -0.09 N e t f u e l cycle cost

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%he c o s t of the p r o c e s s i n g p l a n t has been t r e a t e d as p a r t o f t h e f u e l c y c l e c o s t t o make i t comparable w i t h f u e l - c y c l e c o s t s of s o l i d - f u e l r e a ~ t ~ r sA. s a r e s u l t , t h e l a r g e s t s i n g l e i t e m i s t h e f i x e d c h a r g e s OR the p r o c e s s i n g p l a n t . (This c o s t w o d c l b e lower i f t h e p r o c e s s i n g p l a n t s e r v e d more t h a n PO00 NW(e) of r e a c t o r c a p a c i t y . ) I f g r a p h i t e h a v i n g no b e t t e r i r r a d i a t i o n r e s i s t a n c e t h a n t h a t a v a i l a b l e today is u s e d i n t h e c o r e , some of it will have t o b e rep l a c e d e v e r y four y e a r s . The c o s t of r e p l a c e m e n t , i n c l u d i n g t h e c o s t of s p e c i a l l a b o r , a p p e a r s t o l i e between 0.1 and 0 . 2 m i l l / k w h . The c a p i t a l c o s t sf t h e r e a c t o r i t s e l f has been e s t i m a t e d u s i n g , where appropriate, d e t a i l e d c o s t i n f o r m a t i o n on a l i g h t - w a t e r r e a c t o r of about t h e same s i z e . A b a s i c assumption i s t h a t t h e m o l t e n - s a l t i n d u s t r y h a s advanced t o t h e point where development c o s t s have b e e n l a r ge3.y absorbed and t h e m a n u f a c t u r e of components and t h e c o n s t r u c t i o n and l i c e n s i n g of p l a n t s have become r o u t i n e . Under t h e s e c o n d i t i o n s , we f i n d t h a t t h e c a p i t a l c o s t s ~f m o l t e n - s a l t and l i g h t - w a t e r r e a c t o r s should b e about the same. While t h e m o l t e n - s a l t r e a c t o r h a s some feat u r e s which add c o s t s , g a r t i c d a r $ y t h e p r o v i s i o n s foap remote maintenance of P d i Q a c t i V e systems, i t a l s o has h i g h t h e r m 1 e f f i c i e n c y and a Iotapressure primary system t h a t reduce costs. I n sum, t h e s i n g l e - f l u i d MSBR w i l l have a r e l a t i v e l y l o w b r e e d i n g g a i n b u t a compensatingly smll f i s s i l e inventory. The t o t a l of t h e f u e l - c y c l e c o s t and t h e c o s t of g r a p h i t e replacement should b e below t h e f u e l - c y c l e c o s t of l i g h t - w a t e r r e a c t o r s , and t h e c a p i t a l c o s t of t h e r e a c t o r and power p l a n t should b e about t h e s a m e as t h a t of a

light-water reactor.

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8

Tne Status of Development, t h e Major Uncertainties, and t h e Alternatives

j o r o b j e c t i v e s of this r e p o r t are to assess the s t a t u s o f MSBW t e c h n o l s t u i d e n t i f y any needed developments whose s u c c e s s f u l a ~ ~ ~is uncertain, ~ ~ ~and iin those ~ ~ cases, e to ~see what t alternatives are available if the approach does not s u c c e e d . Q U ~ csncPusions about t h e s e s u b j e c t s , broken down i n the s a m e way they are t r e a t e d in t h e r e p o r t , are as f~llows:

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F u e l and Coulant C h e ~ s t r y There i s no d o u b t a b o u t t h e c h o i c e of t h e f u e l s a l t - t h e E~P-E~F~-%~F~-U s yFs L t e+m m e e t s E B R requirements f a r better t h a n any o t h e r mixture. Its most serisras s h s r t c s m i n g i s the l o w s o l u b i l i t y o f oxide ( 3 0 ppm s'->, which will r e q u i r e that the ingress 0% air o r m0i.st u r e b e carefully ~ ~ n t s ~ l l eMere d . t h e Xds experience provides confidence, s i n c e i t s o x i d e content changed l i t t l e d u r i n g p l a n t life. F i s s i ~ n - p ~ ~ ds h~ecmt5 s t r y i n f l u o r i d e s a l t s i s w e l l u n d e r s t o o d , w i t h substantial i n p u t f r o m t h e :+SE experience me p h y s i c a l b e h a v i o r of t h e noble-metal f i s s i o n p r o d u c t s , which e x i s t i n elemental form,

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cannot b e p r e d i c t e d w i t h as much confidence as w e would l i k e , however. The r e a c t o r d e s i g n e r , t h e r e f o r e , must u s e c o n s e r v a t i v e assumptions as t o t h e i r d e p o s i t i o n on metal and g r a p h i t e and t r a n s f e r i n t o t h e offgas u n t i l d a t a from o p e r a t i o n of a n o t h e r r e a c t o r have reduced t h e s e uncertaintiese A f l u o r o b o r a t e m i x t u r e ( t h e 92-8 m d e % MaBF4-MaP @ u t e c t i c ) a p p e a r s t o b e t h e b e s t c h o i c e f o r t h e l o o p t h a t i s needed between t h e f u e l and steam s y s t e m s . E f f e c t s of s t e a m inleakage on c o r r o s i o n and consequences of mixing f l u s r o b o r a t e and f u e l n u s t b e e x p l o r e d f u r t h e r . Perhaps the most important need i s a b e t t e r u n d e r s t a n d i n g of t h e b e h a v i o r of h y d r o x i d e i o n and of mechanisms by which t r i t i u m , d i f f u s i n g f r o m t h e f u e l s y s t e m , can b e t r a p p e d i n t h e S l u ~ ~ o b o ~ a t e . Fuel and c o o l a n t salts in t h e HSRE were analysed by removing samples from t h e r e a c t o r and t a k i n g them t o an a n a l y t i c a l l a b o r a t o r y , However, c o n s i d e r a b l e p r o g r e s s h a s been made i n t h e l a s t few y e a r s towards developi n g o n - l i n e methods of a n a l y s i s f o r s a l t . Most i n v o l v e e l e c t r o a n a l y t i c a l t e c h n i q u e s b u t v i s i b l e - l i g h t and i n f r a - r e d s p e ~ t r o s c o p ya l s o of fer promise. One c o r r o s i o n l o o p i s now o p e r a t i n g w i t h a c o n t r o l l e d voltammetry i n s t r u m e n t t h a t r e p o r t s t h e U3+/U4+ r a t i o i n t h e s a l t , which i s e x t r e m e l y i m p o r t a n t i n r e a c t o r o p e r a t i o n , Methods s u i t a b l e f o r hydrogen, chromium and o t h e r c o r r o s i o n p r o d u c t s , salt i m p u r i t i e s , and c e r t a i n f i s s i o n p r o d u c t s are b e g i n n i n g to emerge from t h e development e f f o r t and, wish c o n t i n u e d p r o g r e s s , may become u s a b l e on a r e a c t o r .

Graphite G r a p h i t e i n m o l t e n - s a l t b r e e d e r r e a c t o r s must m e e t t h r e e p a r t i c u l a r requirements: %t must s t a n d up t o n e u t r o n i r r a d i a t i o n ; i t must have p o r e s s m a l l enough t h a t c a p i l l a r y f o r c e s e x c l u d e fuel salt, which does not w e t g r a p h i t e ; and i t must have a %ow enough p e r m e a b i l i t y t o g a s e s t o keep S E had down t h e a b s o r p t i o n of xenon. The g r a p h i t e manufactured f o r t h e M t o exclude s a l t , and a s p e c i a l small-pore material w a s developed by t h e m a n u f a c t u r e r s , b u t t h e t o t a l r a d i a s i o n dose w a s t o o ISW t o make r a d i a t i o n damage a problem, and exclusion of xenon was n o t a s p e c i f i c a t i o n . Thus, a l t h o u g h a g r a p h i t e s t r i n g e r removed from t h e M S Z showed no e f f e c t of two and one-half y e a r s i n c o n t a c t w i t h f u e l s d t , it would not have m e t t h e r a d i a t i o n damage anel gas p e r m e a b i l i t y r e q u i r e m e n t s of an EgSBR. R a d i a t i o n damage i n g r a p h i t e is caused b y h i g h energy n e u t r o n s and i n most g r a p h i t e s r e s u l t s i n s h r i n k a g e followed by expansion. These changes i n c o n v e n t i o n a l g r a p h i t e s r e s u l t i n t h e volume s t a r t i n g t o i n crease r a p i d l y a t n e u t r o n f l u e n c e s t h a t are t o o low t o b e of i n t e r e s t f o r MSBR'ss. However, i n t h e l a s t s e v e r a l years9 s p e c i a l g r a d e s of g r a p h i t e t h a t a p p e a r to be made b y a n uncalcfned-coke process show l i t t l e c o n t r a c t i o n and a l o n g e r p e r i o d b e f o r e r a p i d expansion b e g i n s One t h a t i s s a i d by t h e m a n u f a c t u r e r t o b e commercially a v a i l a b l e has been t e s t e d i n the H F I R a t MSBB t e m p e r a t u r e s and bund t o b e .able t o m e e t t h e 4-yr l i f e assumption of: t h e r e f e r e n c e d e s i g n . Consequently, a material t h a t h a s a d e q u a t e r a d i a t i o n r e s i s t a n c e seems t o be a v a i l a b l e , b u t l o n g e r g r a p h i t e l i f e i s d e s i r a b l e , and there i s hope t h a t o u r grawi n g u n d e r s t a n d i n g of r a d i a t i o n b e h a v i o r will l e a d t o longer i r r a d i a t i o n life e

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P r o g r e s s w i t h s e a Z i n g graphite to e x c l u d e xenon has not gone as f a r . Two techniques t h a t invslve u s e of pyrolytic carbon - one that d e p o s i t s it i n t h e s u r f a c e pores and the Other t h a t puts On a Ohin CQatiIlg - Can seal the material a d e q u a t e l y , b u t the permeability 0 % most ~f t h e s m d l sm1ples t e s t e d has increased e x c e s s i v e l y under neutron i r r a d i a t i o n , Some u n d e r s t a n d i n g of why the p e r m e a b i l i t y of t h e c o a t e d s a m p l e s i n c r e a s e s h a been gained r e c e n t l y f r o m r e n a r k a b l y sharp photographs o b t a i n e d u s i n g a neb7 technique W i t h t h e SCanniRg @ l e C % r O n IIIicrOscOpe. me f a i l U P e s aFe I ~ W t h o u g h t to r e s u l t f r o m defects seen in the u n i r r a d i a t e d materiaE, and a new procedure f o r d e p o s i t i n g t h e c o a t i n g h a s p r ~ d u c e df l ~ ~ q - f r eSe X I I ~ ~ t h a t are now b e i n g i r r a d i a t e d . However, the s e a l i n g method has not yet been proven to Wabk, and s c a l e - ~ p of the p r o c e s s to \&ere it be used f o r large pieces i s s t i l l in f r o n t of u s even i f the method turns o u t ts b e a success. Sealing g r a p h i t @ .by iIIIp~egIIatiEIg the SuZ'faCe pCJres With fUs%--free salt is a. possibility if pyrocarbans c a n n o t b e u s e d , but i f no method w i l l work, t h e breeding r a t i o of the MSBW w i l l decrease s s m e w h a t because sf increased n e u t r o n c a p t u r e in ' 3 5 X e e %e a d d i t i o n a l loss i n b r e e d i n g r a t i o will depend on t h e rpate of s t r i p p i n g by t h e noble-gas sparging system b u t w B l Z prob By l i e between 0.005 and 0.01.

B a s t e l l s y N w a s developed f o r use with molten s a l t s at the h i g h temperatures ne ed in aircraft power p l a n t s , and s i n c e i t h a s good s t r e n g t h a d good eo a % i b i % f - t yW i t h fLbkQ?Zide S d I s S , it W a s Used f o r the c Q n s t r u e t i s n of e K S a . \dhFle t h e M S E b e i n g b u i l t , ewerimencs r e v e a l e d t h a t the c r e e p d u c t i l i t y of Mastellay N is reduced by n e u t r o n irradiation. T h i s e m b r i t t l e w e n t i s caused by h e l i i a m produced b y therwnal-w@utron c a p t u r e s in the alloy, i n c o n t r a s t with the embrittleIcent due Void foKEEition bq" f a s t neu%rsl?S t h a t ha% been O f COnCePbl. for fast reactors. Analyses showed that stresses in t h e %fS low enough f o r the reactor ts be o p e r a t e d s a f e l y in spite s f d e c r e a s e d d u ~ t i ~ i t by u2t t h i s w o u l d not h e t r u e of f u t u r e reactors I ana 8 development program w a s begun to find a cure f o r t h e problem. The approach followed was t h a t of a d d i n g c a r h i d e - f s r n a h g elements Which have been US@d t 0 alIl62liarate t h e efa$rittleKEnt Sf S t a i n l e s s S t g e l by f a s t n e u t r o n s , a d 0.5% titanium w a s found to s u s t a i n t h e d u c t i l i t y of Masteaiaoy M a t the ssm t e m p e r a t u r e of l 2 0 0 " F . However, at k300"F, the o u t l e t temperature in the 6KiJL-design NSBW, changes in the structure 0 % t h e carbides i n t h e a l l o y caused t h e remedy t o be l o s t . , b u t this was ove.pcBme by r a i s i n g the t i t a n i u m c o n t e n t to &out 2 % . some further gain was made by ad ng niobium w i t h t i t a n i u m , and hafnium i n c s n j u n c t i a n with niobium w found to be very effective, b u t p r o b l e m with weldab i l i t y and cos have caused u s t o limit o u r e f f o r t on h a f n i u m - c o n t a i n i n g alloys Transmissisn electrons micrographs that d i s c l o s e the c a r b i d e s t r u c t u r e have been of g r e a t v a l u e i n r e v e a l i n g t h e f a c t o r s i n and per&% the p r o p e r t i e s of a s le to be judged r a t h e r re1i b e f o r e it. i s i r r a d i a t e d ,

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S m a l l commercial h e a t s o f 100 1b each of H a s t e l l o y pu' modified by 2% titanium a d d i t i o n have been o b t a i n e d from t h r e e vendors and found t o have a minimum creep d u c t i l i t y of g r e a t e r t h a n 4 % a t E400"F a f t e r i r r a d i a t i o n , which a p p e a r s t o b e a d e q u a t e . The material w a s f a b r i c a b l e i n t o s m a l l t u b e s and w e l d a b l e under h i g h r e s t r a i n t , s o a s o l u t i o n t o t h e e m b r i t t l e m e n t problem ~f H a s t e l l o y N seem to have been found. The remaining s t e p s are t o show t h a t a c c e p t a b l e material can b e o b t a i n e d i n l a r g e c o m e r c i a l h e a t s d e t e r m i n e t h e time-at-temperature l i m i t s a t h i g h e r t e m p e r a t u r e s and c o l l e c t m d i a n i c a l p r o p e r t i e s d a t a f o r code approval E x t e n s i v e n a t u r a l - c i r c u l a t i u n and f o r c e d - c i r c u l a t i o n loop tests r e v e a l e d t h a t t h e c o r r o s i o n rate o f Hastelloyr N by d e a n f u e l s a l t i s and i t w a s no s u r p r i s e when salt a n a l y s e s and s u r v e i l l a n c e s p e c i mens from the MSRE showed t h a t the g e n e r a l i z e d c o r r o s i o n rates were Q ~ Pow V i n t h e fuel s a l t and n o t d e t e c t a b l e i n the coolant s a l t . Near the end of %RE o p e r a t i o n and d u r i n g t h e p o s t - o p e r a t i o n e x a m i n a t i o n , howeverp t h e r e was a s u r p r i s e when a l l H a s t e l l e y N t h a t had been i n c o n t a c t w i t h f u e l s a l t w a s found t o form s h a l l o w , i n t e r g r a n u l a r s u r f a c e c r a c k s when i t w a s s t r a i n e d a t roan t e m p e r a t u r e . The c r a c k s were g e n e r a l l y less t h a n 8.81 i n . deep, and t h e maximum depth d i d n o t s e e m t o have i n c r e a s e d w i t h exposure t i m e . S i n c e material from t h e core and from t h e h e a t exchanger showed similar e f f e c t s , irradrfaS~ the t i o n d i d n o t seem t o b e i n v o l v e d , b u t a s t r i k i n g ~ O R ~ I - Z Lbetween f u e l - s a l t and c o o l a n t - s a l t s i d e s o f che h e a t exchanger t u b e s i n d i c a t e d i t probably had t o do w i t h f i s s i o n p r o d u c t s i n the f u e l s a l t . S a m p l e s w e r e c a r e f u l l y l e a c h e d and a v a r i e t y o f f i s s i o n p r o d u c t s w e r e found i n the material t o a depth of about 0.003 i n . A t t h e h i g h e s t c o n c e n t r a t i o n w a s t e I P u r i u m , and t e l l u r i u m and a l l o t h e r elements on which s u s p i c i o n might f a l l w e r e d e p o s f t e d on H a s t e l l o y N samples and h e l d a t PISEE temperat u r e f o r 1060 h o u r s . T e l l u r i u m caused c r a c k s t u â‚Ź o m when t h e material w a s s t r a i n e d , b u t no o t h e r f i s s i o n p r o d u c t d i d . As a consequence o f t h e s e and many o t h e r tests sf s t r e s s e d and uns t r e s s e d s a m p l e s a t v a r i o u s t e m p e r a t u r e s t i m e s and methods of f i s s i o n p r o d u c t d e p o s i t i o n , t h e e v i d e n c e seem s t r o n g that t e l l u r i u m i s i n d e e d t h e culprit. mere i s r e a s o n to s u s p e c t t e ~ L u r i u m(and a l s L s e l e n i u m s although i t h a s shown no e v i d e n c e of misbehavior) b e c a u s e of i t s similarity t o s u l f u r , which can b e trsublessme w i t h n i c k e l - b a s e materials. I n a t t e m p t i n g t o f i n d a remedy f o r t h e problem, a v a r i e t y o f n i c k e l b a s e and i r o n - b a s e a l l o y s have been t e s t e d a l o n g s i d e of H a s t e l l o y N . Our e x p l o r a t o r y experiments i n d i c a t e t h a t a u s t e n i t i c s t a i n l e s s s t e e l s are n o t a f f e c t e d , n o r are Mend and copper. Menhers of t h e HastelHoy f a m i l y c o n t a i n i n g about 20% chromium (versbls 7% i n M a s t e l l o y N) h a v e not been a f f e c t e d , n o r have samples of m o d i f i e d H a s t e l l o y N c ~ n t a i n i n g a b o u t 9% niobium. I n c o n e l 680, of which t h e A i r c r a f t R e a c t o r Experiment w a s b u i l t , w a s u n a f f e c t e d i n two tests b u t showed s h a l l o w c r a c k s i n o n e , An i m p o r t a n t r e s u l t i s t h a t t h e materials t h a t c o n t a i n o v e r 16% chromium are u n a f f e c t e d . This b e h a v i o r is c o n s i s t e n t w i t h t h a t found w i t h s u l f u r i n s t u d i e s made f o r j e t a i r c r a f t e n g i n e a l l o y s , where chromium c o n c e n t r a t i o n s of g r e a t e r than 15 t o 16% are needed t o p r e v e n t damage by s u l f u r .

12 Based on t h e s e o b s e r v a t i o n s , t h e r e appear to b e a l l o y s that are not a f f e c t e d b y tellkarium, and ELIXXIg thew are â‚ŹKlodi%iCationSQ f Hastelloy % f a n i n c r e a s e i n the chrsniuw c o n t e n t of H a s t e l E o y P; i s r e q u i r e d , o r a n Ineonel o r a stainless steel must b e u s e d , the ~ O ~ K O S ~ C rate X I will b e h i g h e r t h a n that w i t h s t a n d a r d H a s t e l l ~ yE9 brat the i n c r e a s e w i l l probably be t o l e r a b l e , C o r r o s i o n experiments will be needed t o f i n d o u t . Except f o r the s t a i n l e s s steels, where t h e work has a l r e a d y been done, a change to one of these materials i s l i k e l y to mean that modifications t o confer r a d i a t i o n r'2SiStanCe W i l l have LO b e f O U n d . I f thboUgh gQod f Q Z t l X ? @ XI a d d i t i o n of niobium t o H a s t e l l s y K s h o d e l s u f f i c e , a c c e p t a b l e c o r r o s i o n b e h a v i o r i s f a i r l y w e l l a s s u r e d , tind the e f f e c t a%niobium on i r r a d i a t i o n r e s i s t a n c e has already been i n v e s t i g a t e d to s o m e extent. I n any ease, in-pile c a p s u l e tests w i l l b e needed to show that t h e same effects a r e seen i n - p i l e as with t e l B u r i u m a d d i t ions o u t - o f - p i l e , and p r e p a r a t i o n s f o r them a r e underway. A clear demonstration that a s a t i s f a c t s r y material has been found w i l l b e n e c e s s a r y b e f o r e another m a l t e n - s a l t reactor can b e built D

A l t h o u g h a a n y of t h e components and systems

an PlSBR power plant

are similar t o t h o s e needed f o r s o l i d - f u e l r e a c t o r s , t h e d e s i g n r e q u i r e ments on o t h e r s are d i f f e r e n t , and a number are u n i q u e t o the ms%ten-sa2t ~yisten. N ? I ~ ~06 Y the d i f f e r e n t 0 % u n i q u e aspests were investigated 111 t h e development programs f a r t h e aircraft reactor and t h e blSRE, b u t n o t a l l have been used o r teated, and i n c r e a s e s in size o r performance a r e required in most cases. Starting f i r s t with pumps, v e r t i c a l - s h a f t centrifugal pumps with overhung impellers were developed f o r m o % t e a ~ - s d ts e r v i c e and used satisf a c t o r i l y on t h e Aircraft R e a c t o r E x p e r i m e n t and t h e PfS as w e l l 8 5 used and t e s t e d i n a Elumber o f salt l o o p s . ( A small o i l - l e a k from t h e MSRE p5.mary pump caused problems with the off-gas system, but t h e pump i t s e l f was used w i t h o ~ ttrotable f o r %Re reactor life, and t h e l e a k was e a s i l y coa~rectecl in a spare penEp.) ~ t h s ~ g s t eh p s t i m aad up to a 10-to i 5 - m a i n c r e a s e i n capacity w i l l b e needed i n a p r o g r e s s i o n f r o m 'die M S a E to faallsize XSBPS, the same b ~ i dce s i g n as t h a t on t h e MSE is s p e c i f i e d t h @ refer@nCE?MSBR d e s i g n , and t h e Scale-up S h o d $ b e ? Z e h t i V & l y §tKEiightf o r w a r d . We b e l i e v e , c o n s e q u e n t l y , that a l t h o u g h several years w i l l be required to d e v e l o p and test l a r g e r pumps, t h e problems are w e l l u n d e r s t o o d and s a t i s f a c t o r y pumps can b e o b t a i n e d . Byron-Jackson, an associate sf Ebasca i n the Molten-Salt Group3,has expressed similar c o n f i d e n c e , The MSRE i n t e r m e d i a t e heat exchanger and a i r - c o o l e d radiator operated w i t h o u t d i f f i c u l t y I and analyses showed decrease i s t pert-ormnce t h ~ ~ u g h o u t the p l a n t l i f e . Heat-transfer experiments, as w e l l as t h e o p e r a t i s n of t h e E E Z units, indicate that s a l t s a c t as ordinary f l u i d s and t h e i r h e a t t r a n s f e r b e h a v i o r can b e p r e d i c t e d r e l i a b l y as l u n g as a c c u r a t e p h y s i c a l d a t a a%e 8 V a i P a b l e . The ZkspeCtS Sf t h e MSBR t h a t d i f f e r fE"QIhl a s i d e frona size, have to $0 w i t h t h e need f o r h i g h performance QfL t h e MSBR to limit t h e fuel-salt inventoryp and t h e r e q u i r e m e n t that e i t h e r f a i l e d t u b e s can be located and plugged in place, o r that the t u b e 9

. . ..... ~;

13 b u n d l e o r e n t i r e u n i t can b e r e p l a c e d . Both of t h e s e create d e s i g n probl e m s . To o b t a i n e o q a c t n e s s , e i t h e r s m a l l e r - t h a n - u s u a l t u b e s o r t u b e s deformed t o enhance h e a t t r a n s f e r have been s h m i n o u r heat-exchanger c o n c e p t s , and u s e o f e i t h e r w i l l r e q u i r e a t e s t i n g program. Some i n crease i n f u e l - s a l t i n v e n t o r y w i l l r e s u l t i f t h e compactness shown i n o u r concept i s n o t a c h i e v e d , b u t s i n c e o n l y 1 7 % of t h e f u e l s a l t i s i n t h e h e a t exchangers, a moderate i n c r e a s e i n t h e i r volume w i l l have a l i m i t e d o v e r a l l e f f e c t . P r o v i d i n g f o r heat-exchanger r e p a i r i s a p a r t of t h e o v e r a l l MSR maintenance problem, b u t new t e c h n i q u e s f o r p l u g g i n g t u b e s b e i n g developed %or o t h e r u s e s s h o u l d be h e l p f u l . There were no steam g e n e r a t o r s on t h e ARE and M S E , and as f a r as w e ~ Q W ,t h e r e h a s been no e x p e r i e n c e w i t h g e n e r a t i o n of steam w i t h highm e l t i n g s a l t s . The major problem i s t h a t i n c o n v e n t i o n a l s t e a m c y c l e s t h e feed-water e n t e r s t h e steam g e n e r a t o r a t a t e m p e r a t u r e below t h e m e l t i n g p o i n t of t h e MSBR c o ~ l a n tsdt. A s a r e s u l t , u n l e s s o t h e r measures are t a k e n , some s a l t would f r e e z e on t h e t u b e s . Allowing a layer sf salt t o form might b e a c c e p t a b l e , b u t t o g e t around t h e q u e s t i o n in our r e f e r e n c e c o n c e p t , w e a l t e r e d t h e stearn c y c l e t o i n c r e a s e t h e t e m p e r a t u r e of t h e steam. e n t e r i n g t h e steam g e n e r a t o r . A s u p e r c r i t i c a l steam c y c l e w a s adopted b u t modified t o mix some e x i t steam w i t h f e e d w a t e r The t o r a i s e i t s t e m p e r a t u r e t o c l ~ s et o t h e s a l t m e l t i n g t e m p e r a t u r e . p e n a l t y i s some a d d i t i o n a l equipment and a s m a l l l o s s i n e f f i c i e n c y , b u t the n e t e f f e c t d o e s n o t a p p e a r t o b e v e r y g r e a t . Other ways of overcoming t h e s a l t f r e e z i n g problem a l s o appear f e a s i b l e , such as t h e r e e n t r a n t t u b e approach t h a t a p p e a r s i n some sodium-heated s t e a r n - g ~ ~ ~ ~ ac o t on cr e p t s . %e P o s t e r Wheeler Company i s now e x p l o r i n g m o l t e n - s a l t s t e a m generator c o n c e p t s under a n OREu'6, c o n t r a c t , and t h e y w i l l c o n s i d e r o u r concept and o t h e r s b e f o r e recommending a d e s i g n . Whether H a s t e l l o y 1'9 h a s a d e q u a t e c o r r o s i s n r e s i s t a n c e f o r u s e i n a high-temperature stearn s y s t e m is b e i n g i n v e s t i g a t e d at p r e s e n t . The sodium fluoride-sodium f l u o r o b o r a t e c o o l a n t proposed f o r t h e MSBR m e l t s at 725째F- This g i v e s i t a 125째F m e l t i n g p o i n t advantage a v e r t h e LiP-BeP2 used i n t h e MSRE and i t i s much c h e a p e r , b u t u n t i l a few years ago w e had .had no e x p e r i e n c e a t a l l w i t h f l u o r o b o r a t e s . During the p a s t several years, howeverT,an i s s t h e r m d MSRE-scale

l o o p has been

o p e r a t e d w i t h f l u o r o b s r a t e , as w e 1 1 as two s m a l l f o r c e d - c o n v e c t i o n l o o p s w i t h h e a t e r s and c o o l e r s , and a number of n a t u r a l - c i r c u l a t i o n l o o p s . A f a i r l y e x t e n s i v e c h e m i s t r y and a n a l y t i c a l c h e m i s t r y program has a l s o b e e n c a r r i e d o u t . The major d i f f i c u l t y w i t h f l u o r o b s r a t e i s t h a t i t h a s a g r e a t e r tendency to p i c k up m o i s t u r e than t h e o t h e r salts w e have u s e d , which makes i t more c o r r o s i v e , b u t t h e c o r r o s i o n r a t e w i t h c l e a n s a l t is modest. The BF3 vapor p r e s s u r e o v e r t h e salt r e q u i r e s s p e c i a l prov i s i o n s i n t h e cover-gas system, b u t t h e s e h a v e been worked o u t s a t i s f a c t o r i l y i n t h e l o o p s t h a t have been o p e r a t e d . The l i k e l i h o o d of steam g e n e r a t o r l e a k s t h a t i n t r o d u c e m o i s t u r e i n t o t h e c o o l a n t w i l l r e q u i r e t h a t a c l e a n u p s y s t e m b e p r o v i d e d . One s f t h e ways t o p r e v e n t t r i t i u m g e t t i n g i n t o t h e s t e a m may be t o t r a p i t i n t h e c o o l a n t and extract i t from t h e r e , and t h e p r o c e s s i n g s y s t e m t o accomplish t h i s probably serve b o t h p u r p o s e s .

14

The n o b l e g a s e s are i m s o l u b l e i n f u e l s a l t , a d , csnsequent%y, the 6ission-proauet pa is stain i n an r n B R can be greatly reduced by sparging on from t h e saLt. T h i s was d e m n s t r a t e d t o be very e f f e c t i v e i n E , where over 88% of t h e 135xe was removed. A more e f f e c t i v e and

b e t t e r c o n t r o l l e d s y s t e m i s proposed f o r t h e XSBR, however, that i n v o l v e s i n j e s t i n g h e l i u m i n t o a b y p a s s stream O f salt and removing i t and t h e n o b l e g a s e s with a c e n t r i f u g d . s e p a r a t o r Experiments u s i n g water have provided designs f o r t h e equipnent and i n d i c a t i o n s of the p e r f o r m n c e t o be expected, b u t testing w i t h salt is needed and is planned f o r an tamscale l o o p now b e i n g built.

The containment p h i l o s o p h y and the containment b u i l d i n g desim f o r the MSBR differ l i t t l e from those f o r s o l i d - f u e l r e a c t o r s , although t h e

1% r e q u i r e more e x t e n s i v e filtration and c l e a n u p p r o v i s i o n s . The prosal t o use the reactor and c o o l a n t sells as ovens i n which t o h e a t the a E % systems, h eve%, i S n o t on%y U K l i q U e to t h e MSBR b u t a l s o iS d i f f e r e n t from t h e F E where components and p i p e s were e n c l o s e d i n i n s u l a t i o n and individually heated. The uncertainties t h a t exfst m a i n l y have to do w i t h she b e s t way of i n s u l a t i n g t h e cell and how t h e equipment will b e s u p p o r t e d and r e s t r a i n e d t o resist an earthquake. We f o r e s e e no l i m i t i n g prsb%ems h e r e , bus i f some a r o s e , an a l t e r n a t i v e would b e t o r e t u r n to t h e concept used s u c c e s s f u l l y i n t h e FIsa. The method of p r o v i d i n g a c c e s s f o r maintenance by removing s e c t i o n s 0 % s h i e l d i n g froa, t h e t o g o f t h e cell. w a s u s e d w i t h o u t d i f f i c u l t y on t h e I%=, and t h e m a j o r diffePenCf2 OR the fu%l-SCa%eMSBR i s t h e l a r g e r Size o f conponents t o which access will b e r e q u i r e d .

Instrumentation and Controls

MSBR's have somi f e a t u r e s t h a t are f a v o r a b l e w i t h r e g a r d t o control sf t h e reactor and a few f e a t u r e s t h a t add d i f f i ~ l t i e s . chief among t h e l a t t e r are the h i g h f r e e z i n g t e m p e r a t u r e s of t h e s a l t s , which r e q u i r e that s p e c i a l p r o v i s i o n s be m d e i n the c o n t r o l and g r o t e s t i s n s y s t e m s t o avoid

f r e e z i n g d u r i n g t r a n s i e n t c o n d i t i o n s and p a r t - l o a d o p e r a t i o n . I n a d d i t i o n , r a t e s of t e m p e r a t u r e change p r o b a b l y h a v e t o b e c ~ ~ l t r o l l eddu r i n g l o a d changes t o p r e v e n t e x c e s s i v e transient stresses i n the system. Wt1iPe contrulb methods have n o t been worked s u c i n d e t a i l , several a l t e r n a t i v e schemes appear ts b e possible, and a t l e a s t one s h o d d b e s a t i s f a c t o r y . The s m a l l amourt of excess r e a c t i v i t y r e q u i r e d in an MSBR and t h e dynanic c h a r a c t e r i s t i c s of t h e r e a c t o r g r e a t l y simplify t h e r e a c t i v i t y control requirements * M a i n t a i n i n g a long-term r e a c t i v i t y b a l a n c e w i l l b e d i f f i c u l t on an MSBR b e c a u s e of t h e csntinmous f u e l p r o c e s s i n g , and new t e c h n i q u e s m y have t o b e developed. Significant e x p e r i e n c e w i t h i n s t r u m e n t a t i o n s y s t e m s has b e e n o b t a i n e d , with h i g h te e r a t u r e f a c i l i t i e s of v a r i o u s k i n d s , and i n p a r t i c u l a r with the MSRE where t h e r e l i a b i l i t y of the thermocouples was p a r t i c u l a r l y

w..

s a t i s f a c t o r y . The p r e s s u r e and flow rate of t h e fuel s a l t w e r e n b t measured d i r e c t l y i n t h e PISRE, however, and h a v i n g t h e e n t i r e ELSE38 1 ~ e a c t o rcell h e a t e d adds t h e c o m p l i c a t i o n t h a t all of the i n s t r u m e n t s i n t h e c e l l must b e a b l e t o o p e r a t e a t h i g h t e m p e r a t u r e . Hence some new i n s t r u m e n t s a d measurement t e c h n i q u e s w i l l b e needed f o r t h e MSBR.

Fuel Proces si*g

Achievement of a s i g n i f i c a n t b r e e d i n g g a i n i n a thermal spectrum r e a c t o r i s dependent on r a p i d removal of t h e f i s s i o n p r o d u c t s , and i n t h e c a s e of the s i n g l e - f l u i d &fSBR, i s also dependent on s e p a r a t i o n of t h e p r o t a c t i n i u m from t h e f u e l s a l t . The chemical. s t e p s i n v o l v e d i n t h e p r o c e s s e s p r e s e n t l y proposed f o r a c c o m p l i s h i n g t h e s e s e p a r a t i o n s have been t h o r o u g h l y i n v e s t i g a t e d and a p p e a r t o b e w e l l e s t a b l i s h e d However, e n g i n e e r i n g development and t h e d e m o n s t r a t i o n of s a t i s f a c t o r y c o n t a i n e r materials have n o t p r o g r e s s e d n e a r l y s o f a r . 7 F l u o r i n a t i o n t o r e c o v e r u ~ a i i i u r nfrom r a d i o a c t i v e f u e l h a s been used s e v e r a l t i m e s , most r e c e n t l y i n t h e f u e l r e p ~ o e e s s i n ga t t h e >ERE. r However t h e scheme proposed f o r t h e MSBR i n v o l v e s c o n t i n u o u s fluorinat i o n , which has o n l y been demonstrated i n s m 1 1 equipment and which req u i r e s b e t t e r c o r r o ~ i o np r o t e c t i o n f o r t h e f l u o r i n a t i o n v e s s e l t h a n h a s b e e n achieved b e f o r e Although many a s p e c t s of c o n t i n ~ o ~f sl u o r i n a t o r s have been i n v e s t i g a t e d , i n c l u d i n g t h e formathan of f r o z e n s a l t layers t h a t are expected to p r o t e c t t h e f l u o r i n a t i o n v e s s e l , a s i g n i f i c a n t development e f f o r t on t h e f l u o r i n a t o r l i e s b e f o r e u s . some of t h e n e c e s s a r y experiments are underway and are p r o g r e s s i n g s a t i s f a c t o r i l y . Direct r e d u c t i o n of UFg f o r r e t u r n to t h e r e a c t o r by i t s a b s o r p t i o n i n t o f u e l s a l t has been demonstrated i n small l a b o r a t o r y experiments and However, no e n g i n e e r i n g experiments t h e b e h a v i o r found t o b e s a t i s f a c t o r y have y e t been o p e r a t e d , a l t h o u g h t h e y are planned f o r t h e n e a r f u t u r e . One f a v o r a b l e r e s u l t of t h e r e c o d a i n a t i o n experiments w a s t h e d i s c o v e r y t h a t gold i s n o t a t t a c k e d by t h e p r o c e s s f l u i d s , and gold p l a t i n g may p r o v i d e a d e q u a t e c o r r o s i o n p r o t e c t i o n f o r the recombiner Reductive e x t r a c t i o n sf realistic c o n c e n t r a t i o n s of uranium and z i r conium, whose b e h a v i o r i s s i m i l a r t o t h a t of p r o t a e t i n i u ~ n , h a s been demons t r a t e d w i t h f u e l s d t and m o l t e n bismuth i n a packed-column c o n t a c t o r . Flooding v e l o c i t i e s and m a s s - t r a n s f e r rates w e r e measured and found to b e as p r e d i c t e d from d a t a on mercury-water and aqueous-organic s y s t e m . A d e m o n s t r a t i o n of r e d u c t i v e e x t r a c t i o n u s i n g r e p r e s e n t a t i v e c o n c e n t r a t i o n s of p r o t a c t i n i u m i s needed, and 38 t o 50 g r a m s f 231Pa is b e i n g o b t a i n e d t o make t h a t p o s s i b l e . A l l of t h e s t e p s i n t h e m e t a l t r a n s f e r p r o c e s s have been ~ ~ I I I Q I - I s t r a t e d i n a s m a l l s i n g l e - s t a g e i n t e g r a t e d experiment, and p r e l i m i n a r y o p e r a t i o n of a l a r g e r , b u t still s i n g l e - s t a g e , experiment has begun. A t h r e e - s t a g e experiment t h a t w i l l be 5 t o 10% of MSBR scale i s b e i n g designed. Losses of f i s s i l e material from t h e p r o c e s s i n g p l a n t must b e k e p t low. Although t h e process f l u i d s c i r c u l a t e r e p e a t e d l y through t h e p l a n t , a c t u a l % ~ s s e sc a n o c c u r only i n t h e wastes. These are t h e r e f o r e c o l l e c t e d t o g e t h e r , h e l d t o await p r o t a c t i n i u m d e c a y 9 and t h e n b a t c h f l u o r i n a t e d t o e

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traces of uranium b e f o r e d i s c a r d . Experience w i t h f l u o r i n a t i o n shows that t h e u r a n i m curltent can b e reduced t o a very l o w l e v e l by this t e c h n i q u e , F u e l s a l t and l i t h i u m c h l o r i d e are compatible with some common c o n s t r u c t i o n materials b u t nick~cel. d i s s o l v e s i n bismuth , and t h e s o l u b i l i t y of i r o n i s g r e a t enough f o r m a s s t r a n s f e r t o o c c u r r a p i d l y i n a s y s t e m h a v i n g s i g n i f i c a n t t e m p e r a t u r e d i f f e r e n c e s . Consequently m a t e r i d s s u c h as molybdenum, g r a p h i t e , and t a n t a l u m w i l l b e r e q u i r e d f o r t h e p r o c e s s i n g p l a n t . F a b r i c a t i o n o f molybdenun h a s always appeared very d i f f i c u l t , b u t we have developed a v a r i e t y of forming and j o i n i n g t e c h n i q u e s d u r i n g t h e p a s t ma y e a r s p and a f a i r l y c o m p l i c a t e d p r o c e s s i n g facility i s p r e s e n t l y b e i n g b u i l t completely from molybdenum. G r a p h i t e s h o d d b e l e s s expensive t o m e t h a molybdenum, and the P ~ O C e s s i n g vessel f o r t h e t h r e e - s t a g e m e t a l t r a n s f e r experiment w i l l . b e b u i l t o u t of graphite. However, we p r e s e n t l y have i n s u f f i c i e n t d a t a on the c o m p a t i b i l i t y of g r a p h i t e with b i s m u t h c s n t a i n i n g l a r g e concent r a t i o n s of lithium o r t r a c e q u a n t i t i e s o f o t h e r materials. A s m a l l n a t u r a l - c i r c u l a t i o n loop has been b u i l t o u t of a tantalum alloy and o p e r a t e d w i t h b i s m u t h ; the c o r r o s i o n rates of t a n t a l u m and of t h e a l l o y seem acceptab%y s m a l l , b u t there Ss some i n c o n s i s t e n t e v i d e n c e o f emb r i t t l e m e n t of t h e a l l o y , Carry-over o f s i g n i f i c a n t q u a n t i t i e s cf bismuth t~ he r e a c t o r where it c o u l d a t t a c k Hastel%oy N n u s t b e avoided. One H a s t e l l s y N n a t u r a l - c i r c u l a t i o n l o o p c o n t a i n i n g f u e l s a l t h a s been run with an open c a p s u l e o f me%ten b i s m u t h i n c o n t a c t with t h e s a l t . No e f f e c t of the bismuth h a s b e e n s e e n , b u t more needs t o b e l e a r n e d about how t o l e r a n t the reactor would b e of s m a l l q u a n t i t i e s o f bismuth i n t h e s a l t . L i t t l e is y e t known about the tendency of bismuth t o b e ent r a i n e d i n s a l t , and its s o l ~ b i l i t yi n s a l t has n o t been measured accurately a l t h o u g h bassic t h e m ~ d y n a m ic~o n s i d e r a t i o n s i n d i c a t e t h a t the so%ubKLi%ymust b e very l o w . Our approach t o p r e v e n t i n g bismuth carq7-over i s t o a t t e m p t to develop s a l t - b i s m u t h c o n t a c t o r s with s t i r r e d irnterfkzces i n which the bismuth and s a l t are n o t d i s p e r s e d , and a p r e l i m i n a r y d e m o n s t r a t i o n o f t h i s t e c h n i q u e has been made i n a metal t r a n s f e r p r o c e s s experiment. Even i f s u c h t e c h n i q u e s are u s e d , however, c a r e f u l a n a l y s i s f o r b i s m u t h , p l u s a final d e ~ ~ t us p t e p , such as p a s s i n g t h e salt throplgh a b e d O f n i c k e l KCOQL, W i L l l i k e l y be W e d . F a i l u r e to d e v e l o p s y a tern f o r r a p i d l y removing p r o t a c t i n i u m and t h e rare e a r t h s would p r e v e n t t h e attainment of a s i g n i f i c a n t b r e e d i n g gain i n a s i n g l e - f l u i d PISSR. F o r t u n a t e l y a l t e r n a t i v e approaches a p p e a r t o e x i s t f o r m s t , b u t net a l l , parts o f t h e p r o c e s s . G r a p h i t e may b e u s a b l e f o r t h e plant material i f molybdenum w i l l n o t s e r v e , and t a n t a l u m and i t s a l l o y s r e p r e s e n t m o t h e r p o s s i b l e a l t e r n a t i v e f o r p a r t s o f t h e plant If some p a r t s of the p r e s e n t l y proposed f l u o r i n a t i o n - r e d u c t i v e e x t r a c t i o n p r o c e s s cannot 3, made to w u r k , an o x i d e p r e c i p i t a t i o n p r o c e s s t h a t h a s been i n v e s t i g a t e d i n a Limited way a p p e a r s t o o f f e r an a t t r a c t i v e a l t e r n a t i v e ; pret.actinium c a n b e s e E e c t i v e l y p r e c i p i t a t e d as Pa205 by t r e a t i n g fuel s a l t w i t h a m i x t u r e o f steam and hydrogen f l u o r i d e , and Indeed, fururanium can s u b s e q u e n t l y b e remved by a similar p r o c e s s . t h e r work m y show t h a t the o x i d e p r o c e s s has advantages over the f l u s r i n a t ion- reduc t i ve ext ract ion me thod ‘ P ~ G Q V ~any P

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We know of no a t t r a c t i v e s u b s t i t u t e f o r t h e m e t a l - t r a n s f e r p r o c e s s b u t b e c a u s e i t s development h a s p r o g r e s s e d f u r t h e r t h a n t h a t s f t h e rem i n d e r of t h e pl-ocessing s y s t e m , it s e e m s most l i k e l y t o b e s u c c e s s f u l . I n a d d i t i o n , i t i s t h e s t e p l e a s t coupled t o t h e r e a c t o r , and r e d u c i n g t h e r a r e - e a r t h removal e f f i c i e n c y s e v e r a l - f o l d would n o t have a p r o h i b i t i v e e f f e c t on t h e b r e e d i n g r a t i o . ( A t h r e e - f o l d r e d u c t i o n would lower t h e b r e e d i n g r a t i o by about 0.01.) One more o b s e r v a t i o n should b e made about t h e p r o c e s s i n g system. No p l a n t has ever p r o c e s s e d material t h a t i s as s h o r t - c o o l e d as t h a t which w i l l e n t e r s h e MSBR p r o c e s s i n g system. Although t h e s a l t and p r o c e s s f l u i d s a r e n o t damaged by r a d i a t i o n o r i n c r e a s e s i n t e m p e r a t u r e , d e m o n s t r a t i o n t h a t t h e accompanying h e a t release can be accommodated w i l l b e p o s s i b l e only i n a p l a n t a t t a c h e d t o an o p e r a t i n g r e a c t o r .

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++Because f i s s i o n p r o d u c t s are c i r c u l a t e d i n t h e primary s y s t e m o f a m o l t e n - s a l t r e a c t o r and a l s o t r a n s p o r t e d to t h e d r a i n tank, t h e o f f gas system, and t h e chemical p r o c e s s i n g system, s p e c i a l p r o c e d u r e s and equipment are needed f o r t h e repail- o r replacement of equipment. Four f l u i d - f u e l r e a c t o r s h a v e been o p e r a t e d a t OIGI\TL, and t h e maintenance philosophy developed f o r them w i l l b e u s e f u l in p l a n n i n g t h e maintenance of MSBW's. The MSRE e x p e r i e n c e w a s p a r t i c u l a r l y encouragfng i n t h a t t h e r a d i o a c t i v i t y remaining i n equipment from which f u e l had been d r a i n e d was n o t readily- d i s p e r s e d d u r i n g maintenance. ~ e v e r t h e P e s s ,M S B R ' ~w i l l i n v o l v e l a r g e r c ~ m p o n e n t s , h i g h e r r a d i a t i o n l e v e l s , and probably more e x t e n s i v e c o n t a m i n a t i o n than w e have dealt w i t h b e f o r e . Much can b e done i n t h e d e s i g n and l a y o u t t o f a c i l i t a t e maintenance, and t h e MSBR d e s i g n must i n c o r p o r a t e such measures t o t h e f u l l e s t . Versat i l e m a n i p u l a t o r s , a u t o m a t i c w e l d i n g equipment, and remote i n s p e c t i o n t e c h n i q u e s are b e i n g developed f o r o t h e r s y s t e m , and t h e s e w i l l be usef u l f o r MSBR's. However, most w i l l need some t a i l o r i n g f o r t h e p a r t i c u l a r reactor. Consequently, a l t h o u g h some g e n e r a l development of maintenance t o o l s and techniques can be done, most of t h e maintenance development e f f o r t must b e d i r e c t e d to p e r f e c t i n g t h e t o o l s and p r o c e d u r e s needed f o r the particular application.

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ORNL cornpietea a c o n c e p t u a l d e s i g n stud; of a m o l t e n - s d t b r e e d e r r e a c t o r i n 1970. A comparative c o s t estimate of t h a t p l a n t and a l i g h t water r e a c t o r w a s made afterwards by taking t h e b a s i c cost d a t a f o r a r e c e n t PIJW and u s i n g i t t o t h e e x t e n t p o s s i b l e t o eetimaee t h e c o s t o f t h e mBR. The d e p t h of the examination in t h e c o n c e p t u a l d e s i g n s t u d y v a r i e d w i d e l y t h r o u g h o u t t h e plants w i t h p a r t i c u l a r emphasis b e i n g g i v e n t o t h o s e p a r t s t h a t are t h e m ~ u n~c o nt v e n t i o n a l o r are unique t o moltens a l t r e a c t o r s * Ebascs S e r v i c e s and i t s partners, as mentioned e a r l i e r , have begun a c o n c e p t u a l desfgn s t u d y of t h e i r own, and i n i t t h e y are

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l o o k i n g a t s o m e f e a t u r e s of the reactor i n r e a t e r d e p t h t h a n has been done by OR&&. The mjsr a s p e c t s of t h e d e s gn t h a t they have i d e n t i f i e d as requiring f ~ r t h e rs t u d y have t o do with t h e t r a n s i e n t thernaE stresses i n t h e primary system f ~ l l ~ i rna pg i d changes i n r e a c t o r o p e r a t i n g c s n d i t i o n s , a d t h e methods s f s u p p o r t i n g t h e r e a c t o r components and p r o v i d i n g K e s $ r a h t to PeSPSt Sh&illg by earthqUakâ‚Ź?s. E ~ ~ S CfaV0rS Q rep%acing g r a p h i t e an element at a t i m e rather t h a n replacing the e n t i r e c o r e as a u n i t , as w e had proposed. In t h e s t u d i e s we have made t o s i z e components and evaluate d t e r n a tives 9 only s i m p l i f i e d e%astic-stress a n a l y s e s have been made Before o n e n t s can b e b u i l t for reactor u s e , however, a d d i t i o n a l mechanical pr i e ~ measurements w i l l have to b e made ( t h e extent depending a n w t e r i d i s u s e d ) , a d e x t e n s i v e stress analyses w i l l have t o b e perfarmed. Design r u l e s analysis methods atid stress l i m i t s t h a t r e f l e c t t h e time-dependenee of m a t e r i d p r o p e r t i e s ana s t m c t u r a i b e h a v i o r w i l l have t o b e u s e d because t h e s t r e n g t h sf l i k e l y materials a t r e a c t o r te e r a t u x e s w i e i be limited by creep e f f e c t s . ~ ~ ~ aretilsas i g n ts C Q V ~these ~ requirements are currently b e i n g developed i n the L W B W p r o g r m and w F l l b e available f o r use in MSBB d e s i g n . Our c a p i t a l cost conparison between a f u l l y developed XSBW and a present-day PI43 i n d i c a t e s t h a t t h e c o s t s are rougtsPy the same. Although the a s c u r a c y of an e s t i m t e s u c h as t h i s is n o t d e p e n d a b l e , m a i n l y because of t h e l i m i t e d d e p t h of the design, w e b e l i e v e t h a t the tecZbnPque Qf u s i n g a c t u a l PWR c o s t breakdowns f o r the basic c a s t data h e l p s t o linit t h e u n c e r t a i n t y . Vnen i t s d e s i g n s t u d y i s c o m p l e t e d , Ebaiseo w i l l make a c o s t estimate f o r t h e %BR that s h o d d p r o v i d e additional i n s i g h t because O f t h e i r eXperit3ICe 8 5 a P C k i t e C t - e n g h e e r QlI SnSny % i g h t - W a t e r r e a c t o r power plants 0

Environmental E f f e c t s and S a f e t y The major u n c e r t a i n t y w i t h r e g a r d t o environmental e f f e c t s i s how to $ea% w i t h tritiun. Tritium i s a s p e c i a l problem b e c a u s e of its h i g h r a t e sf p r o d u c t i o n in t h e f u e l s a l t and because i t r e a d i l y d i f f u s e s through metals a t XSBR t e m p e r a t u r e s . '%he d i s t r i b u t i s n of t ~ i t i u min the X3.E w a s determined and found to a g r e e r e a s o n a b l y w e l l w i t h an a n a l y t i c a l model developed f o r p r e d i c t i n g i t s behavior When t h i s model is used t o estimate 'now t r i t i u m w o d d behave i n the Y f B R with no s p e c i a l measures taken t o b l o c k i t s p a s s a g e , a n excessive a m m t (790 ~ i l s t a y )is feud t o reach the steam s y s t e m . Several m o d i f i c a t i o n s and o p e r a t i o n o f f e r ways f o r d r a s t i c a l l y r e d u c i n g e s c a p e by t h i s r o u t e . The o b j e c t i v e of limiting t r i t i u m release t o w i t h i n p r e s e n t AEC guidelines f o r light-water-cooked r e a c t o r s a p p e a r s a t t a i n a b l e , but the b e s t measures are yet. t o b e chissew a d demonstrated. The s i t u a t i o n w i t h r e g a r d t o k i n e t i c s and n u e l e a r s a f e t y i s unique because of t h e c i r c u l a t i n g f u e l . The kinetic behavior a f m o l t e n - s a l t reactors i s ~ e l Pu n d e r s t o o d , however, and p r e d i c t a b l e b y methods proved i n t h e Msm. The smlP d e l a y e d n e u t r o n fract n causes no d i f f i c d t RE on a 3 3 ~f u e l w i t h an problem, as demonstrated by operation of t h e e f f e c t i v e delayed n e ~ t ~ o 9fraction t of o n l y 0.8619. Thus t h e r e i s ample e

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b a s i s f o r b e i n g c o n f i d e n t t h a t damaging n u c l e a r e x c u r s i o n s are h i g h l y improbable. Of t h e p o t e n t i a l sources of r e a c t i v i t y i n c ~ e a ~ e st h, e one t h a t w i l l r e q u i r e t h e most s t u d y i s t h e h i d e o u t of f i s s i l e materialC o n d i t i o n s t h a t c o d d lead t o such h i d e o u t are known ( o x i d e p r e c i p i t a t i o n ) , but i t appears t h a t t h e s e conditions can b e s a f e l y avoided. The a f t e r h e a t s i t u a t i o n i s a l s o u n i q u e . The major s o u r c e i s m c h less i n t e n s e t h a n i n s o l f d - f u e l c o r e s b e c a u s e in an MSRR t h e b u l k O € t h e f i s s i o n p r o d u c t s are i n c o r p o r a t e d i n a l a r g e m a s s of f u e l s a l t . F u r t h e r mre, t h i s h e a t s o u r c e can b e g o t t e n i n t o a r e P i l y cooled s i t u a t i o n ( t h e d r a i n t a n k ) under any a c c i d e n t c o n d i t i o n . A s s m e w h a t s e p a r a t e probl e m is t h e smaller r a d i o n u c l i d e h e a t s o u r c e s i n t h e p r o c e s s i n g plant, i n t h e reactor o f f - g a s system, and d e p o s i t e d om s u r f a c e s i n t h e f u e l s y s t e m , which w i l l also r e q u i r e c o o l i n g . The M S E p r o v i d e d u s e f d i n f o r m a t i o n on f i s s i o n p r o d u c t b e h a v i o r b u t u n c e r t a i n t i e s i n nob le-metal b e h a v i o r d i c t a t e c o n s e r v a t i s m i n d e s i g n f o r c o o l i n g t h e f u e l loop and off-gas s y s t e m . O n t h e whole, however, a f t e r h e a t promises t o be less of a problem i n GdSBR's t h a n in o t h e r r e a c t o r s . I n p a r t i c u l a r , t h e d i l u t e heat s o u r c e makes t h e "China syndrome" less of a concern. T h e d e s i g n - b a s i s a c c i d e n t i n an M§BR i s a r u p t u r e i n t h e f u e l s y s t e m that q u i c k l y s p i l l s t h e e n t i r e f u e l imventory, and t h e containment of t h e r a d i o a c t i v i t y i n t h i s e v e n t i s t h e c h i e f s a f e t y c o n s i d e r a t i o n €or a n MSBR. The containment must b e t i g h t , b u t t h e b e h a v i o r of t h e s p i l l e d s a l t and i t s f i s s i o n p r o d u c t s i s p r e d i c t a b l e and t h e r e a p p e a r s t o be no need f o r " i n n o v a t i v e development of containment technology t o take care of t h F s . event. It appears from b a s i c c o n s i d e r a t i o n s t h a t s i t e r e q u i r e m e n t s f o r a n MSBR p l a n t s h o u l d e v e n t u z l l y b e no d i f f e r e n t from t h o s e f o r o t h e r react o r s of l i k e power and i t s s a f e t y p r o v i s i o n s should be no more e x p e n s i v e . Because of t h e u n u s u a l n a t u r e of a n MSBR, however, i t w i l l b e necessary t o b e g i n w i t h f u n d m e n t a l p r i n c i p l e s and develop c r i t e r i a a p p r o p r i a t e to t h i s k i n d sf r e a c t o r , then t o perform a s a f e t y a n a l y s i s conparable i n d e p t h to those for reactors now going i n t o o p e r a t i o n . ~

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As i n any r e a c t o r development program, achievement of economic. mo%ten-sdt breeder r e a c t o r s w i l l r e q u i r e t h a t t h e b a s i c technology b e w e l l e s t a b l i s h e d i n r e s e a r c h and development programs and b e demons t r a t e d and expanded by t h e c o n s t r u c t i o n and o p e r a t i o n of several i n c r e a s i n g l y l a r g e r r e a c t o r s and t h e i r i n t e g r a l p r o c e s s i n g p l a n t s . The technology program is i n p r o g r e s s now, and w e f a v o r t h e c o n s t r u c t i o n of a 150- t o 208-MWCt) Molten-Salt B r e e d e r Experiment (MSBE) as t h e n e x t r e a c t o r i n t h e sequence t o an MSBR. The MSBE would have t h e power d e n s i t y and dl t h e f e a t u r e s and s y s t e m of a f u l l - s c a l e b r e e d e r ~ e a c t o r . Other s t e p s are p o s s i b l e , and one f a v o ~ e dby t h e Molten-Salt B r e e d e r Weact o r A s s o c i a t e s , an o r g a n i z a t i o n c o n s i s t i n g of Black 6% Veatch C o n s u l t i n g Engineers and a group of u t i l i - t i e s 181, i s t h e c o n s t r u c t i o n o f a l a r g e r b u t lower performance c o n v e r t e r r e a c t o r that wodcl e v o l v e into a b r e e d e r . W e b e l i e v e , however, t h a t t h e more d i r e c t r o u t e of t h e b r e e d e r experiment is p r e f e r a b l e

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I n t h e technology program s e v e r a l advances must b e made b e f o r e w e can b e c o n f i d e n t that the next r e a c t o r can be built and o p e r a t e d s u c c e s s f u l l y . %le most i m p o r t a n t problem t o which this a p p l i e s is t h e s u r f a c e c r a c k i n g sf H a s t e l l o y K O Sone other developments, such as t h e t e s t i n g of 68DIe O f t h e CQElPOXIâ‚ŹZI%s QT t h e batter Stages O f the p l 3 3 C e s s h g p%ant development, could a c t u a l l y b e completed w h i l e a reactor i s b e i n g deed and built. The mjor developments t h a t we b e l i e v e should b e pursued d u r i n g t h e next s e v e r a l y e a r s are t h e f o l l o w i n g : A m o d i f i e d H a s t e % k o y N s or an a l t e r n a t i v e material t h a t i s i m u n e t o by teiiarrium, mustb e selected ana its e o m p a t i b i i i t y w i t 1 1 f u e l salt demonstrated w i t h out-0%-pile forced convection loops and i n - p i l e equate r e s i s t a n c e t o radiacapsule experiments; means for g i v i n g it proauction O f the ge must b e faun i f needed, and c o m e r c i have to be demonstrated; the mechanical o p e s t i e s data needed for eode q u a l i f i c a t i o n must be a c q u i r e d i f t h e y do not a l r e a d y exist 0

2.

of intercepting and isolating t r i t i u m t o prevent i t s passage into t h e stea~zss y s t e m m s t be demanstrated at r e a l i s t i c ~ o s l d i t i ~ z nand s a large enough s c a l e to s h o w t h k t it i s f e a s i b l e f o r a r e a c t o r .

3.

The v a r i o u s s t e p s in t h e p r o c e s s i n g s y s t e m must f i r s t b e demonstrated i n separate experiments; these s t e p s must then b e combined in an i n t e g r a t e d demonstration of t h e complete p r o c e s s , i n c l u d i n g the materials c o n s t r u c t i o n ; ana ~ n a ~ after ~ y , t h e KSBE p l a n t is c o n ~ ~ p t ~ a l i y d e S i p C ? d , a WCk-up COb%taillingC O I R p O R e n t S that as Close as p o s s i b l e in design to thase which will be used i n the a c t u a l p r o c e s s m u s t be b u i l t and its OperatiOn and minteellance procedures demons t r a t e d *

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sped and dem0asCrated bander c o n d i t i o n s and a t s i z e s t h a t a%How c o n f i d e n t e x t r a p o l a t i o n t o the XSBE i t s e l f . These i n c l u d e the xenon s t r i p p i n g s y s ~ e r nf o r t h e f u e l salt, ~ f f - g a s and c l e a n u p systems f o r t h e c o o l a n t salt (facilities in which these c o u l d be done are a l r e a d y under c o n s t r u c t i o n ) t e s t s of steam g e n e r a t o r modules and s t a r t u p s y s t e m s , and t e s t s of p r o t o t y p e s of pumps t h a t would a c t u a l l y go in t h e reactor. The c o n s t r u c t i o n s f an engineering mock-up sf t h e major components and systeans of t h e reacts% wouBd be d e s i r a b l e , but whether o r n o t that is done would depend on how far the development program had proceeded 2n t e s t i n g v a r i o u s cowonents and system i n d i v i d u a l l y

5.

Graphite elements t h a t are s u i t a b l e f o r the MSBE shsubd be purchased i n s i z e s and quantities that assure t h a t a co pro due t ion c a p s exist, and t,he r a d i a t i o n b e h a v i o r ky-produced mteriai s h s u l a be conf s e a l i n g graphite to exclude xenon s h o d d c o n t i n u e t o be explored.

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Other r e s e a r c h and development w i l l b e r e q u i r e d i n a number of areas, b u t t h o s e l i s t e d are t h e major and most c o s t l y u n d e r t a k i n g s . They r e p r e s e n t a d e s i r a b l e program f o r advancing and t e s t i n g m o l t e n - s a l t b r e e d e r technologj7 i n t h e a b s e n c e of a c o r n i t m e a t t o b u i l d a r e a c t o r , and most become n e c e s s a r y i f a ~ e a c t o ri s t o b e b u i l t .

%he I n c e n t i v e s f o r W B R Development

'phe f o r e g o i n g d i s c u s s i o n i n d i c a t e s t h a t c s n s i d e r a b l e p r o g r e s s has been made towards t h e development of m o l t e n - s a l t b r e e d e r r e a c t o r s b u t a l s o reveals that a s u b s t a n t i a l development program w i l l b e r e q u i r e d b e f o r e commercial M S B h become a n a c t u a l i t y . We t u r n now t o t h e quest i o n of whether t h e r e are i n c e n t i v e s f o r p u r s u i n g such a program. A f u l l statement of t h e r a t i o n a l e f o r t h e development sf moltens a l t b r e e d e r r e a c t o r s c o d d l o g i c a l l y make t h r e e p o i n t s . F i r s t , b r e e d e r s are needed. Second, i n a d d i t i o n t o t h e LME3RR, whish h a s a l r e a d y been e s t a b l i s h e d as a n a t i o n a l g o a l , one o r more d i f f e r e n t c o n c e p t s that are also c a p k b l e of meeting b r e e d i n g needs s h o u l d b e pursued a t a p p r o p r i a t e l e v e l s of e f f o r t . F i n a l l y , t h e MSBR h a s a unique and s i g n i f i c a n t r o l e as an a l t e r n a t e b r e e d e r . Tke argument f o r t h e f i r s t p o i n t has b e e n a d e q u a t e l y made i n a number of p l a c e s - m a s t n o t a b l y i n t h e 1962 r e p o r t to t h e P r e s i d e n t [la] and does n o t weed t o b e r e p e a t e d . The second p o i n t i n v o l v e s c o n s i d e r a t i o n s t h a t go beyond t h e s e o p e of t h i s r e p ~ r tand t h u s t h e arguments t o support i t w i l l . a l s o be o m i t t e d , a l t h o u g h we are convinced of i t s v a l i d i t y . We are t h u s b r o u g h t d i r e c t l y t o t h e t h i r d p o i n t and must c o n s i d e r how w e l l t h e MSBR meets t h e r e q u i r e m e n t s for a n a l t e r n a t e b r e e d e r . For t h e development of any b r e e d e r t o be worth p u r s u i n g , t h e system, i n c l u d i n g t h e r e a c t o r s and t h e a s s o c i a t e d f u e l i n d u s t r y , must p o t e n t i a l l y b e a b l e t o m e e t t h r e e b a s i c requirements

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1. Its f u e l u t i l i z a t i o n c h a r a c t e r i s t i c s , by which w e mean some combinat i o n 06 b r e e d i n g r a t i o and f i s s i l e - f u e l i n v e n t o r y , must b e good enough

that i f i t were b u i l t i n q u a n t i t y , t h e c u m u l a t i v e amount sf uranium ....

t h a t must b e mined t o s a t i s f y t h e growing U.S. n u c l e a r power economy would s t a y w i t h i n a c c e p t a b l e bounds. ( D e f i n i n g t h e Patter i s , of c o u r s e , t h e d i f f i c u l t y . R e f e r e n c e s 9 and 10 i n c l u d e a n a l y s e s p e r t i nent t o t h i s . )

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Its power c o s t a t t h e t i m e t h a t i t i s i n t r o d u c e d as a commercial produet must be low enough t h a t i n a f r e e e c o n ~ m yi t would b e chosen by u t i l i t i e s on ~ ~ ~ R Q Tgrounds K ~ C i n p r e f e r e n c e t o the c o n v e r t e r react o r s t h e n a v a i l a b l e . Inherent i n t h i s i s t h e requirement t h a t t h e r e a c t o r ' s r e l i a b i l i t y and m a i n t a i n a b i l i t y b e good enough t o y i e l d high plant a v a i l a b i l i t y .

3.

I t must b e s a f e enough t h a t t h e r i s k of i n j u r y t o t h e p u b l i c i n an a c c i d e n t and t h e amounts of r a d i o a c t i v i t y r e l e a s e d d u r i n g n o r m 1 o p e r a t i o n are b o t h a c c e p t a b l e .

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2 s d i s c u s s e d i n t h e f o l l o w i n g p a r a g r a p h s , M S B R ' s appear p o t e n t i a l l y c a p a b l e o f s a t i s f y i n g all t h r e e c r i t e r i a . F u e l U t i l i z a t i o n . - The r p i d removal of f i s s i o n p r o d u c t s and p r o t a c t i n i u m from a molten-sale b r e e d e r r e a c t o r , coupled with the a b s e n c e Sf s t r o n g l y ~ ~ U ~ K Q Ia -bIs o r b i n g materials i n the c o r e s t r u c t u r e , makes i t f e a a i b l e t~ achieve a s i g n i f i c a n t b r e e d i n g g a i n i n a t h e r m a l r e a c t o r , When combined w i t h i t s low s p e c i f i c i n v e n t o r y , t h i s r e s u l t s i n good u t i l i z a t i o n of uranium o r e r e s o u r c e s . Tiiis p o i n t i s i l l u s t r a t e d by F i g . 1 . 2 , ~ h i c hshows that 11either t h e b r e e d i n g gain nor the d o u b l i n g time i t a themselves are a d e q u a t e measures s f t h e a b i l i t y of a b r e e d e r r e a c t u r t o limit the amount of uranium ore t h a t must b e wined t o f u e l a growing n u c l e a r power economy. The f i s s i l e i n v e n t o r y i s also i m p o r t a n t , and i t i s t h e i r ~ Q W s p e c i f i c i n v e n t o r y that makes i t p o s s i b l e f o r m o l t e n - s a l t b r e e d e r P e a c t o r s to serve a8 w e l l as f a s t b r e e d e r s i n l i m i t i n g t h e r e s o u r c e requirements Tu d e m o n s t ~ a t ef ~ r t h ethe ~ importance of t h i s p o i n t t h e peak UPaniUPn Ore Kequirefnentยง Obtailaed. from CUPTTeS l i k e t h o s e Show72 in Fig. 1 . 2 have been cross-plotted as a f u n c t i o n of the s p e c i f i c i n v e n t o r y and d o u b l i n g t i m e i n F i g . 1 . 3 . Cansequenthy, o u r c o n c l u s i o n i s that molten-salt b r e e d e r r e a c t o r s , i l l Spite Sf t h e i r Small b r e e d i n g gELiEk, Can Serve W a l l &S f a s t l r e a C t Q P S i n esnserviwg uranium. I n a d d i t i o n , molten-salt c o n v e r t e r reactors fed w i t h p l u t a n i u m can have high c o n v e r s i o n r a t i o s and very f a v o r a b l e f u e l c y c l e costs. Thus, even i f m ~ l t e n - ~ a % breeders t a r e not S U ~ ~ ~ S S 8% ~ U % not needed, the molten-salt teehnology can b e used in a ~ o n v e r t e rthat serves as a c o ~ ~ p a n i o lto a a f a s t b r e e d e r to p r o v i d e low power C O S % and a balanced f u e l E C O ~ O I I I ~ [ 9 , p. 6-521 ~ h r o t n g ~ t=h ~i s~ st e c t i o n tnave d i s c u s s e d the c o n s e r v a t i o n of urani u m ore b u t have n ~ mentioned t t h o r i m , even though t h e MSBR i s a t h o r i m cycle reactor. T h e r e a s o n i s t h a t i t i s fissile f u e l that i s i n s h o r t s u p p l y ami n o t fertile m a t e r i a l . 111e W.S. reserves of bot11 2 3 8 ~and t i k s s i u m a r e a d e q u a t e t o s u p p l y the need f o r f e r t i l e materials f o r taun$reds s f y e a r s , and the c o s t of power i s r e l a t i v e l y i n s e n s i t i v e t o their c o s t . A s a l r e a d y n o t e d , d o u b l i n g t h e c o s t sf thorium from $5/_lb t o $ l O / l b would add ondy O o Q 5 r n i h I / h h t o t h e f u e l - c y c I e c o s t i f no changes were t o ecenonnize on t ~ m r i u mu s e . o

Power C a s t . - Avoidance o f f u e l f a b r i c a t i o n , rapid removal ~f fiss i o n p r o d u c t p ~ i s o n sand pratactfnium, and a low f i s s i l e i n v e n t o r y result i n low f u e l - c y c l e c o s t s f o r 'a.ISBWPs in s p i t e of i n c l u s i o n sf a s u b s t a n t i a l c a p i t a l c o s t f o r t h e o n - s i t e p r o c e s s i n g p l a n t , Capital c a s t s f o r t h e r e a c t o r are l e s s c e r t a i n t h a n f u e l - c y c l e csosts, brat a d e t a i l e d comparison indicates t h a t when f u l l y d e v e l o p e d , the c o n s t r u c t i o n c a s t s of MSBR's s h ~ u l db e about t h e s e as tbmse 0 6 l i g h t - w a t e r r e a c t o r s . The h i g h a. e f f i c i e n c y of t h e MSBR, t h e ]bow primary-system p r e s s u r e , and t h e l a r g e t e m p e r a t u r e d i f f e r e n c e s a v a i b a b l e f o r heat t r a n s f e r a r e t h e key f a c t o r s w~xichh o i a NSBB capita^ c o s t s dot%m9wllereas remote maintenance r e q u i r e m e n t s on p a r t s of t h e p l a n t e n t a i l added c ~ s t s .

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Some p e n a l t y must b e p a i d f o r t h e c o s t of r e p l a c i n g g r a p h i t e , b u t i f t h i s must b e done as f r e q u e n t l y as every f o u r y e a r s i s o u r estimate i s t h a t the c o s t w i l l f a l l i n t h e r a n g e 0% 0 . 1 t o 0.2 mill/kwh. The need t o p e r form remote maintenance on p a r t s of t h e p l a n t may add a d d i t i o n a l downtime r e q u i r e m e n t s b u t t h i s should be o f f s e t by t h e h i g h a v a i l a b i l i t y r e s d t i n g f r o m on-stream r e f u e l i n g , which o b v i a t e s t h e need f o r a n n u a l r e f u e l i n g shutdowns I n sum, w e b e l i e v e t h a t power c o s t s of M S B R P s should b e c o m p e t i t i v e w i t h t h o s e of l i g h t - w a t e r r e a c t o r s , and t h e a t t a i n m e n t of low ~ Q W ~ Tc -o s t does n o t a w a i t development of a l a r g e f u e l - c y c l e i n d u s t r y . 6

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S a f e t y . - Molten-salt r e a c t o r s have c e r t a i n i n h e r e n t f e a t u r e s t h a t a s s i s t t h e d e s i g n e r i n p r o v i d i n g a s a f e p l a n t . The s a l t systems s p e r a t e a t low p r e s s u r e w i t h l i t t l e s t o r e d energy; t h e salts d o n o t r e a c t r a p i d l y w i t h a i r cx water; some f i s s i o n p r o d u c t s a r e removed f r o m t h e primary system c o n t i n u o u s l y ; and i o d i n e and s t r o n t i u m form s t a b l e compounds i n t h e s a l t . Continuous f u e l p r o c e s s i n g e l i m i n a t e s t h e need f o r excess r e a c t i v i t y , and a prompt n e g a t i v e t e m p e r a t u r e c o e f f i c i e n t i s a s s o c i a t e d w i t h t h e h e a t i n g of t h e s a l t . A s a f e t y d i s a d v a n t a g e i s t h e accumulation of f i s s i o n p r o d u c t s i n t h e primary system, t h e o f f - g a s system, t h e f u e l s t o r a g e t a n k s , and t h e proce s s i n g p l a n t , which r e q u i r e s p r o v i s i o n s t o i n s u r e t h a t t h e f i s s i o n p r o d u c t s will b e c o n t a i n e d and t h e i r decay h e a t w i l l b e removed under all conceiva b l e circumstances. P a r t i a l l y o f f s e t t i n g t h i s i s t h e a b i l i t y t o drain t h e f u e l i n t o a tank t h a t has an always-ready, redundant c o o l i n g system. I n t h e YยงBR r e f e r e n c e d e s i g n , t h i s t a n k i s used a l s o a s a hold-up t a n k f o r t h e s t r o n g l y h e a t g e n e r a t i n g o f f - g a s , which means t h a t i t s c o o l i n g system i s always i n u s e and need n o t come i n t o o p e r a t i o n j u s t i n an emergency. An added advantage of t h e d e s i g n is t h e u s e of a n a t u r a l c i r c u l a t i o n c o o l i n g system that does not need power t o o p e r a t e and can p i c k up i n c r e a s e d l o a d w i t h o u t a c t i o n by t h e c o n t r o l system o r t h e o p e r a t o r . Two o t h e r f a c t o r s may p r o v i d e Some s a f e t y margins over SQlbid-fUeb r e a c t o r s . One i s t h e comparatively %ow power d e n s i t y of f i s s i o n p r o d u c t s i n the f u e l salt, which should permit catch b a s i n s or crucibles a t the b o t t o m o f t h e containment: b u i l d i n g t o b e coolbed w e l l enough t h a t "China syndrome" p e n e t r a t i o n of t h e containment s t i l l would n o t o c c u r i f all else f a i l e d . The o t h e r i s the o n - s i t e p r o c e s s i n g , which e l i m i n a t e s t h e need t o t r a n s p o r t f i s s i o n p r o d u c t s a t a t i m e when t h e i r h e a t g e n e r a t i o n rate i s s t i l l s i g n i f i c a n t .

I n addition t o being a b l e t o s a t i s f y t h e s e general c r i t e r i a f o r a b r e e d e r , t h e MSBR i s p a r t i c u l a r l y s u i t a b l e for development as an a l t e r n a t i v e t o t h e Liquid-Metal F a s t Breeder R e a c t o r . The r e a s o n i s t h a t i t i s completely d i f f e r e n t from t h e L R, and i f t h e LMFBW w e r e t o encounter d i f f i c u b t t e c h n i c a l , s a f e t y , o r economic problems, t h e r e is a good chance t h a t t h o s e problems would n o t b e s h a r e d by t h e MSBR. These d i f f e r e n c e s i n c l u d e : f l u i d f u e l v e r s u s s o l i d f u e l , slow-neutron spectrum v e r s u s f a s t .;.;..... . . B

26

BpeCtPUbB, 233u-nl f k k d CyCke V@YSUG h-23 8u C y d e , Il'~0lteIl-Sd.t C Q O l a l a t versus s o d i m c ~ o l a n t ,p r o c e s s i n g fuel o n - s i t e versus s h i p p i n g t o a cent r a l f a e i l i e y , graphite c o r e s t ~ u c t u r ev e r s u s s t a i n l e s s - s t e e l c l a d d i n g S t r U C t U r e , and S l o w %eac%orkinetic8 VeTSUS fast k i l l e t i c s . A further advantage arises f r o m t h e d i s s i m i l a r i t y : if b o t h r e a c t o r s a r e developed s u c c e s s f u l l y , t h e d i f f e r e n c e s w i l l p r o v i d e a n o p p o r t u n i t y f o r f u l l economk c o m p e t i t i o n i n the s u p p l y of b r e e d e r s t o u t i l i t i e s , extending back t o t h e mining 0% thorium and uranium o r e . Thus we conclude t h a t t h e MSBR c a n satisfactorily meet t h e requirements f o r a b r e e d e r i f i t s p o t e n t i a l i s r e a l i z e d , and the d i f f e r e n c e s ben it and an D f F l R p r o v i d e advantages t o i t as an a l t e r n a t i v e to t h e R. In the next section w e examine t h e p r o s p e c t s f o r s u c c e s s i n aehievi n g t h e p o t e n t i a l O f the concept. The Likelifisod of S u c c e s s The development program f o r a power reactor m i g h t b e c o n s i d e r e d a s u c c e s s FP it b r i n g s a l l sf tile t e c h n o l o g y needed f o r the r e a c t o r t o t h e n u f a c t u s e r s can use it t o p r s d u c e power p l a n t s t h a t can be sold t o u t i l i t i e s . A f t e r h a v i n g e o ~ ~ p l e t ethis d review, w e conclude t h a t there i s a ~ e a s ~ r t a b lexpectation e t h a t an MSBR deveHopment p r o g r a m can acconpiish t h i s T~ a. s o , i t f i n d s ~ ~ . ~ t fi o~r nthe s t e c h n i c a l problems w e have i d e n t i f i e d and muse d e v e l o p d l of t h e materials c5nponerits and systems that are needed Our C O R C ~ U S ~ O ~ S a b o u t the major problems are a s fo%lows: a

1. Recent experiments i n d i c a t e t h a t t h e r e p r o b a b l y are s o l u t i o n s to tine inter gKanU%aX=CraCkFng prQbl@Tâ‚Źl%hathas hung IlleKMCingl~ O V e % t h e

p r o g ~ a r nduring the p a s t y e a r . 8x1 i m p o r t a n t question a t t h e moment is Whether 'Che reIX2dg C a l l be a S I I l E d a Change ill the CoDIpOSitisn s f Hastel$oy N, 0% i n s t e a d w e m u s t s u b s t i t u t e an alloy of s i g n i f i c a n t l y d i f f e r e n t c s m p o s i t i s n that w i l l r e q u i r e a n e x t e n s i v e program t o qualify i t f o r reaCtClP U s e . miS fnatter is b e i n g i n t e n s i V e % y i n v e s t i g a t e d a t p r e s e n t , and. a p r e l i m i n a r y answer s h ~ u l db e a v a i l a b l e w i t h i n a few months, 2.

Our research program g i v e s h o p e t h a t means w i l l b e f o r t h c o m i n g f o r r e d u c i n g the e s c a p e of t r i t i u m t o eke steam s y s t e m w i t h o ~ ta signif i c a n t change i n o u r c o n c e p t o f t h e reactore W e should be a b l e to s e l e c t t h e mast promising meth and demonstrate it in a system o f r e a s o n a b l e s i z e within one 01: t w o y e a r s .

3.

:+iueh work remains t o be done in the development and demsnstratim O f t h e p r o c e s s i n g s y s t e m f o r the s i n g l e - f l u i d b r e e d e r r e a c t o r , but: p r o g r e s s so far has been v e r y s a t i s f a c t o r y , and t h i s remains one of the b r i g h t s p o t s i n t h e >mBR development program. T h e p r o s p e c t s f o r s u c c e s s f u l l y developing t h e fluorinstion-reduceive extraction-metal transfer system are g o d , and t h e r e are same a l t e r n a t i v e appr~oaches i n ease p a r t s o f the p r e s e n t l y p r e f e r r e d s y s t e m e n c o u n t e r ~ K I S U ~ Q able d i f f i c u l t i e s . W e s h o u l d n 5 t e that a c s m p l e t e d e m o n s t r a t i o n of the p?ZCXesSFElg p l a n t C a l l Only b e lâ‚ŹEide QL% a % $ a C t O % , Where repreSenti3tive concentrations of p r o t a c r i n i m and short-cooled f i s s i o n p r o d u c t s agfe a v a i l a b l e

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A f t e r t h e s e major t e c h n i c a l q u e s t i o n s have been f a v o r a b l y r e s o l v e d , a h o s t of t a s k s remain t o b e accomplished i n t a k i n g t h e e n g i n e e r i n g PEE s c a l e t o MSBR s c a l e . Those t h a t w e r e c u g n i z e are d e s c r i b e d in t h i s r e p o r t ; some are d i f f i c u l t , b u t a l l seem a c h i e v a b l e . There may b e o t h e r s ; i f so, t h e y c a n b e s t b e i d e n t i f i e d by d o i n g t h e det a i l e d d e s i g n of r e a c t o r p l a n t s and c a n b e b r o u g h t i n t o the s h a r p e s t f o c u s by development of equipment and systems f o r t h o s e p l a n t s .

S o l v i n g t h e t e c h n i c a l problems and d e v e l o p i n g an o p e r a b l e r e a c t o r , however, are n o t d o n e a .guarantee of s u c c e s s f o r a b r e e d e r . The b r e e d e r must not o n l y b e o p e r a b l e , i t must m e e t t h e perfornnance c r i t e r i a w e l i s t e d earlbier. T h e r e f o r e w e t u r n t o t h e q u e s t i o n of how l i k e l y it i s t h a t t h e c h a r a c t e r i s t i c s claimed f o r t h e MSBR r e f e r e n c e d e s i g n w i l l be. a c h i e v e d a

F u e l U t i l i z a t i o n . - O u r e x p e r i e n c e w i t h t h e MSRE and w i t h t h e H i g h Temperature L a t t i c e T e s t Reactor at Hanford shows that t h e r e is l i t t l e u n c e r t a i n t y i n o u r a b i l i t y t o c a l c u l a t e the b r e e d i n g r a t i s and f u e l conc e n t r a t i o n of a m ~ l t e n - s d t reactor that has a s p e c i f i e d care composition. More u n c e r t a i n i s t h e b e h a v i o r s f f i s s i o n p r o d u c t s i n t h e MSBR; h e r e t h e M S E d a t a do n o t p r o v i d e a complete b a s i s f o r p r e d i c t i o n , b u t the u ~ c e r t a i n t y does n o t a p p e a r t o b e g r e a t enuugh f o r t h e r e t o b e a major e r r o r i n the e s t i m a t e d b r e e d i n g r a t i o . The f i s s i l e i n v e n t o r y depends on t h e volume of the r e a c t o r primab-y s y s t e m and t h e amount of uranium h o l d u p i n t h e p r o c e s s i n g p l a n t , as w e l l as on t h e c o n c e n t r a t i o n i n t h e f u e l s a l t ; and t h e s e c o u l d be somewhat h i g h e r t h a n e s t i m a t e d i n t h e r e f e r e n c e d e s i g n . The u n c e r t a i n t i e s are whether t h e h e a t exchanger c a n b e as compact as p o s t u l a t e d i n t h e d e s i g n , whether t h e p l e n a i n the r e a c t o r v e s s e l are l a r g e enough f o r a d e q u a t e flow d i s t r i b u t i o n , and whether t h e hold-up t i m e i n t h e p r o c e s s i n g p l a n t can b e as s h o r t as p u s t u l a t e d , While w e c o u l d have been o v e r l y o p t i m i s t i c about some of these, none a p p e a r s l i k e l y t o change enough t o have a major e f f e c t on t h e f u e l u t i l i z a t i o n . Power C o s t . - T h e p r o b a b i l i t y of a c h i e v i n g o u r power c o s t c r i t e r i o n i s more d f f f i c u l t t o e v a l u a t e b e c a u s e i t n o t ~ ~ l iln vy o l v e s u n c e r t a i n t i e s i n MSBR c o s t s but a l s o u n c e r t a i n t i e s a b o u t what t h e c o s t of t h e competing systems w i l l be. The majo6- c o s t item i n the fuel cycle i s t h e c a p i t a l c o s t sf t h e p r o c e s s i n g p l a n t , and t h i s i s probably t h e most u n c e r t a i n o f t h e estimates. W e can o n l y s a y that w e think w e have m d e a r e a s o n a b l y c o n s e r v a t i v e estimate, i n c l u d i n g , f o r example, an a l l o w a n c e of $200 a pound f o r t h e c o s t of f a b r i c a t i n g molybdenum; and t h e r e is a d d i t i o n a l c o n s e r v a t i s m in t h e p r o c e s s i n g c o s t s b e i n g based on u s i n g t h e p r o c e s s i n g p l a n t f o r only 1000 MW(e) of r e a c t o r c a p a c i t y , whereas t h e u n i t c o s t s of p r o c e s s i n g p l a n t s come down v e r y r a p i d l y i f t h e throughput i s i n c r e a s e d . Because t h e f i s s i l e i n v e n t o r y i s f a i r l y l o w and t h e c r e d i t f o r sale of b r e d f u e l i s modest, t h e f u e l c y c l e e c ~ n o r n i c sof MยงBR's are n o t very s e n s i t i v e t o t h e s e factors nox t o t h e c o s t o f e n r i c h e d uranium. Increasing UraEltum ore c o s t f r o m $8 t o $16 a pound Without r e Q p t i d Z a t i Q i 3 Qf t h e reactor would o n l y i n c r e a s e t h e f u e l c y c l e c o s t s by about 0 . 1 milP/kwh.

Other factors have a small e f f e c t on t h e f u e l c y c l e c o s t ; d s u b b i n g t h e cost: of ?Lis for example, would add 0 . 0 6 m i Y L s / k w i i 9 and doubling t h e c o s t Of t h o r i u m Would a d d 8,05 mial/kWh. h re%atfVe8y h i g h fiX@d-Chal-ge r a t e Qn t h e f u e l inVetltoPy has been Used in she eS6iPnatea The graphite replacement c o s t w a s e s t i m a t e d a s s u d n g that the graphite lifetime w i l l . be only as great as t h a t 0 % g r a p h i t e that has a l r e a d y t e s t e d , a d exgectea impro~efilentsin lifetime w i u reduce tile fiequency and t h u s the cost of replacement, The cost of t h e graphite has been estimated to b e about $ k O / l b , which is much higher th o f m o s t s'sspecialtyP'g r a p h i t e s b u t could b e %ow f o r a seabe meeting t h e unique requirements sf the I4SaSBR. However, a l l o w i n g an additional $ 5 / l b to cover a possible u n d e r e s t i m a t e of the sealing c o s t wsuPd add odgr abaut 0-1mi%l/kwh t o t h e power s s s t . We KLUst aCkIIOW%ed@? t h a t eStiE3tiCXt O f Capita%. c o s t s Q f p l a n t ยง %O b e b u i l t far in the f u t u r e w i t 1 1 yet undeveloped techwoi~gyis m-1 uncertainties. Because o f the w a y EWR c o s t data w e r e used, ttaese u n c e r tainties, as we j u d g e I t , h ve more to do with the d e s i g n of the p l a n t than W i t h OUP a b i l i t y to DldCe C O S t cCiE@3risCX%3 f a r Et g i v e n d e s i g n . Nevert h e l e s s , there i s limited room f o r error in the comparison w i t h an LWR because the c o s t sf 8 ~ r e a c t 0 equipmenttF r (which includes 9 the reactor i t s e l f , the s a l t pumps, t h e heat exchangers a a t o r s , t h e s a l t s t o r a g e tanks, and the o f f - g a s system) is O n l y one-third of t h e t o t a l 6 6 6 % a f the power plant. a c t o r t h a t can affect the power cost is p l a n t a v a i l a b i l i t y . t r e a c t o r s do no% have to be shut down f o r refueling, and tile f r e q u e n s y O f graphite replacement is %OW aask b e sc'kseadea to COi n c i d e with major turbine maintenance, MSI3R's start o f f with an availability advantage over L \ - R ' s s . The KSBR plant must, however, b e made relia b l e and must be s p e c i a l l y designed s o that t h e i n i t i a l advantage is sat o f f s e t by t h e increased d i f f i c u l t y of maintenance. Our- estimate h a s the cost of power from an KSBR b e i n g about 0.5 m i l % / kwh less t h a n t h a t of a light-water react^^ a t p r e s e n t uranium o r e p r i c e s . If uranium o r e costs increase b y $$/ab b y the time breeders are introduced, Thus there t h e c o s t advantage sf an MSBR would increase b y Q - 3 mill/kwh iS 2, f a i K marP@n f8H $%Tor i n CoIllpariSC?n With present day uJRgSs. MOWever, LWR c o s t s are certain to change same in t w o or s o decades, and K T G R P s r a t h e r than %WRSS could b e the cQlnverter w i t h which to compete a t the time. Thus strong c o n c l u s i o n s a b o u t the MSBR meeting our cost criterion are not p o s s i b b e , b u t t h e chances seen reasonably good with l o w uranium prices, of course, increase as t h e c o s t o f uranium o r e goes up.

..... u.s,

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En c o n t t a s t t o t h e p r o b a b i l i t y of a b i g a c c i d e n t , t h e w i d e r d i g t r i b u t i o n of r a d i o a c t i v i t y i n a m o l t e n - s a l t r e a c t o r and i t s p r o c e s s i n g p l a n t i n c r e a s e s the chances of small releases. The a b i l i t y t o r e s t r i c t t h e release of r a d i o a c t i v i t y d u r i n g n o r m 1 o p e r a t i o n o r maintenance p e r i o d s t o a d e s i r e d l e v e l a p p e a r s t o be a matter of c o s t , and t h e p r o v i s i o n of a d e q u a t e containment and clean-up s y s t e m s h o u l d r e d u c e t h e release rate to 85 I S W a8 d e s i r e d .

These c o n s i d e r a t i o n s convince us t h a t t h e l i k e l i h o o d of b e i n g a b l e t~ d e v e l o p an ICBR t h a t can m e e t t h e r e q u i r e m e n t s f o r a s u c c e s s f u l b r e e d e r

i s good. W e must n o t e , however, that s k e p t i c s w i l l sometimes acknowledge uments t h a t w e have c i t e d b u t t h e n raise q u e s t i o n s about o t h e r factors t h a t t h e y t h i n k d & t be iKLIpOKtant. One q u e s t i o n has to do with t h e p r a c t i c a l i t y of o p e r a t i n g and m a i n t a i n i n g a r e a c t o r in which f i s s i o n p r o d u c t s s p r e a d throughout several p a r t s of t h e p l a n t . W e b e l i e v e t h a t t h i s i s a s e r i o u s matter t o be t r e a t e d t h o r o u g h l y i n t h e d e s i g n , b u t w e are convinced that i t can b e h a n d l e d e c o n o m i c a l l y . Our views are b a s e d on e x p e r i e n c e w i t h t h e o p e r a t i o n and maintenance of f o u r f l u i d - f u e l react a r s , and m o s t i m p o r t a n t l y , by o u r f a v o r a b l e e x p e r i e n c e w i t h the MSW. L a r g e r p l a n t s w i l l have l a r g e r C O T D ~ Q ~ ~ ItIo~ Sbe handled and h i g h e r l e v e l s of r a d i o a c t i v i t y , b u t w e b e l i e v e t h a t t h e I S R E m i n t e m a n c e approach, used with c a r e f u l d e s i g n of t h e p l a n t so t h a t maintenance r e q u i r e m e n t s are a n t i c i p a t e d , w i l l p e r m i t r e p a i r o r replacement t o b e done i n r e a s o n a b l e times A second q u e s t i o n i s whether t h e chemical n a t u r e of a m o l t e n - s a l t r e a c t o r and the r e q u i r e m e n t s f o r o p e r a t i o n of a p r o c e s s i n g p l a n t i n conj u n c t i o n with i t w i l l make u t i l i t i e s u n w i l l i n g t o purchase such s y s t e m s . Our r e s p o n s e i s t h a t u t i l i t i e s have been w i l l i n g t o take on o t h e r advanced t e c h n o l o g i e s , such a s n u c l e a r energy and t h e u s e of s u p e r c r i t i c a l stearn, and t h e y seem w i l l i n g t o u n d e r t a k e o p e r a t i o n of s y s t e m c ~ n t a i n i ~ molten lg sodium. None o f t h e u t i l i t i e s t h a t have e v i n c e d an i n t e r e s t i n moltens a l t r e a c t o r s h a s i n d i c a t e d t o us that t h e r e q u i r e m e n t f o r chemical reprocessing would c a u s e them t o b e u n w i l l i n g to sperate an MSBR, The f i n a l q u e s t i o n i s sometimes s t a t e d this way: "If m o l t e n - s a l t r e a c t o r s a r e as g ~ o das you i n Oak Ridge s a y , why a r e n ' t i n d u s t r i a l f i r m p r e s e n t l y working on them?" The answer t o t h i s h a s several f a c e t s . F i r s t of a l l , t h e commitments o f t h e p r e s e n t u t i l i t y s u p p l i e r s t o other systems w e r e a11 made b e f o r e t h e MSW had o p e r a t e d and provided a d e m o n s t r a t i o n t h a t t h e technology w a s more p r a c t i c a l t h a n some had e x p e c t e d . Second, t h e m a n u f a c t u r e r of an MSBR cannot e x p e c t t h e s i g n i f i c a n t f u e l s u p p l y and r e p r ~ c e s s i n gb u s i n e s s - t h e "razor b l a d e " b u s i n e s s - t h a t can accompany the s a l e of a s o l i d - f u e l r e a c t o r , and t h u s the p o t e n t i a l f o r f u t u r e p r o f i t s seems l e s s w i t h m o l t e n - s a l t ~ e a c t o r s . F i n a l l y , the budget of t h e Atomic Energy C o m i s s i o n f o r m o l t e n - s a l t r e a c t o r development has been r e l a t i v e l y s m a l l , and t h e AEC h a s mde no commitment t h a t i t w i l l assist i n t h e development of m o l t e n - s a l t b r e e d e r r e a c t o r s . Hence a m a n u f a c t u r e r who cons i d e r e d u n d e r t a k i n g m o l t e n - s a l t r e a c t o r development could not be s u r e of r e c e i v i n g t h e k i n d of development s u p p o r t t h a t h a s been forthcoming f o r o t h e r r e a c t o r concepts a

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The objective of developing breeder reactors is to o b t a i n a s o u r c e sf low-cost energy f o r ourselves and for future generations Molten-salt breeder reactors have attributes sf fuel utilization, e c s n s d c s , and s a f e t y that make them w e l l s u i t e d to serve t h a t purpose. '%he h i g h l y successful operating experience sf t h e Molten-Salt Reactor Experiment and the developments in chemical processes t h a t have allowed an important simplification in the bPeeder ConCept provide SkkPpO%t f0BT t h e C Q n t e H n C i C N I that P&3CtOBfG having these characteristics can be successfully developed Because they d i f f e r in lD.2ifa)p respects f%Qm LiqUid-Metal F S t Breeder &38CtoKS, ?d%BFP% serve particularly w e l l as insurance for t h e nation's energy supply in W encounters i n s u r m u n t a b l e obstacles a Moreover, if both system are suc eSsf%illy deVelOped, t h e 2 h i l i t y sf t h e H Q l t e n - S d t reaC%C!I? to startea IL as a breeder or operated economically as a converter on pEutonium, 2 4 5Y or 2 3 3 ~makes it: a s u i t a b l e companion f o r an UEBW to aneed fuel economy. In t h i s case, t h e differences between t h e t w o concepts, starting back at t h e mining of o r e , also provide increased sppsrteantity for a competitive breeder i n d u s t r y * Thus far t h e work on n o l t e n - s d t reactor technology has established what we believe to be a f i m foundation f o r success. There are still some b a s i c proble notably surface cracking of Mastelkoy N and tritium ment 9 whose solutions h e not been f u l l y demonstrated, We a l s o i z e some major engineeri tasks, such as d e m n s t r a t i o n of the dependable, e c o n o ~ e a maintenance l of an MSB and scale-up of reactor e q u i p n e a t to MSBR size, Nevertheless, t h e p tential of molten-salt reactors is p r o e s i n g ensugh to ju ify a continued effort. Favorable resolution of t h e b ie problems must come f i r s t , then more extensive development of cs%ap ents and system. If these proceed s a t i s f a c t o r i l y , the construction a %a r e a c t o r should corn next, but t h e scale-up need not be large since a 156 - 200 N"(t> reactor c o d d demonstrate d l of t h e techlnOlogy t h a t i s esSenfLial % o r a EK3Eten-sa%t b r e e d e r , This reactor should provide sufficient Pnformakion for concluding whether f u l l - s c a l e E B B ' S w i l l b e technicalPy and e c o n o ~ c a l l yattractive enou to justify completing t h e i r development We b e l i e v e that a s t r e n g l y ~ o t i ~ and ~ t ad : ~ UEitely ~ funded pPJgrZLrrt t h a t f O l H O W S t h i s r o u t e W i l l lead t o molten-s t bPeedeP Ke%rCtO%S that 6 a R p l a y a 'iilZi.jOr role i n p r o viding the natio s future ener 0

h..

E . .

II

References f o r Chapter 1

1

e

2.

“AuthorEzing A p p r o p r i a t i o n s f o r t h e Atomic Energy C o n d s s i o n f o r F i s c a l Year 1973,” House of R e p r e s e n t a t i v e s , 92d Congress Report N o . 92-1066. D . Fb. Cardwe11 and B. N . Naubenreich, Indexed Abstracts of SeZected OM Molten-Salt Reactor TecianoZogg, OWL-m-3595, December

Refeyences 1991.

.&... S.

USMC T a s k F o r c e , Repore on t h e F l u i d P w Z Reactors T a s k F m c e , TID-8507 F e b r u a r y 1959 ~

... ~

4.

ConceptwZ B e r i p Study of a Single-FZuid MoZten-Salt Breeder i?eactor, ORNL-4541, J u n e 6371.

5.

H’sitelz Salt Reactor YechnsZogy, T e c h n i c a l Report of the MoltenSalt G ~ P Q U P , P a r t I , Ebasco S e r v i c e s , Inc., December 1971.

6

E V a h a t i O l . , of a IOOO-MW(e) MoZter,-SaZt Breeder Reactor, Technical Report of t h e Molten-Sa%t Group, P a r t 11, Ebasco S e r v i c e s , Pnc., October 1971

(1111 ....

.~

.... ....

L m e

... “.y .~

7

2800 ~ W l e bfoZten-SaZt ) &ee&r Zeaetor Conceptual Desigrz Study, F i n a l Report

-

Task 1, Ebasco Services, Pnc., F e b r u a r y 1 9 7 2 .

... .&

8.

Molten-Salt Breeder R e a c t o r A s s o c i a t e s Fina’c RepYdt, P h s e I Studg - Project f o r I n v e s t i g a t i o n 07Jo! Zten-SaZt Breeder R ~ a c t o ~ ~ Black and Veatch C o n s u l t i n g Engineers , Kansas C i t y Mo. (1970).

9.

Ps-keiztiaZ JPzcZear Fouer G ~ o u t hPatterns, p r e p a r e d by the S y s t e m

.... : .a

Analyses Task F o r c e under the d i r e c t i o n of the D i v i s i o n of R e a c t o r Development and Technology of the USAEC, WASH 1098, December 1970

... ..... s&

10.

Cost-Beneflt AnaZysis of t h e U.S. Breeder Propam, D i v i s i o n of R e a c t o r Development and Technology, USAEC, ILGH 1 1 2 6 , A p r i l 1969.

11.

C i v L Z i c n z FPzcZearr Power - A Report t o t h e Fpesident - 2 9 6 2 , U.S. A t o m i c Energy Cormissfon, U . S . Government P r i n t i n g O f f i c e , Washington, D. C

2.

EVOLUTION AND DEVELOPMENT OF MOLTEN-SALT REACTORS P. N . Haubenreich

Origins

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. L 2

. ..

h%en t h e i d e a of t h e b r e e d e r w a s f i r s t s u g g e s t e d i n 1 9 4 3 , t h e r a p i d and e f f i c i e n t r e c y c l e of t h e p a r t i a l l y s p e n t core w a s r e g a r d e d as t h e main problem el]. This problem, which i s s t i l l c r u c i a l in b r e e d e r economics, w a s a t t a c k e d i n t w o ways - by s t r i v i n g f o r v e r y Long burnup and by s e e k i n g t o s i m p l i f y t h e e n t i r e r e c y c l e o p e r a t i o n . The. l a t t e r p u r s u i % i n e v i t a b l y l e d to c o n s i d e r a t i o n of f l u i d - f u e l e d r e a c t o r s as t h e u l t i m a t e i n fuel cycle simplificatian. Neutron-multiplying systems c o n s i s t i n g of aqueous s o l u t i o n s and s l u r ries w e r e i n v e s t i g a t e d soon a f t e r t h e d i s c o v e r y o f n u c l e a r f i s s i o n , and t h e f i r s t e f f o r t toward a f l u i d - f u e l e d b r e e d e r w a s b a s e d on t h e s e s y s t e m s , i n which t h e f l u i d i s b o t h t h e f u e l and t h e moderator [ 2 , pp. 1-91 The Hom~geneousR e a c t o r Program, o r g a n i z e d at ORNL i n 6 9 4 9 , had as i t s o b j e c t i v e a r e a c t o r w i t h a u r a n y l suPfate-DZ0 s o l u t i o n c o r e and a thorium oxide-B20 s l u r r y b l a n k e t , s e p a r a t e d by a Z i r c a l o y c u r e t a n k , T h i s conc e p t , w i t h i t s s u p e r i o r n e u t r a n econumy, o f f e r e d good 2 3 3 U b r e e d i n g performance * About 1950 t h e i d e a of a v e r y d i f f e r e n t f l u i d - f u e l r e a c t o r f o r power g e n e r a t i o n emerged a t Brookhaven N a t i o n a l Laburatory f m m s t u d i e s on Powm e l t i n g a l l o y s and s l u r r i e s of uranium and thorium i n liquid metal. T h i s w a s t h e l i q u i d - m e t a l - f u e l r e a c t o r concept [ a , pp. 699-9252]. A v e r s i o n of t h e LQ'R u s i n g g r a p h i t e moderator, U-Bi s s % u t i o n c o r e , and ThOZ-Bi s l u r r y b l a n k e t appeared c a p a b l e of b r e e d i n g . r Meanwhile y e t a n o t h e r f l u i d - f u e l e d r e a c t o r had been conceived f ~ an a l t o g e t h e r d i f f e r e n t purpose - a i r c r a f t p r a p u % s i o n . Several d i f f e r e n t c ~ n c e p t sof compact r e a c t o r s were b e i n g c o n s i d e r e d f o r g e n e r a t i n g h e a t t~ b e used i n a j e t e n g i n e . The Oak Ridge i d e a w a s t o u s e a high-temperature liquid fuel that c o u l d be circulated to r e m o v e heat from t h e core and b e d r a i n e d f o r r e f u e l i n g . Experiments t o i n v e s t i g a t e m o l t e n - s a l t f u e l s w e r e begun i n 1947, and 3 y e a r s l a t e r m o l t e n f l u o r i d e s w e r e chosen f o r t h e main e f f o r t sf t h e A i r c r a f t Nuclear P r o p u l s i o n (ANI?) program a t ORB% [3]. The f l u o r i d e s w e r e p a r t i c u l a r l y w e l l s u i t e d because they o f f e r low vapar p r e s s u r e a t jet-engPne t e m p e r a t u r e s r e a s o n a b l y good h e a t t r a n s f e r p r o p e r t i e s s and immunity to r a d i a t i o n damage, and they do n o t react v i o l e n t l y w i t h a i r or w a t e r . (See Chapter 5 . ) A s m a l l r e a c t o r , t h e A i r c r a f t Reactor Experiment, was built t h a t used a f u e l m i x t u r e of NaF, zKP4, and UFb e i r e p l a t i n g i n Pnconel t u b i n g through a moderator assembly of B e 8 b l o c k s [ 2 , p p . 673-881. I n 1954 t h e ARE w a s o p e r a t e d s u c c e s s f u l l y â‚Źor 9 days a t o u t l e t t e m p e r a t u r e s r a n g i n g t o above l680'F and powers t o 2 . 5 MGJ(t) i n i n v e s t i g a t i o n s o f t h e n u c l e a r dynamics o f t h e c i r c u l a t i n g fuel system. It was r e c o g n i ~ e dfrom t h e o u t s e t that m o l t e n - s a l t r e a c t o r s might b e a t t r a c t i v e f o r c i v i l i a n power a p p l i c a t i o n s , and i n E956 a group was formed a t QRNL t o s t u d y t h e c h a r a c t e r i s t i c s , performance, and economics of moltens a l t r e a c t o r s f o r c e n t r a l s t a t i o n power g e n e r a t i o n [ 4 ] . A wide v a r i e t y sf

33

34

R e l a t i o n t o Other Fluid-Fuel

Programs

Early i n I959 a t a s k f o r c e &sembled by t h e M C made a comparative e v a l u a t i o n of t h e t h r e e f l u i d - f u e l r e a c t o r c o n c e p t s then b e i n g pursued The ccsnclusion w a s that the r i o T t e n - s a l k reactor, a l t h o u g h l i m L t e d i n p o t e n t i a l b r e e d i n g a i n , had " t h e highest p r o b a b i l i t y of a c h i e v i n g t e c h U S n i c a l feasibility" [5] * Soon t h e r e a f t e r work on the ~ C ~ U ~ Qhomogeneous and Liquid-metal-fuel r e a c t o r s w a s d i s c o n t i n u e d , Leaving the n i ~ b t e n - s a b t r e a c t o r as t h e Tone fluid-fuel breeder concept still being s u p p o r t e d by t h e usme.* Although t h e Nolten-Salt Reactor Program, as s u c h , was r e l a t i v e l y young, t h e r e w a s an e x t e n s i v e t e c h n o l o g i c a l b a s e from t h e ANP program, where $60 m i l l i o n ksaa beern i n v e s t e d i n m o l t e n - s a l t r e a c t o r t e c h n o ~ o g y . Some of this h a d gone f o r developments s p e c i f i c t o the c~mpact:a i r c r a f t raration, b u t a l a r g e f r a c t i o n of t h e technology w a s e q u a l l y appPit o t h e c i v i l i a n power reactors t h a t were b e i n g e n v i s i o n e d . The physical c h e m i s t r y of i n t e r e s t i n g f l u o r i d e s a l t m i x t u r e s had been exp l o r e d , and a c o n t a i n e r a l l o y had been developed t h a t w a s e s p e c i a l l y cornp a t i b l e w i t h f l u o r i d e s a l t m i x t u r e s and which had s i g n i f i c a n t l y h i g h e r s t r e n g t h than Hnconel a t the 1500-l6OQQF t e m p e r a t u r e s r e q u i r e d i n an a i r c r a f t r e a c t o r , Originally called IKOW-8, t h i s a l l o y i s now g e n e r a l l y known as H a s t e l l o y N o Techniques f o r producing, p u r i f y i n g , and a n a l y z i n g f l u o r i d e m i x t u r e s had been worked o u t , and c o n s i d e r a b l e e x p e r i e n c e was g2iRed in handPing the f u e l . The f l ~ ~ r i v d oe l a t i l i t y p r o c e s s was developed and was s u c c e s s f u l l y used t o recover t h e uranium f r o m t h e A E f u e l i n 1957-58, En addition to t h e g e n e r a l l y a p p l i c a b l e &'P work, there was some s p i n o f f % S t h e mobten-s2lt teChnSlogy frclRl t h e aq%keQUSkOlni3geneoUS Pea c t o r ana l i q u i d - m e t a l - f u e l reactor p r o g r a m he H C X W ~ ~ I I ~ ~ e Q a~c~t o r Program had b u i l t and a p e r a t e d t w o r e a c t o r s u s i n g c i r c u l a t i n g aqueous f u e l s o l u t i o n s a t 250-3OQ"C. c o n s i d e r a b l e maintenance w 2 s r e q u i r e d on r a d i o a c t i v e p a r t s o f t h e s e r e a c t o r s , 2nd one s i g n i f i c a n t c o n t r i b u t i o n t o r e a c t o r techno1ogy was t h i s e x p e r i e n c e with maintenance of h i g h l y radioactive systems [ 7 ] . A chemical p r ~ c e s s i n gscheme e x p l o r e d f o r t h e l i q u i d metal f u e l r e a c t o r i n v o l v e d molten salts and molten b i s m u t h . The e x p e r i e n c e of this e f f o r t , and t h e g e n e r a l background of experience with molten b i s m u t h , p r o v e d valuable when e x t r a c t i o n system i n v o l v i n g molten bismuth became the heart of t h e p r o c e s s i n g concept f o r MSBW'ss.

a,:.>

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di

Work h a s c o n t i n u e d a t KEKA2 A r n h e m , N e t h e r l a n d s , on a c o n c e p t u s i n g an aqueous s u s p e n s i o n f u e l [ S I .

z - ~ ~ c ~ Q L -

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35

E a r l y MSBR Concepts

I n t h e e a r l y days of t h e Molten-Salt R e a c t o r Program, s e r i o u s CORs i d e r a t i o n w a s g i v e n t o homogeneous r e a c t o r s i n which t h e core c o n t a i n e d n o t h i n g b u t s a l t . These i d e a s w e r e abandoned a f t e r c a l c u l a t i o n s showed t h a t t h e l i m i t e d muderation by l i k e l y f l u o r i d e s a l t c o n s t i t u e n t s a l o n e would r e s u l t i n a t h e r m a l r e a c t o r w i t h i n f e r i o r b r e e d i n g performance. Breeding appeared p o s s i b l e i n i n t e r m e d i a t e - s p e c t r u m r e a c t o r s , b u t t h e i r g a i n s w e r e n o t h i g h enough t o compensate f o r t h e i r h i g h e r f i s s i l e invent o r i e s . S t u d i e s Sf f%St-SpeCtrum mC9lten-Sdt r e a c t o r s (Using c h l o r i d e s a l t s ) i n d i c a t e d good b r e e d i n g r a t i o s , b u t f i s s i l e i n v e n t o r i e s were excessive u n l e s s u n c o n v e n t i o n a l h e a t t r a n s f e r systems were used t o minimize holdup o u t s i d e of t h e core. A f t e r e x p e r i m e n t s showed t h a t b a r e g r a p h i t e could probably b e used i n t h e c o r e of a m o l t e n - s a l t r e a c t o r , M S B e f f o r t s c o n c e n t r a t e d on g r a p h i t e moderated r e a c t o r s h a v i n g w e l l - t h e r m a l i z e d n e u t r o n s p e c t r a and How f i s s i l e Two g e n e r a l t y p e s w e r e c o n s i d e r e d - s i n g l e - f l u i d r e a c t o r s i n inventories which thorium and uranium were combined i n one s a l t , and two-fluid r e a c t o r s i n which UF4-bearing f u e l s a l t w a s s e p a r a t e d from f e r t i l e s a l t c o n t a i n i n g En any ease t h e dilraent f l u o r i d e m i x t u r e would b e 'LiF-BeF2 i n s t e a d ThP4. of t h e NaF-ZrFb m i x t u r e used i n t h e a i r c r a f t r e a c t o r s ; t h e 7LiF-BeF2 abs o r b e d fewer n e u t r o n s and d i s s o l v e d more ThFk w i t h o u t excessive l i q u i d u s temperatures The s i n g l e - f l u i d r e a c t o r w a s r e l a t i v e l y s i m p l e and promised l o w power c o s t s , b u t b r e e d i n g appeared t o b e i m p r a c t i c a l b e c a u s e of R ~ U t r o n l e a k a g e atnd l o s s e s t o p r o t a c t i n i u m and f i s s i o n p r o d u c t s [ 8 ] . ( A t t h a t t i m e i t w a s n o t clear t h a t Pa and f i s s i o n p r o d u c t s could b e s e p a r a t e d The two-fluid r e a c t o r could b e deeconomically on a v e r y s h o r t cycle.) s i g n e d w i t h a f e r t i l e b l a n k e t t o reduce l e a k a g e , and P a losses would b e reduced b e c a u s e t h e f e r t i l e s a l t would b e a t a lower average f l u x . The only processing required f o r the f e r t i l e salt w a s fluorination t o recaver t h e b r e d uranium. The f u e l s a l t could b e p r o c e s s e d by a combination o f f l u o r i n a t i o n and an aqueous p r o c e s s . The two-fluid r e a c t o r w a s more comp l e x i n t h a t i t u s e d t w s s a l t s t h a t had to b e k e p t s e p a r a t e , b u t i t d i d o f f e r a t t r a c t i v e b r e e d i n g performance. e

e

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By l 9 6 Q a fairly clear p i c t u r e of a f a m i l y o f m o l t e n - s a l t r e a c t o r s had emerged. The t e c h n i c a l f e a s i b i l i t y appeared t o b e on a ~ . o u n d f o o t i n g - a c o m p a t i b l e combination of salt, g r a p h i t e , and c o n t a i n e r m a t e r i a l - b u t a r e a c t o r was needed t o r e a l l y p r o v e t h e technology. 'khat w a s t h e p u r p o s e o f t h e Molten-Salt Reactor Experiment: t o demons t r a t e t h a t some of t h e key f e a t u r e s of t h e proposed m o l t e n - s a l t power r e a c t o r s c o u l d b e embodied i n a p r a c t i c a l r e a c t o r t h a t could b e o p e r a t e d s a f e l y and r e l i a b l y and b e m a i n t a i n e d w i t h o u t e x c e s s i v e d i f f i c u l t y . For s i m p l i c i t y i t was to b e a f a i r l y s m a l l , o n e - f l u i d r e a c t o r o p e r a t i n g a t 16 W ( t ) o r less, w i t h h e a t r e j e c t i o n t o t h e a i r v i a a secondary s a l t .

36

Figure 2.2 shows some deThe x3R.E flowsheet is shown as Fig. 2 s1. The fuel was LiF-BeF2-%rFq-UP4 tail 0% the 5-ft-diameter reactalvessel. (Q4-%Q-5-l mole x>, the secowdary sa%t was LiF-BeF2 &M-34 mole X), the moderator was rade CGB gYL3phite, and all. other parts contacting salt ~2s the surge space for were of Hastellsy N. The bQW1 of the fueB &M the circulating loop, and here absut 50 gpm 0 fuel was splrayed into the gas space $6 a%Bcw xencm and krtyptsn to escape from the saEt. Also in the pump bowl was a port through which saLt samp%es could be taken or capsules 0% concentrated %uel emishing salt (UF4-EiF or I?uF3) csuld be intrsduced. The fuel system was located in sealed ce%%s, laid out for maintenance with long-handled tosls tkmu apernings in the top shieldimg~ A tank uf LIF-BeFp ~~31% was used ts flush he fuel circulating system before and after maintenance. In a cell adjacent to the reas%sr was a simple facility ~CJP bubbling as th~~klgh the fuel or flush salt: B2-I-IF ts remove oxide, F2 to remove uraflium as UFg o References 9, 10, and %k provide more detailed descriptions of the reactor and processing plant.

Beve%opment

and

Construction

Most sf %he 'PEW effort from 196Q t&rough 6964 was devoted to design, developmen%, and cQnskPuc%isn of the %%sEE, Pr~ductisn 2md further testing of graphite and Bastelloy N, both in-pile and out, were major development ace ivisies * Qthers included wosrk cm reactor ekemis try9 development of fabrication techniques for Hastelloy N, development of reactor csmponents p and remote-maintenance gPannin apld preparations. (A csnvenienk summary of developments through the end of major construction is given in reference 12.1 Befsre the MS development began3 tests had shown that salt would nst permeate raphite irk which %he pores were very sma%%, Graphike wiU-k ti-ie desired p -re structure was available mby im small, experimentakly prepared pieces, however, and when a manufacturer set out. to produce a new grade (6GB) to meet the MSWE requirements, difficuPties were encsuntered [la, ppe %-I%-%89]. A series of pitch impregnations and heat treatments

praduced

the

desired

high

density

and

small

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structure,

but im the final steps occasional cracks appeared in many of the 2-1/4-h. square baafs o Apparently the cracks resulted because the structure was so tight that gases from the pyrolysis of the impregn t csubd ~0% escape rapidly el40ugh D Tests shswed, howeveap) that the cracks did not propagate, ekes when filled with salt and subjected to repeated freeze-t After analysis showed that heating in salt-filked cracks woul cessive, the graphite was accepted and used in the MSRE. The choice of Hastelloy N for the MSRE was on the bases 13f the prsmising results -0% tests at k&P csnditfsss and the availability sf much of the required metaliurgical data.* Develegment for the SE generated the

Any attempt ks develop a less-expensive suited to KS CsRditioms s was precluded by gs2, p* %%k].

aHHoy, possibly even better time and s~st considerations

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38

FLEXIBLE C O N D U I T TO CONTROL ROD D R I V E S

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PORT C Q O b l N G JACKETS

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MOD E RATOW SUPPORT GWBO

39

f u r t h e r d a t a r e q u i r e d f o r ASME code a p p r o v a l . It a l s o i n c l u d e d p r e p a r a t i o n of s t a n d a r d s f o r H a s t e l l o y N procurement and f o r component f a b r i c a t i o n . Material f o r t h e MSBE, amounting t o a l m o s t 200,000 l b i n a v a r i e t y o f s h a p e s , w a s produced commercially. A f t e r weld-cracking i n e x p e r i m e n t a l h e a t s w a s overcome by minor composition changess t h e s e w a s no d i f f i c u l t y i n o b t a i n h g a c c e p t a b l e material Requests f o r b i d s on component f a b r i c a t i o n went t o s e v e r a l companies i n t h e n u c l e a r f a b r i c a t i o n i n d u s t r y , b u t a l l d e c l i n e d t o submit lump-sum b i d s b e c a u s e o f l a c k o f e x p e r i e n c e w i t h t h e new a l l o y . Consequently a l l major components w e r e f a b r i c a t e d i n AECowned shops a t Oak Ridge and Paducah [12, pp. 63-82]. After appropriate p r o c e d u r e s were worked o u t H a s t e l l o y N f a b r i c a t i o n p r e s e n t e d no unusual problems * A t t h e tfme t h a t d e s i g n stresses w e r e set f o r t h e M S E , t h e few d a t a t h a t w e r e a v a i l a b l e i n d i c a t e d t h a t t h e s t r e n g t h and c r e e p r a t e of H a s t e l l o y N w e r e h a r d l y a f f e c t e d by i r r a d i a t i o n . An a r b i t r a r y allowance w a s made f o r p o s s i b l e e f f e c t s , however, by e x t a b l i s h i n g d e s i g n stresses 28% below Code v a l u e s f o r u n i r r a d i a t e d H a s t e l l o y N . A f t e r t h e construct i o n w a s w e l l a l o n g , t h e s t r e s s - r u p t u r e l i f e and f r a c t u r e s t r a i n were found t o be d r a s t i c a l l y reduced by thermal-neutron i r r a d i a t i o n . The MSRE stresses were r e a n a l y z e d , and i t w a s concluded t h a t t h e r e a c t o r would have a d e q u a t e l i f e t o r e a c h i t s g o a l s . A t t h e same t i m e a program w a s launched t o improve t h e r e s i s t a n c e of HastelEoy N t o t h e embrittbement. (See Chapter 7 and r e f e r e n c e 1 3 . ) An e x t e n s i v e o u t - o f - p i l e s o r r o s i ~ nt e s t program w a s c a r r i e d o u t f o r H a s t e l l o y PJ [12, pp. 334-3431 which i n d i c a t e d e x t r e m e l y l o w c o r r o s i o n rates a t M S E c o n d i t i o n s Capsules exposed i n t h e Materials T e s t i n g R e a c t o r showed t h a t s a l t f i s s i o n power d e n s i t i e s o f more t h a n 200 W/cm3 had no a d v e r s e e f f e c t s on c o m p a t i b i l i t y of f u e l s a l t , H a s t e l l o y N , and g r a p h i t e . F l u o r i n e gas w a s found t o b e produced by r a d i o l y s i s of f r o z e n s a l t s , b u t o n l y a t t e m p e r a t u r e s below about 100°C 61.2, pp. 252-2871. The r e s u l t s of t h i s program are d e s c r i b e d i n some d e t a i l in Chapter 5 . Components t h a t were developed e s p e c i a l l y f o r t h e MSRE i n c l u d e d f l a n g e s f o r 5-inch l i n e s c a r r y i n g molten s a l t , f r e e z e valves (an a i r c o o l e d s e c t i o n where s a l t could b e f r o z e n and thawed), f l e x i b l e c o n t r o l r o d s t o sperate in thimbles at 1200°P, a d the f u e l sampler-enricher [12, p p . 167-1901. C e n t r i f u g a l pumps w e r e developed s i m i l a r t o t h o s e used suceess€ub$y i n t h e a i r c r a f t r e a c t o r program, b u t w i t h p r o v i s i o n s f o r remote maintenance, and i n c l u d i n g a s p r a y s y s t e m f o r xenon removal. Remote maintenance c o n s i d e r a t i o n s pervaded t h e MSRE d e s i g n and developments i n c l u d e d d e v i c e s f o r r e m o t e l y c u t t i n g and b r a z i n g t o g e t h e r 1-1/2-inch p i p e , removable h e a t e r - i n s u l a t i o n u n i t s , and equipment f o r removing s p e c i mens of m e t a l and g r a p h i t e from t h e c o r e . The MSW development program d i d n o t i n c l u d e r e a c t o r p h y s i c s e x p e r i ments o r h e a t t r a n s f e r measurements. There w a s enough l a t i t u d e i n t h e MSRE t h a t d e v i a t i o n s from p r e d i c t i o n s would n o t compromise s a f e t y QP accomplishment of t h e o b j e c t i v e s of t h e MSKE* C o n s t r u c t i o n of t h e primary s y s t e m components and a l t e r a t i o n s of t h e o l d ARE b u i l d i n g (which had been p a r t l y remodeled f o r a proposed 6O-W(t) a i r c r a f t r e a c t o r 9 were s t a r t e d i n 1962. I n s t a l l a t i o n of t h e s a l t s y s t e m w a s completed i n mid-1964. OWL w a s r e s p o n s i b l e f o r q u a l i t y a s s u r a n c e ,

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nagement of c o n s t r u c t i o n 6141. The primary s y s t e m were L f o r c e s ; s u b c o n t r a c t s r s m o d i f i e d t h e b u i l d i n g and i n s t a l l e d a n c i l l a r y sys tens *

O p e r a t i o n o f t h e M S B spanned 5 y e a r s , from t h e l o a d i n g of s a l t in 1964 through t h e end sf n u c l e a r o p e r a t i o n i n December, 1969. As d e s c r i b e d i n r e f e r e n c e s 9 and 15, a l l of t h e o b j e c t i v e s of t h e experiment were achieved d u r i n g this p e r i o d . Checkout and parenuclear t e s t s i n c l u d e d 16QO h r of c i r c u l a t i o n o f f l u s h s a l t and fuel c a r r i e r s a l t . Nuclear testing of t h e MSW began in ~ u n e$965, w i t h t h e addition of e n r i c h e d 2 3 5 ~as U F ~ - L ~ eFu t e c t i c t u t h e c a ~ l g i e rs a l t to make t h e reactor c r i t i c a l . A f t e r zero-power experiments t o measure rod worth and r e a c t i v i t y c o e f f i c i e n t s [ 1 6 ] , t h e r e a c t o r was s h u t clown and f i n a l p r e p a r a t i o n s made f o r power o p e r a t i o n . Power ascens i o n w a s d e l a y e d when vapors from oil t h a t had Leaked into t h e f u e l pump were p o l y m e r i z e d by the r a d i o a c t i v e o f f g a s and plugged gas f i l t e r s and valves. M a x i m u m power, which was l i m i t e d t o 7 . 4 M W ( t ) by t h e c a p a b i l i t y sf t h e h e a t - r e j e c t i o n system, was reached i n May 1 9 6 6 . A f t e r t w o months of high-power o p e r a t i o n , t h e r e a c t o r was down f o r 3 months b e c a u s e of t h e failure o f one of t h e main c o o l i n g blowers. Some f u r t h e r d e l a y s w e r e e n c ~ ~ ~ t e br eec d a u s e of o f f g a s l i n e p l u g g i n g , b u t by t h e end of 1966 most of t h e s t a r t u p were behind. ring t h e n e x t 15 months, t h e r e a c t o r w a s critical 80% 0 6 the t i m e , w i t h runs of P, 3 , ~ S B .6 months t h a t WE u n i n t e r r u p t e d by a f u e l d r a i n . BY M ~ K I I , 1968, t h e o r i g i n a l o b j e e ~ i v e sof t h e MSRE had been accomplished, and R U C L ~ Zo~p ~e r a t i o n w i t h 3 5~ was c o t a c ~ u d e d . By this time, a m p l e 2 3 3 U had became a v a i l a b l e , s a t h e MSRE program was exterlaed t o ineiuae s u b s t i t u t i o n 0 6 2 3 % f o r t h e uranium i n t h e fuel s a l t and o p e r a t i o n t o observe t h e new n u c l e a r c h a r a c t e r i s t i c s . Using the o n - s i t e p r o c e s s i n g equipment9 t h e f l u s h salt and f u e l s a l t w e r e 233UFt+-LiF f l u o r i n a t e d t o r e c o v e r t h e uranium i n them as UF6 ell] e u t e c t i c w a s then added t o t h e c a r r i e r s a l t , and i n October 1 9 6 8 , t h e became t h e ~ ~ o r 1 c i 'fsi r s t r e a c t o r t o o p e r a t e on 2 3 3 ~ . TIE 2 3 3~ zero-power experiments and dynamics tests confirtnea t h e p r e d i c t e d n e u t r o n i c characteris t i c s An unexpected consequence o f proce s s i n g the salt was that its p h y s i c a l p r o p e r t i e s w e r e a l t e r e d s l i g h t l y so t h a t more than t h e u s u a l amount of gas w a s e n t r a i n e d from t h e f u e l pump i n t o the e i r c u i a t i n g ioop. m e gas ana t h e power f l u c t u a t i o n s t h a t accompanied i t w e r e e l i m i n a t e d by o p e r a t i n g t h e f u e l pump a t s l i g h t l y lower speed. O p e r a t i o n at h i g h power f o r several months permitted very a c c u r a t e measurement of t h e ~ a p t ~ r e - t o - f i ~r a~ t ii o~ , n f o r 243%r ill t h i s % e E i C t Q r , COXRpleting tktg UbjeCtiVes O f the 2 3 3 U O p e r a t i o n .

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I n t h e concluding w.?nth§ of o p e r a t i o n , xenon s t r i p p i n g , d e p o s i t i o n of f i s s i o n p r o d u c t s , and t r i t i u m b e h a v i o r w e r e i n v e s t i g a t e d . The f e a s i b i l i t y of u s i n g plutonium i n m o l t e n - s a l t r e a c t o r s w a s emphasized by adding PuF3 as makeup f u e l d u r i n g t h i s p e r i o d . A f t e r t h e f i n a l shutdown i n December 1 9 6 9 , t h e r e a c t o r w a s l e f t i n s t a n d b y f o r a l m o s t a y e a r . Then a l i m i t e d examination program w a s c a r r i e d o u t , i n c l u d i n g a moderator b a r from t h e c o r e , a c o n t r o l rod t h i m b l e , h e a t exchanger t u b e s , p a r t s from t h e f u e l pump bowl, and a f r e e z e v a l v e t h a t had developed a l e a k d u r i n g t h e f i n a l shutdown. The r a d i o a c t i v e systems were t h e n c l o s e d t o a w a i t u l t i m a t e d i s p o s a l .

Results The b r o a d e s t and perhaps most i m p o r t a n t c o n c l u s i o n from t h e MSRE e x p e r i e n c e i s t h a t this w a s a q u i t e p r a c t i c a l r e a c t o r . It r a n f o r l o n g p e r i o d s of t i m e , y i e l d i n g v a l u a b l e i n f o r m a t i o n , and when maintenance w a s r e q u i r e d i t w a s accomplished s a f e l y and w i t h o u t e x c e s s i v e d e l a y . * The r e n a r k a b l e performance of t h e PlSRE c l e a r l y shows t h a t w i t h p r o p e r d e s i g n and c a r e f u l c o n s t r u c t i o n and o p e r a t i o n , t h e unusual f e a t u r e s of a n MSR i n no way compromise i t s s a f e t y and d e p e n d a b i l i t y . In many r e g a r d s , t h e MSRE s e r v e d t o confirm e x p e c t a t i o n s and p r e d i c t i o n s [15]. For example, we had c o n f i d e n t l y e x p e c t e d t h e observed i m u n i t y of t h e f u e l s a l t t o r a d i a t i o n damage, t h e complete absence of a t t a c k on t h e g r a p h i t e , and t h e v e r y minor g e n e r a l c o r r o s i o n of t h e H a s t e l l o y N . Noble g a s e s w e r e s t r i p p e d from t h e f u e l s a l t by t h e s i m p l e s p r a y system even b e t t e r t h a n a n t i c i p a t e d , r e d u c i n g t h e 1 3 5 X e p o i s o n i n g by a f a c t o r of about 6 . The b u l k of t h e f i s s i o n product elements remained s t a b l e i n t h e salt. A d d i t i o n s o f uranium and plutonium t o t h e salt d u r i n g o p e r a t i o n w e r e q u i c k and u n e v e n t f u l , and t h e r e c o v e r y of uranium by f l u o r i n a t i o n w a s q u i t e e f f i c i e n t . '6ne n e u t r o n i c s , i n c l u d i n g c r i t i c a l l o a d i n g , r e a c t i v i t y c o e f f i c i e n t s , dynamics, and long-term r e a c t i v i t y changes, a g r e e d v e r y closely with prior calculations I n o t h e r areas, t h e o p e r a t i o n r e s u l t e d i n improved d a t a o r h e l p e d t o r e d u c e u n c e r t a i n t i e s . me 2 3 3 ~c a p t u r e - t o - f i s s i o n ratio i n a t y p i c a l MSR n e u t r o n s p e c t r u m i s an example ~f b a s i c d a t a t h a t w e r e improved. The e f f e c t of f i s s i o n i n g on t h e redox p o t e n t i a l of t h e f u e l s a l t w a s r e s o l v e d . The d e p o s i t i o n of some e l e m e n t s ("noble metals") was e x p e c t e d , b u t t h e MSRE p r o v i d e d q u a n t i t a t i v e d a t a on r e l a t i v e d e p o s i t i o n on g r a p h i t e , m e t a l , and l i q u i d - g a s i n t e r f a c e s . H e a t t r a n s f e r c o e f f i c i e n t s measured i n t h e MSRE a g r e e d v e r y c l o s e l y w i t h c o n v e n t i o n a l d e s i g n c a l c u l a t i o n s ( u s i n g c o r r e c t v a l u e s f o r s a l t p r o p e r t i e s ) and d i d n o t change o v e r t h e l i f e of e

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t h e f i n a l shutdown s a l t had c i r c u l a t e d i n the f u e l s y s t e m a t t e m p e r a t u r e s around 1200°F f o r 2 1 , 788 h o u r s . The r e a c t o r had been c r i t i c a l f o r 17,655 h o u r s , producing 13,172 e q u i v a l e n t full-power h o u r s of n u c l e a r h e a t . During t h e 15-month phase of t h e t e s t program devoted t o t h e d e m a n s t r a t i o n of s u s t a i n e d o p e r a t i o n , t h e r e a c t o r w a s c r i t i c a l 80% of t h e t i m e and a v a i l a b l e 86% of t h e t i m e ( i n c l u d i n g t i m e s p e n t i n s c h e d u l e d replacement of c o r e specimens).

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t h e r e a c t o r . L i m i t a t i o n of oxygen a c c e s s t o t h e s a l t proved q u i t e e f f e c t i v e , and t h e tendency s f f i s s i o n p r o d u c t s t o b e d i s p e r s e d f r o m contamin a t e d equipment d u r i n g maintenance was less chan w e had a n t i c i p a t e d O p e r a t i o n of t h e XSRE provided some i n s i g h t s i n t o t h e unusual problem o f tritium in a m o l t e n - s a l t r e a c t o r . It:was observed t h a t about 6-10s/, of t h e c a l c u l a t e d 54 C i / d a y p r o d u c t i o n d i f f u s e d o u t of t.he f u e l s y s t e m i n t o t h e containment c e l l atmosphere and a n o t h e r 6-10% r e a c h e d t h e a i r through the heat removal system [IS] Tie f a c t t h a t t h e s e f r a c t i o n s w e r e not h i g h e r i n d i c a t e d t h a t s o ~ e t h i n g(probably o x i d e c o a t i n g s ) part i a l l y n e g a t e d t h e easy t r a n s f e r of t r i t i u m through hot metals. The one q u i t e unexpected f i n d i n g of g r e a t importance was t h e sha%%sw i n t e r g r a n u l a r c r a c k i n g observed i n a11 metal. s u r f a c e s exposed t o t h e f u e l s a l t . This w a s f i r s t n o t e d i n t h e specimens t h a t w e r e removed from t h e c o r e a t i n t e r v a l s d u r i n g t h e r e a c t o r o p e r a t i o n . P o s t - o p e r a t i o n examinaP t i o n a %p i e c e s of a c o n t r o l - r o d t h i m b l e , heat-exchanger t u b e s , and pump bawl p a r t s r e v e a l e d t h e u b i q u i t y of t h e c r a c k i n g and emphasized i t s i m p ~ tawce t o t h e MSR concept F u r t h e r i n v e s t i g a t i o n s and p o s s i b l e consequences aipe discussea in c h a p t e r s 9 ana 1 4 of t h i s r e p o ~ t .

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S i n c e t h e M S E , the X o l t e n - S a l t R e a c t o r Program has been a technology program, not focused on b u i l d i n g a p a r t i c u l a r r e a c t o r , b u t s e e k i n g t o i d e n t i f y and accomplish t h e develwprnents t h a t a r e needed b e f o r e moltens a l t b r e e d e r r e a c t o r s can became a r e a l i t y 1181. In t h e f u r t h e r a n c e of this prograrr,, e f f o r t s on c o n c e p t u a l d e s i g n have been e s s e n t i a l i n d e f i n i n g t h e needs f o r development, w h i l e e x p e r i m e n t a l f i n d i n g s , i n t u r n ; s h a p e t h e concept. This s e c t i o n d e s c r i b e s t h e reactor c o n c e p t s t h a t have been c o n s i d e r e d i n the c o u r s e o f t h i s i n t e r t w i n e d p r e c e s s . A s d e s c r i b e d p r e v i ~ u s l y , at: t h e time t h a t she MSRE was conceived, t h e two-fluid reactor, d e s p i t e its r e l a t i v e complexity, seemed to h e l d t h e most promise as a b r e e d e r . During t h e e a r l y y e a r s of t h e MSRE, r e l a t i v e l y l i t t l e e f f o r t was devoted t o r e f i n e m e n t 0% c o n c e p t u a l designs. Basic c h e m i s t r y s t u d i e s ~ s n t i n u e d ,however, and l e d i n 1964 to an import a n t development t h a t s i m p l i f i e d t h e p r o c e s s i n g in t h e two-fluid b r e e d e r p l a n t [ l 2 , p . S Q S ] . This was t h e s e p a r a t i o n of r a r e - e a r t h f l u o r i d e s front L i F and BeP2 by d i s t i l l a t i o n a t 1QOO"C. (The p r a c t i c a l i t y was Eater demonstrated w i t h a portion of t h e MSWE: f u e l [ I 9 1 Thus i t w a s , when t h e MSWE s e t t l e d i n t o o p e r a t i o n , t h a t d e s i e f f o r t s f o c u s e d on t h e twof l u i d concept S t u d i e s a t f i r s t i n d i c a t e d o u t s t a n d i n g r e s o u r c e u t i l i z a t i o n , mainly because s f an extremely low s p e c i f i c i n v e n t o r y of about 0.8 leg fissiEe/m$(e) [%O]. Then in 1 9 6 9 , when irradiation of g r a p h i t e to very h i g h n e u t r o n flueraces revealed more r a p i d d i n t ~ n s i ~ changes ~al than had been p r o j e ~ t e d , t h e two-fluid concept w a s dealt a severe b l o w . Accommodation of t h e d t f f e r e n t i a l growth of t h e g r a p h i t e E I d e t h e C O r e d e s i g n and asSePil$ly 8 0 complex t h a t it seemed necessa y t o r e p l a c e t h e e n t i r e r e a c t o r vessel and i t s c o n t e n t s whenever t h e r a p h i t e c o r e t u b i n g became u n s e r v i c e a b l e me reference a e s i -NM(~> i n c l u d e d f o u r 556-m~t)

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r e a c t o r s t h a t could b e r e p l a c e d a t s t a g g e r e d i n t e r v a l s t o improve p l a n t a v a i l a b i l i t y [ a x ] . The two-fluid r e a c t o r could b e s c a l e d down w i t h o u t s e r i o u s l y a f f e c t i n g b r e e d i n g g a i n , b u t performance w a s h u r t b e c a u s e i n o r d e r t o e x t e n d g r a p h i t e l i f e t o 8 full-power y e a r s , t h e power d e n s i t y i n t h e r e f e r e n s e d e s i g n w a s reduced from 80 W/cm3 t o 20 W / c m 3 > a t t h e expense of r a i s i n g t h e s p e c i f i c i n v e n t o r y t o 1 . 3 kg fissile/MW(e). A t about t h i s t i m e a chemical p r o c e s s i n g development o c c u r r e d t h a t g r e a t l y improved t h e p r o s p e s t f o r economical b r e e d i n g i n a s i m p l e r , s i n g l e f l u i d r e a c t o r . This w a s t h e l a b o r a t o r y d e m o n s t r a t i o n of t h e b a s i c chemical s t e p s i n a c o n t i n u o u s p r o c e s s f o r removing p r o t a c t i n i u m and uranium from molten f l u o r i d e m i x t u r e s t h a t c o n t a i n t h o r i u m f l u o r i d e . When LiF-BeF2-%hFq-UPq-$aPq s a l t was c o n t a c t e d w i t h molten bismuth c o n t a i n i n g d i s s o l v e d thorium and l i t h i u m , f i r s t t h e U and t h e n t h e Pa w e r e r e d u s e d and passed from t h e s a l t i n t o t h e P i q u i d m e t a l . The P a c o u l d b e seques- _. t e r e d u n t i l . i t decayed, w h i l e t h e uranium w a s r e t u r n e d t o t h e f u e l s a l t . by e l e c t r o l y s i s This r e d u c t i v e - e x t r a c t i o n p r o c e s s which could draw upon t e s h n o l o g y developed a t Argonne and Brookhaven f o r p r o c e s s i n g f a s t r e a c t o r f u e l s and t h e U-Bi f u e l of a n EblFR, appeared p r a c t i c a b l e f o r continuous s e p a r a t i o n of p r o t a c t i n i u m . It a l s o appeared t h a t i t might b e a d a p t a b l e t o removal of r a r e - e a r t h f i s s i o n p r o d u c t s , t h u s p e r m i t t i n g a r e l a t i v e l y s i m p l e p r o c e s s i n g p l a n t t h a t would keep b r e e d i n g l o s s e s due t o Pa and f i s s i o n p r o d u c t s t o a c c e p t a b l y low l e v e l s . A f t e r t h e r e c o g n i t i o n of t h e Pa-removal p o s s i b i l i t y , o n e - f l u i d b r e e d e r c o r e d e s i g n s w e r e e x p l o r e d more thoroughly than i n e a r l i e r s u r v e y s . A s a r e s u l t , i t w a s found t h a t b r e e d i n g performance could b e s i g n i f i c a n t l y improved by a scheme proposed s e v e r a l y e a r s b e f o r e . By d e c r e a s i n g t h e g r a p h i t e f r a c t i o n i n t h e o u t e r p a r t of t h e c o r e , t h e n e u t r o n s p e c t r u m t h e r e can b e hardened, i n c r e a s i n g t h e f r a c t i o n of c a p t u r e s i n thorium, w h i l e t h e f i s s i o n n e u t r o n p r o d u c t i o n i s more conc e n t r a t e d i n t h e i n n e r , well-moderated p a r t of t h e c o r e . The e f f e c t i s t o r e d u c e n e u t r o n l e a k a g e , whish had always been a s i g n i f i c a n t f a c t o r i n one-fluid b r e e d e r s The combined e f f e c t of t h e new Pa-removal s y s t e m and t h e improved c o r e d e s i g n w a s to i n c r e a s e t h e b r e e d i n g r a t i o t h a t could b e a c h i e v e d economically i n a one-fluid breeder t o about 1.05-1.07'. Consequently, t h e P ~ B Q U P C u~ t i l i z a t i o n c h a r a c t e r i s t i c s became a c c e p t a b l e , and i n 1968 t h e major emphasis sf t h e PISRP w a s s h i f t e d t o t h e development of t h e s i m p l e r s i n g l e - f l u i d b r e e d e r r e a c t o r . Later, s u b s t a n t i a l improvements were made i n t h e p r o c e s s i n g system, i n c l u d i n g e l i m i n a t i o n of t h e elect r o l y s i s c e l i l s , storage of P a i n s a l t f n s t e a d of i n bismuth, and development of a more e f f i c i e n t p r o c e s s f o r removal of rare e a r t h s . (See Chapter 11.1 Throughout t h i s e v o l u t i o n , t h e primary long-range o b j e c t i v e of t h e MSRP remained t h e s a m e - e f f i c i e n t b r e e d i n g i n t h e thorium-23% c y c l e . T h i s p u r s u i t l e d by 1970 t o t h e r e f e r e n c e c s n s e p t u a k d e s i g n of a 1000-W(e) MSBR p l a n t [ 2 2 ] d e s c r i b e d i n Chapter 3 , which i s t h e focus of t h e MSRP development e f f o r t . I n a d d i t i o n , O W L has r e c e n t l y i n v e s t i g a t e d several o t h e r v e r s i o n s of o n e - f l u i d m o l t e n - s a l t r e a ~ t ~ t~h ra ts a l s o m e e t t h e e s s e n t i a l c r i t e r i a of s a f e t y , P e l i a b i l i t y , and low power c o s t s , w h i l e o f f e r i n g one advantage o r a n o t h e r r e l a t i v e t o t h e r e f e r e n c e MSBR. ~

-'.

44

One a l t e r n a t e u f f e r s a way around t h e n e c e s s i t y of r e p l a c i n g t h e at bk-year iRtE2rValS. T h i s d i f f i c u l t j o b is avoided by s h p l y making t h e c o r e ~f t h e b r e e d e r Barge enough and t h e damage flux low enough. t h a t the core g r a p h i t e w i l l . l a s t t h e %Q-greah-l i f e ~f t h e p l a n t . Such a "perm ~ e ~ ~ t - K~~ E~L Cr~ eQ E"can have a b r e e d i n g r a t i o as h i g h as i n the r e f e r ence design, b u t t h e l a r g e c o r e means a g r e a t e r i n v e n t o r y and l o n g e r doubling tiate pq. h o t h e r p o s s i b l e s i m p l i f i c a t i o n i s t h e e l i m i n a t i o n of most of t h e chemical processing. Hf i t should happen i n a breeder p l a n t t h a t p r a t actinium and f i s s i o n - p r o d u c t removal were stoppedS the r e a c t o r could c o n t k n u e t~ s p e r a t e f o r months, or even years9 as a n e a r - b r e e d e r w F t h only t h e 5f u.k-aniuw. ~ a t e r n a t i v e l y t h e r e a c t o r s o u i d b e built as a c o ~ l v e r t e rw i t h no p r o c e s s i ~ g ( o t h e r than perhaps o x i d e rea u v d ) , Some s t u d i e s i n d i c a t e t h a t an economical made of o p e r a t i a n would b e t o run f o r 6 e q u i v a l e n t full-power years, recover the uranium by b a t c h . ~ " - f ~ - u o r i n a t i o (as n demonstrated i n the KSRE), d i s c a r d t h e s a l t w i t h the ith her 2 3 5 u cx f i s s i o n p r o a u c t s , ana ~ I ~ S U Iw~i It h~ f r e s h c a r r i e r s a l t . plutonium could b e u s e d f o r s t a r t u p and f e e d of s u c h a m o l t e n - s a l t c o n v e r t e r reactor. A limited amount of c ~ ~ ~ ~ e pdteus ai pl w a s done on a 356-MW(e) conv e r t e r t h a t positively o ~ e r c o m et~h e p r o b l e m s of g r a p h i t e replacement ana t r i t i ~ r nc o ~ ~ t a i n m w i~t ~ h ~a t m i n i ~ ~om f additional development. me c o r e is l a r g e enough SO that p r e s e n t l y a v a i l a b l e g r a p h i t e would l a s t 30 yearss and t r i t i m containment is e n s u r e d by u s i n g an i n t e r m e d i a t e s a l t loop c o n t a i n i n g H i t e c [ 2 4 ] . The Mitec, a " i O g - 6 9 a N O ~ - N a o ~m i x t u r e , r e a c t s w i t h t r i t i u m t o form water, which c o u l d b e s t r i p p e d continuousLy from the s a l t . Because the n i t r a t e - n i t r i t e m i x t u r e wouLd p r e c i p i t a t e uranium and might r e a c t v i ~ l e n t r yw i t h g r a p h i t e i f i t leaked into the f u e l s y s t e m , a compact h o p c o n t a i n i n g LiF-BeF2 (which i s q u i t e compati b l e w i t h t h e f u e l ) is i n t e r p o s e d between t h e f u e l and H i t e c s y s t e m , T h e d i s a d v a n t a g e s of the extra bosp and t e m p e r a t u r e l i m i t a t i o n s Hitec a r e weighed a g a i n s t s i m p l i f i c a t i o n u f t h e steam s y s t e m because of t h e relatively &ow m e l t i n g p o i n t of E i t e s (288"F>. I n any evenc this s t u d y i s an offshoot f r o m t h e main l i n e o f 8KXL e f f o r t , which is d i r e c t e d at the high-performance b r e e d e r . I n c o n s i d e r i n g t h e most e x p e d i t i o u s route t o the ultimate moltens a l t b r e e d e r , we h a v e d e v o t e d some a t t e n t i o n t o the c o n c e p t u a l d e s i g n ~f what w e c a l l t h e K ~ k t e n - S a I t Breeder Experiment (MSBE). This r e a c t o r would b e designed t o o p e r a t e under c o n d i t i o n s a t l e a s t as severe as t h o s e e plant. Design s t u d i e s show t h a t a g r a p h i t e damage f l u x twice that i n the r e f e r e n c e XSBR and power d e n s i t y , s a l t composition, and prsta c t i n i u m and f i s s i o n - p r o d u c t c o n c e n t r a t i o n s l i k e t h o s e i n the r e f e r e n c e d e s i g n could b e a t t a i n e d in a ass-m(t> r e a c t o r w i t h a 4 - f t core i n a 7 . 5 - f t v e s s e l [ 2 5 ] . The NSBE would produce steam and would include a complete p r o c e s s i n g f a c i l i t y . Although i t s small dimensions limit i t s b r e e d i n g r a t i o to about 0 . 9 6 , t h e MSBE provide a d e f i n i t i v e test of a16 t h e b a s i c equipment and psacesses required f o r a breeder.

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Most of t h e work on m o l t e n - s a l t r e a c t o r s is now, as i n t h e p a s t , c o n c e n t r a t e d i n t h e M o l t ~ ~ - S aR l te a c t o r Program a t ORNL, b u t some s i g n i f i This s e c t i o n o u t l i n e s t h e MSW c a n t a c t i v i t i e s are going on elsewhere. a c t i v i t i e s (which a r e f u l l y d e s s r i b e d i n o t h e r c h a p t e r s ) and b r i e f l y describes the other program

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Reactor Program

T h e Molten-Salt Reactor Program i s i n c l u d e d w i t h t h e LWBR and the gas-cooled f a s t b r e e d e r i n t h e AEC ' s "high-gain b r e e d e r " development p r o gram. A t o t a l of $ 6 4 m i l l i o n h a s been s p e n t by t h e PlSRP from i t s incept i o n i n 1 9 5 7 through f i s c a l y e a r 1 9 7 2 , i n c l u d i n g t h e $16 m i l l i o n c o s t of desf-ing and b u i l d i n g t h e MSRE. The MSRP a l s a h a s b e n e f i t e d from b a s i c work c a r r i e d o u t under t h e A E C ' s p h y s i c a l r e s e a r c h programs. The MSW budget f o r FY-6973 is $5 m i l l i o n , now a l l o c a t e d approximately as f o l l ~ ~ s :

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Reactor d e s i g n and anaEys i s R e a c t o r e n g i n e e r i n g technology Keactor metals Graphite Chemistry and a n a l y t i c a l chemistry Fuel processing P r o c e s s i n g materials

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The MSW d e s i g n and a n a l y s i s e f f o r t i n c l u d e s e v a l u a t i o n of t h e p o t e n t i a l of m o l t e n - s a l t r e a c t o r s and p r e p a r a t i o n of r e f e r e n c e d e s i g n s and a l t e r n a t i v e s t h a t d e f i n e t h e r e s e a r c h and development n e e d s . This h a s been c u t back i n r e c e n t y e a r s , and n e a r l y h a l f of t h e c u r r e n t e f f o r t is a s t u d y b e i n g done under s u b c o n t r a c t by an i n d u s t r i a l group headed by Ebasso Services The bulk of t h e engineering development effort is p r e s e n t l y devoted t o two MSW-scale l o o p s : t h e Coolant S a l t Technology F a c i l i t y anel t h e Gas S y s t e m T e s t F a c i l i t y , d e s c r i b e d i n Chapter 8. A l s o under t h i s headi n g is a s t u d y of m o l t e n - s a l t steam g e n e r a t o r s b e i n g c a r r i e d o u t by P o s t e r Wheeler under s u b c o n t r a c t t o ORNL. R e a c t o r c h e m i s t r y is mainly concerned a t p r e s e n t w i t h t h e b e h a v i o r of t r i t i u m and c e r t a i n f i s s i o n p r o d u c t s . A n a l y t i c a l development is aimed a t t h e t e c h n i q u e s needed f o r t h e o p e r a t i o n of a b r e e d e r and i t s p r o c e s s i n g plant. R e a c t o r m e t a l s development i s focused on improving H a s t e l l o y N ( o r f i n d i n g a n a l t e r n a t i v e ) t o overcome t h e problems o f n e u t r o n e m b r i t t l e m e n t and s u r f a c e c r a c k i n g by f i s s i o n p r o d u c t s . S e a l i n g t o exclude xenon and b e t t e r s t r u c t u r e f o r l o n g e r l i f e are b e i n g i n v e s t i g a t e d i n t h e g r a p h i t e program. P r o c e s s i n g materials work i s now c e n t e r e d on molybdenum f a b r i c a t i o n , w i t h some e f f o r t on g r a p h i t e .

46

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The emphasis i n f u e l p r o c e s s i n g i s on ~ e d u c t i v ee x t r a c t i o n - the chemis t r y of f l u o r i d e - b i s m u t h and chloride-b ismuth sys tern and e n g i n e e r i n g equipment t o e x p l o i t t h i s shemis t r y F l u o r i n a t i o n and f u e l r e c o n s t i t u t i o n a r e being developed, and a l t e r n a t e p r o c e s s e s such as o x i d e p r e c i p i t a t i o n are b e i n g s t u d i e d .

-

here have been ~ V Qp r i v a t e l y f m a e d c o n c e p t u a l design s t u d i e s and e v a l u a t i o n s of MSW'ss. The first vas by t h e Molten-Salt Breeder Reactor Associates (NSB > ,headed by t h e e n g i n e e r i n g firm o f Black & Veatch and dwestern u t i l i t i e s . The M S B M s t u d y identifaed problem areas b u t c ~ n ~ l ~ dt hea d t t h e econsmics o f molten-salt r e a c t o r s w e r e a t tract i v e r e l a t i v e t o light.-water r e a c t o r s , and favored a program l e a d i n g t~ e a r l y c o m e r c i a % a p p l i c a t i o n o f a moIten-salt c0nverter [ a s ] . S i n c e t h e h a s bee^ rekat i v e l y inacti v e c o n c l u s i o n of t h e i r s t u d y in 1 4 9 0 t h e XSB The second p r i v a t e l y funded o r g a n i z a t i o n is t h e Molten-Salt Group (MSG) Whose %Ormatfon Was afanQUnC@dill 1969 [ a s , P o l - l ] me MSG is headed by Ebasco Services and i n c l u d e s 5 o t h e r i n d u s t r i a l firms* and 15 companieseasi. pn t h e f a n ai t h e MSG conpietea an e v a l u a t i o n of t h e s t a t e of b%% technologgi 6281 and a c r i t i q u e of t h e OR", lOQO-MFi(e) breeder d e s i g n 1291 They c o n ~ % u d e d in t h e first r e p o r t t h a t t h e e x i s t i n g t C ? C h t % O l O g y Was S k l f f i c i e n t t o j u s t i f y CQnStKUCtion O f a dâ‚ŹXmnStPatiQn p l a n t t h a t W Q U ~b r~e e d p p r o v i d e d t h e p r o c e s s i n g works as i n t e n d e d , b u t t h a t i t s m a i n t a i n a b i l i t y , r e l i a b i l i t y , C Q S ~ S . , and p l a n t life c o u l d n o t b e p r e d i c t e d r e l i a b l y from the e x i s t i n g t e ~ h ~ o l o g g[ ar $ , p . 61. En the second r e p o r t , they concluded t h a t t h e OmL r e f e r e n c e d e s i g n ~HlbPaCed SQBlE! t e C h R Q b o g i c a l d i f f i C U 1 t i e s b u t W a s a S U i t a h l e d e p a r t u r e point f o r e x p l o r i n g MSBR t e c h ~ ~ l b o g [y2 9 * p. 4 1 . The MSG members have a g r e e d to s u p p o r t s t u d i e s o f a demonstration p l a n t and a l t e r n a t e m o l t e n - s a l t r e a c t o r concepts and an u p d a t i n g o f their MSBR technology e v a l u a t i o n . These s t u d i e s a r e p r o c e e d i n g c o n c u r r e n t l y with the Me-funded MSBR d e s i g n s t u d y that i s b e i n g done by p a r t of t h e GPQUP'S WQrking fo%Ce. There have been o t h e r i n d i c a t i o n s of i n t e r e s t i n m o l t e n - s a l t r e a c t o r s by i n d u s t r y and u t i l i t i e s . Xany h a v e s e n t r e p r e s e n t a t i v e s t o MSRP annual i n f o r m a t i o n meetings, and several have made p r i v a t e studies o f t h e i r p o s s i b l e role i n XSR development. A few have a s s i g n e d s t a f f members t o work in the MSRP ( f a r up t o 2 years), and m a t e r i a l s p r o d u c e r s have cont r i b u t e d by p r o v i d i n g e x p e r i m e n t a l g r a p h i t e and a l l o y s f o r evaluation. e

a

T h e I n d i a n Department of Atomic Energy i s i n t e r e s t e d i n m o l t e n - s a l t reactors i n c o n n e c t i o n with t h e i r vast t h o r i u m % ~ S Q U E ^ C ~ and G the anticip a t e d a v a i l a b i l i t y s f pHutonium i n I n d i a f o r MSR s t a r t u p . A s m l l program

*Babcock

Ed tJilcox, Byron Jackson9 Cabot Corp. and Union Carbide.

Continental O i l ,

....

t.C.3

&.,

47

of r e s e a r c h on t h e MSBR concept h a s been underway a t t h e Bhabha Atomic Research C e n t r e s i n c e 11969. The program i s m o s t l y concerned w i t h i n v e s t i g a t i o n s of t h e c h e m i s t r y o f m e l t s c o n t a i n i n g PuF3. The USAEC and t h e DAE have been exchanging m o l t e n - s a l t i n f o r m a t i o n , and an agreement p r o v i d i n g f o r somewhat b r o a d e r c o o p e r a t i o n i s b e i n g c o n s i d e r e d . Euratom h a s s u p p o r t e d r e s e a r c h OR v a r i o u s t o p i c s p e r t i n e n t t o moltens a l t r e a c t o r technology. Prom 1964 t o 1966 t h e r e was an exchange o f m o l t e n - s a l t i n f o r m a t i o n through a formal agreement w i t h t h e USAEC, b u t t h e exchange i s now r e l a t i v e l y inastive. Development work i n v o l v i n g cons t r u c t i o n and o p e r a t i o n of a m o l t e n - s a l t steam g e n e r a t o r t h a t w a s begun w i t h Euratom s u p p o r t i s c o n t i n u i n g a t Delft U n i v e r s i t y , however. Other European m o l t e n - s a l t r e a c t o r work was conducted a t Kernforscherngsanlage JPiliek i n 1 9 6 3 to 1 9 6 7 , mostly i n c o n n e c t i o n w i t h t h e e p i t h e m a l reactor c o n c e p t , MOSEL [3Q]. This h a s been d i s c o n t i n u e d . The U W A h a s s u p p o r t e d a sm11 effort on m o l t e n - s a l t r e a c t o r s f o r s e v e r a l years. S t u d i e s and a l i m i t e d amount sf e x p e r i m e n t a l work are c o n t i n u i n g , w i t h emphasEs on c h l o r i d e - f u e l e d , lead-cooled f a s t r e a c t o r s .

References for Chapter 2

1. 2.

J. A . Lane, H.

G . :~lasHherssn, and F. Maslan, F l u i d

Fuel Reactors,

....

U.X.'

Addison-Wesley, Reading, Mass., 1958. 3.

... ~. -........

4.

5. . ..

u.:s

6.

7.

8.

4. 16

0

11

P

12

0

13.

15

D

49

16,

17

e

B. E . P r i n c e ,

S. J. B a l l , J . €2. Engel, P . 1'9. Baubenreich, and T . W. K e r l i n , Zero-Power Ph2sics Experiments WL t h e lGShZ3 OWNL-423.3 ( F e b r u a r y 1968).

R. B e B r i g g s , " T r i t i u m i n Molten-Salt

Reactors,

I'

Reactor Technokqd,

1 4 , 335-42 (Winter 1976-72) 18.

PI. G . MacPherson, "Development of Materials and S y s t e m f o r the Molten-Salt Reactor Concept, I' €?@actorTechnol. 1 5 136-155 (Summer 1972)

-

14.

9. R. Hightower, L. E . McNeese, B. A. Hannaford, and H . D. Cochran, LozJ-PTesawe DistiZZation of a Portion of the Fuel C m i e r S a l t f ~ o m -the MSZE, ORNIL-4577 (August: 1971) e

20.

I?. R. Kasten, E . S . B e t t i s , and R, C. Robertson, D e s i p Studies sf lBOO-MTY'(e) Molten-SaZt Breeder Reactors, ORNL-3996 ( 1 9 6 6 ) I

21.

R. C. Robertson, 8. B . B r i g g s , 0 . %. S m i t h , and E. S. B e t t i s , 2 % ~ -

f l u i d MoZ.ten-SaZt Bpeeder Reactor Design Stud$ (Status as of J a n . 1, 2368), OmL-4528 (1970)

-

Concept-ml Design Study of a Single-FZuid Molten-Salt Bme&r !%actor,

22

OBWL-454a. ( 1 9 7 1 ) .

24.

E . S . B e t t i s , L. G. Alexander, a ~ PI. d L. Watts, D e s i p Sttrdies of Idolten-Salt Reactor Derzonstration P h e , OWL-TM-3832 (June 19 7 2 )

25.

J. R. MtWherter Molten-Salt B~eaderEqwfiment Design Bases, QML-TM-3177 (November 1970)

Q

.

e

26.

Molten-Salt Breeder Reactor A s s o c i a t e s S t a f f , F i n a l R e p o r t , Phase 1 Study - Project f ~ r Investigation of Molten-Salt Breeder Reactor, Black & Veatch C o n s u l t i n g E n g i n e e r s , Kansas C i t y , M o . (19709.

27.

b000-NbJ(e) Molten-Salt Breeder Reactor Conceptual Design Study, F i n a l Report -Task I, Ebasco Services, I n c . , New Ysrk, February 1972.

28.

MoZten-Salt Weactop TeehnoZogy, T e c h n i c a l Report

o f t h e Molten-Salt

Group, P a r t I , Ebasco Services, I n s . , December 6991.

Evaluation of a 1000-1We MoZt-en-SaZt Breedem? Reactor, 'Fechmical Report of t h e Molten-Salt Groups Part PI, Ebasco S e r v i c e s , HIPC.,

29

October 1971 30

e

0

P e €3. KasteR, "The MOSEL R e a c t o r Concept '' a"vzird YeU s Intern. Peaceful Uses of A t . B~argj, Genawa, A/CBEu'F 2 8 / H / 5 2 8 ( 1 9 6 4 )

Conf.

3.

DESIGN CONCEPT OF THE SINGLE-FLUID MSBR

M. W. Kosenthal 9"ne p r e c e d i n g c h a p t e r d i s c u s s e d the development of m o l t e n - s a l t reactor technology and the e v o l u t i o n of d e s i g n concepts o v e r t h e y e a r s . I n t h i s chapter i s d e s c r i b e d t h e s i n g l e - f l u i d thema1 b r e e d e r r e a c t o r that w a s selected i n 1968 as the focus of QmL's development pr~gr~i:rra.A t t h a t t i m e w e began t h e conceptual d e s i g n of a lOOQ-PIW(e) MSBR t h a t e x p l o i t e d t h e new developments i n chemical p r o c e s s i n g and the new approach t o c o r e d e s i g n that w e r e mentioned eaPlier, and i n 1971 we i s s u e d ORNL-454l [I], which d e s c r i b e s t h e concept as w e v i s u a l i z e d i t i n 1970. I n i t s g e n e r a l f e a t u r e s , , t h a t concept c o n t i n u e s t o b e the b a s i s f o r t h e QRNL program, a l t h o u g h our i d e a s about s p e c i f i c f e a t u r e s of some of t h e s y s t e m and components have changed. The OWL-4541 concept w i t h some m o d i f i c a t i o n s i s g e n e r a l l y r e f e r r e d t o as t h e r e f e r e n c e d e s i g n . Most s f t h e ~ ~ ~ ~ h c h a p t e r s o f this r e p o r t t r e a t s p e c i f i c f e a t u r e s o f t h e p l a n t , and samet i m e s newer ideas are p r e s e n t e d than t h o s e given i n ORNL-4541. When t h i s is done, h m e v e r , the changes from t h e e a r l i e r d e s i g n and t h e reasons f o r them are g e n e r a l l y d i s c u s s e d . In a d d i t i o n t o OWE'S a p p r ~ a c hsometimes having changed i n t h e l a s t two y e a r s , t h e views of Ebasco S e r v i c e s and i t s a s s o c i a t e s on s p e c i f i c f e a t u r e s o f MSBRs sometimes d i f f e r from those of BmL. The major p o i n t s o f d i f f e r e n c e are l i s t e d later in this c h a p t e r , and more i n f o r m a t i o n about them appears i n t h e l a t e r c h a p t e r s . F i n a l l y , a t t h e end of t h i s chapter w e c a l l a t t e n t i o n t o ways i n which t h e d e s i g n of s i n g l e - f l u i d MSBWs might d i f f e r i f the c r i t e r i a w e r e changed from t h o s e t h a t w e followed i n s e l e c t i n g t h e r e f e r e n c e concept. ... .....

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Design

In selecting the reference d e s i g n , w e g e n e r a l l y a t t e m p t e d t o a t t a i n o b j e c t i v e s i n f o u r areas: Q P ~e o n s e m a t i s n , power c o s t s , s a f e t y and env i r o n m e n t a l c o n s i d e r a t i o n s , and t e c h n i c a l f e a s i b i l i t y * The goals were n o t stated q u a n t i t a t i v e l y , however, and o u r approach has been more t o see how w e l l t h e colacept can b e made t o do and t o d e c i d e whether t h a t i s 86c e p t a b l e , t h a n to m e e t s p e c i f i c c r i t e r i a . C o ~ ~ ~ p ~ o mamong ises the factors were a necessary and continuous p a r t of the design e f f o r t , and OULK views of the r e q u i r e ~ ~ have ~ t s s h i f t e d some as a t t i t u d e s i n the n a t i o n and i n the atomic energy programs have s h i f t e d . Nevertheless, we have h e l d t o the f o l l o w i n g g u i d i n g p r i n c i p l e s .

i

n

g

52

breeder that by itself can s a t i s f y both t h e wear-tern and long-term needs f o r a breeder reactor 0% (2) a reactor having lower perfomance Q K diff e r e n t characteristics that, as a campanion to a n o t h e r type of breeder, could improve the overan1 n u c l e a r eeonomy. o u r g o a l w a s a concept t h a t s a t i s f y the first requirement, although we reeo ized t h a t the techdemanding than needed f o r the second wou% in m3s-C aspects be f the h i ~ h - ~ ~ r f o ~reactor ~ n c e and, thus, would g e n e r a l l y become availablbe a l s o from the work on t h e o t h e r concept. translated into wore s p e c i f i c requirements This g e n e r a l objective w by computing t h e cumulative uranium o r e requirements f o r t h e U.S. u e i n t h e AEC's p r o j e c t i o n of nuclear power growth betmeen now and 2600 and postulating dates of i n t r o d u c t i o n s f breeders havin various f u e l u t i l i zation characteristics These studies showed t h a t s i n c e the breeding r a t i o sf a thermal b r e e d e r cmnot r e a t l y exceed 1 . 0 , the f u e l inventory must b e kept low t o a c h i e v e 8 t i S f t 3 e t O r ) p pePfQPaanCe, F u r t h e r Studies then i d e n t i f i e d the MSBR desi conditions that gave what appeared to b e acceptable uranium ore requirements. Consideration sf t h e a v a i l a b i l i t y and anticipated demands f o r o t h e r materials needed t o s u p p o r t a l a r g e MSBR i n d u s t r y i n d i c a t e d that MSBW development would n o t b e hindered by s h o r t -

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ages and r i s i n g c o s t s 621 * c.... s. ....

- A s w i t h o t h e r t y p e s of been fie pPOtectidaIl Qf the ~ T O S U to ~ ~ r a d i o a c t i v i t y , both as t h e ~ ~ n s e q u e n eof e 8 ~ from lower level release durim n o m a l uperaticans o r maintenance. NSBRs d i f f e r from s o l i d - f u e l reae o r s , n o t only i n t h a t t h e f u e l i s i n l i q u i d form, but a l s o i n that the p r o c e s s i n g plant i s a t the reactor site and an i n t e pal part of the p l requires Consideration from those O f S o l i d - f U e l SyS te t h e s a f e t y question has been to examine the b a s i c cansi e r a t f o n s that r e l a t e t o safety an to attempt in t h e d e s i g n to p r o v i d e 0

reaet p u b l i c from

53 means f o r t r e a t i n g each of t h e s e a d e q u a t e l y . En c o n s i d e r i n g how these f a c t o r s a f f e c t t h e concept, w e have t r i e d t o make t h e d e s i g n such t h a t i t could be l o c a t e d on any s i t e a c c e p t a b l e f o r u t h e r kinds of r e a c t o r s . The g u i d e l i n e s on p e r m i s s i b l e release of f i s s i o n products haire changed i n r e c e n t t i m e s . Thts h a s r e q u i r e d t h a t we re-examine some o f the approaches towards low-level releases t h a t appeared a c c e p t a b l e e a r l i e r , and, i n p a r t i c u l a r , w e have had t o d e v o t e more a t t e n t i o n t o means f o r keeping t h e t r i t i u m release l o w - S a f e t y and environmental c o n s i d e r a t i o n s are t r e a t e d t o g e t h e r i n Chapter 14,

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T e c h n i c a l F e a s i b i l i t y . - The v a r i o u s m o l t e n - s a l t r e a c t o r concepts i d e n t i f i e d i n t h e p r e c e d i n g c h a p t e r i n v o l v e technology t h a t ranges froarm t h a t which i s w e 1 1 i n hand to f e a t u r e s t h a t r e q u i r e i n v e n t i o n s tu aecornplish. I n the r e f e r e n c e d e s i g n , we have attempted t o r e s t r i c t t h e requirements t o technology t h a t e i t h e r has a l r e a d y been demonstrated QBP can r e a s o n a b l y be expected t o emerge from an i n t e n s i v e deve%opment program i n time t o b e used on a r e a c t o r experiment whose c o n s t r u c t i o n would s t a r t i n a f e w y e a r s . G e n e r a l l y t h i s meant t h a t i n c r e a s e s i n scale w e r e acc e p t e d , as w e r e f o r e s e e a b l e improvements i n materials and processesI b u t features t h a t r e q u i r e d i n v e n t i o n s o r extremely l a r g e improvements i n performance w e r e excluded. A s examples, pumps having many t i m e s t h e c a p a c i t y of the PISRE pumps w e r e s p e c i f i e d , and a gas s p a r g i n g s y s t e m t h a t removes xenon more e f f e c t i v e l y t h a n t h e MSWE s y s t e m was used i n the d e s i g n . Wowever, a seven-fold improvement i n t h e r a d i a t i o n resistamce of g r a p h i t e t h a t would wake i t l a s t t h i r t y years w a s considered an e x c e s s i v e extraponvt l a t i o n ; and, in f a c t , t h e g r a p h i t e l i f e t i m e w a s s p e c i f i e d as 3 x lQZ2 (>50 keV), which is t h e maximum dose s m a l l samples have been shmn t o w i t h s t a n d w i t h o u t e x c e s s i v e volume i n c r e a s e s . Thus means replacing g r a p h i t e w e r e included i n the p l a n t design. 6ne s p e c i f i c requirement s e t down a t t h e beginning had a s t r o n g i n f l u e n c e on t h e d e s i g n and performance of t h e concept: replacement o r r e p a i r of a l l components whose f a i l u r e i s c r e d i b l e o r whose l i f e t i m e i s expected t o be less than t h i r t y y e a r s must b e made f e a s i b l e . and aceomp l i s h a b l e in a reasonabBe time, General Concept of the Single-Fluid Breeder

A s i n g l e - f l u i d breeder reactor i l l u s t r a t e d i n Simple f o m in P i g . 3.1. The key f e a t u r e of t h e concept, as mentioned i n the p r e c e d i n g chapter, 5s the use of a s i n g l e s a l t that c o n t a i n s both uranium and thorium. To m a k e t h i s a c c e p t a b l e , ways had t o be foumd f u r r e d u c i n g neut r o n l e a k a g e from t h e c o r e w i t h o u t using a s e p a r a t e f e r t i l e b l a n k e t , andl means had t o b e developed f o r e x c l u d i n g most of the 234Pa from the h i g h blk?UtPoHl f l u x r@gion of t h e reactor. The fO?3tK?riS a@COIfkpUshedby ntaking the s a l t volume f r a c t i o n in the o u t e r r e g i o n sf t h e r e a c t o r s e v e ~ a ltimes as g r e a t as i t i s i n the main p a r t of the core. By v a r y i n g the s a l t volume f r a c t i o m and hence t h e q o d e r a t o r - t o - f u e l r a t i o , the c o r e i s made t o b e w e l l moderated b u t the o u t e r region is mdermodeKated, and here thorium c a p t u r e s predominate t o form a low-power-density f e r t i l e b l a n k e t .

54

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The p r o t a c t i n i u m is removed by e x t r a c t i o n from the f u e l s a l t i n a c o n t i n uous p r o c e s s i n g p l a n t d e s c r i b e d l a t e r , w h i c h h o l d s i t up o u t s i d e of t h e c o r e u n t i l i t has decayed i n t o 2 3 3 ~ The b a s f e f e a t u r e s of t h e concept are d e s c r i b e d i n t h e paragraphs t h a t f o l l o w , and p a r t i c u l a r s y s t e m and components are d e s c r i b e d i n g r e a t e r d e t a i l s i n l a t e r c h a p t e r s . F u r t h e r i n f o m a t i o n can b e found in QlWk-454l [I] F e a t u r e s of t h e Reference Design. - The fuel s a l t i s a m i x t u r e of t h e f l u o r i d e s of b e r y l l i u m , P i t h i m - 7 , thorium, and uranium having t h e

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Other p r o p e r t i e s are l i s t e d i n Chapter 5 Lithiurn-? and b e q l l i u m f l u o r i d e s , which have low n e u t r o n a b ~ o r p t i 0 n c r o s s s e c t i o n s , are used to o b t a i n a composition t h a t has a hiquidus t e m p e r a t u r e and other p h y s i c a l p r o p e r t i e s t h a t are a c c e p t a b l e f o r r e a c t o r u s e . Fuel s a l t is pumped through a core formed from b a r e g r a p h i t e s t r i n g e r s and b l o c k s ; t h e salt does n o t w e t g r a p h i t e and w i l l not penet r a t e i n t o i t i f material having small p o r e s i z e s i s used. To exclude xenon from t h e g r a p h i t e , i t s surface i s s e a l e d t o a low p e r m e a b i l i t y by d e p o s i t i o n of p y r o l y t i c carbon. A Cross s e c t i o n of t h e c o r e used in t h e OrnL-4541 design i s shown i n F i g . 3 . 2 . The r e a c t o r v e s s e l and t h e t o p head are s e e n t o have been extended above t h e core f a r enough f o r a mec h a n i c a l c l o s u r e t o b e used and f o r t h e c l o s u r e t o be d i r e c t l y a c c e s s i b l e when t h e head must b e removed. Heat i s t r a n s f e r r e d from t h e f u e l s a l t t o a c o o l a n t salt in an i n t e r m e d i a t e h e a t exchanger. A e u t e c t i c m i x t u r e of sodium f l u s r o b o r a t e and sodium f l u o r i d e i s used as the c o o l a n t ; i t s composition and p r o p e r t i e s have been l i s t e d above. The c o o l a n t s a l t p a s s e s through a steam generator where s u p e r c r i t i c a l steam at 1000°F and 3600 p s i is g e n e r a t e d , y i e l d i n g an o v e r a l l themal e f f i c i e n c y of 44%. Drain t a n k s connected t o t h e f u e l and ~ 0 ~ 1 a rst at l t systems can cont a i n t h e salt when n e c e s s a r y . The f u e l s a l t d r a i n tank h a s a reliable n a t u r a l c i r c u l a t i o n c o o l i n g system for d i s p o s i n g of f i s s i o n - p r o d u c t decay heat. Thsis system u s e s MaK t o t r a n s f e r h e a t from the d r a i n t a n k t o t a n k s of w a t e r , where i t i s e i t h e r disposed o f by f o r c e d c o o l i n g o r , i n an emergency, by b o i l i n g away of t h e w a t e r . The d r a i n tank is a l s o used as the initial holdup volume f o r t h e o f f - g a s system, so t h a t its h e a t removal system i s always i n u s e and i s n o t j u s t c a l l e d on t o come i n t o operation d u r i n g an emergency. e

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A l l m e t a l surfaces that c o n t a c t salt are made from HasteEloy N. (As d e s c r i b e d in a later c h a p t e r , SQIW o t h e r material may b e s u b s t i t u t e d . ) The primary system and the steam g e n e r a t o r s y s t e m are l o c a t e d i n s e p a r a t e celPs, as s h m i n F i g . 3 . 3 . These cells serve as s h i e l d i n g and containment b a r r i e r s f o r r a d i o a c t i v e materials and have c o n t r o l l e d atmosphere which can b e h e a t e d above t h e l i q u i d u s temperature of the salt o r cooled t o p r e v e n t o v e r h e a t i n g of the r e a c t o r equipment from decay energy when t h e salt fs d r a i n e d . Access f o r maintenance can b e achieved by temoval of s h i e l d b l o c k s at the top of t h e c e l l . Since the g r a p h i t e must be r e p l a c e d a t i n t e r v a l s , a s p e c i a l s h i e l d e d carrier i s shown above t h e r e a c t o r f o r t r a n s p o r t i n g i t from t h e c o r e t o another cell for d i s p o s a l . Noble gases have very l o w s o l u b i l i t y i n the fuel s a l t , which makes i t j j o s s i b l e t o s t r i p them from t h e salt and reduce t h e p o i s o n i n g e f f e c t of 35Xe. This s t r i p p i n g is accomplished by i n j e c t i n g bubbles of helium i n t o a s i d e stream and subsequently removing them w i t h c e n t r i f u g a l separators. The off-gas c o n t a i n i n g the xenon and k q p t o - n i s t h e n passed through c h a r c o a l t r a p s i n &I cleanup system. To a c h i e v e good b r e e d i n g in an MSBR, some of t h e s a l t - s o l u b l e f i s s i o n p r o d u c t s , and p a r t i c u l a r l y t h e rare e a r t h s , must be removed r a p i d l y . A p ~ ~ ~ e s s concept i n g f o r doing t h i s i n c o n j u n c t i o n w i t h t h e removal of p~otaetiniumh a s been d e v e l ~ p e d . The processl i l l u s t r a t e d i n g r e a t l y s i m p l i f i e d â‚Źom i n P i g . 3 . 4 , c o n s i s t s of f l u o r i n a t i o n to remove uranium followed by r e d u c t i v e extraction of p r o t a c t i n i u m , and f i n a l l y removal of rare earths and some of the o t h e r fission p r o d u c t s by the " m e t a l - t r a n s f e r p ~ o c e s s . ~ 'The p r o c e s s i n g system is d e s c r i b e d in g r e a t e r d e t a i l i n Chapter 11s In t h e f l u o r i n a t o r , uranium is v o l a t i l i z e d from t h e s a l t as UFg by c o n t a c t i n g i t with f l u o r i n e . The reductive e x t r a c t i o n p r o c e s s u s e s l i q u i d bismuth c o n t a i n i n g d i s s o l v e d l i t h i u m t o e x t r a c t the p r o t a c t i n i u m from t h e f u e l s a l t and t o t r a n s f e r i t t o a n o t h e r salt; here i t remains i n s o l u t i o n until it decays to uranium and then is v o l a t i l i z e d w i t h f l u o r i n e for ret u r n t o the reactor. L i q u i d bismuth i s used in t h e m e t a l - t r a n s f e r p r o c e s s t o e x t r a c t raree a r t h f i s s i o n products from the uranium- and p r o t a c t i n f u m - f r e e salt and t r a n s f e r them t o lithium c h l o r i d e , hence the name of the p r o c e s s . The fission p r o d u c t s are ultimately e x t r a c t e d from the l i t h i u m c h l o r i d e f o r storage and d i s p o s a l . hs shown in Pig. 3 . 4 , t h e UP6 f i n a l l y i s i n j e c t e d i n t o t h e p u r i f i e d f u e l s a l t , which r e t u r n s i t t o s o l u t i o n and p r e p a r e s the salt f o r return t o the reactor. I n the r e f e r e n c e p l a n t , t h e fuel s a l t i n v e n t o r y of the r e a c t o r is processed on a ten-day cycle, which means t h a t the f l o w rate O f the s a l t t h ~ ~ t~h eg phr o c e S S h g p l a n t is about 0.9 The d e s i g n and performance c h a r a c t e r i s t i c s of the MSBR are summarized i n Table 3.1, and more d e t a i l s are p r e s e n t e d i n o t h e r c h a p t e r s .

58

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Simplified flowsheet for processing a molten-salt breeder

gable 3.1. Characteristics of a 1000-hI&V(e)MoItern-SaIt Breeder Reactor Useful heat generation. MW(thj Net electrical output of phnt, MWCc) Overall plant thermal efficiency. % Fuel salt inlet and o u t k t temperatures, 'F Coolant salt i n k t m d outlet temperatures, Throttle steam conditions Reactor vessel inside diameter and height, ft Core height. f t Core diameter. ft Radial blanket thickness, ft Graphite Eflector thicknCS§: ft Number of core elements Size of core eIernents, ft Sait volume fraction in core. 'T Sait volume fraction in reflector, 5

2250 1000 44 1050.1300 850, 1150 3500 psia, 1000°F 22,20 13

Tutal weight ofgrxphite in reactor, kg

669.000

Maximum salt velucity in core. fps Pressure drop through reactor due to flow, psi Average core power density. \v/crn3 ~ a x i r n u mtherms1 neutron flux. neutrons cmm2 sec-' Graptritc damage flux (>io ire^) at point of maximum damage, neutrons cm sec-' Estimated graphite life a t maxirnuni darnage point, y e a s " ~ ~ t salt c volume i ~ in primary system, Et3 Thorium inventor). kg Fissile fuel inventory of rrrictor system and processing piant, kg Breeding ratio Fissile fuel yield, Z;iyearb ~ u e douhiing i time iexponential). years*

8.5 18 22 8.3 x 1014

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14

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Alternatives t o t h e Reference Design

Ebasco V a r i a t i o n s from OWL Design

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Ebasco Services and t h e i r a s s o c i a t e s i n Reference 3 p r e s e n t t h e i r c o n c e p t u a l d e s i g n of a s i n g l e - f l u i d m o l t e n - s a l t b r e e d e r r e a c t o r that i s expected t o s a t i s f y t h e same g e n e r a l c r i t e r i a t h a t were t h e b a s i s f o r t h e ORNL d e s i g n . This s t u d y r e p r e s e n t s o n l y the first phase of a series of t a s k s t h a t f i a s c o i s t o undertake f o r QmL. Its o b j e c t i v e was t o i d e n t i f y t h e g e n e ~ a lf e a t u r e s of t h e concept, whi& is b e i n g examined i n more detail i n s ~ b s e q p a e ~s t u d i e s . F o r t h i s i n i t i a l examination, Ebasco w a s r e s t r i c t e d i n some a s p e c t s t o u s i n g c o n d i t i o n s s p e c i f i e d by OWL; for example, t h e composition of the s a l t and t h e s a l t volume fraction i n the core w e r e s p e c i f i e d , and t h e performance c h a r a c t e r i s t i c s of the p r o c e s s i n g p l a n t were d e f i n e d f o r Ebasco and w e r e n o t t o b e s t u d i e d . However, i n t h e i r examination of o t h e r a s p e c t s of t h e p l a n t , Ebascs i n some cases s e l e c t e d d i f f e r e n t ways of d e s i g n i n g f e a t u r e s o r components of t h e reactor from t h o s e in t h e ORNL r e f e r e n c e d e s i g n . Notable were the following:

1.

In o r d e r t o a v o i d the d i f f i c u l t i e s of s e a l i n g t h e i n t e r i o r s u r f a c e s , Ebasso uses a s l a b geometry f o r t h e g r a p h i t e c o r e elements r a t h e r t h a n t h e s q u a r e element w i t h a c e n t r a l h o l e used by QRNL.

2.

They propose to r e p l a c e i n d i v i d u a l g r a p h i t e a s s e m b l i e s rather than r e p l a c i n g t h e core as a u n i t , as proposed by ORNL. This a l l o w s some elements to b e l e f t i n the c o r e l o n g e r t h a n o t h e r s , and i t reduces t h e d i f f i c u l t i e s of h a n d l i n g t h e large, r a d i o a c t i v e c o r e .

3.

t e d the Equipment a d p i p i n g i n t h e r e a c t o r c e l l are s ~ p p ~ ~ from bottom r a t h e r than from t h e top, a d t h r e e t i e r s of h o r i z o n t a l seismic r e s t r a i n t s are provided

..... %!&'

....ii,

...., .,..... ..,

I

e

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..

4.

The p i p i n g is lined t o m i t i g a t e t h e e f f e c t of shock by thermal tran-

s ienmts

.

>,;;....... a1

- ;<

....

%.:%

....4

i

*.... P)&

... ..... .:.:Ed

......,

. . . . . yP

5.

The c o o l a n t puung, is put in t h e Cold l e g to h S u r e i n l e a k a g e t o the primary system i n case a heat-exchanger t u b e leaks.

6.

The f u e l - s a l t s t o r a g e t a n k is p r e s s u r i z e d t o improve t h e performance of t h e j e t pumps t h a t r e t u r n s a l t t o t h e r e a c t o r and t o p e r m i t enough a d d i t i o n a l d i l u t i o n of t h e off-gas f o r i t t o b e r e t u r n e d d i ~ e c t l yt o t h e ~ e a c t o rw i t h o u t passage t h r o ~ g ht h e 47-hour c h a r c o a l beds shown i n t h e ORNL d e s i g n .

Some of t h e s e and o t h e r changes proposed by Ebasco and t h e companies a s s o c i a t e d w i t h i t appear t o us t o b e u s e f u l i m p r o v e ~ ~ ~ e o nv t se r ehe OWL45-41 design and w i l l b e i n c o r p o r a t e d i n f u t u r e d e s i g n s and f a c t o r e d i n t o the development program.

62

In the earlier discussion of the principles f o l l m e d in selecting 6, refeh-ence d e s i we noted t h a t if a thermal breeder alone is to s a t i s f y the requirements of a growin nuelear econof&4p, the f u e l inv e n t o r y mu~sl: b e k e p t r@assnabl.y IQW. If t h i s requirement is a l t e r e d because the molten-salt breeder is n o t the only breeder in use ar because sf either a lower rate of nuclear power growth 5r a greater availability Qf UrXL~UITlOre, en the r @ q U i r wts fer low inventory will be eased. e csllld lead to a d e s w i t h a %m<er power density c o r e , which would have some advantages over the reference design. For example, if the power d e n s i t y , ana hence t h e neutron flux, were reduced enough f o r the graphite t o $. S % t h i r t y y@aKS, %Owe blpsrtant sifnlsl%ficatiOnS Could b e wade: the equipment for r e p l a c i n the core and f o r d i s p o s i n e design of t h e cere i t s e raphite would n o t be needed, 1ifiec-1, and an aii-weiaed reactor vessel w i t h o u t a removable top could be used. In addition, r e d u c i n t h e power d e n s i t y l o w e r s the velocity of the fuel salt in the CQre, i c h can lower the mass transfer %ate sf Xe%tBn e1%QM to obviate t h e need f o r sealing the graphite. e sf the Hewer potrer density is the increased m e major dis fissile inventory9 owe S t u d i e s 64, p. 2 ? ] have S h O W n to b e 48 to 55% higher than that sf t h e reference d e s i g n . ( I n t e r e s t i n g % y , the avera power d e n s i t y caw be si 4-year-li fe d e s i g n b eea e of improved power flatten2 and reduces graphite temperature peakin in t h e large C Q r e , ) er the power c o s t her lower than the refelge~ga e s i is uncertain. me and drain tank should require larger ell and building VQ%UlDeS, Which add to the C O S $ ; hOWeVf?r, ekilTdnat.8on U f t h e C Q S t Sf Sealing t h e g r a p h i t e and of p r o v i d i n g weans $8 replace it, and avoiding the ontof-pOCk@t r@plaCelllent C O S t S , PrQKi.de O f f s e t t i n g Savings. In s p i t e of the advantages o f f e r e d by reduced power density, the %OWek- f u e l i I l l v E % l t O r y Sf t h e KeferefsCe d@si remains a desirable goal, and the ~efe~-ence d e s i g n continues ts be t h e foeus of OIW!Lts program. Nevertheless, l o w power density way b e appropriate f o r e a r l y power p l a n t s , w i t h later e v o l u t i ~ts ~ ~higher power density. This would be particularly appropriate if more radiation-resistant g r a p h i t e s are developed that permit 30-year core life t~ be attained with l e s s penalty in f u e l i n v e n t o r y ,

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R e a c t o r p h y s i c s c o n s i d e r a t i o n s i n t h e d e s i g n of m o l t e n - s a l t r e a c t o r s are, f o r t h e most p a r t , stmilar t o t h o s e f o r o t h e r thermal r e a c t o r s . I n p a r t i c u l a r , t h e g r a p h i t e - m o d e r a t e d MSR h a s much i n cornon w i t h t h e HighTemperature Gas-Cooled R e a c t o r (HTGR): g r a p h i t e m o d e r a t o r a t an a v e r a g e t e m p e r a t u r e of 600-700"C Th-2 33U f u e l c y c l e , and s i m i l a r f u e l - m o d e r a t o r r a t i o s . Thus, much of t h e d e s i g n t e c h n o l o g y of t h e r m a l r e a c t o r s i n gene r a l and of HTGR's i n p a r t i c u l a r i s d i r e c t l y a p p l i c a b l e t o t h e FER. This i n c l u d e s n u c l e a r d a t a and methods f o r c a l c u l a t i n g n e u t r o n f l u x e s , power d i s t r i b u t i o n s , e f f e c t s o f h e t e r o g e n e i t i e s i n COR s t r u c t u r e , c o n t r o l rod worthis, t e m p e r a t u r e c o e f f i c i e n t s of r e a c t i v i t y , and s o f o r t h . There a r e , however, a few i m p o r t a n t d i f f e r e n c e s . The need t o e s t a b l i s h a c c u r a t e l y t h e r e a c t i v i t y l i f e t i m e of t h e f u e l , S O i m p o r t a n t t o t h e economics of s ~ l i d - f u e h r e a c t o r s , h a s no a n a l o g i n t h e NSR, s i n c e f u e l can r e a d i l y b e added o r r e m ~ v e d , as r e q u i r e d , i n o r d e r t o m a i n t a i n c r i t i c a l i t y . The problem of a c c u r a t e c a l c u l a t i o n of t h e r e a c t i v i t y l i f e of t h e f u e l i s t h u s r e p l a c e d by the problem o f d e s i g n i n g , b u i l d i n g , a d ope r a t i n g d e v i c e s t o m i n t a i n t h e d e s i r e d c o m p o s i t i o n of t h e f l u i d f u e l . T h i s i s n o t t h e same as a d j u s t i n g t h e f e e d rate f o r s o l i d - f u e l r e a c t o r s w i t h C O I I ~ ~ ~ U Q Uon-stream S r e f u e l i n g , s i n c e i n t h e l a t t e r case t h e d i s c h a r g e exp0supt.e of t h e fuel remains a c r u c i a l economic p a r a m e t e r . S i m i l a r l y , t h e problem of c a l c u l a t i n g power-density d i s t r i b u t i o n s i n KSR c o r e s t a k e s a somewhat d i f f e r e n t form than i n s o l i d - f u e l r e a c t o r s . In p a r t i c u l a r , s i n c e t h e fuel i s c o n s t a n t l y mixed and i t s cornposition remains e s s e n t i a l l y uniform t h r ~ u g h o u tt h e r e a c t o r , t h e problem o f t i m e dependent power d i s t r i b u t i o n s i s much less i m p o r t a n t in f l u i d - f u e l t h a n i n solid-fuel reactors. With r e s p e c t to t h e i r dynamic b e h a v i o r (i.e. t h e s h o r t - t e r m t i m e dependence s â‚Ź o p e r a t i n g v a r i a b l e s such as power and neutron f l u x l e v e l s , f u e l t e m p e r a t u r e s , e t e . ) t h e c i r c u l a t i n g f u e l r e a c t o r s - and e s p e c i a l l y t h o s e o p e r a t i n g w i t h a33U f u e l - have unique c h a r a c t e r i s t i c s r e q u i r i n g s p e c i a l s t u d y , and t h e s e w i l l b e d i s c u s s e d i n a s u b s e q u e n t s e c t i o n of t h i s chapter. W e s i m p l y n o t e f o r t h e moment that a n E B R t y p i c a l l y h a s a much smaller d e l a y e d n e u t r o n f r a c t i o n t h a n do o t h e r types of r e a c t o r s and t h e t r a n s p o r t of t h e d e l a y e d neutron emitters i n t h e moving f u e l a l t e r s t h e r e s p o n s e of t h e reactor t o changes i n r e a c t i v i t y . On t h e o t h e r h a n d , most o f t h e power g e n e r a t i o n is i n t h e c i r c u l a t i n g f u e l i t s e l f , which i s a l s o t h e p r i m a r y r e a c t o r c o o l a n t ; t h u s , no h e a t t r a n s f e r l a g s between f u e l and c o o l a n t are p r e s e n t . A s w e s h a l l see, t h e s e two f a c t o r s t o g e t h e r produce s a f e , s t a b l e o p e r a t i n g c h a r a c t e r i s t i c s o v e r a w i d e r a n g e of c o r e d e s i g n parameters. %he central q u e s t i o n i n t h e p h y s i c s of t h e M o l t e n - S a l t B r e e d e r Rea c t o r would t h u s a p p e a r t o b e t h e b r e e d i n g r a t i o i t s e l f . T h i s i s so bec a u s e o f t h e v e r y s m a l l b r e e d i n g g a i n ( b r e e d i n g r a t i o minus one) t h a t i s

65

characteristic sf thema1 breeder reactors. mereas f a s t breeders typisa! 'by achieve their disirable breedin perfomance With lar gains, in combination w i t h r e l a t i v e l y l a r g e fuel inventories, the thema% breeder, w i t h a much smaller breeding gain, must succeed by maintaining a relatively Haw fuel inventory." Because the b r e e d i n g gaim is l o w s t h e expected p e r f o ~ ~ ~ ~ofn ca et h e m a l breeder reactor is especially sensitive to uncertainties in the calculated breeding ratio, and it becomes wesess a r y to establish the ne~tronba8a11~e in the reactor, on which the breeding r a t i o depends, w i t h greater precision t h a n would be required f o r ai f a s t breeder reactor

l l i "

0

Breeding in Molten-Salt Reactors

The quality of p e r f o m a n e e of a breeder reactor, in a nuclear power eeowomy postulated to f o l l o w a p a r t i c u l a r p a t t e r n of r Q W f I 1 , is O f t e n evaluated in terms of the cumulative amount of bllrani ore that would have to be mined up to the time when t h e breeders themselves c o u l d sati s f y a l l requirements f o r f i s s i l e materials. It is ener d re CQg n h e d that t h i s quantity depends both on the breeding r a t i of the reactor and on its s p e c i f i c f u e l i n v e n t o r y . ~n ~ i g .4 . 1 ( a i s o staSta as p i g . a,2>, we shops t h e a n t i c i p a t e d ore reqUireUlentS f o r a U.S. nUCl@aP power industry based On VaKi5US 2>oS%U%ated combinations 5f present-day converters and possible future breeders, having d i f f e r e n t b r e e d i n g m i s s ana specific f u e l inventories ( ~ c gf i s s i i e / m ~ e ) ) . me total installed nuclear-electric capacity is assumed to reach 1 4 0 W ( e ) in 1980 and 930 &'(e> in 2 0 0 0 , and %a increase thereafter at a rate of LOO a J ( e ) per year. It is further assumed that o n l y light-water reactors are b U i P t prior to 1982, that the first breeders come on l i n e in 1 9 8 2 and t h a t o n l y breeders are added to the system after 1998, Also a h o m on Fig. 4.1 are t h e price ranges within which the usmc currently estimates t h a t incremental amounts of uranium m y be available from domestic U.S. ores i n c l u d i n g estslfgsted prob&,ke ~ ~ S O U ~ asCwell ~ S 3s reasonably-assured reserves A c r o s s - p l o t of data taken f r o m curves like those of Pig. 4 . 1 produces a p l o t of resouree requirements vs specific fuel inventory, f o r different values of the d o u b l i n g time, as shorn in F i g . 4 . 2 ( a l s o s h o r n as Fig. 1.3) E % may be n o t e d frr m these curves that a breeder reactor with a (compound) doubling t i m e 0 20 Yearsp ana a specific i n v e n t o r y of 1 . 5 kg/MW(e), would be expected to r e q u i r e very l i t t l e mre ore t h a n a breeder w i t h a doubling t h e o f 10 years and a s p e c i f i c inventory of 4 kg/Md(e). (These might be, respectively, a thermal breeder w i t h a ratio of 1.07 and a f a s t breeder w i t h a breeding satis of 1.35.) r

k

The combined importance s f these t w o f a c t o r s , b r e e d i n g fuel inventory, w i l l be explained in t h e next section.

k.3

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CUMULATIVE URANIUM REQUIREMENTS (millions o f s h o r t tons bi30,)

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Pig. 4.2. Maximum uranium o r e r e q u i r e m e n t s . Basis: U.S. n u c l e a r power c a p a b i l i t y r e a c h e s 140 W(e) i n 1980, 930 GW(e) in 2000, thereafter increases 100 GW(e) p e r y e a r ; f i r s t b r e e d e r s on line i n 1982, o n l y breeders b u i l t after 1998,

69

Thus, a thermal b r e e d e r r e a c t o r w i t h a low s p e c i f i c f u e l i n v e n t o r y may have b r e e d i n g performance comparable t o a f a s t b r e e d e r w i t h a l a r g e r fuel i n v e n t o r y , even i f t h e doubling t i m e of t h e f a s t b r e e d e r i s much s h o r t e r than t h a t of t h e thermal b r e e d e r * However, i t is clear t h a t t h e low b r e e d i n g g a i n of t h e thermal b r e e d e r makes i t s p e r f o m a n c e wore sens i t i v e t o u n c e r t a i n t i e s i n b r e e d i n g r a t i o , and i t b e c ~ ~ n ~ eec es s s a r y t o examine carefully t h e S Q ~ ~ C @and S probable magnitudes of such u n c e r t a i n ties.

Uncertainties

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The c a l c u l a t e d n e u t r ~ nb a l a n c e f o r t h e r e f e r e n c e s i n g l e - f l u i d MSBW i s shown i n Table 4.1. This n e u t r o n b a l a n c e i s based on t h e c u r r e n t m e t a l - t r a n s f e r chemical-processing f l o w s h e e t , w i t h a 18-day p r o c e s s i n g c y c l e , and t h e n o r m a l i z a t i o n i s such t h a t a t o t a l of one n e u t r o n i s absorbed i n t h e f i s s i l e n u c l i d e s , 233U -1- 235U. The b r e e d i n g r % t i o , w i t h this n o r m a l i z a t i o n , i s e q u a l to the number of c a p t u r e s i n 232Th and 234%y ( a b s o r p t i o n s l e s s f i s s i o n s ) minus a b s o r p t i o n s i n 2 3 3 P a , i.e., BR = 0 . 9 9 3 8 + 0 . 8 8 l 5 - 0.0045 = 1.0708. The number of n e u t r o n s a v a i l a b l e f o r c a p t u r e i n t h e f e r t i l e materials depends on t h e neutron p r o d u c t i o n plcS p e r n e u t r o n absorbed i n f i s s i l e f u e l , and on t h e l o s s e s t o moderator, c o o l a n t , f i s s i o n p r o d u c t s , and leakage. Thus, t h e g r e a t e s t s i n g l e s o u r c e of u n c e r t a i n t y in b r e e d i n g r a t i o is i n t h e n e u t r o n p r o d u c t i o n t e r n , r1s9 which depends mainly on t h e spectrum-averaged v a l u e of r1 f o r 2 3 ~ ~ s P e r r y [I] has made a d e t a i l e d a n a l y s i s of the e f f e c t on b r e e d i n g r a t i o (and on f u e l c y c l e c o s t ) of u n c e r t a i n t i e s i n t h e c r o s s s e c t i o n s o f all c o r e c o n s t i t u e n t s and h i s r e s u l t s are summarized i n Tables 4.2 and 4.3. S i n c e t h e s e u n c e r t a i n t i e s are all independent, they m y be combined by t a k i n g t h e s q u a r e r o o t of the sum of t h e s q u a r e s as t h e o v e r a l l uncert a i n t y i n b r e e d i n g r a t i o o r i n f u e l - c y c l e c o s t a t t r i b u t a b l e t o crosss e c t i o n u n c e r t a i n t i e s . The r e s u l t i n g va lue s,

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r e f l e c t p r i m a r i l y t h e u n c e r t a i n t y i n t h e a v e r a g e thermal n of 23311 (e.g., 6 B % 0.012). ( I f a l l t h e assessed c r o s s - s e c t i o n u n c e r t a i n t i e s are added up i n the same d i r e c t i o n , t h e r e s u l t i s C(GB)i = 0.6% and C(SPCC>i = 0.08. W e r e g a r d t h i s , however, as an extremely improbable combination of c i r c a s t a n ~ e ~a ,view t h a t i s s t r e n g t h e n e d by t h e s a t i s f a c t o r y r e s u l t s of c r i t i c a l i t y c a l c u l a t ~ O R sdESCl?ib'Zd bdOW.)

Fissions

Absorptions 2XTh

0.9968

2”pa

8.0045 0.9242

233u 2 3 4 ~

0.0758

‘Mu

0.0074 0.0044 0.0032 0.01 41

YP

Li

3-i %e

0.0070

I9F

0.0203

Grsphite Fission products Leakage

0.0510 0.0150

.rje Breeding ratio

0.8145 0.0004 0.0618

0.0819

235u

237

0.0030

0.00448

0.0221c

2.2317 1.0708

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71 ..... ...

i-i

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Table 4.2. Effect of heavy-element cross-section uncertainties on MSBR performance

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Wncertainty in breeding ratio. buncertainty in fuel cycle cost.

....,

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+0.010 20.5% +O.OI

0.008 0.009 0.003 0.006

0.013 0.015 0.005 0.010

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0.001

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0.001

72 .’-

Assigned

0.003 0.002 0.001 0.001

0.005 0.003 0.002

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0.003

0.005

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0.006

73

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The absence of thorium from t h i s l i s t i s n o t an o v e r s i g h t ; * i n a real s e n s e thorium absorbs a l l n e u t r o n s t h a t o t h e r materials do n o t , and i n p r i n c i p l e t h e thorium c o n c e n t r a t i o n would b e a d j u s t e d S O t h a t t h i s w i l l b e the c a s e . I n p r a c t i c e , i t i s easier t o a d j u s t t h e uranium c o n c e n t r a t i o n , s o t h a t over s h o r t p e r i o d s ( i f tihe e f f e c t i v e a b s o r p t i o n c r o s s - s e c t i o n of thorium were much d i f f e r e n t than expected) t h e c r i t i c a l c o n c e n t r a t i o n of uranium might prove t o b e s l i g h t l y d i f f e r e n t t h a n exp e c t e d . However, o v e r l o n g e r p e r i o d s t h e uranium c o n c e n t r a t i o n may b e p l a c e d a t almost any d e s i r e d l e v e l , and t h e t h o r i m a d j u s t e d f o r c r i t i cality. In any e v e n t , on the b a s i s of c r i t i c a l - e x p e r i m e n t r e s u l t s , w e would not a n t i c i p a t e a p p r e c i a b l e d e v i a t i o n s of t h e s e c o n c e n t r a t i o n s from s a l c u l a t e d v a l u e s . F u r t h e r ~ u p p ~ rf ot r t h e c a l c u l a t e d v a l u e s of 14 has been d e r i v e d from a measurement i n t h e MSfaE of t h e c a p t u r e / f i s s f o n c r o s s s e c t i o n r a t i o s f o r b o t h 233LT and a 3 5 U . Measured and c a l c u l a t e d v a l u e s i n t h e E R E spectrum, which w a s similar t o t h e r e f e r e n c e E B R spectrum, are compared in Table 4 . 4 . The agreement i s well w i t h i n t h e e x p e r i m e n t a l e r r o r s , which c o r r e spond t o less than 90.01 i n average 0 . F u r t h e r d e t a i l s of t h e experiments and c a l c u l a t i o n s may be found i n References 3 and 4 . The f i s s i o n - p r o d u c t poison f r a c t i o n s h o w i n T a b l e 4 - 1 (0.015) i n c l u d e s a nominal allowance of 0.005 t o cover 1 3 5 X e , o t h e r noble-gas f i s s i o n p r o d u c t s , and any of t h e i r daughter products t h a t may b e produced by decay of n o b l e gases w i t h i n t h e g r a p h i t e moderator. This i s done t o a v o i d t h e n e c e s s i t y s f combining t h e complex g a s - s t r i p p i n g and d i f f u s i o n model with t h e n e u t r o n i c and f u e l - c y c l e c a l c u l a t i o n , i n which t h e e x p l i c i t t r e a t m e n t of t h e noble gases assumes t h e i r removal from t h e r e a c t o r on a 5Q-sec c y c l e . While a poison f r a c t i o n no g r e a t e r t h a n 0.8Q5 i s probably a t t a i n a b l e f o r 13%e a l o n e , i t p r e s e n t l y seems much less l i k e l y t h a t t h e combined e f f e c t of all t h e n o b l e gases (and t h e i r d a u g h t e r s b o r n i~ t h e g r a p h i t e ) can b e k e p t as low as 0.005. The a d d i t i o n a l poisoning e f f e c t of t h e other n u c l i d e s i n q u e s t i o n has been c a l c u l a t e d t o b e about 20% of t h a t of 1 3 5 X e i t s e l f , a t t h e end of a 4-yr g r a p h i t e l i f e . Thus, an addit i o n a l p o i s o n f r a c t i o n of 0.001-8.002 may occur. A s w a s p o i n t e d out above, t h e o t h e r p r i n c i p a l f a c t o r i n b r e e d i n g performance - t h e f u e l i n v e n t o r y - is i n s e n s i t i v e t o reactor p h y s i c s u n c e r t a i n t i e s , because of t h e i n h e r e n t f l e x i b i l i t y of t h e m o l t e n - s a l t r e a c t o r w i t h r e s p e c t to adjustments im f i s s i l e and f e r t i l e material conc e n t r a t i o n s . Over a v e r y c o n s i d e r a b l e range of f u e l c o n c e n t r a t i o n s , e s s e n t i a l l y any d e s i r e d v a l u e can b e achieved and maintained. The quest i o n i s only t h a t of t h e b r e e d i n g r a t i o t h a t corresponds t o a p a r t i c u l a r fuel c o n c e n t r a t i o n , as a l r e a d y d i s c u s s e d . It m y b e noted i n t h i s conn e c t i o n t h a t t h e r e f e r e n c e MSBR h a s n o t been chosen OR t h e b a s i s sâ‚Ź h i g h e s t p o s s i b l e b r e e d i n g ratio. Ih modest i n c r e a s e i n b r e e d i n g r a t i o [ 5 ] could be achieved by i n c r e a s i n g t h e f u e l i n v e n t o r y (and t h u s d e c r e a s i n g l o s s e s i n c o m p e t i t i v e n e u t r o n a b s o r b e r s such as t h e moderator and t h e

*Other small.

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n u c l i d e s are o m i t t e d because t h e i r p o i s o n f r a c t i o n s are very

74

u (meaured) 0: (calculated)

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2.227

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c a r r i e r s a l t ) . I n s t e a d , t h e d e s i g n h a s b e e n o p t i m i z e d on t h e b a s i s of t h e r a t i o of t h e b r e e d i n g g a i n t o t h e s q u a r e o f t h e ( s p e c i f i c ) f u e l i n v e n t o r y , which i s a n a p p r o x i m a t e measure of t h e cumulative. uranium o r e r e q u i r e m e n t f o r e s t a b l i s h i n g a s e l f - s u f f i c i e n t power e c o n ~ m yb a s e d on breeders The i n v e n t o r y i s n o n e t h e l e s s s u b j e c t t o some u n c e r t a i n t y , t o t h e e x t e n t t h a t t h e volume of f u e l s a l t i n t h e s y s t e m depends on d e t a i l s of t h e m e c h a n i c a l and t h e r m a l - h y d r a u l i c d e s i g n of t h e system, i n c l u d i n g h e a t e x c h a n g e r s , p i p i n g , p l e n a , e t c . I t way b e n o t e d t h a t a n i n c r e a s e of 200 f t 3 i n f u e l - s a l t vokume, w i t h o u t any r e o p t i m i z a t i o n , w o u ~ dp r o d u c e a f r a c t i o n a l change i n t h e r a t i o G / 1 2 of a b o u t t h e same s i z e as t h e ( f r a c t i o n a l ) u n c e r t a i n t y i n G(= BR - 1) t h a t arises from n u c l e a r d a t a and r e a c t o r physics u n c e r t a i n t i e s . T h e r e are a d d i t i o n a l p o t e n t i a l s o u r c e s of e r r o r i n the b r e e d i n g r a t i o t h a t l i e o u t s i d e t h e area of r e a c t o r p h y s i c s . These i n c l u d e t h e c h e m i c a l b e h a v i o r of c e r t a i n f i s s i o n p r ~ d u c t s ,n o t a b l y t h e %oble" m e t d s , a,N O , Ru, T e ; a p a r t of t h e s e f i s s i o n p r o d u c t s i s known t o b e d e p o s i t e d and h e l d on p r i m a r y - c i r c u i t s u r f a c e s , i n c l u d i n g c o r e g r a p h i t e . The e s t i m a t e d b r e e d i n g r a t i o f o r OUT r e f e r e n c e MSBR d e s i g n i n c l u d e s a n a l l o w a n c e [ 6 ] f o r d e p ~ s i t i o nof t h e s e n u c l i d e s on g r a p h i t e t o a n e x t e n t Q i . e . , 10% of t h e m o u n t s produced) t h a t a p p e a r s r e a s o n a b l e i n view of d a t a o b t a i n e d f r o m samples from t h e MSRE and from a n i n - p i l e loop.* The e f f e c t o f t h e s e n u c l i d e s on t h e b r e e d i n g ratio i s shown i n P i g . 4 . 3 as a f u n c t i o n of t h e i n - c o r e l i f e of t h e g r a p h i t e . For a 4-year g r a p h i t e l i f e , t h e S i n c e t h e b e h a v i o r of t h e s e average poisoning e f f e c t i s about 0.004. s e e Chap. 5) w e cannot e x c l u d e f i s s i o n p r o d u c t s i s n o t f u l l y ~ n d e r s t ~ o( d t h e p o s s i b i l i t y t h a t a l a r g e r f r a c t i o n of t h e s e f i s ~ i o n - p r o d u ~pto i s o n s might b e r e t a i n e d by the core g r a p h i t e . O t h e r f a c t o r s t h a t c o u l d h a v e an a d v e r s e a f f e c t on b r e e d i n g p e r f o r n ance would b e f a i l u r e t o a c h i e v e a d e q u a t e s e a l i n g u f g r a p h i t e s u r f a c e s a g a i n s t a d s o r p t i o n s f I 3 5 ~ eo r a d e q u a t e s t r i p p i n g o f xenon from t h e c i r c u l a t i n g salt, f a i l u r e of t h e c h e m i c a l p l a n t t o remove f i s s i o n p r o d u c t s from the s a l t , o r n o n - r e c o v e r a b l e l o s s e s of f i s s i l e m a t e r i a l d u e t o u p s e t s at most i n r e a c t o r o r c h e m i c a l p l a n t o p e r a t i o n . The f i r s t of these WQUICI r e d u c e t h e b r e e d i n g ratio by 0.815, w h i l e the l a s t two w o u l d cause t e m p o r a r y r e d u c t i o n s i n b r e e d i n g r a t i o p e n d i n g r e s t o r a t i o n of normal p l a n t operations. According t o t h e c u r v e s of F i g . 4 . 2 , t h e c u m u l a t i v e r e s o u r c e r e q u i r e ments are less s e n s i t i v e t o e r r o r s OK u n c e r t a i n t i e s i n d o u b l i n g time f o r low-speci%is-inventory breeders than f o r hfgk-specigic-inventory breeders. T h i s i s p a r t l y due t o t h e i r r e d u c i b l e o r e r e q u i r e m e n t s f a r c o n v e r t e r reactQrS, assumed t~ be b u i l t during-the e a r l y y e a r s of t h e p o s t u l a t e d a

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0,094

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Change in b r e e d i n g r a t i o due to noble-metal f i s s i o n p r o d u c t s i n MSBR. e

77

growth p a t t e r n , as w e l l as t o t h e smaller a b s o l u t e m o u n t s of i m v e n t o r y r e q u i r e d f o r t h e low-inventory b r e e d e r s . For example, a system p r e d i c a t e d on m o l t e n - s a l t r e a c t o r s w i t h a s p e c i f i c i n v e n t o r y of 1 . 5 kg/ml(e) and a d o u b l i n g t i m e of 35 y e a r s would r e q u i r e p e r h a p s 2 . 5 x lo6 s h o r t t o n s of U 3 0 8 , while a system u s i n g b r e e d e r s w i t h t h e same i n v e n t o r y b u t a ZQ-year d o u b l i n g tine would r e q u i r e about 2 x 1 0 6 s h o r t tons of u ~ Q ~ *~*h u s ,a r e d u c t i o n of b r e e d i n g r a t i o from 1.09 t o 1 . 0 4 , s h o u l d i t occur f o r any of t h e r e a s o n s o u t l i n e d a b ~ v e ,would n o t markedly i m p a i r t h e a b i l i t y of the m o l t e n - s a l t r e a c t o r t o l i m i t t h e m ~ u n tof o r e n e c e s s a r y t o a c h i e v e a s e l f - s u f f i c i e n t n u c l e a r power economy.

Reactor S t a t i c s

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The m u l t i p l i c a t i o n f a c t o r of a r e a c t o r , l i k e t h e b r e e d i n g r a t i o , i s a d i r e s t r e f l e c t i o n of t h e n e u t r o n b a l a n c e . While c r i t i c a l i t y calcudations, b e c a u s e of t h e a d j u s t a b i l i t y of f u e l c o n c e n t r a t i o n , are n o t of c r u c i a l i m p o r t a n c e p e r s e , t h e y serve t o e s t a b l i s h r e a c t o r c o n d i t i o n s f o r which ~ t h e rq u a n t i t i e s such as c o n t r o l rod worths and r e a c t i v i t y coe f f i c i e n t s m u s t b e d e t e r m i n e d , and they may p r o v i d e a d d i t i o n a l confidence i n t h e c a l c u l a t e d n e u t r o n b a l a n c e on which estimates of b r e e d i n g performa n c e a l s o depend. TIE ag~eementbemeen p r e d i c t e d and observed c r i t i c a i fuel copIcent r a t i o n s i n t h e %ISRE w a s g r a t i f y i n g ( s e e T a b l e 4 . 5 ) b u t s u b s e q u e n t s t u d i e s E73 h a v e shown t h a t t h e c a l c u l a t e d c o n c e n t r a t i o n s are r a t h e r s e n s i t i v e t o p e r m i s s i b l e changes i n n u c l e a r d a t a , t o methods of c a l c u l a t i n g n e u t r o n t r a n s p o r t cross s e c t i o n s , and t o d e t a i l s of t h e r e a c t o r r e p r e s e n t a t i o n u s e d i n the c o m p u t a t i o n a l model. However, i t h a s a l s o been shown t h a t p r a c t i c a l l y a l l of t h i s s e n s i t i v i t y (up t o 3% i n 6k) i s a s s o c i a t e d w i t h n e u t r o n l e a k a g e , which i n t h e MSRE w a s unusual%y h i g h : 312 of a l l n e u t r o n s l e a k e d from t h e f u e l e d r e g i o n s o f t h e r e a c t o r w i t h 2 3 5 ~f u e l and 35% with the 2 3 3 ~f u e l . ~n a large m o ~ t e n - e a ~ power t r e a s t o r , t h e n e u t r o n l e a k a g e would b e ICIW~Iby a f a c t o r of 28-30, and t h e s e n s i t i v i t y t o n e u t r o n t r a n s p o r t e f f e c t s p r o p o r t i o n a t e l y less. A series of c r i t i c a l i t y and r e a c t i v i t y measurements 683 has r e c e n t l y been performed on b e h a l f of t h e MSR Program i n t h e High Temperature L a t t i c e T e s t R e a c t o r (HTLTR) a t t h e B a t t e l l e Northwest L a b o r a t o r y . I n these e x p e r i m e n t s , t h e m o l t e n - s a l t f u e l was s i m u l a t e d by c o a t e d - p a r t i c l e fuels (ThQ;, and UOz-ThQ2 grains i n a g r a p h i t e matrix) i n c o n c e n t r a t i o n s and g e o m e t r i c a l a r r a n g e m e n t s r e p r e s e n t a t i v e of t h e r e f e r e n c e MSBR c o r e . Rea c t i v i t y e f f e c t s o f f u e l s a l t c o n s t i t u e n t s s u c h as E i , B e , and F were

* he

r e f e r e n c e mBR i s c a l c u l a t e d t o have a n i n v e n t o r y o f 1 . 5 Beg/ MTJ(e>, b r e e d i n g r a t i o of 1.07, and d o u b l i n g t i m e of 1 9 y e a r s .

7

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Predicted concentration Obsened concentratieid Qbsewed/predict&

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"Rractor isothernial at -E bOO" F, fuel not circulating. b ~ i s s i i euranium, grams per liter of salt. rsce Ref. 9. %e, Ref. io. 'Uncertainties in adjustments for residual plutonium and fission products from L K U and ~ for dimensional changes in graphite cure structure due to fast-neutron irradiation, fLJncertainty due mainly to uncertainties in salt density and sdt volume. g ( M / k ) (akialrf) = 0 . 3 6 ; I% &l.E 0.4% irk.

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..... ..~.,

i n d i v i d u a l l y measured i n a c e n t r a l l y l o c a t e d sample p o s i t i o n , as were t h o s e of s i m u l a t e d c o n t r ~ lr o d s and of v a r i a t i o n s i n l a t t i c e cell gesme t r y . Measurements w e r e made o v e r a r a n g e o f t e m p e r a t u r e s from 26' t o LOQO째C. Although a n a l y s i s and i n t e r p r e t a t i o n of t h e s e measurements i s n o t y e t c o m p l e t e , r e s u l t s so f a r a v a i l a b b e show good agreement between measu r e d and c a l c u l a t e d q u a n t i t i e s . A comparison of km v a l u e s i s shown i n T a b l e 4.6. (?Thile t h e c a l c u l a t e d and measured v a l u e s compare v e r y f a v o r a b l y , i t must b e acknowledged t h a t w e do n o t r e a l l y claim such h i g h acc u r a c y for o u r c a l c u l a t i o n s , s i n c e changes l a r g e r t h a n t h e d i f f e r e n c e s n o t e d i n T a b l e 4.6 would b e produced by v a r i a t i o n s i n c r o s s s e c t i o n s well w i t h i n o u r p r e s e n t r a n g e of u n c e r t a i n t y . ) It t h u s a p p e a r s t h a t p r e s e n t l y a v a i l a b l e d a t a and methods c a n y i e l d t h a t are r e l i a b l e t o w i t h i n less t h a n 1%. predictions sf

Power-Dens ity D i s t r i b u t ions C a l c u l a t i o n s of p ~ w e r - d e n s i t y d i s t r i b u t i o n s i n a l a r g e MSW h a v e mush i n common w i t h those f o r o t h e r power r e a c t o r c o r e s w i t h low l e a k a g e and kw c l o s e t o 1 . 0 . I n p a r t i c u l a r , w e would e x p e c t a h i g h s e n s i t i v i t y of power d i s t r i b u t i o n t o s m a l l v a r i a t i o n s i n km w i t h i n t h e r e a c t o r c o r e . While no d i r e c t e x p e r i m e n t a l d a t a f o r m o l t e n - s a l t r e a c t o r s are a v a i l a b l e , mush r e l e v a n t e x p e r i e n c e has b e e n a c q u i r e d w i t h l a r g e gas-cooled g r a p h i t e r e a c t o r s and w i t h heavy-water r e a c t o r s . It i s u s u a l w i t h s u c h r e a c t o r s t o p r o v i d e i n s t r u m e n t a t i o n to measure power d i s t r i b u t i o n s w i t h some d e g r e e of a c c u r a c y 9 and to p r o v i d e s m a l l . amounts of r e a c t i v i t y c o n t r o 1 , distrib u t e d o v e r t h e c o r e , t o r e g u l a t e the power d i s t r i b u t i o n . W e would e x p e c t t o r e q u i r e some means f o r making routi-ne measurements of t h e power d i s t r i b u t i o n , a t l e a s t i n e a r l y slzcs8ten-salt power r e a c t o r s , We11 as SQm@ means of c o n t r o l l i n g i t (Such measurements would n o t n e c e s s a r i l y require i n - c o r e f l u x sensors. O t h e r p o s s i b i l i t i e s would i n c l u d e s a l t - o u t l e t t e m p e r a t u r e measurements o r n e u t r o n - f l u measurements at several p o i n t s outside the reactor vessel.) However, t h e t o l e r a n c e f o r u n c e r t a i n t y i n t h e power d i s t r i b u t i o n m y b e somewhat g r e a t e r i n m o l t e n - s a l t r e a c t o r s t h a n i n most o t h e r t y p e s of power r e a c t o r . The p r i n c i p a l l i m i t a t i o n appears t o b e r a d i a t i o n damage t o t h e g r a p h i t e , which depends p r i m a r i l y on t h e i n t e g r a t e d power d e n s i t y over l o n g p e r i o d s of o p e r a t i o n . Both t h e n e u t r o n f l u e n c e and t h e g r a p h i t e t e m p e r a t u r e h a v e an i m p o r t a n t i n f l u e n c e on changes i n g r a p h i t e p r o p e r t i e s , and b o t h would b e a f f e c t e d by deviations of power d e n s i t y from e x p e c t e d v a l u e s . However i t c a n b e shown. f o r t h e r e f e r e n c e MSBW t h a t t e m p e r a t u r e e f f e c t s are much smaller t h a n t h e d i r e c t e f f e c t of f a s t ~ e u t r o nf l u x , which i s a p p r o x i m a t d y p r o p o r t i o n a l to the power d e n s i t y . I f a POX d e v i a t i o n of power d e n s i t y from i t s nominal v a l u e s h o u l d p e r s i s t over t h e l i f e of t h e c o r e , t h e g r a p h i t e , i n s t e a d of r e t u r n i n g just t o i t s o r i g i n a l volume, W O U ~expand ~ a b o u t 2% ( i e e a , 8.02 6 Q f L , 0.06 6v/v) which i s probably about the limit of \ghat Could be t o l e r a t e d . C o n s i d e r a b l y l a r g e r short-term- deviations i n power d e n s i t y s h o u l d b e acc e p t a b l e , particularly if adequate s t e p s are taken f n t h e d e t a i l e d d e s i g n sf t h e r e a c t o r t o ensure good mixing of t h e s a l t i n t h e c o r e o u t l e t plenm.

k,

300째C

20째C

k , (measured)

1.0291

k, (calculated)

1.0300

f

measured /<-(-,)

mlculatd

o.wi

2

0.0012

o.ooi2

1.0124

f

0.0018

627째C

1.0045

f

1.0138

1.0057

o.wm 2 o m n o

i.0008 f

0.0010

o.ooio

1000' c

Ak, (200"

-+

l0OO"C~

1.0037 * 0.0022

-0.0090 k 0.0016

B.0030

-0.0108

i.oowf

0.0012

0.83 f 0.15

%, fOr bare critical core of gwen composition. bQuoted errorv,mclude only expenrnentd errors; uncertaintie, in calcuhtited quantitiees aye undoubtedly greater than these (see text).

<..... .x.:.

8%

Reactivity Control

...,. ..>&.

Requirements f o r r e a c t i v f t y c o n t r o l i n m o l t e n - s a l t r e a c t o r s are somewhat different t h a n in m o s t s o l i d - f u e l reactors. h n g - t e m r e a c t i v i t y changes are t o be compensated by a d j u s t m e n t s i n f u e l salt composition. Shutdown rods w o r t h a few percent: i n Clk a r e l i k e l y t o b e r e q u i r e d , b u t these w o d d nOrmally b e full. withdP8Wn f o r t h e re8Ctole. SmLlhl Z l M o U l l t S of r e a c t i v i t y a d j u s t m e n t f o r normal o p e r a t i o n a l maneuvering s h o u l d b e a v a i l a b l e , and i f p o s s i b l e these c o n t r o l d e v i c e s s h o u l d R Q % have a n adv e r s e e f f e c t on t h e b r e e d i n g r a t i o . W e t h e r e f o r e v i s u a l i z e a n a d e q u a t e comp%ement of neutron-absorbing safety rods which W Q U % ~b e f u l l y withdrawn d u r i n g normal o p e r a t i o n s . Maneuvering, as now planned, w i l l b e aecomp l i s h e d by g r a p h i t e r o d s which d i s p l a c e f u e l salt from s p e c i a l p a s s a g e s i n the core. Techniques f o r c a l c u l a t i n g t h e e f f e c t i v e n e s s sf the a b s o r b e r rods are w e l l e s t a b l i s h e d , and generaPPg. r e l i a b l e t o w i t h i n less than 10% of t h e rod worth, which is quite s u f f i c i e n t . Predicted and measured r o d ~ ~ p r t h s i n t h e b%sRE a g r e e d t o w i t k i n 5% of t h e rod w o r t h , as may b e seen from Table 4 . 7 . The g r a p h i t e displacement r o d s , t o b e used f o r maneuvering, are unc o n v e n t i o n a l . T h e i r r e a c t i v i t y worth i s expected t o b e s m a l l (e.g., 6k/k PI, O.OQ% p e r r o d ) and they depend on somewhat d i f f e r e n t p h y s i c a l e f f e c t s t h a n d~ normal "black" a b s o r b e r rods C a l c u l a t i o n s show that displacement s f fuel s a l t by the g r a p h i t e rods i n c r e a s e s r e a c t i v i t y , rather t h a n d e c r e a s i n g i t as one might e x p e c t , and i t a p p e a r s t h a t changes in resonance n e ~ t r ~c anp t u r e i n n e i g h b o r i n g f u e l p a s s a g e s are a t least p a r t l y r e s p o n s i b l e . * Some of t h e r e a c t i v i t y specimens i n t h e HTLTR experiments 161 gave q u a l i t a t i v e c o n f i ~ ~ ~ aof t i t~hne p o s i t i v e r e a c t i v i t y a s s o c i a t e d with d i s p l a c i n g f u e l by g r a p h i t e but c a l c u l a t i o n s p r e c i s e l y c o r r e s p o n d i n g t o t h e e x p e r i m e n t a l s i t u ~ i t i ~ nhave s not y e t been made. T h e r e a c t i v i t y requirement f o r maneuvering i s n o t a r i g i d ones but i t w i l l b e n e c e s s a r y t o e s t a b l i s h more f i r m l y t h e e f f e c t i v e n e s s of t h e graphi t e rods b e f o r e they c o u l d b e adopted f i n a l l y as t h e b a s i s f o r MSBR d e s i g n . Reactivity Coefficients

A l a r g e s i n g l e - f l u i d MSBR has t e m p e r a t u r e c o e f f i c i e n t s of r e a c t i v i t y ( s e e Chap. 1 4 , T a b l e 14.1) which are nut e s p e c i a l l y l a r g e f o r a f l u i d - f u e l r e a c t o r . Both t h e o v e r a l l , i s o t h e r m a l t e m p e r a t u r e c o e f f i c i e n t , and t h e c o e f f i c i e n t of t h e salt a l o n e r e p r e s e n t small ( a l g e b r a i c ) sums of much l a r g e r i n d i v i d u a l e f f e c t s , e.g. thorium Doppler c o e f f i c i e n t ( n e g a t i v e ) and moderator c o e f f i c i e n t ( p o s i t i v e ) . Direct e x p e r i m e n t a l c o n f i m a t i s n

*A

s i m i l a r e f f e c t , w i t h a s i m i l a r e x p l a n a t i o n , i s noted i n n a t u r a l uranium g r a p h i t e r e a c t o r s , where removal of a l l f u e l from a single channel i n c r e a s e s r e a c t i v i t y . I n t h i s case, good agreement i s found between experiments and calculations e

2

Uranium concentration

Configuration

Reactivity (% 6 k / k ) Observed=

Redicted

23SUb

Initial crrtrcal concentration 1.1 Y initial concentration a33Ur

1 Pod 3 rods

2.26

2.28

5.59

5.89

I rod

2.08

2.09

1 rod

2.58

2.75

3 rods

6.9

4.01

.... &a

.... a

....

of t h e c a l c u l a t e d magnitudes of a l l t h e s e e f f e c t s h a s n o t been o b t a i n e d f o r a m o l t e n - s a l t r e a c t o r , though a l l t h e important e f f e c t s w i l l b e i n f e r r e d from the-HTLTR-MSBR l a t t i c e experiments. T h e c r i t i c a l i t y calcul a t i o n s c i t e d i n Table 4.6 show s a t i s f a c t o r y agreement between measured , o v e r t h e temperature range between 28" and and c a l c u l a t e d changes i n k 1 0 0 0 " ~ . ~ i t h o ~ ge fhf e c t s of s a l t e x p m ~ i o nare not d i r e c t l y reproduced i n t h e s e experiments, t h e major components of t h e o v e r a l l t e m p e r a t u r e c o e f f i c i e n t (Doppler and thermal-base c o e f f i c i e n t s ) are i n c l u d e d . F u e l d e n s i t y e f f e c t s w e r e t e s t e d i n one of t h e r e a c t i v i t y samples, b u t analys i s of t h e s e measurements i s n o t y e t complete. C a l c u l a t e d and measured t e m p e r a t u r e c o e f f i c i e n t s f o r t h e b%sRE [ 9 ] showed agreement t o w i t h i n about l o % , brat t h e s e depended mainly on n e w t r o n l e a k a g e e f f e c t s ; a l t h o u g h t h e agreement i s encouraging, t h e r e s u l t s are n o t d i r e c t l y a p p l i c a b l e t o a l a r g e E R . The r e a c t i v i t y e f f e c t s of f u e l a d d i t i o n s w e r e measured i n PEE f o r b o t h 245Y and 2 3 3 U f u e l l o a d i n g s , w i t h r e s u l t s shown i n Table 4 . 8 .

Radiation Calculations Design prsb%ems r e l a t e d t o r a d i a t i o n t r a n s p o r t , such as s h i e l d i n g , r a d i a t i o n damage, and gamma o r n e u t r o n h e a t i n g , p r e s e n t a somewhat d i f f e r e n t a s p e c t i n m o l t e n - s a l t r e a c t o r s t h a n i n many o t h e r r e a c t o r t y p e s , b u t t h i s i s because of t h e m o b i l i t y of t h e f u e l and o t h e r r a d i a t i o n s o u r c e s (e.g., fission g a s e s ) , and n o t because of any e s s e n t i a l d i f f e r ences i n t h e transport problem p a r s e e I n gas-cooled r e a c t o r s such as t h e natural-uranium, g r a p h i t e react o r s , r a d i a t i o n s t r e a m i n g from f u e l channels w a s p e c u l i a r l y i m p o r t a n t . I n EPFBR's, n e u t r o n p e n e t r a t i o n through t h i c k composite r e g i o n s of i r o n and sodium h a s proved t o be an i m p o r t a n t problem r e q u i r i n g new e x p e r i mental d a t a and improved methods of a n a l y s i s . I n t h e c a s e of t h e molten s a l t r e a c t o r , w h i l e i t may b e premature t o conclude t h a t no unique probl e m s of r a d i a t i o n t r a n s p o r t w i l l appears none are now e v i d e n t . I n s t e a d , it seems a p p a r e n t t h a t t h e p r i n c i p a l problems w i l l r e l a t e t o determining the d i s t r i b u t h n s of t h e s o u r c e s of r a d i a t i o n , and e s p e c i a l l y of f i s s i o n p r o d u c t s , throughout t h e r e a c t o r p l a n t . These a s p e c t s of t h e problem a r e t r e a t e d elsewhere i n t h i s r e p o r t .

Keactor Dynamics

Questfons of c o n t r o l and s a f e t y of m o l t e n - s a l t reactors are d i s c u s s e d elsewhere in t h i s r e p o r t (Chapters 10 and l 4 ) * E t i s o u r purpose h e r e o n l y t o c l a r i f y t h e s t a t u s of o u r u n d e r s t a n d i n g of t h e r e l e v a n t n e u t r o n i c c h a r a c t e r i s t i c s of t h e r e a c t o r . C i r e u l a t 2 n g - f u e l r e a c t o r s e s p e c i a l l y if o p e r a t e d on t h e T I I - ~3 3 ~ f u e l c y c l e , have u n u s u a l l y s m a l l delayed-neutron f r a c t i o n s . Calculated v a l u e s f o r m o l t e n - s a l t b r e e d e r r e a c t o r s f a l l i n t h e r a n g e 0.00lQ-0.60l5, depending on d e t a i l s of reactor d e s i g n . A t the same t i m e , t h e g r a p h i t e moderated E R , i n common w i t h most o t h e r graphite-moderated r e a c t o r s , h a s a very l o n g prompt-neutron g e n e r a t i o n t i m e , e.g., 0.4 msec.

4

Table 4.8. Messwed and calculated reactivity coefficients of fuel concentration for EMd 0.223

0.244

0.369

0.389

...

85 With r e s p e c t t o t e m p e r a t u r e c o e f f i c i e n t s of r e a c t i v i t y t h e s i t u a t i o n i s q u a l i t a t i v e l y s i m i l a r t o t h a t of t h e n a t u r a l - u r a n i u m , g r a p h i t e moderated, gas-cooled r e a c t o r s , i.e, a prompt n e g a t i v e t e m p e r a t u r e c o e f f i c i e n t f o r t h e f u e l is accompanied by a d e l a y e d p o s i t i v e c o e f f i c i e n t f o r t h e moderator. I n t h e case of t h e r e f e r e n c e MSBR, t h e s e c o e f f i c i e n t s n e a r l y o f f s e t e a c h o t h e r i n magnitude. T h i s g i v e s r i s e t o a s m a l l S ~ Q W o v e r a l l c o e f f i c i e n t , i n c o n t r a s t to t h e much l a r g e r n e g a t i v e prompt coefficient. We have not found i t v e r y u s e f u l t o t r y t o f o r m u l a t e s i m p l e g e n e r a l i z e d s t a t e m e n t s a b o u t t h e dynamic b e h a v i o r of EX'S i n terns of t h e s e u n d e r l y i n g c h a r a c t e r i s t i c s . I n s t e a d , w e have t r i e d to d e v e l o p r e l i a b l e c o m p u t a t i o n a l models f o r p r e d i c t i n g t h e i r b e h a v i o r , and have g a i n e d conf i d e n c e i n t h e u s e o f t h e s e models by comparisen w i t h o b s e r v e d b e h a v i o r i n t h e case o f t h e MSRE.

.

... i..... _.

... .;.; .:2 -

....

E f f e c t s o f Fuel, Circulation Models f o r t h e r e a c t i v i t y e f f e c t of f u e l c i r c u l ~ ~ t must i o ~ ~take i n t o a c c o u n t t h e t r a n s p o r t of d e l a y e d n e u t r o n p r e ~ u r s o r si n n t h e moving f u e l and t h e w e i g h t e d c o n t r i b u t i o n s O f d e l a y e d n e u t r o n s e m i t t e d o u t s i d e t h e c o r e , as w e l l as t h e skewed d i s t r i b u t i o n of d e l a y e d n e u t r o n s e m i t t e d w i t h i n t h e c o r e . The u s u a l r e a c t o r k i n e t i c s e q u a t i o n s must b e m o d i f i e d to t a k e t h e s e e f f e c t s e x p l i c i t l y i n t o a c c o u n t , s i n c e t h e i r i m p o r t a n c e i s n o t i n d e p e n d e n t of r e a c t o r p e r i o d . C o n f i r m a t i o n of t h e models d e v e l o p e d f o r t h e MSRE w a s o b t a i n e d d u r i n g t h e c o n t r o l rod c a l i b r a t i o n experiments. The r e a c t i v i t y e f f e c t of f u e l c i r c u l a t i o n ( w i t h 235U f u e l ) was measured t o b e 0.212 C 0.604% 6k/k, and t h e c a l c u l a t e d value was 0.222% 191. ( N e g l e c t of d e l a y e d n e u t r o n s e m i t t e d i n t h e upper and l o w e r p l e n a y i e l d s I n a d d i t i o n , good agreement w a s oba c a l c u l a t e d v a l u e of 0.30% &/k.) t a i n e d betweeA rod c a l i b r a t i o n C U K V ~ S i n f e r r e d from p e r i o d measurements u s i n g t h e c o n v e n t i o n a l i n h o u r e q u a t i o n w i t h t h e f u e l s t a t i o n a r y , and t h e m o d i f i e d e q u a t i o n s w i t h t h e f u e l c i r c u l a t i n g . The r e a c t i v i t y e f f e c t s f f u e l c i r c u l a t i o n i s thus b e l i e v e d t o b e w e l l understood.

Frequency Response and R e a c t o r S t a b i l i t y

..... ...., .....

. d

<q*

... ........ .., I .

I

& .,$

...,

2.e

The dynamic b e h a v i o r sf a m u l t i p l e l o o p s y s t e m , s u c h as t h e MSlU3 o r the r e f e r e n c e MSBR, depends sf c o u r s e on t h e p r o p e r t i e s of all p a r t s of t h e s y s t e m and on the way t h e p a r t s a r e l i n k e d t o form the s y s t e m . N e u t r o n i c c h a r a c t e r i s t i c s are i m p o r t a n t , b u t s o are power d e n s i t i e s and h e a t c a p a c i t i e s , h e a t t r a n s f e r c o e f f i c i e n t s , s a l t c i r c u l a t i o n rates, e t c . The s h o r t - t e r m time-dependence of r e a c t o r p a r a m e t e r s such as n e u t r o n flux o r c o r e - o u t l e t s a l t t e m p e r a t u r e w i l l depend at s h o r t t i m e s (or h i g h freq u e n c i e s ) p r i m a r i l y on t h e c h a r a c t e r i s t i c s of t h e r e a c t o r i t s e l f , w h i l e a t l o n g e r t i m e s (and a t l o w e r f r e q u e n c i e s ) the i n f l u e n c e of o t h e r p a r t s of t h e system w i l l , b e f e l t .

Fuel-Cycle Economics

... ,&&i

87 .... .... ., i .Y

...

ORN h- BWG 7 8-5 2 19

103

..,

;.v3

5 ... ..... ,.... :-

.... ..... :.:.:4

10-3

..... ..... ..,

2

90

..A1

60

..... .:.a

-8

30

w m

o

-e,

... .... ..... .... !e. . . . %

Q:

I

a

- 38

!:a -60

-90 f6-2

2

5

lo-'

2

5

100

2

FREQUENCY (rodrans/seel

Fig. 4 . 4 .

MSaE f requermey respsnse-PrnS signal.

5

IO'

88

Table 4.9. MSBR fuel eyeb cost

KilIs!kWhr( e) Fixed charges on carrier salt at 13.2%year 7LLF BeF* ThF4

0.058 0.008

0.033 0.079

Salt makeup (15 calendar y e a cycle) 7~iF BeF2 ThF4

0.019 0.004 0.016

0.039 Fixed charges on fissile inventory at I3.2%/year

Q.36ff

Fixed charges OR processirrng plant at 13.4%/yrar

0.49 - 0.69

,

Roccssir.g pIant operating costs Gross fuel cycle cost Fuel productions credit Net fuel cycle cost

0.05 1.02-1.22 -0.09 0.93-1.13

89 ....

*:::b

.... ..... .<.p

.... ,.:.:3

........ ..,. .. .p.

.... .:<3.P <+

$3

c o s t of t h e chemical p r o c e s s i n g p l a n t 1141. While other components of t h e f u e l c o s t have remained r e l a t i v e l y s t a b l e , they are undoubtedly s u b j e c t t o change, e i t h e r as a r e s u l t of changes i n assumed u n i t c o s t s of materials o r as a r e s u l t of changes i n r e a c t o r d e s i g n . The p o s s i b l e magnitudes of such changes are e s t i m a t e d h e r e . It s h o u l d b e noted t h a t t h e f u e l c y c l e c o s t s shown i n Table 4.9 a r e blot t h e lowest a t t a i n a b l e , and do n o t n e c e s s a r i l y correspond w i t h t h e lowest power c o s t . The r e f e r e n c e %fSBR w a s optimized on t h e b a s i s of b r e e d i n g performance, u s i n g a " f i g u r e of m e r i t " p r o p o r t i o n a l t o t h e b r e e d i n g g a i n d i v i d e d by t h e square of the s p e c i f i c f u e l i n v e n t o r y ( G / 1 2 ) . S i n c e t h e r e s u l t i n g f u e l c y c l e c o s t s were f a v o r a b l e as compared w i t h t h o s e p r o j e c t e d f o r o t h e r r e a c t o r s , no s e r i o u s a t t e m p t has t h u s f a r been made t o r e o p t i m i z e t h e r e a c t s r d e s i g n and f u e l c y c l e parameters s o l e l y on t h e b a s i s 0 % power c o s t . It should b e understood, t h e r e f o r e , t h a t changes i n f u e l cycle c o s t a s s o c i a t e d w i t h changes i n material c o s t s or r e a c t o r performance are l i k e l y to b e compensated by adjustments i n fuel c y c l e parameters

...,

_..& .i < . ....

.... *:.:.I

....

;:v..> <d

The cost of s e p a r a t e d 7 L i has been assumed t o be $120/kg f o r l i t h i u m c o n t a i n i n g 50 ppm %i,when produced i n s u b s t a n t i a l q u a n t i t i e s . Based on t h i s p r i c e , t h e 7 L i c o n t r i b u t e s 0.057 milHs/kWh(e) t o t h e fuel c y c l e c o s t . i any compensating a d j u s t m e n t s ) ~ h u s ,doubling t h e c o s t of 9 ~ (without would add 0.059 mills/kWh(e) t o t h e f u e l c o s t . Doubling t h e nominal f e e d r a t e ( i e e a 96 . 7 % of the %i i n v e n t o r y per y e a r ) would add about 0.02 mills/kbJJ(e) (but i t should b e n s t e d t h a t t h e nominal feed r a t e on whlch t h e above makeup c o s t i s based i s a l r e a d y 50-16OZ h i g h e r than w e t h i n k t h e a c t u a l f e e d r a t e i s l i k e l y to h e ) . I t s h o u l d a l s o b e noted t h a t t h e assumed l i t h i u m f e e d p u r i t y of 9 9 . 9 9 5 % 7 L i may b e u n n e c e s s a r i l y h i g h . T h e a s s o c i a t e d n e u t r o n c a p t u r e r a t e i n 6 L i , t a k i n g i n t o account burnout and replacement of 6Li, i s 0.6818 n e u t r o n s p e r ?-IC S Q U I X ~ n e u t r o n s , compared w i t h a c a p t u r e r a t e (There i s an a d d i t i o n a l c a p t u r e r a t e of 0.0OP4 n e u t r o n 0 % 0.0161 i n 7 L i . Doubling t h e 6 L i i n t h e 6Li t h a t i s formed by ( n , a ) r e a c t i o n s i n B e . ) c o n t e n t i n t h e l i t h i u m f e e d would t h u s d e c r e a s e t h e b r e e d i n g r a t i o , a t e q u i l i b r i u m , by about 0.002, which might b e an a c c e p t a b l e a l t e r n a t i v e to a c c e p t i n g changes i n t h e p r i c e of l i t h i u m .

Thorium

d;&

....

.... .:<.2

A t $6.5O/Pb of r%hF~+, thorium c o n t r i b u t e s 0.05 mills/kh%(e) t o t h e f u e l c y c l e c o s t (of which s l i g h t l y more t h a n 6.002 milbls/kW%(e) i s act u a l l y f o r burnup). Any s i g n i f i c a n t i n c r e a s e i n t h e p r i c e of thorium would be p a r t l y csnpensated by a r e d u c t i o n i n thorium c o n c e n t r a t i o n s i n (11% R e f . 5, i t i s shown t h a t t h e b r e e d i n g performance i n the reactor. t h e r e a c t o r f s q u i t e i n s e n s i t i v e t o v a r i a t i o n s i n thorium c o n c e n t r a t i o n s around t h e v a l u e s e l e c t e d f o r t h e MSBR - i . e . , 1 2 mole p e r c e n t . )

Be ry P Iium

Uranium

w

F u e l cycle c o s t s for the r e f e r e n c e MS istfiuencea by the p r i c e of fissile uranium p r i m a r i l y t h r o u g h the i n v e n t o r y c h a r g e s , which are 0.36 d b l a / k k h C e ) , as compared w i t h a f u e l p r o d u c t i o n c r e d i t of 0.09 r n i l l s / k r n ( e ) ( f o r 8 b r e e d i n g ratio of 1 . 0 7 ) . Doubling t h e p r i c e 0 % f i a s i l e baramaim, without compensating changes i n t h e fuel c y c l e , would t h u s add 0.27 ~ L P l s / k ~ ( e ) .(Doubling t h e cost $8 to $16/Pb Uq08 would add 0,09 w i l l s / k b h ( e ) . ) Some a d j u s t m e n t s in f u e l salt c ~ m p ~ s i t i ~ n , as well as i n d e t a i l s ~f c o r e d e s i g n , would of c o u r s e b e p o s s i b l e . Et is not t o $e a p e c t e d , baowever, t h a t a p p r e c i a b l e reauctions in fissile i n v e n t o r y wouhd b e p o s s i b l e w i t h o u t a m j o r r e d u c t i o n i n b r e e d i n g g a i n . TdiliLe the t r a d e - ~ f % sbetween s p e c i f i c i n v e n t o r y and b r e e d i n g gain depend on many d e t a i l s of r e a c t o r d e s i g n , a sough a p p r o x i m a t i o n is t h a t a 10% reductisn in inventory fwitfisut: altering the design O f the primnary circuit a t e P n a P t0 t h e r e a c t o r C Q % e I d c o s t a b o u t 0.015 i n b r e e d i n g r a t i o . A p p l i e d to t h e r e f e r e n c e t h i s i n d i c a t e s t h a t a saving o f 0,636 i n i n v e n t o r y c h a r g e s would b e partly o f f s e t by a r e d u e t i o m of 8,021 i n t h e f u e l p r o d u c t i o n credit. A c t u a l l y , t h e relation between r a t i o and s p e c i f i c i n v e n t o r y i s hi laPy non-1inear: a major decrease in inventory (e.g. ~ Q rXe d u e t i o n ) ~ ~ u be i ap O s s i t ~ e ,at t h e expense of reducing t h e eonversisw ratio n e a r l y t~ z e r o ; on t h e o t h e r Eaand, a l a r g e p e r c e n t a g e i n c r e a s e i n i n v e n t o r y c o u l d g a i n a t m o s t a v e r y f e w p e r c e n t a g e p o i n t s i n b r e e d i n ratio. Thus, t h e possible range f o r a d j u s t w e n t s i s r a t h e r l i m i t e d whether breeciimg performance o r f u e l c o s t alone is the guide,

Graphit e

Wep%aeement of the g r a p h i t e core s t r u c t u r e , as a consequence of rad i a t i o n damage, i s estimated t o c o n t r i b u t e 0.17 milPs/kWh(e) t~ t h e power C o s t f o r t h e r e f e r e n c e NSBW. A partial breakdown of t h i s cost is shown i n T a b l e 4.10, (Inclusion sf this c o s t component w i t h t h e f u e l c y c l e c o s t is of C Q U ~ Sa ~r b i t r a r y , b u t c o n v e n t i o n a l , i n keeping w i t h t h e i n c l u s i o n of E e o r B2Q mkeup c o s t s for gas-cooled and heavqT-~ater-moderated reactors ) G r a p h i t e a l o n e c o n t r i b u t e s & Q U ~ 6.12 miIs/kk%(e) t o t h e c o s t of Core P@p%aCelE%lt(at foulf-year intervaks). bkKh Of t h e U l l c @ K t a h t y in g r a p h i t e c o s t i s a s s o c i a t e d with c o a t i n g o r impregnating the g r a p h i t e t o r e d u c e i t s p e m e a b i l i t y t o xenon. In our c o s t estimates9 t h i s r e p r e s e n t s about $5/Eb sf an a v e r a g e $l1/Hb c o s t of t h e g r a p h i t e that i s r e p l a c e d , The u n c e r t a i n t y i n g r a p h i t e e o a t i m c o s t s is substantial - p r o b a b l y a

-

k.,

k...,

....

.... ,x.w

91 .... ..... .

!..%

...

i......

... .,,.

.... i

...

.:*j

Table 4.10. MSBR core replacement cast 4 calendar year replacement schedule; replacement assumed to

take place during planned shutdown for maintenance o f turbines and other equipment [ 151 Miilions of dollars

lilills/kWhr(e)

Hastelloy N

1.09

0.035

Graphite

3.75

0.119

Special labor cast

0.50 5.34

.:.:.*

... ..... < :.:s

0.016 ~

0.17

.... ,...~.

92

93

+

ORN b-QWG 9 2 - 8579

0.20

.

0.1 8

~

.

0.1 6

0.1 4

8.1 2

0.1 0

0.08

,;.;.;q

..>

8.06

..'..,;., .....

0.04

..;..... ;.;.,9

0.02

...

,y.*;

0

$ Il/lb

T--

I -

0

4

8

12

16

20

24

28

GRAPHITE LIFE [years) x:. ....

....

F i g . 4.5. Graphite replacement c o s t as a f u n ~ t i o nof graphite price and replacement life.

94 References for Chapter 4

2.

Y&R PPogrm Semiann. PPogE?. W e p t . Feb. 28, 1 9 7 1 , o w - 4 6 7 6 , p a 44.

5.

A . M. P e r r y , H. P . Bauman, â‚ŹluoZ. AppZ. Tech. 8, 214 (1970).

6,

A . E%. P e r r y , E. I?.

....... .,. e&..

Bauman, PJtscZ. App2. Tech. 8, 215 (1978). s

11. T. W. Kerlin, S . J. Ball, R. C . Steffy, 'Theoretical Dynamics Analysis Of t h e EISRE,"'NZh@Z. Tech. 10, 118 (n971). 12.

15.

T. W. K e r I i n 9 S. by. Ball, R. C . S t e f f y , PI. R. Buckner, "Experfences namis Testing Methods at the MSrn,8' NikcZ. Tech. 10, 103 (1971)

0

Conceptual Design Stud3 ef a SingZe-PZaid Molten-Salt Breedela Reactor, 8mL-4541, p . 188 (1971) 0

.... i.4 ... .Y

... .~..

.... i

W. R. Grimes, E. G. Bohlwann, A . S . Neyer, and J. M. Dale

......

. i . , i

..., ........ ....,. i

... ,X.<<2

... $r<;

S t u d i e s of molten s a l t systems s u i t a b l e f o r use i n h i g h - t e ~ ~ ~ p e r a t u r e n u c l e a r r e a c t o r s , and examinations of t h e chemical problems i n h e r e n t i n such u s e , have been under way f ~ more r t h a n 20 y e a r s (see Chapter 2 ) . Many i n d i v i d u a l molten s a l t mixtures have been s t u d i e d , b u t o n l y two classes of s a l t s , c h l o r i d e s and f l u o r i d e s , have been given s e r i o u s COLIsideration Molten c h l o r i d e s w e r e c o n s i d e r e d , e s p e c i a l l y f o r f a s t r e a c t o r f u e l s , a t a r e l a t i v e l y e a r l y d a t e [I, 21, b u t l i t t l e experfmental work with such systems a p p e a r s t o have been done u n t i l much l a t e r . A small e x p e r i m e n t a l e f f o r t a t IXAEA, Hamell, devoted t o molten cfi%oridem i x t u r e s as f u e l s f o r advanced f a s t r e a c t o r s h a s been i n p r o g r e s s s i n c e I965 K31. (The newt r o l l Cross s e c t i o n O f Ch%orin@rules Out itยง U8e in thelXlal reactors.) F l u o r i d e ~ d ~ t u r have e s been t h e subject of a chemical r e s e a r c h program a t OWL s i n c e 1949 [ 4 ] * These s t u d i e s first developed NaF-ZrF4-UF4 m i x t u r e s , which f u e l e d t h e A i r c r a f t Reactor Experiment i n 1 9 5 4 . S i n c e 1958 t h i s program has been d i r e c t e d t o molten f l u o r i d e m i x t u r e s s u i t a b l e f o r u s e i n t h e r m a l b r e e d e r r e a c t o r s . S e v e r a l reviews of t h i s chemical e f f o r t have been p u b l i s h e d [5, 6 , 7 , 81. In a d d i t i o n , o u r e x p e r i e n c e w i t h t h e chemical a s p e c t s of t h e XSM9 which w a s f u e l e d w i t h a m i x t u r e of L I P , BeF2, Z r F b p and LEI,, has been r e p o r t e d i n d e t a i l [ 9 ] . We a t t e m p t i n t h i s chapter t o assess t h e s t r e n g t h s and weaknesses sf p e r t i n e n t molten salts and of our knowledge of these materials f o r u s e i n a m o l t e n - s a l t b r e e d e r r e a c t o r . The choice of optimum salt mixt u r e s , the p r e s e n t s t a t u s ~f t h e i r technology, and o u r e v a l u a t i o n of t h e i r s u i t a b i l i t y and ~f remaining problem areas are b r i e f l y p r e s e n t e d i n s e p a r a t e s e c t i o n s f o r the f u e l and t h e c o o l a n t m i x t u r e s . Behavior 0 % f i s s i o n products i n the f u e l c i r c u i t , an important and complex matter which i s less well documented, i s t r e a t e d i n some d e t a i l in a s e p a r a t e s e c t i o n of t h e c h a p t e r . F i n a l l y , w e d e s c r i b e t h e methods f o r d e t a i l e d chemical. a n a l y s i s of f u e l and c o o l a n t streams and t h e i r a n c i l l a r y systems and t h e problems remaining b e f o r e an W B R could b e o p e r a t e d w i t h c o n f i dence 6

e

Fuel S a l t s

Basis f o r Choice of Composition :.:.:.:%, ....

:......., ......, ,...<,,

A s i n g l e - f l u i d B B R [lo] makes s t r i n g e n t demands upon i t s f l u i d f u e l . T h i s f u e l must have a low capture c r o s s s e c t i o n f p r n e u t r o n s , and i t must dissolve more than the critical c ~ n e e ~ ~ t r aof ti~ uranium n o r plutonium and

.... ..... .s:v

95 ..... .. .:.=

ii...

96

high c o n c e n t r a t i o n s of t h o r i m a t temperatures comfortably below the ternperatrare of t h e primary heat exchanger. The mixture must b e t h e r m a l l y stable, and i t s vapor pressure needs to be low over a t e m p e r a t u r e range (600-75Q"C) sufficient8y h i g h t o permit g e n e r a t i o n of h i g h - q u a l i t y steam. The fuel mixture must p o s s e s s heat t r a n s f e r and hydrodynanic p r o p e r t i e s adequate f o r i t s s e r v i c e as a heat-exchange f l u i d . I t must b e ~ ~ n a g g r e s sive toward some material of c o n s t r u c t i o n and toward some suitable modera t o r mteria9.. The f u e l must b e s t a b l e toward r e a c t o r r a d i a t i o n , must b e able t o survive f i s s i o n of the uranium (or p l u t ~ n i u m t ) , and must t o l e r a t e f i s s i o n g r ~ d u c taccumulation w i t h o u t serious d e t e r i o r a t i o n of its useful p r o p e r t i e s . An a d d i t i o n a l demand is t h a t the f u e l b e m e n a b l e to e f f e c t i v e recovery of b r e d f i s s i l e material and t o removal of f i s s i o n p r o d u c t poisons9 as d i s c u s s e d i n Chapter 11. The reqUaKeIIIent t h a t the mBB f u e l CoRsiS%, except f o r i t 8 f i s s i l e and f e r t i l e material, e n t i r e l y of nuclides of very l o w n e u t r o n c a p t u r e C T B 8 8 Section restricts t h e Choice Of mteria1.S to CORIpOundS Of beryl1iuID9 bismuth, b o r o n - l l , carbon, deuterium, f l u o r i n e , lithium-7, nitrogen-15, oxygen, and t h e f i s s i l e and f e r t i l e materials. Other n u c l i d e s can b e t o l erated o n l y as minor ~ ~ n s t i t u e n t s .Host of t h e compounds of t h e p o t e n t i a l 81 rnajor c o n s t i t u e n t s " are e l b i n a t e d by t h e o t h e r f u e l r e q u i r e m e n t s . No deuterium-bearing csmpounds are p r a c t i c a l i n such m e l t s . Carbon, n i t r o g e n , boron, and oxygen form high-melting, and q u i t e u n s u i t a b l e , b i n a r y compounds with t h e f i s s i l e and f e r t i l e metals. The oxy gnated anions e i t h e r l a c k t h e required thermal stability (e.g., NQgNQZ-1 o r f a i l as s o l v e ~ ~ tfor s high COIlCeRtPatiOn§ of th0riLml ColRpOUndS (e,g. 6032'). It quickly de~ e l ~ tph e~r e, f ~ r e ,that fluorides are t h e o n l y s u i t a b l e s a l t s . UrilniUlll t e t P a f l U O r i d e @P4> PS t h e Qnly flUOPide Sf UraniUH1 t h a t appears as a constituent of m o ~ t e nm o r i a e fuels; m4 is reiat i v e l y s t a b l e , n o n v o l a t i l e , and n e a r l y n o n k y g r ~ ~ ~ o p i cI.n t h e pure state uranium txifluoride &UP3) d i s p r o p o r t i s n a t e s a t temperatures above about 1BBQ"C by the r e a s t i o n

En molten f l u o r i d e s o l u t i o n , disproportionation o c c u r s a t c o n s i d e r a b l y I Q W temperatures. ~ ~ Uranium trifluoride i s , as i s d i s c u s s e d i n more det a i l below, tderable i n r e a c t o r f u e l s only i n t h e p r e s e n c e of a l a r g e excess sf UF4. T h o r i m t e t r a f l u o r i d e (ThF4) is t h e o n l y known f l u o r i d e of thorium. B i l u e w t f l u o r i d e s are c l e a r l y necessary because of the very h i g h melting p o i n t s of UFL, and ThF4 (1035°C and laPluc respective%y). Nuclear properties a l o n e f a v o r as dilasents t h e f l u o r i d e s of B e , Bi, and 'LF in t h a t order. he stability of t h e s e ~ I U Q I - ~ ~ ~ S e l i m i n a t e s b i s muth from ~ o n s i d e ~ a t i oand n l e a v e s the ~ % B E Q Tof~ ~beryllium ~ S and l i t h i m - 7 as the preferred d i l u e n t s . Fortunately the phase b e h a v i o r ( d e s c r i b e d i n d e t a i l below) of LiF-BeF2-UF, and LIF-BeP2-ThF4 makes t h e s e materials usef u l as f u e l s . The breeder f u e l s a l t r e q u i r e s a h i g h c o n c e n t r a t i o n of ThP4 (10 t o 14 mole X) and somewhat less t h a n 0.3 mole x 233?JFL+ Beryllium f l u o r i d e i s very v i s c o u s , but t h e v i s c o s i t y of LiF-BeF2 m i x t u r e s d e c r e a s e s r a p i d l y as t h e L ~ F / B ~ ? ? ;rI a t i o increases above & O h a t 2 . The LiF/BePz r a t i o i s

.... & < ..

0

. .. we..

... ........ .._.

t h e r e f o r e ckao~en t o o p t i m i z e t h e c o n f l i c t i n g demands f o r low v i s c o s i t y and a low m e l t i n g point. I f t h e l i q u i d u s temperature i s to b e k e p t a t o r below 5 Q Q a C f o r a m e l t w i t h 12 mole X of ThF4, t h e b e r y l l i u m s o n c e n t r a t i o n limits r a n g e (as d e s c r i b e d below) from I6 t o 25 mole The most l i k e l y c h o i c e f o r t h e MSBR f u e l - a n d t h e p r e s e n t d e s i g n c o m p o s i t i o n - is, a c c o r d i n g l y , 7%iF-BeF2-ThF4-UP4 a t 7 1 7'-16-12-8 3 mole % respectively It s h o u l d b e n o t e d t h a t t h e o b j e c t i v e s of t h e ?%%E did not require t h e f u e l t o c o n t a i n ThF4. A c c o r d i n g l y , the fuel chosen f o r "IRE w a s a d x t u r e of k i ~B, ~ P Z~ ~ ,Q , and w4 (65, 29 .I, 5 , and 0.9 mole X > he ZrFb w a s added, as dissus%edl below, to p r e c l u d e inadvertent precipitation Sf uo2. F u e l selecti~ni s no g r e a t problem f o r t h e MSBR s i n c e , as w i l l b e d e t a i l e d below, t h e phase b e h a v i o r of LIF and BeF2 w i t h UF4 and ThFh i s e n t i r e l g s % t k f a C t O 9 p . The requiPE%l,ent O f Very IOW C T O S S Section requpires, i n p r i n c i p l e , t h a t t h e f u e l m i x t u r e b e f r e e from e x t r a n e o u s h i g h - c r o s s - s e c t i o n i o n s . P u r i t y r e q u i r e m e n t s d i c t a t e d by o x i d e - f l u o r i d e e q u i l i b r i a and of c o m p a t i b i l i t y - b o t h of which are d e s c r i b e d i n some d e t a i l below - are r a t h e r more s t r i n g e n t t h a n t h o s e posed by c r o s s - s e c t i o n considerations. % e

.... ,.:.:.:.: ....

:,5;2

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I n d u s t r i a l p ~ - o c e s s e sb a s e d on m o l t e n s a l t s ( e . g . , p r o d u c t i o n of a l u minum by e l e c t r o l y s i s of A I 2 0 3 i n molten K3AlF6) have b e e n u s e d f a r many y e a r s . However, when t h e om%,p%og%m began i n 1 9 4 9 , although t h e c l a s s i c p a p e r s of Telakin and Flood and F e r l a n d [ l 3 ] had b e e n p u b l i s h e d , relat i v e l y l i t t l e w a s known a b o u t m o l t e n s a l t c h e m i s t r y , and v i r t u a l l y n o t h i n g was known about m o l t e n f l u e r i d e b e h a v i o r . The s i t u a t i o n has improved markedly s i n c e t h a t t i m e , p a r t l y , though by no means ent:irely, b e c a u s e of s t i m u l a t i o n of t h e f i e l d by t h e Ifolten S a l t R e a c t o r Program. The ARE program 15, 1 4 1 , w h i c h W ~ Scon~erneclw i t h a d i f f e r e n t fuel s y s t e m (NaF-ZrF4-UF4) and a d i f f e r e n t metal ( P n ~ ~ n er al t h e r t h a n Bastell o y N) , produced l i t t l e chemical i n f o r m a t i o n d i r e c t l y a p p l i c a b l e t o the MSBR but y i e l d e d a g r e a t d e a l of v a l u a b l e background e x p e r i e n c e and i n formation. P r e p a r a t i o n and h a n d l i n g t e c h n i q u e s f o r m o l t e n f l u o r i d e s 66, 153, f o r example, were u s e f u l w i t h minor m o d i f i c a t i o n s f o r t h e LiF-BeF2-based c o m p o s i t i o n s . Techniques f o r rapid and e f f e c t i v e s t u d y of p h a s e b e h a v i o r and f o r d e t e r m i n a t i o n of p h y s i c a l p r o p e r t i e s of m o l t e n f l u o r i d e s 1161 w e r e developed i n t h e s e early days and s u b s e q u e n t l y app l i e d to NSBR-related materials. C ~ r r o s i o nof metals, and e s p e c i a l l y of n i c k e l - b a s e d a l l o y s , by f l u o r i d e s w a s shown t o b e t o l e r a b l e , t h e g e n e r a l mechanisms by which c o r r o s i o n occurred w e r e ~ ~ ~ o g n i z amd e d , t h e importance of ~ t r a n e o u si m p u r i t i e s i n the c o r r o s i o n p r o c e s s was d e m o n s t r a t e d [Sa. C o m p a t i b i l i t y of many m o l t e n f l u o r i d e s w i t h g r a p h i t e was d e m o n s t r a t e d , v a l u e s f o r s o l u b i l i t y of We, K r , and Xe i n m o l t e n f l u o r i d e s [I?] were e s t a b l i s h e d , and the g e n e r a l s t a b i l i t y S â‚Ź m o l t e n f l u o r i d e s t o r a d i a t i o n and f i s s i o n was d e m o n s t r a t e d [ s 9 181.

98 <.... <.>

ny chemical s t u d i e s which immediately preceded operation of were directed a t LiP-BeFz-based f u e l s , and much w a s learned t h a t ars directly releQant t o the E l 3 R system and that is described in some detail in subsequent sections of this chapter. Operation of the HSRE, with its fuel mixture of %iF-BeP2-%rP2-UP4, provided much chemical information that w a s r e a s s u ~ i n g191- S a l t samples removed routinely from the f u e l and c~olantcircuits (one to three per week froen the f u e l system) were analyzes for uranium, m j o r f u e l constituents, p o s s i b l e corrosion p r s d u c t s , and (less frequently) f o r o x i d e ion cont m i n a t i o n khaagrSeS f a r UlPaELFW by cou~OmetPiCtitration 1191 Showed good re-p r o d u c i b i l i t y and h i g h precision (0.5I) b u t on-line reactivity balance calculations w e r e about 10-fold more sensitive than t h i s in establishing changes in uranium ~oncentrationswithin t h e circuit. A11 the data suggest strongly t h a t the fuel was completely s t a b l e and that losses of uranium, if any, were extremely sma3.P. Betemination of uranium OW or in a graphite moderator bar led to the ~ o n c l ~ s i othat n the entire stack contained less than 10 grams of uranium, a quite negligible m o u n t [ 2 0 ] . Oxide concentration in the radioactive MSKE s a l t w a s determined by careful evaluation of B20 produced upon treatment of t h e salt samples w i t h a n ~ ~ y d r o uPEP. s AH samples examined showed less than IBB ppm of G-; no perceptible increase with time w a s apparent [21]. This is moderately reassuring i n s o f a r as the practicality of maintaining oxfde contamination at very l o w l e v e l s in f u t ~ r ereactor systems is concerned, though better methods of a n a l y s i s f o r oxides are clearly needed. KS%%Emaintenance operations involved flushing the interior of t h e fuel circuit with a S ~ i ~ - (66.0-34.0 ~ e ~ 2 mole X > mixture. ~~-~a~grsis of t h i s s a l t before and a f t e r each use showed that an amount of uranium w a s added to the f l u s h salt in each f l u s h i n g operation equivalent to 23 kg of fuel-salt residue (about 0.5% of the charge) from the reactor circuit. The magnitude and t h e reproducibility s f this f i g u r e seem to confirm the narkwetting characteristics of t h e clean f u e l salt toward metal ne f i s s i o n process is n i i a i y oxidizing toward dissolved ~ 3 fin the f u e l . In t h e MSRE a convenient means f o r restorin the b'3+ concentration was to suspend beryllium rods in a perforated capsule of nickel in the salt in the p m p bowl. This active metal r~i~iictedwith UF4 0

ICL

k . :

t....z

a

and converted some ~ O Ograms O E u4+ to u,+ during an 8 - h o ~ r treatment. The s a l t near the B e a p p a r e d to be slightly overreduced, but the overreduced salt mixture clearly reacted and achieved equilibrium w i t h the Parge excess of unreduced s a l t in the p u p bowl and reactor circuit. ( I n an MSBW, the on-line processing system would b e used t o maintain t h e nP,/OP3 ratio at the desired level.) Many fuel s a l t samples were analyzed at r e g u l a r intervals for Fe, Ni, and Cr due to ~ o ~ ~ o s processes i o n 68, 9, 2 2 , 21, 231. A 1 1 samples showed relatively high values f o r i r o n (120 ppm) and nickel (58 ppm), with considerable scatter and no perceptible trend. These values s e e m f a r t o o

&.L....

99

h i g h f o r '%lanks" i n t h e a n a l y t i c a l p r o c e d u r e s ; i t i s a p p a r e n t , f o r reasons d e s c r i b e d below, t h a t i n many cases they do n o t r e p r e s e n t d i s s o l v e d Fe2+ and Mi2*- ~ o l y b d e nc o~n c e n t r a t i o n s w e r e shown, i n t h e few a t t e m p t s m d e , t o b e below t h e d e t e c t i b l e l i m i t (ca. 25 ppm) f o r chemical analy-

sis *

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BERE was o p e r a t e d f o r n e a r l y t h r e e y e a r s w i t h 235UP4 as i t s f u e l and f o r a s h o r t e r p e r i o d w h i l e f u e l e d w i t h 233UFb. Corrosion b e h a v i o r of t h e system d u r i n g t h e s e two p e r i o d s was g e n e r a l l y s i m i l a r , b u t some q u a n t i t a t i v e d i f f e r e n c e s seem to b e real. During U,NQ hours of 2 3 5 ~ ~f u4 e l s f r c u ~ a t i o n( i n c l u d i n g a number of shutdowns) the chromium c o n c e n t r a t i o n i n the f u e l s a l t rose from an i n i t i a l v a l u e n e a r 48 ppm t o ;I f i n a l v a l u e of about 85 ppm. 1$ c o n s i d e r able s c a t t e r i n t h e ~ u f n h ewas ~ ~ a p p a r e n t , b u t t h e i ~ c r e a s ewith t i m e and w i t h r e a c t o r o p e r a t i o n was c l e a r l y r e a l . All e v i d e n c e s u g g e s t s t h a t t h e a n a l y t i c a l l y determined chromium was l a r g e l y , i f n o t e n t i r e l y , p r e s e n t as d i s s o l v e d C r 2 + * This observed i n c r e a s e i n c h r ~ m i mc o n c e n t r a t i o n corresponded t o removal of less than 258 grams of t h i s element from t h e MsEgE c i r c u i t . If this w e r e removed uniformly i t would d e p l e t e t h e ckromiurn i n t h e a l l o y t o a depth of less t h a n 8 . 2 mil.* Such an estimate of c o r r s s i o n seems e ~ n s i s t e n tw i t h o b s e r v a t i o n s of metal specimens (see Chapter 7) showing very s l i g h t a t t a c k by t h e f u e l d u r i n g M S E o p e r a t i o n . I n s e r t i o n of t h e m e t a l l i c B e rods in n i c k e l cages ( d e s c r i b e d above) i n t o t h e c i r c u l a t i n g f u e l m i x t u r e should have r e s u l t e d i n reduction s f Fe2+ or ~ i 2 " ana p l a t i n g of t h e s e materials on t h e r e d u c i n g assembly i f they had been p r e s e n t . N e i t h e r of t h e s e w a s e v e r observed d u r i n g t h e o p e r a t t o n w i t h 2 3 ~ ~a l t,h o u g h i n one case a d e p o s i t of p u r e Cr-0 was observed [SI]. During o p e r a t i o n of MSRE w i t h t h e 2 3 3 ~ ~f u4e l , t h e r a t e sf a t t a c k , though still q u i t e a c c e p t a b l e , was more r a p i d . During t h e 6590 hours of o p e r a t i o n w i t h t h i s f u e l , the chromium c o n t e n t of t h e f u e l r o s e f r o m an i n i t i a l v a l u e n e a r 35 ppm t o a f i n a l v a l u e of about 108 ppm. I n i t i a l rates of i n c r e a s e i n er2f c ~ n t e n tw e r e more r a p i d t h a n w a s t h e c a s e f o r t h e 235UP4 u p e r a t i o n , and t h e s a l t c l e a r l y appeared t o b e more aggress i v e . A s d e s c r i b e d i n r e f e r e n c e 23a, t h e changeover from 235Y t o 233Y involved f l u o r i n a t i o n of t h e o r i g i n a l f u e l m i x t u r e t o remove t h e uranium as UF6, attempted r e d u c t i o n o f the FeP N i P 2 , and CrFs rLntroduced duaFwg t h i s o p e r a t i o n , and a d d i t i o n of t h e 23%F4a I n s e r t i o n o f B e r o d s d u r i n g e a r l y s t a g e s of the 233UF4 o p e r a t i o n produced a p p r e c i a b l e d e p o s i t s of c r y s t a l l i n e i r o n and nickel on t h e a s s e m b l i e s , c l e a r l y i n d i c a t i n g t h a t t h e 2 3 3 ~ ~f u4e l w a s less pure than w a s t h e o r i g i n a l 2 3 5 ~ ~p r4e p a r a t i o n . Whether t h i s d i f f e r e n c e w a s due t o i n g r e s s of a i r into t h e r e a c t o r system d u r i n g t h e long shutdown f o r p r e p a r a t i o n of t h e 233YP4 f u e l o r t o incowp l e t e r e d u c t i o n of i m p u r i t i e s i n t r o d u c e d d u r i n g t h e f l u o r i n a t i o n i s n o t known. I n any e v e n t , t o t a l c o r r o s i o n d u r i n g o p e r a t i o n w i t h b o t h f u e l mixtures was e q u i v a l e n t t o uniform removal of chromium from 0.5 m i l of the r e a c t o r m e t a l .

*I f

t h i s 250 grams of C r 2 + were due e n t i r e l y t o admission of oxygen t o t h e system d u r i n g s k u t d o m of t h e r e a c t o r a t o t a l of some 80 grams of About PO s e f of a i r c o u l d have f u r n i s h e d O2 would have been r e q u i r e d . have r i s e n about the fuel t h i s 0 2 ~and t h e 02- c o n c e n t r a t i o n 15 ppm. T h i s mechanism might p o s s i b l y have accounted f o r much of t h e corrosion.

Although o p e r a t i o n of MSRE g e n e r a l l y v e r i f i e d t h e b e h a v i o r p r e d i c t e d f o r t h e fuel s a l t , n o t a l l t h e news w a s good. Fission p r o d u c t b e h a v i o r (to be d e s c r i b e d s u b s e q u e n t l y ) w a s even more complex t h a n a n t i c i p a t e d . Our methods f o r sampling t h e M%RE s a l t w e r e r e s t r i c t i v e , and some of OUK methods f o r analysis needed ked improvement. Behavior of tritium ( s e e Chapter 1 4 ) portended a problem i n l a r g e m o l t e n - s a l t r e a c t o r s . F i n a l l y , i n s p i t e of t h e e x c e l l e n t p i c t u r e on g e n e r a l i z e d C O K I P O S ~ O ~ , the grain bsrandaq a t t a c k r e s u l t i n i n s u p e r f i c i a l c r a c k i n g of t h e Hast e l l o y N exposed t o t h e f u e l w a s a major and d i s a p p o i n t i n g o b s e r v a t i o n ( s e e Chapter 7 ) .

P r e s e n t S t a t u s of F u e l Chemistry Phase Behavior among F l u o r i d e s . - Phase equilibria among t h e p e r t i n e n t BEXiR f l u o r i d e s have been s t u d i e d i n d e t a i l , and t h e e q u i l i b r i u m d i a g r a m , though r e l a t i v e l y complex, are w e l l understood. The b i n a r y system LiF-BeF2 has m e l t i n g p o i n t s belm 560°C over t h e c o n c e n t r a t i o n range from 31 t o 6 8 mole % BeF2 [ 2 4 , 25, 261. The phase diagram, p r e s e n t e d i n Fig. 5.1, i s c h a r a c t e r i z e d by a s i n g l e c o n g r u e n t l y ~ e l t i n gcompound, 2LiPeBeP2, and a s i n g l e eutectic between BeP2 and

2LiFOBaFz. The BeFp-UFb 624,251 and B ~ E ' ~ - % I R I ?[a71 ~ systems are very s i m i l a r i n phase b e h a v i o r . Both systems show s i m p l e s i n g l e e u t e c t i c s c o n t a i n i n g very s m a l l C o n c e n t r a t i o n s of the heavy metal f l u o r i d e . ThP4 and UFk are isostructural; t h e i r b i n a r y phase diagram shows a c o n t i ~ o u sseries of solid s o l u t i o n s w i t h n e i t h e r maximu111 n o r minimum. The binary d i a g r f o r LiF-UFk [B] amd LIF-ThFb [%9] are r e l a t i v e l y Similar. The LiF-UF4 system ShWS three collapoUfldS (aton@ Elre Congruently m e l t i n g ) and a s i n g l e e u t e c t i c , a t 27 mole X Up4, m e l t i n g a t 490°C. The LiF-ThP4 system c o n t a i n s f o u r b i n a r y e o m p ~ u n d ~ one ., of which (3LiFeThF~) melts c o n g r u e n t l y , w i t h mo e u t e c t i c s , a t 570'C and 22 mole 2 ThF4 and a t 560°C and 29 mole X T~I%PL+. The t e r n a r y system LiF-ThF4-UP4 [30], shown i n F i g . 5 . 2 , shows no t e r n a r y compounds and a s i n g l e e u t e c t i c f r e e z i n g a t 488°C w i t h 1.5 mole 2 TkP4 and 26.5 mole % UF4. L i q u i d u s t e m p e r a t u r e s d e c r e a s e g e n e r a l l y t o the LiF-UF4 edge of t h e d i a g r m . Because t h e NSBR f u e l needs a c o n c e n t r a t i o n of ThF4 much h i g h e r t h a n t h a t of UF4, i t s phase b e h a v i o r is d i c t a t e d by t h a t ~f t h e LPF-BeF2-ThF4 system. F i g u r e 5.3 g i v e s the t e r n a r y system LiF-BeF2-ThP4; t h i s system shows a s i n g l e t e r n a r y e u t e c t i c a t 47 mole X LIF and 1.5 m o l e X ThF4, m e l t i n g a t 3 6 0 " ~624, 291. The system i s complicated by t h e f a c t t h a t t h e compound ~ L I F ~ Tcan ~ Pi n~c o r p o r a t e ~ e 2 * ions gn b o t h i n t e r s t i t i a l and s u b s t i t u t i o n a l s i t e s to form s o l i d s o l u t i o n s whose c o m p s s i t i o n a l extremes are r e p r e s e n t e d by t h e shaded t r i a n g u l a r r e g i o n n e a r t h a t compound. Ins p e c t i o n of t h e diagram r e v e a l s t h a t a c o n ~ i d e r a b l erange Sf c o m p s s i t i o n s w i t h more than 10 mole 2 ~ h w~i l l4 b e completely molten a t o r below 500°C. The maximum ThF4 c o n c e n t r a t i o n a v a i l a b l e a t t h i s l i q u i d u s tekperature i s j u s t above 14 mole 2 . A s expected from t h e - g e n e r a l s i m i l a r i t y of ThF4 and - and e s p e c i a l l y from t h e s u b s t i t u t i o n a l behavior shown by t h e

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Phase d i a g r m of the system LiF-BeP2.

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Pig. 5.2.

The s y s t e m LiF-fiF4-UP4.

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LiF-UF4-ThF4 system (Fig. 5.2) - s u b s t i t u t i o n of a s m a l l q u a n t i t y of UFc, f o r ThF4 scarcely changes the phase b e h a v i o r . Accordingly, and to a very good approximation, P i g . 5.3 r e p r e s e n t s t h e b e h a v i o r of LiF-BeP2-ThPt+-UFq mixtures i n which the mole f r a c t i o n of ThP4 is much g r e a t e r t h a n that of

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Effect of Qxide. Phase behavior of the pure f l u o r i d e system LIPBeF~-ThP4=-UP4, as indicated above, i s such that a wide c h o i c e of adequate fuel m i ~ t u ~ - e s a s s u r e d . The behavior of system such as t h i s , however, i s markedly a f f e c t e d by a p p r e c i a b l e c o n c e n t r a t i o n s of o x i d e i o n , which might b e produced by i n a d v e r t e n t contamination of the f u e l system. wken a m e l t c o n t a i n i n g only L S , BeF2, and UF4 i s treated w i t h a reactive oxide (such as B20) 9 p r e c i p i t a t i o n of UB2 ,-Jo results gs, 311 I f t h e m e l t c o n t a i n s , i n a d d i t i o n , c o n s i d e r a b l y more ZrF4 t h a n UP4s i n a d v e r t e n t oxide contamination y i e l d s monoclinic Zr02 c o n t a i n i n g about 250 ppm of UQ;1 9321. P r e c i p i t a t i o n of c u b i c U02 ( c o n t a i n i n g a small c o n c e n t r a t i o n of Z r 0 2 ) begins only a f t e r p r e s i p i t a t i o n of Zr02 h a s dropped t h e ZrP4 c o n c e n t r a t i o n t o n e a r t h a t of t h e UF4. T R ~e f f e c t of added o x i d e on the NSRR f u e l mixture, with its cont a i n e d ThF4, UF4, PaF4, and perhaps PuF3, i n a d d i t i o n t o LiF and BeF2, has been carefully examined in a series of recent studies [ % 3 , 3 4 , 3 % , 3 6 , 3 7 , % 8 , 3 9 , 4 0 ] . The f i n d i n g s of t h e s e s t u d i e s are s ~ ~ ~ ~ n a i ~n i the zed following : The s o l u b i l i t i e s of t h e a c t i n i d e d i o x i d e s i n EBBR f u e l s a l t are low, and they decrease in t h e o r d e r ThQ2, PaQ2, WO2, P u O ~ . The solubility products 0

Q-02 =

A&+

xi2-

are p r e s e n t l y e s t i m a t e d as f o l l o w s :

,... Y.

(kO.8)

S i n c e all these o x i d e s have the same f l u o r i t e s t r u c t u r e and n e a r l y the same l a t t i c e ~ ~ x - E I I ~ I ~ ~ ~ they K s , can f o m s o l i d s o l u t i o n s with owe a n o t h e r .

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i n v o l v i n g an oxide s o l i d s o l u t i o n phase are e s t a b l i s h e d . ing equilibrium quotients

The sorrespond-

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I n a d d i t i o n , Pa205 ( o r an a d d i t i o n compound of i t ) i s v e q i n s o l u b l e i n

MSBR fuel:

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..... ..... :.:.:<,

.. ..... .... .X.YJ

Because of t h e l o w s o l u b i l i t y of Tho2 and U 0 2 , it b i n a r y s o l i d s o l u t i o n r i c h i n U02 ( t y p i c a l l y 95%) could be p r e c i p i t a t e d from an MSBR f u e l i f s u f f i c i e n t l y h i g h o x i d e c o n c e n t r a t i o n s are reached. The o x i d e l e v e l req u i r e d ( t h e o x i d e t o l e r a n c e ) i s i n d i c a t e d i n Fig. 5 . 4 . The amount of P a 8 2 i n t h e s o l i d s o l u t i o n s h o u l d b e n e g l i g i b l e ; i . e . , t h e Pa/U r a t i o i n t h e oxide s h o u l d b e %1/7 t h e Pa/U r a t i o i n t h e f u e l . The oxide c o n c e n t r a t i o n a t which P a 2 8 5 can b e p r e c i p i t a t e d depends on b o t h the p r o t a c t i n i u m c o n c e n t r a t i o n and t h e o x i d a t i o n s t a t e of the f u e l - as r e f l e c t e d by t h e U4+/U3* r a t i o . The s i t u a t i o n i s i n d i c a t e d by the equilibrium

0 WRL -BWG 72- 8 326

700

5 -.,

500

r"'

200

58

y..... ,.&.

20

I

*..,

10

4 .o

4.4

Fig. 5 . 4 .

4.2

Oxide tolerance sf MSBR f u e l .

.... ,.=,

107 *.:.i

...

f o r which w e estimate t h e e q u i l i b r i u m q u o t i e n t .... .....

"C.?

...>io

i....

.

.."+ ...A

.... <.:.:.:e

.... ....... '.'A

..... :<a,

The r e s u l t i s t h a t w i t h 100 ppm P a and 38 ppm oxide p r e s e n t , t h e U4*/U3' r a t i o must b e k e p t below about IO5 i f i n a d v e r t e n t p r e c i p i t a t i o n of Pa265 i s t o b e avoided. Such o x i d i z i n g c o ~ d i t i o n ss h o u l d b e e a s y t o a v o i d i n r a t i o of t h e o x i d e p r a c t i c e . There i s a l s o a dependence on t h e U4*/U3+ c o n c e n t r a t i o n a t which Pu02 p r e c i p i t a t i o n o c c u r s . However, even s t r o n g e r o x i d i z i n g c o n d i t i o n s ( ~ 4 + / ~ 3 + lo8) are r e q u i r e d t o p r e c i p i t a t e P U O ~ from an MSBR f u e l . S e l e c t i v e p r e c i p i t a t i o n of P a as Pa205, of U as U02 and p o s s i b l y of Pu as Pu02 may be of v a l u e (see Chapter 1 1 ) i n f u e l r e p r o c e s s i n g c y c l e s . E t i s c l e a r t h a t t h e MSBR f u e l must b e p r o t e c t e d from o x i d e contamin a t i o n t o avoid i n a d v e r t e n t p r e c i p i t a t i o n . Because of t h e l o w o x i d e t o l e r a n c e ( P i g . 5 . 4 ) , t h i s w i l l r e q u i r e some care, b u t t h e s u c c e s s f u l o p e r a t i o n of t h e MSRE over a three-year p e r i o d l e n d s c o n f i d e n c e t h a t oxide c O n t m i n a t i Q n of the. f u e l system can b e k e p t t o a d e q u a t e l y low l e v e l s . This c o n f i d e n c e , when added t o t h e p r o s p e c t t h a t t h e b r e e d e r f u e l w i l l be r e p r o c e s s e d (and i t s o x i d e l e v e l reduced) on a continuous b a s i s , s u g g e s t s very s t r o n g l y t h a t s u c c e s s f u l o p e r a t i o n can b e a c h i e v e d .

. .

..iii, .....A

Physical Properties.

-

Some p e r t i n e n t p h y s i c a l p r o p e r t i e s of t h e Liquidus temperatures a r e h o w n w i t h accuracy. Vapor p r e s s u r e s of t h e f u e l s have been e x t r a p o l a t e d from measurements on s i m i l a r m i x t u r e s ; v a l u e s are c o n s i d e r a b l y less t h a n 0 . 1 torr a t 680째C. D e n s i t i e s w e r e c a l c u l a t e d from t h e molar volumes of t h e p u r e components by assuming t h e V Q I U tIoI ~ be~a d d i t i v e . B e a t c a p a c i t i e s w e r e e s t i mated by assuming t h a t each gram atom i n the m i x t u r e c o n t r i b u t e s 8 cal/"C ( t h e approximate a v e r a g e from a set of s i m i l a r f l u o r i d e m e l t s ) . The v i s c o s i t y of t h e MSBR f u e l w a s e s t i m a t e d from measurements on o t h e r LiP-BeF2 and NaF-BeF2 m i x t u r e s . Methods f o r such e s t i m a t i o n a r e , i n most cases, q u i t e r e l i a b l e ; d e n s i t i e s and h e a t c a p a c i t i e s are probably good t o +3%, but v i s c o s i t y and thermal c o n d u c t i v i t y are probably no b e t t e r t h a n 215%. S u r f a c e t e n s i o n s of t h e molten f u e l s are known to b e h i g h , b u t t h i s moderately i m p o r t a n t p r o p e r t y i s n o t w e l l e s t a b l i s h e d . Measurements w i t h s e v e r a l s y s t e m ( b u t n o t w i t h WSp o r MSRE f u e l s ) by t h r e e d i f f e r e n t methods s u g g e s t [413 t h a t t h e e q u a t i o n NSRE and MSBW f u e l s a l t s are l i s t e d i n Table 5.1 [ 8 , 4 l ] .

::-

,.;.;.;.; ...,_

..... <yp

.... .... .<<,.

.i.. ~

..., ......>

y =

<.&

..

.... i.. i

260

-

0.12 P"C

approximates t h e s u r f a c e t e n s i o n of b o t h f u e l s o v e r t h e range 550 t o These v a l u e s a r e , however, u n l i k e l y t o b e b e t t e r t h a n about 530%. 700째C. This p r o p e r t y , which i s of importance i n a s s e s s i n g w e t t i n g b e h a v i o r and i n e s t a b l i s h i n g ( f o r n s n w e t t i n g eases) a d e g r e e o f p e n e t r a t i o n of t h e

salt i n t o ~ ~ K Q Ub oS d i e s and the s i z e of o r i f f c e o r annulus i n t o which t h e salt w i l l flow under p r e s c r i b e d p r e s s u r e s , c l e a r l y needs t o b e b e t t e r known.

Table 5.1. Cornpsition and properties of MSRE and W B R fuels

Composition, mole % '

LKpidul. "C

"F

6QO"C (1112째F) Densty, 'g/;'cm3 Heat capacity, c&(g-'''C~ or Beu/(Ib-" F) Viscosity centi poises

MSWE fuel

MSBW fuel

LLF 65 BeF* 29.1 ZrF4 5 UE4 0.9

EIF 71.4 BeFa 16 ThF4 12 GF4 0.3

434 81 3

500 932

2.24

3.35

0.44 9 4 . 1

0.324 12

<o 1

0.014

0.012

ROFItESdt

Vapor plZSSUIe, toFES Thermal conductivity, watts/ (" C-cm)

.... %..%

..... ,:.:.a

109 ....

<..<.A .A.

-

.... C*#

...

?.<<a

.... ........ :.z

..... L+:*

..... ....... . . A d

......,

i. L.. .. ....

Chemical C o m p a t i b i l i t y of MSBR blaterials. %he e x c e l l e n t compatib i l i t y o f Hastelloy N w i t h f l u o r i d e s a l t s c o n r a i n i n g L i p , BeP2, ThP4, and UF4$ shown i n c o r r o s i o n t e s t s [42, 4 3 , 4 4 , 453 and i n t h e M S M , i s a r e s u l t sf t h e f a c t t h a t t h e s e f l u o r i d e s are themodynam%cal%ys t a b l e toward t h e Hastelloy N.* That i s , t h e m j o r f u e l components ( L I P , BeF2, UF4, and T~IPL+)a r e much more s t a b l e t h a n t h e s t r u c t u r a l m e t a l f l u o r i d e s (NiE'Z9 FeF2, and CrPz), and g r a p h i t e does not react chemically w i t h such f l u o r i d e m i x t u r e s . T h i s b a s i s s i t u a t i o n , combined w i t h p r o p e r p u r i f i c a t i o n p r o c e d u r e s , p r o v i d e s l i q u i d s whose o v e r a l l c o r r o s i v i t y i s w i t h i n tolerable l i m i t s . Experimentation o v e r many y e a r s has d e f i n e d t h e thermodynamic prope r t i e s of many species i n molten LiF-BeP2 s o l u t i o n s [ 4 6 ] . Table 5.2 l i s t s p e r t i n e n t d a t a â‚Ź o r t h e major components of MSRE and MSBR f u e l s and f o p c o r r o s i o n p r o d u c t s i n molten 2LiPeBeP2. The chemistry of t h e UF4-UP3 conversion 1471 i s s i g n i f i c a n t s i n c e i t a f f o r d s redox b u f f e r i n g t o t h e f u e l mixture. o p e r a t i o n w i t h a s m a l l f r a c o f t h e uranium as UP3 i s advantageous i n s o f a r as cort i o n (perhaps 1%) r o s i o n r e a c t i o n s and t h e o x i d i z i n g e f f e c t of t h e f i s s i o n p r o c e s s are concerned. I f w e a c c e p t the d a t a of Table 5.2 as a p p l i c a b l e (as is approximately t r u e ) t o t h e MSBR f u e l and c o n s i d e r t h e r e a c t i o n

...

iiii,

.... .... . . . .,.a

when upq and U F ~are d i s s o l v e d i n t h e MSBR f u e l , w e observe t h a t at WO'K (1166'F) t h e e q u i l i b r i u m c o n s t a n t (K> f o r t h i s r e a c t i o n has the v a l u e

.... ..<.:*

..... '<<.

...I.:

...... :.:::::,

N i n d i c a t e s t h e mole f r a c t i o n of the d e s i g n a t e d s p e c i e s , and a i n d i c a t e s t h e thermodynamic a c t i v i t y . POP the NSBR f u e l , where NUF = 3 x 1 0 - ~ , 9 where NUF i s h e l d a t 3 X PO-5, t h e n the e q u i l i b r i u m uranium a c t i v i t y i s

hY1'.

.:;:.:.:,

Even i f 5% of t h e d i s s o l v e d uranium i s UF3, t h e e q u i l i b near 2 X such o p e r a t i o n w i t h a small rium a c t i v i t y of uranium i s below 10-1% f r a c t i o n of t h e uranium as UF3 should r e s u l t i n an extremely d i l u t e (and p h y s i c a l l y u n d e t e c t a b l e ) a l l o y ~f uranium w i t h t h e s u r f a c e of t h e cont a i n e r a l l o y . All e v i d e n c e to d a t e s u g g e s t s t h a t o p e r a t i o n w i t h relat i v e l y l i t t l e UP3 i s completely s a t i s f a c t o r y . For t h e MSBR, where t h e f u e l r e t u r n e d t o t h e r e a c t o r from t h e p r o c e s s i n g p l a n t can have a cont r o l l e d c o n c e n t r s t i o n of UF3$ t h i s e q u i l i b r i u m can b e of real s e r v i c e .

.:.:.:*

....

*EIastellsy

...... ......, ,.>....,

.. ... ... :.&

. ..

W$>

N used i n MSRE w a s N i w i t h 17% Mo8 7% Cr, 5% Fe. P r o b a b l e composition of modified H a s t e l l o y M f o r f u t u r e r e a c t o r s i s %ai w i t h about 12%Mo, 9% C r , 4% Fe, and 1% Ti.

,......... , . % >

Table 5.2. Standard free energies s f f ~ m t b ~ ~ for species in molten 2LiF.BeP.p

773- 1000"K MaterialQ

,>)11 _..

=The standard state for t i F and BeFa is the molten 2LiFeBeFz liquid. That fer MloFs(& is the gas at one atmosphere. That for all species labeled (d) is that hypothetical solution with the solute at unit mole fraction and with ehe activity coefficient it would have at h f i i t e dilution.

ii.

BPI It i s a l s o c l e a r from Table 5.2 t h a t , of t h e s t r u c t u r a l metal f l u o r i d e s shown, CrP2 i s t h e most stable. Accordingly, C r should b e seBect i v e l y a t t a c k e d i n a l l o y s such as H t s t e l l o y N by any extraneous o x i d a n t s i n t h e system. I m p u r i t i e s i n t h e p e l t should react

as sho :Ed o x i d i z e d f i l m s on t h e metal

followed by r e a c t i o n of t h e NIP2 w i t h C r . Reactions such as these w i l l proceed e s s e n t i a l l y t o completion at r e a c t o r t e m p e r a t u r e s ; they can l e a d to r a p i d i n i t i a l c o r r o s i o n b u t n o t t o a s u s t a i n e d a t t a c k . I f t h e fuel i s p u r e and t h e metal c l e a n , UP4 i s t h e s t r o n g e s t o x i d a n t i n t h e MSBR f u e l system. The r e a c t i o n

has, f r o m t h e d a t a of Table 5 . 2 , at 900째K an e q u i l f b r i u m c o n s t a n t

~f the MSBR fuel w i t h nUFLI = 3 x 10-3 and w i t h no cr2+ or U F ~p r e s e n t i n i t i a l l y w e r e p e r m i t t e d t o e q u i l i b r a t e a t 900째K w i t h a H a s t e l l e y N surf a c e w i t h aCr = 6.05, the e q u i l i b r i u m s o l u t i o n would c o n t a i n s l i g h t l y more ~n p r i n c i p l e , t h e r e f o r e , t h a n 10 ppm of ~ r + ~1vUF3 = about 2.5 x IO-', a m i x t u r e i n which t h e UP3 m o l e f r a c t i o n could be maintained a t a b o u t 3 X I O m 5 s h o u l d c o r r o d e the m e t a l very l i t t l e . Indeed, i t seem l i k e l y t h a t c o r r o s i o n could b e kept Go q u i t e t o l e r a b l e l i m i t s i n t h i s way even if a l l o y s (such as ~ n s o n e ~w)i t h c o n s i d e r a b l y ~.ai&erchromium concentrat i o n s (and c o r r e s p o n d i n g l y h i g h e r v a l u e s f o r a ) were used. Cr

112 The c o r r o ~ i o nby UFq c a n n o t , i n p r i n c i p l e , b e completely e l i m i n a t e d , s i n c e t h e UP4-Cr r e a c t i o n h a s a s m a l l temperature c o e f f i c i e n t . Conseq u e n t l y , c i r c u l a t i o n of the s a l t through a temperature g r a d i e n t t e n d s t o remove Cr from the h o t t e s t s u r f a c e and t o e n r i c h t h e c o l d e s t a l l o y i n this element. The rate of such a r e a c t i o n is c o n t r o l l e d by t h e r a t e a t which Cr can d i f f u s e from the b u l k alloy t o t h e s u r f a c e o r (more l i k e l y ) the rate at which t h e C r can d i f f u s e from the s u r f a c e i n t o t h e a l l o y i n t h e coldeb- r e g i o n . Experience i n d i c a t e s t h a t no real d i f f i c d t y i s t o b e expected from this reaction. Modified H a s t e l l s y N will c o n t a i n t i t a n i u m , w h i l e t h a t i n MSRE d i d not. E s t i m a t e s I l l ] of t h e i r f r e e e n e r g i e s of formation s u g g e s t t h a t t h e f l u o r i d e s of t i t a n i u m a r e s l i g h t l y mare s t a b l e than CrP2. Titanium s h o u l d , t h e r e f o r e , b e expected t o react a p p r e c i a b l y w i t h t h e UP4. S i n c e T i d i f f u s e s less r e a d i l y than does C K , however, i t would n o t appear t h a t suck ccsrroaion would b e p a r t i c u l a r l y d e l e t e r i o u s . G r a p h i t e does n o t react w i t h , and i s n o t wetted b y , molten f l u o r i d e mixtures of the t y p e t o b e used i n t h e E B R . A v a i l a b l e thermodynamic d a t a Ill] s u g g e s t t h a t t h e most l i k e l y r e a c t i o n :

s h o u l d Come to @ g E u i l i b r i at ~ CFL, pressures below atm. This Conside r a t i o n , taken with t h e w e a l t h of f a v o r a b l e e x p e r i e n c e , s u g g e s t s t h a t no prUbleUX5 are l i k e l y f K o H l t h i s SOLXrCe. It should be noted t h a t a t least one source e481 l i s t s c h r o m i m c a r b i d e (Cf~362) as s t & l @at MSBR t e m p e r a t u r e s . I f 8 0 , i t should be p o s s i b l e t o t r a n s f e r C'hPO1I1iUltl, a t t h e Kate it Could d i f f u s e from t h e bulk alloy t o react w i t h the salt, t o t h e g r a p h i t e . NO evidence of such b e h a v i o r h a s been observed w i t h H a s t e l l o p M i n MSRE o r other e x p e r i mental a s s e m b l i e s . Although i t may b e possible w i t h a l l o y s of h i g h e r chromim c o n t e n t , i t should not prove g r e a t l y d e l e t e r i o u s , sirfce its rate would be controlled by the rates at. which chromium could d i f f u s e t o t h e a l l o y s u r f a c e and should b e l i m i t e d by a film of Cr3C2 farmed OR the graphite It: must b e emphasized t h a t n ~ n eof the above throws any light upon t h e s p e c i a l g r a i n boundary attack upoat Hastelloy N i n t h e MSIU f u e l c i r c u i t . It i s c o n c e i v a b l e that some h e r e t o f o r e u n t e s t e d combination of o x i d i z i n g regime, r a d i a t i o n , and f u e l i n t e r a c t i o n was r e s p o n s i b l e , b u t i t seems much more p r o b a b l e t h a t some fission product ( l i k e l y tellurirare) w a s r e s p o n s i b l e . This matter i s d i s c u s s e d i n d e t a i l i n Chapter 7.

b..

..... .

e

I n t e r a c t i o n of E B W F u e l w i t h Extraneous Materials. - n e complex mixture comprising t h e N B R f u e l reacts r e a d i l y , though not v i o l e n t l y 87~ even e n e r g e t i c a l l y , w i t h w a t e r vapor to produce o x i d e s of t h e a c t i n i d e elements and HF vapor. ( I n f a c t , water vapor i s a p o s s i b l e r e a g e n t i n a s e l e c t i v e p r e c i p i t a t i o n scheme for f u e l p r o c e s s i n g d e s c r i b e d i n Chap. 11.1 Rapid a d d i t i o n would c e r t a i n l y p r o d ~ c ea m i x t u r e of oxide p r o d u c t s whose e q u i l i b r a t i o n would b e r e l a t i v e l y slaw. This admixture of water and f u e l ' s a l t would lead to a p p r e c i a b l e corrosion due t o t h e HF s o produced, b u t would h a r d l y prove c a t a s t r o p h i c .

. ..

e . : ;

....., .:.=

113 None sf t h e MSBR fuel c o n s t i t u e n t s can release P2 upon r e a c t i o n w i t h oxygen ( o r n i t r o g e n ) . Reactions suck as ;.:.:.:.I

....

have been p o s t u l a t e d [ 4 9 ] , b u t such r e a c t i o n s seem most u n l i k e l y i n d i l u t e s ~ P u t i o nin MSBR fuel. N o r e a c t i o n of Lip, BeP2, o r T u b With 02 is OSs i b l e a An i n l e a k a g e of a i r i n t o the MSBR f u e l c i r c u i t c a n n o t , t h e r e f o r e , cause e n e r g e t i c or v i o l e n t r e a c t i o n s . However, s i n c e t h e WBR metal s u r f a c e s w i l l be oxide-free (because of the f l u x i n g a c t i o n of t h e fluorides), rapid r e a c t i o n of the a i r w i t h the metal c i r c u i t w i l l occur. Such react i o n s as

f o r example, w i l l i m e d i a t e l y r e s u l t i n

and r a p i d c o r r o s i o n . It will, aecordinghy, b e n e c e s s a r y t o minimize i n g r e s s of a i r b o t h d u r i n g o p e r a t i o n and d u r i n g maintenance. T h i s i s of e s p e c i a l importance because, as i n d i c a t e d e a r l i e r , t h e o x i d e t o l e r a n c e of the KSBR f u e l i s low (not much above 30 ppm of 02-1 The consequences of mixing MSBR f u e l w i t h t h e secondary c o o l a n t , as would occur as a r e s u l t of a l e a k i n t h e primary h e a t exchanger, are d i s cussed under Coolant Chemistry i n a subsequent s e c t i o n of t h i s c h a p t e r . e

...

....... .>. <

.. . ..... .... <.:E.*

.... ........ -., %

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....

..I ..!..X .!

.;,

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:.... ::;:*>

.... ..... ,:=I

...

-

P u r i t y Requirements. The i n i t i a l p u r i f i c a t i o n procedures â‚Ź O K t h e s a l t s h a r g e for a molten-salt r e a c t o r do n o t p r e s e n t formidable problems. Nuclear poisons suck as boron, cadmium, rape e a r t h s , e t c . , are n o t c o w o n contaminants of t h e c o n s t i t u e n t materials. Enriched rpranim t e t r a f l u o r i d e commonly c o n t a i n s s m a l l q u a n t i t i e s of U Q 2 , UP59 and U02F2. ThFk and BeP2 c o n t a i n a p p r e c i a b l e q u a n t i t i e s of oxides and o x y f l u o r i d e s up t o O.E% CI-, and Fe3+ t o t h e e x f e n t of perhaps PO0 ppm. A l l t h e s e compounds c o n t a i n some water, and a l l are r e a d i l y hydrolyzed t o oxides and oxyfluor i d e s a t e l e v a t e d temperatures. Lip and BeF2 g e n e r a l l y c o n t a i n a small q u a n t i t y of s u l f u r ( p r i m a r i l y as s u l f a t e ) P u r i f i c a t i o n p r o c e s s e ~ El%, 6 , SO] which were used t o p r e p a r e mat e r i a l f o r t h e ARE, t h e =RE, and f o r many l a b o r a t o r y and e n g i n e e r i n g tests have t r e a t e d t h e mixed materials a t h i g h temperature i n equipment of N i ( u s u a l l y $80'6) w i t h gaseous ]H??-H2 m i x t u r e s and t h e n w i t h p u r e Hz. Tke HF-H2 t r e a t m e n t s e r v e s t o reduce t h e U5+ and U6+ t o U4+, t o reduce s u l f a t e t o s u l f i d e and remove i t as HZS, t o remove Cl' as H C I , and t o c o n v e r t t h e oxides and o x y f l u o r i d e s t o f l u o r i d e s . F i n a l t r e a t m e n t with H2 s e r v e s t o reduce FeF3 and FeF2 t o i n s o l u b l e Fe and t o remove NiP2 which may have been produced d u r i n g h y d r o f l u o r i n a t i o n . A l l preparatfons t o d a t e have been performed i n b a t c h equipment, b u t continuous equipment i s under development 651,521. For E R E [SO] t h e f u e l s o l v e n t was p r e p a r e d a

in large (ca. 300 lb) batches, while the enriched uranium f l u o r i d e w a s purified separately (as the LiF-UPk eutectic) It seems likely that a generally similar proqedure would be desirable got- BfSBR.. The most difficult specification f o r MSBR will probably be that f o r vergr o x i d e concentration. ~ x p e r i e n e ewith the process f o r h i g h T ~ F ~ concentrations is limited. However, all the preparations to date and conm n y kattoraeory-scale researches have successf u l l y droppea the centration be lo^ that r e q u i r e d to p r e c i p i t a t e WQ2-Th82, SktouPd t h i s prove very difficult on a large scale, it would be possible ts process t h e EiF-BeF2-ThF4 melt with fl~orine;it seems p o s s i b l e t h a t the r e p ~ ~ e essing fluorination (see Chap. 11) might be used If necessary as the final polishing step in this treatment. e

-

Radiation Stability. An early concern was the p o s s i b i l i t y that radiation ( i n c l u d i n recoiling fission f r a e n t s ) from t h e f i s s i o n process might l e a d to adiolytic instability the fluoride. a@combination in mobten salt sf '*dissociated"species Ci.e. a fluorine atom and an d e e t r ~ n )s h o u l d be very rapid. Nevertheless, it seemed (and S t i l l SeeElS> l i k e l y t h a t thehe exists a p O W e K level sufficient t o damage a molten f l ~ ~ ~ i byd dissociation e into metal and fluorine. $

k . . . .

irradiation tests W@XT C O n d U C t & ? d p r i o r to 1959 W i t h NaFZrF4-'LIF4 ~ i ~ t ~ r in r e%nconeab s a t temperatures at or above I5BQ"F [ 6 , 7 ] and quite h i g h f i s s i o n power densities, f r o m 80 to lOQO watts/cm3 of fuel. Eo instability o f the f u e l system was apparent, and the corrosiorn did exceed the C O n s i d e P E L b a b e 2SiWuHat expected froIl3 baboratOry-SCde

tests The ARE t e s t s had not included graphite, and several irradiation t e s t s w e r e performed in the e a r l y days sf the NfsbFR program [ 5 3 , 5 4 , 5 5 , 561 primarily to test wetting of graphite under irradiation, These tests used mixtures of LiF, BePzP and ZrF4 w i t h ll mole 2 ThP4 and 1.5 mole X UF4 in sealed Bastelboy N capsrx es, irradiated at power levels above 200 watts/cm3 f u e l to burnups as hi as 8% of the 2 3 5 U . Examination of these capsules a f t e r storage at ient temperatures f o r many weeks revealed a p p r e c i a b l e quantities of 6%"4 and, in most cases, considerable quantities of fluorine in the cover gas [57,58]. Careful examination strongly s u g g e s t e d that the P2 generation had not ~ c c ~ r r eatd the h i g h temperature, b u t by r a d i o l y s i s of t h e ~ ~ ~ x t in u r the e solid state. This suggestion w a s confirmed by irradiation in EflR of two arrays of Mastelloy bJ capsules, all containing graphite and EiF-BeF2-ZrP4-UF4 mixtures. Two 0% t h e capsules in each array had gas i m l e t and exft lines to PeTXlit SaDIpling Sf t h e COVB% as as desired. as samples dram from t h e test capsules at operating temperatures and at various p ~ ~ e levels r up to 80 wattslcm3 showed no ~2 (t~aoughan occasional sample from t h e first array showed detectable traces s f CF4). During reactor shutdowns, however, with the capsules at about 35'C, pressure rises were observed (usually after an industion p e r i o d s f a few h o u r s ) , and F2 was evolved. In the second array the capsules were kept h o t during r e a c t o r shutdown as well as d u r i n g operation; no evidence of F2 o r GF4 was observed. Such F2 generation at ambient temperatures was subsequently f o l l o ~ e df o r several L h o t cells. The generation diminished w i t h time in a, mangler 0

.... p ->

115

,:.y&.

corresponding closely with decay of fission product activity; Fz evolutiom at 35째C corresponded to about 0.02 molecule per 100 ev absorbed, could be completely stopped by heating to 100째C or above, and c o u l d be markedly reduced by chilling to -70째C. The F2 evolution resumed, usually after a few h o u r s , when teMperatUre w a s returned to 3 5 - 5 0 ' ~ . These and subsequent experiences, including operation of WW, strongly indicate that radiolysis of the molten fuel at reasonable power densities is not a problem. Radiolytic fluorine must be dealt with, k ~ w ever, if irradiated fuel mixture is chilled below about 100째C.

X<>>

Evaluation and Summary of Needed Work

I

..... ...

..... i......

.:.a

.:..... ...i >

..... ...

.;'it

2

. .. ..., :.=

.......>

.... .... ..,..P.,

En general, most of the chemical behavior of the MSBR fuel rests on a s o l i d background of data and information. Some areas described in this chapter require additional effort, but it appears unlikely that these areas of uncertainty threaten feasibility of the MSBR concept. The phase behavior of I S B R materials has been studied im detail, and little remains to be done if EiP-BeP2-ThF4-UF4 fiixtures are used. Should the fuel composition be changed appreciably from the 71.9-lS-l2-0.3 mole X now adopted, it would be necessary t o do some confirmatory testing in the imediate vicinity of the new design compositions. Should PuF3 b e adopted as t h e fissionable component, a program of phase equilibrium study would be required.* Oxide limitations of the fuel are clearly important. The oxidefluoride behavior seems t o be reasonably straightforward and well understood. Et is, however, very difficult experimentally, and some of the data have been obtained in systems containing only one or two of the actinide elements. It seems certain that additional, and eonfirmtory, experiments with the total system should be conducted. As indicated above, several of the physical and heat transfer properties have been estimated from measurements on molten salts of other compositions. Although t h e estimates are adequate for the present, an ongoing reactor program should provide for measurement of these properties Thermodynamic data have been defined with accuracy f o r many solute species in molten 2LiFeBeF2, and considerable experimental study suggests that the data in LiF-BeF2-ThPq mixtures will be similar. They will n o t , however, be identical, and methods for estimating them from the existing system are uncertain. It seems necessary, therefore, t o do experimental determinations of the free energies of formation of important and typical materials in the more complex MSBR fuel mixture. Compatibility of the MSBR fuel (in absence of fission pr~ducts)with Hastelfoy N and with graphite seems well assured. However, the thermodynamic data do not quantitatively predict t h e magnitude of attack in m' ny D

.... .... +x.?

......

.'A;<.

.... .... .:.m

.... ,..*.

*Phase behavior

of PuF3-bearing systems i s under study at Bhabka Atomic Research Center, Trombay, India. ..... ...... ,:<,

..... .:.:<I

.....

;.:.... .>.,

,

cases. A p l a u s i b l e mechanism has existed f o r years to explain the minor c o r r o s i o n observed, but i t i s s t i l l p o s s i b l e t h a t e x t r a n e o u s o x i d a n t s are p a r t l y r e s p o n s i b l e for t h e o b s e r v a t i o n s . S m e e s p e c i a l l y c a r e f u l tests of these p o i n t s would b e welcome -and newer on-line analytical methods seem t o make t h e s e tests p o s s i b l e . Such t e s t i n g will become e s p e c i a l l y v a l u a b l e i f albloys Other than khtelloy N must b e Considered f o r MSBR, While t h e e q u i l i b r i u m b e k a v i ~ rof MSER f u e l with contaminants such as s t e m , a i r , EF9 and i s w e l l under~tood, l i t t l e i s ~ H Q about I ~ the rates of some s f t h e s e r e a c t i o n s . S t u d i e s of t h e r e a l l y p e r t i n e n t ones should be i n i t i a t e d It i s s t i l l n e c e s s a r y t o demonstrate that l a r g e - s c a l e i n i t i a l p u r i f i c a t i o n of the MSBW fare1 s o l v e n t can drop the 02- c o n c e n t r a t i o n t o the d e s i r e d value, well below 30 ppmn. mile other f a c e t s sf the p u r i f i c a t i o n scheme a l s o l a c k demonstration, no o t h e r s p e c i f i c a t i o n would appear t o b e troublesome R a d i a t i o n s t a b i l i t y of the PSBR f u e l a t elevated temperatures would w s t a p p e a r ' t o pose p r o b l e m . The 72-16-12 mole % composition of L i F , B ~ F and ~ , TP~F has ~ s c l l i d compounds q u i t e different from t h e mixes t e s t e d , and t h e r e i s reason to s u s p e c t t h a t P2 g e n e r a t i o n may b e less of a problem (perhaps n e g l i ib1e) at ambient temperature. T h i s p o i n t , t o which a f a v o r a b l e answer might s i m p l i f y some s t o r a g e and h a n d l i n g problems, shoukd be checked. It s h o u l d b e emphasized t h a t n o t all MSB chemistry i s w e l l . unders t o o d . S p e c i a l problem areas t h a t are chemical i n n a t u r e , though covered elsewhere i n t h i s d o c m e a t , Are concerned w i t h (1) r e t e n t i o n and c o n t r o l o f tritium, (2) w i t h t h e s p e c i a l g r a i n boundary c o r r o s i o n and c r a c k i n g i n Mastelaboy N, and ( 3 ) w i t h b e h a v i o r of f i s s i o n p r o d u c t s . C o n s i d e r a b l e chemical d@QElkOpment W i l l grObEibly b e ZeqUi%ed to d e f i n e andl to Solve t h e s e problems. e

a

.. ..s <

.... t.> >

.

I.. d?,Y

F i s s i o n Product Behavior

General C i r c u l a t i n g l i q u i d f u e l s i m p l i f i e s f u e l r e c y c l e by making p o s s i b l e as r e q u i r e d t o increase b r e e d i n g g a i n . However, t h i s c h a r a c t e r i s t i c also means t h a t f i s s i o n p r o d u c t s are s p r e a d through a131 p a r t s of the fuel c i r c u l a t i n g system and p e r i p h e r a l system suck as o f f g a s , drain tanks, e t c . 'khis s u b s t a n t i a l l y a f f e c t s t h e r e a c t o r operation and performance as re a r d s b r e e d i n g , materials b e h a v i o r , a f t e r h e a t , and of t h e fates of the fission maintenance. Thus a horougk prQdUCtS in MSBR's is illlportalat $8 t h e i r d e v d o p w e n t . As o p e r a t i o n of t h e M S E and c o n c u r r e n t i n v e s t i g a t i o n s emphasized t h e inpsrtance of t h e f i s s i o n p r o d u c t s , i n v e s t i g a t i o n s of t h e i r f a t e s i n were pursued i n a v a r i e t y of ways. Arrays of g r a p h i t e and m e t a l specimens were examined after exposure i n t h e core f o r p e r i o d s of s e v e r a l thousand h o u r s . Samples of f u e l s a l t were dipped from t h e a g i t a t e d p o o l i n t h e pump bowl o r were pulled from b e n e a t h t h e s u r f a c e of t h e same p o o l into evacuated c a p s u l e s w i t h f u s i b l e seals. The gas above the s a l t i n

in

B ~ $ Mprocessing,

.... c.*..

117

.... .... &.<*

,&&

.... <pxt

..... ..... ..., .L..A

......

2L.w ii...

.... .....

-.A!*

t h e pump bowl w a s a l s o sampled w i t h evacuated c a p s u l e s . Metal and graphi t e were exposed t o t h e gas o r s a l t i n t h e p m p bowl f o r p e r i o d s of up t o a f e w hours t o measure d e p o s i t i o n of f i s s i o n p r o d u c t s . The cover gas flowing o u t of t h e f u e l - p u p bowl w a s sampled (some d i s t a n c e ~ O W I I S ~ K ~ ~ ~ ) and f i s s i o n - p r o d u c t c o n c e n t r a t i o n s and i s o t o p i c r a t i o s measured. E f f e c t s of n e u t r ~ na b s o r p t i o n by t h e f i s s i o n p r o d u c t s (notably xenon-135 b u t a l s o o t h e r s ) could b e d i s c e r n e d i n p r e c i s e measurements of r e a c t i v i t y . A remote gamma-ray s p e c t r o m e t e r aimed a t t h e v a r i o u s co~tponentsdetermined t h e f i s s i o n p r o d u c t s t h e r e b o t h d u r i n g o p e r a t i o n and w i t h t h e f u e l d r a i n e d . F i n a l l y , some d a t a w e r e o b t a i n e d from samples from t h e m i s t s h i e l d and sampler cage from t h e f u e l pump bowl, from s h e l l and t u b e specimens from t h e h e a t exchanger, from a g r a p h i t e c o r e s t r i n g e r , and from a c o n t r o l r o d t h i m b l e , o b t a i n e d d u r i n g t h e p o s t - o p e r a t i o n examination one y e a r a f t e r shutdown e

Plajor Groups and Y i e l d s The f i s s i o n p r o d u c t s f a l l i n t o s e v e r a l groups a c c o r d i n g t o t h e i r chemical b e h a v i o r i n molten f l u o r i d e s . These g r o u p s , i n o r d e r of t h e i r importance as n e u t r o n p o i s o n s , are: noble g a s e s , r a s e - e a r t h s t a b l e s a l t - s e e k i n g f l u o r i d e s , n o b l e metals," and o t h e r s t a b l e s a l t - s e e k i n g f l u o r i d e s . Table 5.3 shows some of t h e s i g n i f i c a n t fission product poisons whish w i l l reduce b r e e d i n g g a i n i f they b u i l d up i n an MSBR. The i n v e s t i g a t i o n s u s u a l l y involved o t h e r i s o t o p e s of t h e same o r chemically s i m i l a r elements which had a p p r o p r i a t e y i e l d s and h a l f - l i v e s . Free e n e r g i e s of formation ( A G O k c a l ) f o r v a r i o u s f l u o r i d e s of inf' terest a r e given i n Table 5 . 4 . S i n c e t h e UF4/UP3 r a t i o i s g e n e r a l l y h e l d a t % l Q O ts i n h i b i t C X I ~ K ~ ~ ~ ~i.e., X I l e a c h i n g of chromium from t h e Mastell o y N [ 5 9 ] - one would expect t h e f l u o r i d e s which appear above CrF2 i n t h e table t o h e s t a b l e i n t h e f u e l s a l t , whereas t h o s e below would b e reduced. Thus, t h e rare and a l k a l i n e e a r t h s , cesium, and z i r c o n i m should appear as s t a b l e f l u o r i d e s i n t h e s a l t m e l t ; and the n o b l e metals (Nb, Mo, Ru, Sb, T e , T c ) should appear i n a reduced - p r o b a b l y m e t a l - form. The n o b l e gases do n o t form any chemical compounds under m o l t e n salt reactor c o n d i t i o n s . The e f f e c t of UPq/eTFq r a t i o on s e v e r a l s p e c i e s of p a r t i c u l a r i n t e r e s t i s shown i n F i g s . 5.5 and 5.6. Note t h a t i o d i n e would b e exp e c t e d t o b e p r e s e n t as i o d i d e under t h e redox c o n d i t i o n s p r o j e c t e d . A s i n d i c a t e d above, o p e r a t i o n of t h e MSRE provided an o p p o r t u n i t y f o r s t u d y i n g t h e b e h a v i o r of f i s s i o n p r o d u c t s i n an o p e r a t i n g molten s a l t r e a c t o r , and every e f f o r t w a s made t o maximize u t i l i z a t i o n of t h e f a c i l i t i e s p r o v i d e d , even though they w e r e n o t o r i g i n a l l y designed f o r some of t h e i n v e s t i g a t i o n s which became of i n t e r e s t . Significant d i f f i c u l t i e s s t e m e d from:

1.

The s a l t s p r a y system i n the p m p bowl c o u l d not b e t u r n e d o f f . Thus the g e n e r a t i o n of bubbles and s a l t mist w a s e v e r - p r e s e n t ; moreover, t h e e f f e c t s were n o t c o n s t a n t , s i n c e they were a f f e c t e d by s a l t l e v e l , which continuously.

*R e f e r r e d

t o as n o b l e because they are thermodynamically more s t a b l e to o x i d a t i o n t h a n t h e chromium in H a s t e l l o y N w i t h t h e redox c o n d i t i o n s g e n e r a l l y maintained i n 1llo1te1-1f l u o r i d e f u e l s .

11%

Percent yield

PiSSklll

product

4 3 3 ~

23SU

239h

6.41 1.13 0.44

7.17 1.32

0.22 3.47 6.00 0.02 0.13

2.36 5.73 0.28 3.98 5.73 0.03 0.17

2.07 4.56 0.62 3.13 4.56 0.23 0.42

1.34

1.71

1.73

0.74 0.56

1.13 0.47

B .32

6.49 6.1f

6.40

5.09 5.03 5.65 5.89 7.10 6.10 5.91 5.67 2.60

6.16 0.76 0.34 1.98 4.00

5.34 5.15 4.41 4.80 2.9 1 1.80 2.60

4.27 6.09 5.78 6.30 6.06 5

.oo

3 .oo 2 .QO

0.80

.... u.x;

I.@1

. .. g..;.:,

<..... *;

.... ...... C.S

*=. ..

.. ... ~ ..,. _&x

..... s2

Table 5.4. Free emergy of formation at 650°C (LLGF,kcal) >-

Lit, Be2+, and E’- are at unity activity; all others, activities in mole fraction units

...... ... . .V

Solid

._.... . I J.

-363.36 -364.64 -341.80

.... :.=

-310.92 -389.79

Dissolved in 2LiFmBcF2

-126.49 -354.49 -356.19 -332.14 -216.16 -300.88 -392.52 -449.89

-316.93 : i i i .

. . . . a;

-308.10 -392.92 (-296.35) -366.49

(- I5 0.7) .... .,.,. .. .a ..

-138.18 - I21 5 8

-152.06 -134.59 -113.40 (-186.3) -62 -306.65 -159.13 -232.26 -200.59 -98.36 -42.15

‘:&3

.... ::x.*

- 39

-50.29 .. ..... ..... :s5+

....

-74.58

Source: C. F. Baes, Jr., “The Chemistry and Thermodynamics of Molten Salt Reactor Fuels,” Symposium on Reprocessing of Nuclear Fuels, ed. by P. Chistti, Nuclear Metallurgy, vcl. 15, p. 617, USAECCONF-690801(1969).

..... c:.,

.... .... w

-189.57 -66.112 -173.72

40"

4 o4

IO2

f Q3

%a

4 8"

405

4 8"

9' 8

/XUF3

Variation of equilibrium concentration of s t ~ t r ~ t u r a l metal f l u o r i d e s and the d i s t r i b u t i o n of i s d i n e as a function of t h e UFLJ1FF3 r a t i o in an B E

Fig. 5.5.

..... u.:;

0 -

b

F i g . 5 . 6 . Variation of p a r t i a l p r e s s u r e of v s l a t i l e f l u o r i d e s as a f u n c t i o n of U F ~ / U F Qr a t i o in an MSR fuel 1353.

3.

A n i s t shield encLosin ment

4,

Lubricating oil from the pump b e a r i n g s e n t e r e d t h e pump bowl at a rate of l t o 3 cs/day.

5.

There was c ~ n t i n ~ o u s lvya r y i n g flow and blowback of fuel s a l t between the p m p bow% and an overflow tank.

t h e sampling p o i n t p r o v i d e d a s p e s i a k environ-

In spite of these p r o b l e m , useful i n f o m a t i o n c o n c e r n i n g f i s s i o n p r o d u c t f a t e s i n HSKE w a s gained.

.... c ;c

S t a b l e Salt- S o l u b l e F l u o r i d e s

- S t a b l e f l u o r i d e s showed l i t t l e tendency t o d e p o s i t on Mastellay N or graphite 6403. Examinations of surveillance specimens exposed i P a the C01pe Q f t h e %w ShSkT@d Qaly 8.1 to 0.2% O f the i S Q t o p e S w i t h o u t n o b l e gas p r e c u r s o r s on graphite and H a ~ t e l E ~N. g ~ The bulk of " t h e m o u n t p r e s e n t s emed from fission r e c o i l s , based on a n estimate b y compere 6611 ana eneral c o n s i s t e n c y with the f l u x pattern 1601. The p e n e t r a t i o n of several fission products into t h e r e l a t i v e l y graphite i s shown i n F i g . 5.7. Note the f l a t p r o f i l e f o r 3 7xe, ~ " ; 2 = 3 . 9 min) i n c o n t r a s t t o the 9 5 ~ and r 3 7 6 S (ph-C?CUsSOK 144Ce9 which do not have noble gas p r e c u r s ~ r ~ .Similar data were obt a i n e d for 89 r (precursor: 89Kr, T I / = 3 . 2 fain) and 1 4 a ~ Ea ~ Q I(prec u r s o r : 1 4 % 3 r a / 2 = 16 s e e ) , althou h in those cases the c o n c e n t r a t i o n f a l l s o f f more w i t h depth i n ttas g r a p h i t e . s he d i p i n " ' 7 ~ s concentrat i o n at the f r e e - f l o w i n g salt surface ( l e f t s i d e of pig. 5.7) w a s estabPished as real i n this and other examinations [629, and s i m i l a r d i p s were noted in eXaK~ifaiY3g t h e g r a p h i t e C Q r e Stringer removed fKOEn the mwm Compere and Kirslis If531 attributed these d i p s t o significant d i f f u s i o n of cesium a t o m i n the graphite; such diffusion would also explain t h e very f l a t 14'7cs p r o f i l e shown in the f i g u r e . The mobility 0% 141cs a

k... .%>

Table 5.5. Stable fluoride fission product activity as fraction of calculated inventory in salt samples from 2 3 3U operation Without significant noble-gas precursor -.-14”Ce 144Ce 147Nd

Nuclide

‘5Zr

Weighted yield, %a Half-life, days Noble-gas precursor Recursor half-life Activity in salP Runs 15-17 Run 18 Runs 19-20

6.01 6.5

6.43 33

4.60 284

0.88-1.09 1.05-1.09 0.95-1.02

0.87-1.04 0.950.99 0.89-1.04

1.14-1.25 1.86-1.36 1.17-1.28

With noble%as precursor 8gSr

131CS

91Y

14%a

1.99 11.1

5.65 52 89Kr 3.2 min

6.57 30 yr. ‘“‘XC2 3.9 min

5.43 58.8 91Kr 9.8 set

5.43 12.8 “‘OXt? 16 set

0.99-1.23 0.82-1.30 1.10-1.34

0.67-0.97 0.84-0.89 0.76)---0.95

0.82-0.93 0.86-0.99 0.81-0.98

0.83-1.46 1.16-l As 1.13-1.42

0.82-1.23 1.10-1.20 1.02-1.20

aAllocated fission yields: 93.2% as3U, 2.3% 235’ti, 4.5% 23gPu. bAs fraction of calculated inventory. Range shown is 25-75 percentile of sample; thus half the sample values fall within this range.

c

.

.

*

-

l 25

TI/^ = 25 s e c ; p r e c u r s o r : 141Xe, TI/^ = 2 s e c ) may account f o r t h e deeper g r a p h i t e p e n e t r a t i o n by l4lCe than I b 4 C e shown i n P i g . 5.7. Some o b s e r v a t i o n s i n d i c a t e s i m i l a r m o b i l i t y f o r ' 9 ~ r Gas Samples. - Gas samples o b t a i n e d f r ~ mt h e gas s p a c e i n t h e pump bow% m i s t s h i e l d were c o n s i s t e n t w i t h the above r e s u l t s f o r the s a l t s e e k i n g I s o t o p e s with and w i t h o u t noble gas p r e c u r s o r s . Table 5.6 [ 6 4 ] shows the p e r c e n t a g e s of t h e s e i s o t o p e s whish were e s t i m a t e d t o b e i n t h e pump bowl s t r i p p i n g g a s , based on t h e amounts found i n gas samples. Agreement w i t h expected m o u n t s where t h e r e were s t r i p p a b l e n o b l e gas p r e s u r s ~ r si s s a t i s f a c t o r y i n c o n s i d e r a t i o n of t h e m i s t s h i e l d , contamin a t i o n prsbbems, and o t h e r e x p e r i m e n t a l d i f f i c u l t i e s . Gama s p e c t r o m e t e r examination of t h e off-gas l i n e showed l i t t l e a c t i v i t y due t o s a l t - s e e k i n g i s o t o p e s w i t h o u t n o b l e gas p r e c u r s o r s 1681. E x a ~ ~ i n a t i ~ofn ss e c t i o n s of t h e uff-gas l i n e a l s o showed only s m a l l amounts of t h e s e i s o t o p e s p r e s e n t [691*

Xoble Metals The s o - c a l l e d n o b l e m e t a l s showed a t a n t a l i z i n g l y u b i q u i t o u s b e h a v i o r i n t h e MSRE, a p p e a r i n g as s a l t - b o r n e , gas-borne, and metal- and g r a p h i t e p e n e t r a t i n g s p e c i e s . S t u d i e s of t h e s e s p e c i e s i n c l u d e d i s o t o p e s of %, Xo, Tc, Ru, A g , Sb, and T e ,

._.

.....

,...A,

Salt-Borne. - A s shown i n P i g . 5.8, t h e c o n c e n t r a t i o n s of f i v e of t h e n o b l e m e t a l n u c l i d e s f ~ u n di n s a l t samples ranged from f r a c t i o n s t o t e n s of p e r c e n t of i n v e n t o r y , with o n l y OR^ 9 9 ~ 0v a l u e a p p r e c i a b l y above %â‚ŹIO%. A l s o , the p r o p o r t i o n a t e c ~ m p o s i t i o of ~ - ~t h e s e i s o t o p e s remains r e P a t i v e l y c o n s t a n t from sample t o sample i n s p i t e of t h e widely v a r y i n g which c l e a r l y would b e a metal i n t h e MSRE s a l t amounts found. '"Ag, and has RO v o l a t i l e f l u o r i d e s , f o l l o w e d t h e P i g . 5.8 p a t t e r n q u i t e w e l l and also w a s c o n s i s t e n t i n t h e gas samples - see T a b l e 5.7 below. This s t r o n g l y supports t h e c o n t e n t i o n t h a t w e were d e a l i n g w i t h metal s p e c i e s . These r e s u l t s s u g g e s t the f o l l o w i n g about t h e n o b l e metals i n t h e

MSRE .... ,= .:.

1.

.

The b u l k of t h e n o b l e metals remain a c c e s s i b l e i n t h e c i r c u l a t i n g h o p , b u t w i t h widely v a r y i n g amounts i n c i r c u l a t i o n a t any particular time.

....

>C<*<'

2.

I n s p i t e of t h i s wide v a r i a t i o n i n t h e t o t a l . amount found i n a part i c u l a r sample, t h e p r o p o r t i o n a l composition i s r e l a t i v e l y c o n s t a n t , indicating t h a t the e n t i r e inventory is i n s u b s t a n t i a l equilibrium w i t h t h e new material b e i n g produced.

3.

The m o b i l i t y of t h e p o o l of n o b l e n e t a l material s u g g e s t s t h a t dep o s i t s o c c u r as an accumulation of f i n e l y d i v i d e d , well-mixed m a t e r i a l r a t h e r t h a n as a " p l a t e . "

:.-....

..... ,:.x.:<

..

.... *a

i

Table 5.6. Fission products in pump bowl gas samples, percenta of MSRE production rate Precursor ISOtOpe ISOtOpe

Tl/z

Percent found in gas samplesb Caldated strippxl

percent into gas

Gauss

Coarected

Isatopes with gaseous precursors R9Sr

“Kr

3.2 tin

14

6.5 * 1

1 “‘cs “IY “%a

‘37Xe 9’Kr ‘““Xe

3.9 min

IX 0.07 0.16

33 tb 0.4 1 0.2 a.1 f a.02

9.8 set 16 aec

5.7 f 1.2 25 + 6 0.004 f 0.01 0.06 ?r 0.01

Salt-seeking isotopes 9SZr ‘““Ce ““Ce 147Nd “As noble gas precursor. ‘Mean value. T!orrectd for estimated mist content [66,67].

0.06 f 0.01 0.03 + 0.01 0.3 f 0.w 0.02 * 0.007

0.01 * 0.004 -0.003 f 0.003 Q.05 f Q.03 0.002 ?I 0.002

5

u.3 rn

u

..&...

..iii,

z

5

2

5

.... ..... . ; . : . x

.. . .:.M

w

e u w

“ 3.:.:.:.‘

2

....

5 .... ..... ..&.,.a

2 10-2

.... ....., :&

&+&

..... +

.....

.... ....

% .A .!.,

.. . ?<.&>

... .....

, 1 . . . . . y 53

:..... . &

2

4

12

(9

44

45

46

9

24 36 42 44 SAMPLE NUMBER

45

55

57

58

59

76

ii

F i g . 5.8. Noble metal i s o t o p e s in salt samples (as percentage of calculated i n v e n t o r y ) [633.

99

49

130 31 74

0.9 f 0.2 1.5 2 Q.5 0.7 f 0.3 2.3 9 (9.7 11 f 3

-1

2

0.8

-1

f

0.8

129

.....

x:,:r

.... ..... .?.!.l<d

<$.&

.... ..<a

..... .... ,w.$

....

*&I

No s a t i s f a c t o r y c o r r e l a t i o n of n o b l e metal c o n c e n t r a t i o n i n t h e s a l t samples and any o p e r a t i n g parameter could b e found. In o r d e r t o o b t a i n f u r t h e r understanding of t h i s p a r t i c u l a t e p o o l , t h e t r a n s p o r t p a t h s and l a g s of n o b l e m e t a l f i s s i o n p r o d u c t s i n t h e MSaE were examined u s i n g a l l a v a i l a b l e d a t a on t h e a c t i v i t y r a t i o of two i s o and 367-aay 1O%us Data from t o p e s of t h e same element, 39.6-day 1 0 % g r a p h i t e and m e t a l s u r v e i l l a n c e specimens exposed f o r v a r i o u s p e r i o d s and removed a t v a r i o u s t i m e s , f o r m a t e r i a l t a k e n from t h e off-gas system, and f o r s a l t and gas samples and o t h e r materials exposed t o pump bowl s a l t w e r e compared; w i t h a p p r ~ p ~ i a it nev e n t o r y r a t i o s and w i t h values c a l c u l a t e d f o r i n d i c a t e d l a g s i n a simple compartment model. This model assumed t h a t s a l t r a p i d l y lost ruthenium f i s s i o n product formed i n i t , some t o s u r f a c e s and most to a s e p a r a t e mobile 'spool's of n o b l e metal f i s s i o n p r o d u c t , presumably p a r t i c u l a t e o r c o l l o i d a l and l o c a t e d t o an a p p r e c i a b l e e x t e n t i n pump bowl r e g i o n s . Some of t h i s "pool" m a t e r i a l d e p o s i t e d on s u r f a c e s and also appears t o b e the s o u r c e of t h e off-gas d e p o s i t s . A l l materials sampled from o r exposed i n t h e pump bowl appear t o r e c e i v e t h e i r ruthenium a c t i v i t y from t h e p o o l of r e t a i n e d material. Adequate agreement of obs e r v e d d a t a w i t h i n d i c a t i o n s of t h e del r e s u l t e d when holdup p e r i o d s of 45-90 days w e r e assumed [ 7 S ] . Niobium. - As shown i n Pig. 5 . 6 , h% i s t h e most s u s c e p t i b l e of t h e noble metals to o x i d a t i o n should t h e U4"/U3" ratio b e allowed t o g e t t o o h i g h . Apparently t h i s happened a t t h e s t a r t of t h e 233U o p e r a t i o n , as w a s i n d i c a t e d by a r e l a t i v e l y s h a r p rise i n CI-'~ c o n c e n t r a t i o n ; i t w a s a l s o noted t h a t 60 t o %IQQ% of the c a l c u l a t e d 95% i n v e n t o r y w a s p r e s e n t i n t h e s a l t samples. A d d i t i o n s of reducing agent (Be'> which i n h i b i t e d t h e Cr+2 b u i l d u p a l s o r e s u l t e d i n t h e disappearance of t h e 95% from t h e s a l t [sl]. Subsequently t h e 9 5 ~ 1reappeared i n t h e s a l t s e v e r a l t i m e s f o r n o t always a s c e r t a i n a b l e r e a s o n s and was caused t o Heave t h e salt by f u r t h e r reducing a d d i t i o n s . A s t h e o p e r a t i o n s continued t h e perc e n t a g e of 95Xb which reappeared decreased s u g g e s t i n g b o t h r e v e r s i b l e and i r r e v e r s i b l e s i n k s . The 95Nb d a t a d i d n o t c o r r e l a t e w i t h t h e Ms-RuT e d a t a shown i n Fi g . 5.8, nor w a s t h e r e any o b s e r v a b l e correlation of i t s b e h a v i o r w i t h amounts found i n gas samples. Gas-Borne. - G a s samples t a k e n from t h e pump bowl d u r i n g t h e 2 3 5 U o p e r a t i o n [ 8 ] f n d i c a t e d c o n c e n t r a t i o n s of n o b l e m e t a l s t h a t implied t h a t s u b s t a n t i a l p e r c e n t a g e s (3O-lOO) of t h e noble metals b e i n g produced i n t h e MSRE f u e l system were b e i n g c a r r i e d o u t i n t h e 4 l i t e r s (STP)/min H e purge gas. The d a t a o b t a i n e d i n n t h e 2 3 3 % 7 o p e r a t i o n w i t h s u b s t a n t i a l l y improved sampling t e c h n i q u e s 1721 i n d i c a t e d much lower t r a n s f e r s t o s f f g a s , as shown i n Table 5 . 7 . I n b o t h c a s e s i t i s assumed t h a t t h e noblemetal c o n c e n t r a t i o n i n a gas sample o b t a i n e d i n s i d e t h e m i s t s h i e l d w a s (The pump t h e same as t h a t i n t h e gas l e a v i n g t h e pump bowl p r o p e r . bowl w a s designed to minimize the amount of m i s t i n t h e sampling area ~t i s o u r b e l i e f t h a t t h e 2 3 3 ~p e r i o d and a l s o a t t h e gas e x i t p o r t . ) data are r e p r e s e n t a t i v e and t h a t t h e c o n c e n t r a t i o n s i n d i c a t e d by t h e gas samples t a k e n d u r i n g 2 3 5 ~o p e r a t i o n are anomalously h i g h because

a. 3Q ........>

.....e

.-

%W CQwSidePkIg t h e r e s u l t s assumed, f o r lack sf o t h e r f i s s i o n products per u n i t area fokllldk OK2 t h e speCim@IKSWere repreSC2ntatiVe 0% a l l the g r a p h i t e Hastelkoy N s u r f a c e s . It was, of course, recognized t h a t t h i s assumption was tenusus a t b e s t , and the exarnibtati~nof p o s t - o p e r a t i o n specimens from t h e KSl3.E showed t h a t it was not a very c l o s e approximation. T a b l e 5.8 shows f i s s i o n p r ~ d u d ~ its t r i b u t i o n s c a a e u l a t e a in t h i s way f o r s e v e r a l Sets Of SUrVeiPIance spl2CiKllen.S and f o r p a r t s O f the COKIpoâ‚Źl@RtS PelllOVed i n the poSt-operatiOn eXallIinatiOn. '%he CaEcUlate d i s t r i b u t i o n s vary widely f o r d i f f e r e n t areas b o t h i n t h e cfrculatin s y s t e m and on t h e

sane component.

The f s u r v e i l % a n c e specimen a r r a y , exposed f o r t h e l a s t f o u r months of o p e r a t i s n , had g r a p h i t e and m e t a l specimens natched as t o csnfiguration i n v a r i e d f l o w c o n d i t i o n s [76]. The r e l a t i v e d e p o s i t i o n i n t e n s i t i e s (1.8 i f t h e e n t i r e inventory w a s s p r e a d evenly over a l l s u r f a c e s ) W e r e a.$ ShUWn in Table 5 . 9 . The examination s f some s e ents e x c i s e d from p a r t i c u l a r r e a c t o r components, i n c l u d i n g c o r e neta and g r a p h i t e , pump bowl, and h e a t exer s u r f a c e s , one year a f t e r shutdown a l s o ~ e v e a l e da p p r e c i a b l e acc m u l a t i s n of these s u b s t a n c e s . The r e l a t i v e d e p o s i t i o n i n t e n s i t i e s a t these l o c a t i o n s are a l s o shown Zn T a b l e 5.9. ~t is evident t h a t net d e p o s i t i o n g e n e r a l l y w a s i n t e n s e OW metal than on g r a p h i t e , and f a r m e t a l , w a s more i n t e n s e under more turbulent f l o w e S u r f a c e ~ ~ u g h e had s s no apparent effect. Extension t o all the m e t a l and g r a p h i t e areas of t h e system would r e q u i r e h o w l e d g e of the e f f e c t s of f l o w conditi~nsi n each r e g f s ~ ,and ( O v e r a l l , metal t h e f ~ a c t i o n iof t o t a l area r e p r e s e n t e d by t h e r e g i o n . area w a s 26% of the total, and g r a p h i t e 7 4 % . ) A t h e o r e t i c a l approach [76a] t r e a t i n g t h e n o b l e metal t r a n s p o r t as an o r d i n a r y c o n v e c t i v e t u r b u l e n t diffusion p ~ o c e s si n c l u d i n g gas interf a c e s as i m p e r f e c t sinks shows some q u a l i t a t i v e agreement w i t h t h e sbserved d e p o s i t i o n b e h a v i o r . Flow e f f e c t s have not been s t u d i e d experimentally; t h e o r e t i c a l approaches based on atom mass transfer through s a l t boundary l a y e r s , though a u s e f u l frame s f r e f e r e n c e , do not i n t h e i r usual form take i n t o account the deposition and release s f f i n e p a r t i c u l a t e m a t e r i a l such as w a s indic a t e d t o have been p r e s e n t i n t h e fuel system. Thus, much more must b e l e a r n e d about t h e f a t e s of n o b l e metals i n molten salt r e a c t o r s b e f o r e t h e i r e f f e c t s OR v a r i o u s operations can be e s t i m a t e d r e l i a b l y .

..

w3

k.,

Table 5.8. Percent noble metal distribution

in MSRE based on examination

of various specimens removed

Percentages assume amount found on a specimen is representative of all graphite or Mastelloy N surfaces. Graphite “Nb

9gbfo

g’Tc

lQ3wu

lQeRU

Hastelloy N

- _._..- ...lllAg

lZSSb

129mTe

132~~

9sNb

99$fo

34

41 19

99Tc

103~~

106~~

lllAg

lZsSb

129111~~

13”Te

Core surveillance specimens Group 2 (32,700 MWh) Group 3 (65,600 MWh) chxlp4 (18,SOOMWh) Group 5 (11,800 MWh)

[16] [8] [60] [62]

36 41

11 9

7

4

15

16

7 4 2 5

4 3 4

6 5

3

3 3

10 5 5

12 3

10

15 3 4

26 53

4

3

8 4

16

12

12 18

E

Post-operation specimens [75] Core stringer, top Core stringer, middle Core stringer. bottom ControA rod thimble, bottom Control rod thimble, middle Mist Shidd. QUtSide iFI Salt Heat exchanger, shell. Meat exchanger, tube

12

47

33"

79

77

138

47'

39

11

17

5

56

70 10 16 56

44a

36

32

27

9

19 19 27

7

31

7

40 15

13

85 35

14=

74

23""

21

11 10 5

28

14

68 113

35’” 67a

7

43a

Table

5.9.

Relative

deposition

Surveillance

intensities

far amble metals

specinr~ews

Gxaphite

Ianinnr Turbulent

0.2 0.2

a.2

0.06 Q.Q4

0.16 (9.10

Metal

Laminar Turbulent

0.3 0.3

0.5 1.3

0.1 (4.1

0.3 0.3

Reactor

Graphite Core bar channel Bottom Middle TQlJ

0.15 0.07 a.9 2.Q

coI-qmlents

Turbulent 0.54 1.09 0.23

0.07

Turbulent Turbulent Tusbulent

0.26 0.33 0.21

0.73 1.Q 1.2

Turbulent Twbwlent

1.42 1.00

1.23 0.73

0.25 B.06 0.29

8.65 1.90 0.18

0.4ha! 0.w 0.6P

0.27 0.10 0.11

0.38 0.19 0.54

2.85 2.62 4.35

0.89� 1.39 2.e

1.54 0.58

a.50 0.42

3.21 1.35

1.69 0.54�

Metal

Pump bowl Heat exchanger shell Heat exchanger tube Core

Rod thimble Bottom Middle

133 Although t h e n o b l e metals t h e y do n o t p e n e t r a t e any more n o b l e gas p r e c u r s o r s , as shown r i o u s p e n e t r a t i o n of H a s t e l l o y 7,

are a p p r e c i a b l y d e p o s i t e d on g r a p h i t e , than the salt-seeking fluorides without by t h e i o 3 R u d a t a i n F i g . 5 . 7 . DeleteN g r a i n boundaries i s d i s c u s s e d i n Chapter

.... ..... >-

Iodine ....

>& ;.

... ..... = <

...., .:.... =‘

The s a l t samples i n d i c a t e d c o n s i d e r a b l e l S a H was n o t p r e s e n t i n t h e f u e l , t h e m i d d l e q u a r t i l e s of r e s u l t s r a n g i n g from 45 t o 71% of invent o r y w i t h a median of 62%. The s u r v e i l l a n c e specimens and g a s samples a c c o u n t e d f o r less t h a n 1% of t h e rest. The low T e m a t e r i a l b a l a n c e s s u g g e s t t h e r e m a i n i n g i 3 1 1w a s permanently removed from t h e f u e l as I3’Te ( Y I / ~= 25 m i l s ) . Gama s p e c t r o m e t e r s t u d i e s i n d i c a t e d t h e 1311 formed i n c o n t a c t w i t h t h e f u e l r e t u r n e d t o i t ; t h u s t h e losses must h a v e b e e n t o a region o r regions not i n c o n t a c t w i t h f u e l , This s t r o n g l y suggests o f f - g a s , b u t t h e i o d i n e and t e l l u r i u m d a t a from gas samples and examinat i o n s of off-gas components do n o t s u p p o r t s u c h a l o s s p a t h . Such l o s s would n o t a p p e a r to i n t e r f e r e w i t h t h e use of i s d i n e s i d e - s t r e a m s t r i p ping u t i l i z i n g t h e r e a c t i o n

HF (g i n He) f

...~. ......

1451-

-k

F- 4- H I 3 5 I(g>

i.

T h i s h a s b e e n c o n s i d e r e d [ a 7 1 as an a l t e r n a t e f o r removal of t h e i m p o r t a n t i 3 5 ~ e( d a u g h t e r ) p o i s o n from t h e f u e l . .&.& ;.... .

Evaluation .a

..... .&

....,

.... ........ &.d

...... -d

i

*&

..... ,:;:x<.

-

... .... ,:.:.:.>,

..... < :=,

The e x p e r i e n c e w i t h t h e MSRE showed t h a t t h e n o b l e gases and s t a b l e f l u o r i d e s behaved as e x p e c t e d b a s e d on t h e i r c h e m i s t r y . T h e n o b l e m e t a l b e h a v i o r s and f a t e s , however, are s t i l l a matter of c o n j e c t u r e . Except f a r Mb under u ~ u s u a l % yo x i d i z i n g c o n d i t i o n s , i t seems c l e a r t h e s e e l e m e n t s are present as metals and that their u b i q u i t o u s p r o p e r t i e s s t e m from t h a t f a c t s i n c e metals are n o t w e t t e d b y g and h a v e e x t r e m e l y low s o l u b i l i t i e s i n , NSR f u e l s . U n f o r t u n a t e l y t h e MSRE o b s e r v a t i o n s p r o b a b l y were s u b s t a n t i a l l y a f f e c t e d by t h e s p r a y s y s t e m , o i l c r a c k i n g p r o d u c t s , and f l o w to and from t h e a v e r f l o w , a l l of which w e r e c o n t i n u o u s l y c h a n g i n g , U~CQIIThe low material b a l a n c e QIZ trolled variables I indicates apprecia b l e undetermined l o s s from t h e MSW, p r o b a b l y as a n o b l e metal p r e c u r s o r (‘Pa, S b ) . T a b l e 5.10 shows t h e e s t i m a t e d d i s t r i b u t i o n of t h e v a r i o u s f i s s i o n p r o d u c t s i n a m o l t e n s a l t r e a c t o r b a s e d on the N3t.E s t u d i e s , Unfortun a t e l y t h e wide v a r i a n c e and p o o r material b a l a n c e s f o r t h e n o b l e m e t a l d a t a make i t u n r e a l i s t i c t o s p e c i f y t h e i r f a t e s wore t h a n q u a l i t a t i v e l y . A s a consequence, f u t u r e r e a c t o r d e s i g n s must a l l o w f o r e n c o u n t e r i n g app r e c i a b l e f r a c t i o n s of t h e n o b l e metals i n all. r e g i o n s c o n t a c t e d by c i r ~ ~ P a t P nfuel. g As i n d i c a t e d i n the t a b l e , c o n t f n u o u s c h e m i c a l p ~ ~ c e s s i s t g and t h e processes f i n a l l y chosen w i l l s ~ b s t a n t i a l l ya f f e c t t h e f a t e s of many of t h e f i s s i o n p r o d u c t s . e

’

Table

Fission product group Stable salt seekers Stable salt seekers (noble gas precursors)

5.10.

Indicated

distribution

products

in mollden

salt reactors

Distribution

Example isotopes ‘“ZP, 144Ck, 147Nd 89Sr, 137cs, “4QBa, 9”Y

of fission

In salt -99 Variable/Ttp of gas

Noble gases Noble metals

a’#~~~Kr, “s%e, ““Xe =Nb, 99Mo, “a6Ru, 1 1 1Ag, 12’Te

LOW/T,/, l--20

Iodine

1311 13SI

50-75

af gas

‘Far example, Zr tends to accumulate with Pa holdup in reductive extraction processing. %articuLte observations su=est appreciable percentages will appzar in processing streams. “Substantial iodine could be removed if side-stream stripping is used to remove 13 s I [‘I’71 .

(7%)

To metal

To graphite

To off-gas

Qther

Negligible Negligible

<I (fission recoils)

Brocessinga

LOW

Negligible

LOW

Negligible Variable/T1/2 of gas High/T,,, of gas

5-30

S-30

Negligible

Processingb

<I

<1

Negligible

PracessingC

E -I=-

L 35 Future Work

.....

....

.... ..... .>..=

S u b s t a n t i a l difficult work will be needed t o bring our understanding of the behavior of noble metal f i s s i o n products (including iodine) to the level of the other f i s s i o n products. This work ~511require simultane~us c o ~ t r ~of l chemical and hydrodynamic conditions and will consequently require experiments of sufficient s c a l e and some complexity t~ achieve this. The major objective will be t o determine the controlling mechanisms as well as the associated rates, in order that extrapolation t o larger and more compkex systems can follow. b o n g factors doubtless important in MSW and in future reactors a r e t h e redox potential of the system (characterized by the U4+/U3+ ratio), t h e presence of oxide and its affinity for various fission product (e. IT%) and c~nstituentelements, the possible agglomeration of metals o n t o gas and bubble interfaces in the absence of colloidal (metallic, graphite, o x i d e , etc.) particles, the d e p o s i t i ~ nof noble metals onto colloidal particles Of VaKiQuS t y p e s , and the d e p Q % i t i o n and PesUspensiOn O f particles bearing n o b l e metals. The exploitation of suitable mechanisms to I - ~ I I I B V ~noble metal fission pTQduCts O'p: t o ~ o t n t r o Pt h e i r depssLt.%on c o u l d b e an attractive r e s u l t of

such studies. Laboratory work in dynamic systems could use tracers f o r some work. A next phase of t h e work, is expected to generate such tracers under dynamic conditions in f u e l or other s a l t using high-intensity netatson pulses, possibly from the Oak Ridge Health Physics Research R e a c t o r . Broad variation of relevant chemical and hydrodynamic factors appears possible.

.>.<A ;.... .

Of necessity, tracer concentrations will be relatively l o w s HOTever, experiments involving particulate participation in noble metal behavior appear t o be practical except where high concentrations are required. In order t o achieve these concentrations along with radiation conditions approaching those sf proposed reactors, while maintaining chemical and hydrodynamic c a n t r o % , sophisticated in-pile l o o p experimentation is required, a major objective being to specify definitive to be

in the aemsnstration r e a c t o r .

Coolant Salts Basis f o r Choice of C ~ ~ = ~ p o s i t i o n

.....

.S.S

$ .:.:.... ..I

.. .... ,...... .

v.... *:

It has never appeared feasible to r a i s e steam directly from the fuel (primary) heat exchanger; accordingly, a secondary coolant must be provided t o l i n k the f u e l circuit to the s t e m generator. $he demands imposed upon this c ~ ~ l a nf tl u i d d i f f e r in obvious ways from t h o s e imposed upon the fuel system. Radiation intensities will be markedly less in t h e coolant system, and the C Q ~ S ~ ~ U ~ X Xs fX Suranium fission will be absent. The esolalat salt m s t , however-,be compatible with metals of construction which will handle the f u e l and the steam; it must not undergo violent reactions with fuel or steam should beaks d e v e l o p in either circuit.

136 The c ~ ~ b a snhto u l d b e i n e x p e n s i v e , i t must p o s s e s s good h e a t t r a n s f e r p r o p e r t i e s , and i t must m e l t a t temperatures s u i t a b l e f o r stem cycle s t a r t u p . An i d e a l c o o l a n t would c o n s i s t of compounds which are t o l e r a b l e i n the f u e l o r which are e a s y t o s e p a r a t e from the v a l u a b l e f u e l m i x t u r e shouPd t h e f l u i d s mix as a consequence of a Peak. r e j e c t e d i t s h e a t t o an a i r - c o o l e d r a d i a t o r a t a minimbun t e m p e r a t u r e of about 1015°F 1781. The c o o l a n t mixture chosen [8,781 f o r This t h a t a p p l i c a t i o n w a s BeF2 w i t h 66 mole % of %iF (see Fig. 5.1). material, which m e l t s a t 851sF, was shown t o be completely s a t i s f a c t o r y f o t~h a t w e [8,9]. An MSBR c o o l a n t , however, must t r a n s p o r t h e a t t o supercritical stem a t minimum temperatures o n l y modestly above 700°F [IO]. U s e of t h e high-melting %m c o o l a n t i n E B R would pose real probIems i n s t e m g e n e r a t o r d e s i g n . The e u t e c t i c m i x t u r e of LiF and BeF2 (Fig. 5.11 m e l t s a t n e a r 70Q"P, but its v i s c o s i t y i s h i g h . MoreF i~x t u r e s a ~ q e u i t e expensive if ~ L I Fis used. o v e r , both these L ~ F - B ~ m If normal L i F is used t h e c o s t is much less, though it is mot t r i v i a l , but a l e a k i n t h e primary h e a t exchanger g r e a t l y damages t h e expensive s a c c o r d i n g l y , been disc~unted as MSBR c o o l a n t s . f u e l . Such ~ ~ i x f u r ehave, The a l k a l i m e t a l s , e x c e l l e n t c o ~ I a n t sw i t h real promise i n o t h e r s y s t e m , are q u i t e u n d e s i r a b l e h e r s s i n c e t h e y react v i g o r o u s l y w i t h b o t h the M B R f u e l a d With steEU3l. More Elofole metals Such as Bi O r Pb UndelrgCJ mo v i o l e n t reactions with e i t h e ~of the other working fluids, but they are only fair c o o l a n t s , and they are n o t compatible w i t h t h e nickel-based a l l o y s i n t e n d e d for u s e i n mBb. m i t e n lnixturea of N ~ N O ~mo3, , m d mo2 have been used industrially (Hitec i s a cornon example) as h e a t t r a n s f e r a g e n t s , b u t not a t temperatures q u i t e s~ high as are d e s i r a b l e i n t h e MSBR. These materials m y be s t a b l e toward i r r a d i a t i o n i n t h e primary heat exchanger, b u t e x t e n s i v e i n v e s t i g a t i o n of t h i s p o i n t would b e r e q u i r e d [79]. They are c l e a r l y not stable toward the f u e l , from which they would p r e c i p i t a t e a c t i n i d e oxides r a p i d l y but n o t v i o l e n t l y , and they would r e a c t dangerously with t h e moderator g r a p h i t e i f a l e a k o c c u r r e d i n t h e primary h e a t exchanger. Thus they are not b e i n g c o n s i d e r e d f o r use i n t h e MSBR secondafgr system. It should b e n o t e d , howeveb-, that these nit~ate-nitritem i x t u r e s have q u i t e compatible with water and s t e a m , excellent melting points, and s h o u l d c e r t a i n l y oxidize t o T2Q any tritium d i f f u s i n g from t h e reactor f u e l system. They mayp i f t h e tritium problem (see Chapter 14) cannot o t h e r w i s e b e s a t i s f a c t o r i l y managed, prove v a l u a b l e i n a t h i r d c o o l a n t HOOP, as mentioned in Chapter 2 . S e v e r a l binary c h l o r i d e systems are known t o have e u t e c t i c s m e l t i n g w e l l below 700°F [80]. Many of t h e s e systems are u n a t t r a c t i v e s i n c e they c o n t a i n high c o n c e n t r a t i o n s of c h l o r i d e s which are e a s i l y reduced and, t h e r e f o r e , c o r r o s i v e o r which are very v o l a t i l e . The o n l y low-melting binary systems S% s t a b l e , ~ ~ o m n - v ~ l a t iclhel o r i d e s are t h o s e c o n t a i n i n g EiC1; L i C l - C s C l (330°C a t 45 mfe Z CsCl), LiC1-KC1 (355°C a t 4 2 mole Such system Would be r e h % KCB), Li61-R.bcl (312°C at 45 mle % w b C 1 ) . t i v e l y a q ~ ~ t a s i vif e m d e from 7 ~ ~ and 1 % they c ~ u l diesa to s e r i o u s contamination of t h e f u e l i f normal LiCl were used. Very few f l u o r i d e s o r m i x t u r e s of f l u o r i d e s are known t o m e l t a t temperatures below 700°F (370eC). Stannous fluoride (SnF2) m e l t s at 212°C. This material i s c e r t a i n l y n o t s t a b l e d u r i n g long-term service

.....

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i n H a s t e l l s y N; moreover, i t s phase diagrams w i t h s t a b l e f l u o r i d e s (such as NaP o r LiF) show h i g h m e l t i n g p o i n t s a t r e l a t i v e l y l o w a l k a l i f l u o r i d e i ~ n s w i l l m e e t t h e Isw l i q u i d u s c o n c e n t r a t i o n s . Coolant c o ~ ~ p o ~ i t which temperature s p e c i f i c a t i o n s may b e chosen from the NaF-BeF2 o r NaF-LiFBeF;! system. These materials are compatible w i t h H a s t e l l s y N , and they p o s s e s s a d e q u a t e s p e c i f i c h e a t s and Pow vapor p r e s s u r e s . They ( e s p e c i a l l y t h o s e i n c l u d i n g L i p > are expensive, and t h e i r v i s c o s i t i e s a t low temperat u r e are c e r t a i n l y h i g h e r thaw d e s i r a b l e . On b a l a n c e , the b e s t m a t e r i a l f u r u s e as t h e ElSBR secondary coolant ~ o r i d e and sudium f l u s r o b o r a t e . appears t o be a m i x t u r e s f ~ o d i uf l u These compounds are r e a d i l y a v a i l a b l e , i n e x p e n s i v e , and appear t o h e s u f f i c i e n t l y s t a b l e t o the r a d i a t i o n f i e l d within t h e primary h e a t exchanger. The m i x t u r e of NaP-NaBF4 w i t h 8 mole Z of NaF m e l t s a t the a c c e p t a b l y l o w temperature of 7 2 5 " ~and ~ its physical p r o p e r t i e s s e e m adequate for its s e r v i c e as a h e a t t r a n s f e r a g e n t . These sompounds are n o t i d e a l l y compatible w i t h e i t h e r steam o r t h e MSBR f u e l , b u t , as des c r i b e d i n more d e t a i l below, t h e r e a c t i o n s are n e i t h e r violent ROI- p a r ticularly energetic. The f a c t t h a t f l u o r o b o r a t e s show an a p p r e c i a b l e e q u i l i b r i u m p r e s s u r e of gaseous BF3 a t e l e v a t e d temperatures p r e s e n t s minor d i f f i c u l t i e s . The BF3 p r e s s u r e s are moderate f b l ] ; they m y b e c a l c u l a t e d from

.... :<.p

log Ftorr $&& .

= 9.024

-

5 -5820 TQK

( y i e l d i n g 208 t o r r a t 850°K) and c l e a r l y p r e s e n t no dangerous situatisns. It i s n e c e s s a r y 9 however, t o m a i n t a i n t h e a p p r o p r i a t e p a r t i a l p r e s s u r e s of BP3 i n any f l o w i n g cover gas stream to avoid composition changes i n t h e

.... <. ;>

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melt*

P r e s e n t S t a t u s of F l u s r s b o r a t e Chemistry

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Phase Behavior. ... ,:<<9

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The b i n a r y system NaP-NaBF4 h a s been d e s c r i b e d

[SS,Sf] as showing a e u t e c t i c a t 60 mle Z NaBF4 w i t h a m e l t i n g p o i n t uf 304°C (580°F). Our s t u d i e s [S2] have shown t h a t t h e s e p r e v i o u s l y p u b l i s h e d diagrams are s e r i o u s l y i n e r r o r . * w i t h q u i t e pure NaP and NaBF4, show that t h e e u t e c t i c a t 8 mole X NaF and a m e l t i n g p o i n t phase diagram [ s a ] f o r this s i m p l e system i s

*B o r i c

Our r e c e n t s t u d i e s , made system c o n t a i n s a s i n g l e of 384°C (723°C). The shown i n F i g . 5.9.

o x i d e s u b s t a n t i a l l y lowers t h e f r e e z i n g p o i n t of NaBF4 m i x t u ~ e s , and i t i s p o s s i b l e t h a t t h e o r i g i n a l a u t h o r s used q u i t e impure materials; i t i s , however, d i f f i c u l t t o see why t h e p r e v i o u s s t u d i e s were s o i n c o r r e c t .

138

ORNL-DWG 67- 9423AW

Pig. 5 . 9 .

The system NaF-NaBP4.

139 Behavior w i t h Hydroxide Ion. - S o d i m hydrowyfluoroborate (NaBF30H) i s a common minor contaminant i n c o m e r c i a l NaBF4 t h a t i s prepared by aqueous p r o c e s s e s . Pure NaBF30H can b e decomposed completely a t temperat u r e s n e a r 100째C 1831 through t h e b i m o l e c u l a r r e a c t i o n :

T h i s material c a n n o t , a c c o r d i n g l y , b e used as a major c o n s t i t u e n t f o r high-temperature c o a l a n t . However, when t h e NaBP38H i s p r e s e n t i n v e r y d i l u t e s o P u t i o n in NaBPk i t i s "matrix i s o l a t e d , " t h e b i m o l e c u l a r decomposition r e a c t i o n is i n h i b i t e d , and t h e material is c o n s i d e r a b l y more s t a b l e [ 8 4 ] . Such h y d r s x y f l u o r o b a r a t e s are a p p r e c i a b l y more rea c t i v e than f l u o r o b o r a t e t o s t r u c t u r a l metals, as i s d i s c u s s e d i n more d e t a i l i n a subsequent s e c t i o n ; however, t h e r e i s c o n s i d e r a b l e evidence that as much as 30 ppm of H can be p r e s e n t as OH- i n t h e f l u a r o b o r a t e m e l t w i t h o u t undue c o r r o s i v e e f f e c t s upon H a s t e l l o y N E8.51. R e l a t i v e s t a b i l i t y of such q u a n t i t i e s of OW" (and, by analogy sf ST> may b e an important a i d t o c o n t r o l o f t r i t i u m (see c h a p t e r 14). If, f o r example, t h e c o o l a n t can b e m d e t o c o n t a i n s e v e r a l ppm of H (18 ppm i s %$s of c o o l a n t ) ana if t h e exchange more than 4 kg of I% i n t h e n e a r l y reac t i s n

.... '.=a

,:.=.,

.....

could b e made t o proceed, t h e coolant mixture would a f f o r d a means f o r holdup of t h e tritium d i f f u s i n g from t h e primary h e a t e ~ h a n g e r . Some i n i t i a l s t u d i e s have been p e r f o m e d i n which B2 h a s been bubbled i n t o , o r a l t e r n a t i v e l y allowed t o d i f f u s e through n i c k e l t u b i n g i n t o , NaF-NaBFh m e l t s 6861. These m e l t s c o n t a i n e d hydroxide i o n equiva l e n t to some 25 gpm of I% and a c o n s i d e r a b l e q u a n t i t y (perhaps 3000 ppm) of oxide. Direst o b s e r v a t i o n by i n f r a - r e d s p e c t r ~ s ~ o pshowed y that QDgrew i n t o t h e m e l t s . No corresponding d e c r e a s e of OH- o c c u r r e d . These s t u d i e s s t r o n g l y s u g g e s t t h a t t h e exchange r e a c t i o n i n d i c a t e d above i s not o c c u r r i n g b u t that t h e added deuterium i s r e a c t i n g w i t h o x i d e impurities, perhaps by

.:.;.;; .-.9

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4.3

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:.... .=

.... .....

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Dq 9 1B2FgQ2-

+ NiQ

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+ Ni

.

F u r t h e r s t u d y of such r e a c t i o n s i s c l e a r l y n e c e s s a r y t o determine t h e p r e c i s e mechanism and t o e s t a b l i s h whether t h e r e a c t i o n can b e made s u f f i c i e n t l y r a p i d and q u a n t i t a t i v e to fix t h e d i f f u s i n g t r i t i u m . Physical P r o p e r t i e s . - P e r t i n e n t physical p r o p e r t i e s f o r t h e eutect i c NaF-NaBF4 s o o l a n t mixture are p r e s e n t e d i n Table 5.11. P a r t i a l p r e s s u r e ~of BF3 above t h e m i x t u r e have been measured w i t h some c a r e , as have Eiquidus t e m p e r a t u r e s [ 4 l ] . However, other p r o p e r t i e s of t h e salt, as were t h e p r o p e r t i e s of t h e MSBK fuel m i x t u r e , have been e s t i m a t e d . The v a l u e s given a r e q u i t e u n l i k e l y to b e i n s e r i o u s e r r o r , b u t an experiment a l program t o f i m up t h e s e e s t i m a t e d values i s c l e a r l y n e c e s s a r y .

140

141

.... .;.a

C o m p a t i b i l i t y w i t h Hastelloy N. - A c c e p t a b l e c o m p a t i b i l i t y of t h e NaF-BF4 c o o l a n t w i t h H a s t e l l o y N under r e a l i s t i c c o n d i t i o n s seem a s s u r e d by numerous c s r r o s i o n tests [ 4 2 , 8 7 , 8 8 ] , though t h e number of s u c h tests is much simaller than t h a t f o r LiF-BePz m i x t u r e s . Thermodynamic d a t a f o r p o s s i b l e r e a c t i o n s of t h e NaF-NaBF4 m i x t u r e i s i n a somewhat less s a t i s f a c t o r y s t a t e t h a n i s t h a t f o r t h e fuel mixt u r e s . The free energy change f o r t h e c h e m i c a l r e a c t i o n

....

:.:.>y

...

....

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a p p e a r s t o b e a b o u t -+ 36 ksal a t 800째K 6893. The r e a c t i o n s o f BF3 w i t h Fe and X i are even less l i k e l y to o c c u r . In a d d i t i o n , t h e s e r e a c t i o n s become somewhat less l i k e l y ( p e r h a p s by 5 kcal o r s o ) when one c o n s i d e r s e n e r g e t i c s of f o r m a t i o n of NaBP4 and i t s dilutiom by NaF. R e a c t i o n s whish produce metal b o r i d e s and f l u o r i d e s are somewhat more d i f f i c u l t to assess. T i t a n i u m , a minor c o n s t i t u e n t of H a s t e l l s y N, h a s a m o d e r a t e l y s t a b l e b o r i d e [ 9 0 ] . The r e a c t i a n

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p r o b a b l y must b e expected to p ~ o c e e &b~u,t t h e very POW rate of d i f f u s i o n u f T i i n Mastellsy N would b e e x p e c t e d t o l i m i t t h e e x t e n t of r e a c t i o n markedly. Thermochemical data. f o r t h e b o r i d e s of F e , Cr, M i , and Mo do n o t s e e m t o h a v e b e e n e s t a b l i s h e d . Unless they h a v e f r e e e n e r f o r m a t i o n more n e g a t i v e t h a n 25 k s a l / B atom t h e Kastellsy N should p r o v e r e s i s t a n t t o p u r e NaF-NaBF4 c o o l a n t . The several c o r r o s i o n tests seem t o h a v e produced no e v i d e n c e f o r f o r m a t i o n of b o r i d e s of t h e s e metals. Oxidizing i m p u r i t i e s i n t h e fluorobsrate mixture s e l e c t i v e l y a t t a c k t h e chromium i n M a s t e l l s y N , as t h e y do i n t h e f u e l m i x t u r e , b u t t h e produ c t of c o r r o s i o n i s CrFq r a t h e r t h a n CrP, [ 4 2 ] . The r e a c t i o n of FeF3 i n f l u s r o b o r a t e m e l t s , f o r example, a p p e a r s t o b e

FeF2(d)

+=

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I f t h e f l u o r o b o r a t e fs s u f f i c i e n t l y impure t h e s o r r s s i o n p r o d u c t CrF3 exceeds i t s s o l u b i l i t y l i m i t and p r e c i p i t a t e s as Na$rFG** While some of t h e i n i t i a l C O K ~ Q S ~ ~ I tests -I w i t h q u i t e impure f l u ~ r ~ b o r a m t ei x t u r e s

produced s u c h p r e c i p i t a t i o n (and severe c o r r o s i o n ) [ 4 2 ] , none s f t h e more recemt s t u d i e s h a v e e n c o u n t e r e d t h i s d i f f i c u l t y .

*S i m i l a r

c o r r o s i o n t o p r o d u c e CrF3 and ultimate p r e c i p i t a t i o n of NaM2CrP6 w a s o b s e r v e d l o n g ago i n s t u d i e s of UF4 disso%ved i n the t e r n a r y e u t e c t i c of NaF-KF-LiF [!In].

142

Interactions with Steam. - Flusroborates react readily with s t e m . The reaction, which is n o t violent or particularly energetic, is

It: is well known t h a t t h e HF so p r o d ~ ~ eis d quite corrssive; it is capable sf reaction with N i and Pe as well as w i t h Cr and can cause generalized attack. The FeF2 and NiF2 so generated are then capable s f reaction w i t h ere in the alloy [ 71. Cantor and Waller e851 have recently shown that the reaction s f OH- in dilute solution (2% ppm and below) with Hastelloy h;* CXCMP~S S%SW~Y;this ~ e a c t i ~can n a p p a r e n t l y be represented as

ress of steam, as from a leak in t h e BR steam g e n e r a t o r s , to rsborate s s o k a n t c2rcuit must, accord g%y, b e expected %Q %es u l t in increased c o r r o s i o n . such an increase has, indeed, been observed in deliberate additions sf steam to an o p e r a t ng test l o o p containing removable specimens in hot and c o l d regions 1 9,931 Relatively r a p i d corrosio~~ foilowed t h e ste addition; chrsmim concentration in the circulating salt rose from 82 ppm to about 320 ppm in a b o u t 11900 hours and remained essentially constant 6933. Examination of specimens removed at intervals from. the loop a l s o i n d i c a t e d that the attack decreased with time after t h e initial exposure to s t e m [ 8 % , 9 3 ] . These data strong1y suggest that t h e Hastellay N system can tolerate inleakage of steam and, once the leak is repaired, c o u l d continue t o operate without extensive damage even if the s a l t were not r e p u r i f i e d [ 9 3 ] . Et is c l e a r , however, that csntinuous inleakage s f s t e m in appreciable quantity would require a pu~ification system f o r the f l u o m b o r a t e s a l t .

b.,

Interactions with F u e l Salt. - The E B R design [lo] will assure that t h e pressure on the coolant is slightly higher than t h a t ow the f u e l s a l t , s o t h a t a minor leak in the primary heat exchanger will result in coolant s a l t e n t e r i n g the fuel. Such a l e a k , even though small, will be recognized at once because of the marked reactivity l o s s resulting from admission of boron into t h e fuel.

*It

is worthy of n o t e that t h e NaF-NiBP4 mixture f o r that study, which was shown to contain at least 25-38 ppm of H along with about 350 ppm C P ~ +and 3900 ppm 0 2 - , was drawn from an operating t e s t l o o p whose p e r f o r nce with respect t o cor~osionwas quite s a t i ~ f a c t ~ ~ y .

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1 43

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Mixing a s m a l l q u a n t i t y S€ NaF-NaBF4 s a l t w i t h t h e f u e l e f f e c t i v e l y d i s s ~ c i a t e st h e MaBFb i n t o NaF and BF3. The NaF w i l l s i i s s o l ~ ei n t h e LiF-BeF2-ThP4-UP4 s a l t m i x t u r e ; t h e BF3 w i l l d i s t r i b u t e between t h e fuel. s a l t and t h e a v a i l a b l e vapor s p a c e and, i f o p e r a t i o n of t h e r e a c t o r were c o n t i n u e d , would b e swept i n t o t h e o f f - g a s s y s t e m . Additions of l a r g e q u a n t i t i e s of c o o l a n t , as might occur i n t h e u n l i k e l y e v e n t of a g r a s s f a i l u r e i n t h e p r i m a r y h e a t e x c h a n g e r p p r o d u c e more complex e f f e c t s and c a n r e s u l t i n a p p r e c i a b l e p r e s s u r e s of BF3. The s o l u b i l i t y of EFQ i n t h e FEBR fuel s o l v e n t has b e e n c a r e f u l l y measured [ 9 4 ] . The s o l u b i l i t y d e c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e and i n c r e a s e s l i n e a r l y with BF3 p r e s s u r e . Prom t h e s e d a t a one can c a l c u l a t e t h e e q u i l i b r i u m p r e s s u r e of BP3 from s m a l l leaks of NaF-NaBF4 i n t o 'PISBR f u e l i n a c l o s e d system. T h i s e q u i l i b r i u m p r e s s u r e c l e a r l y depends upon t h e amount ~f NaP-MaBP4 a d m i t t e d and t h e a v a i l a b l e vapor s p a c e . If w e assume t h a t t h e o n l y v a p o r s p a c e a v a i l a b l e i s t h e s m a l l b u b b l e f r a c t i o n (assumed t o b e 1%) i n t h e f u e l , * t h e n one can show t h a t i n l e a k a g e a t 1250°F of 1 c u b i c f o o t (116 I b s ) of NaF-MaBP4 c o o l a n t r e s u l t s i n a BF3 p r e s s u r e of 0.17 atmosphere. It seems c l e a r t h a t l e a k s of t h i s o r d e r do n o t r e s u l t i n a dangerous s i t u a t i o n . A d d i t i o n of s u b s t a n t i a l q u a n t i t i e s ~f NaBF4 t~ several f l u o r i d e m i x t u r e s g e n e r a l l y s i m i l a r t~ t h e PBBR fuel r e s u l t e d i n l i q u i d - l i q u i d i m m i s c i b i l i t y [ 9 % ] . Mixing e q u a l w e i g h t s , f o r example, sf 2LiEeBeF2 and b?aBP4 at 600°C produced ma l i q u i d p h a s e s . The less d e n s e p h a s e w a s r i c h i n BF3 and c o n t a i n e d l i t t l e BeF2; t h e d e n s e phase w a s r i c h i n BeF2 w i t h l i t t l e BP3. LIP and NaF p a r t i t i o n e d between t h e s e p h a s e s , w i t h t h e l i g h t p h a s e r i c h i n NaF and t h e heavy p h a s e r i c h i n L i F . O t h e r e x p e r i ments [ 9 5 ] showed t h a t UP4 (presumably 'PhF4 wou%d behave similarly) w a s a l m o s t c o m p l e t e l y r e t a i n e d i n t h e heavy p h a s e . No s u c h e q u i l i b r a t i o n s t o d e f i n e t h e m i s c i b i l i t y l i m i t s o r t h e e q u i l i b r i u m d i s t r i b u t i o n s of t h e several i o n s i n t h e two p h a s e s h a v e b e e n performed w i t h t h e MSBR f u e l c o m p o s i t i o n . C o n s e q u e n t l y , t h e e x t e n t t o which this l i q u i d - l i q u i d i m m i s c i b i l i t y l i m i t s t h e 13F3 p r e s s u r e upan mixing P a r g e q u a n t i t i e s of NaF-MaBFb, w i t h MSBR f u e l c a n n o t b e a c c u r a t e l y assessed. However, t h e f a c t t h a t c o n s i d e r a b l e p r e s s u r e s of BF3 (in r e a s o n a b l e a c c o r d with e s t i mates based on t h e measured s s l u b i b i t y 1941 of BF3) are developed upon mixing MSBW f u e l w i t h o n e - t h i r d i t a volume s f NaF-NaBF3 coolant h a s b e e n d e m o n s t r a t e d e x p e r i m e n t a l l y [%I. I t a p p e a r s c e r t a i n t h a t small Peaks of coolant i n t o t h e f u e l s y s t e m pose no real problems. It is c l e a r %however, t h a t a d d i t i o n a l s t u d y of mixing S % t h e s e f l u i d s i n r e a l i s t i c g e ~ w e f i r i e sand i n f l o w i n g s y s t e m i s needed b e f o r e o n e can be c e r t a i n t h a t $10 p o t e n t i a l l y damaging s i t u a t i o n c a n arise as a consequence of a sudden major f a i l u r e of t h e h e a t exchanger.

*This

i s c l e a r l y a w o r s t case. volume i n t h e o f f - g a s s y s t e m .

I t c o m p l e t e l y i g n o r e s t h e large

144

-

P u r i f i c a t i o n ~f Flusroborate Mixtures. I n i t i a l purifieati~nof %Sd?-b?aB??~, Elf-xtUreS f o r LISâ‚Ź! i l a C O T X C J S ~ Oand ~ Other e n g h 2 e r i a g tests has not posed s e r i o u s p r o b l e ~ i ~ ssince , t h e p u r i t y s p e c i f i c a t i o n s are less s e v e r e i n s e v e r a l ways t h a n are those f o r the fuels, and q u i t e pure MaBF4 preparations are available commercially at r e a s o n a b l e C O ~ ~ S Recent . p r e p a r a t i o n E971 methods have c o n s i s t e d simply in (1) mixing the MaBP4 w i t h the r e q u i r e d quantity of NaF, ( 2 ) heatin t h e mixed powder a t a c o n t r o s l e d rate t o 30O6C under redused p r e s s u e , ( 3 ) h e a t i n g t h e material t o 500°C under a static atmosphere of i n e r t gas9 ( 4 ) mixing t h e molten mixture by b r i e f w i t h BF3$ (5) purg ng t h e BF3 by a b r i e f treatment w i t h f l o w i n and (4) transferrin the s a l t m i x t u r e t o i t s cak analyses u f mt r i a l prepared i n t h i s simple storage containe way show oxide concentrations of Out 325 ppm and hydlrogebl (prOtofl) Conc e n t r a t i o n s of about 15 ppm. Ana ses f o r ~ e 2 +S ~ O W values n e a r 150 ppm; t h i s eoaahd almost certainly be decreased by a K L Q stringent ~ ~ purifieat i Q n pPOc@dUre Simple prosadurea such as that d e s c r i b e d above m y s u f f i c e for the o r i g i n a l coolant l o a d i of an %BR, but it seems c e r t a i n that a d d i t i o n a l , on-line treatmnent W i l l e r e q u i r e d d u r i n g r e a c t o r o p e r a t i o n . The inevit s b i l i t y i of s m a l l inleakages of steam, f o r example, will ~ e q u f ~ some e repurifi~ationr e p r o c e s s i n g . &reover, i f the f l u o r o b o r a t e mixture is to help with t h e tritium p r o b l e m (by tritium exchange w i t h NaBF30H U T o t h e r reactions yielding NaBF3QT), some p r o c e s s i n g method f o r removFng t h e c o n t a i n e d T on a reasonably short time eye w i l l be n e c e s s a r y . The afeactian O f f P U Q r O b O P a t E 2 W i t h Ste

i s a r e v e r s i b l e one, and treatment with P%F ( a p p r o p r i a t e p r e s s u r e s of in31 condition. It a p p e a r s , however, that t h i s reaetioin m y b e f o r we i n a p r a c t i c a l system. Such p u r i f i c a t i o n c ~ u b c l c e r t a i n l y be aseomplished by use of f l u o r i n e ; t h i s r e a g e n t (mixed with B F g ) should certainly remove the 6pb COT> as well as the contained o x i d e s . ~ O Qi n e f f i c i e n t

and

It is possibhlsle that d i r e c t f l u o r i n a t i o n (presumably using a frozen-wa$% f l u o r i n a t o r ) may be n e c e s s a r y , but. s t u d i e s are needed t u determine whether less a c t i v e rea e n t s can s e r v e the p u ~ p o s e .

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R a d i a t i o n S t a b i l i t y . - The f l u o m b o r a t e c o o l a n t salt w i l l b e exposed t o i n t e n s e gamma r a d i a t i o n and an a p p r e c i a b l e delayed n e u t r o n f l u x i n t h e primary h e a t exchanger. Consequently i n v e s t i g a t i u n s o f such r a d i a t i o n e f f e c t s w e r e undertaken [ 9 8 ] . The gama i r r a d i a t i o n was c a r r i e d o u t i n s p e n t High Flux I s o t o p e Reactor (HFIR) f u e l elements. A 2.0 cm ID x 9 CHI H a s t e l l o y M c a p s u l e c o n t a i n i n g 32 g NaBF4-NaF (92-8 mole %> was i r r a d i a t e d f o r 1468 hr a t 600째C i n t h r e e s u c c e s s i v e elements d i s c h a r g e d from t h e HF]CR. The t o t a l dose w a s 9.7 x IO" R (0.1s w/g a v e r a g e , Q - 5 ~ / maximurn) g ; f o r comparison, the a n t i c i p a t e d gama dose i n a PBOO-m(e) mBR is " 4 . 2 5 W / g a The p r e s s u r e i n t h e c a p s u l e was monitored d u r i n g t h e i r r a d i a t i o n and showed o ~ l yr e s u l t s c o n s i s t e n t w i t h t h e expected BP3 e q u i l i b r i u m p r e s s u r e . A n a l y s i s of t h e gas at t h e c o n c l u s i o n of t h e experiment: (ambient " C > showed I%Q HF, BP39 OP f l u o p i n e . Examination of t h e s a l t on opening t h e c a p s u l e showed no o b s e r v a b l e e f f e c t s u f the i r r a d i a t i o n A 29-crn2 ~ a s t e l l o yN c o ~ ~ o s i ospecimen n exposed i n t h e c a p s u l e showed n e g l i g i b l e weight l o s s (0.8607 g ) . The r e s u l t s i n t h e i r r a d i a t e d c a p s u l e were i n a l l respects comparabEe to t h o s e observed i n an unfrradiated control. experiment. A l i t e r a t u r e s e a r c h and analysis i n d i c a t e d t h e d i r e c t n,a r e a c t i o n

w o ~ l db e t h e m j o r s o u r c e of f l u o r i n e due t o t h e delayed n e u t r o n flux. The y r a d i a t i o n and o t h e r c o n s i d e r a t i o n s i n d i c a t e t h a t secondary e f f e c t s from t h e Li and 0: recoils a r e of l i t t l e consequence, a p p a r e n t l y because of r a p i d recombination of fragments from c o l l i s i o n s w i t h BP4-. Thus, i f N ~ B F ~ - N (92-8 ~F mole X > i s exposed t o an e s t i m a t e d 15 x 1016 delayed w/sec i n an MSBR primary heat exchangers t h e f l u o r i n e p r o d ~ ~ ewould d m o u n t t o onPgr 8 moles of f l u o r i n e p e r y e a r .

E v a l u a t i o n and S u m a r y of Needed Work .... <:$&

= ..... ,

A CQnsidWX3bk s t u d y of m n y aspects of fPuoroborate chemistry has been conducted d u r i n g t h e p a s t f e w y e a r s . N e v e r t h e l e s s , o u r understanding of t h e chemistry of t h e NaF-NaBP4 system i s less complete, and o u r knowledge of i t s b e h a v i o r rests on a l e s s s e c u r e f o u n d a t i o n , t h a n t h a t f o r t h e MSBR f u e l system. There are s e v e r a l areas, a c c o r d i n g l y , where f u r t h e r o r a d d i t i o n a l work i s needed, though i t seems u n l i k e l y t h a t t h e f i n d i n g s w i l l t h r e a t e n f e a s i b i l i t y of NaF-NaBF4 i n t h e MSBR concept. Phase b e h a v i o r of t h e s i m p l e MaF-NaBF4 system and t h e e q u i l i b r i u m p r e s s u r e of BP3 over t h e p e r t i n e n t t e m p e r a t u r e i n t e r v a l are w e l l unders t o o d . I f t h e MaP-NaBP4 e u t e c t i c or some n e a r v a r i a n t of i t i s t h e f i n a l c o o l a n t c h o i c e , l i t t l e e f f o r t need b e s p e n t i n t h e s e areas. A d d i t i o n a l i n f o r m a t i o n is needed, however, on t h e b e h a v i o r of oxide S o l u b i l i t y of Na2B2F60 i n and hydroxide i o n i n t h e f k u o r o b o r a t e m e l t s . the mixture i s not well known, e q u i l i b r i a ( i n i n e r t c o n t a i n e r s ) among M28, NaBP30H, and Na2B2F60 are s t i l l needed, and r a t e s of r e a c t i o n

d i l u t e xaBP36K SOBUtions W i t h n e t d s 32eed definition. I n a d d i t i o t l , the mechanism by whish tritium, d i f f u s i n g from the fuel system, can b e BF3OT- needs additional study b e f o r e its value can really b e assessed. A s imdicatecl above, several of the p h y s i c a l property values have ted. These e s t h a t e s are almost certainly adequate f o r the p r e s e n t , but the p r a ram needs to provide for measurement of these Of

quantities. Compatibility of the UaF-Ha F4 With H a s t d l O y N UndeP IIQlX€laEOpe%sting conditions see a s s u r e d . Additional s t u d y in realistie f l o w i n g systems, of the corrosive effects of s t e m imleaka is n e s e s s a q . T h i s s t u d y , claseHy allied F.Jith t h e e q u i l i b r i a and kine ics among the hydroxides ana oxides d e s c r i b e d above, needs uitimate~y culminate in a demonstration loop c a p a b l e of simulating steam i n l e a k e and coollant repurificatisn. xiwg o f c o s l a n t and f u e l clearly requires additional s t u d y . The on which results from e q u i l i b r a t i o n of these f l u i d s is reasonably well u n d e r s t o o d , and, even where large leakages 0% C C K I Iinto ~ T Ithe ~ €ere% are assmed, the ustimate s v @ q u i i i b . k - i mseem rF to pose %to real danger. M O W ~ Q ~ Pthe , real situation may well n o t approximate an equilibrium

and necessary Purification roceciures € Q % t h e c o o l a n t mrrixture are adequate f o r the p~esentand can be used to provide m t e r i a i f a r the msty necessary t e s t s . These are n o t adequate fer ultimate a n - l i n e p r o c e s s i ~ l gof the coolant mixture during operation. F l u ~ r i ~ a t i oofn the c o o l a n t , on a reasonable cycle time, would almost certainly suffice thou h it has n o t been demonstrated. A process using a l e s s aggressive reagent is clearly desirable. The fluomborate mixture has shorn completely adequate r a d l a t i o n s t a b i l i t y in t h e single ethsugh r e a l i s t i c a l l y severe) t e s t run. Adait i o n a l radiasit3n testing O f t h i s W t e p i a l in a flOWiIlg syStEi¶l would seem desirable and should u l t i m a t d y be done, but this study would mot at p r e s e n t have a h i g h p r i o r i t y . Qf the several alternative secondary salts mentioned in t h e text the b e s t candidates lithim. m e r e seems l i t t i e doubt t h a t S ~ V @ral of these m t e % i d s ( L i G l - K C l mixtures, f o r example) C Q d d be shown to b e s u i t a b l e coolants, although a c o n s i d e r a b i e program of chemical development and c o ~ r o s i o ntesting would be necessary. The same would be true f o r the nitrate-nitrite mixtures before they e s d d be used at high temperature in an MSR tertiary l ~ ~ p . systearas are Backin

e

Analytical Chemistry Reauirements

In o r d e r to exploit f u l P y the unique features of the MSR concept and ensure safe and efficient reactor o p e r a t i o n , it will be necessary to m i n tain adequate sur~eillanceof the composition s f various reactor streams. Ideally, all such analyses would be performed autonatisally with transducers located in the salt s t r e , since a n a l y s i s of discrete samples in h o t c e l l s i s s u b j e c t to unavoidable delays and is expemsive.

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A t p r e s e n t , i t appears t h a t i t m y n o t be p r a c t i c a l t o measure mjor , f u e l c o n s t i t u e n t s such as Ei, B e , Th, f l u o r i d e , and perhaps U by i n - l i n e methods i n an MSBR. F o r t u n a t e l y , a continuous monitoring of t h e s e cons t i t u e n t s will not b e c r i t i c a l to t h e o p e r a t i o n of a r e a c t o r . %%lemore c r i t i c a l d e t e r m i n a t i o n s , on t h e o t h e r hand, are g e n e r a l l y m e n a b l e t o i n l i n e measurement. Determinations which appear of most s i g n i f i c a n c e t o the program i n c l u d e t h e redox c o n d i t i o n of t h e f u e l , * c o r ~ ~ s i oproduct n i o n s ( p a r t i c u l a r l y C r 2 + and p s s s i b P y T i 4 + > oxide, bismuth, hydrogen and tritium, c e r t a i n f i s s i o n p r o d u c t s , and p r o t a c t i n i u m i n f l u o r i d e streams. S i m i l a r d e t e m i n a t t o n s may be r e q u i r e d in c h l o r i d e streams of t h e reproce s s i n g system. I n - l i n e a n a l y s e s f o r permanent gas contaminants I m o i s t u r e t r i t i u m , hydrocarbons, and f i s s i o n product gases w i l l be needed i n the f u e l c o v e r gas. To t h i s l i s t must b e added BP3> HF, hydrogen, and h y d r o l y s i s p r o d u c t s i n t h e coolant cover gas and perhaps N P , P 2 > and UP6 i n gaseous streams from t h e r e p r o c e s s i n g system. It should b e noted t h a t i n a d d i t i o n t o economics o f t i m e and expense, the i n - l i n e techniques w i l l p r o v i d e i n f o r m a t i o n n o t a t t a i n a b l e by d i s c r e t e sampling methods. A n o t a b l e example is t h e i33*/u4+ r a t i o i n t h e fuel. 'This r a t i o is p r o h i b i t i v e l y s e n s i t i v e to atmospheric contamination d u r i n g sampling and sample t r a n s f e r i n hot s e l l s , and i s r a t h e r neaningless on frozen samples because t h e r a t i o undergoes changes d u r i n g c o o l i n g as a Peslldt O f I 2 q U i l i b r i U s h i f t s . h o t h e r example i s t h e detE?I-RIinatiQn of trace csnstituents i n g a s e s , which i s n o t o r i o ~ ~ ldyi f f i c u l t i f n o t imp o s s i b l e to do by withdrawing samples. It i s e v i d e n t t h a t the u l t i m a t e need i s an a n a l y t i c a l S ~ S ~ I f ~ oM an ~ MSBR that i n c l u d e s t h e most complete i n - l i n e a n a l y t i c a l measurements possible, backed up by adequate hot. cell and analytical l a b o r a t o r i e s . I n t h e i n t e r i m p e r i o d i t i s n e c e s s a r y t o develop c a p a b i l i t i e s and t o p r o v i d e a n a l y t i c a l s u p p o r t f o r t h e technologgr programs.

Experience

The mjor development of a n a l y t i c a l methods f o r d i s c r e t e samples w a s a s s o c i a t e d w i t h the o p e r a t i o n of t h e MSRE. T h e analytical methods f o r t h i s r e a c t o r were developed t o s u p p o r t the o b j e c t i v e s of t h e chemical s u r v e i l l a n c e program [ S , p . 13. With t h e e x c e p t i o n of i n - l i n e a n a l y s e s of the off-gas and remote gama s p e c t r o m e t r y ( d e s c r i b e d l a t e r i n t h i s s e c t i o n ) , a l l a n a l y s e s w e r e performed on batch samples either in East c e l l s 8% bg. bench t o p Hlgthoas. P r i o r to t h e MSRE program, we had s u b s t a n t i a l e x p e r i e n c e i n t h e laan$ l i n g and a n a l y s i s of n o n r a d i o a c t i v e f l u o r i d e s a l t s i n t h e program Ionic o r i n s t r u m e n t a l methods had been developed f o r most m e t a l l i c cons t i t u e n t s , and methods were a v a i l a b l e f o r P- (gyrohydrolysis) Kg91 and a

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is a measure sf t h e redox p o t e n t i a l o f t h e f u e l which i n f b u e n c e s t h e rate of c o r r o s i o n and t h e d i s t r i b u t i o n of c e r t a i n f i s s i o n products and t r i t i u m i n the r e a c t o r system ( s e e 5-21 t o 26).

sulfur [lO0]. For RE a p p l i c a t i o n i t was n e c e s s a r y to adapt t h e s e n e t h o d s t o ho -cell OpeKatiOnS. ki teChniqUe i n v O k V h g t h e @ V O l U % i O H a of e l e m e n t a l oxy en by r e a c t i o n w i t h BF3 has s i n c e r e s u l t e d i n t h e versaPPL) method [loll f o r oxide i n i n o r g a n i c samples. A n o n s e l e c t i v e ~ e ~ s ~ r ofe "reducing ~ e ~ t p o . ~ e ~of " adequate s e n s i t i v i t y had been developed (hydrogen evoabution method) [l6B2]. A g e n e r a l e x p e r t i s e 6183% in the r a d i ochemical s e p a r a t i o n and measurement of f i s s i o n r o d u c t s was a v a i l a b l e from earlier reactor p r o g r a m a t 8 experience with i n - l i n e as a n a l y s i s , p a r t i c u l a r l y p r o c e s s y [ % 0 4 ] ,was a v a i l a b l e f K O m Other p r o ation of t h e and i n t h e subsequent technoa_ogy Pro ~ ~ ~ of eEE?%kOdS ~ f Q f S~C r t 2 t e~ Sampl@S @ W~a s cQntiI2Ued, ~ and t h e Laboratory has acquired i n s t r u m e n t a t i o n f o r newer a n a l y t i c a l techInstrumental methods whisk have or are expected t o c o n t r i b u t e niques. i n c l u d e : x-ray a b s o r p t i o n , diffraceion, and f h ~ r e s c e n e e s p a r k s o u r c e mss s p e c t r o ~ ~ ~ e ESCW t ~ y , and Auger spee%on ~ c r o p r s b emeasurements> scanning e l e c t r o n microscopy, try, F o u r i e r t r a n s f o r m s p e c t r o m e t r y , n e u t r o n a c t i v a t i o n a n a l y s i s , delayed n e u t r o n n e t h o d s , photon a c t i v a t i o n a n a l y s i s , and scany p a r t i c l e s , e . g . p r o t o n s . The d e t a i l e d d e s c r i p t i o n s f a l l a n a l y t i c a l methods availabbe t o t%se program i s beyond t h e scope of t h i s r e p o r t . A t a b u l a t i o n of o u r a n a l y t i c a l c a p a b i l i t i e s i s given elsewhere [lO5]. C e r t a i n deveEopmewts m e r i t additional mention and are d e s c r i b e d below.

- The p r e p a r a t i o n of homogenized s m p l e s of MS e l e m e n t a l a n a l y s e s p r e s e n t e d problems beeabase of t h e r a d i o a c t i v i t y and t h e hygroscopic n a t u r e of the salt [ 9 , p. 273. Salt samples were t a k e n i n s m a l l copper l a d l e s which w e r e sealed under h e l i u m i n a t r a n s p o r t c o n t a i n e r i n the sampler-enricher [IO61 f o r d e l i v e r y t o t h e h u t c e l l . There t h e l a d l e w a s unloaded and s e c t i o n e d . The s a l t w a s removed from the t r u n c a t e d l a d l e and homogenized by a v i g o r ~ ~s hsa k i n g i n a pulverizer vessel. Salt t r a n s f e r was t h e n mde w i t h minimal atmospheric expos u r e to a p o l y e t h y l e n e vial t h r e a d e d i n t o the bottom of t h e p u l v e r i z i n g ~ s s e i . his p-oceaure a f r e e - f ~ o w i n g powdered S E Z T I w ~ ~ i t ~h i n two hours of r e c e i p t of the l a d l e . Atmospheric exposure w a s s u f f i c i e t k t t o compromise t h e d e t e r m i n a t i o n of oxide and U3+ but d i d n o t a f f e c t s t h e r measurements. 0

oxide. - ~ e c a u s eof t h e sensitivity the pulverized sale: to u11a v o i d a b l e atmospheric contamination, we a d o p t e d t r a n s p i r a t i o n t e c h n i q u e s in which the e n t i r e samples could b e analyzed. For t h e more c r i t i c a l d e t e r m i n a t i o n s , the most s u c c e s s f u l a p p l i c a t i o n sf t r a n s p i r a t i o n techniques w a s t h e d e t e r m i n a t i o n of o x i d e by h y d r o f l ~ r i n a t i o n[ l O 7 ] . The method i s based on t h e evoEution sf water which o c c u r s when m e l t s are sparged w i t h m i x t u r e s of anhydrous MF i n hydrogen. By removing s u r f a c e n o i s t u r e w i t h a p r e m e l t i n g h y d r o f l u o r i n a t i o n step and by measuring t h e water evolved from 50-g samples as an inte r a t e d s i g n a l from an e l e c t r o B y t i c m o i s t u r e m o n i t o r , we measured o x i d e c o n c e n t r a t i o n s of about 50 ppm with p r e c i s i o n b e t t e r t h a n +lo ppm.

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Uranium. - Analyses f o r uranium by eou%ometric titration [Is] showed good reproducibility and high precision ( 0 -5%) but on-line reactivity balance calculations were about 10-fold more sensitive than t h i s in establishing changes in uranium concentrations within the circuit. We have demonstrated that it is possible quantitatively to collect t h e decontaminated UPg from the fluorination of 50-g samples of molten f u e l [lQ8]. The technique w a s used primarily t o separate uranium f o r precise i s o t o p i c analysis, but sufficient work w a s done t o establish its potential for a more accurate uranium determination by measurement of the separated uranium outside t h e hot cell.

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U3*e - We tested a hydrogenation transpiration method for the determination of ~ 3 +in f u e l [IOS]. he rate of produstion of MP from the spar i n g of fuel with hydrogen is a function of the instantaneous ratio of U5+/U4+* Because corrosion products a l s o contribute HP the integrated y i e l d from a batch hydrofluorination is related to f u e l composition by an equation [ l o g ] that cannot be explicitly solved f o r uranium ratios. By use of computer techniques w e devised a 4 - s t e p , %-temperature reduction procedure to produce HP yields sensitive to ratio change. During 2 3 5 ~ + in reasonable operation (with 0.9 mole z UP^) we obtained ~ 3 + / ~ 4 ratios agreement with "book values" obtained from reactor charging and operating data (Fig. 5.10). Nowever, t h e method proved inadequate f o r t h e lmer concentrations of uranium in the 2 3 3 ~f u e l . u3+/u4' we also applied a voltametric method to the measurement ratios in remelted fuel samples [1aC1] (see section on E l e s t r ~ ~ h e ~ ~ ~ i c a l W e performed these measureResearch f o r a description of voltametry). ments with electrodes inserted in samples remelted in their l a d l e s . More atmospheric exposure w a s incurred than in the oxide determinations, because it was necessary ts cut o f f t h e top of the ladles to acsornmodate the eHectrodes. AccordingPy, we obtained ratios below those expected. We were, however, able to observe normally shaped VO~~~XIETIQ~I-~IILS for Cr2+ waves and to f o l l o w t h e reduction of the f u e l by hyand u4+ drogen spargirtg. We a l s o observed changes in r a t i o s with temperature t h a t were c o n s i s t e n t w i t h thermodynamic predictions sf equilibrium s k i f t s between the uranium couple and corrosion product i o n s . This indicated that the radiation l e v e l of the samples had negligible effect on the method and supports the potential of voltametry for application to reactor salt streams. Spectrophotometry of Radioactive Samples. - We constructed a facility [IlO, pp. 202-284] which permitted the measurement of highly radioactive samples- within a hot cell-by using t h e components of a spectrophotometer Located outside the cell (Fig. 5.1%). A system s f extended o p t i c s directed t h e chopped reference and sample beams through the cell walls, and r e t ~ l - n e d focused t h e sample hem at the center Sf an optical i=Ur:ba~e, the two beams through the w a l l to the m~nochrsmatoH-detestsb-section of t h e instrument. The system design included devices for remelting large salt samples under inert atmosphere and dispensing portions to spectrophotometric celPs, but because of the imminent shutdown of the MSRE we

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devised a sample s y s t e m to fill windowless cells by d i r e c t immersion i n the fuel ~ e s p i t ep r e c a u t i o n s t o p r e v e n t atmospheric exposure the ~ 3 + i n these samples was c o m p l e t e l y o x i d i z e d b e f o r e measurements ~ o u l db e mde. we were ame, ~ ~ Q ~ e vto eg-~ t h e s p e c t r a sf u4+ ana ( i = ~ i l o w S O ~t h e speca reduction w i t h u r a n i ~ metal) t h a t of u 3 t C ~ K I E J ~ I - ~ sf: t r a sf these samples w i t h t h o s e of n o n r a d i o a c t i v e p r e p a r a t i o n s indicated no a d v e r s e effects from t h e activity of the f u e l and demonstrated t h e f e a s i b i l i t y sf t h e technique. he f a c i l i t y has since been used to measu r e t h e s p e c t r a of transuranium elements and p r o t a c t i n i u m i n m o l t e n s a l t s .

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c e l l as a t r a n s d u c e r . By means of an o x i d a t i o n and a b s o r p t i o n t r a i n Ella8, p. 1961 w e were able t o measure b o t h t o t a l i m p u r i t i e s and hydrocarbons i n the off-gas. The sampling station a l s o i n c l u d e d a system f o r t h e c r y o g e n i c c o l l e c t i o n of xenon and k r y p t o n on molecular sieves to p r o v i d e concentrated s2mples f o r t h e p r e c i s e determination of t h e i s o t ~ p i cr a t i o s sf krypton and xenon by mass s p e c t r o m e t r y . During t h e last two r u n s O f MSW, we set up equipment [Ilk, p. 183%at t h e reactor ts c o n v e r t the tritium i n v a r i o u s gas s t r e S t C i Water f o r EiC2asuk~tllent by sCin'Ci%latiOn C O U f l t i n g . * - By means os a precise collimation s y s t e m mounted OB a maintenance s h i e l d , r a d ation from aeposftea fission products on compsnents w a s d i r e c t e d t o a h i h-resolutfon hithiUlll-dri%ted gemaniuna diode [aQa, p. 361. Prom t h e g a s p e c t r a o b t a i n e d w e were a b l e t o i d e n t i f y s p e c i f i c i s o t o p e s such as noble metal fiseiaw p r o d u c t s and to reap their d i s t r i b u t i o n by moving t h e ssllimating s y s t e m [ll2]. t h e latter runs of the r e a c t o r s u c h me U%emC?ntS W e r e KWde dUKing power o p e r a t i o n s [ l l 2 ] .

Bismuth. - The i n v e s t i g a t i o n of t h e metal t r a n s f e r r e p ~ o ~ e s s i nsysg t e m d e s c r i b e d i~ chap. 1.1 r e q u i r e d the development s f more s e n s i t i v e methods f o r the d e t e r m i n a t i o n of bismuth i n fuelsa W e found ehe i n v e r s e pokarog r a p h i c t e c h n i q u e to b e most wefbll, w i t h d e t e c t i o n aimits of about 50 ppb [ l l 6 , p . 2081. The bismuth i s d e p o s i t e d i n a pendent mercury drop eEect r o d e from HCE s o l u t i o n s i n which copper i s masked with thiocyanate, and measured duriw an a n o d i c s c a n . 19e a l s o developed a speetrsgraphic method of a t l e a s t e q u i v a l e n t s e n s i t i v i t y ; however, i t i n c o r p o r a t e s a preesncewtration by extraction w i t h dithieone and r e q u i r e s Parge salt samples.

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Electrochemical Research. For the analysis of molten-salt streams, electroanalytical tech~iquessuch as voltmetry and potentiometry appear to o f f e r the most convenient transducers for remote In-line measurements, Voltametq is based on t h e principle that when an i n e r t electrode is inserted into a molten salt and subjected to a changing potential v e r s u s the salt potential, negligible current will flow until a critical potential is reached at which one of the i o n s undergoes an e%ectrockernical reduction o r oxidation. The potential at which this reaction takes place is characteristic of the particular ion. If the potential is varied line a r l y with time, the current-voltage curve follows a predictable pattern which allows the concentration of the dissolved i o n to be determined (Fig. 5.12) We have studied the v ~ l t m e t r yof the c ~ r r ~ s f oproducts n which will be present i n ehe reactor s a l t streams in the ppm range. Relatively high concentrations of these corrosion products m y be measured by observing t h e current passing through the electrode system as the respective i o n s are reduced. Lower concentrations can be measured with the technique of stripping voltametry through observation o f the current produced when a corrosi~nproduct is oxidized from an electrode on which it has previously been plated (Pige 5.13). We have studied the electrochemical behavior of these elements in the MSW fuel solvent, EiF-BeP2-ZrFq [113,l14,%08, p . 192, lU], and in the proposed MSBR coolant s a l t , NaF-NaBF:, [ll4,lP6, 1151. Most of this work was concerned with the determination of the sxidation states of the elements, the most suitable e l e c t r o d e materials for their analysis, and the basic electrochemical characteristics of each element. Work is continuing to study the effect of the presence of one element upon the determination of another and the effects t h a t a flowing salt stream may have with regard to the determination. We have developed a voltametric methbd f o r the determination of the U3+/U4+ ratio in the MSRE fuel [llo]. T h i s method involves the measurement of the potential difference between the equilibrium potential of the melt, measured by an inert platinum electrode, and the voltammetric equivhe reltability alent of the standard potential of the u"/IJ'++ couple. of t h e method was. verified by comparison with values that were obtained We have completely automated this spectrophotolaetrically (Table 5 2.2) determination with a PDP-8 computer [ll?'] which operates the voltammeter, analyzes the data and computes the U ~ + / U ~ ' B - ratio ~ e c a u s eprocessing (chapter 11) presents the possibility P Q having ~ bismuth as an impurity in the fuel, a method fur Fts detemination i s rein LIPquired. We have characterized the reductive behavior of Ei3' BeP2-ZrF4 [%I53 and have found tliat it is rather easily reduced to the metal. A s an impurity in the fuel salt, bismuth will probably be present in the metallic state, s o that some oxidative pretreatment of the melt will be necessary before a voltametric deteminathon of bismuth can be peb-fomea. The measurement of the concentrations of protonated species in the proposed MSBR coolant salt is of interest because of the potential use of the coolant for the containment of tritium. The measurement couHd also be used to evaluate the effect of p r o t o n concentrations on corrosion rates and as a p o s s i b l e detection technique f o r heat exchanger leaks. We are p r e s e n t l y investigating a rather unique electroanalytical technique that is specific for hydrogen [ 1 1 4 , p . 7 4 , W5]. The method is e

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based on t h e d i f f u s i o n of hydrogen i n t o an evacuated p a l l a d i m t u b e e l e c t r o d e when NaBF4 m e l t s are e l e c t r o l y z e d a t a c o n t r o l l e d p o t e n t i a l . The p r e s s u r e g e n e r a t e d i n t h e e l e c t r o d e i s a s e n s i t i v e measure of p r o t o n s a t ppm c o n c e n t r a t i o n s . The technique o f f e r s t h e advantages of s p e c i f i c i t y , a p p l i c a b i l i t y t o i n - l i n e a m a l y s i s , and t h e p o s s i b i l i t y of a measurement of t r i t i u m t o hydrogen r a t i o s i n t h e c o o l a n t by counting a sample c o l l e c t e d from t h e evacuated tube. En a l l e l e c t r o a n a l y t i c a l measurements i t i s a d i s t i n c t advantage t o have an i n v a r i a n t r e f e r e n c e p o t e n t i a l t o which o t h e r e l e c t ~ o c h e ~ ~ i c d r e a c t i o n s may b e r e f e r r e d on a r e l a t i v e p o t e n t i a l s c a l e . A p r a c t i c a l r e f e r e n c e must b e f a i r l y rugged and of u n i t c o n s t r u c t i o n . W e were a l s o c o n f r o n t e d w i t h f i n d i n g s t r u c t u r a l materials which would b e compatible Success w a s f i n a l l y r e a l i z e d w i t h a M i / N i ~ ' 2 with the fluoride m e l t s . r e f e r e n c e e l e c t r o d e , shown i n Fig. 5.14, where t h e r e f e ~ e n c es o l u t i o n (LiF-BeF2 s a t u r a t e d with NiP2) i s c o n t a i n e d i n a s i n g l e - c r y s t a l %aF3 cup [ I l l , p. 1 8 4 , 1181. W e have determined s t a n d a r d electrode p o t e n t i a l s (Table 5 - 1 3 ] f o r s e v e r a l metal/metal-ion couples which w i l l b e p r e s e n t i n the r e a c t o r s a l t streams [110, p . 2 O l ] . These e l e c t r o d e p o t e n t i a l s provide a d i r e c t measure of t h e r e l a t i v e thermodynamic s t a b i l i t y of e l e c t r o a c t i v e s p e c i e s i n t h e m e l t s . This i n f o ~ ~ l l a t i oins used i n e q u i l i b rim c a l c u l a t i o n s t o determine whish i o n s can b e expected t o b e p r e s e n t at different m e l t potentials. Spectrophotometric Research. - The effort i n o u r s p e c t r o p h o t o m e t r i c r e s e a r c h program f o r molten s a l t s i s d i r e c t e d toward t h e d e ~ e l o p m e n tof methods t h a t can be used f o r t h e i n - l i n e d e t e r m i n a t i o n of d i s s o l v e d species i n t h e s a l t stream of t h e KSBR and t h e s a l t r e p r o c e s s i n g system. Analyses of molten s a l t s are a l s o performed f o r r e s e a r c h s t u d i e s r e l a t e d t o t h e MSR program, and where a p p l i c a b l e , s p e c t r o p h o t o m e t r i c methods a r e used t o c h a r a c t e r i z e the v a r i o u s s p e c i e s of imterest i n these s a l t s . Materia%s problems are encountered i n t h e d e s i g n o f compartments t o h o l d t h e molten samples f o r s p e c t r o p h o t o m e t ~ i cexamination. Because t h e molten f l u o r i d e s react w i t h t h e u s u a l l y employed l i g h t - t r a n s m i t t i n g glasses, other cell d e s i g n s had to be cle.ireloped. The p e n d e n t - d ~ ~ p techn i q u e e1191 t h a t w e developed first w a s Eater r e p l a c e d w i t h the c a p t i v e l i q u i d c e l l [l20] i n which molten s a l t s are c o n t a i n e d by v i r t u e of t h e i r s u r f a c e t e n s i o n , 88 t h a t no window material i s r e q u i r e d . A concept h a s been prsposed f o r t h e u s e of t h i s c e l l i n an i n - l i n e system [l2I]. A l though t h e l i g h t p a t h l e n g t h through a salt i n a c a p t i v e - l i q u i d c e l l i s d e t e r m i n a b l e , i t i s not f i x e d . The need for a f i x e d p a t h l e n g t h p r o m ~ t e d t h e d e s i g n and f a b r i c a t i o n of a g r a p h i t e c e l l w i t h s m a l l diamond p l a t e windows ( P i g . 5 - 1 5 ) [108, p . 1681, which h a s been s u c c e s s f u l l y used i n a number of r e s e a r c h a p p l i c a t i o n s . Another fixed-path-length c e l l which is s t i l l i n t h e development stage makes use of "porous m e t a l " [ E l 7 , p a 1611. Porous m e t a l i s a f o i l t h a t c o n t a i n s a number of s m a l l i r r e g u l a r p i t s formed by an e l e c t r o c h e m i c a l p r o c e s s ; many of t h e s e p i t s are e t c h e d completely through t h e f o i l , s o t h a t l i g h t can b e t r a n s m i t t e d through t h e ' metal. We have some porous metal wade from H a s t e l l o y N and p l a n t o t e s t its USE? f Q 8 Cell CoIlStrUctiQn.

w-

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i

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159

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Table 5.1 3. Standard electrode potentials in molten fluorides <:.,<,....

Electrode couple

Be(II)/Bc Zr(W)/Zr U(IV)/WI)

a-(nr)icr Gr(IEH)/Cr(II) E.e(II)/Fe Ni(II)/Ni Fe(III)/Fe(II) .... ..... .... ....A

I

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In

-1.480 -0.901 -0.514 -0.390

0.000

0.000

0.166

-8.200

y..4

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0.413 0.0

astandad Ftate for an solutes except beryllium(BI) is the hypothetical unit mole fraction solution. The beryllium(I1) standard slate is the solvent composition kiF-BeF2 (66-34 mole

5%). bC E . Baes, Jr., Themmiyizamics, vol. 1 , MEA. Vienna, 1966 (values in LiF-BeF2. converted t o 500째C).

.... " .i'

500"Cb

-2.211 1.772 -1.517

-2.120 -1.742

-0.410

Calcuiated,

The latest innovation in cell design is an optical probe which lends itself to a sealable insertion into a molten salt stream [H14, p. 7 1 1 . The probe makes use of multiple internal reflections with a slot of appropriate width cut through some portion of the internally reflected light beam (Fig. 5.l6). During measurements the slot would be below the surface of the m o l t e n s a l t and would provide a known path length for absorbance measurements. It is proposed that the probe could be made of LaF3 Spectrophotometric studies uf uranium in the 4-3 oxidation state have shown that it is a likely candidate f o r in-line determination in t h e reactor fuel t l 2 2 , 163, p. 1631. An extremely sensitive absorption peak f o r ~ 4 - 9 -suggests its use for monitoring possible leakage O S uraniumbearing fuel i n t o the coolant s a l t [l89, p. 1 6 4 5 . Quantitative characterizations, including absorption peak positions, peak intensities, and the pe2+, , cr2+* 61-36, u5+, assignment 0 % spectra, have been made f o r ~ i ~ + P U ~ + ,~ r ’ - % ~ d~ 3 + ?~m3+, UO&+, ~ u 2 + , %’+$ m3+, CO’+, MO?+, cr0h2-> ~r and H O ~ + ~Semiquantitative characterizations i n c l u d i n g absorption peak positions, approximate peak intensities, and possible assignment of spectra, have a l s o been made f o r ~ i ~ v2+$ f ,v3+, E U ~ +sm2+9 ~ cm3+, and 0 2 - * Me &re d S Q investigating protonated species in the proposed coolant salt by spectrophotometric methods. Evidence for the existence of hydrogen-containing impurities in XaBP4 was first obtained from nearinfrared spectra of the molten s a l t and in mid=-infrared spectra of pressed pellets of the crystalline material [116, pp. 9 4 - 9 6 ] . Deuterium exchange studies are being perf~meclto characterize the protonated species in the molten fluoroborate melts [114, p p . $31. Two very sensPtive absorption peaks have been identified and are attributed to species that contain -OH and -OD. The abs~rptionspectra of several other species have been observed in flusroborate melts [ U 6 , p . 1361. Our spectrephotometric program is also providing data for the identification and determination of solute species in the various melts of interest f o r the f u e l salt reprocessing system [l15’je a

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Transpiration and Cas Analysis. - Although the transpiration approach offers the advantage of locating transducers for effluent gas analysis uts si de sf the highest radiation zones, these devices will still receive exposure from fission-product gases and their daughters and possibly from particulate radioactive materials, and thus they will require remote operation. The only research performed on such transducers has been on methods for batch samples of the MSM fuel. The electrolytic moisture monitor was demonstrated to provide more than adequate sensitivity f o r the measurement o f water f r o m the hydrofluorination method for ox2lde and to have adequate tolerance for operation at the anticipated radiation levels [lO8, p . l881. We have developed a method for the remote measurement of micromolar quantities of HF generated by hydrogenation of f u e l samples using a trappingthermal-conductivity method [108, p . 1891.

LIGHT BEAM

Pig. 5.16.

% % s t t e do p t i c a l probe for spectral analysis.

163

Commercial gas chromatographic components f o r t h e high-sensitivity measurement of permanent gas contaminants are not expected t o be acceptable a t the radiation levels of the E B H P off-gas. Valves contain elastomers which are subject to radiation damage and w%ioseradiolysis products would contaminate the carrier gas. The more sensitive detectors generally depend on ionization by weak radiation sources and would obviously b e a%f e c t e d by s a m p l e activity. A p r ~ t ~ t y pof e an all-metal sampling valve 61231 has been constructed to effect 6-way, double-throw switching of gas streams with closure effected by a pressure-actuated metal diaphragm. We developed a helium breakdown detector capable of measuring sub-ppm concentrations of permanent gas impurities in helium. Use of t h i s detector in a simple chromatograph on the purge gas of an in-pile capsule t e a t (&nR-49-61 demonstrated that it w a s n o t affected by radioactivity [ l 2 4 ] . Ironically, subsequent tests with a more h i g h l y purified carrier gas revealed sporaaiciuy n o i s y operation caused bgr u n s t a b l e d i s c h a r g e s ~ 1 2 3 1 . Tests t o circumvent this by controlled impurity additions were suspended because of more exigent problems. The analysts of the coolant cover gas involves less radioactivity but more complex chemical problems. Currently we are investigating methods f o r the determination of condensable material tentatively i d e n tified as BP3 hydrates and hydrolysis products [llO, p . 2Q%] and for other â‚Źoms of protons and tritium. We believe that "dew-point" and diffusion methods offer promise f o r such measurements ElI-4, p . '921. W e have developed an improved Karl F i s c h e r c o ~ l o ~ ~ i e t titrator ric to p r o v i d e calibration measurements of "H20'' in both simulated and actual C Q V ~ ~ gas s m p l e s .

In-Line Applications. - We recently demonstrated the first successful chemical analysis for a flowing molten fluoride s a l t stream [ll4, pp. 6 9 - 7 0 ] by measuring U3+/U4* r a t i o s in a l o o p being operated to determine the effect s f salt QR Hastellsy N under b o t h oxidizing and reducing conditions. The test facility is a Hastellay N thermaP--convectisn loop (NCL-21) in which LiF-BeF2-ZrFq-UP4 circulates at about f i v e linear feet per minute. The analytical transducers are platinum and iridium e l e c t ~ ~ that c l ~ are installed in a surge tank where the temperature is + over a p e r i o d c u n t r o . ~ e c iat 650"~. ~e have monitored the u ~ * / L J ~ratio of several months on a completely automated basis. We desfgned a new cyclic voltameter, which provides several new capabilities f o r e l e c t ~ o chemical studies on molten-sale system, f o r use with this system. The voltammeter can be directly operated by the PDP-8 family of computers [ U 6 , p . 1381. A PDP-8/1 computer is used to control the analysis system, analyze the experimental o u t p u t , make the necessary calculations, and were being established, print out the results. A s equilibrium c~nditi~n~i increases ~n the ~ 3 +concentration were f o l l o w e d as chromium SIQWIY d i s s s ~ v e cfrom ~ the ~ a s t e ~ l oNy, causing ~ 4 fto be reduced. Precipitous d r o p s in the U3* concentrations were also observed due to the i n t r ~ d u c t i ~ n of oxidizing Contaminants when metal specimens were inserted into the melt (Pig. 5 . 1 7 ) . Work is continuing toward the application of o u r electroanalytical research experience with t h e C O ~ ~ S S ~ Q I p- Ir o d u c t i o n s f o r their determination in this system.

164

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165

P r o v i s i o n s h a v e b e e n m d e i n t h e d e s i g n of t h e two MSRP e n g i n e e r i n g I o o p s , t h e C o o l a n t S a l t Technology F a c i l i t y (CSTP) and t h e Gas System Technology F a c i l i t y (GSTF), f o r t h e i n s t a l l a t i o n s f o u r a n a l y t i c a l t r a n s d u c e r s . T h i s w i l l p r o v i d e us w i t h e x p e r i e n c e on s y s t e m s where t h e opera t i n g c o n d i t i o n s w i l l more n e a r l y r e p r e s e n t t h o s e which w i l l b e e n c o u n t e r e d w i t h an o p e r a t i n g r e a c t o r .

F u t u r e Work

.......? -.,

.... <.=;

A v a r i e t y of t a s k s must b e performed t o a c h i e v e a c o m p l e t e l y v i a b l e i n - l i n e s y s t e m f o r a n o p e r a t i n g r e a c t o r . The e l e c t r o c h e m i c a l t e c h n i q u e a p p e a r s t o b e t h e prime c a n d i d a t e f s r p r a c t i c a l i n - l i n e f u e l a n a l y s i s bec a u s e of t h e s i m p l i c i t y of i t s t r a n s d u c e r s ; however, t h e a d v e n t of t u n a b l e Lasers 11251 and t h e development of e x t e n d e d p a t h c e l l s may make t h e s p e s t r o p h o t s m e t r i c methods c o m p e t i t i v e . On t h e b a s i s of p r e s e n t p r ~ j e c t i o n s ,a s i g n i f i c a n t f r a c t i o n of t h e development e f f o r t s h o u l d b e expended i n t h e a d a p t a t i o n o f e l e c t r o c h e m i c a l methods t o t h e i n - l i n e a n a l y s i s of t h e s a l t i n e n g i n e e r i n g t e s t f a c i l i t i e s s u c h as t h e CSTF and GSTP. The i n i t i a l i n - l i n e a p p l i c a t i o n sf e l e c t r o a n a l y t i c a l methods ( i n NCL-2%) uncovered p r a c t i c a l problems, a n d , w h i l e t h e s e problems have b e e n r e s o l v e d , we e x p e c t t h a t o t h e r s w i l l b e enc o u n t e r e d i n t h e h i g h e r f l o w s y s t e m s . In the immediate f u t u r e w e will y sat etme t o c o n c e n t r a t e o u r e l e c t r o a n a l y t i c a l r e s e a r c h on t h e f l u ~ ~ ~ b ~s p d e t e r m i n e t h e n a t u r e of t h e p r o t o n a t e d s p e c i e s and e q u i l i b r i a i n v o l v e d so t h a t i n - l i n e voltammograms can b e i n t e r p r e t e d . I n f u t u r e r e s e a r c h t h e â‚Źrandamenta% c h e m i s t r y of t h e m u r e n o b l e m e t a l s $ e . g . , M o 9 Nb, T c , and Ku s h o u l d b e s t u d i e d . Nost of o u r e l e c t r o c h e m i c a l r e s e a r c h h a s b e e n p e r f s m e d i n MSW s a l t c o m p o s i t i o n a t around 580'6 w i t h some s t u d i e s of t h e e f f e c t s of t e m p e r a t u r e on d i f f u s i o n c o e f f i c i e n t s [ 1 2 6 , 1 2 7 , 1 2 8 ] , and much of the f u t u r e r e s e a r c h s h ~ u l db e performed u n d e r t h e s e same c o n d i t i o n s t o p e r n i t a d i r e c t i n t e r s o m p a r i s o n of r e s u l t s . B e f o r e a p p l i c a t i o n of voltammetry t o r e a c t o r s , d i f f u s i o n c o e f f i c i e n t s i n LiP-BeF2-ThP4-UF~ t y p e melts must b e measured a t o p e r a t i n g t e m p e r a t u r e ; t h i s awaits sel e c t i o n of t h e exact c o m p o s i t i o n of the b r e e d e r f u e l . To f u l l y e x p l o i t i n - l i n e measurements i t will b e n e c e s s a r y to dev i s e methods f o r t h e o x i d a t i o n of d i s p e r s e d metals i n s a l t streams. Such t e c h n i q u e s are d e s i r a b l e f o r c o r r o s i o n p r o d u c t s and are e s s e n t i a l f o r the measurement of b i s m u t h whfch i s p r e d i c t e d t o be t r a n s p o r t e d p r i m a r i l y as e l e c t r o - i n a c t i ~ e d i s p e r s e d m e t a l . Gaseous o x i d a n t s s u c h as HP and f l u o r i n a t e d h y d r o c a r b o n s s h o u l d b e i n v e s t i g a t e d f o r t h i s a p p l i catFon The s p e c t r a l r e s e a r c h program staouPd be c o n t i n u e d w i t h i n c r e a s e d emphasis on t h e i n situ measurement of p r o t o n a t e d s p e c i e s i n NaBF4. These t e c h n i q u e s are needed to i n v e s t i g a t e exchange rates of hydrogen i s o t o p e s i n order t o e v a l u a t e t h e use of t h e c o o l a n t f o r t r i t i u m cont a i n m e n t . The F o u r i e r t r a n s f o r m s p e c t r o m e t e r shouHd a l s o b e used t o i n v e s t i g a t e i n f r a r e d e m i s s i o ~t~e c h n i q u e s f o r measurement of csntamiants, suck as h y d r o l y s i s p r o d u c t s , i n t h e c o o l a n t and i t s c o v e r g a s . Emphasis should then b e s h i f t e d t o s p e c t r a l s t u d i e s of r e p r o c e s s i n g stream e

166 I n - l i n e methods for r e p r o c e s s i n g streams must u l t i m a t e l y b e developed, b u t t h e a n a l y t i c a l requirements are n o t y e t e s t a b l i s h e d . Hethods f o r t h e i n - l i n e a n a l y s i s of t h e f u e l w i l l b e r e a d i l y a d a p t a b l e t o f l u o r i d e r e p r o c e s s i n g streams, and measurements i n t h e less c o r r o s i v e c h l o r i d e stream should b e much s i m p l e r . Moreover, t h i s less formidable s o l v e n t has encouraged o t h e r s t o work i n t h e m e d i m and t h e l i t e r a t u r e can be e x p l o i t e d when requirements are e s t a b l i s h e d . The l o w t o l e r a n c e of t h e $EBB f u e l to o x i d e contamination wecessitates the development of i n - l i n e techniques f o r o x i d e measurement. P r e s e n t l y , w e feel t h a t a c o u n t e r - c u r r e n t h y d r o f l u o r i n a t i o n t e c h n i q u e ( t r a n s p i r a t i o n ) o f f e r s t h e most promising approach t o t h e i n - l i n e measurement ~f o x i d e , w i t h ekectrocherdcal measurement of OH- a f t e r BF e q u i l i b r a t i o n o r t h e spectrophotometry of sxyanions [ I 1 6 p a 136 ] as a l t e r n a t i v e s . The in-line a p p l i c a t i o n of t r a n s p i r a t i o n methods w i l l r e q u i r e t h e development of p r e c i s e metering system f o r loa s a l t f l o w s . W e have an immediate need f o r t r a n s d u c e r s (under development) f o r measurement of h y d r o l y s i s p r o d u c t in the cover gas of the GSTP. Later, methods of improved s e n s i t i v i t y w i l l b e r e q u i r e d t o a n a l y z e t h e helium cover gas of t h e GSTP. We have a c q u i r e d an u l t r a s o n i c d e t e c t o r 61291 which w e w i l l c o u p l e w i t h an e x i s t i n g chromatograph t o p r o v i d e an i n s t r m e n t f o r the s e n s i t i v e d e t e r m i n a t i o n of contaminants Pn GSTP

<."' -...

D i r e c t y-spectrometry (of demonstrated value i n t h e EEXU%>must b e i n c o r p o r a t e d i n t h e MSBR. Some e x p e r i m e n t a l work, e.g., measurement The of P a , w i l l b e needed but does n o t appear t o merit h i g h p r i o r i t y . d e s i g n of s y s t e m for the s a f e i n s t a l l a t i o n of t r a n s d u c e r s i n radioa c t i v e streams i s b a s i c a l l y an e n g i n e e r i n g probPem and has been d e l a y e d , as has i n v e s t i g a t i o n sf t h e e f f e c t s of r a d i a t i o n on t h e i n - l i n e methods; t h e s e need t o be pursued a f t e r t h e b a s i c methods are developed.

The a n a l y t i c a l research and development program h a s c l e a r l y demons t r a t e d t h e f e a s i b i l i t y of performing c e r t a i n c r i t i c a l d e t e r m i n a t i o n s i n - l i n e ana has p r o v i d e d strong i n d i c a t i o n s that w e can ultimately a c h i e v e an optimum program f o r t h e a n a l y t i c a l sequirem@nts of P E B b . W e b e l i e v e t h a t with t h e p o s s i b l e e x c e p t i o n sf t h e i n - l i n e oxide det e r m i n a t i o n , p r o p e r l y funded a n a l y t i c a l development can keep pace w i t h t h e TXst O f the MSW teChnQ%OgyPPOgPXII.

'551

. ..

,.... ......,

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16%

References f o r Chapter 5

1. Clark Goodman e t a l . , i h c l e a r Problems of Wsn-Apeou P l u i d F w l e d !?eactors, Massachusetts Institute of Technology USAEC R e p o r t ~

11HT-5000 (Oct

0

15, 1952) *

2.

George S c a t c h a r d e t a l . , Chemlcal Problem of JJon-Aqueous Fluid Pue Zed Reactors, Massachusetts Institute of Technology , USAEC Report MIT-5BOB ( O c t . 15, 1 9 5 2 ) .

4.

W. R . G r i m e s and %a. G . ~ 1 1 High , Temperature FtleZ Systems. L i t a a t u r e Smvey. Y-659 (July 2 8 , 1950).

5.

W. R. G r i m e s e t aZ., "Chemical Aspects of Molten S a l t Reactor fuel^,'^ in F l u i d Fuel Reactors, J. A . Lane, E. G . EfasPherson, and P r a n k Mashan, e d s , Addison-Ideskey Cambridge, Mass. (1958) e

6.

W. 8. G r i m e s ,

P ~ b l i s k i ~C g oo

a

Ins

"Phterials Prsblems i n Molten S a l t R e a c t o r s , " i n

Materials m d F u e k f o r High l'emperutum JJucZear Enepgy A p p l i @&ions, e d , by M. T. Simnad and E. R. Zumwalt, the M . B . T . Press

Mass

(1964)

8.

hTs R. G r i m e s , NucZ. AppZ. Tech.

9.

R . E. ~ h o m a ,Chemical Aspects o f !.ERE Operat-lon, Om%-4658 (December 1971)

137 (2.970).

L

10. ConceptzlaZ Design Study of a Single-Fluid Molten-Salt Breeder Reactor, OWadE-454% (1971). 11.

L. Brewer e t aZ., PIDBC-155% (1945) and L. B r e w e r , The C k m L s t q ma' MetaZZurgy of IdiscelZaneous MatemGzk; Thermodynamics L. L . Q u i l l , ed., M c G r a w - H i l l ,

13.

Mew York, pp. 76-192

(1950).

PI. Flood and T . F o r l a n d , Acta Chim . Scand. 1, 592 ( 1 9 4 7 ) , and H. Flood, 91. F o r l a n d , and K. G r j o t h e i m , Z. znorg.. AZZgem. C"nem. 276, 289 (1954) e

14.

R. C. B r i a n t , A . M. Weinberg, E.

JJuc. sci. EEg.

2,

79% ( 1 9 5 9 ) .

S. B e t t i s ,

and W. K. Ergen, e t ale,

17. W. R. Grimes, N o V. Smith, and @. M. Watson, J . P h y s . Chem. 62, 862 (1958) e

21. f G R Program S e ~ a n n .Prsgr. R e p t . Feb. 28,

2968, o m - 4 2 5 4 , p . 88.

-

I....

.....

riii. % . ! . %

24.

R. E. Thoma, e d . , Phase D i a g p m s of Nuclear Materials, o m - 2 5 4 8 (NQV. 6 $ a959>.

25 *

L. V. Jones e t a l . ,

""Base E q u i l i b r i a in the Ternary Fused-Salt System LiP-BeF2-UP4," J . Am. C~PCTRI.SSC. 4 5 , 79-83 (1962)

26 s 27

&'

R. E. Thoma e t a l e , "Phase E q u i l i b r i a in the System BeF2-ThF4 LiF-BeFy-ThF4,'s €7. P h y s . aem. 66b9 865 (1960)*

and

_p_

28

29

e

0

R. E. Tksma et d.,"Phase Equilibria in the Fused S a l t System LiP-rnFi+ and NaF-TkF4,B' ei. P k I S . nem. 6 3 , 1266 (1959) s __g

30

e

21

a

e. F. w@aver e$ GZ., '2?hase Equilibria in t h e systems UP4-ThF4 and %~F-UPL,-T%FL+," 6. Am. C e ~ m .So@. 4 3 , 213 (1960) &E€? Program Semiam. Progr. R e p t . JuZy 32, 9964, O m - 3 7 0 8 , p . 2 1 4 .

.-

z"

....

169

32.

K. A . Romfserger e t aZ., "Phase E q u i l i b r i u m Studies in the U r a n i u m ( 1 V ) Oxtde-Zirconim Oxide S y s t e m , " presented at 151st National ~ e e t i n g of American Chemical Society P i t t s b u r g h , Pa %Iarch21-31 1966 a a

34.

C.

E. B m b e r g e r , R . G . Ross, and C. F. Baes, Jr., J . ITn02ng- nsilcz.

eiZem. 3 3 , 767 (1971) 35.

C . F. Baes, J r . , NucZem li&taZZw?gy, Vo1. 15, Symposium on Reprocessing 0 % Nuc%ea~F u e l s , e d . by P. Chfotti, USAEC-COXF 690801, 63.7 (1969) e

46.

MSR Program bS@mimneP ~ o g r .R e p t . Feb. 28, 2970, ORNL-4548, p . 1 5 2 .

41.

S . Cantor e t aZ., Physical Prspcwties of MoZ-t:e~SaZt ,?eactor Fuel, OmL-TM-2316 (Augue t 1868) 0

43.

W. D. bfanly e-t: ak., Ppogress i n Nuclear Pnergg S e r i e s p . 164, Pergamon Press, Inc., L o n d ~ s t (1960).

44.

id. D. Manly e t aZ., FZuid FueZ Reactors, p . 595, e d . by 9. A. Lane, E. G . MacPherssn, and Frank Maslan, Addison-Wesley Publishing eo , Cambridge, Mass. (1958)

117, V s l .

2,

a

45. ..... .:<$

. .. .....

J. H. ~ e ~ ama n R. B. Evans EPP, p . 557 in Confgrence on Corrosion of Reactor MatemkZs, June 1 9 6 2 , Proceedings, Vol. HE, International Atomic Energy Agency , Vienna (1962) e

@.

46

F. B a e s J P . "The Chemistry and Thermodynamics of Molten S a l t R E ? ~ C ~ QFluoride P Solutions )'' i n Pmceedilzgs of IAEA S~~mposiwn on Themnodynamics u i t h Emphmis on IducZear MateriaZs and A t o r r ~ cTlrcznsp o r t in So22kk, Vienna, Austria ( J u l y 1 9 6 5 ) .

47.

6 . Long,

Reactor Chsm. Biv. Ann. Progr. H e p t . Dec. 31, 2965, ORNL-

3 7 8 9 , p . 65.

48.

J. F. E l l i o t t and Eikol%y Glieser, Thermochemistry for Steelmaking, Q o l . 1, Addison-Wesley Publishing Co. , Inc. Reading, >lass (1960) e

49*

J. J. Kata and E . R a b i n s v i t c h , The Chemistry 06 Uranium, P a r t I , p. 401, P l s G r a w - H i 1 1 Book Company, Ins. N e w York (1951)

51

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52 * 53 * 54

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56

57

58

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6

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59

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62.

63

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64

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65 * 66

67.

68

69

C. F. Baes, JP. "The Chemistry and Thermodynamics of Halten S a l t Reactor F u e l s 9 ' ' Nuclear MetaZZUP6Jl.J 617-44, USLIE6 Coni=. 690803. (August 1969).

e

0

78 *

71.

MSR Frogram Sevriann. Progr. Re@.

74.

P. F. Blankenship and S. S. Kirslis, R e a c t m Chemistry D ; V . PPO~P.Rept. Des. 34, 9969, Owp9L-4229, p . 15.

75.

MSR Program Semiann. Progr. R s p t . Azlg. 31, 1971, 0 E-4928, pp. 54-5.

76,

IdSR Program Semiann. P’rogr. Rept. Peb. 29, 1972, OkNL-4782, in press.

77.

8. P . Wichner, Side Stream Processing f o r I o d i n e and Xenon R e m o v a l f r o n the MSBR, Om-CF-72-6-12, in press.

78.

P . N. Maubenreich, J. R. Engel, AhcZ. A p p l . Tech. 8, 118 (1970).

78.

E . G . Bohlmann, Heat Wansfer S a l t a t i o n , OWL=-Tbf-3744 (in press)

Peb. 28, 1969, OWLYL-4396, p . 139.

Ann.

s

$02”

Pifgh TempeFature S t e r n Gener-

e

& :.<.?

... ....

88,

E. 6%. Levin, 6. W. Robbins, and H . P. MsMurdie, Phase Diagrams fop Ceramists, The American Ceramic Society, Inc. Ohio ( 1 9 6 4 )

81.

V . 6 . Selivanov and V . V. Stender, Zhur. Neorg. Khim. % ( 2 ) , 448

(1958)

. A d

82.

0

Program Semiam. Progr. R e p t . Feb. 29, 1968, QRNL-4254, p . 21.

.... ..a,.

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84.

J. €3. Bates, J. P. Young, M. M. Murray, M. W. Kshn, and G . E. Boyd, J . InoPg. NucZ. Chem. to b e published (1972).

85.

flSR Program Semiam. Progr. Rep&. Feb. 29, 2972, OREU’L-4782, in press.

.....

.?L,,

86, IdSR Program Serniann. F ~ o g r .R e p t . Feb. 28, 1972, 8aE3L-4782, in p r e s s . .... .... .:.xq

87.

!SIR Progrm S e r r k m . P r o p . Wept. Aug. 32, 2971, O W - 4 7 2 8 , p . 1 4 5 .

88. NSR Program Semiann. P r o p . Rep$. Peb. 28, 2972, Q W - 4 7 8 2 , i n p r e s s . 89.

6. E. Wicks and P. E. Block, “Thermodynamic P r o p e r t i e s of 65 EPenaents , Their Oxides , Halides @arb i d e s 9 and N i t r i d e s p 11 Bureau sf Mines B u l l e t i n 605 (1963). $

90 e

s%aFJm( J o i n t Amy-Navy-Air Force) Interim Thermochemical Thermal Research Laboratory gan *

Tables, Dsw Chemical Company, Wdland, Michi-

91 92

93

e

0

94. 95

a

96

e

sa. 98

0

99

a

100

D

181

182

183

D

0

104.

105

s

106

e

107

e

E. L. C o v e r e , H. 6. Savage, and J. PI. Baker, J . Nuc2. Mater. 99 (1970).

34,

173

109.

MSR Paoogram Serniann. Progr. R e p t . Feb. 28, 1967, QRPJL-4119, p . 158.

110. NSR Prsgrm Semiann. P r a g r . Rept. Peb. 28, 2969, O W L - 4 3 9 6 , p . 200.

112.

A . Hsutzeeb and F. F. Dyer, G m a Spec-trrometric Stm&'%es of Fiss?:cn OmL-3151 (August 1 9 7 2 ) .

Prodwts i n the M%E3 113.

B. L. Manning, e. Maoaantov, "Rapid Sean V o l t m e t r y and ~%ranopotentiometric S t u d i e s of I r o n in Molten F l u o r i d e s ,Ii J . EZectroanaZ, Chem. 7 , 102-108 (1964)

114. MSR P r o g r m Semiann. Progr. Regt. Aug. 31, 2971, OWL-4728,

l119.

p . 75.

3 . P . Young and J. C . White, "A High-Temperature CeHb Assembly for ~pectrsphotometric studies in Mo1tem F l u o r i d e s " Anal Chem. 3%,

1892 ( 1 9 5 9 ) .

120.

J. P . Young, " W i n d o w l e ~Spectrephotometric ~ C e l l f o r Use w i t h Corr o s i v e L i q u i d s , " Anal. Chem. 3 6 , 390 ( 1 9 6 4 ) .

121. !dSE Program Senriaiizn. P r o p . Rept. Auy. 31, 2965, QRNL-3872, p . 1 4 5 .

124.

1GR Program Semiann. P ~ o g r . R e p t . &Zy

125.

B u l l e t i n MQ. 7012, Avcs Everett Research L a b o r a t o r y , Everett, Mass.

32, 1964, QKXL-3708, p . 3 2 8 .

(197%). 126.

D. %. bknning, "Voltametry of Iron in H o l t e n Lithium F l u o r i d e Potassium Fluoride-Sodium F l u o r i d e ," J , BZectroanaZ. Chem. 6 302

(1944). 127.

D. L. Manning, "Voltammetry of I r o n in Ms1ten L i t h i u m F l u o r i d e sdim F h ~ d d e - h t a s s i ~ m F i t l o r i d e , '' J . BZectroanaZ. Chem. 7 , 302 (1964) e

1128. G . Namantov and D. L. Planni-ng, "VoLtametry and Related S t u d i e s of Uranium in NoPten L i t h i u m Fhuoride-Beryllium Fluoride-Zirconium F l u o r i d e , ' 8 AnaZ. Chem. 3 8 , 1494 (1966).

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R e l a t i o n s h i p Between G r a p h i t e and Core Design ....

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The g r a p h i t e i n a s i n g l e f l u i d m o l t e n - s a l t r e a c t o r serves no struet u r d purpose o t h e r t h a n t o d e f i n e t h e f l o w p a t t e r n s of t h e s a l t and, of c o u r s e , t o s u p p o r t i t s o m weight. The requirements on t h e material are d i c t a t e d M O S ~ strQr@gr by n u c l e a r ~~nsiderations, namely s t a b i l i t y of t h e material a g a i n s t r a d i a t i o n - i n d u c e d d i s t o r t i o n , n o n p e n e t r a b i l i t y by t h e f u e l - b e a r i n g molten salt, and nonabsorption of xenon i n t o t h e g r a p h i t e . The p r a c t i c a l l i m i t a t i o n s of meeting t h e s e requirements i n tmrn.impsse c o n d i t i o n s on t h e c o r e d e s i g n , s p e c i f i c a l l y t h e n e c e s s i t y t o p r o v i d e f o r p e r i o d i c g r a p h i t e replacement and t o l i m i t t h e c r o s s - s e c t i o n a l area sf t h e g r a p h i t e prisms. We s h a l l f i r s t c o n s i d e r t h e n u c l e a r requirements imposed on the material.

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R a d i a t i o n damage i n g r a p h i t e has been e x t e n s i v e l y s t u d i e d s i n c e 1845 r e l a t i v e t o t h e Hanford p r o d u c t i o n r e a c t o r s , and more r e c e n t l y under t h e v a r i o u s European and American gas-cooled r e a c t o r programs [I]. I n t h e mid 1 9 6 0 ' s i t became i n c r e a s i n g l y a p p a r e n t t h a t g r a p h i t e h a s a f i n i t e l i f e t i m e i n a f a s t n e u t r o n environment, and t h e a n i s s t r s p i c a l P y - i n d u c e ~ c r y s t a l l i t e growth due t o damage u l t i m a t e l y works t o d e s t r o y t h e polyc r y s t a l l i n e bulk material. The flmence t h a t i s d e f i n e d as t h e u s e f u l l i f e t i m e sf t h e g r a p h i t e depends s ~ m e w h a ton t h e f a i l u r e c r i t e r i o n employed. The g r a d u a l d e t e r i o r a t i o n of t h e material would f i r s t r e f l e c t i n i n c r e a s e d xenon a d s o r p t i o n , followed by salt p e n e t ~ a t f ~and n eventually l o s s of mechanical i n t e g r i t y . The d e f i n i t i o n p r e s e n t l y assumed i s t h a t the m a t e r i a l undergoes no significant r a d i a t i o n - i n d u c e d bulk expans i o n , c e t a i n l y a c o n s e r v a t i v e assumption. I f t h e g r a p h i t e w e r e t o s u r v i v e the l i f e sf the p l a n t i n a high-power d e n s i t y m o l t e n - s a l t ~ e a c t o r (a peak power d e n s i t y of 100 watts/cm3), i t would have to endure a dama n e u t r ~ n s e c m -which ~~ is about t e n t i m e s fluence of t h e o r d e r of 3 x what t h e b e s t e x i s t i n g material w i l l w i t h s t a n d . S a l t p e n e t r a t i o n into t h e g r a p h i t e i s r e s t r i c t e d by s u r f a c e t e n s i o n i f t h e e n t r a n c e p o r e d i a m e t e r s t o t h e i n t e r n a l id s t r u c t u r e of t h e g r a p h i t e are of t h e o r d e r s f 1 urn o r less. Seepage of salt i n t o t h e g r a p h i t e would l e a d t o l o c a l hoe: s p o t s which could e a s i l y a t t a i n temperat u r e s of l%00-120Q째C a t which t h e g r a p h i t e damage rate i s i n c r e a s e d by a f a c t o r of two o v e r t h a t a t 700째C [ 2 ] . F o r t u n a t e l y t h e p o r e s i z e requirement i s e a s i l y m e t by any h i g h - q u a l i t y f i n e - g r a i n e d g r a p h i t e , and t h i s r e g u i ~ e m e n tl e a d s t o no d e s i g n OK r n a t e ~ i a lr e s t r i c t i o n . The e x c l u s i o n of xenon-$35 from t h e p o r e s i n t h e g r a p h i t e w i t h i t s a t t e n d a n t i ~ p r o v e r n e n tFn b r e e d i n g r a t i o i s d i s c u s s e d i n d e t a i l elsewhere ( s e e Chapters 4 and 8 above). T r a n s l a t e d t o a materials requirement,

.= ... .....

175 gs

xenon e x c l u s i o n i m p l i e s e f f e c t i v e gas p e r m e a b i l i t i e s of cm2/sec helium STB o r less, roughly a pore e n t r a n c e d i a m e t e r requirement of 0.01 p o r l e s s . Such p o r e t e x t u r e s are n o t a t t a i n a b l e i n t h e o r d i n a r y f a b r i c a t i o n of b u l k g r a p h i t e . The requirement can b e e a s i l y m e t by pyrol y t i c d e p o s i t i o n of carbon o n t o a b u l k g r a p h i t e , a l t h o u g h q u e s t i o n s of r a d i a t i o n s t a b i l i t y again arise.

The e x i s t e n c e of a f i n i t e g r a p h i t e l i f e t i m e f o r c e s t h e r e a c t o r des i g n t o %ow power d e n s i t i e s o r t o p e r i o d i c g r a p h i t e removal, as d i s c u s s e d i n Chapter 4 . W e s h a l l concern o u r s e l v e s h e r e w i t h t h e problem of graphi t e f a b r i c a t i o n and i t s e f f e c t on d e s i g n . The requiremmt f o r s a l t exe l u s i o n , and thereby a f i n e - g r a i n e d g r a p h i t e , a l s o determines t h a t t h e geometric c r ~ s s - s e c t i o n sf t h e g r a p h i t e prisms b e k e p t small. This is n e c e s s i t a t e d by t h e i n a b i l i t y to c o ~ t r 0 1m i c r o s t r u c t u r e t o t h e d e s i r e d d e g r e e i n forming and h e a t - t r e a t i n g l a r g e c r o s s s e c t i o n s . S m a l l s e c t i o n s a l s o have t h e advantage of minimizing thermal g r a d i e n t s i n t h e g r a p h i t e r e a c t o r o p e r a t i o n and t h u s r e d u c i n g t h e r a t e of r a d i a t i o n damage. Pat t h e s e v e r a l design s t u d i e s f o r M S R ' s , the problems of graphite removal and p r i s m geometry have been s o l v e d i n s e v e r a l d i f f e r e n t ways. I n t h e r e f e r e n c e design 633 t h e care c o n s i s t s e n t i r e l y of s q u a r e p r i s m s approximately .four i n c h e s on a s i d e . In t h e c e n t r a l core zone (Zone e> t h e reqUir@lllent 0% 1 3 . 2 VSlUrn@ p e r c e n t s a l t leads to SeCtiOnS W i t h SmEllE h o l e s o r i n t e r p r i s m s l o t s (see F i g . 6*l)* S a l t volume is t r a d e d between c e n t r a l h ~ l eand s l o t s to s i m p l i f y o r i f i c i n g of t h e s a l t flow. For %he o u t e r c o r e region (Zone 11) t h e r e q u i r e d s a l t volume of 37% is o b t a i n e d by opening up the c e n t r a l a x i a l h o l e (Fig. 6 . 2 ) . The e n t i r e c o r e is supp o r t e d by Mastelloy t i e r o d s and g r i d p l a t e a d is p e r i o d i c a l l y removed as a u n i t . Although t h e s q u a r e c r o s s - s e c t i o n p e r m i t s e a s y f a b r i c a t i o n of t h e base s t o c k g r a p h i t e , t h e p o s s i b l e need t o p y r o l y t i c a l l y treat the i n t e r i o r s u r f a c e of t h e h o l e p r e s e n t s a formidable f a b r i c a t i o n problem. ~taisp r o ~ e mwas circumvented in t h e ~ b a s c os t u d y ~ 4 1 ,which s u b s t i t u t e d a s l a b d e s i g n f o r the s q u a r e p r i s m s ( s e e F i g s . 6 . 3 and 6 - 4 ) - Tke s l a b s are assembled i n t o h e x a g o n a l e l e m e n t s , each of which can b e removed as a u n i t ts p e r m i t p a r t i a l c o r e replacement. A s i m i l a r s l a b design w a s u t i l i z e d i n t h e study of a demonstration r e a c t o r 151, except t h a t RCJ p r s v i s i ~ nw a s made f o r g r a p h i t e replacement due to t h e l O W power sbeHlsity in t h e Core. Mechanical a n a l y s i s [ 6 f h a s i n d i c a t e d there a r e no s i g n i f i c a n t t h e r m a l o r r a d i a t i o n - i n d u c e d stresses i n any of t h e d e s i g n s .

General Background

G r a p h i t e h a s been employed as a n u c l e a r material as lofag as t h e r e have been r e a c t o r s . It formed t h e moderator in t h e Stagg F i e l d experiment and t h e p r o t o t y p e Oak ~ i d g eI%X3phite Reactor. The f i r s t e x t e n s i v e ex-

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G r a p h i t e moderator element for Zone P sf t h e MSBR df2Sigfi.

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Fig. 6.3. Top detail of t h e gb-aphite moderator element as proposed in t h e Ebasco Design Study.

186

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Fig. 6 . 4 . Cross-section of the Zone 1 moderator element as proposed i n t h e Ebaseo Design Study.

181

p e r i e n c e w i t h g r a p h i t e w a s a c q u i r e d i n t h e Hanford p r o d u c t i o n r e a c t o r s and somewhat l a t e r i n t h e B r i t i s h ga~-coolied r e a c t o r s , a l b e i t a t lower t e m p e r a t u r e s and f l u e n c e s t h a n apply t o t h e MSR's. basre r e c e n t l y t h e Dragon Reactor i n i t i a t e d t h e u s e of g r a p h i t e a t t e m p e r a t u r e s i n t h e lOQO"6 range, followed s h o r t l y by t h e Peach Bottom Reactor in t h e U.S. and t h e AVR Reactor i n Germany. C u r r e n t l y , t h e gascooled r e a c t o r s are beimg designed o r o p e r a t e d to t a k e g r a p h i t e temperat u r e s i n t h e 1200-l300"6 t e m p e r a t u r e range. Pauch of t h e e x p e r i e n c e and d a t a o b t a i n e d i n t h e gas-cooled r e a c t o r program i s d i r e c t l y a p p l i c a b l e t o MSR's. In p a r t i c u l a r , d a t a t a k e n a t H a f o r d i n t h e mid-1968's spanning t h e temperature range 300-%100"6 f i r s t i n d i c a t e d t h e f i n i t e l i f e t i m e of g r a p h i t e s u b j e c t t o neutron-induced damage, i.e., i t s e v e n t u a l dimensional e ~ p a n s i o nand l o s s o f mechanical integrity. In l a t e 1968 a program w a s i n i t i a t e d a t BRNL t o evaluate g r a p h i t e s %OK m o l t e n - s a l t r e a c t o r a p p l i c a t i o n , and more s p e c i f i c a l l y , to determine what l i m i t a t i o n s g r a p h i t e might impose on r e a c t o r d e s i g n . A program p l a n w a s proposed [ 7 ] t o demonstrate f e a s i b i l i t y of improving g r a p h i t e by 1895, and t o b r i n g such improvements t o commercial a p p l i c a t i o n by 1988. The p r o p o s a l w a s a m b i t i o u s and h a s n o t been f u l l y implemented due t o f u n d i n g limitations: C o n s i d e r a b l e p r o g r e s s h a s , n e v e r t h e l e s s , been achieved tsward d e m o n s t r a t i n g t h e c a p a b i l i t y of e x i s t i n g materials t o meet MSR r e q u i r e m e n t s and t o d e l i n e a t e areas f o r f u t u r e development.

Current S t a t u s The MSR g r a p h i t e program h a s evolved i n t o a four-pronged a t t a c k t o s u r v e y e x i s t i n g commercially a v a i l a b l e g r a p h i t e s f o r their a p p l i c a b i l i t y t o an MSBR; t o g a i n s u f f i c i e n t i n s i g h t i n t o t h e damage mechanism t o b e a b l e t o estimate t h e d e g r e e of improvement t o b e e x p e c t e d i n f u t u r e graphites; t o develop an in-house c a p a b i l i t y t o f a b r i c a t e g r a p h i t e s i n o r d e r t o r e l a t e damage behavior t o s t r u c t u r e and f a b r i c a t i o n t e c h n i q u e ; and t o d e v e l o p methods of sealing the g r a p h i t e a g a i n s t xenon-135 d i f f u s i o m . Included i n t h e s e areas are t h e n e c e s s i t y t o develop d e s i g n d a t a and c o s t estimates

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I r r a d i a t i o n Damage S t u d i e s The b a s i c i r r a d i a t i o n damage phenomena i n g r a p h i t e are determined by t h e extreme a n i s o t r o p y O S t h e c r y s t a l . The carbon atoms are a r r a y e d i n tightly-bound hexagons i n p l a n a r a r r a y . The p l a n e s are w e l l - s e p a r a t e d a d weakly coupled. P n t e r s t i t i a l s produced by weiutron bOmbaPdment wander f r e e l y between p l a n e s and r e i n t e g r a t e as new p l a n e s . Vacancies L e f t beh i n d are c o l l a p s e d . W e are t h u s l e f t w i t h t h e p i c t u r e of a s i n g l e c r y s t a l expanding i n d e f i n i t e l y i n one d i r e c t i o n and c o n t r a c t i n g i n t h e o t h e r two w i t h l i t t l e change in n e t volume. an a p o l y c r y s t a l l i n e m a t e r i a l , each c r y s t a l l i t e is thus expanding and c o n t r a c t i n g i n v a r y i n g d i r e c t i o n s , and i t i s h a r d l y s u r p r i s i n g t h e material e v e n t u a l l y d e t e r i o r a t e s . What i s

182

remarkable i s i t s a b i l i t y t o w i t h s t a n d t h e s e changes P a r t i a l l y oriented p y r s l y t i c s i r r a d i a t e d i n BPIR t o fluences of 3 x 102’ neutrons/cm% a t MSR t e m p e r a t u r e s expanded ~ B O Xi n t h e preferred e-axis d i r e c t i o n w i t h o u t l o s i n g neckanical i n t e g r i t y ! During t h e p e r i o d 1963-1971, over e i g h t y different e x p e r i m e n t a l and c o m e r c i a l l y a v a i l a b l e graphites were i r r a d i a t e d i n HFIR t~ e s t a b l i s h t h e i r dimensional behavior 683. A picture of t h e mi.crsstructura% propi f i c a n t t o r a d i a t i o n damage has g r a d u a l l y emerged. Our cone as f o l l o w s . 08’C t e m p e r a t u r e range of i n t e r e s t t o m o l t e n - s a l t rea c t o r s , b u l k g r a p h i t e s can b e c l a s s i f i e d i n t o three b e h a v i o r modes depending on t h e i r f a b r i c a t i o n h i s t o r y s namely c ~ n v e n t i ~ n materials, al black-baaed materials, and m o n o l i t h i c materials 181. By c o n v e n t i o n a l materials we inc$ude a11 normal commercial g r a p h i t e s formed from c a l c i n e d coke 01- graphite f i l l e r s b i n d e r e d w i t h t h e r m o s e t t i n g o r thermoplastic These materials way b e i s o t r o p i c materials and s u b s e q u e n t l y heat trea,ted. o r aIIiSQt.rQpiC, but show an immediate volume c o n t r a c t i o n under damage followed by rapid and c a t a s t r o p h i c expansion. T h e i r l i f e t i m e s are i n t h e range fHQlrrr 1 2 . 5 X BO2’ n@UtrOnS/cI?l2 (a 566 kev) ( s e e Pig. 6 . 5 ) . me expansion is c h a r a c t e r i s t i c a l l y p a r a b o l i c w i t h f l u e n c e . The second class black-based graphites, employs carbon b l a c k s as f i l l e r s , the i n d i v i d u a l blacks h a v i n g a r o u ly s p h e r i c a l c r y s t a l l i t e o r i e n t a t i o n c a p a b l e of wiehs t a n d i n g h i g h ta e n t i a % s t r a i n . Depending on h e a t t r e a t m e n t t e m p e r a t u r e , they may c o n t r a c t r a p i d l y a t f i r s t anel expand l i n e a r l y w i t h f u r t h e r i r r a d i a t i o n (see Fig. 6.6) The d i f f e r i n g expansion b e h a v i o r f HOW t h e more c o n v e n t i o n a l g r a p h i t e s i s t e n t a t i v e l y e x p l a i n e d by t h e a b i l i t y of t h e b l a c k p a r t i c l e s to w i t h s t a n d s t r a i n . The t h i r d c l a s s , and the one of i n t e r e s t to u s , i s t h e m o n o l i t h i c materials which appear to be b i n d e r l e s s , o r f o r which t h e f i l l e r material is chemically a c t i v e and r e a c t s w i t h t h e b i n d e r . The r e s u l t is an extremely homogeneous s t r u c t u r e u s u a l l y unmarked by m i c r o s t r u c t u r e s . Under i r r a d i a t i o n t h e s e mateska1s undergo a prolonged s t a b l e i n d u c t i o n p e r i o d h e f o r e b r e a k i n g i n t o p a r a b o l i c expansion (see P i g . 6.7). The l i f e t i m e s of t h o s e t e s t e d t o d a t e l i e i n the 2 t o 3 x 102’ ~ e ~ t r o n ~ /range c ~ ~ ? (E > 50 key) The b e s t t e r i a l s of t h i s t y p e are i n v a r i a b l y i s o t r o p i c , and t h e i r i n d u c t i o n p e r i o d i s a t t r i b u t e d t o t h e i r m i c r o s t r e n g t h and ability t o flow p l a s t i c a l l y to r e l i e v e s t r a i n . The p a r a b o l i c expansion of b o t h these materials and t h e c o n v e n t i o n a l g r a p h i t e s can b e r e l a t e d t o v o i d g e n e r a t i ~ nas the s t r u c t u r e f i n a l l y f r a c t u r e s a t t h e c r y s t a l l i t e l e v e l E91 Ira s u m a r y , w e f e e l t h e general nature of damage i n p o l y c r y s t a l l i n e g r a p h i t e is understood, and i t s r e l a t i o n s h i p to m i c r o s t r u c t u r e a t l e a s t q u a l i t a t i v e l y demonstrated. a

Based on t h e R P I R i r r a d i a t i o n d a t a , a program w a s i n i t i a t e d i n 1990 t o e x p l o r e the f a b r i c a t i o n of m o n o l i t h i c g r a p h i t e s s p e c i f i c a l l y aimed a t r a d i a t i o n damage r e s i s t a n c e . The program i s rather modest i n Both object i v e and scope. S m a l l samples up t o three i n c h e s i n diameter o n l y are

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Xenon C o n t r o l The problem of e f f e c t i v e l y s e a l i n g the g r a p h i t e a g a i n s t xenon can take three forms: d i r e c t P ~ ~ p ~ - e g n aby t i ~hydrocarbons n followed by h e a t treatment to l e a v e a carbon r e l i c in the p o r e ; impregnation With a l i q u i d OIP S o l i d Salt $0 fill the p o r e s ; Or S b a K f a C e treatment t o Seal Q f f t h e p o r e s at o r R ~ B Pthe s u r f a c e . Sufficient e x p e r i e n c e h a s been enerated i n the g r a p h i t e i n d u s t r y to i n d i c a t e t h e l i m i t a t i o n s of d i r e c carbonaceous impregnation. ?Tlae decomposing hydrocarbon g e n e r a t e s gaseous p r o d u c t s which muse escape to t h e surface o r r u p t u r e t h e bulk i e c e . A p r a c t i c a l l i m i t a t i o n i n p e r s u e a b i l i t y i s of the o r d e r of 10- cm2/see, a f a c t ~ r100 l a r g e r t h a n r e q u i r e d f o r e x c l u d i n g xenon. This approach h a s t h e r e f o r e n o t been exp l o r e d i n our program. The u s e of s a l t s to f i l l the pores has been looked a t c u ~ s o r i k g r [ 8 ] and is s t i l l b e i n g i n v e s t i g a t e d . 'Pke limitation a n t i c i p a t e d i s t h e d i f f u s i o n o f uranium i n t o t h e s a l t . N e v e r t h e l e s s , i t h a s been demonstrated that s u c k a t e c h n i q u e can reduce gas p e r m e a b i l i t i e s bo the desired range. The u s e of p y r o l y t i c decomposition of hydrocarbons h a s been extens i v e l y s t u d i e d f o r r e a c t o r a p p l i c a t i o n s p r i m a r i l y under t h e ga9-cooled reactor p r o g r a m The background developed there on p r ~ c e s sparameters p r o p e r t i e s and i r r a d i a t i o n b e h a v i o r formed the b a s i s for our program. The f i r s t approach Ell] w a s t o u t i l i z e a gas impregmation process to fill t h e p o r e s near the s u r f a c e , this b e i n g p r e f e r r e d Q V W a c o a t i n g p r o c e s s because sf i t s g r e a t e r resistance t o h a n d l i n g damage, The p r o c e s s sists of a l t e r n a t e l y p u l s i n g hydrocarbon gas and vacuum, thus effecta decomposition of t h e g a s deep w i t h i n t h e p o r e s of the graphite, and has proven t o b e e a s i l y c o n t r o l l a b l e a d effective. Apparent permeabil%ties*in the 10-8 cm2/see r a g e and below are r e a d i l y attalneci. M O ~ O l i t h i c - t y p e s u b s t r a t e s were impregxated and i r r a d i a t e d i n BFIB, b u t the

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low p e r m e a b i l i t y was q u i c k l y 10st [ 1 2 I . Dirrtensi~nald a t a r e a d i l y showed why. En f i l l i n g t h e p o r e s w e had a l s o locked t h e c r y s t a l l i t e s i n t h e s u r f a c e r e g i o n of t h e b a s e g r a p h i t e t o g e t h e r and prevented t h e p l a s t i c flow n e c e s s a r y t o r e l i e v e t h e i n t e r c r y s t a l l i n e s t r a i n s produced d u r i n g damage. Coating was n e x t i n v e s t i g a t e d , u t i l i z i n g b a s e g r a p h i t e s and c o a t i n g s t r u c t u r e s known t o b e dimensionally s t a b l e under i r r a d i a t i o n . F i r s t i r r a d i a t i o n r e s u l t s [a] were mixed; a few samples r e t a i n e d t h e i r i n i t i a l low p e r m e a b i l i t i e s t o t h e maximum f l u e ~ c ee ~ i ~ p l o y e dabout , 2 x neutrons/cm2, b u t t h e m a j o r i t y were no b e t t e r t h a n t h e gaseous-impregnated materials. It is now ~ROWII t h a t t h e c o a t i n g s w e r e flawed b e f o r e irracliat i o n , and a r e v i s e d p r o c e s s has been developed [Is]. Samples w i t h unflawed c o a t i n g s are c u r r e n t l y b e i n g assembled f o r i r r a d i a t i o n t e s t i n g . One of t h e major r e c e n t d i a g n o s t i c advances had been development of s c a n n i n g e l e c t r o n microscopes c a p a b l e of examining g r a p h i t e s u r f a c e s . The flawed samples alluded t o above appeared p e r f e c t l y sound even mder t h e l i g h t . micPsscQpe. Under t h e ScanniRg e l e c t r o n microScope, v a r i o u s types sf flaws are r e a d i l y a p p a r e n t as w e l l as changes i n m i c r o s t r u c t u r e (see Fig. 6.8).. The d e f e c t s have been found t o b e due t o f a u l t y gas c i r c u l a t i o n , s o o t i n c l u s i o n s , a d t o o s h a r p c o r n e r s on t h e g r a p h i t e c y l i n d e r s b e i n g coated. These have a l l been e l i m i n a t e d i n t h e c u r r e n t c o a t i n g process

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Thermal C o n d u c t i v i t y It w a s o r i g i n a l l y a n t i c i p a t e d t h a t changes i n thermal c o n d u c t i v i t y due t o r a d i a t i o n damage m d e r MSR c o n d i t i o n s would b e s l i g h t . Recent d a t a , however, have implied t h i s may n o t b e t h e c a s e [ T I , and e x p @ r i ~ ~ $ ~ % s have been i n i t i a t e d i n HFIR t o determine t h e s e r i o u s n e s s of t h e degradat i o n i n c o n d u c t i v i t y [8] P r e l i m i n a r y r e s u l t s imply t h e d e c r e a s e may b e by a f a c t o r o f t h r e e . The importance of thermal c o n d u c t i v i t y i s i n c o n t r o l l i n g t h e i n t e r n a l g r a p h i t e t e m p e r a t u r e s , and thereby t h e r a t e of damage accumulation. "%he e

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as though t h e p r i s m were a t i t s mean temperature throughout [ 6 ] . Since damage r a t e i n c r e a s e s w i t h temperature, the d e s i r e t o minimize i n t e r n a l temperature g r a d i e n t s i s obvious S t r e s s e s and Creep. - The g r a p h i t e c o r e prisms, as mentioned above, are r e q u i r e d f o r no s t r u c t u r a l purpose e x c e p t t o d e l i n e a t e t h e s a l t flow and t o s u p p o r t t h e i r OW^ weight when t h e r e a c t o ~i s drained. However, t h e q u e s t i o n s t i l l exists as t o t h e magnitude of thermal radiation induced stresses. These have been c a l c u l a t e d f o r t h e reference d e s i g n w i t h c o n v e n t i o n a l g r a p h i t e a t t h e worst p o s i t i o n i n t h e c o r e , i.e., on t h e c e n t e r l i n e j u s t above t h e midplane [ G I . The c a l c u l a t e d stresses are s h o r n i n Fig. 6.9 and are obviously t r i v i a l . We conclude t h a t thermal and r a d i a t i o n - i n d u c e d stresses are no problem even f o r t h e r e l a t i v e l y p o o r l y behaved c o n v e n t i o n a l type g r a p h i t e s

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2 3 TIME AT 80% PLANT FACTOR (years)

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M a n u f a c t u r i n g C a p a b i l i t y and C o s t s The e x t e n s i v e s u r v e y program of v a r i o u s commercial g r a p h i t e s des c r i b e d above n e t t e d one g r a p h i t e t h a t i s a c c e p t a b l e t o t h e MSBR r e f e r e n c e d e s i g n , a second a c c e p t a b l e but limited i n a v a i l a b l e s i z e s , and two o t h e r g r a d e s which are p ~ t e n t i a l l ya c c e p t a b l e . These s p a n , h a p p i l y , f o u r i n d e pendent vendors Great Lakes Carbon C o r p o r a t i o n g r a d e H-364 i s a v a i l a b l e i n t h e proper g e o m e t r i e s and possesses a l i f e t i m e b e f o r e s i g n i f i c a n t e x p a n s i o n o c c u r s o f t h e O P ~ ~o fP 2.5 x 10%' neutrsns/cts2 (E 9 50 ke'$i) at 7 ~ 5 ' ~ mis . is 19% less than s p e c i f i e d i n t h e r e f e r e n c e d e s i but i s c l o s e enough $0 b e cornpensatable by a l l o w i n g more e x p a n s i o n r e d u c i n g t h e maximum power d e n s i t y , o r r e p l a c i n g t h e g r a p h i t e somewhat s o o n e r . POCO grade M F i s t h e b e s t c o m e r c i a l material w e h a v e e n c o u n t e r e d with a l i f e t i m e of t h e Orden^ O f 3 to 3 . 5 X lo"%, b u t is C u r r e n t l y a v a i l a b l e only in S h o r t l e n g t h s . Material s u b m i t t e d by Airco Speer and P u r e Carbon Companies a l s o may fall i n t o t h e c l a s s o f these materials b u t t o d a t e have o n l y been i r r a d i a t e d to 1 . 5 x 18"'. Their b e h a v i o r appears to b e s i m i l a r t o t h e b e s t of t h e monolithic g r a d e s . We h a v e been unable t o obtain f i ~ mp r i c e estimates on these grades f o r Q U ~ Ca p p l i c a t i o n , b u t t h e y a p p e a r t o f a l l i n t o t h e range of $5-BB.00 p e r pound of f i n i s h e d g r a p h i t e , evem on a f i r s t - o r d e r b a s i s . P r i c e s of $5.06 per pound o r lower ~ e ~ t a i n la y p p e a r t o b e p r o b a b l e if the market becewes s u f f i ~ i e n t l ylarge t o p e r ~ t -t h e g r a p h i t e to b e h a n d l e d as a s t o c k itern. t i e c o a t i n g 01-s e a l i n g , there is an e x i s t i n g such c o a t i n g s p r i n a r i l y f o r a e r o s p a c e a p p l i c a t i o n s . However, t h e most irradiatian-resistant t y p e of coating (%'%I%,o r low t e m p e r a t u r e i s o t r o p i c ) employs p r o c e s s p a r a m e t e r s q u i t e d i f f e r e n t . from t h e i n d u s t r i a l - d e v e l o p e d p r o c e s s e s Cost-es t i m t i n g i s d i f f i c u l t s i n c e a p r o c e s s has n o t been d e v e l o p e d , b u t w e guess t h a t $25-30 p e r %b of f i n i s h e d g r a p h i t e in t h e slab geometry s h o u l d c e r t a i n l y cover any r e a s o n a b l e p r o c e s s d u r i n g its e a r l y development. EventualPy c o s t s s h o u l d d r ~ pt o $5-7.00 p e r kb f o r r e a s o n a b l e p r o d u c t i o n q u a n t i t i e s . e

..... *x.>

A .$.

a

uncertainties and F u r t h e r Work

A number of u n c e r t a i n t i e s remain, none of which p a r t i c u l a r l y a f f e c t t h e v i a b i l i t y o f the molten-salt b r e e d e r c o n c e p t - These u n c e r t a i n t i e s may e f f e c t f u r t h e r compromises i n d e s i and perhaps economics, b u t i n no case are t h e y vital t o t h e t e c h n i c a l O X economic u s e of graphite i n the reactor. S i n c e t h e s e u n c e r t a i n t i e s are r e a d i l y r e s o l v a b l e by f u r t h e r work on g r a p h i t e , w e discuss t h e two t o p i c s t o g e t h e r .

*........ .....

I

191

I r r a d i a t i o n Damage and G r a p h i t e F a b r i c a t i o n

...... :.=.

*:.... .;.x.

.....

Yllcl

The p o t e n t i a l f o r improved g r a p h i t e s t h a t can b e employed i n MSBR's beyond a f l u e n e e of 3.5 x l o 2 2 i s , w e b e l i e v e , good. %he q u e s t i o n remains s p e c u l a t i v e as to t h e degree o f improvement t o b e a n t i c i p a t e d . Our conf i d e n c e i n a n t i c i p a t i n g a t l e a s t i n c r e m e n t a l improvements has i n c r e a s e d s i g n i f i c a n t l y i n t h e p a s t y e a r as o u r m d e r s t a n d i n g of t h e r e l a t i o n s h i p s between m i c r o s t r u c t u r e and radiation damage h a s improved. The a v a i l a b i l i t y of H F I R ( o r fast r e a c t o r s i n t h e f u t u r e ) t o o b t a i n f u l l f l u e n c e s i n l e s s than a y e a r e n a b l e s a g r a p h i t e development program t o proceed a t a reasonable rate. The f a b r i c a t i o n p r s c e s s whish i s c ~ r r e n t H yb e i n g s t u d i e d a t ORNE has only y e t been b r i e f l y explored. Areas a w a i t i n g examination where frartkgr p r o g r e s s can b e a n t i c i p a t e d are t h e u s e of b l a c k s i n ~ K O C ~ Sanalogous S ~ ~ to t h e green-coke r o u t e , and t h e u s e of h i g h - p r e s s u r e p r o c e s s i n g for b o t h r a w materials and c a r b o n i z a t i o n . To d a t e v e r y l i t t l e e f f o r t has been expended by i n d u s t r y and o t h e r government l a b o r a t o r i e s t o i n c r e a s e the life o r s t a b i l i t y of g r a p h i t e , and t h e development of new p r o c e s s e s and d i a g n o s t i c t e c h n i q u e s s u g g e s t much more r a p i d p r o g r e s s can b e made. W e b e l i e v e t h e s e a l t e r n a t e f a b r i c a t i o n t e c h n i q u e s and t h e i r r e l e v a n c e t o damage r e s i s t a n c e can b e at l e a s t i n d i c a t e d w i t h i n two to t h r e e y e a r s , The f a c t t h a t p y r o l y t i c materials have s u r v i v e d t o f l u e n c e s g r e a t e r t h a n neutrons/~~~ a t? 1258'6: i m p l i e s l i f e t i m e s of t h e o r d e r of 1.5 x 5 x 1022 neutrons/cm2 a t ~ Q O " C s h o u l d b e a t t a i n a b l e .

Xenon C o n t r o l The a b i l i t y t o e x c l u d e xenon from s h e g r a p h i t e by means of p y r o l y t i c lempregnation o r c o a t i n g h a s n o t been demonstrated. A l t e r n a t i v e t e c h n i q u e s e x i s t b u t c u r r e n t l y remain unexplored. Both c o a t i n g s and s u b s t r a t e s have s e p a r a t e l y been shown t o s u r v i v e t o >3 x Hence, t h i s is s t r o n g ~ : ~ B S Q Ito I b e l i e v e a m~110layer c o a t i n g can b e made t o work i n t h e MSBR. However, i n t h e gas-cooled program where c o a t i n g s have been shown t o s u r v i v e e q u i v a l e n t fluences, i t has b e e n found n e c e s s a r y t o decouple t h e s u b s t r a t e and c o a t i n g . Both l o w d e n s i t y p y ~ ~ l y t i c and s i l i c o n c a r b i d e i n t e r c o a t i n g s have been employed, and analogous t e c h n i q u e s can b e u t i l i z e d h e ~ ea l b e i t at an ecsnomlc p e n a l t y . I f such t e c h n i q u e s are r e q u i r e d , some two t o three y e a r s ' e f f o r t will b e needed t o develop them. I n any e v e n t f u r t h e r work t o u p s c a l e and p r e p a r e f o r t r a n s i t i o n t o c o m e r c i a l s u p p l i e r s w i l l be r e q u i r e d . Two f u r t h e r t e c h n i q u e s are t h e f i l l i n g of p o r o s i t y i n t h e graphi t e w i t h e i t h e r l i q u i d o r s o l i d s a l t . S o l i d s a l t , and bismuth as a s t a n d - i n , have been shown t o a t least y i e l d t h e r i g h t o r d e r of gaseous d i f f u s i o n rates. The u n c e r t a i n t y remains as t o whether t h e l i q u i d o r s o l i d d i f f u s i o n rates are s u f f i c i e n t l y low. The p o t e n t i a l of t h i s app ~ o a c hcan b e determined i n about one y e a r . Underlying all of t h i s are q u e s t i o n s as t o the e f f i c a c y of t h e helium bubbles and t h e impedance of xenon d i f f u s i o n a c r o s s t h e s a l t i n t e r f a c e t o l i m i t d i â‚Ź f u s i o n i n t o g r a p h i t e q u i t e i n d e p e n d e n t l y of t h e p e r m e a b i l i t y , a s u b j e c t wh'ich is d i s c u s s e d i n d e t a i l i n Chapter 8.

192

me t h e m l c o n d u c t i v i t y d e g r a d a t i o n with damage remilas t o b e est a b l i s h e d . This leaves u n c e r t a i n the maximum c r o s s - s e c t i o n a l area of the g r a p h i t e prisms p e r m i t t e d . Although r e p r e s e n t i n g only a q u e s t i o n of d e s i g n , i t must be answered. W e estimate two t o three y e a r s will b e req u i r e d t o o b t a i n t h e n e c e s s a r y i r r a d i a t i o n h i s t o r y and d a t a .

,_. .., .\

S t r e s s e s and Creep P r e s e n t 'benowledge on c r e e p i n g r a p h i t e l e a d s t o a m a n a l y s i s i n d i c a t i n g snly t r i v i a l stresses are developed im t h e g r a p h i t e . Recent unp u b l i s h e d r e s u l t s o b t a i n e d a t Hanford m y i n d i c a t e t h e a b i l i t y of t o c r e e p d e t e r i o r a t e s a t h i g h fluences. I f s o , th@ problem can a g a i n b e avoided by d e s i g n , b u t t h e s i t u a t i o n i s u n c e r t a i n . We estimate a minimum of three t o f i v e y e a r s t o o b t a i n t h e n e c e s s a r y i n f o r m a t i o n .

.... ..... Y.W

...

G. :.

Evaluation

In general9 g ~ a p h 2 i t ep r e s e n t s no s e r i o u s problem t o the m o l t e n - s a l t reactor. A t least one vendor h a s a v a i l a b l e a s a t i s f a c t o r y material i n the r e q u i r e d s i z e s , and t h e r e i s every r e a s o n t o b e l i e v e the l i f e t i m e of f u t u r e g r a p h i t e s can be i n c r e m e n t a l l y e x t e n ed t o perhaps t w i c e t h a t of the b e s t e x i s t i n g materials. Cost estimates u t i l i z i n g p r e s e n t material c a p a b i l i t i e s y i e l d 8.17 mill/kWnr, f o r replacement sf t h e entire c o r e on a four-year c y c l e i n t h e refe~etnced e s i g n , o r a somewhat lower c o s t i f only the most h i h l y i r r a d i a t e d m.ate.IPk3l f s KC?plZLC@dE%ZiCh time. Inc?ZeaSi n g t h e l i f e t i m e to e i g h t years reduces t h e f u e l egpeabe c o s t by about 0 l mIll/kWhr b u t beyond t h i s t h e c o s t s a v i n s are s m a l l . W e can t h u s s t a t e t h a t e x i s t i n b a s e g r a p h i t e s are a c c e p t b l e , and f u t u r e g r a p h i c e s cam probably b e developed t o reduce replacement c o s t s . ' The p r e s e n t methods of p y r o l y t i c a l l y c o a t i n g the graphite appear t o be s a t i s f a c t o r y , although ~adiatisnt e s t i n g w i l l r e q u i r e a t l e a s t a n o t h e r year t o demonstrate t h i s . A l t e r n a t i v e r o u t e s e x i s t , b u t t h e q u e s t i o n is e v e n t u a l l y one of ecsaamics - t h e v a l u e of narginal i n c r e a s e s i n b r e e d i n g g a i n versus t h e c o s t of the c o a t e d material. We have n o t y e t a c q u i r e d sufficient data on the thermal and mechani c a l p r o p e r t i e s of g r a p h i t e s of t h e t y p e used in t h e mBR. Enough i s h o r n to b e c e r t a i n t h e s e do not a f f e c t t h e exact shapes of g r a p h i t e perw i t t e d and t h e mems by which t h e g r a p h i t e i s supported, b u t a d d i t i o n a l d a t a must y e t be s e c u r e d f o r d e s i g n purposes. Ill SUlll, there are no PB;a%OlaS t o expect g r a p h i t e t o limit the O V e ~ E d l f e a s i b i l i t y of m o l t e n - s d t breeder reactors, and acceptable materials are a v a i l a b l e today r

<<.... *<;

k..,

~.... . ~

l i i i i

..... E.....?

193

References f o r c h a p t e r 6

P.

J. M. W. Simmons, Bgdiation Damage in G ~ q h i t e ,Pergamon P r e s s (1965).

2.

6. B. E n g l e and W. P E a t h e r l y , ''4 Review of High-Temperature Graphite Irradiation Behavior" i n High Temperature-'&& Pressures ( t o b e published).

3.

Conceptual Uesi_p Sku&

of a Single Fluid Molten-Salt Eeactor, OWNE-

4528 ( l 9 7 0 ) .

4.

's1060 m(e) Molten-Salt B r e e d e r Reactor Conceptual Design S t u d y , " F i n a l R e p o r t - Task I., Ebascrs Services, Inc. ( 1 9 7 1 ) .

5.

E . S. B e t t i s , E. G. A l e x a n d e r , and H . L. Watts, Des<.,m Studies of a Molten-SaZt Beactor ikmunstratioz Plant, m L - T M - 3 8 3 2 (1972)

8 , 179 (1970). 6 * D. Scott and W. P. E a t h e r l y , i"Jucl. A p p l . !Tech. -

7.

W. P . E a t h e r k y e t a l . , Technical Analysis m d P r o p a m Proposal: G m p h i t e f o r IdoZten-Salt Reactops, QmL-CF-6 8-ll-18 (19 68) *

8.

MSR P m g m m Semkmnu. Fregr. R e p t . Aug. 32, 2971, Om%-4728.

11. ,VSR Propam S e h m n u . P r o p . R e p t . Feb. 28, 2969, ORNE-4396.

.... & ,& .

Semiannu. Prcgr. B e p t . kug. 32, 2970, 086aL-4622.

12.

l@SRProgram

13.

@Sf? Frogram Semimznu. Pz1ogr. R e p t . Peb. 29, 1392, OWNL-4782.

I u . ...2

....

"-

i......,

. .. 6L.a

7. .....? _._

MATERIALS FOR SALT-CONTAINING VESSELS AND PIPING

H. E. McCoy Material Requirements

... ..s .,

......?

.... ....

The m e t a l used i n f a b r i c a t i n g a molten s a l t reactor w i l l b e exposed t o several environments. The i n s i d e of t h e primary c i r c u i t w i l l b e exposed t o % ~ P - B ~ F ~ - T ~ F L +t h- eU Fc o~o~l a n t c i r c u i t t o NaP-NaBF4, and the steam c i r c u i t t o s u p e r c r i t i c a l steam. Thus, t h e t u b e s i n t h e i n t e r m e d i a t e h e a t exchanger w i l l be exposed to bot11 s a l t s and those i n the steam g e n e r a t o r to b o t h c o o l a n t salt and steam. The b u l k f u e l s a l t temperature will range f r o m 1650" t o 1306째F and the c o o l a n t from 850 t o El50"P. The steam i n t h e s a l t - h e a t e d s t e m generator e n t e r s a t 780째F i n the r e f e r e n c e l o o p s The o u t s i d e s of the metal components w i l l b e and i s heated t o 1000'F. exposed t u containment c e l l environments composed p r i m a r i l y of n i t r o g e n , w i t h enough in-leakage of a i r t o make i t o x i d i z i n g . The most b a s i c requfrement of t h e s t r u c t u r a l materials i s t h a t t h e y be chemically compatible w i t h t h e s e v a r i o u s environments. The chemical p r s p e r t i e s of t h e s a l t s were d i s c u s s e d in Chapter 5, where i t w a s p o i n t e d o u t t h a t t h e 5elective l e a c h i n g of chrsmium would be t h e primary mechanism f o r c o ~ ~ o s i o tof a iron- and nickel-base alloys by molten f l u o r i d e s . Thus t h e c o n c e n t r a t i o n of chromium i s an important consideration i n s e l e c t i n g Iron i s more e a s i l y o x i d i z e d an a l l o y t o b e used i n m o l t e n - s a l t c i r c u i t s . by t h e s a l t s t h a n n i c k e l , s o t h e p r e f e r e n c e ( a l t h o u g h n o t n e c e s s a r i l y a requirement) of a nickel-base a l l o y o v e r an iron-base a l l o y i s immedia t e l y obvious. Good r e s i s t a n c e t o oxidation in N2-02 enviruramewt:~is favored by h i g h chromium c o n c e n t r a t i o n s . The material. requirements f o r steam g e n e r a t o r s are d i s c u s s e d i n Chapter 8. S a t i s f y i n g t h e need f o r c o m p a t i b i l i t y w i t h t h e c o o l a n t s a l t and resistance to s t r e ~ s - c ~ r r ~ sc ria~c kni n g in t h e steam be d i f f i c d t w i t h a s i n g l e a l l o y s u g g e s t i n g t h e use of duplex t u b e s . The subject: of d e s i g n stresses will be discussed more fully i~ Chapter 13, b u t i t i s obvious t h a t the material must be capable of withs t a n d i n g w i t h o u t % a i l u r e t h e stresses that w i l l b e imposed d u r i n g service. The r e l a t i v e l y hFgh t e m p e r a t u r e s involved will r e q u i r e t h a t s u i t a b l e e l a s t i c - p l a s t i c a n a l y s e s b e made of all s t r u c t u r e s . An MSBR w i l l s p e r a t e at: r e l a t i v e l y l o w p r e s s u r e s s s o a h i g h - s t r e n g t h material does n o t s e e m n e c e s s a r y . However, thermal stresses will l i k e l y c o n t r o l the d e s i g n and i t i s q u i t e l i k e l y t h a t a material w i t h moderate s t r e n g t h w i l l be used * The ~ K I I IcE i r~ c u~i tY , pa~ti~ula~ t hley r e a c t o r vessel, will be exposed t o neutron i r r a d i a t i o n , b u t no m e t a l l i c s t r u c t u r a l members w i l l b e i n t h e h i g h e s t n e u t r o n f l u x r e g i o n s . A t t h e v e s s e l wall, t h e peak t h e r m a l and and 1 . 2 x 18" n e u t r ~ n s - c m - ~ ~ s e c - ~ , f a s t (>6.8 MeV) fluxes will be 6.5 x and over .a 30-year l i f e t i m e w i t h an 86% l o a d f a c t o r , t h e peak thermal and .and 1 x l O 2 O weutr9ns/cm2, r e s p e c t i v e l y . fast fluelaces will b e 5 x These relatively l o w f l u e n c e levels are due t o t h e e f f e c t s s f t h e g r a p h i t e

;il%

.:=

195

r e ~ ~ e c t omra s o u i d be redtlced even f u r t h e r if necessary. me f a t fkuence is not high ensugh f o r void f o r m t i ~ nt o b e a problem, and t h e irradiation damage is primarily the high-temperature embrittlement due t o helium generation 111. obvious requirement of t h e structural material is t h a t it must be f a b r i c a b l e into the form needed t o b u i l d m en ineerlng sys tern. Basic shapes required include p l a t e , p i p i n g , t u b i n 3 m d f o r g i n g s - P O K assembly, the ~ ~ ~ t e r i a l b e ~ e l d a b l eb o t h der ~ ~ l l - c ~ n t r o l l shop ed c o n d i t i o n s and i n the field. Many iron- and nickel-base alloys s a t i s f y these requirements, dthotagla the technology is more advanced for alloys than f o r others. e b a s i c ability to work with a material is more important, however, an having a c u r r e n t l y v i a b l e technology in several fabrication shops. The Patter f a c t o r would simply nake the f i r s t u n i t cheaper. ry9 one mst keep s i g h t of the b a s i c requirements that the material be CB a t i b l e w i t h its environments, have acceptable d after exposure to t h e mechanical p r o p e r t i e s , both ~ n i r ~ a d i a t eand m a x i m u m expected n e u t r o n f l u e n c e , and be capable of b e i n g f a b r i c a t e d w i t h reasonable ease.

Backgssmd

Table 7.1. Clmeqical composition of Hastelloy N Content (% by weight)'"

.... <uxz

.... ..... ... *,L.

..... ,.!.&*

....

Element

Standard alloy

Nickel Molybdenum Chromium Iron Manganese Silicon Pho sphurus Sulfur Boron Titanium and hafnium Niobium

Base 15- 18 6-8 5 1 1 0.015

0.020 0.01

Favored modified alloy Base 11-13 6-8 O.â‚Źb

0.15__ 0.25 0.1 0.01 0.01 0.001 2 0-2

'"Single values are maximum amounts allowed. The actual concentrations of these elements in an alloy can be much lower. bThese elements are not felt to be very important. Alloys are now being purchased with the small concentration specified, but the specification may be changed in the future to allow a higher concentration.

19

is important because i t forms c a r b i d e s t h a t r e s t r i c t g r a i n g r ~ w t hd u r i n g high-temperature t r e a t m e n t s and improve t h e s t r e n g t h . Elements such as s u l f u r , phc~sphorus, and boron, and many o t h e r s n o t i n c l u d e d i n Table 9 . 1 , are tramp o r impurity elements t h a t serve no known u s e f u l purpose i n t h e alloy These elements e n e r a l l y have l i t t l e e f f e c t on t h e alloy behavior as l o n g as they are kep a t r e a s o n a b l e c o n c e n t r a t i o n s . S i l i c o n i s introduced by t h e r e f r a c t o r i e s used i n t h e a i r m e l t i n g practice and i s an important element. k s t e % l o y %a c ~ n t a i n i n g0.5 t o 1% s i l i c o n c o n t a i n s s t r i n g e r s of c o a r s e carbides and w i l l form some fine carbides d u r i n g annealing a t 1200 to 1606°F [s] These c a r b i d e s are 0 % t h e MgC type, w i t h M having the composition of 27.9% Ni, 3.3X Si, 0.6% Fe, 56.1% No, and 4BX 6r. They a r e n o t easily d i s s ~ l v e dd u r i n g a n n e a l i n g , s o t h e alloy h a s s t a b l e p r o p e r t i e s over a broad range of o p e r a t i n g tempera t u r e s , S e v e r a l meltin p r a c t i c e s a r e currently i n u s e that r e s u l t in l o w s i l i c o n concentrations. e c a r b i d e s i n these a l l o y s a r e of t h e N2C typeo Where %% is 80 to 98% mokYbden%yqpw i t h t h e reminder C h r Q m i m . ‘%hey a r e more e a s i l y d i s s o l v e d than the M s G t y p e that c o n t a i n s i l i c o n . %US, & S t d % o g P M is b a s i C a % l y an a l l o y s t r e n g t h e n e d W i t h DlolybdenUm and c o n t a i n i n g enough C ~ K O U I ~ UfBo r m ~ d e r a t eoxidation r e s i s t a n c e . The c a r b i d e t y p e is c o n t r o l l e d by the s i l i c o n ~ ~ n ~ e n t r a t i ~ n . D

e

C O I T Q S ~ U ~R e s i s t a n c e of HastePloy N

Several hundred thousand hours of corrosion experience with B a s t e l I s y N and f l u o r i d e s a l t s have been o b t a i n e d i n thermal convection [ 2 , 3 ] and pumped systems 681. A s d i s c u s s e d i n Chapter 5 , t h e s e experiments sh~wedthat the predominant corrosion mechanism i n c l e a n f l u o r i d e s a l t s c o n t a i n i n g uranium w a s t h e s e l e c t i v e l e a s h i n g of chromium. Only 7% of t h e a l l o y is chromium and t h i s must d i f f u s e to t h e s u r f a c e b e f o r e i t can b e r e ~ ~ ~ vbye dthe s a l t . DeVan measured the r a t e of chromium d i f f u s i o n in ~ a s t e H l o yN 691, and t h e measured d i f f u s i o n c o e f f i c i e n t s were used t u estimate t h e chrolaim profile after 30-year s e r v i c e a t 650 and 7’00°C in salt o x i d i z i n g enough t o csmpPete%y d e p l e t e t h e s u r f a c e of Cr. A s even i n this extreme s i t u a t i o n , t h e depth of removal

The e a r l y work w i t h k s t e l l ~ yK and o t h e r alloys r e v e a l e d t h e import a m e of c ~ ~ - ~ t r o P li imnp u r i t i e s i n t h e s a l t . rarity f l w r i d e s such as FeF2, HoP2, and NFP w i l l ~ e a c tw i t h Cr t o for r P 2 , a more s t a b l e f l u o r i d e . Water w i l l r e a c t with t h e f l u o r i d e mixtures t o form MF t h a t w i l l form f l u o r i d e s with a l l the s t r u c t u r a l metals. Such i m p u r i t i e s l e d t o r e l a t i v e l y h i g h corrCl%iQnrat@% Of even HCistePlCIy N t h e early experiments, However, w e l e a r n e d how to p r e p a r e p u r e salt mixtures, m d very low corrosiom rates were o b t a i n e d . The u l t i m a t e proof of t h i s a b i l i t y w a s the o p e r a t i o n of t h e NSRE where the o v e r a l l C O Z - I - Y A S ~ ~was ~ held low f o r almost f o u r years at temperature. me p r e c e d i n g d i s e u s s i o n ap i e d t o the removal of material, but the s a l t c i r c u l a t e s from h o t t e r t o d e p o s i t i o n i s a l s o of coneern. c o o l e r r e g i o n s , t h e s o l u b i l i t i e s of the c o r r o s i o n p r o d u c t s i n the s a l t d e c r e a s e , and i f c o n c e n t r a t i o n s are high enou In, material way be d e p o s i t e d . T h i s p r ~ ~ e is ss complex, depending upon chemical d r i v i n g f o r c e s and f a c t o r s

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F i g . 7.1. C a l c u l a t e d c o n t e n t r a t i o n p r o f i l e s f o r Cr removal and T e enrichment based on measured d i f f u s i o n c o e f f i c i e n t s . The t i m e s used i n t h e c a l c u l a t i s n s were 3 y r s for t h e MSRE and 30 y r s for t h e MSBR.

such as geometry and flow c o n d i t i o n s . P o r t u n a t d y , t h e s a l t s b e i n g cons i d e r e d f ~ an r MSBR tend strongly to d e p o s i t m t e r i a l r a t h e r uniformly throughout t h e c ~ l dr e g i o n and have a m i n i m a l tendency t o p l u g h e a t ger tubes and s a l t passages i n c o o l e r p a r t s of t h e system.

The p h y s i c a l and mechanical p r o p e r t i e s of H a s t e l l o y K were e v a l u a t e d r a t h e r extensiuely b e f o r e the MSRE w a s c o n s t r u c t e d . These p r o p e r t i e s haue been sL.mlmarized p r e v i o u s l y [ a 1. ?%e S t r e n g t h sf t h i s allQgP iS quite goodl because of t h e 16%mslybdenum. The p r o p e r t y changes w i t h t i m e are sw;lP% s i n c e the a l l o y does n o t form i n t e r m e t a l l i c compounds b u t only small ZinQUlItS O f f i n e c a r b i d e s .

F a b r f c a t i o n . - Although t h e power level of t h e MStaE was small, t h e system was complex and r e q u i r e d t h e a b i l i t y t o c a r r y o u t a l l of t h e b a s i c f a b r i c a t i o n s t e p s [ll]. Eany thousands of psunds of b a s i c product forms were procured from t h r e e vendors. Some of t h e components were b u i l t by c s m e r c i a l vendors, b u t most of t h e f a b r i c a t i o n w a s done i n t h e A E C l n l o n Carbide shops a t Oak Ridge and Paducah. Welding, b r a z i n g , and i n s p e c t i o n procedures fer the reacts% developed. one of t h e final s t e p s w a s to make u s e of t h e h e a t e r s a n t h e vessel to postweld a n n e a l the f i n a l v e s s e l c l o s u r e weld.

Operation. - A s d i s c u s s e d i n Chapter 2 , the r e a c t ~ ro p e r a t e d very satisfactorily. The primary system w a s ihb~ve5OO'C f o r 30,807 h o u r s and f i l l e d with f u e l s a l t f o r 21,046 h o u r s . The only f a i l u r e invoEving H a s t e l l o y M was through-wall c r a c k i n g o f a f r e e z e value c ~ i r t c i d e n twith f i n a l shutdown of the system 6121 This f a i l u r e was due t o f a t i g u e from d i f f e r e n t i a l . thermal expansion i n a p a r t t h a t w a s c o n s t r u c t e d t o o ri e

C ~ X T C S ~ Q -~ . C ~ r r o s i ~clurirtg n the o p e r a t i o n of t h e PISRE was f o l l o w e d b o t h by a n a l y z i n g the salts and examining s u r v e i l l a n c e specimens removed from the COBTe. %e pt-iWrgr C O l P t - o S i o R p r s d u c t , c r F 2 , KeIlItiined below its s o l u b i l i t y l i m i t s i n t h e s a l t ; so its ~ ~ ~ ~ e n t r acould t i o nb e used as a measure of t h e amount of chromium b e i n g removed from the metal. The r e s u l t s of such a n a l y s e s have been d e s c r i b e d i n d e t a i l , (reference E3 and Chap. 5 ) A s i m p l e summary is t h a t t h e chrsrnim removal w a s very 11: the t o t a l amount accumulated in t h e f u e l s a l t was e q u i v a l e n t ts t h a t which would b e r e m ~ v e d from a l l metal s u r f a c e s t o a d e p t h ~f Q,4 m i l ; the E1ElQra6nt appearing in t h e cOO~ZXl%Sal% W a s p r a c t i c a l l y nil. S u r v e i l l a n c e samples l o c a t e d i n t h e c u r e of t h e MSRE were p e r i apically removed f o r examination and t e s t i n g . Samples of both s t a n d a r d and modified HastePEsy N were always i n e x c e l l e n t p h y s i c a l c o n d i t i o n w i t h only a s l i g h t amount 5f d i s c o l o r a t i o n [1,14,l%,16], and visual

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m e t a l l o g r a p h i c e x a m i n a t i o n f a i l e d t o reveal any changes t h a t were a t t r i b u t a b l e to c o r r o s i o n . (As d i s c u s s e d i n d e t a i l l a t e r , a s e r i o u s problem w a s r e v e a l e d a f t e r e x a m i n a t i o n of t e n s i l e specimens t h a t w e r e s t r e s s e d to failure. So t h a t t h e r e a d e r w i l l n o t l a t e r t h i n k t h a t w e have b e e n i n c o n s i s t e n t , w e n o t e h e r e t h a t t h e c a u s e o f t h e problem w a s not, i n our terminology, "corrosion" 1 The chromium g r a d i e n t s i n some o f t h e s e samples w e r e measured by t h e e l e c t r o n m i c r o p r o b e a n a l y z e r , and t h e w o r s t case w a s a g r a d i e n t t h a t extended a b o u t 0 . 8 m i l i n t o t h e m a t e r i a l el?]. S t a n d a r d m e t a l l o g r a p h i c [%'SI (".LOO m a g n i f i c a t i o n ) e x a m i n a t i o n s f several t u b e s from t h e c o l d e s t p a r t of t h e h e a t exchanger r e v e a l e d o n l y d e p o s i t s of a few i r o n c r y s t a l s . The MSRE c o o l a n t c i r c u i t c o n t a i n e d LiF-BeF2 (66-34 mole 2) a t 55065B'CI f o r about 26,000 h o u r s . The chromium c o n t e n t of t h e c o o l a n t s a l t d i d n o t change measurably d u r i n g t h i s t i m e , and no chromium d e p l e t i o n c o u l d b e d e t e c t e d by m e t a l l o g r a p h i c methods. Thus, t h e MSW confirmed i n s e r v i c e t h e b a s i c c o m p a t i b i l i t y of f u e l s a l t , H a s t e l b o y N , and g r a p h i t e t h a t had b e e n i n d i c a t e d by m n y t e s t s .

R a d i a t i o n E m b r i t t l e m e n t - Kany s f t h e s u r v e i l l a n c e samples from t h e MSRE were s u b j e c t e d t o m e c h a n i c a l p r o p e r t y tests t h a t confirmed our p r e v i o u s knowledge t h a t H a s t e l l o y N i s e m b r i t t l e d by n e u t r o n i r r a d i a t i o n [ 1 , P4,15,16]. A s d i s c u s s e d f u r t h e r i n l a t e r s e c t i o n s , t h i s embrittlement o c c u r s o n l y a t e l e v a t e d t e m p e r a t u r e s and i s due t o h e l i u m formed i n t h e m e t a l ; i t is q u i t e u n i v e r s a l among i r o n and n i c k e l b a s e a l l o y s [18-30] '%he d e g r e e o f e m b r i t t l e m e n t i n t h e MSW was e q u i v a l e n t t o t h a t n o t e d i n samples i r r a d i a t e d i n t h e ETR and ON%. Thus, t h e m e c h a n i c a l p r o p e r t i e s were n o t degraded d i f f e r e n t l y when exposed t o s a l t t h a n when exposed only t o i n e r t gas. F r a c t u r e s t r a i n w a s t h e p r o p e r t y of gn~stc o n c e r n w i t h r e s p e c t t o t h e KSRE. The f r a c t u r e s t r a i n s of some samples from the c o r e w e r e o n l y 0.5% i n c r e e p tests a t 12QO0F, i n c o n t r a s t t o s t r a i n s of > l o % f o r u n i r r a d i a t e d Surveillanee specimens exposed a l o n g s i d e o f t h e r e a c t o r vessel samples a t lower f l u x had s t r a i n s of o n l y 2% [ l , l k j ] . The c o n t r o l rod t h i m b l e s w e r e the o n l y m e t a l in the core, and they w e r e s u b j e c t e d t o small compress i v e f o r c e s . The vessel w a s s u b j e c t e d t o v e r y s m a l l stresses. Csnsequenthy, t h e r a t h e r low s t r a i n limits were n o t exceeded and t h e s y s t e m o p e r a t e d w i t h o u t f a i l u r e from r a d i a t i o n damage. The e n t i ~ earea of t h e d e s i g n of c o ~ ~ p o n e n tfso r h i g h t e m p e r a t u r e service is g e t t i n g c o n s i d e r a b l e a t t e n t i o n . Although t h e s t r a i n l i m i t s h a v e n o t been f i r m l y e s t a b l i s h e d , i t seems l i k e l y that l o c a l s t r a i n s above t h o s e a l l o w e d by s t a n d a r d K a s t e l l o y N m u s t b e accommodated. e

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Grain-boundary Cracks. - A s e c o n d problem n o t e d w i t h H a s t e k l o y N removed from t h e MSEIE: w a s t h a t s h a l l o w i n t e r g r a n u l a r c r a c k s formed in s u r v e i l l a n c e samples and a l l s t h e r s u r f a c e s i n c o n t a c t w i t h t h e f u e l [1,14,15,16,17]. These cracks g e n e r a l l y e x t e n d e d to d e p t h s of o n l y about 5 m i l s , b u t SQEE w e r e as deep as 13 mils i n p a r t s removed from t h e pump bowl. Although r e c o g n i z a b l e ( i f you were Booking f o r them) i n metallog r a p h i c s e c t i o n s of some material j u s t as t h e y were when rearwved from che MSRE, more w e r e v i s i b l e and t h e y w e r e opened much w i d e r Pn specimens such

as that shown i n Fig. 9 - 2 t h a t had been s t r a i n e d i n t h e h o t cell. Cracks f0Wd a f t e r S t K E t i K h material that had been exposed i n t h e c o r e were no more p e r v a s i v e o r deeper than t h o s e i n t h e heat-exchanger t u b e s , which had heen exposed %Q i n s i g n i f i @ a n t laeUtr5n flux. By CQntleolled d i s s o l u t i o n of s e v e r a l samples, a n o f f i s s i o n p ~ o d ~ n c were ts found w i t h i n t h e material to a d e p t h s f several mils. '$$lis s u g g e s t e d t h a t t h e c r a c k i n .....

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p a r t i c u l a r l y t e l l g a ~ i u r n ,which w a s found at t h e and s e t o f f t h e i n v e s t i g a t i o n which i s d e s c r i b

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HastelEoy N ( b o t h s t a n d a r d and modified c ~ ~ ~ ~ p o s i t i has o n s )been shown o t h e r i n - p i l e tests, and l a r g e number of o u t - o f - p i l e loops t o have excellent corrosion r e s i s t a n c e i n s a l t s containin mF4, illEd UF4 [ 2 , 3 , 8 , 3 1 ] . T h i s e x t e n s i v e experience c o n f i r m t h e behavior t h a t would be p r e d i c t e d from calculations such as t h o s e plotted i n F i g , 7.1.

C o r r s s i o n s t u d i e s with the p r o p o s e d c o o l a n t salt, sodium f l u o r s borate, have been more limited [ 3 2 , 3 3 , 4 5 ] . However, w e have o p e r a t e d f o u r therm1 convection l o o p s and t w o pumped s y s t e m i n t h e materials p r o g r m for t Q t a l test: time O f about l % B , Q B O h.% ( S e e chap. 8) This e x p e r i e n c e reveals that: the flusroborate s a l t a b s o r b s m o i s t u r e quite r e a d i l y , W i t h atteIldaIlt generakized C O r r Q s i Q n . &IO C C Z S i O I X W h e n leaks d ~ e l ~ p e dt h,e c o r r s s i o n rate has imcreased and t h e n d e c r e a s e d as the i m p u r i t i e s w e r e exhausted. During these p e r i o d s of high c o r r o s i o n , a l l COmpon@-6k$s of t h e allogr W e r e r e m O V e d UnifO9d.gi f r Q m t h e h o t l e g a d dep o s i t e d i n t h e soEd l e g . C r y s t a l s of Ka3CrF6 a d NagFeFG d e p o s i t e d i n t h e c o l d regions as t h e i r s o l u b i l i t i e s were exceeded. Nevertheless punped l o o p s in which t h e s a l t is h e a t d ana coolea between 1270 a d 7 9 5 ~ have been o p e r a t e d f o r several thousan s of h o u r s with c o r r o s i o n rates of 4l.l mpy, s o w e b e l i e v e t h a t s a t i s f CtOry pPQCE?dUPes f o r Using t h e salt can be develope me s s r r o s i o n b av io r of s e v e r a l o t h e r n i c k e l - b a s e a l l o y s was inv e s t i g a t e d in s c r e e n i n g t e s t s i n t h e aircraft. propulsion p ~ ~ g ~[ 2a, 3m] The proposed s e r v i c e temperature w a s l508'F and most of these a l l o y s w e r e not c o n s i d e r e d f u r t h e r because i n t e s t s a t t h a t temperature l a r g e amounts Qf ChrorniUEL W e r e remaVed, W i t h fOl3ltl.tion Sf Voids i n t h e h o t r e g i o n s O f &!ยงe: loops afld d @ p O S i t i Q nof ChKUIIIiUIll C r y s t a l s in t h e Cold IfegionS. bc s n e l $80 received the most study of a r n ~a l l o y b e s i d e s H a s t e b l o y N , and t h e e v a l u a t i ~ np~~9grtl.111 on i t involved s e v e r a l thermal ~ ~ ~ ~ v el oco pt si ~ n and 4 f o r c e d c o n v e c t i o n l o o p s t h a t o p e r a t e d f o r a t o t a l of 79,368 hr [ 8 ] . Although the CCXX-CX~QTI r e s i s t a n c e of P T I ~ O R ~600 % w a s n o t as good as t h a t of Bastelloy N , at temperatures i n t h e range of MSBWfs the rates were s ~ m e t i r n e1o-w ~ enough to be of interest. For example, one Inesnek 600 l u s p o p e r a t e d a t a peak temperature of 125Q'P f o r 8801 Ear with i n t e r g r a n u l a r penetrations of 1.5 m i T h i s p e n e t r a t i o n is h i g h by o u r current standards, b u t w a s only s l i % l y high@K than that ObSerVed f o r ksteHl5gT N e

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Fig. 7.2. H a s t e l l o y N samples strained to failure a t room temperature. The MSRE rod thimble was at h i g h temperature f o r 31,000 hr, with t h e Power surface exposed to N2-Q2 gas. This surface w a s oxidized, and the cracks only pernetrate the oxide. The upper surface of the thimble sample w a s exposed to fuel salt for 21,000 h r , during which time the Te concentration built up. The Power sample was vapor plated with enough tellurium to produce a concentration of 8.1% in the o u t e ~5 mils and annealed 1000 h K a t 650째C.

204

t e s t e d i n s a l t of comparab%e p u ~ i t y . Thus, it i s l i k e l y t h a t m a l l o y c o n t a i n i n g 15% c h ~ ~ ~ i( eu, gm, , Inconel 600) would have a c c e p t a b l e c o r r o s i o n r e s i s t a n c e at 12(30°F 8% less. The c o m p a t i b i l i t y of iron-base a l l o y s with f l u o r i d e s a l t s has r e c e i v e d ~elatively l i t t l e a t t e n t i o n because t h e thermodynamic data i n d i c a t e that n i c k e l - b a s e a l l o y s w i t h a m i n i m u m chromium c o n t e n t w i l l b e mre c o r r o s i o n resistant than iron-base a l l o y s . %e i n i t i a l s c r e e n i n g tests on types 300 and 400 s t a i n l e s s steels i n d i c a t e d that t h e s e alloys were unsatisfactolPy [ 2 , 3 ] . Eowever, one t y p e 384L stainless s t e e l thermal convection loop c o n t a i n i n g a f u e l s a l t has been i n o p e r a t i o n f o r over 9 years w i t h o u t plugi n g [%Sa; the c o ~ = r o s i o nrate at t h e peak te eratulpe of 1278°F i s about . % Dpy. It iS q u i t e l i k e l y t h a t the CQFrQS n r a t e could b e ~ e d ~ c et od an acceptab%e value by d e c r e a s i n g t h e temperature to 1280"F, b u t tests a t h i g h e r v e l o c i t i e s would b e required to p ~ o v i d emore c o n c l u s i v e i n f o r m t i o n A nost k € l p O H t i % I l t COnsfdePation i n %he S u i t a b i l f t y Qf iTXXI-baSe a l l o y S is t h e possibility t h a t , throu some m i s o p e r a t i o n , the s a l t could become o x i d i z i n g enough t o corrode th is process would not. be diffusion CQntrOlk?d, and t h u s large EUWUIl e r i a l c ~ u l db e t r a n s f e r r e d quickly from the h o t t e r re i o n s to t h e c o o l e r r e g i o n s of the system. While t h i s i s a l s o t r u e f o r n c k e l , it can occur with i r o n at less s e v e r e c o n d i t i o n s . l~mepTer~ we believe t h a t the o x i d a t i o n s t a t e Can be e o n t r o i i e a c l o s e l y

u..

a t i b i l i t y of sodium f l u o r e b a r a t e with i r ~ n - b a s e a l l o y s i s unknown. Corrosion in t h i s salt is ont trolled p r i m a r i l y by i m p u r i t i e s E but i r o n seems to be a t t a c k e d as r e a d i l y as chromium. I f the s a l t could b e maintained v e r y p u r e , iron-base EaPloys might b e a c c e p t a b l e .

I r r a d i a t i o n Ernbr it tlement

The peak f a s t f l u e n e e a t the i n s i d e s u r f a c e of t h e r e a c t o r vessel E ~ ~ K ~ I I S / C I I ? , which i s t o o l o w t o cause detectable swellin peak t h e m a d f l u e n e of 5 x 1021 neutrens/era2 i s reat enough to produce s i g n i f i c a n t axmaants of h e l F m , about 5 pprn f r o m r alduaa 1% and p o s s i b l y ansther 100 t o 200 pm by t r a n s m u t a t i o n s involvin n i c k e l t h a t have only r e c e n t l y been reco i z e d k s o c c u r [ S S ] In s t a n d r d H a s t e l l o y N t h e helium would reduc rain boundary cohesion m d i n c r e a s e the tendency rain boundary f r a c t u r e , with t h e result that the f r a c t u r e s t a i n s a t t e a temperatures become q u i t e HOW. Our approach t o combating &is e m b r i t t l e nt problem i s to add d e ments suck as t i t a n i u m , hafnium, zirc8niuI11, and n obiurn t h a t promote the formation of finely dispersed MC t y p e c a r b i d e s [ 3 1. These c a r b i d e s produce nUIX63rOUB intE2KfaCes t h a t $rap t h e heliLEFi %at er than a l l o w i n g i t t o 8 the g r a i n b o u n d a r i e s . Typical compositions sf modified iven i n Table 7.1. all of the c a r b i d e - f o m i n elements are b e n e f i c i a l i n improving t h e % K a C t U r e S t P a i I l , b u t there Zi%e s e v e r a l p r a c t i c a l r e a s o n s why t i t a n i u m and niobium are more desirable. Zirconium has been f o ~ tdo cause weld metal in c o n c e n t r a t i o n s as s .65W E391 and f o r this reason, a very u n d e s i r a b l e a l l o y i t i o n . Hafnfm causes weld m e t a l c r a c k i n g a t c o n c e ~ ~ t ~ a t isf o nabout ~ O.7%, but the g r e a t e s t problem w i t h

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u s i n g t h i s element is i t s very h i g h chemical r e a c t i v i t y . I n s m a l l Eabor a t o r y m e l t s i n which t h e metal only comes i n c o n t a c t w i t h a water-cooled copper mold, the hafnium i s p r e s e n t as d e s i r a b l e f i n e l y d i s p e r s e d c a r b i d e s . I n commercial m e l t i n g p r a c t i c e s where t h e m e l t i s c o n t a c t e d with a ref r a c t o r y c r u c i b l e , t h e hafnium p r e s e n t is p r i m a r i l y a c o a r s e compound. This l i k e l y o c c u r s because hafnium i s chemically r e a c t i v e enough t o reduce t h e oxides and o t h e r compounds i n t h e r e f r a c t o r y crusible. These coarse compounds d s n o t r e s u l t i n gsod mechanical p r o p e r t i e s a f t e r i r r a d i a t i o n . W e have found t h a t niobium a d d i t i o n s a l o n e do n o t r e s u l t i n imprsved res i s t a n c e t o i r r a d i a t i o n e m b r i t t l e m e n t , b u t they a r e b e n e f i c i a l when titanium i s p r e s e n t [ 3 8 ] . However, b o t h niobium and t i t a n i u m f o m b r i t t l e Nig (%i,Nb) cornpomds m d t h e i r t o t a l c o n c e n t r a t i o n must b e HimLted. S i n c e t i t a n i u m seem t o b e t h e most e f f e c t i v e s i n g l e a d d i t i v e i n improving t h e r e s i s t a n c e t o i r r a d i a t i o n , w e have c o n c e n t r a t e d on a l l o y s w i t h about 2% t i t a n i u m . "he amount of t i t a n i u m r e q u i r e d f o r good r e s i s t a n c e t o n e u t r o n 19r a d i a t i o n depends s t r o n g l y upon t h e s e r v i c e temperature [38]. A t 1200'P a l l o y s w i t h 8.5% t i t a n i u m have f r a c t u r e s t r a i n s of above 4 % , b u t at. an i r r a d i a t i o n temperature of 1405'F, 2% t i t a n i u m i s r e q u i r e d t o o b t a i n t h e same p r o p e r t i e s . D i r e c t t r a n s m i s s i o n e l e c t r o n microscope o b s e r v a t i o n s have shown t h a t t h i s i s due t o t h e f i n e c a r b i d e becoming less s t a b l e and more t i t a n i u m b e i n g n e c e s s a r y f o r s t a b i l i z a t i o n as t h e s e r v i c e temperature is increased. S e v e r a l 108-lb commercial melts c o n t a i n i n g 1 . 5 t o 2 . 1 % t i t a n i u m w e r e procured from t h r e e vendors and e v a l u a t e d . The u n i r r a d i a t e d mechani c a l p r o p e r t i e s and w e l d a b i l i t y of t h e melts are s u p e r i o r t o t h o s e of s t a n d a r d H a s t e l l o y ba. The c o m p a t i b i l i t y of t i t a n i u m - c o n t a i n i n g a l l o y s w i t h f u e l s a l t has been i n v e s t i g a t e d u s i n g specimens of modified a l l o y s i n n a t u r a l c i r c u l a t i o n l o o p s , and some specimens were exposed in t h e MSRE core. Although t h e titanium is r e a c t i v e w i t h t h e s a l t , i t d i f f u s e s l e s s r a p i d l y than t h e chromium and does n o t c o n t r i b u t e d e t e s t a b l y t o t h e c o r r o s i o n r a t e 6401. H a s t e l l o y M modified by t h e a d d i t i o n of about 2% t i t a n i u m h a s t h u s been found t o b e adequately r e s i s t a n t t o r a d i a t i o n a t 1400째F, t o b e weldable w i t h o u t unusual d i f f i c u l t y , and t o b e f r e e of a d d e d corrosion problems.

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i c a l composition does n o t appear t o b e one t h a t w i l l p r e s e n t p r o b l e m . E x p l o r a t o r y i r r a d i a t i o n s t u d i e s have shown t h a t I n c o n e l 600 and a l l o t h e r n i c k e l - b a s e a l l o y s are embrittled a t e l e v a t e d temperatures by thermal n e u t r o n i r r a d i a t i o n [18, 19, 21, 2 2 , 28-30]. The f r a c t u r e strains vary f o r d i f f e r e n t a l l o y s , i r r a d i a t i o n , and t e s t c o n d i t i o n s . However9 t h e f r a c t u r e s t r a i n s w i l l l i k e l y b e t o o low f o r a l l o y s such as PnconeP 608 w i t h o u t c l o s e r c o n t r o l s on chemistry, g r a i n s i z e , and o t h e r f a c t o r s . The s t a i n l e s s s t e e l s are a l s o enmbrittled by i r r a d i a t i o n , b u t i t is p o s s i b l e t h a t t h e f r a c t u r e s t r a i n s under MSBR s e r v i c e c o n d i t i o n s will b e adequate [4H]. I f n o t , s i g n i f i c a n t improvements have been made i n types 304 and 316 s t a i n l e s s s t e e l by c o n t r o l l i n g t h e g r a i n s i z e o r a l t e r i n g t h e composition (such as adding small amounts of T i ) [ 4 2 ] .

206

A s a l r e a d y n o t e d , ‘ i n t e r g r a n u l a r c r a c k i n g w a s observed i n t h e surme most v e i l l a n c e s a m p l e s and several components from t h e MSRE [ l 7 ] . s i g n i f i c a n t c h a r a c t e r i s t i c s of t h e cracks are :

1.

Cracks were formed on dl s u r f a c e s exposed t o fuel salt.

2.

3.

Some cracks w e r e visible i n p o l i s h e d sections from some components ( p a r t i c u l a r l y the h e a t exchanger) whem they w e r e removed from service, b u t deformation a t i e n t %eVeKatU%e W a reqUf.h-ed tQ m k e moat show up.

4.

The material removed from the PISRE had been h e a t e d and exposed to fission p r o d u c t s %IX t i m e s r a n g i n g from 2500 t o 25,080 h r . Although the fKequWlCy O f Cracks ita@lpeaS@d W i t h t i m e , the ximum d e p t h d i d not i n c r e a s e d e t e c t a b l y e

W e have n o t been a b l e to produce s i m i l a r i n t e r g r a n u l a r cracks by To determine if cob-rosion c ~ u l db e t h e cause, the salt i n adding F ~ P ~selective . one f u e i - s d t l o o p w a s made q u i t e oxiafzing E L I - I U I ~ ~ attack occurred, b u t the a t t a c k w a s very s h a l l o w and t h e ea grain b o ~ ~ ~ d a r di ieds not open f u r t h e r during s t r a i n i n g . ‘$he d most convinein evidence that c o ~ r oiso n (chrsmfm d e p l e t i o n ) e d i r e c t l y from examination of HSRE samples. caepietion coeb~dnot h e d e t e c t e d in s a w p i e s from the and i n a s e c t i o n of t h e c o n t r o l rod thimble that was under ? these samples t ~ e r ecracked as s e v e r e l y as those (e.g. t h e b a r e c o n t r o l rod thimble) i n which chromium d e p l e t i o n was d e t e c t a b l e . u n l i k e l y t h a t c h r ~ m i u md e p l e t i o n alone can account f o r t h e CO~IXXS~QR.

ible mechanism to b e c o n s i d e r e d i s that OW o r several elements d i f f u s e d i n t o t h e material p r e f e r e n t i a l l y along t h e b o ~ a d a r i e sand degraded them i n some way- The p r u c e s s respon t h e cracking could b e (1) the formation sf a compound that is very brittle, (2) f s r a a t i o n of low-melting phases a l o n g t h e grain boundaries that become l i q u i d at operating t e m p e r a t u r e , 0% ( 3 ) a change i n compositiom along the g r a i n boundaries s o that they are s t i l l s o l F d b u t very Weak. ‘61a@ f i r s %and t h i r d FWchank3mS W o d d require SQEE defOKHlathn to form the c r a c k s , b u t the second mechanism w o d d ~ l s tr e q u i r e s t r a i n , and samples could have c r a c k s p r e s e n t before pos t s p e r a t i a n d e f o C l e a r l y , i t i s extremely important that t h e elements r e s p o n s i b l e f o r the c r a c k i n g b e identified and t h a t t h e HngchaniSn? b e determined. h a l y t i c a l data from materials from the MSRE show t h a t a l l sf the f i s s i ~ n p r o d u e t s with s u f f i c i e n t h a l f - l i v e s t o b e d e t e c t a b l e a f t e r two y e a r s were

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p r e s e n t i n t h e m e t a l a t d e p t h s up t o a few m i l s and some n u c l i d e s w i t h h a l f - l i v e s t o o s h o r t to d e t e c t could have a l s o been present. h e sample w a s o x i d i z e d t o p a s s i v a t e t h e o u t e r s u r f a c e t o t h e r e a g e n t and t h e n s t r a i n e d S Q t h a t o n l y t h e c r a c k s w e r e l e a c h e d . Several f i s s i o n p r o d u c t s p l u s s u l f u r and phosphorus were p r e s e n t in h i g h c o n c e n t r a t i o n s . Thus, i t seemed p r o f i t a b l e t o look a t a l l of t h e e l e m e n t s i n t h e f i s s i o n spectrum with s u f f i c i e n t h a l f - l i v e s t o d i f f u s e i n t o t h e m e t a l . Our f i r s t a t t e m p t a t t h i s is shown i n T a b l e 7 . 2 , which c o n t a i n s t h e i n f o r m a t i o n t h a t w e f e e l t o b e most r e l e v a n t . Some of t h e d a t a are from o u r c u r r e n t r e s e a r c h , and o t h e r s w e r e o b t a i n e d from t h e l i t e r a t u r e [ 4 3 ,

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aS shown i n Table 7 . 2 , s u l f u r and s e l e n i u m had d e t r i m e n t a l e f f e c t s m d e r some t e s t c o n d i t i o n s , b u t t e l l u r i u m had a more pronounced e f f e c t i n a l l t y p e s of t e s t s run t o d a t e . These t h r e e e l e m e n t s form r e l a t i v e l y u n s t a b l e f l u o r i d e s and w s d d l i k e l y b e d e p o s i t e d on t h e metal and g r a p h i t e s u r f a c e s . A r s e n i c , antimony, and t i n a l s o wou1d b e d e p o s i t e d , b u t no d e l e t e r i o u s e f f e c t s of t h e s e e l e m e n t s OR t h e m e c h a n i c a l p r o p e r t i e s s f n i c k e l a l l o y s have been n o t e d . Zinc and cadmium may e i t h e r b e d e p o s i t e d o r p r e s e n t i n t h e s a l t , depending on t h e o x i d a t i o n s t a t e of t h e s a l t . Both of t h e s e e l e m e n t s are r e p o r t e d t o b e i n s o l u b l e i n n i c k e l , and w e have n o t observed m y d e l e t e r i o u s e f f e c t s i n o u r tests. Ruthenium, t e c h netium, molybdenum, and rhodium s h o u l d d e p o s i t on s u r f a c e s , b u t w e have s e e n no d e l e t e r i o u s e f f e c t s from them i n o u r tests. Zirconium, s t r o n t i u m , cesium, a d cerium form v e r y s t a b l e f l u o r i d e s and s h o u l d remain i n t h e s a l t . W e have no e v i d e n c e , p o s i t i v e o r n e g a t i v e , on t h e e f f e c t s of s t r o n tium a n d cesium on t h e m e c h a n i c a l b e h a v i o r , b u t p r e s e n t l y b e l i e v e t h a t t h e s e e l e m e n t s w i l l s t a y i n t h e s a l t and n o t e n t e r t h e m e t a l ; z i r c o n i u m and c e r i u m d o n o t have a d v e r s e e f f e c t s when added t o H a s t e l l ~ yN. Niobium can b e e i t h e r i n t h e s a l t o r d e p o s i t e d , depending on t h e o x i d a t i o n s t a t e , b u t as mentioned i n d i s c u s s i n g i r r a d i a t i o n b e h a v i o r , i t h a s f a v o r a b l e e f f e c t s on t h e mechanical p r o p e r t i e s Thus, a l t h o u g h some e x p l o r a t o r y work remains, i t a p p e a r s t h a t t h e c r a c k i n g could b e caused by t h e inward d i f f u s i o n of e l e m e n t s of t h e s u l f u r , s e l e n i u m , t e l l u r i u m f a m i l y w i t h t e l l u r i u m having t h e m s t a d v e r s e effect Our s t u d i e s c o n s e q u e n t l y have c o n c e n t r a t e d on t e l l u r i u m . S i n c e t h e s e e l e m e n t s a l l behave s i m i l a r l y , an u n d e r s t a n d i n g of how t e l l u r i u m c a u s e s c r a c k i n g s h o u l d l e a d t o an u n d e r s t a n d i n g of t h e b e h a v i o r of t h e o t h e r elements. Numerous l a b o r a t o r y e x p e r i m e n t s have been r u n t h a t d e m o n s t r a t e v e r y c l e a r l y t h a t s m a l l m o u n t s of t e l l u r i u m w i l l cause i n t e r g r a n u l a r c r a c k i n g i n M a s t e l l o y N. These e x p e r i m e n t s i n c l u d e : ( 1 ) t h e measurement of g r a i n boundary and b u l k d i f f u s i o n c o e f f i c i e n t s of t e l l u r i u m i n H a s te1Poy N t y p e 304 s t a i n l e s s s t e e l , and n i c k e l ; ( 2 ) ~ X ~ Q S U Eof n u m e r ~ ~materials s t o e l e c t r s - QP v a p o r - p l a t e d t e l l u r i u m w i t h s u b s e q u e n t s t r a i n i n g and m e t a l l o g r a p h i c e x a m i n a t i o n ; (3) t u b e b u r s t specimens of H a s t e l l o y %J and t y p e 304 s t a i n l e s s s t e e l e l e c t r o p l a t e d w i t h t e l l u r i u m and s t r e s s e d i n s a l t ; ( 4 ) c r e e p t e s t s of H a s t e l l o y N, t y p e 304 s t a i n l e s s s t e e l , n i c k e l , and I n c o n e l 600 i n i n e r t g a s - t e l l u r i u m v a p o r environments; ( 5 ) s t r a i n cycle e x p e r i m e n t s of B a s t e l b o y N e l e c t r o p l a t e d w i t h t e l l u r i u m t o d e t e r mine c r a c k p r o p a g a t i o n rates; and (6) mechanical p r o p e r t y tests QR a l l o y s c o n t a i n i n g s m a l l amounts of f i s s i o n p r o d u c t .

Tnb,le7.2. Fbssibleeffects of severalelementson the crackingof kiastelloyP

Element

Sulfur Selenium Tellurium Ai%fliC

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Tin %inc Cadmium Ruthenium Technetium Niobium Zirconium M0lybd~Wl-f strontium Cesium cerium Rhodium

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aThe symbols used in this table should be interpreted in the following way: A plus refers to nondetrimental behavior, and a minus indicates detrimental effects. Two minuses indicate particularly bad effects. hWesults of current rrJtiruch. cC. 6. Bieber and R. F. Decker, “‘The Melting of Malleable Nickel and Nickel Alloys,” Trans. AI&E 221, 629 (1961). %. R. Wood and W. M. Cook, “Effects of Trace Contents of Impurity Elements cm the Creep-Rupture Properties of Nickel-Base Elements,“” AWetullurgia (BOO,109 (1963). ePrivate communication, W. R. Grimes, QRNL. hay appear as H2S if HF concentration of melt is appreciable. Way appeu in salt if salt mixture is sufficiently oxidizing.

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The d i f f u s i o n rate s f t e l l u r i u m i n t o H a s t e l l o y N w a s measured. Samples w i t h 1 2 7 ~ ed e p o s i t e d on t h e s u r f a c e were annealed f o r 3000 hr at 650 and 760°C. A t 650°C t h e p e n e t r a t i o n w a s s o s h a l l o w t h a t t h e l a p p i n g t e c h n i q u e used d i d n o t g i v e v e r y r e l i a b l e v a l u e s , b u t a c c u r a t e r e s u l t s w e r e o b t a i n e d a t ? 6 0 a C and t h e d i f f u s i o n c o e f f i c i e n t i n t h e b u l k material w a s 1 . 0 1 x cm2/sec, about e q u i v a l e n t t o t h a t of chromium a t 650°C. me p e n e t r a t i o n p r o f i l e s a l s o were used t o o b t a i n t h e p r o d u c t of t h e g r a i n boundary width and t h e g r a i n boundary d i f f u s i o n c o e f f i c i e n t , and t h e measured q u a n t i t i e s were then used w i t h t h e F i s h e r mode1 [ 4 5 ] t o compute t h e g r a i n boundary p e n e t r a t i o n . Ar; shown i n Fig. 7.1, t h e M ~ X imum p e n e t r a t i o n of t e l l u r i u m i n an blSBR a t 760°C would b e 8 m i l s i n 30 y e a r s . The l e s s a c c u r a t e e x p e r i m e n t a l v a l u e s o b t a i n e d at 650°C were used t o estimate t h a t t e l l u r i u m s h o u l d have p e n e t r a t e d t h e g r a i n b o u n d a r i e s i n t h e MSRE to a d e p t h of 2 to 3 m i l s , and the p e n e t r a t i o n of an MSBR o p e r a t i n g a t 650°C f o r 30 y r s h o u l d b e about 4 m i l s . The r e l a t i v e l y l o w s e n s i t i v i t y of t h e p e n e t r a t i o n depth t o t h e t i m e i s due t o t h e v a r i a t i o n w i t h t i m e t o t h e one-fourth power f o r g r a i n boundary d i f f u s i o n compared w i t h t h e one-half power f o r b u l k d i f f u s i o n . These computed d e p t h s of p e n e t r a t i o n are q u i t e a c c e p t a b l e , b u t seve r a l f a c t o r s can move t h e c u r v e s . &e f a c t o r t h a t could reduce t h e penet r a t i o n is t h a t t h e supply of t e l l u r i u m t o t h e H a s t e l l o y N would c o n t r o l t h e r a t e of p e n e t r a t i o n rather t h a n d i f f u s i o n through t h e m e t a l . This i s q u i t e p o s s i b l e , s i n c e t h e c o n c e n t r a t i o n of t e l l u r i u m i n t h e salt would b e v e r y low, and o t h e r f i s s i o n p r o d u c t s such as mlybdenum would d e p o s i t and p o s s i b l y i n t e r f e r e w i t h t e l l u r i u m a c t u a l l y r e a c h i n g t h e H a s t e l l o y N. A t l e a s t one f a c t o r could i n c r e a s e t h e p e n e t r a t i o n . Cracks SOU^^ form and t h e d i f f u s i o n f r o n t move inward, such as p r o b a b l y o c c u r r e d i n t h e specimen t h a t w a s exposed t o t e l l u r i u m w h i l e b e i n g s t r e s s e d i n a c r e e p machine. Another f a c t o r could move t h e p r o f i l e s e i t h e r way; compounds such as n i c k e l - t e l l u r i d e s may form a l o n g t h e g r a i n b o u n d a r i e s , and the t e l l u r i u m may d i f f u s e at h i g h e r o r lower rates through t h e s e compounds than through H a s t e l l o y N . Thus, a l t h o u g h t h e d i f f u s i o n measurements p r o v i d e an e x p l a n a t i o n of t h e l i m i t e d p e n e t r a t i o n i n t h e MSRE and o f f e r some encouragement t h a t t h e depth of p e n e t r a t i o n of t e l l u r i u m would n o t b e v e r y g r e a t i n an MSBR, they cannot be t a k e n q u a n t i t a t i v e l y . L i t t l e 2s known about t h e c h e m i s t r y o f t e l l u r i u m , b u t most l i k e l y i t i s s i m i l a r t o t h a t of s u l f u r . The b a s i c problem w i t h n i c k e l a l l o y s c o n t a i n i n g s u l f u r i s due t o a low m e l t i n g n i c k e l - s u l f u r e u t e c t i c t h a t forms when s u l f u r s e g r e g a t e s in the g r a i n b o u n d a r i e s and causes t h e s e r e g i o n s to b e weak compared w i t h t h e matrix. A l l o y i n g a d d i t i o n s such as chromium raise t h e m e l t i n g p o i n t of t h e e u t e c t i c and reduce the magnitude of t h e problem. Some p r o p r i e t a r y work on s u p e r a l l o y s shows t h a t about 16X chromium is r e q u i r e d t o make a s u p e r a l l o y resist embrittkement by s u l f u r . Assuming p a r a l l e l b e h a v i o r of telbkurium, i t s d e l e t e r i o u s e f f e c t s on H a s t e l l s y N might b e o f f s e t by t h e a d d i t i o n of chromium. A d d i t i o n s o f t e l l u r i u m , s e l e n i u m , and s u l f u r are o f t e n made to s t e e l s t o o b t a i n improved m a c h i n a b i l i t y b u t they cause e m b r i t t l e m e n t a t h i g h t e m p e r a t u r e s . Small cerium a d d i t i o n s have been e f f e c t i v e i n r e d u c i n g t h e e m b r i t t l e m e n t . Thus cerium a d d i t i o n s t o H a s t e l l o y N may a l s o be e f f e c t i v e i n making t h e t e l l u r i u m innocuous.

210

Fortunately, t e l l u r i u m probably behaves i n n o n - f i s s i o n i n g m e l t s much as i t does i n a f i s s i o n i n g s a l t , s o t h a t l a b o r a t o r y experiments can b e used t o answer many q u e s t i o n s . Assuming this is s o , o v e r sixty a l l o y s were e l e c t r o p l a t e d w i t h telluri~mand annealed f o r l o n g p e r i o d s of t i m e t o a t e t h e e f f e c t s Sf COSIlpQSition, ibtC]lkllding h i g h e r ChlrOmiklnm COnceIlt r a t i o n OR t h e c r a c k i n g phenomenon. Included w e r e s e v e r a l n i c k e l - b a s e a l l o y s , r e p r e s e n t a t i v e a l l o y s of types 200, 300, 4 0 0 , and 500 s t a i n l e s s steel, n i c k e l , copper9 i r o n , Moanel, two c o b a l t - b a s e a l l o y s , and s e v e r a l h e a t s of modified and s t a n d a r d H a s t e l l o y N. A f t e r b e i n g annealed, t h e samples w e r e s t r a i n e d at room temperature and s e c t i o n e d for m e t a l l o g r a p h i c examination. No c r a c k formed i n i r o n , c s p p e ~ ,M ~ ~ b e lthe , stainless s t e e l s , o r t h e n8Ckel-baS@ a%lQyPsCOntaifliIlg more than 15% C h r s m i W . However, cracks d i d form i n s t e l l s y B ( 1 X e h ~ o ~ ~ ~maximum), iurn H a s t e l l o y W (5% C ~ ~ Q E I ~ Uand E I )i n most h e a t s of Wastelloy N (7% chromium). Some of the heats of modified H a s t e l l o y N had better r e s i s t a n c e t o c r a c k i n g than standard Mastelloy N . These a l l o y s c o n t a i n e d s e v e r a l a d d i t i o n s , b u t t h e only a d d i t i o n CQITIITI~~t o the improved heats w a s 2% niobium, and the two a l l o y s t h a t c o n t a i n e d 2% niobium were completely f r e e of c r a c k s . Typical pkotsmiersgraphs of s e v e r a l a l l o y s a f t e r exposure t o t e l l u r i u m m d d e f o r anatlsn a t room t e m p e r a t u r e are shown i n P i g . 7 . 3 . A s i m i l a r t y p e of experiment was r u n i n which test samples were exposed t C l Sknall ~ O U t l t Ss f tellblriUID Vapor. meSC?@Xgerilllents were ‘KUHl i n q u a r t z , which i s n o n r e a c t i v e w i t h t h e materials, and i n c l u d e d vacuum Thus, the oxygen levels were low and the condio u t g a s i n g and bakestat. t i o n s s h o u l d r e p ~ e s e d kthose t h a t would b e expected i n a r e d u c i n g s a l t . S e v e ~ a lmaterials have been exposed under t h e s e c o n d i t i o n s and s t r a i n e d t o failure. f i e r e s u l t s o b t a i n e d t h u s f a r g e n e r a l l y a g r e e w i t h t h o s e obtained i n the experiments where the t e l l u r i u m was e l e c t r o p l a t e d the t e s t sarmple. HasteEIoy N formed i n t e r g r a n u l a r c r a c k s , b u t the i n t e n s i t y of c r a c k i n g v a r i e d w i t h composition. N i c k e l formed some i n t e r g r a n u l a r c r a c h . Type 384 StaiIl%essS t e e l d i d n o t Crack. I n C O n g l 660 had DOC eraeked i n t h e p l a t i n g e x p e ~ i m e n t sbut d i d form s h a l l o w i n t e r g r a n u l a r c r a c k s im t h e vapor experiments. Assuming t h a t 14% chromium is r e q u i r e d f o r protection a g a i n s t t e l l u r i u m embrittlemen as it is a g a i n s t sulfurP, t h e 15% chromium i n Ineonel 600 should be m a r i n a l i n p r e v e n t i n g embrittlement. Thus, t h e d i f f e r e n t b e h a v i o r in t h e two t y p e s of experiments nay b e a r e s u l t sf the e x p e r i m e n t a l techniques o r something more nebulous such a8 small. chemical v a r i a t i o n s i n the two heats of material involved. These l i m i t e d o b s e r v a t i o n s i n d i c a t e t h a t many materials are more resistant than Hastelboy N t o i n c e r g r a n u l a r c r a c k i n g by t e l l u r i u m , with most showing no d e l e t e r i o u s e f f e c t s . Among t h o s e u n a f f e c t e d i n t h e tests, a n o t e d , w e r e n k k e l - b a s e a l l o y s c o n t a i n i n g 28% or more c h r o d u ~ ~ , s t a i n % e s s s t e e l s , coppers and Monel. me r e s u l t s on Ineonel 600 (15% CklfQfllibura)W e r e inC0IbclWSiVe. me tests O f t h e modified heats of HaStel%Oy N o f f e r e d some encouragement t h a t t h i s a l l o y can be made resistant by c ~ m p o s i t i ~ n achanges. l These r e s u l t s s u g g e s t t h a t t h e r e may b e several lIlaterkals Whose U s e F J O U l d avoid t h e CraCkhg prQbhXl.

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212

me psrecedb c u s s i o n i n d i c a t e s t h a t t h e metal t o b e used f o r f a b r i c a t i o n of an IRUSt S a t i s f y three I W i b r@guiPeIilentS: (1) COKIpatibi%i.ty with the working f l u i d s ( f u e l salt, c o o l a n t s a l t steam) ( 2 ) adequate p l a s t i c i t y a f t e r n e u t r o n i r r a d i a t i o n , and ( 3 ) r e s i s t a n c e t o i n t e r g r a n u l a r c r a c k i n g by f i s s i o n products. A s i n g l e material. need n o t s a t i s f y a l l sf these, s i n c e a l l p a r t s of the system do not have t h e same requirements. However, the use of dissiIl-Lk3.r materials i n t r o d u c e s cornp l e x i t y 0% desi s o the p o s s i b i l i t i e s f o r matting t h e system of one material need t o b e considered. Severall of t h e materials that w e p r e s e n t l y view as b e i n g r e a s o n a b l e c h o i c e s are l i s t e d i n Table 7 . 3 . The first shown, a m d f f i e d Mastelloy N , is highly p r e f e r r e d b u t i t s u s e , of course, depends upon b e i n g able to a l t e r t h e compos i t i o n t o s t o p t h e i n t e r g r a n u l a r c r a c k i n g Whether H a s t e l l o y N can b e used i n the s t e a m g e n e r a t o r will depend upon its compatib i l i t y with steam, which, as d i s c u s s e d more f u l l y i n Chapter 8, is s t i l l s u b j e c t t o question. The peak temperature w i t h t h e materials used i n s e l e c t i o n h w s d d IikePy b e 1300째F. OUK second c h o i c e tsouEd b e t o use t y p e 384 stainless steel in the r y c i r c u i t because i t appears t o have excellent r e s i s t a n c e to damage by t e l l u r i u m . The a d d i t i o n of about 0.2X T i to t h i s material has already been s h o ~ ~ xt o i b e an adequate s o l u t i o n t o t h e problem of i r r a d i a t i o n embrittlelIEnt. "%hel E 3 h qUeStk3Il KegaKdin type 304 s t a i n l e s s steel conc e r n s its corrosion in fuel salt, and t h e outlet f u e l temperature i n the r e a c t o r might have to b e r@dUced to IoWelP t h e COlfrClSiQn K a t e . StZiiH-rlesS s t e e l w i l l l i k e l y n o t have adequate c o r r o s i o n r e s i s t a n c e i n t h e s o s l a n t t r a n s i t i o n to WastePEoy M would b e made i n t h e i n t e r m e d i a t e era This would r e q u i r e a duplex t u b e of t y p e 384 s t a i n l e s s i n s i d e and HasteElsy N on t h e o u t s i d e . B u r third c h o i c e a t t h i s t i m e would b e a system made e n t i r e l y o f a n i c k e l - h i g h chromium a l l o y . The a v a i l a b l e C O K ~ O S ~ Q I Idata on I h e o n e l 608 (1% &romfum) sug est t h a t such a system would have an a c c e p t a b l e corrosion r a t e with f u e l salt a t a b o u t 1280째F. However, these d a t a w e r e obtained a number sf years ago on ~ ~ ~ a t i v ie~ il pyu r es a l t s , t ~ a~a adi t i s n a i C Q r P O S i O n t e s t i n g Will be r@qui?Zed, h C o E X 3 l 688 has no%:been tested under c o n t r o l % e d additions i n sodium flrasrsbaara e s b u t OM% presmt derstanding of t h e chemical b e h a v i o r of t h i s s a l t ives reasonable hope Of a c c e p t a b ~ ecompatibility. nis a l l o y has been in many steam gene r a t o r s and the e x p e r i e n c e has been f a v o r a b l e . The main problem with Inconel 600 i s embrittHment b y neutron i r r a d i a t i o n . We have been able to improve the r e s i s t a n c e of H a s t e l l o y N and t y p e s 304 and 316 s t a i n l e s s s t e e l by c o n t r o l l i n g variables such as g r a i n size, heat treatment, and c ~ ~ ~ p o s i t i obw u t, t h i s a b i l i t y muat be demonstrated f o r a nickel-higl? chromiuln alloy. The f o u r t h materials s e l e c t i o n would i n v o l v e the u s e of the p a r t i a l l y developed 22 Ti-modified H a s t e l l s y N i n the e n t i r e system w i t h the surfaces exposed t o f u e l s a l t b e i n g cov ed ( w e l d overlay, duplex t u b i n g , c l a d d i n g ) by s t a i n l e s s s t e e l o r Monel. i s would r e q u i r e t h a t t h e d e t a i l s of the processes b e developed to i n c l u d e j o i n i n g to insrare integrity d U K h g S e K V i C e

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several of these selections involve duplex t u b i n g and: clad struct u r e s . Methods f o r wakin duplex t u b i n g techniques for wela overlaying generally e x i s t f o the materials involved. %e greatest complication comes about in j o i n i n where, a l t h ~ ~ gthe h basic ability to make such j o i n t s is a v a i l a b l e , jo t d e s i p s a d w e l d i n g procedures must ~ s e developed for each material. h e further method that has been considered for handling the cracki n g problen is to getter the fission product tellurium frorn t h e s a l t with some reactive material. The ammt of tellurium produced is quite small, and a very efficient filter would be r e q u i r e d . To be effective, this f i l t e r would have to be placed near the reactor outlet, and the pressure d r u p , heat generation rate, and salt holdup associated with it would likely be Very h i g h . 'FhUS, W e have deV0-d Only lianited attention t o t h i s approach Our preferences in Table 7 . 3 clearly favor s t a y i n g with HastePloy N as a structural material. Its resistance to corrosion by f l u o r i d e s a l t s has been w e l l demonstrated, and irradiation e m b r i t t l e m a t appears to be taken care of adequately by t h e a d d i t i o n u f titanium. Consequently, a change to another material should be made Q ~ P Yif it becomes clear that Hastelloy N cann t be further m s d i f i e d to improve its resistance to interranular cracki In the event t h a t a change of materials is necessaryr Fckel-base a l l a p p e a r preferable t~ iron-base a l l o y s because t h e s a l t can b e &uoWed to b e m o r e Q X i d i Z i l l w i t h n i c k e l . H o w e v e r , th@ s t u d i e s t h u s f a r i n d i c a t e t h a t the iron-ba e alloys offer more resistance to intergranular c r a c k i ~ g . Thus, these two factors must be balanced against each o t h e r i n s h o o s i n a material, and this w i l l be p o s s i b l e only when more data are available on t h e resistance of different alloys to cracking a d their corrosion resistance in s a l t . a

Further Mark 6%OSt p r e s s i n g problelll W i t h &iStE?l;bQyN is its S u ยง C e p t i b i % i t y to grain boundary cracking when exposed eo f i s s i s n products in f u e l salts, Work in t h e immediate future will concentrate on determining whether acceptable chemical modifications to H a s t e l l o y N will adequately fmprsve its resistance to cracking. Experinents already run indicate that the addition of 2% niobium may be effective, and Hastellays containing more than 162 chromium are n o t attacked. Nodifications of Hastelloy N con-taining v a r i o u s concentrations of chrumium, i r o n man m e s e , silicon, titanium, and cerium w i l l be annealed in the presemce of t e l l u r i u m , and evaluated f o r crack susceptibility. If an alloy near the Kaste11oy N composition can b e shown t o b e i m u n e t o tellurium, it must then b e irradiated 60 determine whether it has adequate ductility in t h e irradiated condition, and tests in salt must b e run t o determine t h e operating ternperature E i ~ ~ L t a t i ~imposed ns by c a r r s s i o n . Further work to develop the irradiation resistant microstructure in the modified a l l o y will be reqtlired if the modificati~nhas altered its resistance t o radiatio18. In addition to working on H a s t e l l s y N, we will evaluate a nickelhigh &KOIE~.UITI a l k ~ y . Inconel 600 ( w i t h 15% chromium) seem to be borderline in its tendency to f o ~ minter r a n u l a r cracks, auad an a l l o y with about $

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20% chromium w i l l l i k e l y b e r e q u i r e d t o resist cracking. If experiments show t h a t this i s t h e case, t h e main u n c e r t a i n t i e s w i l l become t h e duct i l i t y o f t h e m a t e r i a l i n t h e i r r a d i a t e d c o n d i t i o n and t h e maximum ope%a t i n g temperature at which t h e c o r r o s i o n r a t e i s t o l e r a b l e . Sample materials of several. high-chromium commercial a l l o y s such as H a s t e l l o y X, H a s t e l l a y C, and bncoloy $06 w i l l b e included i n o u r experiments t o determine whether they r e s i s t c r a c k i n g under very s t r i n g e n t t e s t c o n d i t i o n s The a l l o y s t h a t are r e s i s t a n t to c r a c k i n g w i l l b e i r r a d i a t e d and t h e i r p o s t i r r a d i a t i o n c r e e p p r o p e r t i e s determined t o e v a l u a t e t h e magnitude of t h e i r r a d i a t i o n embr i t t lement problem. "he c a r b i d e s i n Encoloy 880 a r e b a s i c a l l y Cr23C+j (such as o c c u r s i n s t a i n l e s s s t e e l s ) and i t i s q u i t e l i k e l y t h a t c l o s e c o n t r o l of t h e titanium, n i t r o g e n , and carbon c o n c e n t r a t i o n s w i l l r e s u l t i n adequate re~ F s t a n s et o i r r a d i a t i o n e m b r i t t l e m e n t 6421 The c a r b i d e s i n H a s t e l l o y s X and C are molybdenum-base j u s t as t h o s e i n H a s t e l l o y N . Thus, we have e x p e r i e n c e w i t h b o t h types of c a r b i d e s i n t h e s e a l l o y s and can l i k e l y modify t h e m i c r o s t r u c t u r e t o o b t a i n improved r e s i s t a n c e to i r r a d i a t i o n embrittlewent i f necessary. The i n i t i a l c o r r o s i o n experiments w f l l PnvoEve thermal convection Poops made of two r e p r e s e n t a t i v e a l l o y s t o determine whether such h i g h chromium l e v e l s can b e t o l e r a t e d a t a r e a s o n a b l e o p e r a t i n g temperature. I f t h e s e r e s u l t s are f a v o r a b l e , a pumped loop w i l l b e p u t i n o p e r a t i o n t o investigate corrosion a t higher f l u i d v e l o c i t i e s Although a l l s t a i n l e s s s t e e l s examined r e s k t i n t e r g r a n u l a r c r a c k i n g b y t e l l u r i u m , t y p e 384 s t a i n l e s s s t e e l would l i k e l y b e our c h o i c e mong them because of i t s m e t a l l u r g i c a l s i m p l i c i t y and e x t e n s i v e i n d u s t r i a l p r o d u c t i o n a d u s e . This a l l o y s e e m s t o have adequate r e s i s t a n c e t o emb r i t t l e m e n t b y thermal n e u t r o n f l u e n c e s of t h e magnitude that w e w i l l e n c o u n t e r . The key f a c t o r t h e r e f o r e i s whether i t p o s s e s s e s adequate c ~ r r o s i o nr e s i s t a n c e a t a r e a s o n a b l e o p e r a t i n g temperature TWQ s t a i n less s t e e l thermal convection loops are c u r r e n t l y i n o p e r a t i o n and t h e n e x t s t e p w i l l b e t o s t a r t a f o r c e d convection loop. Because of t h e importance of t h e i n t e r g r a n u l a r c r a c k i n g problem, simultaneous p r o g r a m should b e c a r r i e d o u t on all t h r e e types of m a t e rials that have b e e n d i s c u s s e d . Materials will be dropped and others added as e x p e r i m e n t a l f i n d i n g s w a r r a n t . The materials t h a t appear a c c e p t a b l e from t h e s t a n d p o i n t s of corros i o n , i r r a d i a t i o n e m b r i t t l e m e n t , and r e s i s t a n c e t o t e l l u r i u m must b e s u b j e c t e d t o some i n - r e a c t o r t e s t i n g . W e a r e reasonably c o n f i d e n t t h a t t e l l u r i u m i s t h e element c a u s i n g t h e c r a c k i n g and t h a t its chemical beh a v i o r w i l l b e e q u i v a l e n t in i n - r e a c t o r and out-of - r e a c t o r tests. Howe v e r , some v e r i f i c a t i o n of t h i s w i l l b e r e q u i r e d . The f i r s t s t e p w i l l b e s t a t i c c a p s u l e tests and a c a p s u l e experiment is being designed f o r t h e O m i n which s t a n d a r d H a s t e l l o y N and a l l o y s t h a t are expected t o b e r e s i s t a n t t o t e l l u r i u m w i l l be exposed t o f i s s i o n i n g salt under i d e n t i c a l c o n d i t i o n s . L a t e r tests should i n v o l v e s t r e s s e d samples. W e p r e s e n t l y f e e l t h a t more s o p h i s t i c a t e d i n - r e a c t o r tests t h a t s i m u l t a n e o u s l y demons t r a t e d l of t h e c o n d i t i o n s t o b e encountered i n a r e a c t o r , i n c l u d i n g h e a t t r a n s f e r and forced-convection f l o w , are n o t n e c e s s a r y s b u t t h i s , w i l l have t o b e re-evaluated as t h e program p r o g r e s s e s . a

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Following t h e path t h a t has been outlined, we should be able to make a conclusive choice of materials within a b o u t t w o years. However, many tion tests w i l l have to operate beyond t h i s time. Additional effort w i l l be needed if a duplex system is required, since methods must b i developed f o r m k i n g clissiaiaar j o i n t s , duplex tubing, and weld overlays 0

h . ,

~... Y

Evaluation

The b a s i c requirements of a structural material are that it b e compatible w i t h its environments, have acceptable mechanical properties b o t h W i r K a d i a t e d and a f t e r exposure to the maximum expected neutron fluence, and be capable of being fabricated w i t h reasonable ease. 'Two cornpatib i b i t y problems exist, one b e i n the selective removal of chrsfnim and t h e o t h e r b e i n g intergranular c ~ ~ ~ l b idue n p to t h e i n f u s i o n of f i s s i o n products ( l i k e l y tellurium) OUK e x p e r l e ~ c ewith H a s t e l l o y %a has been very favorable so far as corrosion is concerned. Chemical modifications have made the irradiation e m b r i t t l e ~ n ttolerable, and t h e r e is reasonable evidence that f ~ r t h e r chemical modifications can be made to c o n t r o l t h e intergranular cracking. Tfie development sf a suitable modification of H a s t e l l o y N t h a t can be safely used with f i s s i ~ ~ i t lf ug e l salt should be the central thrust of the materialbs development program. Nickel-high chromim a l l o y s appear t o resist i e r g r a n u l a r cracking by tellurium, b u t t h e extent of t h e i r irradiation e KittleIXnt n % U s t be e v a l u a t e d by experiments and t h e i r C O ~ X - C I S ~behav Q ~ r aust be s t u d i e d in nore d e t a i l . Previous tests w i t h relatively i n p u r e s a l t s and ~ ~ n s i d e r ation of chromium d i f f u s i o n r a t e s in the n e t a l indicate t h a t the peak ) be about 120Q'F. erature f o r I n c o n e l 600 (15% c h ~ ~ m i u mwould e s s a r y f i r s t to determine the minimuan chromium concentration r e q u i r e d to p r e v e n t i n t e r g r a n u l a r cracking, and then t h e q u e s t i ~ n i r r a d i a t i o n e ~ ~ b ~ i t t l em~dn t c o r r o s i o n must be evaluated. Type 304 stainless s t e e l offers excellent resistance to intergranular cracking by tellurium and has acceptable resistance to embrittlewent by n e u t r o n i r r a d t a t i o n , b u t its c ~ r r ~ s i oresistance n m u s t be evaluated more ~ o m ~ l and e ~ vee r ~ y ~ likely it will net be usable above l260'P. Other materials such as Hone1 aRd copper resist cracking by telluriUEa ibFbd Can P Q s s i b I y b@ Used as C o a t i n s in the psl-imary c i r c u i t . However, COnSiderZib%e deV@lOpElent Work W Q U d be required to follow this route * Our work t h u s shows t h a t there may be several materials that will s a t i s f y the basic requirements f o r MSBB piping and vessels. However, some further i n v ~ i ~ ~ t i g awt i lol ~be necessary b e f o r e choosing the most d e s i b a b l e QptiCXl. Tellurium does not form v e r y stable fluoride in MSBW fuel s a l t , 80 it d e p o s i t s on metab s u r f a c e s i n t h e reactor leading to t h e i n t e r g r a n ular cracking that we have observed. Since t h i s pr~cessinvolves the interaction O f the t1K1 meta$s, ft Should net d i f f e r in ii nbad.eaP eXlVirOIllnent and a laboratory e eriment. This means t h a t most ef t h e e e

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work can be conducted in the laboratory, with o n l y P f m f t e d in-reactor work being required f o r confipfaati~n. Consequently, we envision t h a t this testing program can continue to move ahead rapidly, and expect that an acceptable remedy can be demonstrated convincingly in about two years, although more extensive tests of a eonfirnative nature will require a longer time.

.......... .._

218

References f o r Chapter 7

1.

2.

3.

4. 5. .... ' . e

6, 7.

J. H. DeVan, MS aaesis ( U n i v e r s i t y of Tennessee, 1940).

12

6

14

e

15

0

219

16.

H. E. McCoy, J K ~An, EzPahat&m o f t h e Molten-Salt Reactor Experiment HmbelZoy 19 S m e i Z l a n c e Specimens - T h i r d Groxp, OR%9E-TM-2647 (1978)

17. H. E. McCoy, Jr., The HSRE m d I t s OpePation, r e p o r t to b e p u b l i s h e d . ...,

:.:.:a

18.

D. la. Harries, "Neutron I r r a d i a t i o n E m b r i t t l e m e n t of A u s t e n i t i c S t a i n l e s s S t e e l s and N i c k e l Base A l l o y s , " J . B ~ z t .2liucZ. E m r g y Ssc.

.. ..... .:.z,

19.

5,

p. 74 (1966).

G. H. Broomfield, D. R. Harries, and A. 6. R o b e r t s , "Neutron I r r a d i a t i o n E f f e c t s i n A u s t e n i t i c S t a i n l e s s S t e e l s and a Nimsnic Allsy," 6. Iron SteeL Inst, (London) 283, p . 502 (1965).

;&

~

20.

N. A. Hughes and 3. Caley, "The E f f e c t of Neutron Irradiation a t E l e v a t e d Temperatures on t h e T e n s i l e B o r p e r t i e s of Some A u s t e n i t i c S t a i n l e s s S t e e l s , I ' J . NucZ. Mater. 18, p 60 (1963)

.... ....

.;.rr)

e

2%.

P. C . Robertshaw e t d.,"Neutron I r r a d i a t i o n E f f e c t s i n A-286 H a s t e l l s y Y and Rene' 4 1 A l l o y s , " ASTM STP 341, American Society f o r T e s t i n g m d MaiSmiaZs, p . 372 (1963).

22.

N e E. Kinkle, " E f f e c t of Neutron Bombardment on S t r e s s - R u p t u r e P r o p e r t i e s of Some S t r u c t u r a l A l l o y s " ASTM STP 642, American S s c i e t g f o p T e s t i n g m d Mate~iaZs, p . 344 ( 1 9 6 3 ) .

.... ;.y*

..... ... ' . . L *

..

..... . :a<,

e . E. P f e i l and D. W. H ~ K P ~ ~" Es f, f e c t s of I r r a d i a t i o n i n ust tenF t i s S t e e l s and O t h e r High-Temperature A l l o y s ASTM STP 380, American Society for T e s t i n g m d MabepiaZs, p . 202 (1965).

2%. P.

=:$

F%.

25.

3. T. Venard and J . W. Weir, Jr., "In-Reactor S t r e s s - R u p t u r e Prope r t i e s of a 28 Cr-25 Ni C o l m b i u m - S t a b i l i z e d S t a i n l e s s S t e e l , " ASTM STP 388, American. Sscfehy ~ Q PT e s t i n g and NateriaZs, p . 269

.... ..... C,!.

...., ..... ...,.

R. M a r t i n and J. R. Weir, Jr., "The E f f e c t of I r r a d i a t i o n Temperature on t h e P o s t - I r r a d i a t i o n S t r e s s - S t r a i n Behavior of S t a i n l e s s S t e e l , " ASTN STP 380, Amt&cm Society f o r Testing and Mderials, p. 2 5 1 (1965).

24.

(1965). 26.

P, @. L. P f e i l , P. J . B a r t o n , and D. R. A r k e l l , " E f f e c t s of I r r a d i a t i o n on t h e E l e v a t e d T e m p e r a t u r e Mechanical Pb-opertrbes sf A u s t e n i t i c Steels, 'I T ~ m s .of American NuGZ. Soc. E, p . 120 (196%)

a

..... .x.x,

27.

P. W. B. H i g g i n s and A. @. R o b e r t s , "Reduction i n D u c t i l i t y of Austenitic S t a i n l e s s S t e e l A f t e r I r r a d i a t i o n , " Nature 206, p . 1249 (1965)

28.

W. R. M a r t i n and J. R. Weir, J r . , " E f f e c t sf E l e v a t e d Temperature I r r a d i a t i o n on t h e Strength and D u c t i l i t y of t h e Nickel-Base A l l o y , H a s t e l l a y N , " AUCZ. AppZ. l ( 2 ) : 160-167 (1965)

...

.?i.&

e

.. &Wj

I

..... ....a i....

29 *

W.

%a. M a r t i n a d J. R. Weir, Jr., " P o s t i r r a d i a t i o n Creep and Stress Rupture of K a s t e l l o y N , " N w Z . A p p l e 2, p . 1 6 7 ($967).

30.

31

32

0

e

33. 34 *

35

D

E. E. B l o o m , "Nue%eation a d Growth of Voids i n Stainless Steel During Fast-Neutron Irradiation, Rdiation-Indufled voids in MetaZs, U.S. AEC Office of Information service^, p . l (1972)

36

3%

e

38 .... c.u

39

m

40 *

C. E . S e s s i o n s and T. %. Lmdy, " D i f f u s i o n of T i t a n i u m i n Modified H a s t e l l o y N s f 8 s. IimZ. Mater. 31, 316 (1969) 0

41 .

43.

C. G. Bieber and E%. P. Decker, "The Melting of Malleable Nickel and Nickel Alloys s . A d m 221, 629 (1361).

44

D. W. Wood and R. M. Cook, ""Effects of Trace Contents of Impurity Elements om the ~ r e e p - ~ u g t u rBe ~ o p e r t i e ssf Miekel-Base Alloys " M e % d l w g i a LQ9 (1963)

0

-

e

45

e

J. 6 . F i s h e r , J . AppZ. Phys.

22:

74-77 C195%>.

8.

REACTOR CCMPONENTS WESB SYSTEEMS

w. a.

Bunlap S c o t t

a.

G. Grindell

A. I. Krakoviak J. L. Crowley

..... ...,.,. . .A%+

... :g .u

Huntley

H. A. McLain E. S. B e t t i s 6 . E. Bettis

The purpose of t h i s c h a p t e r i s t o d e s c r i b e t h e p r e s e n t s t a t u s of t h e technology of componertts and systems for m o l t e n - s a l t r e a c t o r s , t o i n d i c a t e t h e importance sf t h e u n c e r t a i n t i e s remaining, t o i d e n t i f y t h e a d d i t i o n a l work needed, and t o e v a l u a t e the p r o b a b i l i t y of s u c c e s s i n o b t a i n i n g reL i a b l e components and systems. Except f o r the ~ ~ n t r 0 and 1 s a f e t y rods, t h e r e a c t o r v e s s e l and i n t e r n a l s are n o t covered i n t h i s c h a p t e r ; t h e s e are d i s c u s s e d in Chapters 3 and 6. The problems r e l a t e d t o the chemistry of t h e s a l t s and t h e materials o f c o n s t r u c t i o n are d i s c u s s e d b r i e f l y only where t h e me~hazficabd e s i g n O F o p e r a t i o n of t h e p l a n t is a f f e c t e d . Otherw i s e the r e a d e r s h o u l d r e f e r to t h e r e s p e c t i v e chapters ( 5 , 4, and 7) f o r more d e t a i l s In p r e p a r i n g t h i s s t a t u s r e p o r t , w e used t h e r e f e r e n c e d e s i g n for t h e MSBR [l] t o determine t h e requirements f u r t h e components and s y s t e m , e x a ~ ~ i n et dh e v a r i o u s c o n c e p t u a l d e s i g n s of t h e components proposed i n t h e r e f e r e n c e d e s i g n m d i n t h e s t u d i e s p r e p a r e d by Ebasco S e r v i c e s [ 2 - 4 ] , F o s t e r bh@ele%[ S I , bfCb?herteK [ 6 ] , and $@ttiยง ffz. [ 7 ] to d e t e d n e t h e p o s s i b l e d i f f i c u l t i e s . W e them reexamined t h e prior experience t o e s t a b l i s h t h e s t a t u s of t h e v a r i o u s t e ~ h n ~ l ~ g and i e s t o determine t h e work needed t o resolve t h e u n c e r t a i n t i e s . as o u t l i n e d i n c h a p t e r 2 , t h i s p r i o r e x p e r i e n c e began d u r i n g t h e A i r c r a f t Nuclear P r o p u l s i o n (I$NP) Programp and progressed through t h e development work a s s o c i a t e d with d e s i g n , c o n s t r u c t i o n , and s u c c e s s f u l o p e r a t i o n of t h e A i r c r a f t R e a c t o r Experiment, and subsequent development f o r a l a r g e r a i r c r a f t r e a c t o r . This e x p e r i e n c e s e r v e d as a b a s i s f o r and c a r r i e d o v e r into t h e development s t u d i e s conducted i n s u p p o r t s% t h e d e s i g n , c o n s t r u c t i o n , and s u c c e s s f u l ~ p e r a t i ~ n of t h e MSW and s u b s e q u e n t l y i n s u p p o r t of t h e c o n c e p t u a l d e s i g n s t u d i e s of t h e MSBR. Operation of the MSRE f o r more than 13,000 e q u i v a l e n t f u l l power hours provided most of t h e e x p e r i e n c e r e l a t e d t o n u c l e a r o p e r a t i o n . Although n o t a l l t h e u n c e r t a i n t i e s r e l a t e d t o f i s s i o n product d i s t r i b u t i o n uncovered d u r i n g t h e MSRE operation have been r e s o l v e d , t h e components and systems o p e r a t e d about as expected and p r o v i d e confidence i n t h e s e areas of n o l t e n - s a l t technology. P r e s e n t l y we are c o n s t r u c t i n g two MSm-scale f a c i l i t i e s f o r t h e s t u d y of t h e problems a s s o c i a t e d w i t h t h e h a n d l i n g and c i r c u l a t i o n of molten s a l t s and the o p e r a t i o n of a u x i l i a r y components i n l a r g e l o o p s . The Coolamt S a l t Technology F a c i l i t y (CSTF) i s n e a r i n g completion and should b e g i n o p e r a t i o n c i r c u l a t i n g NaBF4-NaP ( 9 2 - 8 mole %> i n l a t e sumer 1992. The Gas System Technology F a c i l i t y (GSTF) should b e g i n o p e r a t i o n i n t h e s ~ ~ l l ~of f i e1973. ~ The GSTP will. c i r c u l a t e molten L i F - k F 2 - n F 4 - r n 4 (71.716-12-0.3 mole %> and w i l l p r o v i d e a means f o r t e s t i n g t h e o p e r a t i o n of the gas h a n d l i n g system and o t h e r components w i t h a t y p i c a l NSBR f u e l s a l t . We e x p e c t t h a t the o p e r a t i o n of t h e s e f a c i l i t i e s o v e r t h e n e x t two y e a r s s h o u l d r e s o l v e many of t h e remaining u n c e r t a i n t i e s i n the gas hand l i n g and the c o o l a n t s a l t technology. 221

222

The d i s c u s s i o n s w h i c h f o l l o w p r o v i d e an e v a l u a t i o n of the te&no%ogy without much d e t a i l , b u t the r e f e r e n c e s c i t e d contain the material needed to substantiate t h e e a s t e n c e and status of the te&nology. Salt Pumps Requirements and C r i t e r i a The pumps f o r m o l t e n - s a l t b r e e d e r r e a c t o r s must c i r c u l a t e f l ~ o ~ i d e

salts i n primary (fuel) and s e c o n d a u (cosPant) s a l t system r e l i a b l y a t temperatures approaching P3QQ’F and meet the g e n e r a l h g ~ d ~ a u l ri ec q u i r e ments p ~ e s e n t e di n Table 8.1. The table presents t h e d e s i g n temperature and the h y d r a u l i c c h a r a c t e r i s t i c s of the s a l t pumps f o r t h e p r i m a r y and secondary s a l t systems for a lQ00-rn(e) MSBR, a 288-W(t) Molten-Salt Breeder Experiment (MSBE) and t h e MS other c r i t e r i a f a % %I[SBR Salt I n e r t gas h a s been pumps are p r e s e n t e d i n condensed form i n Table 8.2. and cooling down mm and ~ i ~ c ~ l a by t e sda l t pumps to a i d i n p r e h e a t i n test f a c i l i t y s a l t systems, and t h e need f o r this pump c a p a b i l i t y may p e r s i s t f o r PISBRVs also.

.

k.15,

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Table 8.1. General pump requirements for M B R salt systems

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Number of salt loops Design temperature: "F Pump capacity, gpm Head, f t Speed, rpm Spcific speed, Ms Net positive suction head required, f t Impeller input power, hp

MSBE, <20Q MW(g

MSBR. 1000 m ( e )

MSRE. 8 MW(t)

Primary

Secondary

Primary

Secondary

Primary

Secondary

1 1300

1 1300

5700 150

1200 300 1190

3-4 1300 21,000-16,000 150 890 3000-2625 21-18 1900-2200

3-4 1300 27,000 --20,000 300 1190 2710-2330 37-30 41 00-3100

1 I300 1200 50 1B50 21 30 10 48

1 I300 850 100

890 I570 9 890

1400

15 1220

1750 1560 10 45

224 Table 8.2. Condensed l i t of criteria for an M%BRprimary salt pump Item

Criteria ,....

w.

Pump hydraubic requirements

See Table 8.1. Pump ma~iufiictuierto study relationship between pump speed. efficiency, NPSH required, salt volume within the pump tank to recommend a hydraulic design suitable to both purchaser and manufacturer.

Pump design pressure and temperature

See Table 8. I.

Operating life requirements Pump structure Pump d m e r Bearings Shaft seals

30 years. 30 years, conveniently replaceable. TQO,OB0 tis, conveniently replaceable. 59,006hr, conveniently replawable.

Codes and standards

Pump to be designed, fabricated, inspected, and tested as though subject to the requirements of ASME BPV Code, Section 111.

Materiais of iwnstmction

$0

Vibration

Avoid resonances that are harmful to the pump and other salt system mmponents.

Shaft forces

Reduce to level consistent with pump bearing life of 100,000 hr.

Ambient temperature

A s specified, which wil1 reflect choice between oven heating of salt system and heating individual system components.

Normal operating conditions Startup

meet the requirements of ASME BPV Code, Section IIE, as supplemented for Hastelloy N.

Pump should safely w i t h s t a ~ dacross-the-line motor startups that produce maxirnnm

acceleration. Meatup and cooldown cycIcs (to and from room temperature) Zero to full power cycles Full to zero power cycles Nuclear heat deposition

58 cycles specified in pump specification.

360 cycles specified in pump specification. 240 cycles specified in pump specification. Provide cooling as required to protect pump components from overheating. Heat deposition rate to Ire supplied in pump specification.

Pump tank vollrme

Provide for maximum anticipated thermal expansion of the primary (fuel) salt.

Variabk frequency supply â‚Źor drive motor

To meet requirements of pump specification.

Lubricant-coolant package

Furnish lubricant-coolant system to meet lubrication and cooIing requirements of pump rotary element. Shaft seals shall be used lo prevent leakage of lubricant-coolant into primary sait or ambient atmosphere. Provide split flows of purge gas (helium) in shaft annulus. Upward flow to prevent diffusion of vapors of seai oil leakage into primary salt. Downward flow to prevent diffusion of salt vapors into shaft seal region.

Pump instrumentation Pump speed

Temperature Liquid lever Maintenance Direct maintenance Remote maintenance

Incipient failure diagnosis

Provide three independent pump shaft speed sensing systems consisting of electromagnetic pulse generator, sensor, and readout. Provide capability of sensing direction of shaft rotation. Provide ungrounded sheathed thermocoupbs to measure pump temperatures as described in punip specification. Fabricate and instal1 liquid level sensor in pump tank to the design provided by the Company. Provide static shutdown shaft seal and purge gas provision to accommodate removal and replacement of shaft bearings and seals subassembly. Provide d l features of alignnrent, quick disconnects, bolting, and devices needed to accomplish the remote removal and replacement of the drive motor and pump rotary element. Make provisions to detect malfunction of principal pump components to anticipate their failure.

&.,

h.

225

Table 8.2 (continued) ~

Item

.... ... .&

..

Upset conditions Sudden shutdowns Seismic loading

Criteria

120 of the nature described in pump specification. Pump should remain operational or be able to regain operational status after seismic loadings of 0.1 g horizontal and 0.06 g vertical. (These d u e s may be very sensitive to geography.)

Thermal displacement of pump

Provide for pump displacements caused by temperature changes as given in the pump specification.

Pump nozzle loadings

Nozzles must withstand moments and forces described in tRc pump specifisation.

Structural requirements, accessibility, remote alignment, jacking bolts, and lifting devices

Provide these features and devices as required in pump specification.

Nuclear radiation protection

Apply nuclear shielding and cooiing, as required, to protect lubricant-coolant and other radiation-sensitive materials. Company to furnish nuclear radiation dose rates and materials.

Rotor dynamics

Provide analysis to ensure that pump design speed is safely below the first critical system. Rule of thumb is pump design frequency of the sha~~-impellea-support speed should not exceed 75 to 80% of first critical frequency.

Drive motor Electrical insulation system

Squirrel cage induction motor should be used. Halogen-free “H� insulation with polyimide or silicon binder approved by Company. lemperature rise at design conditions should be in accord with NEMA MGI-1967. Wngrounded Chromel-Aiumel thermocouples should be used to measure temperatures of stator coils and rotor bearings. Life expectancy of 100,000 hr.

.... .....

& :.:.< ,

Bearings ... .....

,S&,

... ..... ...... :.:c*c

..... <M

....

..... ..... ... -id

226

Short-Shaft Pump. - A c o n c e p t u d drawing of a s h o r t s h a f t c e n t r i f u g a l pump is shorn in Fig. 8.1. It is the pump f o r t h e primary salt system i n t h e reference d e s i g n f o r a single f l u i d W B R [ 9 f Except f o r its large c a p a c i t y , t h i s pump i s very s i m i l a r t o those used in 1954 i n t h e ARE, those proposed for the A i r c r a f t Reactor Test (ART) in the late 1950's [ l o ] , and t h o s e o p e r a t e d for o v e r 20,006 hours i n t h e PIS in the 1 9 6 0 P s [ l a ] . It consists of three p r i n c i p a l parts: the rotaryr element, the pump tank and t h e d r i v e r . The r o t a r y element contains t h e c o n v e n t i o n a l , o i l - l ~ b ~ i c a t e bde a r i n g s that support t h e s h o r t shaft from which t h e i m p e l l e r is overhm and also the S h a f t s e d s t h a t hUPd t h e beaKiTng and seal lubricant- o o lan t i n the b e a r i n g housing. " h e pump t a n k incorporates t h e pump casin ( v o l u t e ) , the n e c e s s a r y n o z z l e s f o r t h e i n l e t and d i s c h a r g e of pumped s a l t a d i n e r t cover g a s , and the mounting bra&ets; the t a n k would be welded permanently into t h e salt system i n an MSBR. me pWkp d r i v e r is preSefatay C O I l S i d e ~ e d to be a thPee-phaSe iHndUctiOn ( s q u i r r e l cage) electric motor i n s t a l l e d i n a wate ooled vessel. me r0taI-y element, pump tank, and d r i v e motor are ass l e d w i t h gasketed joints t o form a g a s - t i t u n i t ; t h e gasketed j o i n t s are connected t o a l e a k - d e t e c t o r system f o r n u c l e a r r e a c t o r a p p l i c a t i o n . 0

"!A-

.

-

A comeeptual drawing

0%

a long-shaft

centrifugal

Pump 8.2. It was c o n s i d e r e d for th@ r e f e r e n c e two-fluid MSBR [ l a ] and i s s i m i l a r in o v e r a l l f e a t u r e s t o that p r e f e r r e d by Byton Jackson [13, 141. The p r i n c i p a l configurational f e a t u r e that d t s t i n g u i s h e s t h i s cOllceI>t fPoHl 8 Short-shaft pump is the long s h a f t SUppQrted at i t s abmer end by a m~lten-sabt l u b r i c a t e d b e a r i n g . Because t h i s p m p configuratFow w a s c o n s i d e r a b l y outside our experience, w e had the r o t o r d p a ~ c ssf the ~htlft-bea~ing-housilragsystem and the sharacteristics o f mlten-salt lubricated bearings examined in some d e t a i l by Mechanical Technology I n c o r p o r a t e d . The results of the s t u d y were reported in [-%SI and summarized i n 6161. The pump s h a f t l e n g t h and design speed f o r the pump shoulbd b e s e l e c t e d to o p e r a t e s a f e l y below t h e % i r s tshaft critical speed if a t a l l p r a c t i c a b l e . I f t h i s cannot b e done, t h e n a p r a c t i c a l means of performing precise dynamic b a l a n c i n of long pump s h a f t s must b e developed. ons side ration s h o u l d a l s o epe given t o c o n s t r u c t i n g a r o t o r d ~ a d sc i ~ i ~ l a t i of na c i l i t y of the shaft-bearing s y s t e m to e~aluatet h e e f f e c t i v e n e s s of t h e dynamic b a l a n c i n g pro~edures, the bearing performance, system s t a b i l i t y . w p i s s u i t a b l e f o r r e a c t o r salt s y s t e m that require l o c a t i n g t h e i m p e l l e r a t relatfvely low e l e v a t i o n s in the system layout. It is s u i t a b l e for c i ~ c u l a t i n ggas only at temperatures above t h e s a l t w e l t i n g p o i n t , and then only i f s p e c i a l p r a v i s i o m are made t o supply -salt l u b r i c a n t t o the 1o~e.g:b e a r i n g when t h e s a l t system i s ut the time 0% the completion sf t h e m~ s t u d y , t h e f o c u s of a t t e n t i o n shifted from the two-fluid t o the s%ngle-fluid systeuLs, and no XlKlKe Work W a 8 pE?rfOKmed OH1 t h e long-shaft pUlDp.

%

&..

h.,

227

O W L - D W G 6Y-6802

..... ,.x.:.y

.... .d

.... ,sx! .... ....

.,l

......., -

.....

13

: in

..... ..... x.u

.....

.... ,:.y,.>

..... .

..'.i' d

Fig. 8.1.

A conceptual s a l t pump f o r Molten-Salt Breede P Reactor.

An example of t:he s h o r t s h a f t pump c o n f i g u r a t i o n

a

228

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Short-Shaft Bump. - Numerous s h o r t - s h a f t c e w t ~ f f u g a lpumps f o r mo%tens a l t and l i q u i d - m e t a l a p g l f c a t i o n s have been designed, c o n s t r u c t e d , and E . Table 8 . 3 is a r6sum6 of t h e s e pumps giving d e s i g n values c a p a c i t y (flow) and speed, t h e n u d e r of umits b u i l t f o r each model, and the t o t a l o p e r a t i n g time a c c m u l a t e d with each model of A v e r y wide range i s r e p r e s e n t e d : c a p a c i t i e s have ranged from m t o I500 gpm; heads, from 56 to 400 f t ; and d e s i g n temperatures, between I200 and 1500째F. M a y p m p s have been o p e r a t e d at 150Q"F, S i n u n i t s that were o p e r a t e d c o n t i n u o u s l y and s a t i s f a c t o r i l y i n c l u d e several EFB pumps f o r p e r i o d s of 15,008 t o 20,000 hr and one MF pump f o r more t h a n 25,000 h ~ *More than 58,006 h r s a t i s f a c t o r y o p e r a t i o n was accumul a t e d with t h e MSW salt pumps in t h e f u e l - and c o o l a n t - s a l t systems i n t h e r e a c t o r . An MSRE prototype pump w a s o p e r a t e d f o r approximately $000 h r with m o l t e n - s a l t . mis was followed by 14,000 hP of o p e r a t i o n of t h e Ma&-2 fuel s a l t p m p which had a deeper pump t a n k and a s l i g h t l y longer s h a f t OVerhang f o r t h e iIIIpe%leK than the Heactor pump. I&US it ketal O f more thah 86,080-hr o p e r a t i o n w a s accmulated with f o u r %RE salt pumps. The models LFB through P a p m p s were designed t o the requirements of t h e 1950 v e r s i o n s of the ASm B o i l e r and P r e s s u r e Vessel Code (ASHE BPV Code), S e e t i o n V I P I , supplemented w i t h m e t a l l u r g i c a l d a t a t a k e n d u r i n g the ANP P ~ o ~ ~ ~ The I I I MSRE: . and ALPHA models of molten-salt P U I R ~ S we%@ designed t o t h e r e q u i ~ e m e n t sof the 1960 v e r s i o n s of t h e ASKE BBV Code, S e c t i o n VIPI, as s ~ p p l e ~ ~ nwt iet h d low cycle f a t i g u e d a t a o b t a i n e d during t h e e a r l y polstion of t h e M S U and w i t h thermal s t r a i n - f a t f g u e a n a l y s e s of' the pump t a n k s [I71 Several concPusions important t o pump d e s i g n w e r e made and reaffirmed as pump o p e r a t i n g e x p e r i e n c e w a s accumulated. The short-shaft pump conf i g u r a t i o n can b e designed and b u i l t t o o p e r a t e s a t i s f a c t o r i l y i n moltens a l t r e a c t o r s amd s a t i s f a c t o r i l y s c a l e d up i n s i z e from 5 t o 1580 g p m . Pump performance characteristics o b t a i n e d d u r i n g w a t e r tests [I$, pp. I1 and 131 of a cewt~ifugalpump can b e related r e l i a b l y to the molten-salt o p e r a t i o n of t h a t pump. Experience has p o i n t e d out t h e importance of q u a l i t y a s s u r a n c e i n a l l t h e prime function^ of d e s i g n , materials prscurement p f a b r i c a t i o n , assembly, t e s t and i n s p e c t i o n , i n s t a l l a t i o n , and o p e r a t i o n to t h e p r o d u c t i o n of s a t t s f a e t o r y s a l t pumps. O c c a s i o n a l l y d u r i n g t h e s c a l i n g up of pumps t o l a r g e r c a p a c i t i e s , a p r i n c i p l e previously a p p l i e d may be o v e ~ l ~ ~ k w ei t d h annoying consequence, such as the l o c a t i o n of t h e p a r t i n g p l a n e i n the catch b a s i n in the MSRE f u e l - and c o o l a n t - s a l t pumps. The eat& b a s i n i s provided t o catch t h e l u b ~ i c a t i n g o i l t h a t leaks p a s t t h e lower s h a f t seal and t h u s p r e v e n t s i t from running down i n t o the moaten salt i n the pump tank. mere are v a r i o ~d e s i g n approaches t o p r o v i d i n g t h e b a s i n cavity, and p r i o r t o d e s i g n i n g t h e MSRE salt pumps, all cavities had a parting l i n e which requjired a s t a t i c seal at an e l e v a t i o n c o n s i d e r a b l y above t h e f l o o r of t h e basPn. I n the PISRE s a l t pumps t h i s p a r t i n g l i n e was placed a t t h e floor of t h e b a s i n , and d u r i n g pump o p e ~ a t f o nt h e two components joined a t t h i s l i n e underwent some ~elativedisplacement t h a t opened the j o i n t and permitted seal o i l ~ t a s l o w rate down into t h e molten s a l t i n the pump tank. leakage t o K U a

2364

LFB

DANA DAC In-Prie Loop MF PKA PKP MSRE fuel silt pump

MSRE coalant salt pump MSRE A h k - 2 fuel silt pump ALPHA

Na, NsK. and rnuntert s d t Na, NaK, and molten salt Molten s a l t k'fdten Sdt NaK and molten salt NaK and molten salt N& and molten ยงdt blolte-n salt Helium Mclteri salt Helium Molten salt Molten salt

92

5

4000

1100-1406

46

466JKM3b

300

150

3750

1000- 1500

10

57,000

50 10 50

60 1

1450 3000

1000- I400

1900 375

3000 3550

B I Q0-I500 1900-1 500

2

3

4,000

8

f4.UOOC 4 1,000"

3

4 0 380 50

1500

3500

70Q-1500

4

12QQ

1175

2e

78

800

1775

50

1200 30

1175

1800-1225 100-1200 1000 1225 100 1200 1000- 1300 850- 1400

300

6500

Total

I 83

734,700

1

.. .. c.3..

21,500 45.005

3 1,600 6,000 24,600 4 QQQ 14,000 6,000

2

..... ..

*&.S

k.

241

The permanent f i x , which r e q u i r e d seal welding t h e edges of the j o i n t s was adopted o n l y a f t e r n u c l e a r o p e r a t i o n of t h e MSRE and d i d n o t f o r e s t a l l the C Q I X ~ and ~ ~ a c t i v i t y needed t o h a n d l e the Consequences of t h e o i l that leaked i n t o t h e MSRE f u e l - s a l t system. Long-Skaft Pump. - The p r i n c i p a l r e s u H t ~of the s t u d y 0% t h e r o t o r dynamic characteris tics and m o l t e n - s a l t l u b r i c a t e d b e a r i n g s f o r the long Shaft pbatnp are presented above in t h e s e c t i o n e n t i t l e d S a l t $UlTIfl Concepts. W e had some e x p e r i e n c e w i t h o p e r a t i n g t e s t b e a r i n g s i n molten salt i n the early 1968's, which i s reported i n [19]. Hydrodynamic l u b r i c a t i o n w i t h molten salt i n j o u r n a l b e a r i n g s w a s demonstrated over t h e t e m p e ~ a t u r e range %200-1580째F. A BKA model pump was modified [ X I , pp. 56-57] to suppc~rt the l ~ e end r of the s h a f t w i t h a m o l t e n - s a l t l u b r i c a t e d beari Although all and was o p e r a t e d f o r approximate.ly 12,500 h r a t H225'P. j o u m a % s and sleeves in t h e s e t e s t b e a r i n g s were c o n s t r u c t e d of Hastelaboy N and were o p e r a t e d w i t h some degree of s a t i s f a c t i o n , i t w a s decided on m e t a l l u r g i c a l grounds that long tern r e l i a b i l i t y r e q u i r e d t h e a p p l i c a t i o n of h a r d materials such as r e f r a c t o r y metals and cemented c a r b i d e s . A f e w material specimens, h a r d faced by the p l a s m s p r a y method, Subsequent c o n c e n t r a t i o n on t h e pump requirements f o r t h e deemphasis of t h i s effort, and t h e test program f o r the specimens was n o t completed.

h d u s t r i d Experience a d IwterPest. - E f f o r t s Were made to e l i c i t i n d u s t r i a l i n t e r e s t i n t h e production of s a l t pumps for the ARE, ART, MSRE, and a s s o c i a t e d m o l t e n - s a l t t e s t f a c i l i t i e s . Hasever, t h e q u a n t i t y of pumps t o be produced a t any one t i m e i n t h e two decades d u r i n g which t h e s e p r o j e c t s w e ~ eviable w a s a p p a r e n t l y too s m a l l to o b t a i n and maint a i n s e r i o u s i n d u s t r i a l interest. I n 1969 a s p e c i f i c a t i o n E211 was w r i t t e n for a s h o r t - s h a f t c e n t r i f u g a l pump t o p r o v i d e t h e requirements of t h e primary and secondary salt systems i n a 100- t o 20o-NW(t> MSBE, (see T a b l e 8.1). Westinghouse EHectro Kechanical D i v i s i o n , Bingham Pump Company, and Byron Jackson Pump Company expressed i n t e r e s t i n cementing OR the s p e c i f i c a t i o n and r e c e i v i n g a r e q u e s t for p r o p o s a l t o produce the pumps. Westinghouse produced a v e r y good r e s p o n s e t o t h e r e q u e s t , t h e only one received, b u t t h e deemphasis of the MSBE in 1970 o b l i g e d us to drop t h e i r p r o p o s a l . W e have had no c o n t a c t w i t h t h e pump i n d u s t r y t o produce s a l t p m p s sf t h e l o n g - s h a f t c o n f i g u r a t i o n .

S t a t u s o f Pump Technolorn The precedtng p i c t u r e of the s t a t u s of t h e technology of s a l t pumps supports t h e b e l i e f t h a t s a t i s f a c t o r y s a l t pumps of the s h o r t - s h a f t conf i g u r a t i o n can b e p r ~ d u c e d for MSBR's. What follows i n t h i s section t e n d s t o emphasize problem areas, none of which s h o u l d b e i n s u p e r a b l e f o r either t h e s h o r t s h a f t o r the l o n g s h a f t pumps.

232

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F a b r i c a t i o n . - A c o n t i n u i n g e f f o r t has been expended i n developing in-house f a b r i c a t i o n e x p e r t i s e with and i n t r o d u c i n g segments of industry t o newer c o n s t r u c t i o n materials such as Pnconel i n t h e early 1 9 5 0 p s and In t h e p r ~ d u e t i ~of n s a t i s f a c t o r y HastelH a s t e l l o y N i n t h e early P960's. l O g i N c a s t i n g s f o r irripeal@Ks and casings %OK t h e M Sm Salt pWIlpS it W a s n e c e s s a r y t o take the best sand c a s t i n g s produced by t h e c a s t i n g i n d u s t r y and u p g ~ a d ethem a t O W L by i d e n t i f y i n g flaws w i t h radiography and t h e n r e p a i r i n g t h e c a s t i n g s by g r i n d i n g out: t h e f l a w s and d e p o s i t i n g w e l d m e t a l i n the cavities u n t i l 'a s a t i s f a c t o r y metal s t r u c t u r e w a s achieved. However, for MSBR salt pumps, the p r o s p e c t of making pump i m p e l l e r s and c a s i n g s by weld j o i n i n g machined p i e c e s appears t o be an a t t r a c t i v e a l t e r n a t i v e t e a castings 0

... ..... ::sfi

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.

.....

w ?ry ..

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,. .:.. xi , ii.

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e - The p r i n c i p a l problems f o r t h e l o n g s h a f t pump, w e b e l i e v e , are t h e d e s i g n of m o l t e n - s a l t l u b r i c a t e d b e a r i n g s and t h e f a b r i c a t i o n of long shafts t o p r e c i s e c o n c e n t r i c i t y , s t r a i g h t n e s s and dynamic b a l a n c i n g requirements e The PTTI s t u d y [I41 i n d i c a t e d a p r e f e r e n c e for the s e l f - a c t i n g pivoted pad b e a r i n g f o r t h i s p m p c o n f i g u r a t i o n and a l s o recornended a rather e x t e n s i v e b e a r i n g d e s i g n and materials program. Mechanical d e v i c e s must be p r ~ v i d e dt o a c c o ~ i ~ i ~ ~ the d a t er e l a t i v e l y large d i f f e r e n t i a l thermal expansion t h a t o c c u r s beltween t h e s h a f t and bearing support c o n s t r u c t e d of PiasteBloy N and t h e j o u r n a l s and sleeves c o n s t r u c t e d of refractory metals O K cemented c a r b i d e s having much smaller c o e f f i c i e n t s of thermal expansion. MTE reearnended an e x t e n s i v e series of bench a d e v a l u a t i o n tests t o select t h e most promising b e a r i n g materials compatible with a p a r t i c u l a r molten s a l t f o l l m e d by proof t e s t e i n molten salt of f u l l size b e a r i n g s construeted O f these m & 2 @ r i a l s . P r e c i s i o n s h a f t s of l e n g t h s approaching 3% ft and d i a m e t e r s of 7 t o 10 i n . must be f a b r i c a t e d t o p r o v i d e a good s t a r t i n g p o i n t f o r t h e prec i s i o n dynamic b a l a n c i n g of the machined shaft. The principalb i d e a i s t o p ~ o d ~ ca eshaft having dynamic c h a r a c t e r i s t i q t h a t are compatible with the film strength and s t a b i l i t y characteristics of its molten-salt l u b r i c a t e d s u p p o r t bearing.

-

Potential Improvements. Imprsvement i n v a r i a b l e speed c o n t r o l of pumps appears t o b e a good area f o r advancing t h e technology of s a l t pumps. In e x p e r i e n c e , t h e S q u i r r e l - c a g e e%ectKicm0tePr and a tPariable frequency supply system are very s a t i s f a c t o r y choices f o r a salt pump d r i v e system. Of the many v a r i a b l e frequency supply s y s t e m the completely static D s c y < j l o ~ ~ n v e ~(OK t e r " d i ~ e r t e ~ - i g l ~ e ~sys t ~tern ~ ~ shows ') most promise f o r i ~ l p ~ ~ ~ e m eIt n t couples . a wide r a n g e of speed c o n t r o l , as much as ten t o one, w i t h the h i g h r e l i a b i l i t y t h a t one e x p e c t s from a completely static system, p a r t i c u l a r l y a f t e r t h a t system has r e c e i v e d adequate development. I n d u s t r i a l Involvement. - An i n t e n s i v e and taidely based involvement of the p u p industry is necessary to t h e p ~ ~ d u s t i oof n r e l i a b l e and e m nomic high-temperature pumps f o r t h e n u c l e a r i n d u s t r y and s h ~ u l db e very

2 34

beneffeial to salt pump technology also. An iterative approach d t h selected vendors should lead ts simpler and, hopefully, less expensive pump designs. Et should also lead to lmer pump construction costs as expertise in Bdentifying and resolving the design problems peculiar to nuclear pumps is obtained and fabrication a d assembly talents are sha~pened. Mu& of t h e industrial e erieace derived from the development of pumps for R's can be expected to apply to pumps f o r EfSBRs.

Effects of uncertainties. BR salt p m p s have t h e usual turbomachinery e l e w n t s upon which are UperilIlpOSed the reqUirETWnts fOK Spe r a t i o n at temperatures in the range l O 0 Q to 13QO"P and in a nuelear radiation e n ~ i ~ ~ ~ ~ ~ i These e n t l.a t t e r requirements generate some p r o b l e m of heat removal and radiation damage that will require directed effort. seals having reater rubbing ve Hmever, n e i t er of these probl will bar the d e s i OK

should be needed,

ities than our e q e r i e n c e has covered. presents a genuine uncertainty that

short s h a f t pumps, b u t if long s h a f t pumps previously mentioned should yield t o ade-

quate development e f f o r t a Confidence in t h e i r l o n g tern re12abikLty will reqUiPe endUrac@ test opE?.ratiQn in m O B t e n s a l t . If s a t i s f a c t o r y operation sf t h e l o n g s h a f t p t supercritical speeds is proven to be difficult to achieve, the d sf t h e pump shaft may b e m o d i f i e d t o increase its stiffness and rais first flexural resonance frequency of the s h a f t safely above the pump d e s i Alternatively, the hydraulic d e s i g n may be modified to deer speed satisfactorily below t h e sritieali freqsaenq of the s h a f t e

The principal features of &e development requirements f o r (a s h s r t shaft salt p m p include proof and endurance testing of t h e s h a f t seal, it W a t e K perf13 ce test sf t h e pump hydraulic d e s i , and endurance testing of a stype p u p with molten salt. I n 8 ition to these i t e m , -shaft salt p will require a bearing materials development oumal mounting method program, a rotordynamic o g r m , and probably verification of t h e capability to fabricate IpUlIIp Shafts to p r @ C i s e cOIlcent%iCity, stKai&tne%S and dynamic balancing requirements. Each production p m p , whether s h o r t 0% long shaft.,should be subjected to a shakedown m d m~lten-salt proof test prior t o installation i n t o an NSBR s a l t system, The diameter and rubbing velocity of t h e shaft seal for an HSBR s a l t are laKger than ally We have e 62Ktestced. HnnanUfactUE?K Should select the s h a f t seal design from among the bellows m o ~ ~ l tfluid , bearing, Visco seal, etc., and p r o v i d e performance and endurance t e s t s until a S a t i s f a a ~ p g raesi is evolved. The proof t e s t of shaft seals i n s t a l l e d in p r o m t y p e and pr~ductionsalt p m p s is performed as p a r t of the shaked m and molten-salt proof testing.

. .. =.-

235

A test s t a n d s h o u l d b e designed and c o n s t r u c t e d t o perfom a series of tests with molten s a l t on the prototype p m p t h a t w i l l verify i t s performance and g i v e confidence i n its ]bong tern e n d u r a b i l i t y . The p r e k i d n a r y d e s i g n of such a t e s t stand s u i t a b l e f o r MSBE salt pumps w a s comp l e t e d [ 2 2 , 233 in December 1969; i t w a s e s t i m a t e d t o cost $860,000 a t t h a t t i m e . A p a r t i a l l i s t i n g of important tests planned f u r fie facilityy, WhiCh are pP2Sented in r e f e r e n c e s 22 and 2 4 , hClUdeS:

I. Obtain the pump h y d r a u l i c perforwamce and c a v i t a t i o n i n c e p t i o n characteristics o v e r a wide range of p m p speeds a d c a p a c i t i e s and t e m peratures 2.

3.

Determine the c h a r a c t e r i s t i c s of the purge gas f l o w i n the s h a f t annulus 0

4-

Determine t h e d i s t r i b u t i o n of salt a e r o s o l s produced by pump o p e ~ a t i o n and o b t a i n the performance c h a r a c t e r i s t i c s of a e ~ ~ removal o l devices, i f necesetary.

5.

Bemomstrate the o p e r a b i P i t y of t h e i n c i p i e n t failure d e t e c t i o n (HFD) devices s

6.

Obtain l o n g tern endurance o p e r a t i o n w i t h a p r o t o t y p a l pump.

7,

Make m o l t e n - s a l t proof tests of advanced i n s t r u m e n t a t i o n f o r moltens a l t systems as i t becomes a v a i l a b l e .

Evaluatf~n

we know h m t o m a k e r e l i a b l e s h o r t - s h a f t c e n t r i f u g a l pumps f o r molten-salt r e a c t o r s kavfmrg b u i l t and o p e r a t e d many with capacities to 1500 gpm. Although it m y take several y e a r s t o produce the larger pumps f o g demonstration of f d f - s c a l e MSBR's, the problem are w e l l understood, and t h e r e fs little q u e s t i o n that s a t i s f a c t o r y pumps can b e obt a i n e d on a s c h e d u l e compatible w i t h o b t a i n i n g the o t h e r p r i n c i p a l r e a c t o r coHLpO3X~RtS. W e have had v e r y l i t t l e e eriencle w i t h the long-shaft pump c o n f i g u r a t i o n f o r m l t a - s a l t system. However, i t has been used i n sodium system, and plans are being processed for i t s use $n t h e l i q u i d - m e t a l f a s t - b ~ e e d e r r e a c t o r ~ E - S ~ K E U I I (LMFBIQ. The i n c e n t i v e t o use long-shaft s a l t p m p s is t o reduce the total deve~opmentrequirements for MSBR'S anel LmBI[%'s. Indeed, the MSBR s h o r t - s h a f t p m p s can b e n e f i t from t h e LB-EBR sodium pump technology p r o g r a m because the two pump c o n f i g u r a t i o n s s h a r e many eomon r e q u i r e m e n t s . The advanced a n a l y t i c a l d e s i g n methods t h a t are b e i n g developed f o r t h e sodium pumps should have much direct a p p l i c a t i o n to the d e s i g n of molten-salt pumps, We e x p e t t h a t the results of the s h a f t seal development PKS~Z-EUII f o r sodium p m p s w i l l also have d i r e ~ tapplbication t o s a l t pumps. TIM f a b r i c a t i o n t e c h n o l o g developed large sodium

236

pumps should have application to t h e fabrication of components f o r MSBR pumps after making some d1mmces for a prob He difference in construct i o n materials The themal shock capability f the Sodium Pump T e s t Facility (SPTF) could b e u t i l i z e d to shock a p r o t o t y p e BR s a l t pump, However, the requirements f o r sodium and s a l t p m p s are a l s o sufficiently different that in other important respects they are unique. '&le density of salt and sodium i l ~ equite far apart and f o r a paefty and head, the pmer ~ e ~ p i r etod d r i v e a s a l t pump developed w o d d be several tines t h e pwer a d pressure f o r a sodPum pump. Hwev@rsbesame of the hi her volumetric heat capacities of t h e s a l t , the t o t a l pump power requi are less f o r salt than sodium. The temperatures for t h e 'S are 180째F Or lllOBTC2 those f o r diU?&reactor SySt therefore t h e s a l t pumps dlbl have to be ea f o r s a i g h t i y 1 able stresses e Obtaining rtaaterials f o r molten-salt P~b%icatedbearin be SatisfactOFj for Steadap KUIIniwg cofsditiOIlS 2s EEQt l i k e l y to be diffkCult. MCWeVeT, StaIptkIg and Stopping Co~ditionsb'SCOW3 mor@ S e V e H e as the temperature is raised above Ib20Q'F. Also, as pointed out above, suitable devices would have to be developed (I) t~ attach salt-bearing materials to retainer pieces having a greatly differing coeffic%ent of intain alignment b e m e e n journal and thermal expansl%on b e a r i n g surfaces w i t h o t h e r s h a f t s u p p o r t bearing at 1PSO"F. Economy in d e s i g n , production, operation, and maintenance favors the EitteIiQt to m&e t h e h y d K a d % C and ?JECh i c a l designs sf pumps for both the primary- and seeondantgr-salt system very s i d l a r , if not identical, e

Coolant sys tern .....

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other than the eutectic NaBF4-IRPaF ($2-8 mle %> which has a m e l t i n g p o i n t of 7 2 5 ' ~ and costs approximately $68/ft3 ( $ 0 . 5 / l b ) . ~t appeared t h a t i t might be p o s s i b l e to c o n t a i n a small c o n c e n t r a t i o n of h y d r s x l ion i n complex i n this coolant which couId b e c o n t i n u o u s l y removed and r e p l a c e d to f u n c t i o n as a trap f o the ~ t r i t i u m . b o n g i t s d i s a d v a n t a g e s are (I) the s e e d for BF3 Fw the cover gas because of the evolution of BF3 from NaBF4 a t MSBR o p e r a t i n g temperatures and (2) an affinity f o r w a t e r , which causes i n c r e a s e d c o r r ~ s i ~ e n ei n~ bo%h s the salt and cover gas systems. A s will be d e s c r i b e d below, t h e s e problems are not s o severe as t o affect our Choice O f t h e f l U Q r O b O r % t @ IIliXtUTX? as t h e coo%Eknt in f u t u r e MSR's, A lower-melting-point f l u o r i d e m i x t u r e of LiF, NaP, and BeP2 with a P i q u i d u s temperature of 640"F, a m i x t u r e of Lf61 and KCB w i t h a l i q u i d u s t e m p e r a t u r e of 680'F, and a m i x t u r e of 'KF and ZrP4 w i t h a Piquidus temperature of 752째F appear to be a l t e r n a t i v e s . A s mentioned i n Chapter 2, some c o n s i d e r a t i o n also has been g i v e n t o a s p e c i a l d e s i g n u s i n g b o t h LiF-BeF, and a nitrate-n%trite m i x t u r e bemeen t h e f u e l and the stem. Addltisnal i n f o r m a t i o n on coolant salts i s g i v e n i n Chapter 5 . The simplified schematic diagram i n Ffg. 8 . 3 shows one of f o u r secondary s a l t circuits r e q u i r e d t o soslb t h e r e f e r e n c e d e s i g n l00Q W ( e > m o l t e n - s a l t b r e e d e r r e a c t o r . I n each circuit sodium f l u o r o b o r a t e s a l % f l o w s from the o u t l e t of a p r i m m y heat e ~ & ~ i n gaet ~l l 5 Q " F to t h e s u c t i o n of a sump-type c e n t r i f u g a l p m p , Salt d i s c h a r g e d by t h e pump flows i n p a r a l l e l through several steam generator-super~eater and steam-reheater u n i t s and returns t o t h e primary h e a t exchanger a t 858'P. The f l o w through each secondary c i r c u i t i s 20,000 gpna and each c i r c u i t c o n t a i n s 2888 ft3 of sodium fluoroborate. The t o t a l ~ i m ~ u nr et q u i r e d is ~ 4 5 8tows. Valves are provided fm t h e salt l i n e s t o c ~ n t r the ~ l d i s t r i b u t i o n sf flow to t h e StGXiI-KaiShg units and to bypass coolant flow around the heatexchanger under p a r t i a l l o a d conditions. (These valves need only t o t h r o t t l e , n o t to s h u t f x a g , ) A pressure-re~ief system is proviaea f o r each s e e o n d a q s a l t c i r c u i t whereby h i g h p r e s s u r e produced by r u p t u r e o f one more t u b e s i n t h e s t e a m - r a i s i n g u n i t s is r e l i e v e d by t h e b u r s t i n g sf r u p t u r e d i s k s and r a p i d blowdown of salt, noneondensable g a s e s , and steam. A C O m O f p GOVeP-giLS System pPOVided f o r t h e f o u r C i r c u i t s which s u p p l i e s a m i x t u r e of BF3 and helium and p o s s i b l y o t h e r g a s e s to t h e tank of each s a l t c i r c u l a t i o n pump t o p r o v i d e a p r o t e c t i v e atmosphere over the free surface of the sodium f l u s r o b o r a t e . A p u r i f i c a t i o n system i s provided to maintain t h e p u r i t y of t h e s a l t i n t h e s e c o n d a q c i r e u i t s . As a mfnimum the purification system fs expected t o remove some c o k r o s i s n prctducts by cold t r a p p i n g a d t o c o n v e r t oxides and hydroxides t o f l u s r i d e s . The p r o c e s s i n g system may a l s o remove HF from t h e salt by cont a c t i n g i t w i t h gas o r by o t h e r means.

&

Experience with Coolant S a l t s , &

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A LiF-BeF2 m i x t u r e was c i r c u l a t e d at 860 gpm i n t h e secondary system o f t h e MSRE f o r approximately 26,008 hr o v e r a t e m p e r a t u r e r a g e of l000 to 128@"F. DUKing the l8fetiFiW of t h e mRE (%4-1/2 gTr) t h e &romiUm Con-

t e n t of the salt remiwed c o n s t a n t a t a b s u t 32 ppm, i n d i c a t i n g remarkably l i t t l e eorrosfon. M e t a l l o g r a p h i c examination of the p i p i n g a f t e r shratdswn

238

BART OF ORML-OW- 69- ( 0 4 9 4 A R

FREEZE VALVE FLOW RATE6 ARE TOTAL FOR 1000 Mar(@)RANT SECONDARY SALT DRAJN TANK

8.3. Secondary s a l t and steam system molten s a l t breeder reactor f l o w diagram-EOQO M%(e) Unit-Mark %I. e

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The compatibility of sodium f l u s r o b o r a t e with the proposed MSBR c o n t a i n e r material ( H a a t e l l o y N) i s s a t i s f a c t o r y (csrrosion rate of 0 . 1 t o 0.2 m i l s p e r y e a r ) provided t h a t m o i s t u r e is excluded from t h e system. Data from e o r r s s i o n experiments show that a d d i t i o n of a small amount of water t o sodium f l u o r o b o r a t e s a l t i n a R a s t e l l o y N c o n t a i n e r a t about 1100째F r e s u l t s i n t h e metal e o ~ r o d i n ga t a rate t h a t i s i n i t i a l l y many m i l s p e r month and t h a t d e c r e a s e s g r a d u a l l y until i t becomes less t h a n 8 . 3 mil/yr [ 2 8 ] . Until r e c e n t l y c h e m k a P analyses indicated that. c~r1-0sion rates t h i s l o w were o b t a i n e d w i t h salt c o n t a i n i n g mare than 1608 ppm of water and o f oxide. T h i s ked to the suggestion that sodium f l u o r s b o r a t e could c o n t a i n water in two f o m s : one that i s h i g h l y c o r r o s i v e and One t h a t iS Only Slij$lt%y c O K 3 3 3 s i V e t o H % s t e l f O y %a. %eCent i R t e H l s i V e s t u d y h a s revealed that the a n a l y t i c a l r e s u l t s w e r e in ~ T K O ~ .S a l t s t h a t W C K ~~ e p o ~ t et o d csrntain more t h a n 1008 ppm of w a t e r are now found t o contain small amounts Of a hydroxyl Compound (presumably s o d i m hydroxgrflusr ~ b o r a t e )and t o c o n t a i n more t h a n 1000 gpm of oxide.

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Heat t r a n s f e r data o b t a i n e d with the forced-convection l o o p FCL-2 are in good agreement with the e m p i r i c a l c o r r e l a t i o n of S i e d e r and '%ate. These data i n d i c a t e that sodium f l u o r o b o r a t e does p e r f o m as a t y p i c a l h e a t t r a n s f e r f l u i d e291 S i n c e sodium fluoroborate e x h i b i t s an a p p r e c i a b l e d i s s o c i a t i o n p r e s s u r e , BFQ is carried o f f i n t h e off-gas stream from t h e pump bowl and i f n o t P e p h e e d W i l l r e s u l t in a S a l t CompoSitfOba S h i f t toWard ii h i g h e r c o n t e n t . In t h i s e v e n t , the t i m e required t o produce a change sf 1 mole p e r c e n t i n the salt composition i n fzhe r e f e r e n c e 1800 rn MSBW i s c a l c u lated t o b e 30 days. During o p e r a t i o n of t h e PKP-1 Hoop, the BP3 c o n t e n t of t h e pump o f f gas stream (as measured by a thermal c o n d u c t i v i t y c e l l ) was found t o b e i n e q u i l i b r i u m w i t h the s a l t composition i n t h e pump bowl over a wide range of BF3 anCB/o~helium flow rates into the pump bowl vapor space, and the NaBP4 t o NaF r a t i o i n t h e s a l t was indeed c o n t r o l l e d by the rate at h i ~ BP3 h w a s admitted to t h e pump bowl, Also this ratio CXXI b e determined by r e l a t i n g t h e BF3 c o n t e n t i n t h e off-gas stream t o t h e total press u r e and s a l t temperature i n t h e pump. An a n a l y s i s of %he s y s t e m a t i c errors r e s u l t i n g from i n f e r r i n g t h e NaBF4 t o NaF ratio from the BF3 cont e n t of the off-gas stream indicates t h a t t h i s method of d e t e c t i n g changes i n s a l t compssition is a c c u r a t e t o 20.5 mole p e r c e n t . Earlier e x p e r i e n c e had shown the error t o b e an o ~ d e rof magnitude g r e a t e r when the mole f r a c t i o n w a s inferred from s t o i ~ l a i ~ m e t r~aitci o s of t h e b a s i c c o n s t i t u e n t s as determined from a number sf chemical a n a l y s e s of t h e s a l t . Near e q u i l i b r i u m concentrations sf BF3 i n helium are r e q u i r e d when the mixed gas i s used i n a bubbler-type l e v e l indicator. The e u t e c t i c salt ~ i i x t u ~i se d e p l e t e d of i t s BF3 c o n t e n t i n the v % c i n i t y of the b u b b l e r tube when p u r e h e l i u m is i n j e c t e d below t h e salt surface. Eventual plugging of the tube by t h e higher-melting NaP-rich salt m i x t u r e results; conv e r s e l y , t h i s type of plug can b e c l e a r e d by a BF3-rich gas mixture. Higher than CdC!Ul%lked OVerprESSUPe w a s K@qUired to SUppreSs PUEQ c a v i t a t i o n d u r i n g c i r c u l a t i o n of the f l u s h salt i n t h e PKP-% loop ( t h e f i ~ s salt t charge w a s used t o clean. t h e system of r e s i d u a l s a l t from prev i o u s o p e r a t i o n s ) . Cavitation d a t a f o r the second b a t c h of f l u s r o b o r a t e salt c ~ ~ r e l a t ewith d t h a t f o r sther f l u i d s .

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A f i n e salt m i s t generated in the vapor space of t h e PKP pump agglsmerated, solidified, and e v e n t u a l l y plugged the off-gas l i n e from t h l a p m p . The line w a s c l e a r e d by t h e a p p l i c a t i o n of heat t o t h e affected areas w i t h subsequent s a l t d r a i n a g e t o t h e pump. F l u o r o b o r a t e salt mist i s a p o t e n t i a l problem w i t h t h e large pumps contemplated for use i n f u t u r e m o l t e n - s a l t reactors, b u t t h e mist problem w i t h f l u o r o b ~ r a t edoes n o t appear to d i f f e r from t h a t with o t h e r s a l t s . A bubbier-type l e v e l indieator wag operated in tpng PKP pump f o r two years. Near %he end of the test t h e tube shwed s i p s of plugging. Examinatim of t h e b u b b l e r t u b e revealed t h a t t h e end of t h e t u b e w a s plugged w i t h a si1ver-gra)p magnetic d e p o s i t rich i n n i c k e l c o n t e n t . It is not clear as to t h e cause of the plug; some speculations are: (1) m o i s t u r e i n the argon supply, (2) m o i s t u r e in the BF3 supply, (3) impurities in t h e s a l t , and (4) high-corrosion rate of Incowel in sodium f l u s r o borate. The CSTF will use the float-type l e v e l indicatsr.

242

h s o d i m f l u s s o b o r a t e Undergoes a s o l i d phase transition a t %470"P, no unusbpaa. problems a s s o c i a t e d w i t h this phenomenon were encountered w i t h the. o p e r a t i o n of the f r e e z e valves used i n the forced conv e c t i o n o r X P k m p s . During t h e o p e r a t i o n of the PKP loop, t h e freeze valve w a s maintained bemeen 268 and 4 8 8 " ~and w a s sthjected to a t o t a l of 16 f i l l - d r a i n cycles. Evidence of t h e c o r r o s i o n p r o d u c t , M ~ $ P F has ~ ~ been found in virtually all loops c i r e u l a t i n sodium f l u o r o b o r a t e . The d e p o s i t i s found i n t h e C B I d @ S t p a r t sf the c rcuit and is expected to d e p o s i t on the tubes of the s t e a m - r a i s i n g equipment if n o t removed by some means. % h e r e f ~ r @ ~ the s o l u b i l i t y of NagCrP6 in s o d i m f l ~ o ~ ~ b o r wa t e d e t e d n e d and cold trapping techniques were used with l i m i t e d suc@ess 8 i s o h t e this mater i a l i n n a t u r a l - and f o r c e d - c i r c u l a t i o n l o o p s . Excessive d r a i n t i m e s were encountered that w e r e a t t r i b u t e d t o t h e accumulation of t h e c o r r o s i o n p r o d u c t , Na3CrFg, i n d r a i n l i n e s . A s a r e s u l t of this e x p e r i e n c e , t h e d r a i n l i n e temperatures of sodium f l u o r o b o r a t e l o o p s should b e maintained t l y higher than, the main l o o p temperature. A l s o , t h e freeze d be located near the d r a i n t a n k rather than near the main loop, This c o n f i u r a t i s n w i l l lengthen the diffusion p a t h between the main l o o p a d t h e coia spot in ~e drain kine. ~n M S P ~ t h e concentration of Na3CrF6 w i l l b e kept l o w t o p r o t e c t t h e steam g e n e r a t o r s heat t r a n s f e r e PKP pump s h a f t annulus s p l i t s i n t o

.9> f l o w s d m n the s h a f t and into t h e pump bawl vapor space; the remainder flows up t h e shaft, p a s t the r o t a t i n g s h a f t seal, and through the o i l c a t c h t a n k . The s h a f t purge inhibits $a& d i f f u s i o n of aoxisus gases from t h e pump bowl t o the sea% r e g i o n m d oil catch tank. The BFg content sf t h e l o w e r seal purge stre= w a s ITBiIItairsked b e h W 1008 ppm, and no d e % @ F X K i O U S OperEltiIlg exTperieflCY2 W i i S encountered.

u n c e r t a i n t i e s i n Use

Of

Fluorsborate w.5

243 A system of i n j e c t i n g hydrogen i n t o t h e s a l t c i r c u l a t i n g system, removing t h e bubbles by means of a c e n t r i f u g a l s e p a r a t o r , and e x t r a c t i n g t h e HF from t h e off-gas could r e s u l t i n t h e a c c s m o d a t i o n of a water l e a k of l t o 35 d / m i I l Without Serious COrrOSfon [30] c. How e f f e c t i v e l y can t r i t i u m be prevented from p a s s i n g t h r ~ u g ht h e c o o l a n t system i n t o t h e steam? P o s s i b l e chemical methods of b l o c k i n g t h e t r a n s p o r t of t r i t i u m are d i s c u s s e d i n Chapter 14. Removal from t h e c ~ ~ l a n t s a l t i s one p o s s i b i l i t y b u t i t has n o t as y e t been demonstrated. a

...

<.$S

,&

F u r t h e r Development F%Q& ... ..... : a,

.... ..:.:.>;

I

Cover G a s Addition t o and Removal from t h e Pump Bowl. - C e r t a i n imp U r i t i @ S , VagfQUsby identified 88 W a t e r , hydrffw f%UoP3bOric a c i d , BP3-I-fzO reaction prQdUctS, etc., have @aUS@dh i g h CoPlfosiCKi r a t e s i B 9 cibCUlE&ting systems and flow r e s t r i c t $ a n i n the off-gas systems o f sodium f k u o r o b o r a t e l o o p s . The i d e n t i t y , S Q U T C ~ , method s f I X I W V ~ ~ , and t h e maximum i m p u r i t y c o n c e n t r a t i o n s t h a t can b e t o l e r a t e d i n t h e cover gas and s a l t need to be e s t a b l i s h e d . The CSTF w i l l u t i l i z e t h e helium p u r i f i c a t i o n u n i t from t h e MSRE t o p u r i f y t h e i n c ~ m i n ghelium and thus e l i m i n a t e one p o s s i b l e s o u r c e of m o i s t u r e and oxygen. The c o o l a n t pump f o r t h e r e f e r e n c e d e s i g n MSBR w i l l o p e r a t e a t l l % Q Q P w i t h a s h a f t purge rate a f n o t less than 5 l i t e r s / m i n (STP) and a pump pressure n o t less than 10 p s i g . I f no recovery p r o v i s i o n s are macle, the f o u r pumps w o u ~release one c y l i n d e r o f B F ~(ZOO f t 3 STP) i n t o the atmosphere p e r day. The CSTP i s equipped with a r e c o v e 7 u n i t that i s expected to reduce t h e BF3 release rate by a factor of 100. D i s p o s a l of the residual BP3 in the off-gas stream from the BF3 recovery u n i t (<2008 ppm) will s t i l l b e a p r o b l e ~ ~ ~P .a s t experience I d i c a t e s t h a t a c i d - l i q u i d f o r mation and plugging n e a r t h e exit (where BF3 meets t h e v e n t i l a t i o n a i r stream) w i l l take p l a c e and remain a n u i s a n c e u n l e s s handled d i f f e r e n t l y . Bubbling through mineral o i l a t t h e release p o i n t may be s a t i s f a c t o r y . Other p o s s i b l e a l t e r n a t i v e s are (1) bubble t h e e f f l u e n t through a s c r u b b e r c o n t a i n i n g mercury and w a t e r o r c a r b o ~t e t r a c h l o r i d e amd w a t e r and (2) r e a c t i n g t h e r e s i d u a l BFq with a l k a l i m e t a l oxides or f l u o r i d e s a t e l e v a t e d temperatures e

Corrosion Product Depositi~n. - To remove t h e c o r r o s i o n p r o d u c t , Ma3CrF6, produced by m o i s t u r e in-leakage into t h e s a l t system, an e f f i c i e n t c o l d trap must be developed. The d e s i g n of t h e cold t r a p s must i n c l u d e considerations of (1) simplicity of o p e r a t i o n , i . e . , easy tempera t u r e c o n t r o l , l o g i c a l flow p a t t e r n t o t a k e advantage of d i f f e r i n g s a l t d e n s i t i e s due to t e m p e r a t u r e s , (2) t e n a c i t y of the d e p o s i t (powder Q P cake) ( 3 ) r e p l a c e a b i l i t y when loaded with Na3CrF6 and ( 4 ) a b i l i t y to

244

Coolant Leaks - A s e x p l a i n e d in Chapter 5 , vis%ent e ~ o t h e % d c ~ e a c t i o i i soccur when f % u s r s b o r a t e s are mixe with steam OF with fluoride f u e l S a l t s . h f a c t , f l U Q r Q b O r a t @ S are ilTlIll s c i b l e with mullten mixtures of Ifthium and beryllium fluorides o v e r a s i g n i f i c a n t range ~f cuaditisns. Uranibam and Other tpi- and fetKaVa%enfZe l e m @ w t S a%e not extracted i n t o flusroborates, and the only high-melting C Q I R ~ X I I I ~ that might b e fopand is sodium f l u o r i d e . Thke~ei s some migration of LiF t o the f l u o m b o r a t e phase, and replacement of NaF by L I F in t h e MaBF4 csmplex r e s u l t s in an almost immediate release of some BF3 gas, The detailed consequences sf 0% the fuel s a l t w i t h t h e s o d i ~ mf l u o m b o r a t e depend on (a) t h e f traixhg of the two B ~ H ~ Z U L S ,(b) the s o l u b i l i t y of t h e BP3 gas in the r e s u l t a n t phase, (c) t h e relative temperatures of the two f l u i d s , ( d ) t h e k i n e t i c s of reactieans bemeen the distributed components 8 and ( e ) which f l u i d c o n s t i t u t e s the continuous phase P r e s e n t evaSbuation of a%P of these factors indicates t h a t there is no mechanism ~ O Kt h e concentration of uranium to prsduce a c r i t i c a l configurati~nand IL~Qcompounds w i l l be formed which cannot be redissolved through t h e addition Q â‚Ź a p p ~ o p r i a t e chemieal agents 6321. For pils R use, BIBKeoveP, t h e a c c i d e n t a l i n troduction of f l u o r s b o r a t e s i n t o the circulating f u e l would cause a large reactivity decrease because of %heborona, and thus even a small leak e

0

245

would be quickly detected. The boron could be removed from t h e f u e l s a l t by treatment with ?a'.some studies of mixing i n a loop system are needed in order to better evaluate the effects.

... .... .....

....

, : . : . y , ,

Evaluation Although sodium f l u s r o b o r a t e is somewhat of a nuisance s a l t compared with LiP-BeF2, Its ope~ationalprobPem are not insurmountable, and its %ewer l i q u i d u s temperature and c o s t make it our choice for t h e MSBR. The major 3?2qufPE%leftt S e f a S i t i V e and early detection Of bnroP.5 tUr@ iEll€%kage to minimize corrosion of the c o n t a i n e ~material and corrosion-product deposition in the s t e a m - r a i a h g equipment. Detection of the r e s u l t a n t HF in the off-gas Pine and detection of chromium by the on-line salt Z X - G ~ . ~ Z ~ K are two promising methods for detecting moisture inbeakage. Processing of the coolant salt to m a k e it serve as a t ~ i t i k l a aslnk ~ is d i s c u s s e d i n Chapters 5 and 14. Beat Exchangers

.... ?$d ... ....

P r i m a r y heat exchangers (salt-to-salt] and steam g e n e r a t o ~ s(saltto-water) comprise t h e coupling between the c i r c u l a t i n g fuel reactor system, the coolant system, and the steam system. O t h e ~heat exchangers a ~ ~ the t standpoint of development required, are the steam less i m p ~ ~ t from KE!heZIterS (Salt-tQ-stea$ and %he 9eP1@at-st@a~-prehE-neatePs (SteaIll-tO-ste~). SOllE? O f t h e ilRpOrtant teTDpeKatures and pKesSUPeS Within Which these heat exchangers must operate are given in Table 8.5, More specific information will be found in t h e references s h m . The steam reheater and the reheat steam preheater are regarded as conventional heat elgchawge~~ and no fundamental problems of heat transfer o r devel~pmentare foreseen. Even though the 656°F reheat steam enters t h e reheater below the 7 B Q F l i q u i d u s temperature of the coolant s a l t , t h e Pow steam-side heat-transfer coefficient leads us to conclude t h a t there will be RO s i g ~ ~ i f i c a aPPoblem tt w i t h f r e e z i n g of the s a l t . The remaining d i s e u s s i o n is therefore directed toward t h e primary heat exchanger and the steam generator.

Requ%rements and Criteria f o r the P r i m a r y Heat Exchanger and Steam Generator

,<.p>

... ..... ,:.:.:.> C I

C.?G2

The general requ5rements and criteria cornon t o the p ~ i ~ t aheat ~ y exchanger and the steam eHaeleat0P OUP Kef@9@nce d e s i g n BPe i68 follOW§. Both are s h e l l and tube eat exchangers fabricated sf HasteEloy M and both must maintain t h e i r structural integrity during a 30-yr d e s i ineludes thermal transients caused by n o m a l operations, various p l a n t upsets, and emer @facies DLffeKent$a% e~~lXSi0T.I bef3TeeKI tubes a d S3hd.l must be accsmodated w i t h o u t the use sf bellows, and thema% stresses a t c r f t b c a l locations, such as tube sheets and nozzles, should b e minimized without the use of a gas space if possib.B)e.

246

Neat exchanger

Steam generator

Steam reheater Reheat steam preheater

Steam (shell) Supercritical steam (tube)

550 I000

650 869

595

3600

44

(...

I

247

The steam g e n e r a t o r tubes w i l l have s u p e r c r i t i c a l steam on one side and sodium fPuoroborate t h e o t h e r . ?The peak t@mpekatUr@O f the steam s i d e will be about POOO'P and t h a t on t h e s a l t s i d e w i l l . b e l150'F. Both of these f l u i d s are c ~ r r o s i v eunder c e r t a i n c ~ n d i t i ~ n s A. s d i s c u s s e d in Chapters 5 and 7, sodium f l ~ o ~ o b o r a it se a g g r e s s i v e when water i s p r e s e n t i n the s a l t . Steam i s o x i d i z i n g t o metals and can produce s t ~ e s sC ~ I T U s i o n c r a c k i n g when i t c o n t a i n s small c o n c e n t r a t i o n s of c h l o r i d e s . Thus t h e material used for steam eneratolp t u b e s in a m o l t e n - s a l t system must resist corrosion by both sodium f l u s r o b o r a t e a d steam, o r duplex t u b e s must be used. With t h e use s f thermal b a f f l e s for t h e pPOteetiOn of the tube sheet, t h e 788'~' feedwater e n t e r i n g the steam g e n e r a t o r w i l l cool some of t h e s t a t i c s a l t below its 725'F l i q u i d u s and f r e e z e i t on the c o l d e r s u r f a c e s . The d e s i p must accommodate t h e f r e e z i n g and thawing of this small amount of s a l t without s t r u c t u r a l damage t o t h e s t e a m g e n e r a t o r . W e b e l i e v e t h a t d i r e c t maintenance of t h e steam g e n e r a t o r w i l l b e p o s s i b l e even though. t h e r e i s some induced sodium a c t i v i t y i n t h e sodium f f ~ o r ~ b o r a t e E. s t i m a t e s place the 24Na a c t i v i t y l o w enough (about 11 u c u r i e s p e r gram of s a l t ) f o r d i r e c t maintenance i f d r a i n e d of salt [333. Although t h e e x t e n t of t h e problem i s u n c e r t a i n a t t h i s t i m e i t i s p o s s i b l e t h a t t h e maintenance p l a n must be a b l e t o accommodate two o t h e r s o u r c e s of r a d i o a c t i v e contamination. Trace elements (such a8 c o b a l t ) in t h e Hastelloy N w i l l b e a c t i v a t e d and could b e s u b s e q u e n t l y d i s p e r s e d by t h e c o r r o s i o n p r o c e s s . F a i l u r e of a primary h e a t exchanger t u b e couPd a l l o w f i s s i o n p r o d u c t s t o enter a d be d i s p e r s e d t h r ~ u g h ~ uthe t secondary c i r c u i t . The d e s i g n of t h e steam g e n e r a t o r must a c e o m d a t e the n e c e s s a r y maintenance and inspection t o meet the requirements for i n - s e r v i c e inspect i o n , f o r minimizing down time, and f o r d e t e c t i o n , l o c a t i o n , and plugging of l e a k i n g o r damaged steam t u b e s . Two s p e c i a l requirements -minimum f u e l salt i n v e n t o r y and maintaina b i l i t y by remote means - are imposed on t h e p r i m a q h e a t exchanger. The low fuel salt i n v e n t o r y i s d e s i ~ a b l et o minimize the doubling t i m e and i n v e n t o r y costs, The u s e of enhanced h e a t t r a n s f e r s u r f a c e s on t h e h e a t exchanger t u b e s will. serve t o reduce t h e t o t a l s u r f a c e area, and t h e use of s m a l l t u b e s will f u r t h e r reduce the f u e l s a l t volume. 'Fhe r a p i d replacement of t h e t u b e bundle ( o r t h e e n t i r e m i t ) by remote means i s necessary t o minimize down t i m e i n t h e e v e n t r e p a i r i s n e c e s s a r y i n t h e h i g h l y r a d i o a c t i v e primary system. Current Conce~ts ..::a

<:.>a

... .... A,+., .....A

... .... ..... ,:.x<.

... r..... i:&

Coneeptual d e s i g n s of molten s a l t primary h e a t exchangers and steam g e n e r a t o r s have been o r are b e i n g p r e p a r e d by OWN%, Ebasco S e r v i c e s I ~ C O K p r a t e d , F o s t e r Wheeler Corporation, and by Black and Veatch. These are b r i e f l y d e s c r i b e d and r e f e r e n c e d i n T a b l e s 8 . 6 and 8.7. One steam g e n e r a t o r c o n f i g u r a t i o n which w i l l receive a t t e n t i o n i n f u t u r e d e s i g n s t u d i e s and has promise of a l l e v i a t i n g the f e e h a t e r tempera t u r e requirement is t h e bayonet Q K r e - e n t r a n t tube. Although i n v e s t i g a tions thus f a r indicate the bayonet tube c o n f i g u r a t i o n i s n o t practical a t s u p e r c r i t i c a l p r e s s u r e s because of the t h i c k t u b e w a l l r e q u i r e d , i t

248

Table 8.6. Molten &t steam

Concept

Configuration

Thpmal rating (hlpvv)

Tube Number

Tube size, OB (in.)

Tube sheet to tube sheet length (R)

Reference

I6

[401

Horizontal U-shell and tube

121

393

%

Ebasco (E3 & W)

Vertical helical coil u

483

815

P

Foster FVheeler

Vertical L

483

1025

Molten Salt Breeder Weastor Associates (B & V)

Vertical huckey stick

483

3450

OW".

Reference

112

Y

~

......... =.=

...

. ..

i1 . i..

249 ..... ..... ...., . a ,

..... ........ ...... <*

.... ...... 'i.2'+ .

:;.... ,.<.... A

Table 8.7. Molten salt primary heat exchanger concepts

.....

::y,z

..... ....... ...<d

..... .......2 ...A.

Thermal rating (MWI

Tube number

Tube size, QD (in.)

Reference

VerticaJ shell with disk and doughnut baffles; L-shaped tubes have helical indentation for enhancement

556

58QU

%

[44I

Same as above

150

1450

%?

145I

OKNL MSDW Reference

Horizontal U-shell and U-tube

125

1368

%

[46 I

Ebasco (B & W)

Vertical straight shell and sine-wave tube

Concept

Basic configuration

ORNL MSBR Reference

ORNL MSBE Reference

has d e f i n i t e p o s s i b i l i t i e s f o r a s u b c r i t i c a l p r e s s u r e system. E b a e o has Hooked a t t h i s eonfiguration [38] and t h e Dutch propose this concept f o r a rYMalten-Salt-heated SteaHa e f l e r a t o r [ 3 9 ] . Heat Transfer Experience The operation of t h e MRl3 r e p r e s e n t s the most r e c e n t l a r g e scale e r i e n c e with s a l t - t o - s a l t heat exchangers [ M I . 7315s o p e r a t i o n proed a consfder&le momt of confidence i n the design techniques. The h e a t t r a n s f e r c o r r e l a t i o n s used f o r the MSrn primary h e a t exc h a n g e ~were based on t h e p r e v i o u s development tests w h i c h showed that f l u o r P d e salts behave as noma1 f l u i d s . When the HSRE o p e r a t i o n r e v e a l e d t h e ~ ~ e r aheat l % t r a n s f e r coefficient to be less than predicted, ree v a l u a t i o n of the p h y s i c a l p r o p e r t i e s d i s c l o s e d t h a t t h e a c t u a l thermal c o n d u c t i v i t i e s of the f u e l and c o o l a n t s a l t s w e r e below those used i n C~lCUlationS d acCoWted for t h e difference [ 4 9 ] . The Q ~ e r ~ a n s f e rcoefficient of t h e MSRE heat exchanger d i d not. change d u r i n g some 22,000 hr sf salt c i r c u l a t i o n and 13,OtBQ e q u i v a l e n t f u l l power hours o f o p e ~ a t f o nthus indicating no b u i l d u p of scale and no e v i d e n c e of gas filming. 'Fke s d t CCKilp3s~t~~nS Used i H 6 the Msm iage not &e Same as preSently proposed f o the ~ MSBR. Hmever, some p r e l i m i n a r y heat t r a n s f e r infomation from the o p e r a t i o n of a smkl ssrrosioat l o o p w 5 t h s o d i m f l u o r o b o r a t e i n d i c a t e s general agreement ~ 5 t ht h e S i e d e r - T a t e correlation [ 5 0 ] . Thus the conclmion i s that tihe use of a c c u r a t e p h y s i c a l property d a t a w i t h c o r r e a a t i o w s f o r noma1 f l u i d s is adequate f o r h e a t t r a s f e r d e s i g n with f l u o r i d e salts. There i s , ~ O W ~ V ~no K , m o l t e n - s a l t heat transfer e x p e r i e n c e with t h e knurEed t u b e s proposed f o r t h e p r i m a r y h e a t exhmger i n the 0 r e f e r e n c e aesi C o r r e l a t i o n s f o r hea! t r a n s f e r and p r e U P e drop W e r e chosen from SpETl l i t e P a t U % e m d adapted f o r U s e i H 1 d e s i ing t h e mBR r e f e r e n c e p r i mary h e a t ex&an er and s t e a m enerator. D c u s s i o n s of t h e w e of t h e s e c o r r e l a t i o n s c e r t a i n c o r r e c t i o n factors a p p l i e d because of b a f f l e s p a c i n g , bypass flow f a c t o r s , e t c . , are f o m d in Ref. 51 f o r the p r i m a q heat exer and 52 f o r the steam generator. Although the operating e x p e r i e n c e with salts i s q u i t e extensive, the available experie~aeein the generation of steam i r t high-temperature ~noltens a l t - h e a t e d steam e n e r a t o r s is n i l . m e r e i s a c o n s i d e r a b l e amorant of b oet ,h i l t k the USA atad Europe, with the use sf Iow-melting s a l t e~pe~ien~ called H i t e e . for the g e n e r a t i o n of low-pressure steam and f o r a heat t%fa?ilSfer m@d%UKD[53]. T h i s S a l t WoUEd b e 83[1 effective b a r r i e r f o r tritium, as d e s c r i b e d in Chapter %, and has therefore been sOwS%dered f o r US@ i n a molten-salt r e a c t o r designed to b e b u i l t w i t h a m i n i m u m of f u r t h e r development e541 *

Flaterfals Experience

As discussed in Chapter 5 and i n the discussion of the c o o l a n t salt earlier i n this c h a p t e r t h e o p e ~ a t i o ~of n the Poops h a s shown t h a t sodium f l u o r o b o r ~ ~ ti es compatible with R a s t e l l s y N in t h e absence of i m p u r i t i e s I

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mainly moisture. I n the absence of m o i s t u r e , metal removal rates o f a 0 . l millpr have been o b t a i n e d , which i s ~ Q Wenough f o r use i n a p l a n t designed f o r a 3O-yr l i f e . However, s i n c e t h e c o r r o s i o n r a t e accelerates when m o i s t u r e i s i n t r o d u c e d and s i n c e t h e p l a n t must have t h e c a p a b i l i t y of ~ e e o v e r i n gfrsm a steam l e a k , a smll p u r i f i c a t i o n system must b e p r o ~ i d e d f o r removing water and c o r r o s i o n p r o d u c t s from t h e s a l t . A method f o r removing water h a s been demonstrated on a small scale and t h e use of c o l d t r a p p i n g t o remove c o r ~ o s f ~p n r o d u e t s h a s also been demonstrated. The c o m p a t i b i l i t y of Hastelloy N w i t h stem i s b e i n g i n v e s t i g a t e d i n a t e s t f a c i l i t y i n TVA's B u l l Run S t e a m Plant. Unstressed t a b s exposed a t 1000째F have v e r y a c c e p t a b l e m e t a l l o s s rates of acb.25 mil/yr. The Bull Run f a c i l i t y h a s been modified t o a c c o m o d a t e s t r e s s e d specimens amd a few have f a i l e d to d a t e . The f a i l u r e t i m e s do n o t seem o u t s i d e the s c a t t e r b a n d f o r f a i l u r e t i m e s o b t a i n e d i n i n e r t g a s . This work i s b e i n g conducted t o e v a l u a t e the p o s s i b i l i t i e s s f stress c o r r o s i o n of Hastellboy N in the p r e s e n c e ~f steam as r e p o r t e d by S p a l a r i s e t aZ. e551 based on t h e i r r a t h e r l i m i t e d work. Some tests are i n p r o g r e s s on duplex t u b i n g manufactured by the I n t e r n a t i o n a l Nickel Ckxnpany w i t h I n c s l o y 800 on the steam s i d e (inside) and n i c k e l on t h e s a l t s i d e ( o u t s i d e ) T h i s combinatisn c o n t a c t s f l u i d s with t h e a l l o y s t h a t have e x c e l l e n t c o m p a t i b i l i t y a

Status of Heat Exchanger Technology

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~ d e x p e r i e n e e and t h e subsequent d e ~ e l o p With the b a c k g r ~ ~of~ MSRE ment o p e r a t i o n , w e a r e c o n f i d e n t of b e i n g able t o p r e d i c t s a l t - s i d e h e a t t r a n s f e r c o e f f i c i e n t s w i t h a c c u r a t e p h y s i c a l p r o p e r t i e s a v a i l a b l e . Much more t e s t i n g and o p e r a t i n g e x p e r i e n c e i s needed t o v e r i f y p r e s e n t i n f s r mation and t h e r e v i s e d s a l t compositions concerning p h y s i c a l p r o p e r t i e s , heat tranSfek, and p r e s s u r e d1POp c O K ~ @ l a t i o n s and , t h e avoidance Q f f % O W i n s t a b l l i t y and s t r a t i f i c a t i o n problems me e x p e r i e n c e w i t h H a s t e l l o y N i n steam is m o s t l y good, b u t some q u e s t i o n s must b e r e s o l v e d before a f i r m c o n c l u s i o n can be reached. "he in e gcompatibility : duplex t u b i n g of nickel-Incoloy 800 looks p ~ ~ ~ i ~ ~ f st h i s e x c e l l e n t , and produstion methods f o r the t u b i n g have been developed s o t h a t a high q u a l i t y product can b e obtained at less c o s t than Hastelloy E t u b i n g . On t h e o t h e r hand, steam g e n e r a t ~ rf a b r i c a t i o n would b e comp l i c a t e d by use of t h e duplex t u b e s . a c o n s i d e r a b l e amount of i n f o r m a t i o n i s a v a i l a b l e on t h e u s e of supesC H i t i C 2 3 . 1 st@alIl: Over 140 S u p e r c r i t i c a l preSSblKe Steam geI3ekatOlP UnftS %$@ now o p e r a t i n g , under construetion, o r on o r d e r i n t h e U . S . , Europe, and Japan [ 5 6 ] . Design of m o l t e n - s a l t steam g e n e r a t o r s can draw on this experience Some work h a s been done w i t h a n a l o g s i m u l a t i o n s on t h e c o n t r o l of the MSBR system. The r e s u l t s indfeated t h a t i n o r d e r t o m a i n t a i n b o t h the primary s a l t and the c s o h n t s a l t c o l d l e g temperatures above t h e i r r e s p e c t i v e f r e e z i n g temperatures, e i t h e r of two c s n t r o l schemes would b e s a t i s f a c t o r y ; b o t h require a v a r i a b l e c o o l a n t salt flow. One c o n t r o l SCheme WQUld peQbBire atfZelllperatiOn Of O u t l e t Steam telllperature b@fOKe r e a c h i n g the t u r b i n e and the second would r e q u i r e a c o n t r o l l e d bypass e

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Tube Sheet Protection. - The tube sheet w i l l have to b e p r o t e c t e d from r a p i d temperature changes which could b e imposed by thermal trans i e n t s i n t h e s a l t . This can b e done by p r o v i d i n a b u f f e r between t h e t u b e sheet and t h e flowing s a l t such as a gas space o r a l a y e r of static salt. In the molten s a l t steam g e n e r a t o r i t i s p r ~ p o ~ et o d provide t h i s p r o t e c t i o n by s t a t i c s a l t behind a thermal b a f f l e . The u s e of a gas s p a c e w i l l b e avoided i f at all p o s s i b l e . S i n c e the salt pump r e q u i r e s a gas s p a c e which operates n e a r the pump suction. p r e s s u r e any a d d i t i o n a l f r e e liquid s u r f a c e s i n t h e steam g e n e r a t o r s w i l l r e q u i r e i n d i v i d u a l c o n t ~ ~ which ls v a r y the gas pressure a c c o r d i n g t o the c i r c u i t f l o w resist a n c e a t t h a t l o c a t i o n . Changes of level w i l l occur i n a f e w seconds when the s a l t pump s t o p s suddenly. Level c o n t r o l i s thus complex r e q u i r i n g salt l e v e l measurement and s e n s i t i v e gas p r e s s u r e controBs w i t h problems of undetermined s e r i o u s n e s s a r i s i n g ~ K O R a c o n t r o l f a i l u r e . If t h i s l i q u i d level tends t o o s c i f h t e t h e r e could b e some u n d e s i r a b l e temperat u r e fluctuations i n the tube walls a t t h e l i q u i d gas i n t e r f a c e . A s mentioned earlier, the we of a thermal b a f f l e to m a i n t a i n a s t a t i c s a l t b u f f e r between t h e tube sheet and the flowing s a l t may result i n some salt f r e e z i n g . The sodium f l u o ~ ~ b ~ r acto eo l a n t s a l t undergoes a volume r e d u c t i o n of about 4 - l / 2 X on f r e e z i n g 6613, and t h e r e is S O R ~ u n c e r t a i n t y 8% to t h e b e s t REafPS O f aCCOPnnrnQdating t h i s VOlUElC? Change. W e regard t h i s t o b j e c t i v e b u t do n o t vfew i t as a problem as an i ~ p ~ i r t a ndevelopment serious uncertainty a t t h i s t i m e .

Plow I n s t a b i l i t i e s in the S t e a m Generator. - The s e n s i t i v i t y to s t a t i c and dyna~icflow i n s t a b i l i t i e s during f u l l and p a r t l o a d o p e r a t i o n i s an imp~.aftantu ~ % @ e f t a f n . t yAlthough . t h e molten-salbt reactffr i s intended to be a base l o a d power plant, t h e steam g e n e r a t o r must b e a b l e to traverse low l o a d s during steam-system s t a r t u p and shutdown. A l s o the steam gene r a t o r could b e used t o remotre f i s s i o n p r o d u c t h e a t after t h e r e a c t o r is shut down if it can b e shown t h a t t h i s can be done w i t h o u t damage. The d e s i g n e r can p r e d i c t amd avoid s t a t i c i n s t a b i l i t y w i t h a reasonably high degree of confidence. Dynamic instability i s much more d i f f i c u l t to analyze and q u a n t i f i e d s o l u t i o n s are n o t a v a i l a b l e . :.:...:,..:.< .<,

254

- The mcertainties in heat e probably less than t h o s e of nce it has been established that salts ere w a s no evidence of gas f i l m 9 uncertainties remain concernrator surfaces and in t h e use of heat exchanger. Verification physical p r o p e r t i e s and resoluded to p r o d d e i n c r e s e d cone

f i d e n c e in their use.

- Transients in operating conditions cause t h e w d heat exchangers by causing the m e t re r a p i d l y than the i n t e r i o r . Blthou not b e very sensitive t o t h e a c c u r a t e definition is a problem which m u s t be more u l l y explored t h a t necessary ~ c c o ~ o ~ a ~can i ~ben made s i n the d e s i erg and the c o n t r o l system. some work has been done i n the the MSBB reference system on a hybrid eomputer system 1641 Themal Transients

50

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The wastage esence of sodium

-

me e x i s t i n u n c e r t a i n t i e s i n the quans e a t i o n of fission produet d e p o s i t i o on components m d pipin t h e h e a t i n g problem b u t also the (see Chapters 5 and 14) a f f e c t n o t on maintenance planning. In particular, e distribution sf fission p ~ s d u c t s d the heat l o a d s imposed must be evaluated i o r d e r to provide for emerof the empty p r f m q ? heat exchan er i n t h e event the s a l t s could n o t remain In the system. 0

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F a b r i c a t i o n Techniques - S p e c i f i c joint d e s i g n s f a b r i c a t i o n proced u r e s , and i n s p e c t i o n procedures have n o t been chosen a t this timae. H m ever, t h e s e p r e s e n t no unusual problems and can be expected t o e v ~ l v e wFth t h e h e a t exchanger d e s i p . S p e c i f i c p r o b l e m w i l l be r e s o l v e d as t h e y arise w i t h t h e partfcipation of i n d u s t r i a l firms. The t u b i n g d t h enhanced h e a t t r a n s f e r c h a r a c t e r i s t i c s proposed for t h e primary h e a t exchanger ~ e p r e ~ e nan t ~u n c e r t a i n t y which must be explored. Using unenhanced t u b i n g would i n c r e a s e t h e h e a t exchanger f u e l salt V Q ~ U I T E about 40 to 58% which means a 4 t o 7X i n c r e a s e i n t o t a l f u e l s a l t i n v e n t o r y .

Development Program f o r Heat Exchangers

- n e most important u n c e r t a i n t y concerning t h e primary heat exchanger t o b e r e s o l v e d by development i s t h a t sf mater i a l s . The materials problems are d i s c u s s e d i n Chapter 9 . The n e x t m ~ s timportant u n c e r t a i n t y f o r t h e primary h e a t exchange^ i s whether t h e enhanced t u b i n g w i l l have t h e assumed s t r u c t u r a l and h e a t t r a n s f e r c h a r a c t e r i s t i c s necessary f o r a l o w salt i n v e n t o q . Heat t r a n s f e r tests w i t h s a l t would b e n e c e s s a r y t o v e r i f y t h e s t r u c t u r a l and h e a t transf e r characteristics The t e s t i n g should a l s o fnclude t h e p r o v i s i o n s f o r remote maintenance t h a t are i n c o r p ~ r a t e di n t h e h e a t exchanger d e s i g n . e

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Steam Generator Materials

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W e plan t o c o n t i n u e o p e r a t i o n of t h e s t e m c o r r o s i o n f a c i l i t y a t TVA's B u l l Run S t e a m P l a n t . T h i s facility w i l l accommodate 688 u n s t r e s s e d coupons and 1 3 s t r e s s e d specimens. The e v a l u a t i o n of H a s t e l l o y N , part i c u l a r l y in the s t r e s s e d s t a t e , w i l l continue u n t i l a c o n c l u s i o n can b e made about i t s c o m p a t i b i l i t y w i t h steam under stress e Enough i n f o m a t i o n already exists ~neoiogr~ O Qand ~ n c o n e i$00 in steam t h a t evaluation p ~ o g r a m son t h e s e materials w i l l not b e necessary. In order t o e v a l u a t e t h e use of Inconel 606 i n c o n t a c t w i t h c o o l a n t s a l t and steam, tests would b e needed t o d i e t e m h e t h e c o m p a t i b i l i t y of Inconel 488 w i t h sodium f l u o r o b o r a t e . The i n i t i a l tests s h o u l d b e thermal convection l ~ ~ j pws i,t h tests i n pumped s y s t e m i n i t i a t e d i f the r e s u l t s from t h e thermal c o n v e c t i o n loops look f a v o r a b l e . 'Eke work most needed on t h e duplex E n c ~ l o y8 0 h i c k e I t u b i n g i s an e v a l u a t i o n of t h e mechanical i n t e g r i t y of t h e p r o d u c t . Each s i d e of t h e tube is compatible w t t h its r e s p e c t i v e environment namely Incoloy 888 w i t h steam and nickel w i t h f l u o r o b s r a t e . The tests of mechanical i n t e g r i t y w i l l b e p r i m a r i l y l o n g - t a m t u b e b u r s t tests i n i n e r t gas e n v i t o n ~ ~ n t . The main q u e s t i o n s t o be a m w e ~ e dconcern the i n t e g r i t y of the b i m e t a l i n t e r f a c e and t h e r e s i s t a n c e of t h e n i c k e l t o i n t e r g r a n u l a r separation. I f t h e s e tests are f a v o r a b l e , t h e q u e s t i o n of j o i ~ i n gtechniques must b e e v a l u a t e d . Welding heads c u r r e n t l y e x i s t t h a t permit welds w i t h f i l l e r metal t o b e made i n s i d e %/sf i n . diameter t u b e s . The e v a l u a t i o n of j o i n t desfgns that utilize t h i s equipment w i l l be a part of our f u t u r e p r o gram a

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ex&anger and the steam generator. coolant system would have to be

p l a n f o r molten-salt heated s t e m d e s c r i b e d in [67].

Task 1. Prepare a conceptual d e s i of a s t e m generator for t h e EOOQ-W(e) MSBR reference p l a n t , T h i s steam generator i s to produce steam at l($QOQFand 3500 psia from feedwater at 908째F.

study some small-scale tests will be perIn addition to the d e s i formed and a ste eTaelPator d e v ~ ~ ~ p ~r @e pnO K t t Will b e prepared if fUfldfll t h e p l a n is to proceed with the p r e l i d n a q deenerator, to conduct tests and evaluations 9 and to demonstrate in small tests of prop e r f o m about as expected. P e r f o m n c e t e s t s of models that contain a few f u l l size tubes would be conducted under f u l l heat flux conditions in a 3-rn facility as described in [69] * The third phase w i l l c o n s i s t of en tests on prototype s t e m generators, The t e s t a would be perfs t of the o p e r a t i o n of the ase,

c

u n i t s in the steam system of a reactor experiment or demonstration plant. h e or more i n d ~ ~ t r i acompanies l w i l l prepare the detailed desi manufacture t h e steam ewerator prototypes With the experienc d u r i n g t h i s phase, the manufacturer would have demonstrated t h e c a p b i l b i t i e s needed f o r 8 %e Steam generators for future needs of the MsBW PKo requirements ? K i l l depend on wBEetlaer ase three specifies a modular steam genL reference generator (stash as p r wheeler and

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With t h e e x c e p t i o n of the materials problem of the priagary heat exchanger (see Chapter 71, n o ~ es f t h e u n c e r t a i n t i e s a s s o c i a t e d with heat exezhangers and steam g e n e r a t o r s i s seen as fundamental. A%%u n c e r t a i n t i e s are c o n s i d e r e d t o be b - e s ~ l v a b l ew i t h t h e a p p l i c a t i o n of an a d e q u a t e l y funded program of a n a l y s i s and development. The res~iewsmade by t h e Nolten S a l t Group and Molten S a l t Breeder R e a ~ t o rA s s o c i a t e s (Black and Veatch) reached t h i s same conc%usion 670, 4 3 p . 59 ] There i s l i t t l e question that primary heat exchangers and steam generators can be developed f o r t h e MSBE and t h e l a r g e r NSBRs. Performance c h a r a c t e r i s t i c s t h a t are n o t q u i t e as good as d e s i r e d may have t o b e a c c e p t e d i n exchange for g r e a t e r r e l i a b i l i t y and ease of maintenance. ~ u c hs f the technology beimg developed f o r t h e h e a t exchangers and s t e m g e n e r a t o r s for ~ M F E R sappears to be applicable to t h e equipment f o r molten s a l t r e a c t o r s . Its use is expected to s u b s t a n t i a l l y reduce t h e work t h a t w i l l b e required t o develop the u n i t s f o r molten s a l t r e a c t o r s , b u t a subs t a n t i a l development and t e s t program w i l l , n e v e r t h e l e s s , be required. W e would p r e f e r to use H a s t e l l o y E9 f o r a l l p a r t s t h a t c o n t a c t s a l t . H u w e v e r , our c u r r e n t t e s t results are n o t s u f f i c i e n t t o allow us t o conclude whether Hastello7 E\' is compatible w i t h stem. A program is i n p r ~ g r e s st h a t w i l l answer this q u e s t i o n . A second materials choice would b e t h e use of Income1 600 throughout the system. This material i s comp a t i b l e with steam, b u t i t s compatib3Pity w i t h sodium flusroborate must b e e v a l u a t e d . A d u p l e x tube w i t h 1ncslo-y $00 on the s t e m s i d e and n i c k e l on t h e sodium f l u s r o b o r a t e s i d e s h o d d have e x s e l b e n t c o m p a t i b i l i t y w i t h the f l u i d s . The mechanical. i n t e g r i t y s f t h i s product and the a b 5 l i t y to make sound j o i n t s remain to b e demonstrated. e

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The s t @ a r ~ - p ~ w esystem r proposed for t h e MSBR referewce d e s i @ 6711 c o ~ l s i s t sof s u p e r c r i t i c a l c y c l e and equipment w h i c h i s c o n v e n t i o n a l e x c e p t

f o r t h e feedwater and r e h e a t steam p r e h e a t i n g f a c i l i t i e s , The cycle used in t h e B u l l Run steam s t a t i o n of t h e TVA was adapted for the PlSBR s t u d y t o make t h e c o s t and performance estimates r e a l i s t i c . The plfSBR c y c l e u s e s steam a t t u r b i n e t h r o t t l e c o n d i t i o n s of 3508 p s i a and IQOQ'F. Steam g e n e r a t o r outlet steam a t t e m p e r a t i o n i s provided f o r t h e ~ o n t o~f t~u rlb i n e i n l e t c o n d i t i o n s at p a r t - l o a d o p e r a t i o n . Some steam is e x t r a c t e d from t h e high p r e s s u r e t u r b i n e for d r i v i n g t h e wain b o i l e r f e e d w a t e r t u r b i n e and f o r t h e f i n a l s t a g e of regeneratlve feedwater heating. Another extraction i s made at about 600 p s i a f o r the p r e h e a t e r and reheater G ~ T X X I ~ % B . The reheated stream is s u p p l i e d to t h e ds&lbe-flm i ~ t e 9 ~ e d i a t e - p r e ~ s ut u r er b i n e s a t about 540 psia and 18064째F (see P i g . 8 . 4 ) . The i n t e r ~ e d i a t e - p r e s s u 9 e t u r b i n e e x h a u s t s eo m s double-flow low-pressure t U d l i l l e S frOsla WhPCh eXtKaCtfOnS 8pTe made folr t h e feE?dWater heater &,its. The e x h a u s t from t h e How-pressure t u r b i n e i s exhausted i n t o f o u r s u r f a c e

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condensers o p e r a t i n g a t about l-1/2 i n . Hg abs. Full-flow demineralizers are used t o o b t a i n t h e h i g h p u r i t y necessary ~ O Konce-through steam genera t o r o p e r a t i o n a%terwhich t h e feedwater i s r a i s e d i n temperature and pressure t o the f i n a l 700°F and 3800 p s i a steam generator i n l e t c o n d i t i o n . me of the two uncsnventional f e a t u r e s i n 0rnLSs a d a p t a t i s n of t h e TBA steam cycle is t h e r e h e a t of e x t r a c t i o n steam i n t w o stages by u s e 0 % a prime-steam-heated p r e h e a t e r and a salt-heated reheater. The o t h e r unconventional f e a t u r e i s the h e a t i n g of feedwater t o 700°F by d i r e c t mixing of t h e 866°F steam exiting t h e above p r e h e a t e r w i t h the high press u r e 556°F feedwater l e a v i n g t h e top e x t r a c t i o n heater. Two b a r g e motord r i v e n canned-rotor c e n t r i f u g a l pumps i n p a r a l l e l t h e n ea& boost about 19.,680 gpm o f f e e d w a t e r from about 3508 p s i a to 33800 p i a . E i g h t s t e p s o f feedwater h e a t i n g are used i n a d d i t i o n to t h e d i r e c t mixing ts o b t a i n the 700°F feedwater temperature. The use of t h e s u p e ~ c ~ - i t i c parle s s u r e a%Hsws the d i r e c t mixing w i t h o u t serious problem Ebasco examined a l t e r n a t i v e s but s e l e c t e d e s s e n t i a l l y t h e same s t e m system as that of the QRME reference system 6721. They concluded t h a t the u s e of t h e d i r e c t mix8ng for feedwater h e a t i n g and the s p e c i a l b o o s t e r pumps are f e a s i b l e and w i t h i n f o r e s e e a b l e t e c h n o l o g i c a l development Ebasco proposes a weans of improving the c y c l e thermal e f f i c i e n c y by rec l a i m i n g reactor decay h e a t and chemical p r o c e s s i n g heat. This h e a t i s i n t r o d u c e d into t h e cycle as an a d d i t i o n a l S O ~ K Cof~ low p r e s s u r e feedw a t e r h e a t i n g steam 9731. e

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Based on the present c o n s e ~ v a t i v eassumption that 700°F feerItaate~ telllperature PS HleCes%a%y, a suPercrft8ca%-pres§uKe %tf?ZUIl System iS t h e only reasonable & o i c e . Heating t h e feedwater to 7CBOQF in a s u b c r i t i c a l g r e s s u ~ ec y c l e would r e q u i r e a v e r y large amount of h e a t transfer s u r f a c e or9 H ~ Q Pl i ~k e l y , u s e of the LoeffEer c y c l e , The steam g e n e r a t o r would become a s u p e r h e a t e r req uf r ing a s t e m compressor and a much larger mass %%ow rate. If use s f f e e d w a t e r at 588'P is determined to be %eas%bllet h e mixFng chamber, p r e s s u r e booster pumps, and r e h e a t s t e m preheaters e o d d b e e l i m i n a t e d from t h e s u p e r c r i t i c a l c y c l e 9941 The imcrease i n e f f i c i e n c y p l u s t h e s i m p l i f i c a t i o n sf the steam system would r e p r e s e n t a s u b s t a n t i a l Alternatively, a s u b c r i t i c a l p r e s s u r e s t e m c y d e becomes f e a s i savings b l e and can b e i n c l u d e d in t h e o p t i o n s f o r a MSBR power system. The feasib i l i t y O f u s i n g l C 3 W e r feeckaater %eIlp@PatureW i l l be inVe§%fgated by F o s t e r h%eeler f o r SUbCKitiCd and S u p e r c r i t i c a l pIPe%SuKe s t e m c y d e s [ 75 Also, the use of t h e n i t r a t e - n i t r i t e salt im a t e r t i a r y system between the secondary system and the steam, as proposed f o r the MSBR, a%lms t h e use of 480°F feedwater temperature amd the choice between a s ~ p e r c ~ i t i ~ a l o r a s u b c r i t i c a l p r e s s u r e steam cycle [?SI. A s previously mentioned, the ~ ~ ~ ~ ~ e n tfeedwater i o ~ a ah el a t i n g needs of the MSBR r e f e r e n c e steam cycle r e q u i r e t h e use of b o o s t e r pumps and m i X i n g C h m b e r S . f i t k o u g h b o t h of these COHt~osLentS CbaKPeIItly in base a t near the d e s i r e d c o n d i t i o n s , the sizes needed f o r a 1 8 8 8 - ~ ( e )MSBR are n o t p r e s e n t l y a v a i l l a b k . A ~ c o ~ d ti o~ Ebasco's ~g i n v e s t i g a t i o n , the e

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canned-rotor booster p needed for t h e MSBR s t e m cycle are about 502 K than t h e EabgeS WIXp m p b u i l t to date [ 7 7 ] . Consequently, dement of larger e a p a e i t y 9 multistage pumps would b e needed. The mixin re a l s o larger than those in use, b u t t h i s does not a p p e a r development problem since a ch,&er similar t o one specR system m d about f o u r - f f f t k s %IS large is in US& at the P l a n t 1781. As an alternative, a high-pressure heat er could be used to obtain the 780째F f e e h a t e r . The e x i t k e a t i n steam could be thela heated to 1000째F in a s a l t - h ~ ~ t eex&anger d and reintroduced into the cycle thereby eliraainating the p r e s s u r e b o o s t e r p u p s e

Evduatisn e f f i c i e n c y can be obtained with the s u p e r e r i t f e a l pressure steam system g44,5x p e r Refe 79) even though the molten-salt steam generimprovement in the efficiency and a t O K ITMY TZ@qUilPe %OO"F feedWZi%X%r.T r e d u c t i o n of capital costs w h i c h c r e a l i z e d by lowering the f e e h a t e r temperature requirement provides a g incentive f o r t h e development e f f o r t in this directfon. The low of the steam pressure and 0 5 feeswater tenparatute could actually be mutually compatible, For example, as discussed in t h e s e e t i o n on heat exchangers, t h e bayonet tube configurat i o n Fapaich was m s a t f s f a c t o q at hfgh pressure may be s a t i s f a c t o r y w i t h s u b c r i t f e a l p r e s s u r e steam a d lower feedwater temperature Although the o v e r a l l plant: efffcierracy would be less wieh the s u b e r i t i s a l pressure cycle, tne simplification aata reduced c a p i t a l costs be o f f s e t t i n The m I t e n - s a l t reactor concept is not s t r o n g l y dependent on the details of the steam system. Haasever, since thhe steam-electric equipwent represents mre than half of t h e c o s t Qf the p l a n t , the o p t i d z a t i s n of this system m e r i t s much development and analysis effort. 6aiIZible %O% t h e st@iXIl system Qf EL K I O l t e l l mere are several options salt r e a c t o r plant, none of w h i involve fundamental uncertainties. All uncertainties are red to b e resolvable with the application sf an adiequateiy t-maed p r o of a n a l y s i s and development, Since the d e t a i l s of t h e steam s y s t e o a e ~ e l a ~an ~ ~the t requirements of t h e s t e m enerator, it is i e that these requirements be d e f i n i t e l y establ i s h e d and verified.

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- The s t a r t u p system must p r o v i d e f o r t h e i n i t i a l c o u p l i n g of t h e s a l t - h e a t e d steam g e n e r a t o r t o the steam system w i t h o u t f r e e z i n g of s a l t and w i t h a minimum of thermal shock. S i n c e the steam g e n e r a t o r o p e r a t i o n may b e u n s t a b l e a t v e r y l o w l o a d s and f l o w s , a n o t h e r of t h e f u n c t i o n s of t h e s t a r t u p system will b e t o traverse t h e t r a n s i t i o n r e g i o n as q u i c k l y and as smoothly as p o s s i b l e . The s t a r t u p system c o n s i s t s of an auxiliary b o i l e r which can d e l i v e r s u p e r c r i t i c a l p r e s s u r e steam at b00O0F, a l o n g w i t h i t s f l a s h t a n k , b o i l e r f e e d pump, ana o t h e r associated auxiliaries. ~ ~ reference a e system and s t a r t u p procedure are d e s c r i b e d i n Ref. 80. S t u d i e s b e i n g made by Ebasco [8l] and F o s t e r !,heeler 6823 i n t h e i n d u s t r i a l program will p r o v i d e i n p u t on s t a r t u p system requirements. Ebasco proposes a s t a r t u p b o i l e r and s y s t e m w h i c h would b e c a p a b l e of s u p p l y i n g enough s t e m f o r about 10% of r a t e d p l a n t load. A s with c o n v e n t i o n a l s u p e r c r i t i c a l b o i l e r s , t h e d e t a i l e d requirements of the s t a r t u p system f o r the molten-salt steam generator depend a g r e a t d e a l on t h e d e s i g n and o p e r a t i n g c h a r a c t e r i s t i c s of t h e s t e a m g e n e r a t o r i t s e l f . Any u n c e r t a i n t i e s Lie i r n t h e a p p l i c a t i o n of more-or-less csnveat i ~ ~ steam ~ a l system equipment t o t h e d e t a i l e d s t a r t u p needs of t h e moltens a l t steam generator. Although basic p e r t i o n s of t h e system o r c e r t a i n s t a r t u p t e c h n i q u e s may b e demonstrated i n s t e a m g e n e r a t o r m ~ d e l .t e s t s , t h e i n t e r r e l a t i o n s h i p between t h e s t a r t u p and t u r b i n e steam systems i s s o couip l e x t h a t o n l y a l a r g e f a c i l i t y , such as t h e E B E , w i l l be a b l e t o ad@q u a t e l y t e s t a complete s t a r t u p system. Whatever d i f f i c u l t i e s a r i s e s h o u l d be r e s o l v a b l e w i t h t h e a s s i s t a n c e and e x p e r i e n c e of q u a l i f i e d i n d u s t r i a l ffrms

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P r e s s u r e Relief System. - To m i n t a i m t h e secondary salt system as a b u f f e r between t h e steam a ~ primary d systems, a p r e s s u r e r e l i e f device must b e provided on t h e s a l t s i d e of t h e s t e m g e n e r a t o r . A r e t e n t i o n system of conduits and holdup t a n k s must a l s o b e provided t o c o n t a i n t h e e f f l u e n t m i x t u r e of steam and s a l t i n t h e event a s t e a m t u b e does r u p t u r e ana a c t u a t e a r e l i e f d e v i c e , The relief d e v i c e must o p e r a t e a t t e m p e r a t u r e s above t h e % i q u i d u s ~f t h e s a l t . It must caperate either in d i r e c t contact with molten salt ( o r i n c l o s e proxbmity v i a a gas s p a c e b u f f e r ) f o r l o n g p e r i o d s of t i m e w i t h o u t l o s s of r e l i a b i l i t y . E t must b e c a p a b l e of having i t s r e l i a b i l i t y checked d u r i n g normal shutdown p e r i o d s . It must c o n t a i n s a l t w i t h o u t any l e a k a g e and y e t r a p i d l y relieve a m i x t u r e of salt and steam i n t h e e v e n t of a t u b e r u p t u r e , The omh, r e f e r e n c e concept proposes a n i c k e l rupture d i s k i n a conm e r e f a l l y a v a i l a b l e snapover-type o r r e v e r s e - b u c k l i n t y p e a c t u a t o r [ 8 4 1 p o s i t i o n e d on t h e salt outlet of the steam g e n e r a t o r . The Ebascs s t u d y concept provides a g a s - f i l l e d r u p t u r e d i s k housing at t h e h i g h p o i n t of t h e s t e a m g e n e r a t o r loop [SSl. F o s t e r rneeler w i l l propose a c o n c e p t u a l d e s i g n of a r u p t u r e d i s k assembly and location as p a r t of t h e i r s t u d y 68611. Although t h e o t h e r two concepts i n c o r p o r a t e a gas s p a c e buffer between t h e d i s k and salt, P o s t e r Wheeler has been r e q u e s t e d t o c o n s i d e r a "hard" system w i t h no gas pocket. The hard system approach b e i n g r e q u e s t e d of P o s t e r Wheeler i s more d e s i r a b l e in that t h e l o e a t i o n of t h e r u p t u r e d i s k

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is n o t restricted and t h e mcertaiwty of maintaining multiple gas pockets is also avoided. As f a r as we h m , no rupture d i s k s have been operated w i t h molten S a l t . bilthOUgh KUpture disks have been Wed 1~6thl i q U i d - E E t d System R program, in most c es the disks have been located in a gas space. me ma r uwcertaianty is one of ~ e ~ @ sf ~ a~ ort.abinatfsm ~ ~ e ~of t materials and aCtUatiOa% dlevfee fllZlt Will operate p e r i o d s f n contact w i t h molten sa%$, Although t h e devel aysten r u p t u r e disk appears feas5b e 9 f a i l u r e to achieve t h i s goal wsuld require reversion to the use of a as pocket fob t h e p.k-oteCtiQnOf t h e disk assembly e Little mcertainty 5s associated w i t h t h e retention system necessary t o handle the effluent f r o m the relief device. However, 8 development must be established f o r the csmpsnents and operating procedures neeessa?ry to provide f o r separation, handling, and d i s p o s a l of the gaSeOus, l i q u i d , and sohid effluents resulting from a rupture, The development infOrmEt.t%on needed a l s o hc%UdeS t h e plPoceduKes d equipment necessary f o r &&2 c%E%3SlUpOf the KelaaaiIIder O f the SeeOnda s a l t system to a l l m r e s m p t i s n of operation in a d n i

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Valves

Experience with Molten-Salt Valves

eew used s u c c e s s f d l y in molten-salt service These valves have continued to be used because d because no me&anical valve has been developed y requirements sf molten-salt service. A freeze

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263 valve c o n s i s t s simply of a section of s a l t - f i l l e d p i p i n g w h i c h can b e cooled when d e s i r e d t o estabP8eh a s h o r t s e c t i o n of f r o z e n salt which e f f e c t i v e l y blocks flow. Both t h e f r e e z e valve and mechanical valve have s p e c i f i c advantages. The mechanical valve can p r o d d e f a s t e r opening and c l o s i n g and can b e used for flow t h r o t t l i n g . The f r e e z e valve prsvides high r e l i a b i l i t y and zero s a l t l e a k a g e across t h e valve and t h u s is part f c u l a r l y w e l l s u i t e d t o a p p l i c a t i o n s when tight s h u t o f f is needed for l o n g p e r i o d s of t i m e . F r e e z e valves have o p e r a t e d s u c c e s s f u l l y i n the MSRE and in many out-Of-pile tests a t 8 L i n s i z e s up t o 1-%82-in. IPS p i p e . Kore than 125 have been used, and they have accumulated more than 650,008 hr O f ope~atingt i m e . These valves o p e r a t e d with salts as diverse. as t h e e u t e c t i c mixture of NaBF4-NaF (92-8 mole W), which has a 725째F m e l t i n g p o i n t , and LiF, which has a 1560째F m e l t i n g p o i n t . The o p e r a t i o n of the 1 2 f r e e z e valves i n t h e MSRE demonstrated rel i a b i l i t y i n an a c t u a l r e a c t o r system [ 8 % ] . These valves were of two s i z e s , lb2 i n . and %-1/2 i n . IPS, and ascumu%ated 208,000 h r of o p e r a t i o n d u r i n g t h e reastorfs l i f e t i m e . me of 1-112 i n . valves f a i l e d and l e a k e d a f e w grams of salt d u ~ i n g t h e final shutdown of t h e r e a c t o r . The failure w a s due i o the ma^. stresses caused by a field m o d i f i c a t i o n of a shroud on t h e valve t o a i d a t t a c h m e n t of a l a r g e r c o o l i n g l i n e . S u i t a b l e d e s i g n m o d i f i c a t i o n s should e l i m i n a t e t h i s prob abem in f u t u r e valves ~

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A i r c r a f t Reactor Program Development Work on Mechanical Valves. T e s t s of bellows-sealed mechanical valves were conducted around 1957 i n t h e A i r c r a f t Nuclear P r ~ p ~ l s i oProgram n i n an a t t e m p t t o d e v e l o p a %-1/2in. I P S Shut-off V d V e f o r temperatures of 1208 to lb588"F with molten salt. The valve seat material w a s c o n s i d e r e d t o b e t h e major problem, and a l though .a s u c c e s s f u l valve w a s n o t developed p r i o r t o c a n c e l l a t i o n of the work., some promising seat and p l u g material combinations were i n v e s t i g a t e d . Five valves were t e s t e d w i t h a v a r i e t y of s e a t - p l u g material combinations and accumulated o v e r 7,888 h r of t e s t i n g e x p e r i e n c e . Le& rates i n t h e more successful tests ranged from 0 t o 5 cc/hr with a 50-psi p r e s s u r e d i f f e r e n t i a l a c r o s s t h e c l o s e d valve seat. T h e cermet materials w e r e the most p'I33lwiSillg Seat-plUg C O l l l b i l l a t i O n s , This eXpeKPeIICe Will b e of V d U e i n f u t u r e P K O ~ I - ~ I I ~tSo develop shut-off valves f o r m o l t e n - s a l t service. OWL 4-in. T h r o t t l i n g Valve. - F i v e t h r o t t l i n g v a l v e s were designed and f a b r i c a t e d at ORB%, around 1955 f o r f l o w c o n t r o l i n f i v e pump loops t h a t o p e r a t e d w i t h molten salts and l i q u i d metals. The valves w e r e des i g n e d f o r t h r o t t l i n g service only and were fabricated completely of Inesnel. They o p e r a t e d a t o t a l t i m e of l l 4 , 0 0 Q h r a t temperatures from 1800 t o 15OO"P, and no be1Bow.s f a i l u r e o r s i g n i f i c a n t ~ ~ ~ h a ~p ri ocb lae ml o e c ~ r r e dd u r i n g t h a t time. The valves w e r e manually o p e r a t e d and w e r e adjusted d u r i n g o p e r a t i o n of %he Poop t o measure pump perfor~lsancecharacteristics. These ORNL sleeve valves are the only known bellows-sealed mechanical valves whish have o p e r a t e d r o u t i n e l y and s u c c e s s f u l l y i n hightemperature moIten-salt service. This experience leads us to b e l i e v e t h a t laager t h r o t t l i n g valves can b e sucsessfu%ly developed when needed.

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~ e l b s w s - s e a E e d valves have been used suscessfully in many sodium applications. For up to a few inches in pipe size, it appears that similar valves would be satisfactory f o r rase in molten s a l t if fabricated of mterials. Hmever, there is very I t h b e l l o w s valves larger & and ~ e ~ e O f~ o ~ ~ e ~ ~ dfscussed by SeFm [ 8 l t e n - s d t salves. Eost so however, have had s o d i m freeze seals on the va is not available f o r moltela-sa3it valves, Aabtho sealed valves f o r molbten-salt reactors conseq n t l y have very little sodium fKOm, V d V e d e s i fabrication, and operation ZB the future p r s d d e much useful i n f o m a t i o n to aid molten-salt valve development.

ve techrasIogy in sizes up to 1-1/2-im.

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sis of a freeze valve predfetab le t e m p e r a t ~ ~ e It seem l i k e l y t h a t p r o t o t y p e s @actorswill have to be exf freeze-thaw cycles attendant seat-p evelopmerat prsb a eveloped, even i le f o r use where needed. The 1 valves, p a r t i e e

experience of t h e

f o r molten s a l t s . 69s comercia1 technolo y e X i S t s f O g fEib3dCatiOn O f BaS%elloy N valves and bellows at the p r e s e n t i m e . HBweVer, t h e r e are no Lnmm meta%%urgieaI which should prevent f a b r i c a t i o n of large valves when re

Effect of uncertainties of t h e MehmicaB Valves

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The two major u n c e r t a i n t i e s Fnvol selection of t h e pab mafLeKiak3 % O r S h U t - O f f Valves a d d e s i and development of The seat-seal of t h e mechanical shut--0 valve requires t h a t seal force be applied at the seal surfaces and be maintained b7hile t h e valve is e l u s e d . The valve m u s t a l s o open oft demmd w i t h o u t d m a g i n g t h e seal S U K ~ E E ~ . 1% such a valve proves to b e m u s u a l l y difficult ts develop, it would be reasonable f o r most a p p I i c a t i o n s to use a freeze valve in

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series as a backup t o this mechanical valve. In t h i s case t h e mechanical valve would be closed to choke-off t h e s a l t flow while t h e f r e e z e p l u g i s e s t a b l i s h e d and then reopened t o p r e v e n t self welding of t h e seat and p l u g . This combination has been u s e d in t h e d r a i n l i n e of some t e s t l o o p s . The valve plug can be mechanically guided i n t o the valve seat OK t h e t h r o t t l i n g sleeve e i t h e r i n t h e s a l t o r on t h e gas s i d e of t h e penetration seal. The l a t t e r scheme r e q u i r e s s t r o n g e r aneders b u t can be done i f t h e valves are t o be l o c a t e d i n a n area o u t s i d e o f the c e l l f u r n a c e or i f t h e operator-guide can be i n a small s e p a r a t e c e l l where it c o u l d be cooled such t h a t t h e b e a r i n g materials f o r t h e guide are n o t o p e r a t e d a t h i g h teTllpeKatUr@e The mechanical t h r o t t l e valves will r e q u i r e o p e r a t o r s t o c o n t ~ 0 1the valve trim p o s i t i o n s . a%hOUgh there are S O m e diffePenceS in t h e r e q u i r e ments f o r t h e s e o p e r a t o r s when used with a shut-off valve and w i t h a throttle valve these d i f f e r e n c e s are swab1 If a r e k k b le t h r o t t l i n g valve cannot b e developed f o r use i n t h e c o o l a n t s a l t system then t h e optimum c o n t r o l scheme f o r t h e r e a c t o r and t h e steam p w e p~ l a n t w i l l b e a f f e c t e d . A d e s c r i p t i o n of the u s e of t h e t h r o t t l e valve is g i v e n i n Chapter 10.

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T e s t i n g p r o g r a m must be c a r r i e d o u t to select s u i t a b l e materials f o r b e a ~ i t n g s , valve p l u g s , and seats f o r mechanical valves. The f a b r i c a t i o n of r e l i a b l e bellows must b e demonstrated, o r some o t h e r hemetic stem seal, such as the torque-tube seal must b e developed [ R e f . 893. A c o m e r c i a 1 c a p a b i l i t y f o r f a b r i c a t i n g l a r g e H a s t e l l o y mechanical valves will have t o b e developed. F i n a l l y , complete valves must b e t e s t e d e x t e n s i v e l y a t o p e r a t i n g c o n d i t i o n s t o v e r i f y performance. The r e l i a b i l i t y of large valve o p e r a t o r s must b e demonstrated a t c o n d i t i o n s similar t o t h o s e i n a r e a c t o r system.

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L i t t l e has been done on valve development f o r m o l t e n - s a l t r e a c t o r s s i n c e t h e work on t h r o t t l i n g valves for l o o p s i n t h e APJP p r o g ~ a mand the. development of freeze valves f o r the MSRE. h active program, spanning several y e a r s , would be r e q u i r e d t o p r o v i d e t h e r e q u i r e d valve technology f o r m o l t e n - s a l t b r e e d e r r e a c t o r s , w i t h much of the t i m e t o be used i n t e s t i n g prototype valves. W e b e l i e v e , however, t h a t such a program can produce f r e e z e and mechanical valves t h a t w i l l be adequate f o r u s e i n t h e fuel and c o o l a n t s a l t systems.

General Description and Design Requirements

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that s e p a r a t e d them from t h e s a l t and t h e r e f o r e r e q u i r e d a u x i l i a r y gas c o o l i n g . Because t h e rods and d r i v e s w e r e s e p a r a t e d from the s a l t , t h e r e w a s IIQ problem o f gas seals f o r f i s s i o n product c o n t r o l , The s a f e t y rods f o r the ARE were suspended from magnets w h i c h w e r e moved w i t h lead-screw type d r i v e s . This d r i v e was a l s o used f5r t h e r e g u l a t i n g r o d . The KSRE c o n t r o l rods were suspended from a c o n t i n u o ~ schain d r i v e which was conn e c t e d t o a motor through magnetic c l u t c h e s to pernit fast i n s e r t i o n , These rods and d r i v e s o p e r a t e d without s i g n i f i c a n t d i f f i c u l t y d u r i n g the l i v e s of t h e r e a c t o r experiments, safety rod Was 134c and s t a i n l e s s The pSiSQn YfkateKial f o r thhe s t e e l served as poison f o r the c o n t r o l rod [ % I . The poison element f o r the MSW c o n t ~ o lrod 1971 w a s a mixture of gadolinium and aluminum oxides, formed and s i n t e r e d i n t o a number 0 % s h o r t c y l i n d r i c a l t u b e s which were i n t u r n canned i n I n c o n e l . Vfsual o b s e r v a t i o n of some of t h e canned elements a t the end of t h e seeactor o p e r a t i o n r e v e a l e d no s i g n i f i c a n t chan i n dimensions O K e x t e r n a l appearance. There has been no e x p e r i e n c e with c o ~ l t r o lrods o p e r a t i n g d i r e c t l y i n t h e salt; however, the p h y s i c a l arPangement and proVisionS f o r c o o l i n g In one might be s i m i l a r t o that i n t h e liquid-metal-cooled r e a c t o r s . p r o p o s a l f o r a c o n t r o l rod f ~ urs e w i t h a liquid-metal-cooled r e a c t o r , the pOiSSll Section iS guided Within a d u c t Which is pOsitiOIIed W i t h i n t h e core. The MSBB r e f e r e n c e d e s i g n u s e s g r a p h i t e d u c t s f o r g u i d i n g t h e s a f e t y rods and t h e g r a p h i t e c o n t r o l r o d s .

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The mterials proposed f o r the p s i s o n elements f o r the MSBR are s i m i l a r to those used i n the ARE. We have had e x p e r i e n c e with forming rare e a r t h oxides and BhC i n t o u s a b l e shapes and then canning the elements to HCWeVeg, WE? have not had everieflce prOt@c%:them f X Q m the eI'IV'fKOllment. w i t h such elements i n a high n e u t r o n f l u x field. The m a j o r problem w i t h the C a n n h g O f &e B 4 c f o r U s e i n t h e S h i m rod O r f o r a C O n t B p O l r5d i S dealing with the helium produced by n e u t r o n a b s o r p t i o n i n t h e 1 0 h~ e ~ method is t o p r o v i d e ample s p a c e t o c o n t a i n thhe helium f o r the life of t h e rod. If t h i s does n o t appeaP feasible for t h e MSBR, one Sf the Part? e a r t h oxides could b e used. Another a l t e r n a t i v e i s t h e use of a rod cowstructed e n t i r e l y of HasteHloy N , the size depending on the ~ e a ~ t i ~ i t y @hang@ needed f Q r t h a t p a r t i c U b f r o d . The cotktrol and s a f e t y rods are t o f i t l o o s e l y i n and b e guided by the s t a t i o n a r y g r a p h i t e duct. Information i s needed on the b e a r i n g prope r t i e s of f ~ i c t i o nand wear I n salt f o r g r a p h i t e on g ~ a p h 8 t eand H a s t e l l o y Ea on g r a p h i t e , and f o r ~theapmaterials on g r a p h i t e i f t h e s e combinations prove t o be m s a t i s f a e t o r y . A s d e s c r i b e d above, t h e r e a c t i v i t y v a l u e of a s i n g l e g r a p h i t e c o n t r o l rod is s m a l l and would r e q u i r e ganging several t o o b t a i n thhe n e c e s s a r y s e n s i t i v i t y f o r c o n t r o l . Nore proof i s needed that t h e u s e of such a rod is f e a s i b l e . The c o ~ l t r o land s a f e t y rod and rod d r i v e development work for t h e LWBR should in p a r t be appUcable t o t h e MSBR if s u i t a b l e in-core guides and contamination c o n t r o l seals can b e clevelb~ped. En p a r t i c u l a r t h e d r i v e s

should b e a d a p t a b l e to XSR use althsar room than w e would l i k e t o p r o v i d e ab of the techniques w i l l be u s e f u l i n d

some of them r e q u i r e more head e reactor. En any event many ng a d r i v e system f o r XSBR's.

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E f f e c t of uncertainties The use of a graphite rod t o p r o v i d e the r e a c t i v i t y c o n t r o l and sh2ming n e c e s s a r y i s uncertain b o t h because of i t s v e r y Pow r e a c t i v i t y Worth a d the problefla 0% gknidhg i f 2 Within the COX'@. I f t h e g r a p h i t e Od k 3 deterwine t o b e unacceptable, then a p o i s o n rod of somewhat reater worth CB ld b e used with an a c c e p t a b l e l o s s i n breeding ratis of 0.005 f o r 8.2% Ak/k pea]e The use of B4C 89 t h e poison, with t h e r e q u i r e d h e a t renaovaP and the e Of the helium produced, might m&e such an a b s o r b e r aacceptable If s o , che BL+C could b e r e p l a c e d w f t h rare earths such as europLum or adsliniura s x f d e which release energy as g a m a r a y s instead of alpha p a r t i c l e s , Hs helium is g e n e r a t e d and t h e g a m a r a y s should not energy Hocally as would the alpha p a r t i c l e . me MSBR d e p o s i t as mu uses t h e B4C poison in t h e s a f e t y o r shutdown rods and reference des expects no t r o u b l e because they can be held o u t of the r e a c t o r C O K ~u n t i l needed and t h e r e f ~ ~doe not have a h e l i u m generation OH heating problem. If further s t u d y sf t h e s h u t d m requirements determines that rapid s k u t down i s neededs then the r a d s might have t o b e i n s e r t e d n e a r enough t o t h e core t o a a h r e q u i r e c o n s i d e r a t i o n of the use of o t h e r poisons.

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Further Work h y f u r t h e r Work dOtae i n the deVE?%OpHlelltO f CXXItKO% and Safety rods d rod d r i v e s s h o d be d i r e c t e d toward the exact needs sf a s p e c i f i c HnoEten-salt r e a c t o r . R e q ~ i ~ e m e n tsuch s as t h e e x a c t amount O S r e a c t i v i t y ts b e controlled, the change rates of r e a c t i v i t y , and the response t i m e s f o r t h e c o n t r o ~ana safety system should b e e s t a b l i s h e d b e f o r e t h e meckaanFcal d e s i of t h e s y s t e m i s s t a r t e d . P r o t o t y p e s of the parts of the r e l a t e d t o the s a l t - as interface, t h e gas seals, the guides or 8 f o r the rods Withi the c o r e , and t h e t r a n s m i s s i o n of motion t o s would be f a b r i s a t e d and operated f i r s t i n water and a i r t o assist t h e d e s i g n , and then in salt and i n e r t gas t o proof t e s t ctancy and overall performance. The seals or a c t i v i t y cont r o l , l%e b e a r i n materials and arran ement, and the methsd of eoolin t h e C o n t r o l eb2EX2nt Over its entire range o f trave%.Would K e C e f V e t h e earliest a t t e n t i a n . After t h e i n i t i a l . component testing full scale rods drives WOUPCI be tested 'UIX+-X s f ~ ~ ~ ~ l ireactor ated ~ ~ n d i t i ~ n s

Evaluation N o fundam@n%al d i f f i c u l t i e s are f o r e s e e n in d e s i g n i n g c o n t r o l and safety rods and d r i v e s f o r u s e i n MSRBs, b u t a thorough development and prototype t e s t i n program w i l l b e r e q u i r e d t o a5sure a d e q u a t e performance in a high-temperature environment b e f o r e i n s t a l l a t i o n i n a reac%oP. mere

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a%-er e a s o n a b l e alternatives f o r most of t h e u n c e r t a i n t i e s . Perhaps a problem requiring much a t t e n t i o n i s t h e b e a r i n g of the moving r o d on t h e graphite duct and o b t a i n i n g an acceptable l i f e t i m e from such an arrangement. H Q W ~ V ~ Pbecause , t h e fit can be l o o s e and the c o n t a c t p r e s s u r e low, We believe t h a t SatIsfaCtQ-~?j guides CiLn be deVehp@d.

Fuel S t o r a g e and Afterheat Remuval ~ e p o s i t o r i e sare needed f o r both k i n d s of s a l t s based in t h e MSBR to p r o v i d e safe and convenient storage any t i m e they are d r a i n e d . me fuel d r a i n tank, because of the i n t e n s e ~ a d i ~ a ~ t i v istf y the s a l t , must p r o v i d e r e l i a b l y f a r the removal of a f t e r h e a t as w e l l as t h e s u r e containment of v o l a t i l e r a d i o a c t i v e products. In some ways, as diseussed in Chapter 1 4 , i t is the m a j o r s a f e t y f e a t u r e of t h e reactor. The f u e l d r a i n tank must have s u f f i c i e n t capacity t o h o l d all the pr5mary salt p l u s the amount of c o o l a n t salt t h a t is i n the heat-exchanger s h e l l ; i n a double-ended heat-exchanger t u b e f a i l u r e , this much coolant Could d r a i n i R t Q t h e primary system. PUek s a l t CXIInot enter t h e Secondary s y s t e m r a p i d l y because 0 % t h e p r e s s u r e d i f f e r e n t i a l between the fcwo syst e m s , and m o n i t o r i n g f o r fissiun products i n the secondary c o o l a n t w i l l give immediate evidence of o u t l e a k a g e , s o that the primary system can be d r a i n e d b e f o r e much f u e l s a l t Is t r a n s f e r r e d . Consequently the cooPantsalt d r a i n tanks are simple t a n k s , with no s p e c i a l c o o l i n g p r o v i s i o n s , l o c a t e d i n h e a t e d sells. In addftion $0 the primary d r a i n tank, there is a f u e l s t o r a g e tank i n t o which the f u e l can be pumped in case a repair o f some palet of t h e primary d r a i n tank system i s r e q u i r e d . T h i s t a n k has a h e a t remuval capab i l i t y O f Silly 1 SEnC@ t h e S a l t Can be heEd in t h e d r a i n tank Unti% t h e r a d i o a c t i v e decay has reduced t h e heat l o a d t o t h i s level.

Draining the Reaetor

I n normal circumstances, the primary system can b e drained i n t o t h e d r a i n tank t:kkOU@3 either Of plug Valves pElralhi?l. This EiXTaXIgement with two valves is, w e think, s u f f i c i e n t a s s u r a n c e of an a b i l i t y t o d r a i n the system. The valve plug does not depend on a valve seat f o r s e a l i n g , b u t i s p ~ ~ v i d ewdi t h a h e a t i n g and cooling system f o r t h e seat s o that t h e f i n a l s e d can b e made by f r e e z i n g the s a l t under the seat. The valves, d e s c r i b e d i n detail on page 51 of ~ e k r e n e e9 9 , are l o c a t e d in the d r a i n l i n e leading from the Pow p o i n t of t h e primary system to the top of t h e d r a i n t a n k . For maintenance purpusess they are l o c a t e d i n the d r a i n tank c e l l w i t h an access plug in t h e shielding directly over them. Leakage o f F u e l S a l t

If there is a leak i n any part of the f u e l system, the leaked salt must b e conveyed to the d r a i n tank and its a f t e r h e a t removal system. The l e a k e d s a l t i s es$%ected i n a catch pan under t h e r e a c t o r whish i n t u r n

2 76

d r a h S h t 0 the? d K Z h tank pit. &re the Salt enters 8 fUIlIE?lb-bik@ d K a i X I pan on t a p sf the drain tank which d f r e s t s the salt to a frangible-disk valve which can be punctured on demnd to d r a i n the s p F l l e d s a l t i n t o the drain tank. No pipe comes b e l m the catch pan so that unless the d ~ a i n Ieaks, all primary salt will. positively end up in the drain tank. r o v i d e f o r the contingency of a leak in the d r a i n tank, it i s enclosed in 8 seeowdaq tank. h y crack or break in the drain tank would only le& salt Lnts the annular space between the drain tank wall and the S U K I ~ O U ~

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Drain Tank Design The drain tank conceptual d e s i g n is shown i n e l e v a t i o n i n P i g . 8.5. '%he tank, as s h m , is dimensioned for a 30B-mQe) r e a ~ t o ~however, ; the system for t h e 1000-W(e) breeder is exactly t h e except i t is larger in d i a m e t e r and has coolant thimbles. The f u r t h e r d e t a i l s of the d e s i g n and the performance of t h e s e d r a i n t a n k s , showing flow rates, temperatures, dimensfons, ete., are g i v e n i n Ref. 113 and Refa 9 9 , p p . 45-47. Also d e s c r i b e d t h e r e are t h e l a y o u t 015 t h e r e - e n t r a n t NaK c 0 0 l i n 8 l i n e s and the aPKallgelTE%lt Of the jet pWpS f o r aUtOlllatfCal1y r e t u r n i n g to t h e primary c i r c u l a t i n g system t h e s a l t that 5s c a r r i e d i n the gas from the bubble s e p a r a t o r s a dKain tank of t h e Same princfple Used SuCCeSSfUEPy I%n t h @ MSI&E. In this ease, water w a s used i n bayonet t u b e s mouurted i n t h e r e e n t r a n t t u b e s and the steam w a s condensed i n a water coaled h e a t exchanger. This system was used only f o r removing afterheat from the s a l t and was not ~ O K off-gas cooling. I n t ~ ~ d u c i n awater g i n t o the bayonet t u b e s d u r i n g s t a r t u p of t h e system p r ~ d ~ c ead thermal shock t o the water tubes which w a s n o t I hazardous but would s h o r t e n t h e l i f e sf t h e tubes, For t h i s K ~ ~ S O T -we chose NaK c o o l i n g in the KSBR d r a i n tank d e s i g n . The MaK ~ i l p c ~ i are t s thermal convection l o o p s , the h o t l e g b e i n g heated by r a d i a t i v e t r a n s f e r (with some gas conduction) between t h e thimbles i n t h e d r a i n t a n k and the bayonet NaK tubes. The c o l d leg l o s e s h e a t by radiative t r a n s f e r (plus some gas conduction) i n pipes which run through t h e w a t e r tank- The NaK c i r c u i t s are completely independent, each w i t h i t s own expansion t a n k and c o n t r o l v a l v e s whPch can be used t o regul a t e t h e h e a t removal tend t o i s s l a t e an NaK system i n case of a leak. Each N a K c i r c u i t p e n e t r a t e s t h e b u i l d i n g containment and t h e d r a i n t a n k cell containment. A t each p e n e t r a t i o n a b e l l o w s seal i s used to psovide for expansion of the l i n e s d u r i n g heat-up. Each NaK circuit runs t o owe of t h r e e water t a n k s through which water f l o w s and is r a i s e d in t e m p e r a t u r e by 20째F. The o p e r a t i o n of any W S of t h e s e w a t e r t a n k s w i l l keep the thimble t e m p e r a t u r e i n t h e d r a i n tank bel o w 1400QF. We b e l l e v e t h i s is s u f f i c i e n t ts guarantee t h a t h e a t is removed s a f e l y from t h e d r a i n tank. The water tanks are cubes a b ~ ~25t ft a l o n g an edge. Pipes run through t h e s e tanks in two t i e r s at right angles t o each o t h e r . There are f o r t y - e i g h t 3-411. s&ed-10 tubes p e r row. Two t a n k s Rave 36 rows o f tubes and the t h i r d t a n k h a s 44 TOWS. They run through the tank w a l k a t each terninus. The water level is about 5 f t above t h e top row o f p i p e s in each tank t o p r o v i d e a water supply for emergencies. a

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A s f a r as t h e h e a t l o a d i s concerned, t h e n u c l e a r decay chains and t h e emergy r e l e a s e d by them are well known. The s t a n d a r d energy release rates have been used i n making h e a t t r a n s f e r c a l c u l a t i o n s . We have t h e MSRE e x p e r i e n c e s wh8&, although 011 a very mu& smaller scale, is n e v e r t h e l e s s h e l p f u l in g u i d i n g t h e design of the p r i m a r y drain tank system. The e x p e r i e n c e in the MSRE should be d i r e c t l y u s e f u l in s c a l i n g up f o r t h e power r e a c t o r s . uncertainties

The o n l y real u n c e r t a i n t y t h a t w e f i n d ibn h a n d l i n g t h e drain tank problem i s t h a t concerning the d e p o s i t i o n of f i s s i o n products. In t h e MSRE, m o s t of %he noble metals adhered %S metal and g r a p h i t e surfaces, but HOW much BOf[lg appeared in t h e Off-ga.53 fKOfla t h e puUlp bowl (see2 Chap. 5) of the noble metals will be e x t r a c t e d through the g a s - s t r i p p i n g s y s t e m f n an MSBW i s uncertain. W e have assumed t h a t the noble metal p a r t i c l e s and t h e i r d a u g h t e r s and the d a u g h t e r s Of t h e WSble gases t h a t enter the d r a i n tank will d e p o s i t u n i f o r t d y on t h e surfaces there, b u t i t i s n o t clear whether or n o t s p e c i a l p r o v i s i o n s must be made t o a v o i d locally h i g h depe

..... .

i.>? .. I ....

..... ..... ;sx,

osition. Evaluation Prom the e x p e r i e n c e with t h e HISRE d r a i n tank c o o l i n g system, w e bel i e v e t h a t t h e d r a i n t a n k system proposed for t h e MSBW deals with t h e afterheat problem in a dependable way. W e thfwbr i t r e p r e s e n t s a "walk awayqtand f a i l - s a f e ~ gtern, ~ s p r o t e c t e d a g a i n s t e ~ e r y t h i n gb u t well ~ P E U I I I ~ ~ and executed sabotagei We have not s t r a i n e d the t e ~ h n o in l ~t ~ his design, and w e b e l i e v e that thhe u n a n t i c i p a t e d probHem encountered in d e s i g n i n g and developing such a system w i l l be minimal. F u e l S a l t Gas-Handling

..... ../..

System

i.......

Purl, os e s

The o b j e c t i v e s sf t h e MSR gas-handling system are:

..... ,..a

1. P r o t e c t t h e f u e l s a l t from an ~xid%zfngatmosphere. :.......

.=,A

2.

Minimize t h e p o i s o n i n g of t h e r e a c t o r due t o t h e noble gases and their d a u g h t e r s - p a r t i c u l a r l y xenon-135 e

.:*u

3.

P r o v i d e p o s i t i v e containment of t h e r a d i s a c t f v e noble gases and daughters and any s t h e r r a d i o a c t i v e material s t r i p p e d from the fuel s a l t .

t

... ..... s , 1

I

.... i ' . .

.iSd

$&$

274

1. 1

2.

k

3. 4. 5.

as system must be able t o acco te v a r i o u s f o r 0 f csntaminasuch as noble metals, hydro68 ecomposition p ducts, o r any a t h e r particulates t h a t may b e carried by the purge gas,

,. ..

G

aseous effluent is to be discharge plant

7.

from t h e reactor

E

Positive containment of all radioactive mat@rial must b e p r o r i and accident c o ~ ~ ~ ~ ~ o 5 3 s 0

-

an the reference d e s i 13R [1QQ p xenon-l35 and are stripped from t h e f alt by i n j e c t i n Hn s f f u e l s a l t t en from the discharge of the f u e l s a l t pump as shown in Fi 8 . 6 . J u s t upstream of t h i s pins, bubbles eontafnnoble gases are removed % r s m t h e s a l t by the use of b u b b l e separators. D

as a l o n g w i t h m y s a l t entrained in it passes t h r o u

to t h e d r a i n tank [,%SI% an the drain tank, t h e e is separated from the gas and returned to the main circulation l o o p by j e t pumps. The l i n e running from the bubble sepa tor to t h e d r a i n tank is p r o v i d e d with a siphon break to prevent d ~ a f n a O f the main loop in case sf a pump failure.. This siphon break is in e form O f a l o o p t h a t rises above t h e l i q u i d l e v e l n t h e pump bowl and a venturi t h a t communicates w i t h t h e p m p bowl as space thkrsugh a pipe. During noma1 s passing through the p bowl i s drawn into the venturi i n t o the drain tank al aS-Salt miXtUKe f l S W le separator tank, thFs gas has a residence time of the order s f I to 2 hr to permit the separation Of most O f t h e particulate matter an e n t r a h e d s a l t and to greatly reduce the decay energy [l02]. The gas then recycled through a cleanup sy tern back to the bubble generator and the pump shaft. seals. Before the as enters t h e cleanup system, a particle trap will b e p r o d d e d if the drain tank is n o t capable Of separatin la. t h e particulate tter and entrained f u e l s a l t from t h e o f f as then f l m s t h r s &arc081 beds having a 4s-hr xenon holdup

r,

. ... ..........

I&.._

,..... &>

.s;i

e

to the bubble generator, b u t p a r t of it i s clean shows a gas compressor in the l i n e O f the gas fa.

. .. u.2

2 75

.....

... ..... *a:

....

".yi

*>.

.... ..... ,:.=

.... ..... ..m

.... :;;.9...

..... :......_ ,.L.X,

... .....

*2<:,

....

F i g . 8.6.

Schematic flow diagram MSBR off-gas system.

276 .......... ->.

enerator, b u t present e f f o r t s are b e i n g d i r e e t e d to developing a enerator that does not r e q u i r e this co gas being recycled to the pump seal p e s through a charcoal bed d t h a 98-day xenon holdup t i m e and an off-gas cleanup system. The additional charcoal bed is sufficient to 1low decay of practically a l l the noble gases except krypton--85. This aseous i s o t o p e , along with any tritium present in the off-gas, is remve and stored in the offcleanup system. Although not shown Pn Fig. 8 . 6 , provisions will be made to remove any oxygen or mofsture t h a t may b e present in this recycled gas stream. These provisions are in t h e f o m of molecular sieve beds to dry t h e gas and titangum sponge beds $8 remve the oxygen. Maketap cover gas wo~abd e n t e r the MSBR f u e l s a l t gas system j u s t upstream of these beds.

l...

Noble Gas Stripping. - me emphasis on the u s e of gas bubbles f o r removing the nable ases from t h e MSBR fuel s a l t is because of t h e demwstrata-capability 6f bubbles to s t r i p out these gases in the experimental aqueous and molten-salt reactors that have been o p e r a t e d [183,l04,%Q5,186, 107,108] A l s o , it appears that such a system would result in t h e smallest f u e l s a l t inventory when compared to o t h e r n o b l e gas removal systems e IHa EIO%ten-Sdt reactOrs d t h g r a p h i t e HItgPde%BtO%, t h e nObk gases tend to diffbase h % o t h e g r a p h i t e ;End

X'eRlEdXt

fZheP@Until they &?Cay

8%

reaet

With neutrons. To l i m i t t h i s , methods are being developed to p u t on a pyrolytic c o a t i n g on the r a p h i t e ( s e e Chapter 6) The gas-stripping system as migration i n t o t h e r a p h f t e effectively to rection to an acceptable level. Small bubbles circulating with the salt appear competitive because of their relatively l a r g e surface for core v o i d fractions less t h a 0.01 6106 1 0

e

>...% u

271 A nets c a l c u l a t i o n a l model t h a t c o n s i d e r s t h e e f f e c t s of t h e gas solu b i l i t y and v a r i a t i o n s i n t h e temperatures and p r e s s u r e s throughout the f u e l s a l t l o o p has been developed. The p u ~ p o s eof t h i s new model i s t o Check t h e assUlIlptions Used i n t h e pKeViOUS EIlodel and t o m&e 73eCeSsary m o d i f i c a t i o n s . R e s u l t s u s i n g the new model are p r e l i m i n a r y , however, and

{

i t is t o o early t o assess t h e d i f f e r e n c e s i n t h e results produced by t h e

I

'h?O

I

IIlodels.

R e s u l t s from t h e w e l l - s t i r r e d tank model [l(B6] w e r e e o ~ r e l a t e di n terne of a t i m e c o n s t a n t d e f i n e d as

I

I

v c

Stripping rate = __ T

v is the W3in f u e l Salt lOSp VOlUm63, c %S the f S O t O p E ? c o n c e n t r a t i o n i n t h e f u e l s a l t , and T is t h e t i m e c o n s t a n t . F i g u r e 8.7 shms t h e e o n t r i b u t i o n s f xen~n-135 i n the g r a p h i t e and f u e l salt t o the poison fraction f o r b o t h uncoated and p y r o l y t i c c o a t e d g r a p h i t e . The c o n t r i b u t i o n of t h e XellOla-135 tIae gas bUbbleS t0 t h e poiSOn fPtlCtion W a s about 0.0803 for most cases that were s t u d i e d since i t was assumed t h a t the purge gas enteri n g t h e fuel salt system c o n t a i n e d l o w q u a n t i t i e s of t h i s i s o t o p e . The d i f f u s i v i t y and the p o r o s i t y of t h e base g r a p h i t e w e r e assumed t o be ftz//kar and 0.1, respectively, I n c r e a s i n g t h i s aiffusivity to 10-3 f t 2 / h r had little e f f e c t on t h e results even when the g r a p h i t e w a s uncsated, s i n c e f o r uncoated g r a p h i t e t h e m i g r a t i o n rate of t h e n o b l e gases t o t h e g r a p h i t e i s e o n t r o l l e d by the a d j a c e n t s a l t boundalpy l a y e r . A s t r i p p i n g system having a t i m e c o n s t a n t of about 30 sec ( q u i t e r a p i d ) would b e r e q u i r e d t o reduce t h e xenon-135 poison f r a c t i o n to 0.005 i n a reactor h a v i n g uncoated g r a p h i t e . P u t t i n g a p y r o l y t i c coating on t h e g r a p h i t e permits u s t o u s e a stripping system having much l o n g e r time c o n s t a n t s F o r example, F i g . 8.7 shows that a c o a t i n g with a ft'/hr d i f f u s i v i t y wsblllbd require a s t r i p p i n g system having a t i m e constant of about 300 sec t o limit t h e xenon-135 poison f r a c t i o n of 0.005. The e f f e c t of t h e csatI I T t h i s @88e, the Tiate O f h g p O r Q S i t g f O n t h i s W a . 8 fOUIld to b e SITd.1. XRBgHatiOTl Salt thâ‚Ź? bulk O f t h e g??aph%teiS C O I l t ? ? o l l @ d by the Pate O f t h e d5ffusiCKl thPQU@i %he c o a t i n g mat@l?ial. The thickness of t h e p y r o l y t i c c o a t i n g for t h e cases s h m n sfn Ffg. 8.7 was assumed to be 0.011 i n . As shmn i n P i g . 8.8, v a r y i n g t h e c o a t i n g t h e r e s u l t s . Here f o p %L s t r i p p i n g thiCknesS CaIl have Et gPeat inf lue nc e system having a t i m e c o n s t a n t of 316 s e e , d e c r e a s i n g the d i f f u s i v i t y o f t h e c o a t i n g would allow a much t h i ~ ~ ct oea t~i n g . The ealcu%ations also showed t h a t n o t c o a t i n g t h e g r a p h i t e s u r f a c e s in t h e r e f l e c t o r and plenum regions had a negPigib1e e f f e c t on t h e c o r e p o i s o n f r a c t i o n . For the bubbles t o s t r i p t h e noble g a s e s , t h e m i g r a t i o n rate t o the bubbles must equal t h e s t r i p p i n g rate. I f t h e gas phase r e s i s t a n c e t o mass t r a n s f e r i s n e g l i g i b l e , Where

e

M i g r a t i o n rate of gas t o bubbles =

2 78

t d

8.7. E f f e c t s sf s t r i p p i n g rate and p y r o l y t i c coating on 35Xe poison ff a c t i o n e

D

B I

f

279

5 .... s2>

-4

z

.:. :ss

Pes e

... ....

../r :.:.:.i'

2

(bp

...

233

3 9

0

........ .&%a

Where

\

2 s the

BkaSS

tranSfeK COefffCient,

c is the Bsotope e o n e e n t r a t i s n in the salt,

i s the bubble surface area, Cb i s t h e i s s t o p e concentra-

t i o n b the gas bubble, W is the Henry's l a w co%bgtant, R is t h e gas eons t a n t , and T i s the temperature. Bssuning a b u b b l e diameter of 0.020 in., a mass transfer coefficient of 2.0 ft/btr, the time constants w e r e c u l a t e d f o r u a r i s u s void f ~ a c t i o n ~and i f r a c t i o n of b u b b l e s removed p e r Off-gaS lOQp cycle. %t w a s CSSUreed t h a t the gas bdhtg E-etuTXled from The r e s u l t s p l o t t e d in F i g . system was essen i a l l y free of xenon-135. 8.9 show that a .2% c i r c u l a e f n g void volume and a 0 . 1 f ~ a e t i g a n a lb u b b l e removal rate giv 8 8 tine! constant of about 258 SBC. Comparing t h i s w i t h P i g . 8.5 y i e l d s a tar et xe~lon-135 p o i ~ ~f rna c t i ~ nof 6.005 if the g r a p h i t e has a p y r o l y t i c ssat g O.OPI in. t h i c k andl diffusivity. me knees in t h e curves of Fig. 8.3 occur where the p a r t i a l pressure of the xenon-135 ifisant r e s i s t a n c e to t h e transfer of t h i s

. .. ,x.s.

h%en t h i s resistance is not si app%OXhlated by the PelatiOII

b i

where db i s t h e bubble diameter and rl, is the v o i d fraction. T h i s i m p l i e s that reducing the bubble diameter and/or i n c r e a s i n g the mass transfer coe f f i c i e n t and the void f r a c t i o n will reduce the t i m e constant. I% w i l l b e seen later that the bubble mass-transfer e erinents i n d i c a t e that f a r the c o n d i t i s n s i n those experiments the mass ansfer c o e f f i e i e n t i s prop a r t i s n a P t o t h e bubble diameter. In this case, t h e bubble system t i m e c o n s t a n t varies i n v e r s e l y w i t h the void f r a c t i o n , However, as the bubbles mall, it 19 questionable t h a t the bubble ma88 tKaIlSft3r coefubble diameter, I f t h i s proves t o b e t r u e , the bubble system t i m e co ant would d e c r e a s e with d e c r e a s i n g bubble diameter below some liaiti s i z e and could p o s s i b l y besome very s m a l l . me above c a h 2 u l a t ~ o mi n d i c a t e a t the f r a c t i o n of the bubbles refkacpVed per l o o p Cycle ahtd/OK t h e Off as recycle time could be smaller than the v a l u e s selected for t h e refe rice d e s i g n P'iSBR s i n c e the b u b b l e s are f a r from b e i n saturated with xenon-135. Because of the u n c e r t a i n t i e s in the model, the parameters above were s e l e c t e d , b u t as further data and experi6nce are o b t a i n e d , it may b e p o s s i b l e t o reduce these v a l u e s . ROWever, i t should b e r e m ered t h a t t h e r e i s some small increase in the Core psison f r a c t i o n as Also t h e s h o r t e r recycle times i n t h e off-gas system might not g r e a t l y d e c r e a s e the sum sf the volumes of a l l of t h e charcoal beds since event u a l l y almsst a l l of the n o b l e gases and their daughters w i l l have to be removed %row the purge as stream b e f o r e i t is r e c y c l e d t o the pump.

w.

.....

*Z.A

. ..

.....A. I . d

281

ORM k- DIN6 72-8% f 8

5 NO RECYCLE OF OFF-GAS MASS TRANSFER COEFFsCIENT TO BUBBLE = 2.0 f 8 / h BUBBLE DlAMETER = 0.020 in.

2

.... ..... :&

.

... ,.;<.:.:, ._

... +$a3

:....,., ~:.=

.... ' i . : . ;c,

0.5 6.6 0.7 0.8 0.9

... .....

: "Y, ; i i ,

.... .;

: ;

.Q 1.2 1.4

.... ......

i i

f.6 ....

:.y<:.*

... .....

0 8.9 6.2 0.3 6.4 0.5 FRACTION OF BUBBLES REMOVED FROM FUEL SALT PEW LOOP CYCLE.

~ i g .8 . 9 .

~ i m esonstants sf the MSBW 135xe s t r i p p i n g systems.

282

I

Iodine Removal. - Since most of t h e xenon-135 produced in a r e a c t o r i s produced i n d f r e c t l y by t h e decay of 6.7 k r half-life iodine-135, use of s i d e s t r e a m i o d i n e strippers has been s u g e s t e d as a method f o r minimizing in the MSBR [EE4,115]1 %h "effective" solubility of i o d i n e , e r a t i s of t h e dissolkved iodide c o n c e n t r a t i o n to the sum of the partLal p r e s s u r e of the i o d i n e and hydrogen i o d i d e in the gas phase, has been found to be a function of the s a l t chemistry as well as the teTTlperatU%e. 'Ghfs "'effectfve" S Q l U b i l i t Y quit@ hf.&ls 9 0 Stripping the iodine with an i n e r t as stream would require very l a r of gas. ~ o ~ v e adding r , yd9-Qgen fluoride t o the S t k i p p i n wouid o x i d i z e the i o a i d e and reduce its F i e f f e e t i d B S O ~ ~ H course the s t r i p p e d s a l t must then b e reduced b e f o r e i t is r e t u r n e d t o the main f u e l c i r c u l a t i o n Esop. The minimum rate t h a t t h i s f u e l s a l t must be processed for i o d i n e and xenon to achieve v a r i o u s xenon-135 po s o n fractions in t h e reactor w i t h uncoated g r a p h i t e are shown i n F i g . .IO. I t can b e seen t h a t s t r i p ping only t h e iodine from a s i d e stream of t h e f u e l salt i s n o t s u f f i c i e n t t o reach the tar et psisow fraction i n the r e a c t o r . However, removing the i o d i n e w i t h the enon is very e f f e c t i v e in reducin the p o i s o n f r a c t i o n . nlerefOre, if t h e g r a p h i t e Cannot be Sealed, all i o d i n e s t r i p p i n g §y%teEl might have t o be used in c o n j m e t i s n w i t h some t y p e of a xenon removal system in ordeb to achieve a xenon poisort fraction of 0.005. d e s i g n studies were made of s t r i p p i n g u n i t s c a p a b l e in one 63% of t h e xenon and 6% of t h e i o d i n e from an 8% f u e l and i n a n o t h e r case of removing 60% of the iodine from a 8.8% f u e l s a l t side stream [115]. In b o t h cases e atmo%pherie p r e s sure gas stream c o n t a i n s 1% hydrogen fluoride to ox ize the s a l t , and about 80 ft3/sece as f l o w r a t e through t h e s t r i p p i n g u n i t m e heat produetisrn rate af the t r i p p e d gases and t h e i r daughters a l o n with any removed n o b l e metals w estimated t o b e about 6 m ( t ) . This would imply a f a i r l y s i z a b P e ga system and t h e drain tank could not b e used as a d e l a y tank because u f the presence of hydrogen f l u o r i d e i n t h i s gas. me hydro en fluoride could come i n e s n t a c t w i t h the f u e l s a l t t h a t D

C o n s i d e r a t i o n lIlbllSt be given $0 K@I€IoVE%lb s f t h e afterheat f n t h e event Of a f a i l u r e in the gas c i r c u l a t i o n system. Spray towers v e n t u r i csntactors , ramp flow u n i t s and packed coEums have been c o n s i d e r e d f o r t h e s t r i p p e r . AliE appeared t o b e f e a s i b l e altkohlgh ELUch deVelOplllellt W O U l d b e r e q u i r e d FOE. any one s f them. They W e r e a l l f a i r l y Har e m i t s (roughly 10 ft h i h amd 18 ft i n d i a m e t e r ) , b u t the l i q u i d holdup i n most of t k e m w a s n o t e x c e s s i v e .

L

m.:

- In t h e bubble s t r i p p i n g system, t h e purge gas e s e p a r a t o r s and the pump bowls and flows directly t o the drain t a n k [l%6]. S i n c e this gas contains m a n y s h o r t - l i v e d f i s s i o n prod u c t s , n o n v o l a t i l e fission p r o d u c t s i n c l u d i n g t h e n o b l e metals, entrained Salt, and deCo€TlpOSed hydfOCaafk20llS O r other f o r d material, much a t t e n t i o n must b e given to the l a y o u t of t h e line discharging from t h e bubble separators and the pump bowls. This is t o a s s u r e that this line will n o t become plugged w i t h p a r t i c u l a t e matter and that i t will n o t e

I b

.... ..... *.&

283

I

I

I

NO IODINE REM

I

II

II

II

I

i

Fig. 8.10. Xenon-13% poison fractions u s i n g combined xenon and iodine stripper with uncoated g r a p h i t e .

284

I

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o v e r h e a t even mder r e a c t o r a c c i d e n t c o n d i t i o n s . Conceptual %ayout s t u d i e s i n d i c a t e that t h i s can be done. To separate the p a r t i c u l a t e s and the entraimed s a l t and to ~ e m o ~ e l a r g e amounts of ener y g e n e r a t e d by t h e s e materials and the r a d i o a c t i v e 88 d u r i n g the first decayP p e r i o d , a large VeSSeP having large VS%UEE and heat s i n k is d e s i r e d gaa7g. me d r a i n tank appears t o me@t these requirements and the s f f - as i s routed f i r s t t o i t . Mere, as d e s c r i b e d @ a K l % e r h t h i s chapter, ab0ELt 1 mgt) of heat and m o s of the nonvolat i l e materials are KeIDDVed from e gas stream. After hour holdup, g e n e r a t i o n rate i n the off-gas stream drops f by about two tude due to t h e decay of t h e s h o r t - l i v e d fission p r o d u c t s , le attention must b e i v e n t o t h e development of a d r a i n that these a i are accomplished and t h h g s such as s h o r t c i r c u i t i n g of the flow of t h e gas i n t h e d r a i n tank do not occur. h y p a r t i c u l a t e material t h a t is not r e m ~ v e dfrom the off-gas i n t h e d r a i n tank should be removed by a fil e%.b e f o r e t h e off-gas enters the charcoal eds so t h a t t h e the bests w i n n o t be r e s t r i c t e d by t h e @cmuHation of f ot nueh e f f o r t has b e e n d i r e c t e d to the design s f a filter f o r this se i n the MSBR. Probably s i n t e r e d metal would b e use e r i a l and much attention would have to b e given t o des b e cleaned o r r e p l a c e d and cooled adequately a t a l l times. Noble Gas Absorption on Charcoal, - IBynadc absorption of t h e moble gases in a c t i v a t e d charcoal reduces t h e volume a c t u a l l y r e q u i r e d t o a l l o w t h e desired decay of these gases. me f a c t o r by which t h i s voiume can b e reduced from that of an empty vessel o r p i p e varies from 500 a t 8B"F, to 58 at 250"F, and to a at 886째F. me capability o f the c h a r c o a l b e d s f o r removing t h e noble gases has been c a l c u l a t e d from t h e computer programs developed f o r t h e H r n - 2 a d the F%sm[118,113,128,%21] Both of t h e s e pFpOg'gaE18 COnsidep %he e f f e c t s of the gas and i s o t o p e flow Pates, pipe geometry, and t e ~ ~ p e r a t u r eon s t h e amount of noble gases removed. A rev i s e d computer program i s now b e i developed, incorpsrating t h e information from the previous programs, a t will o p t i ~ e ethe d e s i g n O f the charcoal beds on t h e b a s i s of s e l e c t e d parameters. Beat g e n e r a t e d i n t h e c h a r c o a l beds w a s calculated by a computer program that considers t h e movement of t h e noble gases throughout t h e off-gas system [3117,122'6. T h i s code assumes t h a t the nonvolatil@ d a u g h t e r s of t h e noble gases remain a t t h e location of t h e i r b i r t h . Typicall r e s u l t s of this program are shown i n P i T h i s h e a t is remove from t h e charcoal beds by having t h e pipes contaiI2ing the C h a P C O d ilDIlErSed $W d o s e d tanks of W a t e r . WateP f S E i l h W e c f to boil in the 47-ha~ xenon h ~ % d bed ~ p tanks w i t h t h e heat: b e i n from the steam in a r e f l u x condenser. However, t h e 90-day xenon holdup bed must b e kept cooler and t h e water in these tanks is c i r c u l a t e d through a c o o l i n g unit, Potential p r o b l e m a s s o c i a t e d w i t h removing heat this way that have n o t been i n v e s t i g a t e d thoroughly are the esnsequenees of a W a t e r leak i f l $ O the ChaKCoal beds and What htapgens f f t h e C O O l i y t g Water 0

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- A f t e r the purge leaves the 90-day xenon holdup e radionuclides have decayed to neglfgtble values except for the krypton-85 and m y tritium present in t h e gas. It has been p ~ o p o ~ e[I221 d t h a t this gas flow through a cleanup system consFstin of a ~ o p p eoxide ~ bed to convert the tritium to %2Q and low-temperature (0째F) charcoal absorbers where t h e 3H20 and the remaining kggrptsn a d xenon are removed. A compressor returns the slemed gas back to the reactor through the pump seals* etc. These Pow-temperature charcoal beds are regenerated periodically by passin t of the clean recycled helium then passes through a liquid through them at 500째F. This helium st nitrogen t r a p where t h e 3 ~ 2 0 , k ~ y p t o n enon are remved a d s t o r e d . after a l l of t h e KadiOnUClFdES have bean ZfeIW2Ved from the purge gas streamD,there might be some m o i s t u r e or oxygen r e m i n i n g in this gas stream. Potential p o i n t s of e n t r y f o r these eontaminants into t h e reactor system one s f t h e @ o d d be illlpbarfties in the Ill.&eUp gas SUpplgi OK a Small leak charcoal beds. &ikcular sieves at room temperatu~e(~86'P) have been used successfully to remove moisture ~KO, t h e fuel salt purge gas stream [l23]1. These beds Faere HegeRerated periodi@dPgP by pubging them With d r y helium at 500째F. It also has been demonstrated that oxygen can b e removed from the f u e l salt pur e gas strean by p a s s i n g it t h ~ o ~ sponge beas at 1 2 0 0 ~e l~a s ] e

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A s t h e s a l t w a s j e t t e d from t h e pump s p r a y r i n g i n t o t h e pool of s a l t i n t h e pump bowl, a l a r g e amount of t h e cover gas was c a r r i e d i n t o t h e s a l t pool [ l 0 4 ] . T h i s gas formed bubbles which tended t o c o a l e s c e and f l o a t back up t o t h e p o o l s u r f a c e . However, some of t h e s e bubbles were c a r r i e d i n t o t h e main f u e l s a l t loop w i t h t h e s a l t f l a w i n g i n t o t h e pump v o l u t e i n l e t a t t h e bottom of t h e pump bowl. It w a s found t h a t t h e amount of gas c a r r i e d i n t o t h e f u e l s a l t l o o p w a s a f u n c t i o n of t h e gas s o l u b i l i t y , t h e s a l t chemistry and t h e pump speed, which determined t h e v e l o c i t y of t h e s a l t b e i n g j e t t e d from t h e s p ~ a yr i n g . The e f f e c t s of t h e s a l t chemistry are n o t understood f u l l y , b u t t h e amount of gas c a r r i e d i n t o t h e main Poop changed s i g n i f i c a n t l y a f t e r t h e s a l t was processed to change t h e f i s s i l e late rial and when b e r y l l i u m w a s immersed i n t h e s a l t i n t h e pump bowl. Bubbles c a r r i e d i n t o t h e f u e l s a l t l o o p had a d r a m a t i c e f f e c t on t h e amount of n o b l e gases p r e s e n t abn t h e PI[Sm [105,106,125]. E a r l y e x p e r i ments on t h e s p r a y s t r i p p e r i n t h e pump bowl i n d i c a t e d t h a t i t Rad an e f f i c i e n c y of about 15% [126]. However, t h e r e a c t o r o p e r a t i o n e x p e r i e n c e i n d i c a t e d t h a t t h e n o b l e gases w e r e b e i n g ~ e w o ~ eadt a rate t h a t i m p l i e d a much g r e a t e r e f f i c i e n c y . It w a s found t h a t t h e two parameters a f f e c t i n g t h e amouht of xenon p o i s o n i n g t h e most i n t h e MSWE w e r e t h e cover gas used and t h e c o r e v o i d f r a c t i o n . The e x p e r i m e n t a l d a t a are s u m a r i z e d in P i g . 8.12, where t h e l o s s of r e a c t i v i t y i s about 0.8 of t h e xenon p o i s o n fraet i o n for t h e MSRE. It appeared t h a t t h e c i r c u l a t i n g bubbles w e r e q u i t e s m a l l , b e i n g i n t h e range of 0.005 t o 0.020 i n . , and t h a t t h e s t r i p p i n g e f f i c i e n c y of t h e s e b u b b l e s i n t h e pump bowl w a s 50 t o 100%.

A n a l y s i s of Noble Gas S t r i p p i n g . - The d a t a i n F i g . 8.12 d i d n o t a g r e e w e l l w i t h t h e v a l u e s p r e d i c t e d by t h e w e l l - s t i r r e d p o t i n s o l u b l e gas model d i s c u s s e d above f o r t h e MSBR, p a r t i c u l a r l y when helium w a s used as a cover gas [106,B25] These c a l c u l a t i o n s i n d i c a t e d t h a t t h e p o i s o n f r a c t i o n would b e a monotonically d e c r e a s i n g curve t h a t i s a f u n c t i o n only sf t h e c o r e v o i d f r a c t i o n and is independent of t h e c o v e t gas used. Part s f t h e assumptions i n t h i s model had been checked e x p e r i m e n t a l l y . It pred i e t e d t h a t t h e major r e s i s t a n c e t o t h e t r a n s f e r of most of t h e n o b l e gases from t h e f u e l s a l t t o t h e g r a p h i t e moderator would be t h e salt boundary l a y e r . A p r e c r i t i c a l experiment i n which krypton w a s i n j e c t e d i n t o and s u b s e q u e n t l y removed from the MSRE f u e l s a l t system i n d i c a t e d t h a t t h e m a s s t r a n s f e r c o e f f i c i e n t s f o r t h e n o b l e g a s e s m i g r a t i n g through t h e boundary l a y e r a d j a c e n t t o t h e c o r e g r a p h i t e w e r e i n r e a s o n a b l e agreement w i t h t h o s e p r e d i c t e d by t h e o r y [10&,125]. Results of an m a l y s i s of d a t a o b t a i n e d [I271 from t h e measu~ementsof t h e d i s t r i b u t i o n of t h e d a u g h t e r s of s h o r t - l i v e d n o b l e g a s e s i n samples of t h e MSRE g r a p h i t e showed t h a t t h e d i f f u s i v i t i e s of t h e n o b l e gases i n t h e g r a p h i t e a g r e e d w i t h t h o s e used i n t h e w e l l - s t i r r e d p o t i n s o l u b l e gas model. S i n c e t h e w e l l - s t i r r e d p o t i n s o l u b l e gas model d i d n o t d e s c r i b e t h e n o b l e gas p o i s o n i n g of t h e E R E a d e q u a t e l y , a new model w a s developed t o d e s c r i b e t h i s b e h a v i o r 1105, 1061 e This model c o n s i d e r e d t h e s o l u b i l i t y of t h e cover gas i n t h e f u e l s a l t by d i v i d i n g the r e a c t o r i n t o f o u r regions, each esntaining a l i q u i d and a gas phase. Bubble s u r f a c e t e n s i o n e f f e c t s were n e g l e c t e d and i t w a s assumed t h a t t h e bubbles i n each r e g i o n a

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Were O f UXIffOXTB S i z e X k d l t h a t t h e i r er was c o n s t a t . S o l u t i o n of t h e rexations d e r i v e d fo this model i n d i c a t e d d i f f e r e n c e s in the v o i d fraction different Kt2 ions of t h e r e a c t o r , brat t h e s e d i f f e r e n c e s w e r e not a S t K O H n g fUnctiota 0% the bubble size. d its p r e c u r s o r s iodine-135 and xenon-l35m in these four re iom using t h e void f r a e t ' d f s t r t b u t i s n c a l c u l a t e d by the ~ e l a t f od ~s c~r i b e d above. A l a r g e H% of c a l c u l a t i o n s usin internakPy c o n s i s t t parameters w e r e made to describe the n o b l e gas The reasonably good f i t t h e c a l c u l a t e d poison red v a l u e s shsm i n Pig. w a s obtained by use sf one s e t of parmeters. C o n s i d e r a t i o n of th@ s o l u b i l i t y of the cove gas was not sufficient by itself t o o b t a i n t h e a .l2. In a d d i t i o n , t h e mass t r a n s f e r coeffic%ent f o r the xenon diffusin $8 the g r a p h i t e had to be reduced by about a factor of sFx, the b u b b l e t r i p p i n g e f f i c i e n c y had to vary w i t h t h e m u n t 8% gas i n g e s t e t h e pump, and an a d d i t i o n a l le EE?ChaXkfSm for XePaQW %Pansport r a p ~ l i t ew a s required to produce wima i n t h e curves.. (Direct i n t e ion of b u b b l e s w i t h was p o s t u l a t e d i n o r d e r t o p r o v i d e a process menable t o mathematical ese same parameters to describe the t r a n s i e n t xenon p o i s o n i n Udden pWeK Chan d i d not a c c u r a t e l y reproduce ehaVioK. Thus h e improved c a l c u l a t i s n a l procedure w a s not a C O l T l p l e t e 8 U C C e 8 8 . b%OKe WOhk i% neCeSSc3Ky to elucidate t h e XenOHP behavior i n t h e m and to a c c u r a t e l y p r e d i c t t h e %a avior in an MSBR. s e of the S ~ o ~ t C and ~ ~ the ~ nmore ~ s comp

sated n a t u r e of t h i s o d e l f o r the MSRE, t h e well-stirred p o t insoabub

a t e d that they would n o t c o n t r i b u t e as much t o as they did in t h e It i s expected ribiwg t h e noble eing developed f o r behavior in t h e MSBR will shed some l i g h t on this. HBW@TP@F, wore exp@rimental data probably will be r e q u i r e d b e f o r e this situation can be cornp l e t e l y resolved * 0

@ n e K d l Y opernuisance t y p e problem were encountered punp bob71 produced 8 l X k t having CQI19 centrations similar to any o r d i n a r y m i s t . Some of the s a l t mist d r i f t e d i n t o t h e off-gas line a t t h e r a t e sf a f e w gram per month, and some of the b"@SUabtantS a l $ depClSitS had to be Kf@mOTPed at iIlteETak3 Of S i x KlOnthS t o a year. Foreign materials, partieuParPy those r e s u l t i n g from t h e f u e l pump l u b r i c a t i n g ail l e a k i n g i n t o the f u e l salt f a m d t h e i r way t o the control valves 9 flow restristors 9 and f i l t e r s These item graelualbly became plugged by t h e s e polymerized OK~ZXXLCS and they had ts b e c l e a n e d This problem was c o r r e c t e d by i n s t a l l i n g out o r r e p l a c e d periodically new f i l t e r s of a modified d e s i g n [130, 13Hq. Considerable a t t e n t i o n w a s

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channels where buoyant f o r c e s become s i g n i f i c a n t , i t can be s e e n i n F i g . 8.13 t h a t t h e mass transfer c o e f f i c i e n t s pass through a minimum and t e n d t o approach the m a s s t r a n s f e r c o e f f i c i e n t s for bubbles r i s i n g f r e e l y i n a liquid. These r e s u l t s are a l i t t l e s u r p r i s i n g in that they are a little lover t h a n a n t i c i p a t e d and show a d i r e c t dependency on the bubble d i a m e t e r . The r e a s o n s f o r this are n o t clear and more d a t a are n e c e s s a r y . A d d i t i o n a l d a t a are now being taken u s i n g a n o t h e r s i z e t e s t s e c t i o n . ~xtrapolation of t h e s e r e s u l t s t o bubbles i n t h e f u e l s a l t may i n t r o d u c e u n c e r t a i n t i e s s i n c e the s a l t p h y s i c a l p r o p e r t i e s amd chemistry are different from t h o s e f o r t h e glycerine-water mixtures When f i r s t c o n s i d e r i n g bubble generator concepts for the MSBR, b t was f o m d t h a t very l i t t l e i n f o m a t i o n was a v a i l a b l e i n t h e l i t e r a t u r e about th5s s u b j e c t f o r systems s i m i l a r t o the MSBR [l(B6]. This u n i t s h o u l d g e n e r a t e a uniform d i s p e r s i o n of bubbles over t h e p i p e area t o g i v e the d e s i r e d void f r a c t i o n and bubble s i z e d i s t r i b u t i o n . Also we decided that we would a t t e m p t t o develop a u n i t t h a t would use the a v a i l a b l e gas s u p p l y p r e s s u r e , s i n c e w e p r e f e r r e d n o t t o d e s i g n and b u i l d a gas compressor for use in t h i s environment Both m e h a n i c a i and f i u i d - p m e r e a generators Were COnSider@d. We decl&ded t h a t t h e fluid-pOWer@d type gC?neKator i s the b e s t approach sfnce no moving p a r t s are i n v o l v e d . This l e d t o the selection of a v e n t u r i type d e v i c e in which gas is ingeetea in t h e v e n t u r i t h r o a t and bubbles are generated by flufd t u r b u l e n c e i n t h e d i f f u s e r sect i o n [ 135 $106] * "Teardrop" and "multivane" type bubble g e R C 3 2 3 t O r s w e r e also t r i e d and appeared t o be c a p a b l e of g i v i n g s a t i s f a c t o r y performance, b u t w e b e l i e v e t h a t t h e v e n t u r i concept o f f e r s the g r e a t e s t s i m p l i c i t y . Tests on MSBE s i z e v e n t u r i t y p e g e n e r a t o r s u s i n g d e m i n e r a l i z e d water with and w i t h o u t the a d d i t i o n of s u r f a c t a n t s aqueous g l y c e r i n e solutions, and aqueous calcium c h l o r i d e solutions i n d i c a t e d that the size of bubbles gene r a t e d by this; unit w a s n o t very dependent on t h e n a t u r e of the f l u i d . HOW~WX, a t h e o r e t i c a l a n a l y s i s i n d i c a t e s t h e diameter should vary as t h e 0.6 pmer of the r a t i o of the s u r f a c e t e n s i o n t o d e n s i t y , ( c / p ) Q * G e Add i t i o n a l tests are i n progress t o v e r i f y this r e l a t i o n s h i p . A m o s t important o b s e r v a t i o n on t h e s e bubble g e n e r a t o r tests in a loop i s t h a t the bubble s i z e i n the l o o p is a f f e s t e d s t r o n g % y by t h e kydKaUliCS Sf t h e C i r c u l a t i n g pWp and O f the c i r c u l a t i n g system [ 1 % , 1 0 6 ] . "he c i r c u l a t i n g pump i n rhe best l o o p s h e a r e d tke bubbles t o a very s m a l l size (about 0.081 t o 0.802 i n . d i a m e t e r ) . These s m a l l bubbles coalesced q u i c k l y i n d e m h e r a l i z e d water, b u t not s o q u i c k l y i n t h e aqueous glycerine and calcium s h l o r i d e s o l u t i o n s These o b s e r v a t i o n s indicate t h a t t h e e f f e c t of the pump on b u b b l e s i z e and the c o a l e s c e n c e of b u b b l e s must b e s t u d i e d i n f u e l s a l t b e f o r e t h e f i n a l design can b e e s t a b l i s h e d f o r the bubb Be g e n e r a t o r The in-lfme c e n t r i f u g a l gas s e p a r a t o r developed f o r t h e aqueous homogeneous r e a c t o r program showed g r e a t promise of meeting t h e MSBR reguirements [106,l28,137,138]. These requirements are t h a t t h e gas removal efficiency must b e h i g h o v e r a wide range of gas i n l e t f l m s , t h e press u r e drop must b e compatible w i t h t h e p r e s s u r e drop a v a i l a b l e i n the p r i mary system, and t h e m o u n t of e n t r a i n e d l i q u i d i n t h e g= removal stream must not be excessive. C ~ ~ ~ ~ i d e r effort a b l e has been d i r e c t e d t o developing it MSBE size s e p a r a t o r which has a &in. i n s i d e dimeter and a s a l t

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flow rate of 408 to 550 pm Kl06,%39,14Q,l41,1421. Figure 8.14 shows t h e test unit that has been eveloped that appears to g i v e a suit gas removal e f f i e i e n c y . This unit has a 44-211. separation le tapered casing, and gas removal at both the swirl and recovery hubs. The early t e s t units p e ~ f o m e dw e l l when u s i n g demineralized water, '$Ut had poor gas SepaKa$iokn efficienC!ies When Using aqueOUS glyc e r ine O K c a l C i U l 3 l Chloride SCllUtiofaS With k h e m a t i c V i S c O s i t i e S S h d b 3 K to t h a t of the MSBR f u e l salt. we p o s t u l a t e d that t h e higher kinematic V i S C O S i t Y ?reSU%ted in a redlaced r a d i a l bubble V e h c f t y to the C e I I t K a l Void O f the separator and an i n c ~ e a ~ine t h e effect of the fluid turbulence. The pump produced much smaller bubbles which d i d not c o a l e s c e as ~ e a d i l g ri n these aqueous s o l u t i o n s as they did in the demTneraPized water and the smaller ave better separation b u t resulted in a vortex instability the m o u n t of gas t h a t couPd be injected and removed from the t e s t fluid. By t a p e r i n g t h e casing and reasssvin gas from i n l e t and o u t l e t hubs t h e separator was made c a p a b l e of h m d l ng a%% of the a n t i c i uid and gas flow rates. ain some m d e r s t m d i n g sf ubble formation and coalescence in the ds and in molten s a l t s , a h a k r t e s t K i g WEkS b U F l t [l42]. Transparent capsUl es con t a i n is these l i q u i d s were shaken to given the d e s i r e d bubble size and void fras t o n . The shaking was s t o p p e d and photographs were taken at f r e q u e n t Fntemals t o study the bubble behavior in t h e l i q u i d . Tests SO far indicate that small bubbles c o a l e s c e very quickly i n demineralized water, but very slowly in aqueous g l y c e r i n e and calcium & l o r i d e s o l u t i o n s . A very significant void fraction of small bubbles remained in these sslutions 28 see after the sh&in had stopped. I n m e w a s not as r a p i d 66-34 mole x LiF-BeF2 salt, e r a l i z e d water, b u t more rapi e g l y c e r i n e and calcium c h l o r i d e a o % u t i o s . The void fraction of saksel3b b u b b l e s in the salt 20 sec after t h e shaki, Rad s t o p p e d w a s very small, indicating that t h e r e would aration from the mw fuel salts than from the calcium 8 . This indicates t h a t the p r o b a b i l i t y of th& present ing the d e s i r e d performance in the MSR f u e l salt system a r a t o s unit

E f f e c t s sf Unkaoms and Uneertainties

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l ~ o p swith aqueous s o l u t i o n s t h a t have ‘ k i n e ~ t i cv i s c o s i t i e s similar to t h a t of t h e f u e l s a l t . The s h e a r i n g of t h e s e bubbles i n t o f i n e r bubbles by t h e pumps i n t h e l o o p s s u g g e s t s t h a t t h e bubbles in t h e MSBR f u e l s a l t will b e s m a l l e ~t h a n w e have assumed i n o u r c a l c u l a t i o n s , T h i s o b s e r v a t i o n and t h e i n d i c a t i o n s t h a t bubbles cf~culatingi n t h e MSRE fuel w e r e v e r y s m a l l led Ebasco to s u g g e s t t h a t elaborate b u b b l e g e n e r a t o r i s not req u i r e d f o r t h e MSBR [14%,144,%45]. A l s o these smaller bubbles would r e s u l t i n a l a r g e r bubble s u r f a c e area f o r a given v o i d fraetFon and Ebasco sugg e s t e d t h a t t h e d e s i r e d PQW xenon poison f r a c t i o n might b e achieved without Sealing the g r a p h i t e mOd@Ka%oP. W e b e l i e v e that w e can g e n e r a t e bubbles i n t h e f u e l s a l t s a t i s f a c t o r i l y , b u t this s t i l l needs to b e demonstrated. The s h a k e r experiments so far s u g g e s t t h a t bubbles i n t h e f u e l s a l t w i l l ~cpaleseemore r e a d i l y t h a n t h o s e i n t h e aqueous ‘test s o l u t i o n s , t e n d i n g to make t h e bubbles i n t h e f u e l s a l t l a r g e r t h a n those observed i n the t e s t s o l u t i o n s in the I o s p s . Smaller bubbles w i l l p r o v i d e a g r e a t e r s u r f a c e area for a g i v e n vodrnrne of b u b b l e s t o compete f o r t h e n o b l e gases in the r e a c t o r . .Although t h e bubble mass t r a n s f e r experiments show t h a t the bubble mass t r a n s f e r coeff i c i e n t i s p r o p o r t i o n a l t o S a u t e s mean bubble diameter over a v e r y limited s i z e r a g e , t h e r e are i n d i c a t i o n s t h a t t h e r e l a t i o n s h i p does n o t e x t e n d far o u t s i d e the measured range. Consequently, i t may w e l l be t h a t use i n t h e f u e l s a l t of bubbles smaller than t h o s e i n t h e experiments would r e s u l t %n a h i g h e r sate sf noble gas t r a n s f e r . However, o u r present. knowledge does not p r o v i d e proof for such a c o n c l u s i o n . The bubble s e p a r a t o r , l i k e the bubble g e n e r a t o r , has been developed t o operate s a t i s f a c t o r i l y i n l o o p s u s i n g the aqueous t e s t s o l u t i o n s but i s y e t t o b e t r i e d i n a m o l t e n - s a l t system. While we are q u i t e c o n f i d e n t that i t w i l l give the d e s i r e d s e p a r a t i o n i n f u e l - s a l t s y s t e m even w i t h smaller bubbles, i t s t i l l has to b e prsven. I f f o r some reason any p a r t of t h e bubble system does n o t work, some s o r t of side-stream gas s t r i p p i n g u n i t would have t o b e i n s t a l l e d i n the f u e l s a l t system, The pemalty f o r t h i s probably would be a l a r g e r f u e l s a l t i n v e n t o r y , much larger m o u n t s s f gas would have t o be handled, and a gas c o ~ ~ p r e would ~ s ~ r have t o be deve%oped f o r u s e in a h i g h temperature and h i g h l y r a d i o a c t i v e environment. A s d i s c u s s e d i n Chapter 6, considerable s u c c e s s has been achieved i n putting p y r o l y t i c c o a t i n g on g r a p h i t e , b u t a c o a t i n g that r e l i a b l y retains i t s l o w p e r m e a b i l i t y when i r r a d i a t e d h a s Rot been demonstrated. Although w e are o p t i m i s t i c t h a t a s a t i s f a c t o r y c o a t i n g can b e developed, we must c o n s i d e r t h e consequences of f a i l u r e t o accomplish t h i s g o a l . Also t h e r e d u c t i o n in t h e c o s t of g r a p h i t e would b e s u b s t a n t i a l i f i t d i d not have t o b e coated. A s s t a t e d above, smaller bubbles wight be able t o s t r i p the n o b l e g a s e s from the f u e l s a l t t o the d e s i r e d l e v e l even w i t h o u t t h e g r a p h i t e b e i n g s e a l e d , b u t t h i s must b e i n v e s t i g a t e d e x p e r i m e n t a l l y . Inc r e a s i n g t h e amount of b u b b l e s i n the s a l t to a c o r e void fraction of 0.02 t o 8.03 has been s u g g e s t e d as a means of l i m i t i n g t h e p o i s o n f r a c t i o n 11439 t h a t might compensate f o r l a c k of g r a p h i t e s e a l i n g . The 0.01 v o i d f r a c t i o n s e l e c t e d by ORHL i s n o t a f i r m l i m i t , b u t i t i s b e l i e v e d t o be r e a s o n a b l e based on t h e MSBR design requirements and t h e MSWE o p e r a t i n g e x p e r i e n c e [ l 4 6 ] . Also w i t h 0.02 t o 0.03 void fraction i n t h e core the void fraction i n t h e s a l t e n t e r i n g t h e c i r c u l a t i n g pump would b e around 0.18 which i s undesirable.

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It was shown earlier that isdine s t r i p p i n PIUS XefaOF1 s t r f p p i w g Qf a f u e l s a l t side stream has proaaise of achievi g t h e d e s i r e d poison fraceven w i t h uncoated graphite. This method has the several dipreadvans that were d i s c u s s e d , b u t it probably could b e made to work. This process probably would be mre e enaive than t h e b u b b l e stripping system and would require continuous oxi tion and reduetion of the sidest~eamand careful â‚Ź m W i t O r i n of the redox eofsditiom of the f u e l s a l t . The fraction of t h e noble-metal fission produets that will find their way i n t o the MSBR off-gas system %a not e r t a i n ; it has been estimated to be frofn 5 t Q 35x OH1 the basis Of %lesme erience %1471. In any ease, the o f f - g a s system must be d e s i ned to prevent this material from accumulating as f l a w O F overheat parts of t h e in depeasi%s t h a t would r e s t e sf and o t h e r particulate II%att@K t h a t could be carried into the off-gas system is ratneeptain, but use of il filter OPI the dkah-tank Will pKOb&%blbybe deSLrk3ble to that the operation of the rest of the off-gas system including t h e ckareoal beds iS Sa$b%%C%Qv e

F u t u r e Work Vork is c o n t i n u i n g on extending our knowledge of mass transfer t o e8 fkswing in Hfqui s o The b u b b l e mass transfer experiments are now kUIl U S h g o t h e r Si e test sections in the experimental loop. Future efforts are beimg planned to investigate mass transfer to bubbles in areas the highly turbulent ~egi.011~ in the reactor such as t h e elbows, ansions, and the pump volute. A t t e m p t s w 5 P l be made to investitransfer to smaller bubbles @cause t h e present method for the bubble size is not capable of i d e n t i f y i n g very small bubbles, a method nust be improved 0% another nust be aevised. MEGS t r a n s f e r rates from the fuel s a l t to t h e bubbles w i l l be determined in a SSP OW being b u i l t and d i s c u s s e d belm. we may have to fse satisfies with j u s t the PafOdUCt Qf the EELS% tPEXisfe% Coeffic%f2nt a d t h e b u b b l e surface area in t h i s Poop if methods are not d e v i s e d to measure t h e bubble size in flowing salt streams. Work a l s o is c o n t i n u i n g on studying the behavior of bubble generators and separators under various f l o w c o n d i t ons Pressure drop, vePocity, and flow stability measurements are b e i n made. New u n i t s will be b u f l t , t e s t e d in the f u e l salt test l o o p now be ng constructed, and modified if necessary to obtain the r e q u i r e d perfsmance s This fuel s a l t l o o p called t h e Gas S y s t e m Technology F a c i l i t y (GSTF) [nlc$,lsss] w i l l be used f o r tests of t h e MSR fuel salt and off-gas system. In addition to t h e tests mentioned above we p l a n to investigate n o b l e IEX38 tPXE3fer to g r a p h i t e , the @ f % e C t O f t h e eoIIQositiOl8 O f &he Salt QTI t h e V a h - h t l S test K E ? S U % t % , pe~fo?ZRaIlCesf the? Off-gaS S y s t e m C O I l l p O ~ e H n t s , and the behavior of the noble gases and noble metals in t h i s system. Various components of the o f f - g a s system that must be tested before they are b u i l t and used in a reactor system include the salt mist s e p a ~ a t ~ ~ , filters, and units to remove and store tritium and krypton-85. Also tests will have to be made to assure ourselves t h a t w e can s a t 2 s f a c t o r i I y predict what will happen to t h e noble metals and any o t h e r particulate matter in t h e off-gas system. e

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P r e s e m t e v i d e n c e l e a d s u s to b e l i e v e t h a t removing t h e noble gases by u s e of bubbles i n t h e f u e l s a l t i s t h e b e s t approach t o a c h i e v e t h e d e s i r e d poison f r a c t i o n i n m o l t e n - s a l t reactors. Experimental d a t a i n d i c a t e t h a t w e have a workable bubble generator and s e p a r a t o r and that t h e mass t r a n s f e r rate of che n o b l e gases t o t h e bubbles i s a c c e p t a b l e . It may be shown i n t h e f u t u r e t h a t t u r b u l e n c e i n t h e pump i m p e l l e r o r o t h e r p a r t s of t h e f u e l s a l t system could reduce t h e bubbles t o s m a l l s i z e s , b u t i t i s premature t o assume t h a t now. Use of smaller bubbles may e l i m i n a t e the need f o r s e a l i n g t h e g r a p h i t e to a c h i e v e t h e d e s i r e d p o i s o n f r a c t i o n , b u t t h i s cannot p r e s e n t l y b e a s s u r e d s o work s h o u l d cont i n u e on s e a l i n g methods. Use of a side stream s t r i p p e r t o remove t h e i o d i n e and xenon from t h e fuel. s a l t a p p e a r s t o b e a f e a s i b l e a l t e r n a t i v e f o r c o n t r o l l i n n o b l e gas poisoning, b u t i s n o t as a t t r a c t i v e as u s i n g bubbles u n l e s s i t i s r e q u i r e d f o r t r i t i u m removal. Data are a v a i l a b l e t o show t h a t a l l t h e components i n the off-gas cleanup system are workable. Care must b e taken i n t h e design of t h i s system t o a s s u r e that p a r t i c u l a t e m a t t e r , ~adioactiveand nonradisactive, does n o t accumulate anywhere i n this system such t h a t i t would retard t h e gas flow o r cause o v e r h e a t i n g . Although much development and t e s t i n g of v a r i o u s p a r t s of the moltens a l t r e a c t o r gas-handling system have been and w i l l be done, the system w i l l have t o b e proved i n an o p e r a t i n g r e a c t o r . Many s u b t l e t i e s and i n t e r a c t i o n s affect the performance of this system, and a ~ e a c t o ri s t h e smly p l a c e where w e can demonstrate that they a l l have been c o n s i d e ~ e d .

The major u n c e r t a i n t i e s of a fundamental nature i n the components and systems f o r MSBRs are r e l a t e d t o the p r o v i s i o n s t h a t m u s t b e made f o r ~ ~ c o ~ t ~ ~ dthe a t iwidespread ng r a d i o a c t i v i t y anel to the exact d i s t r i b u t i o n of f i s s i o n p r o d u c t s and a s s o c i a t e d h e a t p r o d u c t i o n c e n t e r s around t h e r e a c t o r system. These u n c e r t a i n t i e s a f f e c t t h e mechanical design sf many of t h e ~ ~ m p o ~ ~ and e n t ssy s t e m such as t h e off-gas. Although the MSBE o r a f i r s t demonstration r e a c t o r would have t o be overdesigned in many res p e c ~ s ,it s h o ~ l db e p o s s i b l e t o b u i l d and o p e r a t e it s a f e l y and r e l i a b l y w h i l e o b t a i n i n g b a s i c infomatisfa needed to optimize l a t e r p l a n t s . The o p e r a t i o n of such 8 ~ e a c t o ri s a n e s s e n t i a l p a r t of a program to p r o v i d e t h e technology f o r EISBRs. A summary of the e v a l u a t i o n of t h e status of each of t h e i m p o r t a n t components and s y s t e m is g i v e n below. O p e r a t i o n of t h e pumps i n t h e ARE, t h e =WE:, and i n t h e l a r g e - s c a l e pump t e s t l o o p s demonstrated the r e l i a b i l i t y of t h e pump designs a d the p r e s e n t s t a t e of t h e technology f o r s a l t pumps. W e know how t o make r e l i a b l e s h o r t - s h a f t pumps having c a p a c i t i e s up to 1500 g p m f o r m e i n m o l t e n - s a l t r e a c t o r s . Although i t may take several years to produce the larger pumps f o r i n t e r m e d i a t e - o r f d l - s c a l e MSBR'S, t h e p r o b l e m a%e w e l l

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understood, and t h e r e is little q u e s t i o n t h a t s a t i s f a c t s r y p w p s can b e o b t a i n e d on a sehe u l e c o n p a t i b l e w i t h o b t a i n i n g t h e s t h e r p r i n c i p a l reactor components. The pump pX'ogr?Xil Will b e n e f i t froan %he LmBks Sodium pump technology program because p m p s f o r liquid metals and f o r molten s a l t s have many COKZMXI requirements. Our e x p e r i e n c e w i t h over 11,000 h r of o p e r a t i o n of an I9.S l n g sodium f l u o r s b o r a t e and with t h e o p e r a t i o n of the - and farced-convection l o o p s f o r material c o m p a t i b i l i t y o m t h a t we can s a f e l y handle t h e s a l t and t h a t it i s a good c a n d i d a t e f o r the coolant s a l t f o r m a l t e n - s a l t reactors. F u r t h e r work is needed EnethodS fQr earlby detectiCKl Sf E t l C ? i s t U a f @ inleakage, C o r r o s i o n p r ~ d u c th a n d l i n g , and t h e migration of t r i t i u m w i t h i n the c o o l a n t system, A t t h i s time we b a s i c problems which would cause elirrii n a t i o n of sodium f l u o r o b o r a t e as t h e c o o l a n t s a l t ; however, t h e r e are a l t e r n a t i v e s a l t s t h a t have o n l y slightly l e s s f a v o r a b l e c h a r a c t e r i s t i c s . The e x p e r i e n c e gained from t h e h e a t exchanger studies i n t h e &a? Program and from the d e s i g n , f a b r i c a t i o n , and o p e r a t i o n of t h e heat exchangers and a i r - c o o l e d r a d i a t o r i n the &ERE h a s s h o w t h a t t h e molten s a l t s behave as c o n v e n t i o n a l h e a t t r a n s f e r f l u i d s amd t h a t , e x c e p t f o r t h e enhanced heat t r a n s f e r t u b e s , none of t h e u n c e r t a i n t i e s a s s o c i a t e d with h e a t exchangers and steam gen r a t ~ r s8r&fundamental. A l l Uncert a P n t i e s a r e r e l a t e d to e n g i n e e r i n d e s i g n optimizatisn and t o maintenance ahpa are considered to be r e s o l v a b l i n a r e a s ~ n a b l efashion w i t h an ade q u a t e l y funded pPogPiiw s% analysis and development. The review made by the Holten S a l t : Group headed by Ebascs S e r v i c e s reached t h e same cornclusion. an5the-n: study devoted t o s t e m enerators now u n d e ~way by t h e F o s t e r Wheeler Corporation i s expected t o r e s u l t i n c o n c e p t u a l d e s i g n s of steam g e n e r a t o r s f o r u s e with molten s a l t and t o d e s c r i p t i o n s of t h e development pregrams needed t o produce them. The studies s f steam systems f ~ urs e w i t h molten s a l t s conducted by n e ~ ~ b eof~ QRXL s and Ebaseo S e r v i c e s have shorn t h a t the conventisnaP s t e m system of an e x i s t i n g modern steam power p l a n t can b e adapted %of m o l t e n - s a l t u s e by the a d d i t i s n of only t h r e e new components. These are a reheat steam preheater i n t h e i n t e P r t l e d i a % e - p r e s s u r e - ~ ~ r bc~i r~ceu i t , chamber f o u~s i n g prime steam for t h e f i n a l s t a g e s f feedwater and b o o s t e r pumps f o r d e l i v e r i n g t h i s feedwater to t h e s t e a m g e n e r a t o r , W e found a l s o t h a t changes w e r e needed i n t h e s t a r t u p system t o p r o v i d e f o r t h e h i g h l i q u i d u s t e m p e r a t u r e of t h e s a l t . Several s p t i o n s are potentPalLy a v a i l a b l e f o r the steam system f o r a m o l t e n - s a l t r e a c t o r p l a n t , none of which i n v o l v e fundamental uncertaii-fties. All e n g i n e e r i n g u n c e r t a i n t i e s are c o n s i d e r e d resolvable w i t h an a d e q u a t e l y funded p1-8gra111 of a n a l y s i s and development. The e x p e r i e n c e w i t h the d e s i g n , f a b r i c a t i o n , and o p e r a t i o n of c o n t r o l r a d s m d d r i v e s i n t h e ARE and t h e PISRE p r o v i d e i n f o r m a t i o n which & r i l l b e u s e f ~ b iin the d e s i g n of r o d s ana drives f o r the ~ B R . m e I I B ~ O P d i f f e r ence is i n t h e need t o o p e r a t e t h e r s d s i n t h e s a l t i n t h e MSBR to p r o v i d e c o o l i n g and reduce t h e p a r a s i t i c EQSS of neutrons. Control r o d s and d r i v e s f o r L?.ZFBRss have t h i s d e s i g n f e a t u r e and much of t h e i n f o r m a t i o n produced i n developing thew should b e a p p l i c a b l e t o t h e development of rods and d r i v e s f o r M S B b . Although a thorough development and p ~ ~ t o t y p e program will b e r e q u i r e d t o a s s u r e adequate performance i n a h i

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f o r MSBRs. VEtPves f o p mo%ten-salt systems have received very little attention since the LWP program. Here again, there are enough a l t e m concepts available t h a t an active pr~gramof seabeetion d testing over about 5 years should be able to p ~ ~ ~ d uthe e e valves need % O r t h e Ilex%. molten-salt reactor, In the meantime, the design steadies d deveEspment tests being conducted in the E r n R progPam will proepide ad for the design of valves for moltew-sa3bt use. Although much smaller in size, the MSWE drain tank is very similar to t h a t proposed for use. with t-he MSB and the experience acquired during the MSRE operation provides some conf ence in the d e s i g n concept, The we o f MaK i n an intermediate thermal convection system to transport the heat to w a t e r is d P f f e r e n t but we believe t h a t it is preferable to rect water cooling of the MSM tank. we belleve that the deals with the afterheat problem realistically and t h a t it I n f o m a t i o n is needed on the detailed d i s t r 5 b u t i o n of the n o b l e ~ t a l sand n o b l e gas daughters c ~ m h gfrom the gas-k before a desi could be completed f o r 8 %000-rn(e) MSBR. We can see no major d i f f i c u Fes i n producing a design sf a drain tank that will satisfy t h e needs of the MSBE, The effectiveness o f the removal 35Xe by gas bubbles w a s demonstrated during t h e ogperati~~-~ of the The presence of the bubbles reduced the effect of xenon to below that originalbly calculated f o r t h e s p r a y &amber i n the pump bowl, and later attempts to calculate t h e effect of b U b b k S als0 l e d to ยงO%ne UIldePeStikW2t%On sf Eheip effeC$iVf3less in removfng xenon. sl model for calculat5wg the xenon distribution in the MSBR 5s still under development. men finished it is expected a l s o ts b e u s e f u l f o r further analyses sf t h e MSm results. E q e r i m e n t a l results f r o m tests usin water solutions indicate that we have a bubble generat~r and bubble sepa a t o r t h a t should work in t h e fuel salt, We believe that t h e bubble stripping method is the best a p p r o a h to a&ie the desired 135X.e poison fraction. The effect O f bubble size on th@ t r a n s fer rate of the noble gases to t h e bubbles is not completely d e f i n e d m d further work is needed before it can be decided whether coating of the graphite is needed. Although much deveabopnen.t: and testing sf various p a r t s sf the gas-kandling system %lavebeen m d ill be- alone, the system will have to be spelpated in a ~eacto'8~ to demonstrate that all the import a n t p r o b l e m have been solved. 0

..... ....-.>..,

i.....

.... ..... ....,>

... ,..,_ ; <.y,

....

.:.:,*

'.... *,.

....

References f o r Chapter 8 I

....

e2L

2.

MoZtePz-Salt Reactor techno lo^, Technical Report of the Molten-Salt Group, Part I, Ebasco Services Inc., December 1971.

3.

EvaZudion of a 1000 ,%de ivoZtere-SaZt Bmeder Reactoa?, Technical Report of the Molten-Salt Group, P a r t PI, Ebascs Services, I n c . , Oct o b e r 1971.

5.

Design Studies of Steam G e n e r a t o r s f o r Molten-Salt Reactors, Monthly Progress Report / k 3 Feb. 14-MarcHz 31, 1993, Foster-Wheeler Corp~r;atiQn DOCUTRefnt NO. N D l 7 2 6 2 2 .

. I

.....

7.

E. s. ~ e t t i s L. , G. Aiexmder, and H. L. Watts, D e s i p S t u d f e s of a MoZten-Salt Reactor Demonstration P l a n t , 0 E-TM-3832 gsme 19S%>

9.

Conceptual D e s i p S t ~ d yof a S i n g l e - F l u i d Molten-Salt Bpeeder R e actoT, OmL-4541 (1971)

-

s

14.

EuaZv.atim of a 1000 [me M ~ l t e n - S a Z tBreeder d i e a c t o ~Technical ~ Rep o r t of t h e Nolten-Salt Group, P a r t 11, S e c t i o n 6.gP Ebaseo Services Ins.

October 1 9 7 1 .

301

16.

Summary of Study of Feasibility o f 8 0 t o r - B e ~ t 5 ~ 1 gSystem f o r a 1250 kp Molten-Salt Fuel Bump Conducted by PTTI on S u b c o n t r a c t 2942, I n t r a Laboratory Correspondence, A. G. Grindell t o I%. B. B r i g g s (June 27, 1968) *

19.

P . G. Smith, High-Temperature Molten-Salt Lubricated Hydrodynamic Jouma1 Bearings, ASHE T ~ m s a c t i o ~ Lt~ 9 s263-274 (1961).

20.

PBR Prsgparn Semiann. P r o g ~E~e p t . Feb. 28,

21.

Oak Ridge National Laboratory, Reactor D i v i s i o n Job Specification 61I-%0544-RB-O01-X-l ( J u l y 2 1 , E969).

22.

A. 6 . G r i n d e l l and 6 . K. McGlsthlan, Conceptuai System D e s i g ~Dee c r i p t i o n of the Salt Pump %st S t m d f o r the MoZten-SaZit; Breedey Experiment, OKTE-TM-2643 (August 1969)

2%.

E. V. Wilson and A. 6. G r i n d e l l , P ~ e Z i m i n a qSystems Design. D e s c ~ p t i o n ( T i t l e d Besicpi of t h e S a l t Pwnp T e s t Stand f o r the IdoItenSaZt Breeder Eqeriment, ORNE-TM-2980 (December 1 9 6 9 ) .

24.

A. G . G r i n d e l l and R. B. B r i g g s , Frogrm P Z m f o r the Pmcu.rement WLd Testing of I!!SBE Salt Pwnps, MSR 69-94 (Oct. E, 1969).

25.

J. P. Sanders, A Review of Pos~L5ZeChoices f o r Secondaq C ~ o Z a n t ~ fop Molten-SaZt Reac%op?s, internal memorandum, Au

29.

W. R. H u n t l e y , B R Program Semimn. P m g r . R q t . Aug. 32, 1974, QRNk-4728, p . 152.

... .... .*y

.... ....!.& ..... ..

,:.....

... .... ..:.:.>> ....

2962, OWL-3282.

302

38.

R. B. B r i g g s , A n Assessment of t h e Effects of Leakage of Water from

the Stecun-fi'aising & p i p e n t m Corrosion i n the Secondmg System of an MSBR, Iwtra-Laboratory C ~ ~ r e s p ~ n d e n cQRNL-%aSR-71-27, e March 19 1971.

33.

Conceptual Besipt Study of a Single-Fluid Molten-Salt Breedem? Reactor, 0mL-4541 (1971), p. 5 4 .

34.

Ibid..

35.

Ibid., p. 69-

36,

I b i d . , p. 81.

42.

Gesign S t u d i e s of S t e m Generator5 f o r Nolten Salt Weactom, M ~ n t k l y P r o g r e s s Report f a , Feba 14-March 31, 11972, F o s t e r Wheeler Corporation

43.

p . 65.

BQCUIRent NO.

NB/72/22.

Project fop Iszznesttgation of MoZten SaZt B r e e d e ~Reaeto~,F i n a l Rep o r t of Phase 1 Study by Black an? Veateh Consulting Engineers, September 1970, p . 7 0 .

I

44.

Study of Q Single-PZuid Mo lten-Salt Bm?eeder ReConceptual Desi actor, QrnTL-4541 (1971) > p . 5 4 .

45.

5 . R. HeWherter, Molten S a l t Breeder E q e r i m e n t TM-3177, November 1970, p a k 8 .

44.

E. S. B e t t i s e t aZ., Design Stzldies of a MsZten-Salt Reactor Bemonstration P l m t , OWL-TK-3832, June 1 9 9 2 , p. 26.

I

Design Bases, ORNE-

.....

.s;?

303 .... ..... .:.:.ya

-_ 47.

1000 M i e ) Molten S a l t BPee&r Reactor CmceptuaZ Design S t u d y , F i n a l I, Ebases Services Inc., February 1972, Pig. 4 . 2 3 .

Report -Task ..... .... ,;.:.:.> ...

...

WJ

49.

e.

H. Gabbard, Reactola $over Measurement and Heat Transfer P e ~ f s r m ip2 t k Molten S a l t Reactor EqeKrnen-t, OW%9E--'1%.f-3002, Kay 1970.

anee ,$<?d

.... .... .:.x<,

....,.6 ....I

% ;.... $ .,

.;... <.y,

....

53.

E. G. Bohlmann, Pieat T r m s f e r S a l t f o r High 2'errrgerattkl.e Steam Generation, OWL-"Pi-3777 ( t o be p u b l i s h e d ) .

54.

E. S. B e t t i s e t a l . , Design Stzldies of a Molten-Salt Reactor Demons t r a t i o n P l m t , 8mL-TM-3832, J m e 1972, p . 3 5 .

55.

C. N. S p a l a r i s e t a l . , Matelaials f o r Nuclear Superheater A p p l i c a tions, GEM?-3875 (1962) 6

57,

MSR Program Semiann. Plaogr. Wept. Aug. 32, 1996, QEW]L-4622, p . 51.

58.

0. W. Burke, Hybrid Comgutep S i m l a t i o n sf'the E B R , Om%--m-3767 (May 1 9 9 2 ) .

59.

Conceptual. B e s i p Study of a Single-Fluid Molten-Salt Breeder Reactor, OrnL-4541 (1971), p. 3 7 .

60.

Puchase Order Subcontract No. 91X-8809OC between Union Carbide Muclear Division and Psster-WReePer C o r p o r a t i o n , Task II or Design Studies of Steam Gewerato~sf o r Molten-Salt R ~ Z X ~ Q E - S .

61. NSR P r o g p m Serniann. P r o p . Rept. Aug. 31, 1969, OaeSL-4449, p . 147.

.... .*.... a

.... .... ::+& ..

304

66.

%bid., p . 156.

67.

P l a n f o r the DevsZopment of S t e m Gene~atsrs$089 Molten S a l t Reactors, enclosure with letter dated Bee. 11, 1978, from %). B. Trauger to HiBtsn Shaw.

$0.

Molten-Salt 8easztor ?'eehmlogz~, Technical Report of the &ltew-Salt Group, P a r t I, Ebases Services Ins., December 1971, p. 53.

71. i%meptuaZ. Design Sttidg of a Single-Fluid Molten-Salt B ~ e e d e rWeL-4541 (1971), p. 7 4 .

73.

Ibid., p . 5-28.

45.

Purchase Order Subcontract No. 91X-886786 between Union Carbide Huclear D i v i s i o n and F ~ ~ t e r - W h @ e E e C~o r p o ~ a t f o n , Task I1 sf Design Studies for Molten-Salt Reactors.

74.

-.

C...

EvaZtlation of a 1500 &Ne hfoLten-Salt B ~ e e d e rReactor, Technical Report sf the Molten-Salt Group, Part 11, Ebasso Services, Inc., Ost s b e r 1 9 7 1 , p . 118.

80.

Pbid., p. 123. L.

....

305

<:...... <. ....

'...... .> .A,,,

.... c.:<#

...... :.... .=<.

86,

Purchase Qrder Subcontract N o . 91X-8807QC between Union Carbide Nuclear Division and Poster-Wheeler Corporation, Task I of D e s i g n S t u d i e s of Steam Generatsrs f o r Molten-Salt Reactors e

87.

R. 6 . Robertson, MSRE B e s i p and Operations Repoaot, P m t I , Bescript i o n of Reaceor Design, OREa%-TM-%28 (January 1965).

88.

0. S. Seim, Large Values f o r Liquid M&al Cooled Reactors, ~ e a c t o r and F u e l P r o c e s s i n g Technology, Vsl. P I , No. 3 S m e r 1 9 6 8 , p p .

127-137.

, PZsu

Controller EvaZuatisn fop Sod-km

89 *

R. A. Winborne N U - S R - 7 5 3 4 Service, Nov. 30, 1963.

90.

Conceptual Design Study of a Single-FZuid Molten-Salt Bpeeder Reactor, ORNL-4541, pp 1 4 p 119-119 (1971) s

92.

o

E. S. B e t t i s , E. 6 , Alexander, and H. L . Watts, Besign. S t u d i e s of a Molten-Salt Reactor Bernmstration P Z m t , OML-TM-3832 (June 1972) e

93.

Conceptual C o w p ~ n e n t sDesign D e s c r i p t i o n f o r t h e Reactor Nuclear

C o n t r o l Components No. 33, BN64%-500, Vo%. 33, Batt@1Pe-Northwest9 Rickland, Washington, A p r i l 2 4 , 1969.

94.

W. 6 . B r i a n t , A. PI. Weinberg, E. S. B e t t i s , W. K. Ergen e t aZ., Iv'ucZ. S c i . Eng. 2 , 797 (1957).

95.

P. N. Haubenreich, J. R. Hwgel, Nucl. AppZ. Tech. 8, E18 (l970).

.... ..... .:.::y4

97.

R. C. Robertson, NSRE D e s i p and Operations Repopt, Part I , Beac~Lpt i o n Q$ Reactor Design, 8mb-Tbf-728 (January 1965).

.... 'i.2'

98.

A. M. P e r r y , p r i v a t e c o m u n i c a t i s n .

...5

.,

... e .? ;# > .:.

306 99.

E . S . Bettis, L. G . KLexawder, amd H. L. Watts, Design Studies of a: MoZten-Sal75 Reactor DemonstPation Plant, om%-TP1-3832 (June 19 72) 0

ea,

P. N. Haul3

i n the 105. J. R. Engel and

16m, 6

, and A . Houtzeel, SpPay, Mist, Bubbles 3627 (June a9so),

S t e f f y , XePzon Behmisr i - n the MoZten-Salt ReL-234-3464 eoet. 1971) e

.C..&..... >

109.

Co?aceptmI Design Stud2 of a single-Fluid Molten-Salt Bpeedefl R%L-4541, p. 61 (1971).

....

$ .:....

....

I

307 .... ......,:%. A,..

118.

T. W. Leland, Desfgn of Charcoal Adssrbers for t h e HKT, QRNE-CF55-9-12, Sept. 6, 1955.

119

C . R. S o l e n b e r g e r e t

120.

S.

121.

R. E. A d a s , W. E. B~o;s~wing, Jr., and a. D. Ackley, Containment of Radioactive Fission Gases by Dynamic A d ~ ~ r p t i ~dnd. n , Eng. &ern.

. ..

,y ....* ~

.. ...... .....,

aZ., Treatment of Off-Gas from the ERT, ORGDP internal correspondence KT-373 (MIT Engineering Practice School memo EPS-%-388) Septennber 1958. J. B a l l , Oak Ridge Nati~nalLaboratory, unpublished data, September 1966 e

..... .....

'.:<<I

51, 1467

..

...

i..

(December 1950).

..L..,

...... :..... :<<,

123.

a. C. Robertson, MSRE Design and @9e~ationaR e p o ~ t ;B a r t I, %zesol--iptisnof R:~CZC&QP Design, O B h y L - ~ - 7 2 8 , pp. 332-336 (January 196%) *

124.

B i d * , p p . 356-381.

125.

R. J. Ked1 and A. Hsutzeel, DeveHopment sf a M ~ d e lf o r Computing 135xe M i g r a t i o n i n t h e m m , BmL-4869, June 1967.

126.

J. R. Waggoner and F. N . PeebbPes, Stripping Ratio of Carbon Dioxide from Water i n Spray Type Liquid-Gas Contactors, Unive~sity of Tennessee Report EM 65-3-1, March 1965.

127.

R e J. R e e l l , A Model f o r Computing the Migration sf Very S h o r t Lived m b l e eases i n t o PISRE G r a p h i t e , OWL-TM-1810, July b967a

128.

D. S c o t t and A . G . Grindell, Components and S y s t e m BevePopment f o r Molten-Salt Breeder Reactors, OML-T&f-b855, June 30, 1967.

129.

A . I. Krakoviak and R. H. Guynon, Experience with the MoltentSalt Reactor Experiment Off-Gas Systems, OWN]&-Tpz( t o be issued).

...>.:..,., .+.,

.... .;+*a

131. MSB PPog.f?m S e ~ m n .i e r s p . W e p t . Peb. 28, 2967, QmL-4119, pp. 42-56. 4

132.

F. N. Peebkes, Removal of Xenon-135 from Circulating Fuel S a l t S% t h e MSBR by Mass Transfer to Helium Bubbles, OmL-TM-2245, July 23, 1968.

t

F

c

S. Kress, Mass Transfer Bemeen Srnal1 Bubbles and L i q u i d s in Cocurrent Turbulent P i p e l i n e Plm, QREJ%-Tb%-3718,A p r i l 1972.

134.

%.

135.

mR

FpIopm

Sepsaimn. P r o p * R e p t . Peb. 28,

1971, OWL-4676, p. 4 9 .

137. J. A , H a f f o r d , Development of the P i p e Line Gas S e p a r a t o r , OWL1602, Pes. 18, 1954.

138. F. N. Peebles, The X o t i ~ nof Gas Bubbles in t h e "2 Reactor Core, ORESL-1E71,

Jan. L C s 1952.

Semitenn.

49-51

146.

I

PP0p0

a q t . Feb.

28, 1971, OWL-4676, p p .

0

J. a. En el, p e r s o q a l communication, July 5, 1972.

....

*;>A

?..+.2

9.

.... y ,

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..%.

.

CELLS, BUILDINGS, AND C O N T A I W N T E. S, B e t t i s

Requirements ....

..+.*

.....y

....

...

..'is.' !.A

..,. .*... ....

The m o l t e n - s a l t reactsr p l a n t d i f f e r s from o t h e r s i n t h a t barge m o u n t s of f i s s i o n p r o d u c t s are d i s p e r s e d throughout t h e r e a c t o r primary system and ~ e v e b - a la u x i l i a r y systems. Much of t h e equipment and p i p i n g must b e p r e h e a t e d and h e l d a t l800"F o r h i g h e r t o keep t h e salts molten. Maintenance of t h e r a d i o a c t i v e equipment must b e accomplished through s h i e l d i n g by u s e of remotely o p e r a t e d t o o l s . F a c i l i t i e s MUS^ b e provided f o r t h e h a n d l i n g and s t o r a g e of f i s s i o n products d i s c h a r g e d from t h e f u e l p r o c e s s i n g p l a n t and f o r materials removed from t h e r e a c t o r systems. Because of t h e d i f f e r e n c e s , c o n s i d e r a b l e a t t e n t i o n w a s g i v e n t o t h e c o n t a i n ment requirements i n t h e NSBR r e f e r e n c e d e s i g n and to a r e a c t o r b u i l d i n g and equipment c e l l s t h a t would s a t i s f y those requirements. The major c r i t e r i o n i s t h a t double containment b e p r o v i d e d at a l l t i m e s f o r equipment t h a t c o n t a i n s t h e b u l k o f t h e r a d i o a c t i v e l i q u i d s and g a s e s . The i n n e r containment must remain s e a l e d a t all times when t h e equipment t h e r e i n i s o p e r a t i n g . The outer containment must a l s o be s e a l e d , b u t c o n t r o l l e d acsess through a i r l o c k s i s p e r m i s s i b l e a t any time when t h e r a d i a t i o n l e v e l s are below t h e l e v e l s s p e c i f i e d f o r human occupancy. When maintenance of t h e doubly c o n t a i n e d equipment i s necessarys t h e b u l k of the r a d i o a c t i v e f l u i d s must b e d r a i n e d o r purged from t h a t equipment amd s e c u r e d i n t a n k s i n o t h e r s e a l e d c e l l s . The i n n e r containment can then b e unsealed and openings made as n e c e s s a r y t o accomplish t h e maintenance. A d e g r e e of i n n e r containment must b e maintained by l i m i t i n g t h e s i z e of opening and p r o v i d i n g a flow s f a i r inward t h ~ o u g ht h e opening. Equipment t h a t is removed must b e w i t h d r a m i n t o casks f o r t r a n s f e r t o r e p a i r p d i s p o s a l , o r s t o r a g e f a c i l i t i e s w i t h i n t h e outer cantainment. During a l l t h e s e o p e r a t i o n s t h e o u t e r ~ ~ n t ~ i i n m must e~~ b et k e p t s e a l e d . All v e n t i l a t i o n streams must be f i l t e r e d , passed through absorbers, and r e c y c l e d where f e a s i b l e . Gases t h a t are d i s c h a r g e d t o t h e atmosphere m y COntaiHl SRPY trivia-? ElIEloUIlts Of f i s s i o l l pKldUCt r a d i o a c t i v i t y .

Description

These g e n e r a l requirements were a p p l i e d i n t h e MSRE, a l t h o u g h less s t r i n g e n t l y , because much less r a d i o a c t i v i t y w a s involved. The MSRE fuel c i r c u l a t i n g system w a s i n s t a l l e d i n a r e a c t o r c e l l t h a t was a s t e e l t a n k imbedded i n c o n s r e t e . The fuel d r a i n t a n k system w a s s i m i l a r l y e n c l o s e d i n a s t e e l - l i n e d c o n c r e t e c e l l . S a l t - c o n t a i n i n g equipment i n t h e c e l l s was enclosed in i n s u l a t i o n that contained electric heaters to maintain t h e s a l t above t h e melting p o i n t w h i l e t h e c e l l atmosphere was h e l d t o 150째F

t

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by s p a c e C Q Q P ~ ~ S The . t o p c l o s u r e of each cell was f ~ m e dby a s t e e l ~ d r a n sandwiched e between t w o layers of c o n c r e t e shield b l o c k s and welded t o t h e t a n k w a l l s . The reactor and d r a i n t a n k c e l l s were i n s i d e t h e r e a c t o r b u i l d i n g . This b u i l d i n g w a s a s t e e l frame s t r u c t u r e that w a s covered w i t h c o r r u g a t e d sidin and l i n e d w i t h s t e e l sheet to make i t moderately t i g h t When t h e r e a c t o r was o p e r a t i n g o r maintenance w a s i n p r o g r e s s , and a t most o t h e r t i m e s , t h e r e a c t o r b u i l d i n g w a s c l o s e d and the interior w a s k e p t a t a slightly ne ative p r e s s u r e by drawing a i r from t h e b u i l d i n g through f i l t e r s and d i s c h a r g i n g i t up a s t a c k . During o p e r a t i o n t h e atmosphere i n the r e a c t o r and d r a i n t a n k c e l l s w a s maintained below 5 p e r c e n t i n oxygen by a d m i t t i n g n i t r o g e n and a t subatmospheric p r e s s u r e by e x h a u s t i n g a small stream p a s t a r a d i a t i o n monitor and tap t h e s t a c k . When a cell w a s opened f o r ~ ~ ~ i n t e n a n tchee, s i z e of the opening was ninimized and a flow of a i r i n t o t h e c e l l s was maintained by means of a l i n e from t h e c e l l s t o t h e b u i l d i n g exhaust system. Materials removed from t h e c e l l s were withdrawn i n t o casks o r bags f o r storage i n o t h e r cells in t h e b u i l d i n g o r f o r removal from t h e p l a n t . The containment system worked well and provided s a t i s f a c t o r y p r o t e c t i o n for the p u b l i c and f o r p l a n t persQp%nel. 0

The reactor b u i l d i n g p r o v i d e s t h e o u t e r b a r r i e r of t h e double containment f o r t h e equipment i n the MSBW p l a n t a l s o . I t i s c y l i n d r i c a l i n shape w i t h a h e m i s p h e r i c a l dome, i s of m o n o l i t h i c c o n c r e t e c ~ n s t ~ ~ ~ t i o n , and is about 189 ft h i g h and 134 ft i n d i a m e t e r . The e n t i r e b u i l d i n g rests 8 % one ~ c o n c r e t e pad, and a m e t a l l i c membrane e n c l o s e s a l l p a r t s of the b u i l d i n g in which r a d i o a c t i v e materials are p r e s e n t . The domed buildi n g w i t h 3-ft-thick c o n c r e t e w a l l s was s p e c i f i e d t o m e e t t h e a c c e p t e d requirements for reactor b u i l d i n g s regardin storm-induced d i f f e r e n t i a l pressure and Inissiles. r o u t i n e speration, t h e reactor b u i l d i n g i s maintained a t a i g h t l y below atmospheric by a v e n t i l a t i o n system t h a t r e c y c l e s the sit- throkagka absorbers and f i b t e r s and discharges a fraction up Stack to compensate f o r a esgatrokled i n f l o w of f r e s h a i r . O p e r a t i n g personnel have access t o t h e b u i l d i n g a t a l l t i m e s through a i r l o c k s except when c e l l s are open d u r i n g some s t e p s i n maintenance o p e r a t i o n s . t h e hemiWithin t h e reactor b u i l d i n g are three ~ a ~ b j ol re % ~ e l Under ~. s p h e r i c a l dome i s t h e crane bay area which i s serviced by a heavy d u t y p o l a r crane with two t r a v e l i n g h o i s t s . A s d e s c r i b e d i n ORKL-4541, t h e major use of this area i s f o r maintenance of equipment i n the c e l l a below it Beneath the c r a n e bay and on the mext lower l e v e l are l o c a t e d t h e r e a c t o r c e l l , t h e chemical p r o c e s s i n g and off-gas c e l l s (which extend to t h e bottom l e v e l ) , v a r i o s hot c e l l s for disassembly of f a i l e d . n t s , and s p a c e f o r the s t o r a e of r a d i o a c t i v e equipment. The bottom level sf the building has t h e drain tank cell and t h e waste storage c e l l . These c e l l s c o n s t i t u t e t h e inner containment of the double containment system f o r c o n f i n i n g the r a d i o a c t i v i t y t o t h e p l a n t .

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s h i e l d i n g and are l i n e d w i t h metal t o p r o v i d e a t i g h t containment, These c e l l s a l s o p r o v i d e a c o n t r o l l e d atmosphere environment f o r t h e equipment. The reactor cell and f u e l - s a l t d r a i n t a n k cell r e q u i r e b o t h h e a t i n g and c o o l i n g . They must b e h e a t e d to about 1080째F b e f o r e t h e reactor can b e f i l l e d w i t h s a l t . Being a b l e t o c o o l them is u s e f u l f o r removing rad i o a c t i v e decay h e a t from the primary system after t h e salt has been d r a i n e d and f o r lowering t h e temperature b e f o r e doing maintenance. For t h i s r e a s o n , t h e s e c e l l s are l i n e d w i t h thermal i n s u l a t i o n and have a f o r c e d c i r c u l a t i o n c l o s e d gas system i n which t h e gas can b e h e a t e d or cooled. The off-gas c e l l and t h e chemical p r o c e s s i n g c e l l s have h e a t e r s o r c o o l e r s on t h e components themselves, and t h e ambient temperature i s maintained a t about 100째F by s p a c e c o o l e r s . B u i l d i n g t h e r e a c t o r and d r a i n t a n k s e l l s as ovens i n t r o d u c e s several problems. The i n s u l a t i o n must be a b l e t~ expand and contract w i t h the h e a t i n g and c o o l i n g of t h e c e l l and b e e f f e c t i v e f o r a t l e a s t 30 years with l i t t l e repair. Some equipment s u p p o r t s and r e s t r a i n t s must operate harmally a t 1000째F b u t b e able t o accornmsdate occasional c o o l i n g t o 200째F. R e l i a b l e blowers must b e provided t o c i r c u l a t e t h e c e l l a t mosphere. I n d u s t r i a l blowers are a v a i l a b l e f o r c i r c u l a t i n g gases i n ovens a t t e m p e r a t u r e s up t o 200B"F, b u t they probably w i l l have t o b e upgraded f o r r e a c t o r s e r v i c e . S p e c i a l a t t e n t i o n w i l l have t o b e given t o p e n e t r a t i o n s through t h e c e l l w a l l s and t o d i s c o n n e c t s f o r instrument and S e r V i C e IfneS. POX' 5 6 m 6 SePviCe t h e i n n e r ends O f the peRetratiOnS and t h e disconnects m y b e at h i g h temperature. POP o t h e r s t h e p e n e t r a t i o n s w i l l t e r m i n a t e behind t h e i n s u l a t i o n at the inner a d . % of the cell and b e a t ]bow temperature. Some s p e c i a l l y cooled thimbles may b e r e q u i r e d t o b r i n g n u c l e a r i n s t r u m e n t a t i o n c l o s e to t h e r e a c t o r vessel. Cooling must b e provided i n the c e l l walls t o remove t h e h e a t t h a t p a s s e s through t h e i n s u l a t i o n and t h a t i s g e n e r a t e d i n t h e w a l l s by n u c l e a r r a d i a t i o n s i n srder t o keep the c o n c r e t e a t low temperature. The b e n e f i t s . d e r i v e d from i n s t a l l i n g t h e r e a c t o r equipment i n avens as opposed t o p u t t i n g the i n s u l a t i o n and h e a t e r s on t h e equipment and p i p i ~ gare s u b s t a n t i a l . I n s u l a t i n g t h e walls i s p o t e n t i a l l y much less complicated and less expensive than prcsviding many s p e c i a l l y f i t t e d and remotely i n s t a l l a b l e p i e c e s around t h e vessels and p i p i n g . I n t h e oven t h e e x t e r i o r s u r f a c e s of t h e r e a c t o r equipment are fa^ mre a c c e s s i b l e f o r remote maintenance and i n s p e c t i o n and f o r i n s t a l l a t i o n of i n s t r u m e n t a t i o n . The m u l t i t u d e of e l e c t r i c a l c a b l e s and t h e ~ ~ ~ o c o u p and l e s associated disconnects and p e n e t r a t i o n s t h a t are r e q u i r e d f o r i n d i v i d u a l p i p e l i n e and v e s s e l h e a t e r s are e l i m i n a t e d . Although t h e h e a t i n g systems on t h e MSRE worked very w e l l , most of t h e p e n e t r a t i o n s , thermocouples, and s e r v i c e l i n e s and much o f t h e compdexity in t h e c e l l s r e s u l t e d from p r o v i s i o n s f o r h e a t i n g t h e s a l t - c o n t a i n i n g equipment and cooling t h e a i r i n t h e cells. During o p e r a t i o n t h e equipment c e l l s are s e a l e d and a c c e s s i s proh i b i t e d . When maintenance i s r e q u i r e d , the r e a c t o r i s s h u t down and d r a i n e d and a c c e s s is achieved by removing s h i e l d i n g blocks a t t h e top of the cells and opening up s e c t i o n s s f t h e s t e e l membrane, as d e s c r i b e d in Chapter 1 2 . When a c e l l i s n o t t i g h t l y s e a l e d , b u i l d i n g a i r i s drawn i n t o

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the c e l l , passed through abs~lpbersand filters, and r e e y e l e d t~ t h e reactor b u i l d i n g o r d i s c h a r g e d up a s t a c k . Radiation i n s t r u m e n t s monitor t h i s effluent gas to prevent release sf activity QUtSide the buiikdhlg. %he bottom Of t h e Heactor c e l l ~ O K I T L S a Catch pala Which CQnneCts through a l i n e t o t h e drain tank. Any b r e a k i n t h e p r i n a a ~ ysalt c i r c u i t w i l l r e s u l t i n t h e leaked salt b e i n g conducted t o t h e d r a i n tank. T h i s feature is d i s c u s s e d f u r t h e r i n Chapter 8. The stem c a l l s are located o u t s i d e t h e main b u i l d i n g containment membrane. This i s t o avoid any p o s s i b i l i t y of a s t e m l e a k g u t t i n g p r e s s u r e on t h e containment s t r u c t u r e . Because t h e S ~ C O E - L ~ ~cKo o ~ l- a n t i s rad i o a c t i v e and t o x i c , t h e s e c e l l s are a l s ~ s e a l e d when t h e equipment is

Status and U n c e r t a i n t i e s

eneral d e s i g n of t h e r e a c t o ~containment b u i l d i n g f o r an MSBR the d e s i g n t h a t has come t o b e r a t h e r s t a n d a r d f o r n u c l e a r and m u n u s u d c o n s t r u c t i o n techniques seem t o b e involved i n he c y l i n d r i c a l shell O H t h e v a r i o u s cells. Heating the reactor

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the S a l t , k i C W e V e r , iS UlSniqUe. The method employed f o r heating r e q u i r e s no i n v e n t i o n s and s h o u l d have minimal troublbes. The u n c e r t a i n t i e s winlly r e l a t e t o the method of i n ~ u l a t i r t gt h e cells and m k i w g t h e p e n e t r a t i o n s , and, as d i s c u s s e d i n Chapter 1 3 , the way to s u p p o r t t h e r e a c t o r components in the hot cell and t o r e s t r a i n them a a i n s t seismic forces. No l i m i t i n g problems are foreseen, but t h e d e s i i n t o be â‚Ź d l y worked out. A c ~ n s i c t e amount of developwent w needed in proving the d e s i g n . The approach Of S e p a r a t e l y insUlEitiHl and h e a t i n g t h e components can b e adopted i f the d i f f i C U B ' k k ? S Qf U ihng t h e Sells as BVefbS prove to be t o o g r e a t . S c a l i n g up the MSW method f o r an MSBW would r e q u i r e much clevelopxent and t e s t i n g also. Top s h i e l d i n g plugs t h a t a r e removable f o r maintenance access were used s u c c e s s f u l l y i n the KRE-2, and MSRE, and a s e a l i n g membrane was w e d in the same g e n e r a l way a t t h e ERE-2 and %RE. Plow of air i n t o the cell through openings was a l s o used to prevent the d i s p e r s a l of radioastivity d u r i n g maintenance. E a r er cell s p e n i n s will b e r e q u i r e d ow an mBR, t h e amounts sf a c t i v i t y i n t h e system will b e greater, and the restrictions on d i s c h a r g e of a c t i v i t y will probably b e t i g h t e r . Methods and equipment will have t o b e developed f o r s e a l i n g openings a r ~ ~ a work td s h i e l d s and t o o l s t o p r o v i d e b e t t e r s h i e l d i n g a g a i n s t r a d i a t i o n and to I p @ S t r i C t the r e q u i r e d a i r flow %Q Pates t h a t W i l l not require eXceSSiVe%y Parge absorber and filter banks.

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No u n u s u a l problems a p p e a r to r e l a t e t o p r o v i d i n g a c ~ n t ~ i ~ ~ ~ ~ n t b u i l d i n g f o r a n MSBR, b u t t h e p r o p o s a l i n t h e O W r e f e r e n c e d e s i g n t o use t h e r e a c t o r and f u e l - d r a i n t a n k c e l l s as ovens f o r p r e h e a t i n g t h e equipment t o about IOOO'F i s unique. D e t a i l e d d e s i g n s are needed and development and t e s t i n g w i l l b e r e q u i r e d to d e t e r m i n e w h e t h e r all d e s i g n r e q u i r e m e n t s can b e s a t i s f i e d i n t h i s approach. I f t h e y c a n n o t , a r e t u r n t o the M S E c o n c e p t o f s e p a r a t e l y i n s u l a t e d and h e a t e d components can b e adopted The double c o n t a i n m e n t a f f o r d e d by the r e a c t o r b u i l d i n g and t h e equipment c e l l s s h o u l d g i v e good c o n t r o l of r a d i o a c t i v i t y d ~ i n nak-mal g o p e r a t i o n o r a c c i d e n t c o n d i t i o n s . The containment p r o v i d e d by t h e reactor b u i l d i n g s h o u l d g i v e s a t i s f a c t o r y p r o t e c t i ~ nt~ t h e p u b l i c a g a i n s t releases of r a d i o a c t i v i t y d u r i n g m a i n t e n a n c e o p e r a t i o n s . C a r e f u l d e s i g n , w e l l developed equipment and p r o c e d u r e s , and c a r e f u l u s e o f a c o n t r o k l e d v e n t i l a t i o n s y s t e m w i l l b e r e q u i r e d f o r p r o t e c t i o n of p l a n t p e r s o n n e l d u r i n g m a i n t e n a n c e . The MSE a f f o r d e d e x p e r i e n c e w i t h a l l sf t h e s e on a s m a l l s c a l e and t h e r e is similar e x p e r i e n c e from o t h e r r e a c t o r p l a n t s and from f u e l r e p r o c e s s i n g p l a n t s . D e s i g n , development, and t e s t i n g w i l l b e r e q u i r e d , b u t no problems are e v i d e n t that might p r e v e n t s a t i s f a c t o r y c o n t a i n m e n t s t r u c t u r e s and a t t e n d a n t s e r v i c e s y s t e m s from b e i n g p r o v i d e d f o r an MSBR.

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Requirements and C u r r e n t Concepts

Systems f o r Normal Operation

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Normal o p e r a t i o n of an BR i n c l u d e s a l l phases of s t a r t u p from cold h o t standby c o n d i t i o n s , p r o d u c t i o n of e l e c t r i c power a t demanded l o a d s between 20 and 108% of d e s i g n capability, and seheduled shutdown. The c o n t r o l systems must r e e o g n i z e t h e d i f f e r e n t requirements for t h e v a r i o u s o p e r a t i n g modes and e s t a b l i s h and m a i n t a i n s a f e and approp r i a t e o p e r a t i n g c o n d i t i o n s . The systems must c o o r d i n a t e t h e o p e r a t i o n of t h e r e a c t o r , t h e primary- and s e c o n d a r y - s a l t l ~ o p s ,the s t e m togs, and system a u x i l i a r i e s . I n g e n e r a l , t h e l o a d demand i s t h e primary signal t o which the c o n t r o l subsystems must respond. Mowever, w h i l e ~l%tchLngt h e power generation w i t h t h e l o a d , the control system must m a i n t a i n system t e m p e r a t u r e s and t h e i r rates of change within a c c e p t a b l e l i m i t s . S p e c i f i c areas of concern are t h e t e m p e r a t u r e s f t h e steam a t the t u r b t n e t h r o t t l e , t h e r a t e s f change of t e m p e r a t u r e i n t h e s a l t l o o p s , and t h e s a l t t e m p e r a t u r e s , which must b e maintained w e l l above t h e f r e e z i n g p o i n t throughout the c i r c u l a t i n g s y s t e m (with t h e possible e x c e p t i o n of surne areas in the steam g e n e r a t o r ) . n e pPeยงent concept is to c o n t r o l t h e nUCleELr power genePatiol3 by g r a p h i t e r o d s , which are used i n an a u t o m a t i c c o n t r o l l o o p t o m a i n t a i n r e a c t o r t e m p e r a t u r e a t a set p o i n t p r o g r a m e d a c c o r d i n g t o t h e needs of the steam system. T h i s arrangement i s a variation s f a scheme successf u l l y demonstrated on t h e IGRE9 where t h e t e m p e r a t u r e s e t p o i n t w a s c o n t r o l l e d by t h e o p e r a t o r . Such a eontrok system makes t h e r e a c t o r power slave to t h e l o a d , w i t h a t e m p e r a t u r e base l i ~ e independently determined t o p r o v i d e steam at t h e d e s i r e d temperature. Maneuverhg f r o m one power l e v e l t o a n o t h e r r e q u i r e s C Q I I ~ ~ of O ~ steam temperature d u r i n g t h e transient. The current concept i n v o l v e s a u t o m a t i c c o n t r o l of s e c ~ n d a qsalt flow r a t e through t h e steam generat o r t o take advantage of the thermal c a p a c i t y of t h e s a l t w h i l e t h e r e a c t o r power l e v e l i s b e i n g r e a d j u s t e d t o t h e new requirements. I n t h e multilbsop p l a n t , such as the r e f e r e n c e mBR, t h e c o n t r o l system must a d e q u a t e l y respond t o loop i n t e r a c t i o n s . The most satisfactory approach a p p e a r s t o b e one i n which each I Q Si~ s c o n t r o l l e d as a u n i t t o produce a s p e c i f i e d amount of s t e m under w e l l - d e f i n e d comditions, wFth t h e bala~ci9b-gof t h e l o o p s under t h e c o n t r o l of a master p r ~ g r a ~ r~ ~perhaps ~er a d i g i t a l computer - t h a t i s r e s p o n s i v e t o t h e needs of t h e power g r i d . T h i s p r o g r a m e r would a d j u s t set p o i n t s on a p p r o p r i a t e closed-loop ~ o R ~ ~ Q B I a~s Is ox c i a t e d w i t h t h e c o o l a n t I S O ~ S . The c o n t r o l system requirements of an MSBR are b a s i c a l l y t h e same as those sf s t h e r power r e a c t o r s . However, t h e y do d i f f e r i n SQIW detail. These differences w i l l be d i s c u s s e d later.

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In a d d i t i o n t o p r o v i d i n w o m a l control f u n c t i o n s t h e i n s t r u m e n t a t i o n and c o n t r o l system must provide p r o t e c t i o n against a v a r i e t y o f mormalous or accident conditions Although the e n t i r e c o n t r o l system s h o u l d cont r i b u t e t o safe and o r d e r l y ~ p e r a t i o n s ,there is always a system dedicated t o p r o t e c t i o n of p e r s o n n e l and t o the p ~ ~ e n t i oofn major equipment damage. This system, t h e p l a n t p r o t e c t i o n system (PPS) i n c l u d e s m o n i t o r i n g l Onditbns logic sUbSystelE3 &S instKUllleIltatiOn t 0 detest O f f - 9 a O ~ ~ C make d e c i s i o n s and i n i t i a t e c o r r e c t i v e a c t i o n s and a c t u a t o r s t o e f f e c t process control a c t i o n s The plant p r s t e c t i o n system must b e c a p a b l e of s h u t t i n g down t h e p l a n t when n e c e s s a r y an o u t o t h e r p r o t e c t i v e f u n c t i o n s 9 such as i n s u ~ h gt h a t s y s t e m are i n o r d e r f o r containing t h e r a d i o a c t i v i t y i n t h e e v e n t ~f a major a c c i d e n t and t h e removal of a f t e ~ h e a tf o l l l w i n g an emergency shutdown where normal c o o l i n g i s impailred. Whereas the c o n t r o l rods w i l l be g r a p h i t e partially inserted i n t o t h e core s o that positive and n e g a t i v e r e a c t i v i t y changes can b e made, the s a f e t y rods will b e neutron-absorbing p o i s o n K O ~ S of c o n s i d e r a b l y more r e a c t i v i t y ~ o ~ t hBecause . of their effect on n e u t r o n economy and b r e e d i n g , t h e s a f e t y rods probably w i l l b e normally withdrawn out of t h e a c t i v e core region. However, i n some n o l - ~ ~ ci li r c u m t a n c e s , having t h e safety r o d s partially i n s e r t e d f o r a s h o r t t i m e m y b e d e s i r a b l e . Theref o r e , continusus adjustment of theirp p o s i t i o n must b e p o s s i b l e . It i s n o t d e a r a t t h i s t h e t h a t a fast "scram" c a p a b i l i t y will b e r e q u i r e d . Tke p%aIIlpt negative f u e l t e m p e r a t u ~ eC Q e f f i C i a t p l u s the c o n s i d e r a b l e therm1 c a p a c i t y of t h e salt and graphite E I K ~ f a c t o r s which make t h e p l a n t less s e n s i t i v e t o r e a c t i v i t y e x c u r s i o n s (see Chapter 14). However, only detailed a n a l y s e s of a p a r t i c u l a r p l a n t design w i l l e s t a b l i s h the precise requirements of t h e PPS.

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The ~ p e r a t i o n dc o n t ~ o ls y s t e m and t h e p l a n t p r o t e c t i o n system w i l l r e q u i r e e x t e n s i v e i n s t r u m e n t a t i o n t o p r o v i d e i n p u t i n t o the a u t o m a t i c decision-=kin p r o c e s s of c o n t r o l Measurements of n e u t ~ o nf l u x levels as well as of t h e nonnuclear v a r i a b l e s such as flow rates, p ~ e s s ~ r e s , telBpe?ZatUreยง, e t c . W i l l be V i t a l ti3 effective c o n t r o l of t h e p l a ' ~ I t . Some i n s t r u m e n t B ~ ~ S O K and S signal t r a n s m i s s i o n l i n e s , and p o s s i b l y some ContainTlEnt p e n e t r a t i o n s W i l l b@ Keq r e d t o operate reliably i n h o s t i l e r a d i a t i o n levels, o r b o t h . The environments of h i g h temperature, h i h i g h r e s i d u a l r a d i o a c t i v i t y i n the reactor c e l l will make d i r e c t maintenance i m p o s s i b l e i n many l o c a t i o n s , s o a c c e s s i b i l i t y of i n s t r u m e n t cowpoenents f o r n t e m ~ t ed i s c o n n e c t and replacement w i l l b e n e c e s s a r y . ~w g e n e r a l , conventional electronic or pneumatic s i g n a l conditioning equipment can meet the needs of the NSBR. However, t h e size and complexity of the p l a n t w i l l make i t h i g h l y d e s i r a b l e t o use d i g i t a l computer rechn i q u e s f o r m u l t i p l e x i n g , d a t a storage and r e t r i e v a l , c a l c u l a t i o n , and other functions Optimization of the plant o u t p u t will r e q u i r e developA high d e g r e e of automation and ment of s o p h i s t i c a t e d c c p ~ ~ t schemes. ~ol 0

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s u p e r v i s o r y c o n t r o l w i l l b e n e c e s s a r y in t h e MSBR, as i n m y l a r g e m u l t i loop p l a n t , because of t h e l a r g e number of i n t e r a c t i n g p r o c e s s e s . U s e of automatic c o n t r o l loops for a l a r g e number of process c o n t r o l f u n c t i o n s i s commonplace; however, t h e i n t e g r a t i o n of these i n t o e f f e c t i v e s y s t e m c o n t r o l i s o f t e n l e f t to t h e o p e r a t o r . S i g n i f i c a n t improvements i n opera t i o n can b e achieved i f o v e r a l l s y s t e m c o n t r o l i s h i g h l y automated u s i n g well-es t a b l i s h e d techniques = HR a d d i t i o n t o those i n s t r u m e n t s n e c e s s a r y for d i r e c t controE of the p l a n t , there must b e a l a r g e number of i n s t r u m e n t s f o r IIIQnitoriPlg p l a n t f a i l u r e d e t e c t i o n i n s t r u m e n t a t i o n , and t h e u s u a l complement of i n s t r u m e n t s f o p s u r v e i l l a n c e o f t h e g e n e r a l h e a l t h o f t h e p l a n t and f o r management e v a l u a t i o n of p l a n t o p e r a t i o n .

F e a t u r e s P e c u l i a r t o MSBR

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A number of f e a t u r e s which are p e c u l i a r t o t h e MSBR a f f e c t the i n s t r u m e n t a t i o n and c o n t r o l system requirements The h i g h f r e e z i n g p o i n t s of t h e MSBR f u e l and coo%ant s a l t s impose r a t h e r s t r i n g e ~ tc o n t r ~ land p r o t e c t i o n system requirements. Care must b e e x e r c i s e d t o p r e v e n t f r e e z i n g of t h e s a l t in a u x i l i a r y l i n e s , as well as in main salt l i n e s and h e a t e x c h a n g e ~ s [I, pp. l22-123] Tne f i l l i n g and s t a r t u p p r o c e d u r e s s although s i m p l i f i e d by t h e oven concept, w i l l b e somewhat complex, as w i l l be t h e procedure f o r a d m i t t i n g f e e d w a t e r into t h e system [ l , pp. 1231. R e l i a b l e i n s t r u m e n t a t i o n must b e provided f o r d e t e r m i n i n g the c o n d i t i o n of t h e s a l t when i t is o u t s i d e t h e r e a c t o r vessel as w e l l as w i t h i n . The e f f e c t s o f f u e l c i r c u l a t i o n on t h e e f f e c t i v e delayed n e u t r o n f r a c t i o n must b e considered in d e s i g n i n g Sole t r a n s i e n t c o n d i t i o n s i n v o l v i n g primary system flow changes. As discussed i n Chapter 4 , t h e s e e f f e c t s are well understood, and e x p e r i e n c e i n t h e d e s i g n and o p e r a t i o n of c i r c u l a t i n g f u e l r e a c t o r s g i v e s confidence t h a t t h i s f e a t u r e w i l l n o t cause any parti CU 1Elk- p rob 1em. F i s s i o n p r o d u c t s i n t h e primary c i r c u l a t i n g l o o p p r e s e n t t h e u s u a l a

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r a d i o a c t i v e loops a l s o has a p o t e n t i a l BOP i n c r e a s i n g unwanted background s i g n a l s i n n u c l e a r i n s t r u m e n t a t i o n . Replacement sf i n s t r u m e n t s e n s ~ r s and i n t e r c o n n e c t i n g s i g n a l l i n e s w i l l i n some cases r e q u i r e remote maintenance t e c h n i q u e s . The r e f e r e n c e MSBR i s d e s i e e d t o have a core d i f f e r e n t i a l temperaAs i n o t h e r r e a c t o r s o p e r a t i n g w i t h a l a r g e ATs m e a n s must t u r e of 258'F. b e provided t o l i m i t thermal. stresses d u r i n g abnormal o p e r a t i o n a l e v e n t s The MSBR does n o t r e q u i ~ et h a t a Large amount of e x c e s s r e a c t i v i t y b e a v a i l a b l e . The a b i l i t y to a d j u s t f u e l concentrati~nd u r i n g o p e r a t i o n ~ R C It h e r e d u c t i o n s f 135xe p o i s o n i n g by gas s t r i p p i n g reduce two of t h e l a ~ g e s tr e a c t i v i t y requirements of o t h e r t y p e s of p l a n t s Total control r e a c t i v i t y r e q u i r e d for o p e r a t i o n will p ~ o b a b %b~ef on t h e o r d e r of 1% & / k . This s m a l l m o u n t of excess greatly reduces t h e p o t e n t i a l f o r l a r g e r e a c t i v i t y e x c u r s i o n s , t h u s e a s i n g requirements on s a f e t y rods. The a b L l i t y t o d r a i n t h e f u e l away f r o m t h e moderator i n t o a n o n c r i t h c a 6 c o n f i g u r a t i o n i s a very i m p o r t a n t f e a t u r e o f t h e molten s a l t r e a c t o r CORc e p t . The i n t e n t i s n o t t o u s e t h e f u e l d r a i n f o r fast shutdown b u t t o e

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loIlg-tel2Il ShUtdOWn wargin lander U F l U s U a l C i r C U E l s t EZlCeS 80 f a s t a c t i n g d r a i n valves are n o t r e q u i r e d . The r e f e r e n c e d e s i g n NSBR has t h e entire primary s a l t system in an %is arrangeoven where the temperature i s maintained a t about 1000'F. ment makes i t unnecessary t o F ~ s u l a t e'the p i p e s and vessels and removes from t h e r e a c t o r c e l l a mu%titucle 0% e l e c t r i c a l cables thermocouples d i s c o n n e c t s and containment penetrations t h a t would $ e required f o r h e a t e r s d i ~ e ~ t on l y the p i p e s and v e s s e l s . Some c ~ n n e c t ~ rand s signal t r a n s m i s s i o n l i n e s must e i t h e r b e designed t o s p e r a t e properly i n such an environment or must b e l o c a t e d in p e n e t ~ a t i ~ nt hs a t are cooled reb tabl y . lXSSlaK@

Experience with t h e MRE and Other F a c i l i t i e s

A l a r g e number of out-of-pile a d i n - p P l e Poops and s t h e r f a c i l i t i e s have been o p e r a t e d with molten s a l t a t ORNL o v e r the p a s t 28 y e a r s , and a l l Sf these have had instrUâ‚ŹR@ntatiQnandl c o f l t r o l S y s t e m O f Varying d e g r e e s sf eomplbexity. I n a d d i t i o n , w e a n d o t h e r s have o p e r a t e d hight u r e system containing molten metals o r gases$ and a number of s of t h e s e types have been a p e r a t e d i n the U.S. and abroad. e p r o v i d e d some experience in instrumentation that is i r e c t and u s e f u l i n f o m a t i o n has come f r o m

S u c c e s s f u l o p e r a t f e n of h u n d r e d s of thermocouples a t t a c h e d to t h e s a l t s y s t e m walls i n t h e MSRE g i v e s confidence that r e l i a b l e temperature measurements can b e made a$ the e l e v a t e d temperatures of m o l t e n - s a l t reactor systems Although t h e r e was considerable s c a t t e r i n t h e r e a d i n g s of t h e csupkes lander d i f f e r e n t h e a t e r s when t h e s a l t was actually isothermal, techniques of b i a s i n g the o u t uts Were used to p r o v i d e t h o r o u a c c e p t a b l e measurements [ 3 , ppe 2 2 - 2 4 ] The i m p u r t a n c e of c a r e f u l s e l t i m and c a l i b r a t i o n , d e t a i l s o f f a b r i c a t i o n and i n s t a l l a t i o n , and s t r i c t y c o n t r o l was e v i d e n t , as o n l y 62 of t h e 330 thermocouples f a i l e five y e a r s of operation. ressure and d i f f e r e n t i a l pressure measurements in the c o o l a n t s a l t systems w e r e made u s i n g NaK-fiIled t r a n s m i t t e r s . No d i r e c t measurement of s a l t p r e s s u r e was made i n t h e p r i m a r y s y s t e m , where gas p r e s s u r e measurements were u s e d t o i n f e r s a l t - s y s tern p r e s s u r e Direct meaaure=nts are d e s i r a b l e i r e an MSBR, m d a d d i t i o n a l development may b e r e q u i r e suck a p p l i c a t i o n s The measurement s f s a l t f l o w rate i n t h e secondary s y s t e m w a s made by m e a m of a v e f ~ t u r iand a: NaK-filled d i f f e r e n t i a l p r e s s u r e t r a n s m i t t e r . No d i r e c t II1eL3SU%k3I[leWC W a s HLade Of flow ill the PriIELKy systefs. bEtsFJtnCh as t h e reactor W ~ Boperated w i t h c o n s t a n t p r i m a r y - s a l t flow rate, no part i c u l a r problem existed i n normal o p e r a t i o n . ks p a r t 0% t h e plant prot e e t i o n system i n s t r u m e n t a t i o n , pump motor c u r r e n t w a s measured. Though n o t a precise i n d i c a t i o n of flow, this measurement p l u s pump speed gave adequate a s s ~ r a n c eof flaw. T h a t is, t h e pump mtsr c u r r e n t would be less than normal even thou the s p e e d w a s normal i f f o r some reason the e

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s a l t f l o w w a s reduced. D i r e c t measurement of the f l s w i n t h e primary s y s t e m would b e d e s i r a b l e f o r a power r e a c t o r , e s p e c i a l l y if v a r i a b l e f l o w i s used. Level measurements w e r e made with s i n g l e - p ~ i n t probes as w e l l as b u b b l e r s and f l o a t l e v e l systems. These o p e r a t e d very well over t h e life of t h e p l a n t , b u t each has l i m i t a t i o n s which m y n e c e s s i t a t e addit i o n a l development f o r application t o MSBR service, Containment p e n e t r a t i o n c a b l e seals were d i f f i c u l t and c o s t l y t o i n s t a l l , and their p ~ ~ f o r ~ w~a ~ s ~ n c~ eg i n &a 2l] . I n t h e f u r n a c e concept of t h e MSBR i t w i l l b e d e s i r a b l e t o Locate t h e seals i n thermalby i n s u -

lated areas. En addition t o valuable e x p e r i e n c e in i n s t r u m e n t i n g m o l t e n - s a l t syst e m , t h e M S B gave an o p p o r t u n i t y t o v e r i f y methods of a n a l y s i s o f t h e dynamics of c i r c u l a t i n g - f u e l r e a c t o r s me o p e r a t i o n w i t h 2 3 3 ~was p a r t i c u l a r l y i n t e r e s t i n g because of the u n u s u a l l y small e f f e c t i v e delayed n e u t r o n f r a c t i o n ( B e f f = O.SOlS>. Analyses and tests made p r i o r t o loading 2 3 3 ~into t h e MSW gave confidence t h a t t h e system w o u l ~ lbe w e l l behaved w i t h r e g a r d t~ s t a b i l i t y and c o n t r o l l a b i l i t y 6 4 , p p . 32-35; 5, p. 4 4 1 . R e s u l t s of tests perforlned a f t e r loading were i n good agreement w i t h the p r e d i c t i o n s [ 6 , p . 91. 'Eke MSM rod c o n t r o l l e r w a s designed t o make t h e reactor o p e r a t e i n a had-fQlhJWing, o r ~ e a c t ~ ~ - ~ l a v e - t o - P o mode a d , i?n t h e power range In t h i s mode the o p e r a t o r s e l e c t e d t h e desired temperature of t h e salt Peaving the r e a c t o r core, and the steady-state reactor power w a s determined e

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by t h e r a t e a t which heat w a s r e j e c t e d by t h e a i r - c o o l e d h e a t exchanger i n t h e secondary s a l t s y s t e m From an e x p e r i m e n t a l viewpoint this allowed e power l e v e l , with p r a c t i c a l l y no easy automixtic c o n t r o l of t e m p e r a t ~ ~and i n t e r a c t i o n between them. For a power reastar t h i s scheme has the p ~ t e n t i a l f o r c o n t r o l l i n g s t e a m temperature independently of ~ B W ~level. K The c o n t r o l l e r used on the MSRE combined many f e a t ~ r e scomonly used a t O W L t o m e e t t h e specific requirements of t h a t reactor. Its performance was good, as p r e d i c t e d by a n a l y s P s , and e ~ c ~ u r a g euss t o use such a c s n t r o l l e r as p a r t of t h e overall MSBR p l a n t c o w t r ~ lsystem. me d i g i t a l data c o l l e ~ t i n ga d computing system f o r t h e KSE W ~ S used e x t e n s i v e l y w i t h e ~ c e l k r~e ts u l t s ..... ,:.:.w

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a f t e r an i n i t i a l debugging p e r i o d was over 95% [7, p . 551. me system proved i n v a l u a b l e for t h e t i m e l y and ~ C O ~ Q colbecting, I R ~ ~ l o g g i n g , and m a l y z i n g of e x p e r i m e n t a l d a t a g e n e r a t e d by t h e MSRE. I n a d d i t i o n , i t was used t~ p r o v i d e o p e ~ a t oguidance ~ through t h e s t a n d a r d p r i n t o u t s f signals i n the form of r o u t i n e p t ~ i o d i cl o g s , alarm signal printout, r o u t i n e c a l c u l a t i o n s such as heat balance and r e a c t i v i t y balance, and QperatOK-demnded f u n c t i o n s and c a l c u l a t i o n s . I t was used e x t e n s i v e l y f o r the c o n t r o l and i n s t r u m e n t a t i o n o f r e a c t o r dynamics t e s t s , such as frequency response t e ~ ~ p e r a rte~s p~o en s e experiments [ S I , f o r r e t r i e v ing and p r o c e s s i n g d a t a p r e v i o u s l y s t o r e d on magnetic t a p e s for a n a l y s i s , and t o p r o v i d e i n f o m a t i o n r e l a t i v e t o the t i m e , cause, and e f f e c t of abnormal operating e v e n t s . Programs w e r e developed t o aid i n calibrat i o n of analog system and i n d i a g n o s i s of troubles A new program w a s developed f o r a fast F o u r i e ~t r a n s f o r m which was p r o g r a m e d to run on l i n e in background t h e and which w a s used routinehgr f o r on-line a n a 8 y s k s f n e u t r o n f l u c t u a t i o n d a t a . By use o f this program i t w a s p o s s i b l e t o monitor t h e bubble f r a c t i o n i n t h e f u e l salt [ 9 , l O ] . e

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p r e l i m i n a r y studies StartbBp,standby and shutaown p ~ ~ ~ e d ~ e s have been carried out on the reference design MSBR, d t h o a f g k o n l y to t h e point of deter~nain f e a s i b i l i t y . I t a naakimg these analyses seve~al b a s i c restraints on ape a t i o n of the p l a n t ~ e reco ~ e ized. The f r e e z i n g temperatures of the p r i m a r y and secondary s a l t s are ch that the s a l t systems must b e filled and circulating i s s t h e r a l l y at l808"P b e f o r e power withdrawal can be initiated by d e s r e a s i n zhe coolant-salt temperature. To avoid f r e e z i n g of t h e salt ent excessive temperature gradi@tat%,the EknifnarTB feedwater o r steam teTRperatUre to the steam generareference d e s i g n system must vary between 1000째F at zero i n the 8 ts 168% power range. I n addition, the a f t e r h e a t

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t h e feedwater and h e a t rejection system remain in operation f o l l o w i n s h u t d a m of t h e main steam s y s t e m * M S S ~of t h e special s y s t e equipment needed to handle t h e startup and shutdown conditions in W station are t h e ~ e f o k - eassociated with the s c e a - p o w e r s y s t e m . me qeairementa impose some d e p a r t u r e from tern used in conventional f o s s i l - f i r e d s u p e r c r i t i c a l t s and will r e q u i r e f u r t h e r study. Different steam for example reentrant or concentric-tube ot as 768"F, and w o l d 1 . An auxiliary boil s a r y f a r s t a r t u p from the cold sonditisn. me pr-oposed general arrmgement of the s t e a m s y s t e m of t h e KSBR reference desi is described in the d e s i PepoKt 61, Sect. 51 and in &ZLpteK 8 Sf t h i s % e p O r t .

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The dynamics and control s t u d i e s of %BR p l a n t s have been cencent r a t e d about the n o m 1 o p e r a t i n g power range, and a series of s t u d i e s h a s been made t o e x m i n e t h e s e o p e r a t i n g c h a r a c t e r i s t i c s [l%,l2]. me s t u d i e s have been implemented w i t h analog and h y b r i d computer s i m u l a t i o n s of t h e p l m t c h a r a c t e r i s t i c s [13,14]. All of t h e s i m u l a t i o n s have been p a t t e r n e d a f t e r the W B R r e f e r e n c e d e s i g n [ l ] ,brat t h e nature of t h e models i s such thag t h e y would have g e n e r a l a p p l i c a b i l i t y . For t h e purpose of t h e s e a n a l y s e s t h e MSBR p l a n t c o n s i s t e d of a graphite-moderated, c i r c u l a t i n g - f u e l reactur, a shell-and-tube h e a t exchanger for t r a n s f e r r i n g t h e g e n e r a t e d h e a t t o a secondary coolant s a l t , a shell-and-tube superc r i t i c a l steam g e n e r a t o r , and several p o s s i b l e c ~ n t r o lsystems. Due t o t h e very n o n l i n e a r n a t u r e of the once-through steam g ~ ~ ~ r a t ~ l ~ i t was deemed n e c e s s a r y to have a highly d e t a i l e d model of this p a r t of t h e system. To g e t a f e e l f o r overall. p l a n t p e r f o r m n c e , t h e e a r l i e r models used lumped-parmeters l e g - m e a ~ - d i g f e r e n % i a l - t e ~ ~ @ r ~atnuar les s i m u l a t i o n of t h e s t e a m g e n e r a t o r , a l t h o u g h t h e accuracy w 8 s known to b e ~everePyl i m i t e d . At t h e same t i m e , a h y b r i d d i g i t a l - a n a l o g model was developed and used i n i t i a l l y t o examine t h e s t a b i l i t y of t h e steam genera t o r [Is]; subsequently, i t w a s expanded and r e f i n e d at t h e newly a c q u i ~ e d ORNL h y b r i d computing f a c i l i t y . The h y b r i d model of t h e steam g e n e r a t o r was combined w i t h t h e a n a l o g model of the o t h e r p l a n t c ~ ~ ~ p ~ ~r ee snu ltt isn,g i n an o v e r a l l simulation. i n which c o n s i d e r a b l e confidence could b e p l a c e d . R e p r e s e n t a t i v e transient r e s p o n s e s u s i n g this model. are d e s c r i b e d i n Refe r e n c e 14. The g e n e r a l v a l i d i t y of t h e a l l - a n a l o g models was confirmed, a l t h o ~ g f n , as expected, BOPlle disagPeement i n a b s o l u t e Values e x i s t s . 'Fhe t r e n d s i n d i c a t e d i n the analog s t u d i e s are C Q P K ~ C % , b u t the magnitude and rates of change of v a r i a b l e s d u r i n g t r a m s i e n t s should b e used o n l y as general guides. The h y b r i d model h a s been used t o s t u d y c s n t r ~ schemes l and normal plant maneuvering. Some ~ O I Y severe t r a n s i e n t s were exmined t o g e t a f e e l f o r system response t o abnormal s i t u a t i o n s . '%he severity of t h e t~ansients t h a t can b e run on t h e h y b r i d s i m u l a t i o n model i s , however, some~hatlimited by t h e steam generator model, which U S ~ S 0.5-se~ond ea%c d a t i s n a l t i m e s t e p s . Consequently, an e f f o r t i s underway t o improve t h e accuracy of an a n a l o g steam-generator model so t h a t i t s greater speed c a p a b i l i t y can b e used t o s t u d y severe t r a n s i e n t s and complement the plant safety analysis.

...... :<.:

Analysis of S t e a d y - S t a t e C o n d i t i o n s .... .2 @..

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The first step i n the f o r m u l a t i o n of a c o n t r o l system to e n a b l e the p l a n t t o undergo changes i n Boadl was t o determine t h e s t e a d y p a r t - l o a d t e m p e r a t u r e and f l o w p r o f i l e s for t h e p l a n t between 20 and lOQ%. POP i n i t i a l c o n s i d e r a t i o n s i t w a s d e s i r a b l e t o f i x o r predetermine t h e s t e a d y - s t a t e v a l u e s of some v a r i a b l e s f o r p a r t - l o a d o p e r a t i o n . Turbine l i m i t a t i o n s r e q u i r e t h a t t h e t u r b i n e t h r o t t l e temperature be held n e a r l y constant (1080째F f o r t h e eases s t u d i e d ) , and t h e feedwater tempera t u r e W i l S h e l d Constant 88 w e l l (70QOP). me prfTiEIPy s a l t f l o w r a t e W a s assumed ~ ~ n s t a n att d e s i p p o i n t f o g s t e a d y - s t a t e ~onsiderations. With

322

these l i m i t a t i o n s imposed, we found t h a t the s e c o n d a r y - s a l t temperature a t t h e steam g e n e r a t o r o u t l e t could n o t b e h e l d above the s a l t f r e e z i n g p o i n t at p a r t l o a d s beLow about 50%. A need is i n d i c a t e d f o r effect i V & deCQtaplil2g Of l o a d e f f e c t s On S d t t e I X p e r a t U K e s . Some p o s s i b i l i t i e s are: (1) a l l o w i n g t h e steam t e ~ ~ ~ p e r a t ut or eincrease above i t s 1000째F d e s i g n p i n t as t h e I s a d d e c r e a s e s , w i t h subsequent a t t e m p e r a t i o n s f the steam with i n j e c t e d feedwater; (2) inereasin t h e f e e dwa t er temp er a t u r e a b O V e its 780째F d e s i g n p o i n t as the load deCKeaSe%; ( 3 ) reducing t h e number ~f steam g e n e r a t o r s i n use as I s a d d e c r e a s e s ; and ( 4 ) u s i n g a s a l t th~ottlingv a l v e t o bypass some of t h e s e c o n d a r y - s a l t f l o w around t h e primary heat exchanger to reduce the temperature of the salt e n t e r i n g the steam g e n e r a t o r . Steam a t t e m p e r a t i o n and secondary s a l t bypass w e r e the s u b j e c t Of a d d i t i o n a l steaay-state a n a l y s i s of t h e p i a n t concept E i t h e r schene o r a combination of the ~ W Qa p p e a r s t o permit t h e establishment of acceptable part-load o p e r a t i n g c o n d i t i o n s .

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Analysis of T r a n s i e n t B e h a Q b r me rnodels described have beera. f o r t r a n s i e n t a n a l y s i s of the p l a n t and ppopo.S@d C o n t r o l SChelraeS. The power o p e r a t i n g range for a typical p l a n t is expected t o b e f r o m approximately %OX t o POOX of f u l l d e s i g n load. T h r o u g h ~ u tt h i s l o a d range t h e stearn temperature t~ t h e t u r b i n e t h r o t t l e must b e h e l d e s s e n t i a l l y c o n s t a n t , the p r i m a r y - and s e c o n d a r y - s a l t temperatures and f l o w rates must b e k e p t w i t h i n a c c e p t a b l e limits, and t h e r e s u l t i n g stresses due t o induced t h e m % g r a d i e n t s m u s t remain within a c c e p t a b l e ranges. A master l o a p r o g r m e r m y b e neeaea to d i v i d e the required i s a a demand among t h e m u l t i p l e coolant lssps and steam g e n e r a t o r s . It should b e p o s s i b l e t o s p e r a t e the p l a n t a t p a r t i a l l o a d s by o p e r a t i n g some l o o p s at 106% c a p a c i t y w h i l e o t h e r loops deliver no power. The c o n t ~ stbtdtes ~ l have shown t h a t stable p l a n t : load control m y be accomplished using two b a s i c c o n t ~ o ll o o p s : a steam temperature c o n t r o l l e r and a KESK~OK autfet tefnpe%atUr@C Q n t r O I l e r . '%S aShieVe c l o s e ContrQB O f Steam teIllperatUrC? d u r i n g ioaa transi n t s i t is necessary t o vary the s e c o n d a r y - s a l t f l o w rate i n the steam e n e r a t o r . An a d d i t i o n a l c o ~ ~ t subsystem r ~ l may b e n e c e s s a r y i f a s a l t b y p a s s valve i s used i n o r d e r t o m a i n t a i n the d e s i r e d cOQlaIllt s a l t tC?mpe9atUr@s. me %eaCtQrOutlet terzBpeKat examined was s i m i l a r ts that used s u c c e s s f u l l y ow t h e M A l o a d demand s i g n a l determines the r e a c t o r outlet t e m p e r a t u r e s e t point. The measured reactor i n l e t temperature i s s u b t r a c t e d from the r e a c t o r o u t l e t : temperature s e t p o i n t , and s i n c e t h e p r i m a r y - s a l t flow r a t e i s c o n s t a n t , a reactor power set p o i n t i s generated by m u l t i p l y i n g this bii" by % . pPC?pOrtiona%ity ConStallt. 'Phi? EEasUred Value Of reactor P O W E T ( f r o m neutron flux) is compared with the r e a c t o r power s e t p o i n t , and any error i S fed t h e C Q I I t r O l rod SerV f o r a p p r o p r i a t e r e a c t i v i t y a d j u s t ment. 'Eke % e a C % O r power set p o i n t , enerated from t h e o u t l e t temperature s e t p o i n t and t h e measured K ~ ~ C ~ Oi nE l-e t t e m p e r a t u r e , is a f u n c t i o n of the reactor inlet temperature d u r i n g a t r a n s i e n t and t h u s a f m ~ t i ~ of n a y n m i c load.

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322

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There are c e r t a i n l y o t h e r p o s s i b l e c o n t r o l schemes %or a c h i e v i n g s a t i s f a c t o r y p l a n t p e r f o r ~ ~ n ~Analog e. s i m u l a t i o n s have shown t h a t an i n t e g r a t e d c o n t r o l scheme is e s s e n t i a l to good performnce. Iâ‚Ź excess i v e thermal stresses are produced by the t r a n s i e n t s t h a t accompany load changes, they can b e reduced by v a r y i n g t h e primary s a l t f l o w rate as a f u n c t i o n of l o a d . ake small i s o t h e r m l temperature c o e f f i c i e n t 0% r e a c t i v i t y ( s e e Chapter 4 ) i m p l i e s t h a t only modest amounts of c o n t r o l r e a c t i v i t y are needed t o accompEish p l a n t load m n e u v e r i n g . FOP the r e f e r e n c e d e s i g n , a t y p i c a l maneuver from 58% to 100% power a t a rate of 5%/min r e q u i r e d 0.05% &k/k and a K a t e Sf Q.OOOB%/seC 6 k / k . m@ m a X h U T U SYStCZEE t@mperatram r a t e of change f o r t h i s t r a n s i e n t was about O.3"F/sec a t t h e r e a c t o r outlet

.

Accident Analyses

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The most l i k e l y a b n o r m l power e x c u r s i o n s W Q U E ~r e s u l t from sudden changes i n l o a d demand OK r a p i d changes i n s a l t flow rate i n e i t h e r t h e primary o r secondary system, as a r e s u l t of pump o r power f a i l u r e . A few l i m i t e d c a s e s of t h P s t y p e have been examined. on the h y b r i d s i m u l a t i o n . Some l e s s - l i k e l y r e a c t i v i t y anomalies were a l s o b r i e f l y examined on t h e h y b r i d model. As d i s c u s s e d in Chapter 4 , c o n c e i v a b l e r e a c t i v i t y changes may r e s u l t from primary flow v a r i a t i o n , f u e l a d d i t i o n a c c i d e n t s , c o r e geometry changes, o r f a i l u r e of one o r more c o n t r o l r o d s . A reactor shutdown QP p r o t e c t i o n system must b e c o o r d i n a t e d with t h e s a l t c i ~ ~ u l a t i ol ono p s and t h e steam p l a n t . I f t h e l o a d is suddenly l o s t , t h e r e a c t o r power g e n e r a t i o n must b e reduced t o avoid o v @ r h @ a t h g . S i m i l a r i l y , i f the r e a c t o r is s h u t down the steam l o a d must b e q u i c k l y reduced t o a v o i d subcooling o r f r e e z i n g of t h e s a l t . S i m i l a r s i t u a t i o n s a r i s e due to s a l t c i r c u l a t i o n pump f a i l u r e . F u r example, i f primary f l o w is l o s t , followed by an a p p r o p r i a t e r e d u c t i o n i n l o a d demand and r e a c t o r power, t h e primary salt could s t i l l f r e e z e i n t h e h e a t exchangers because of the ilICrei3sed d w e l l t i m e Unless SecQndaafy %POW iS a l s o lfeduced. The p l a n t emergency procedures c l e a r l y w i l l b e somewhat complex bec a u s e of the h i g h salt f r e e z i n g t e m p e r a t u r e s , and a c a r e f u l analysis will b e needed t o d e r i v e s a t i s f a c t o r y s o l u t i o n s e

Reactivitv Control

Long-term r e a c t i v i t y adjustments are expected t o b e accomplished by v a r y i n g the f u e l c o n c e n t r a t i o n . Normal r e g u l a t i n g and shimming f u n c t i o n s f o r load f o l l o w i n g and shutdown are w i t h i n the c a l c u l a t e d c a p a b i l i t i e s of a f e w g r a p h i t e r o d s , as proposed for t h e r e f e r e n c e d e s i g n p. 641. Some e v e n t s may b e a n t i c i p a t e d t h a t would r e q u i r e a d d i t i o n a l n e g a t i v e r e a c t i v i t y o r r e a c t i v i t y rates beyond the c a p a b i l i t y of t h e g r a p h i t e rods a l o n e . Poison r o d s could be used to p r o v i d e t h i s a d d i t i o n a l r e a c t i v i t y ~ o n t r o and l t o p r o v i d e s u b s t a n t i a l shutdown margin, Having poison rods in t h e c o r e d u r i n g normal ~ p g ~ f a t i ois n u n d e s i r a b l e because of t h e i r a d v e r s e e f f e c t on b r e e d i n g . The probable role of t h e poison r o d s , then, i s t o b e h e l d o u t s i d e of t h e c o r e , p o i s e d for r a p i d s h u t d ~ w ni f needed.

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324

"hey may a l s o b e used f o r a d d i t i o n a l skimming d u r i n g c o r e l o a d i n g o r f o r o t h e r o p e r a t t o n s o r a b n o r m a l i t i e s b u t t h e exposure a t power will b e short

and che e f f e c t on b r e e d i n g and r d life w i l l be s m l l . We do n o t presently a n t i c i p a t e t h a t extremely fast insertion, or "scram,t' of t h e r o d s w i l l b e n e c e s s a r y , although r e l i a b l e i n s e r t i o n must b e assured e

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Ins t r u m e n t a t i o n ,........_I

In t h e r e f e r e n c e MSBR, t h e entire r e a c t o r cell w i l l b e at about 1000°F. Thus any nuclear d e t e c t o r s which are located i n t h i s space must be capable at Such h i g h temp@ratUI'e QT e l s e the)' m U S t b e Cooled. No e presently a v a i l a b l e f o r o p e r a t i o n above 6O0-9QOoF, and even for these terngePatUres Cmlgr S p e C i a P deVâ‚Ź2%8plllentalt n s d e h e X i S t. S i d l a r p r o b l e m e x i s t in t h e l i q u i d meta% breeder r e a c t o r p r o g ~ a m , and some development work i s b e i n g done, b u t no s i g n i f i c a n t progress has been announced [%8]. A c o o r d i n a t e d d e t e c t o r aeveiopment program is needed f o r t h e %%oPten-SaPt Reactor Program. It may be possible 5 s l o c a t e i o n i z a t i o n chambers i n specially cooked wells OK thimbles l o c a t e d o u t s i d e the reactor v e s s e l . For u s e i n t h e r e a c t o r p r o t e c t i o n s y s t e m , such chamber welabs W Q U l d have t o b e designed w i t h performance r e l i a b i l i t y as r e q u i r e d of t h e p r o t e c t i o n system, s i n c e f a i l u r e s f t h e c o o l i n g systems would bring a b o u t f a i l u r e a$ the d e t e c t o r s . Neutron f l u c t u a t i ~ na n a l y s i s proved t o b e a v a l u a b l e tool for monitO%ing aIl0Ed.QU.S bC?haVior in t h e M S m [ g , 1 8 ] . UnfoPtUlately, Qne O f t h e requirements f o r obtainin good r e s u l t s w i t h t h i s t e c h n i q ~ eis a h i g h d e t @ c t i Q ne f f i c i e n c y f8P C Q P g c o u p i e c ~~ l e u t r o n s . mile no detailed ealcbnl a t i o n s have been made of i - ~ e ~ t rf l~unx e s o u t s i d e t h e r e f l e c t o r and vessel, w e estinate t h a t i n t h e NSBR t h e s e f l u x e s will b e t o o low t o p r o v i d e %he a l - t o - n o i s e ratio f o r some types of f l u c t u a t i ~ na n a l y s i s the proposed nuclear d e t e c t o r l o c a t i o n s are w i t h i n the hight e m p e r a t u r e p r i r y containment oven and have i n ~ o ~ f r mt~h n e problem of containment p e n e t r a t i o n seals. G e n e r a l l y , t h e s p e c i f i c a t i o n s f o r penetrations f o r nuclear d e t e c t o r s are demanding t h a n t h o s e f e r process sensors, because ~f t h e t y p i c a l l y v e r y s m l l s i g n a l c u r r e n t s d e l i v e r e d . The l o c a t i o n m d d e t a i l e d r e q u i r e m e n t s of these p e n e t r a t i o n s have n o t y e t been determined, but t h e need f5r some development work in this area is a n t i c i p a t e d . The s i g n a l t r a n s m i t t i n g lines w i l l r e q u i r e s p e c i a l d e s i g n and SQHle deVelopwent because Of the high-t@mperature enViPonXllent. Process Iststrbaraentrat$~~~

325

..... ;.= ,>

a p p l i c a b l e t o t h e MSBK. S i m i l a r l y , e x p e r i e n c e b e i n g g a i n e d by t h e u t i l i t i e s i n d u s t r y w i t h i n s t r u m e n t a t i o n of s u p e r c r i t i c a l p r e s s u r e s t e a m s y s t e m s w i l l b e a p p l i c a b l e t o t h e PTSBR. MSBR p r o c e s s i n s t r u m e n t a t i o n l o c a t e d o u t s i d e t h e b i o l o g i c a l l y s h i e l d e d areas and n o t an i n t e g r a l p a r t of t h e c o n t a i n m e n t s y s t e m can b e c o n v e n t i o n a l equipment. Some s t a n d a r d components, however, may req u i r e u p g r a d i n g , and a s t r i c t q u a l i t y c o n t r o l program w i l l b e r e q u i r e d to e n s u r e a l e v e l o f r e l i a b i l i t y and performance commensurate w i t h MSBR requirements. A l l p r o c e s s i n s t r u m e n t a t i o n components l o c a t e d w i t h i n t h e c o n t a i n ment c e l l s o r as an i n t e g r a l p a r t s f t h e c o n t a i n m e n t s y s t e m must p r o b a b l y b e c o n s i d e r e d d e v e l o p m e n t a l . These components are p r e d o m i n a n t l y p r i m a r y s e n s i n g e l e m e n t s f o r measurement of f l o w rates, p r e s s u r e s s l e v e l s , w e i g h t s , and t e m p e r a t u r e s i n t h e s a l t - c o n t a i n i n g p i p e s and v e s s e l s , i n t h e a s s ~ ~ i a t ep d u r g e and o f f - g a s s y s t e m s , and i n t h e s a l t c h e m i c a l p r o c e s s i n g f a c i l i t i e s * O t h e r s u c h components are f i n a l c o n t r o l e l e m e n t s ( s u c h as o f f - g a s C Q R ~ ~v aOl v~e s ) , Peaa-tJire and p i p i n g c o n n e c t i o n s t o t h e s e n s i n g and final c o n t r o l e l e m e n t s , r e m o t e l y o p e r a t e d d i s c o n n e c t s , and c o n t a i n m e n t p e n e t r a t i o n seals. The e l e c t r i c a l c o n d u c t i v i t y of t h e MSBR s a l t s w i l l b e a f a c t o r i n s e l e c t i n g t h e t y p e S % primary s e n s i n g e l e m e n t s t h a t can b e used. The c o n d u c t i v i t i e s of MSBK s a l t s are e s t i m a t e d t o b e a b o u t 1 mho/cm - a b o u t t h e s a m e as MSRE s a l t s . T h i s means, f o r example, t h a t m a g n e t i c flowmeters p r o b a b l y c a n n o t b e u s e d , and most of t h e d e v i c e s will b e similar t o t h o s e used o~ t h e M S E . Some new t e c h n i q u e s are b e i n g i n v e s t i g a t e d which show some p r o m i s e f o r u s e w i t h Pow-conductivity s a l t s . S O M development ~ w i l l b e r e q u i r e d t o a d a p t MSRE c o n t r o l c ~ m p o n e ~ l t s t o t h e h i g h e r p r e s s u r e s and t e m p e r a t u r e s t h a t w i l l e x i s t i n p o r t i o n s of t h e MSBK. Development s f o t h e r equipment and t e c h n i q u e s , s u c h as elect r i c a l p e n e t r a t i o n s i n t o s a l t - c o n t a i n i n g p i p e s and vessels, would undoubte d l y l e a d t o improved i n s t r u m e n t a t i o n .

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The d e t a i l e d rod r e q u i r e m e n t s w i l l b e a f u n c t i o n of t h e p a r t i c u l a r r e a c t o r d e s i g n . "he rod w o r t h s w i l l v a r y w i t h t y p e , s i z e , and l o c a t i o n , S O t h a t d r i v e s p e e d s c a n n o t b e s p e c i f i e d u n t i l t h e p h y s i c a l and n u c l e a r d e s i g n s are w e 1 8 advanced. The m e c h a n i c a l desPgn of t h e d r i v e m e c h a n i s m is d i s c u s s e d i n C h a p t e r 8.

S a l t T h r o t t l i n g Valves One of t h e more p r o m i s i n g p l a n t c o n t r o l schemes depends upon t h r s t % l i n g i n a s e c o n d a r y s a l t bypass a r o u n d t h e p r i m a r y h e a t exchanger. ( T i g h t s h u t - o f f is n o t r e q u i r e d af the valves i n t h i s b y p a s s . ) The m a x i m u m and minimum f l o w rates and t h e r a t e o f change of f l o w r a t e nece s s a r y t o a c h i e v e s a t i s f a c t o r y p l a n t c o n t r o l will weed t o be f a c t o r e d i n t o t h e development of a valve far this service. Valve d e s i g n i s d i s c u s s e d in mapter 8.

Digital Computer A p p l i c a t i o n f o r Control and Data Handling

Chemical Plant I n s t r u m e n t a t i o n and C o n t r o l

The i n s t r u m e n t a t i o n requirements of a f u l l - s c a l e chemical p r o c e s s i n g p l a n t have, so f a r , received only niraimal a t t e n t i o n from instrument des i g ~ t e r s . %e p ~ o c e s s e sinvolved have been instrumented a d c o n t r o l l e d on l a b o r a t o r y o r pilot p l a n t scales, b u t n o t w i t h t h e volumes and r a d i a t i o n l e v e l s expected i n t h e f u l l - s c a l e p l a n t . E a r l y e v a l u a t i o n of potential problems is needed t o enable i n i t i a t i o n of r e q u i r e d development on a timely basis

-

Uneert ain ti e s and Alt ernat i v e s

There are s e v e r a l u n c e r t a i n t i e s r e g a r d i n g the o v e r a l l control of: an MSBW t h a t w i l l r e q u i r e additional analyses and c s n s i d e r a t i o n of alternat i v e s . En p a r t i c u l a r , t h e h i g h f r e e z i n g temperatures of t h e s a l t s create t h e need f o r s p e c i a l c o n s i d e r a t t o n s i n load and flow control. Urnusual c o n d i t i o n s o r f a i l u r e s , such as a failure of a pump i n a s a l t l o o p , will r e q u i r e s p e c i f i c responses t o a v o i d s a l t f r e e z i n g . The behavior of mult i p l e loops of a lar e p l a n t w i l l need t o b e c a r e f u l l y p r o g ~ a m e dt o avoid f r e e z i n g prolaleas. As mentioned e a r l i e r i n t h i s chapter, m a i n t a i n i n g desirable o r accepta b l e s t e a m a d c s o i a n t - s a i t t e m p e r a t u r e s in t h e s y s t e m under papt-ioad n d i t i a n s i s a fundamental problem. S e v e ~ a lapproaches have been investited f a r p o s s i b l e r e s o l u t i o n of t h i s d i f f i c u l t y . One is the u s e of flowp r o p o r t i o n i n g v a l v e s t o bypass c o o l a n t around t h e primary heat exchanger a d t h i s i s a very attractive scheme from s t r i c t l y t h e e s n t r o l v f e q o i n t . Relatively complete s e p a r a t i o n of l o a d e f f e c t s from the s a l t operating c s n d i t i s n s i s p o s s i b l e u s i n g one 0% two v a l v e s , and s a l t temperatures and steam conditions can be optimized more o r less i n d e p e n d e n t l y . p r o p o r t i o n ing valves fop molten s a l t w i l l have to b e developed if t h i s scheme is to b e used. The second agsp~oach, which h a s been briefly examined, is t o allow t h e temperature s f the steam leavin t h e generator t o rise at reduced h a d e and t o attemperate i t w i t h feedwater addition t o r e g a i n p r o p e r eond i t i o n s f o r the t u r b i n e . Attemperation i s used i n modern s u p e r c r i t % c a % fossil-fired steam p l a n t s but is u s u a l l y f o l l ~ w g dby a reheatel- ~r super-

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h e a t e r t o a s s u r e t h a t no feedwater is c a r r i e d over t o t h e t u r b i n e s . The a p p l i c a t i o n of t h i s t e c h n i q u e t o an PISBR p l a n t w i l l r e q u i r e c a r e f u l 8 tudy b e f o r e i t s p r a c t i c a b i l i t y can b e a s s u r e d . A t h i r d p o s s i b i l i t y f o r maintaining s a t i s f a c t o r y conditions during p a r t - l o a d o p e r a t i o n i s t h e s t a g i n g of t h e m u l t i p l e l o o p s , t h a t i s , opera t i n g some l o o p s n e a r d e s i g n p o i n t w h i l e o t h e r s are i d l i n g . This method of o p e r a t i o n h a s n o t y e t been i n v e s t i g a t e d on t h e computer s i m u l a t i o n s . C o n t r o l and t r a n s i e n t s t u d i e s have not y e t produced complete d a t a on t h e t h e r m a l t r a n s i e n t s t h a t can r e a s o n a b l y be expected t o occur a t c r i t i c a l p o i n t s i n t h e vessels and p i p i n g . The c o n t r o l schemes p r o p o s e d s o f a r have i n v o l v e d m a i n t a i n i n g t h e r e a c t o r i n l e t temperature n e a r l y c o n s t a n t w h i l e t h e o u t l e t t e m p e r a t u r e v a r i e s as some f u n c t i o n of l o a d ; t h e primary f l o w remains c o n s t a n t . If thermal stresses are determined t o b e a problem a t normal maneuvering rates o r under o t h e r a n t i c i p a t e d t r a n s i e n t c o n d i t i o n s , then a l t e r n a t i v e schemes way need t o be c o n s i d e r e d . One p o s s i b i l i t y i s t o v a r y t h e primary flow rate 80 as t o m a i n t a i n t h e r e a c t o r t e m p e r a t u r e rise more n e a r l y c o n s t a n t as l o a d i s v a r i e d . Some c o n t r o l of primary flow, perhaps on-off r e d u c t i o n t o pony-motor flow, may b e d e s i r a b l e t o avoid r a p i d changes i n s a l t temperatures under some emergency c o n d i t i o n s I t w i l l b e d e s i r a b l e t o m a i n t a i n a long-term r e a c t i v i t y b a l a n c e i n an MSBR system. The e s t a b l i s h e d t e c h n i q u e i n v o l v e s c a r e f u l l y a c c o u n t i n g for a l l s i g n i f i c a n t r e a c t i v i t y a d d i t i o n s and withdrawals from t h e r e a c t o r system, i n c l u d i n g c a l c u l a t i n g t h e b u i l d u p or burnout of p o i s o n s . This w i l l be d i f f i c u l t i n an MSBR, however, because many f a c t o r s t h a t can a f f e c t r e a c t i v i t y may n o t b e d e t e r m i n a b l e w i t h continuous o n - l i n e p r o c e s s i n g . Neutron f l u c t u a t i o n a n a l y s i s was a p p l i e d t o t h e MSRE f o r measurement of v o i d f r a c t i o n i n t h e f u e l and h a s been used i n o t h e r r e a c t o r s f o r s u b c r i t i c a l i t y measurement. With f u r t h e r development, i t may prove u s e f u l i n t h e MSBR. S u i t a b l e Ibocations f o r i o n i z a t i o n chambers have n o t been determined. The f u e l w i l l have a very s t r o n g i n h e r e n t (a,rz> s o u r c e , which i s h e l p f u l f o r e a s i n g s t a r t u p i n s t r m e n t a t i o n s e n s i t i v i t y requirements b u t a t t h e same t i m e t h e g r a p h i t e r e f l e c t o r w i l l b e an e f f e c t i v e s h i e l d f o r d e t e c t o r s located outside the r e a s t o r vessel.

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s t a g e of i n v e s t i g a t i o n whether o r n o t i t w i l l b e n e c e s s a r y t o l o c a t e det e c t o r s i n t h e c o r e . This d e t e r m i n a t i o n is a n i m p o r t a n t t a s k t o b e performed e a r l y in a s p e c i f i c MSBW d e s i g n . Complete i n s t r u m e n t a t i o n of t h e primary system, i n c l u d i n g s a l t p r e s s u r e and flow measurements, is v e r y d e s i r a b l e . These measurements will r e q u i r e development of s u i t a b l e s e n s o r s . The MSRE was o p e r a t e d s u c c e s s f u l l y w i t h o u t d i r e c t measurement of primary s a l t p r e s s u r e and f l o w r a t e , and p o s s i b l y they are n o t e s s e n t i a l f o r a n MSBR, b u t i t would b e c o n v e n i e n t t o know t h e primary f l o w rate, e s p e c i a l l y i f t h e flow 2s t o b e v a r i e d by changing pump speed.

32 8

Evaluation

assessme t of the c o n t D l l a b i l f t y Of aR HSBa COmp Ked W i t h O t h e r power p l a n t co-ncepts reveals a number of f a v o r a b l e f e a t u r e s and a few features which add difficulty. bong the f a v o r h b l e -features are t h e n ~ c l e a rcharasteristics ID which be d e s c r i b e d as a o c i k . Comfortably long promp%-neutrOn %ifetheS a d a large pKODIgSt n@gatiVe teI!lperEktU%e c o e f f i c i e n t of react ivity y i e l d very d e s i r a b l e control characteris tics [ 3 , p . 621. Thus t h e c a p a b i l i t y f o r f a s t t r a n s i e n t s as a r e s u l t of conceivable r e a c t i v i t y anomalies is minimal [l, p . 1173. A p o s i t i v e moderator c o e f f i c i e n t c o n t r i b u t e s to make the i s o t h e r m 1 t e m p e r a t u r e c o e f f i c i e n t of reactivity f a i r l y small. This r e s u l t s i n v e ~ ymodest control r e a c t i v i t y requirements f o r mneuvering and perFaits v e r y small loaded e x c e s s r e a c t i ~ i t y . The l a r g e heat capacity of the molten s a l t serves as a b u f f e r t o absorb t h e e f f e c t s of r e a c t i v i t y t r a n s i e n t s and Lessen t h e i r i n f % w n e e on the p l a n t , a d m e l t i n g of fuel is mot a l i m i t a t i o n s i n c e F t i s already molten. Gaseous f i s s i o n p r o d u c t s are continuously s t r i p p e a from t h e salt, g r e a t l y reducing t h e i r u s u a l r e a c t i v i t y e f f e c t s , ZEKd the e n t i r e %eaetOr f u e l system opeKatâ‚ŹS from a l o w base pressure. The h i g h freezing temperatures of t h e s a l t s are negative features that complicate b o t h c o n t r o l a d p r o t e c t i o n to some e x t e n t i n t h a t special p r o v i s i o n s must b e made to avoid f ~ e e z i n gof t h e salt d u r i n g power OK Analysis indicates t h a t s p e c i a l c o n t r o l measures are neeintain proper s a l t temperatures under p a r t - l o a d c o n d i t i o n s . 1 s i t u a t i o n s , such as loss of salt c i r c u l a t i ~ n ,require he load m d reaucin flow i n adjacent l o o p s as well as re-

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e s i r c u l a t i n f u e l system a l t e r s t h e e f f e c t i v e delayed n e u t r o n f r a c t i o n s i n c e some of t h e d e l a y e d n e u t ~ o nare ~ e d t t e a o u t s i d e t h e reactor c o r e area. V a r i a t i o n of the f u e l salt flow rate, t h e r e f o ~ e ,w i l l affect: r e a c t i v i t g r SQIWZ extell%, b u t t h i s FS not expected to p r e s e n t ia S i g n i f i c a n t CCRltrpOl prob%@m. g f t h On-line f U d prOeeSsing, EkCCUKate F I I V ~ D ~ ~O o~n~t .r s la d l ~ n g - & e rr ~ e~ a ~ t i ~ ia tc e~o m t i n g w i l l b e difficult than i n p a s t e x p e r i e n c e , s i n c e a l a r g e number of variable f a c t o r s a f f e c t the reactivity balance to some degree. The n e t e f f e c t of d l these factors, however, is n o t e p e c t e d to present any s h o r t - t e ~ m control o r - t e r m bookkeeping u n c e r t a i n t i e s . BVe%l CQnCep%fob^ e a t i n g sf t h e s a l t system will make maintenance o p e r a t i o n s easier than i f the p i p i n g and vessels were i n d i v i d u a l l y h e a t e d and i n s u l a t e d , b u t more of t h e instrument s y s t e m s w i l l b e exposed t o t h e high-temperature environment. Because o f this and s o m e o t h e r requirements adequate instruments for a l l a p p l i c a t i ~ n sare n o t a v a i l a b l e o f f t h e shelf. Development has been S ~ Q W , however, because the r e q u i r e ments are such a strong function of t h e p a r t i c ~ l aa~p p l i c a t i o n and

~

~ ~i2 i ~ ~ r n ~ ~ ~ In s u m a r y , same of she c o n t r o l and i n s t r u m e n t a t i o n p r o b l e m w i l l b e c h a l l e n g i n g , b u t B Q W ~ i s expected t o b e beyond e x i s t i n g technoks c a p a b i l i t i e s . I n s t r u m e n t a t i o n and c s n t ~ o l .development problems sho n o t have a d e t r i m e n t a l e f f e c t on t h e o v e r a l l development s c h e d u l e f u r I

Os.

k..

329

References f o r Chapter 18

1.

Conceptual B e s i p Study o f a Single-Fluid Molten-Salt B ~ e e d e ~ Reactor, ORNL-4541 (19 71) 0

$.Fa-

2.

a. L. Moore, Fwther Discussion o f Inst-ntgtisn m d Contmls Beuehpment &xded for the Molten S a l t Bmedero Reactor, ORNE-TN330% (Aug. 5, 1971).

5.

MSR P m g m m Semimn. P P O ~ P .W e p t . Aug. 34, 1968, 88EaE-4344.

7.

6. D. Martin, J r . , hstmmenta%ion and Controls &k. Ann. P m g . Report, S e p t . 1, 1970, ORNE-4620.

8.

R. C. S t e f f y , Jr., P~equencyEesponse Testing of t h e IdoZ$en-Sa%t Reactor Experimerzt, OIRE3%-T?+-2823 (March 1 9 7 0 ) .

10.

e. Robinson, B. N . Fry, Det-e~nrincrfiionof the Void P~actioni n t h e MSRE Using S m l l Induced Presswe Pertwhation, OFW%-a%l%-23b$ (Peb. 6 , 1969) J.

0

12.

W. PI. S i d e s , Jr., ControZ S t u d i e s of a 2080-Mu(e} MSBR, OmL-W2927 (May 18, 1970).

13.

w.

14.

0. Id. Burke, Hybrid Conputer SimZation o f the IGBR, 0RML-'6p1-3767 (May 5, 1 9 9 2 ) .

15.

C. K. Samathan and A. A . Sandberg, U n i v e r s i t y of I l l i n o i s , Chicago, I P P i n o i s , and P. H. C l a r k , 0. W. Burke, and 8. S . S t o n e , ORNL, " T r a n s i e n t Analysis and Design E v a l u a t i o n of a Once-Tfnrough Steam Generator with t h e Aid of a Hybrid Computer," s u b m i t t e d f o r p u b l i c a t i o n in NucZear EiagineeAng m d B e s i p .

H . S i d e s , Jr., MSBR Control Studies: OR.NL-TPI-31Q2 (May 1971)

Analog Simulation Progrc&m,

330

11. FUEL PROCESSING

L. E. McNeese ~ r~e e~dnecr ei s Operation of a m o l t e n - s a l t r e a c t o r as a h i g h - p e ~ % ~ ~ - b made p o s s i b l e by t h e continuous p r o c e s s i n g of t h e fuel s a l t i n a f a c i l i t y t e r a t i o n s cont h a t is l o c a t e d a t the r e a c t o r s i t e . The most i ~ ~ p o r t a no p sist in HC2IilOVing fission product9 ( p P h c i p 8 P B y the H a r e earths) and %SOl a t i n g 233Pa from t h e r e g i o n of h i g h n e u t r o n f l u x d u r i n g its decay t o 2 3 % i n order t o h o l d n e u t r o n a b s o r p t i o n i n these mterials t o an a c c e p t a b l y l o w l e v e l . I t i s a l s o n e c e s s a r y t h a t excess uranium produced i n the system b e removed %OK sale, that t h e fuel s a l t b e maintained a t t h e p r o p e r redox p o t e n t i a l , and t h a t t h e oxide and c o r r o s i o n p r o d u c t c o n c e n t r a t i o n s i n t h e salt b e maintained at t o l e r a b l e levels. me rates a t which the f u e l s a l t must b e processed f o r 2 3 3 ~ aremoval and raPe-eartk removal are mutually dependent. I t w i l l be convenient t o d e f i n e t h e tern o'processing c y c l e as t h e t i m e r e q u i r e d f o r processi n g a volume of f u e l s a l t e q u a l t o t h a t c o n t a i n e d i n t h e r e ~ i c t o rsystem. me 'erewovaP t i m e s t for a given material i s t h e n an e f f e c t i v e cyePe time t h a t i s e q u a l t o the p~ocessing c y c l e t i m e d i v i d e d by the f r a c t i o n of %he material t h a t i s removed i n a p a s s through t h e p r o c e s s i n g system. A s shown i n F i g . 11.1, f o r a p a r t i c u l a r s i n g l e - f l u i d MSBR h a v i n g a b r e e d i n g r a t i o of l,O7, t h e r e q u i r e d r a r e - e a r t h removal t i m e can range from 58 days f o r a p r o t a c t i n i u m removal t i m e of 2 days t o about 18 days f o r a p r o t a c t i n i u m removal ti= of 20 days. The optimum c h o i c e of p r o t a c t i n i u m and r a r e - e a r t h removal t i m e s i s l a r g e l y dependent on the c h a r a c t e r i s tics of t h e p r o c e s s e s employed, For example, t h e present ~ a ~ e - e a ~ r et mho v d p r o c e s s r e q u i r e s t h a t p r o t a c t i n i u m b e removed from t h e s a l t p r i o r t o t h e removal of e a r t h s . Hence, w i t h t h i s process, t h e r a r e - e a r t h removal t i m e w i l l always b e as l o n g as o r l o n g e r t h a n the p r o t a c t i n i u m removal time. A s w i l l b e discussed l a t e r , a p r o t a c t i n i u m removal t i m e of 10 days and 8 ra~e-eartla removal t i m e of about 27 days are used w i t h t h e referemee p r o c e s s i n g sys tern.

...

.&

P r o c e s s e s i n v o l v i n g t h e selective chemical r e d u c t i o n of materials from t h e f u e l s a l t i n t o l i q u i d bismuth appear t o b e t h e most promising p r o c e s s i n g methods c u r r e n t l y a v a i l a b l e , and t h e development of these p r o c e s s e s has been t h e subject of most 0% t h e r e c e n t WOK^ o m f u e l processi n g , We have noted p r e v i o u s l y [I, p . 1701 t h a t t h e iscslatisn of p r o t a c tinium is s t r a i g h t f o r w a r d s i n c e i t s e x t r a c t i o n b e h a v i o r i s s i g n i f i c a n t ~ y d i f f e r e n t from t h a t of uranium, thorium, and l i t h i u m . Hmever, u n t i l r e c e n t l y , t h e removal of rare e a r t h s w a s d i f f i c u l t s i n c e t h e rare e a r t h s and thorium e x t r a c t i n almost t h e same manner from molten f l u o r i d e m i x t u r e s . I n 1969, S m i t h and F e r r i s [2, p . 2851 noted t h a t t h e rare e a r t h s d i s t r i b u t e seleet%ve.lyi n t o molten lithium c h l o r i d e from bismuth s slutions c o n t a i n i n g thorium; t h i s o b s e r v a t i o n allowed McNeese [ 3 , pp. 2-15] t o

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D i s t r i b u t i o n o f Metals Between Noaten S a l t s and Bismuth

Bismuth i s a low-melting (271째C) metal that i s essentfaPPy*i d s c i b l e w i t h molten h a l i d e mixtures c o n s i s t i n g of f l u o r i d e s , c h l o r i d e s , and b r e mides. Tke vapor p r e s s u r e of bismuth i n t h e temperature range of i n t e r e s t (500 t o 700'6) i s n e g l i g i b l e , and t h e s o l u b i l i t i e s of Iftkium, thorium, uranium, p r o t a c t i n i u m , and most s f the fission p r o d u c t s are a d e q u a t e f o r processing applfcatisns. Under the cOElditiOnS O f iflterest, PedUctiV@ e x t r a c t i o n PeaCtionS between materials i n s a l t a d metal phases can b e r e p r e s e n t e d by t h e f o l l o w ing reaction:

i n which t h e m e t a l halide mn in t h e s a l t reacts with l i t h i u r n from t h e bismuth phase t o produce M in the bismuth phase and t h e r e s p e c t i v e l i t h i u m halide i n the salt phase. The valence of PI i n t h e s a l t is +fi9 and x represents f l u o r i n e , c h l o r i n e , and bromine. I t has been found [ 4 ] t h a t a t a c o n s t a n t t e m p e r a t u r e t h e d i s t r i b u t i o n c o e f f i c i e n t D f o r m e t a l M depends on t h e l i t h i u m c o n c e n t r a t i o n i n t h e metal phase (mole f r a c t i o n ) , XLi9 as follows:

log B = n log

xLf

4- l o g

,y,*

0

*

The q u a n t i t y K i s dependent only on temperature, and t h e d i s t r i b u t i o n c o e f f i c i e n t i s m d e f i n e d by t h e r e l a t i o n :

mole f r a c t i o n of K i n metal phase D- m o l e f r a c t i o n of MX i n salt phase n

-

I:.....:

......, -......,.

..... *.&. ......, i

... ....

e

The ease w i t h which one component can b e s e p a r a t e d from a n o t h e r i s indic a t e d by t h e ~ a t o i f ~ t h e r e s p e c t i v e distribution c o e f f i c i e n t s , t h a t i s , t h e s e p a r a t i o n f a s t o r , A s the s e p a r a t i o n f a c t o r approaches u n i t y , separ a t i o n of the components becomes i n c r e a s i n g l y d i f f i c u l t . On the o t h e r hand, t h e g r e a t e r t h e d e v i a t i o n from u n i t y , t h e easier t h e s e p a r a t i o n . D i s t r i b ~ t i o nd a t a o b t a i n e d [ 4 ] f o r a number of mate~ialsbetween f u e l s a l t (72-16-12 mole 2 LiF-BeP2-ThF4) and blsmuth a t 640째C are summar i z e d in F i g . 11.2. The l i n e s for the v a r i o u s elements have s l o p e s t h a t correspond t o the i n d i c a t e d o x i d a t i o n states. Under the expected p r o c e s s c o n d i t i o n s , the Pa-?& s e p a r a t i o n f a c t o r i s about 1200, w h i c h i n d i c a t e s that protactfnia~lrnas w e l l as U P ~ ~ ~ U Eand I I zirconium can b e e a s i l y e x t r a c t e d from a salt stream containing ThF4. However, t h e r a r e - e a r t h t h o r i u m s e p a r a t i o n f a c t o r s are c l d a e t o u n i t y (1.2 t o 3.5), i n d i c a t i n g that removal of t h e rare e a r t h s from a s a l t c o n t a i n i n g thorium f l u o r i d e will b e d i f f i c u l t . The p ~ e v i o u s~ a ~ e - e a r t removal h system, which w a s based on these

3 34

MOLE F R A C f l O M Li IN BISMUTH

Fig. 11 2

e

Distribution data between fuel s a l t and bismuth

e

.. ~.~ ....

335

Em s e p a r a t i o n f a c t o r s , r e q u i r e d a l a r g e number of s t a g e s , a high mtalt o - s a l t flow r a t i o , and a l a r g e e l e c t r o l y t i c cell f o r p r o v i d i n g thorium and rare earth r e f l u x at t h e ends of t h e e x t r a c t i o n cascade [I, p p . 190-7 5, p p . 52-77]. F%ehave found, however, t h a t w i t h L i C 1 o r LiBr, much more f a v o r a b l e thoriUU€-Tar@-@aKthSeparatioIl f a c t o r s are obtained [2, p . 2851. D i S t r i b u t i o n d a t a f o r L i ~ [l 6 , p . 3.71; 7 1 a t 640°C are s h m n i n Fig. 11.3. The data f a l l roughly i n t o t h r e e groups. The d i v a l e n t r a r e - e a r t h and a l k a l i n e earth elements d i s t r f b u t e most r e a d i l y t o the LPC1, w i t h thorium-raree a r t h s e p a r a t i o n f a c t o r s u f about POs. The t r i v a l e n t rare earths form t h e s e c o ~ dgroup and the t h o r i ~ ~ t - ~ a r e - e a r st he p a r a t i o n f a c t o r s are about l o 4 T e t r a v a l e n t materials , such 8 s thorium and p r o t a c t i n i u m , d i s t r i b u t e o n l y s l i g h t l y t o t h e L i C 1 . S t u d i e s on the temperature dependence of t h e d i S t r i b U t i O n data ShCW @SSentiallgP no e f f e c t f O k the d i v a l e n t e ~ ~ ~ e ~ t § , a W h O K e f f e c t f o r the trivalent elements, and a SOllEWhat greater e f f e c t for the t e t r a v a l e n t elements. The d i s t r i b u t i o n coefficient f o r thorium is decreased s h a r p l y by- t h e a d d i t i o n of f l u o r i d e t o the LiC1, although the d i s t r i b u t i o n c o e f f i c i e n t s f o r the rare e a r t h s are a f f e c t e d by o n l y a minor amount. n u s , contamination of t h e LiCl w i t h several mole p e r c e n t f l u o r i d e will n o t a f f e c t the removal of t h e rare e a r t h s b u t w i l l cause a s h a r p i n c r e a s e i n t h e t h o r i m discard r a t e . Data with LiBr [ 7 ] are similar t o t h o s e with LiC31, and the d i s t r i b u t i o n b e h a v i o r w i t h L i C l - L i B r e

.&&.

m i x t u r e s would l i k e l y n o t d i f f e r a p p r e c i a b l y from t h e d a t a w i t h t h e p u r e materials. The p o t e n t i a l h e l d by LiCl f o r selective e x t r a c t i o n of t h e rare e a r t h s from MSBR fuel salt i s best i l l u s t r a t e d by c o n s i d e r i n g t h e equilibrium c o n c e n t r a t i o n s of rare e a r t h s , thsrium, and l i t h i u m in fuel s a l t , bismuth c o n t a i n i n g ~ e d ~ c t a n and t , LiCl as shown i n Table 11.1. The eoncentrations of t h e rare e a r t h s and a l k a l i n e e a r t h s i n t h e f l u o r i d e s a l t correspond t o a 25-day removal time f o r these materials i n the r e f e r e n c e MSBBa me thSkiUTR COnCf3RtPEitiOn i n t h e bislmuth 1s 90% O f the ~ f l % l S l p i ~ s s l u b i l i t y at 64O'C. A s can be seen, the ~ a ~ e - e a r t and h afialine-earth elements are p r e s e n t i n t h e L i C l at Pow c o n c e n t r a t i o n s and al-e a s s o c i a t e d w i t h a n e g l i g i b l e amount of thorium. A r a r e - e a r t h removal system based on t h i s e f f e c t w i l l b e p r a c t i c a l only i f a s u i t a b l e means i s a v a i l a b l e f o r r e m v i n g the l-al-e-earth and a l k a l i n e - e a r t h e l e ~ ~ n from ts the L i e 1 e The d i s t r i b u t i o n c o e f f i c i e n t s for these elements are s t r o n g l y a f f e c t e d by t h e c o n c e n t r a t i o n of l i t h i u m i n the bismuth phase, and the best method for removing these materials from the EiCl appears t o be e x t r a c t i o n i n t o bismuth c o n t a i n i n g l i t h i u m a t a c o n c e n t r a t i o n o f 8.85 t o 0.50 mole f r a c t i o n . S u f f i c i e n t data have been o b t a i n e d w i t h 1 i t h i u m c o n c e n t r a t i o n s i n the bismuth as high as 8 . 3 8 mole f r a c t i o n t o show t h a t no deviation o e c u r s from the r e l a t i o n s e s t a b l i s h e d i n i t i a l l y w i t h much lower l i t h i u m c o n c e n t r a t i o n s .

P l - o t a ~ t i n i mRemoval System

336

QWIUL-DWG-7Q-12482

I

I

I

I

..... , .a

a

..... w

..... e

C

w

i

...

<&

.... & :&

C,&

.... ..... <.=

Table 11.1, Equilibrium concentrations in fuel carrier salt, bismuth, and lithium chloride at 640°C Element Li Be T 11 Sr Zr Ba Ea Ce Nd Pm

Sm Eu Ub prb

... ..... ..... D

&...... < ...

Mote fraction I n fuel carrier salta

0.42 0.16 0.12 7.44 x 33.8 x 2.83 X 5.46 x 10” 19.3 x 12.1 x 1.24 X 10“ 1.34 x 1.55 X lom6 4.98 X 4.69 X

In bismuth Q.00201 0 approx 0.0025 0.664 x Q.069802 0.253 X 0.266 X IO-’ 1.38 x lo-6 0.680 x 0.0439 X 0.0622 x loW6 0.0359 X 0.281 X 1Qs6 0.264 X loe6

En lithium chloride

4.31 x 0.0155 0.236 x O.OQ123 0.375 x lo-6 0.636 X 0.219X 10 0.0424 x 0.0000 19 4.39 X 0.090 x 10” 0.0849 X

‘“Concentrations of the fission products in the fuel carrier salt :ire based on an assumed processing cycle time of 10 days and a removal efficiency of 4096, which results in a 25-day iernoval time. ’Concentrations for Y and PP were calculated using Nd distribution data.

338

....

339

UP4 and approximately 0.0035 mole z BaF4 i s withdrawn from t h e r e a c t o r . About 99% of t h e urawiUÂśR is rem0Ved from the salt by f l u o r i n a t i o n i n Order t o avoid t h e use sf l a r g e q u a n t i t i e s sf r e d u c t a n t i n t h e subsequent p r o t a c t i n i u m removal s e e p . The s a l t stfeam i s f e d c o u n t e r c u r r e n t t o a bismuth stream c o n t a i n i n g P i t h i m and thorium, w h e ~ et h e r e m i n i n g uranium and t h e p r o t a c t i n i u m transfer t o the metal strem. These materials are t r a n s f e r r e d fr'om the bismuth t o a captive secondary s a l t by h y d r o f l u o r i n a t i n g t h e bismuth stream EeavPng the e x t r a c t i o n colurntaa i n t h e p r e s e n c e of t h e secondary s a l t . The secondasry s a l t which flows through t h e hydroflusr i n a t o r a l s o c i r c u l a t e s through a f l u o r i n a t o r , where about 3OX of the uranium is removed, and through a tank t h a t c o n t a i n s most of the p r s t a c tiniurn. L i t h i m i s added to t h e bismuth leaving the h y d r o f l u o r i n a t o r , and t h e r e s u l t i n g stream i s r e t u r n e d t o t h e t o p of t h e e x t r a c t i o n colbum, The salt l e a v i n g the e x t r a c t i o n column i s e s s e n t i a l l y f r e e of uranium and p r o t a c t i n i u m b u t csntafns the rare e a r t h s a t e s s e n t i a l l y the r e a c t o r conc e n t r a t i o n . This stream is fed t o t h e r a r e - e a r t h removal system. Rare-Earth Removal P r o c e s s

A s i m p l i f i e d f l o w s h e e t f o r t h e ~ a r e - e a r t h emo oval system [9 pp. Fuel s a l t , which i s f ~ e eof uranium and p r o t a c t i n i u m but c o n t a i n s t h e rare e a r t h s , i s c o u n t e r c u r r e n t l y csn%acted w i t h bismuth c o n t a i n i n g reductant i n o r d e r t o e x t r a c t a significant f r a c tion of the rare e a r t h s i n t o t h e bismuth. The bismuth stream, which contains the rare earths and thorium, i s then c o u n t e r c u ~ ~ e ~ ct ol ny t a c t e d w i t h l i t h i u m chloride Because of h i g h l y favorable d i s t r i b u t i o n c ~ e f f i CientS, S i g n i f i c a n t fractionS O f t h e e a r t h s t r a n s f e r to the L i c P a l o n g w i t h a n e g l i g i b l e amount of t h o r i m . The f i n a l steps of t h e process c o n s i s t fn e x t r a c t i n g t h e rare e a r t h s from t h e % i @ kby contact w i t h b i s muth having lithium c o n c e n t r a t i o n s of 5 and 50 a t . 2 . T h i s p r o c e s s has a number of v e r y d e s i r a b l e c h a r a c t e r i s t i c s . O f primary i ~ ~ p o r t a n ci es t h e f a c t t h a t t h e r e i s net consumption of reductant i n t h e two upper c s n t a c t o r s . The p r o c e s s is n o t s e n s i t i v e t o minor v a r i a t i o n s i n o p e r a t i n g c o n d i t i o n s . E s s e n t i a l l y no materials o t h e r than t h e rare-earth and alkaline-earth elements are r e m ~ v e dfrom or added t o t h e f u e l s a l t ; t h e major change c o n s i s t s i n repdaeing the e x t r a c t e d rare e a r t h s w i t h an e q u i v a l e n t amount of l i t h i m as LiF. The amourat of L%F added to t h e fuel salt i n t h i s manner d u r i n g 30 y e a r s of o p e r a t i o n wsuld b e less than 10% Sf the E i F iEWentOr)P in t h e reactor.

1-15] is shown i n Pig. 11.5.

e

ConceDtual P r o c e s s i n n Flowsheet

The r e f e r e n c e p r o c e s s i n g flowsheet [a, p p . 3-21] i s shmn i n P i g . 1 1 . 6 . Fuel salt is WithdrENll frofa t h e reactor (an a 10-day C y c k ; f o r a l 0 0 0 - m ( e ) reactor, this r e p r e s e n t s a flow rate of 0.88 gpm. The f l u o r i n a t o r , where 99% of the uranium i s removed, has an active d i a m e t e r of 8 i n . and a h e i g h t sf 15 f t . The p r o t a c t i n i u m e x t r a c t i o n c o % u m i s 3 i n . i n diameter and is packed w i t h 3/8-in, R a s & i g r i n g s , The column i s e q u i v a l e n t t~ f i v e e q u i l i b r i u m stages and h a s a height of 15 f t a The

340

---I

I

FUEL SALT (No U or P d

--- Bi - Li (0.5

MOLE FWAC. Li 1 ..... ..

LL..!

OR

bi-Li

- - m + DIWALEN?

Bi -Li

I--

-g

+ TRIVALENT

RARE EARTHS

..... . ..

Fig. 11.5. Metal transfer process f o r remvd of rate earths from s i n g l e - f l u i d S B R fuel salt. a.... s..

341

c:<c.....

.... :.:=

ORNb DWG 71-7852 SALT PISCARD .... .....

---I

..d..%i

I

....

..... .-....

FRAC

(.... .%

RARE

.... ,=

..... :,*

....l ,.. ~. ...

bi

Fig. 1 1 . 6 . Conceptual flowsheet for p r o c e s s i n g a s i n g l e - f l u i d MSBR by fluorinatiQm-reductive extraction and the metal transfer process.

;%

....

,:.;.yi

I

.. .

~&.&

,.... .:=>

. .. :?m,