Ornl 4037 by The "E" Generation

C o n t r a c t No. W-7405-eng-26

MOLTEN-SALT REACTOR PROGRAM SEMIkVNIIAL PROGRESS REPORT

For Period Ending August 31., 1966 R. B. B r i g g s , Program D i r e c t o r

. JANUARY 1 9 6 7 OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee o p e r a t e d by UNION CARBIDE CORPOWATTOM f o r the U . S . AroMrc ENERGY COMMISSION

3 4456 0548376 0

PaArt1. Molten-Salt Reactor Experiment 1. MSRE Operations and Ana1ysi.s

The r e a c t o r power 1 . ~ was ~ 1increa.sed i n . s t e p s t o t h e maximum a t t a i n a b l e value of '7.2 Mw. The power l l m i t a t i o n w a s imposed by .the h e a t t r a n s f e r c a p a b i l i t y of the a i r - c o o l e d r a d i a t o r , which was much lower t h a n t h e design value. The h e a t - t r a n s f e r c o e f f i c i e n t s of t h e primary f u e l - t o - c o o l a n t - s a l t h e a t exchanger were a l s o substap-tially lower -.i;l-ian had been expected. Two periods, each about two weeks long, of r e l a t i v e l y steady o p e r a t i o n a t t h e maximum power were achieved. Aside from t h e power lirni%ai;ion, t h e performance o-f 1;he z-eactor The i n h e r e n t nuclear s t a b r i l i t y increased with system w a s favorable i n c r e a s i n g power as had been predi-cted. The nuclear poisoning by "'Xe was only 0.3 t o 0.4 of t h e expected val-ue, apparently because of t h e presence o f c i r c u l a t i n g helium bubbles i n t h e !Aiel s a l t which had no-1; Zzro-power been observed i n e a r l i e r o p e r a t i o n s a t s i m i l a r conditions r e a c t i v j t y balances showed a s l o y l y i n c r e a s i n g p o s i t i v e anornaly which had reached a maximum of 0.3% Gk/k a t shutdown. 13adiati.m. h e a t i n g of t h e primary-system components was i n t h e expected range, and r a d i a t i o n s h i e l d i n g and containment w e r e adequate. a

A system shutd.own t o remove i r r a d . i a t i o n specimens from t h e core, which w a s planned a f t e r an accumulated exposure of 10,000 M w ? i ~ ' , w a s advanced when a c a t a s t r o p h i c f a i l u r e of one of t h e main r a d i a t o r blower's occurred a t 7800 Mw'nr. I n a d d i t i o n -to t h e removal and replacement of t h e core i r r a d i a t i o n specimens and t h e r e p a i r of t h e main blovers, a number of o t h e r maintenance jobs were perfo,med i n t h e ensuing shutdown. These included:

1. rflechanical and e l e c t r i c a l r e p a i r of heat-induced damage t o t h e r a a i a t o r enclosure,

1-eplacement of t h e p a r t i c l e trap i n t h e main r e a c t o r off-gas lia.e, which had developed i n t e r n l i t t e n t high r e s i s t a n c e t o flow-,

m o d i f i c a t i o n of the treated-cooling-water r a d i o l y t i c ga s ,

system t o e l i m i n a t e

4* r e p a i r of water l e a k s i n the r e a c t o r c e l l ,

modification of -the component-cooling system t o improve r e l i a b i l i t y ,

6. g e n e r a l improvement of the iri-plant el.ectrica1 system. The MSHC instrumentation and c o n t r o l s system continued .to p e r f o m w e l l . There w a s t h e normally expected reduction i n b o t h malfunctions and misoperation of instruments as inst-rument and operating personnel gained experience and developed r o u t i n e s Wnile t h e r e were inany design changes, most of' t h e s e were improvements and add.i.tions to the system r a t h e r Ynan c o r r e c t i v e measures t o the instruments and c o n t r c l s . A

iii

iv disappointingly l a r g e number o f f a u l t y commercial :reI.ays and. e l e c t r o n i c swi.tcbes were ~ . s c l o s e d . These f a u l t s were i n t h e a r e a s of 530th r e l a y design a.nd fabrica,tion, and cori-ective s t e p s have been taken.

Component Developmeiit,

The o p e r a t i o n of f r e e z e Val-ve FV-103 w a s improved by the d e l e t i o n of t h e h y s t e r e s i s f e a t u r e of one of t h e t e m p e r a t u r e - c o n t r o l modules, which had caused thermal cycling of t h e valve before t h e temperature reached equilibrium.

The t h r e e corilirol rods have operated without d i f f i c u l . t y The indicated. changes i n rod leng-th were random and were 0.05 i n . f o i - rod I., 0.16 i n . f o r rod- 2, and 0.1.2i.n. f o r rod 3.

Several s m a l l d i f f i c u l t i e s were encountered i n the operation of '&e con-trol-rod d r i v e u n i t s . 1-0each case t b e d i f f i c u l . t y was diagnosed and adequate ternporary changes were made t o p e n n i t contInii.ed. operation o.f t h e r e a c t o r . Tne d l f f i c u l t i e s involved t h e f a i l u r e of a synchro t r a n s m i t t e r and a reference potentiometer, which have been replaced during t h e c u r r e n t shutdown. The e x c e l l e n t condition OP t h e g e a r s i n t h e d r i v e uiii.ts i n d i c a t e d t h a t t h e r e was no high-temperature damage 'io the lubricant. The racli a t o r -do o r - ope r a t Trig me chani sm h a s pe r f ormed sa-ti sf a et015 ly since t h e l a s t rnodifications. Excessive a:ir leakage around. t h e s e a l s on t h e doors r e s u l t e d from daniage s u s t a i n e d during t h e thermal cycl.i.ng during iloimal. operation. Laboratory t e s t s were conducted on s e v e r a l arrangements of the metal. s e a l surfaces, r e s u l t i n g in t h e choice of a new h a r d - s e a l scheme which w a s i - n s t a l l e d on t h e door. I n addri.tion, al-tera'cions were made t o t o e door s t r u c t u r e t o reduce bowing, and t h e i n s t a l l a t i o n of a. second soft, r e s i l i e n t s e a l w a s propose& t o back up t h e ex?-sting s e a l . The sampler-enricher has been used t o i - s o l ~ a t ea t o t a l of 119 LO-g samples and 20 50-g sampl~esand -tomake 87 enrichments t o t h e f i e 1 sy-stern. The only major maintenance r e q u i r e d has been replacement of t h e rnanipula,tor booi;s, replacement of t h e d r i v e - u n i t capsule l a t c h , r e p a i r of an open e l e c t r i c a l c i r c u i t , and recovery of a capsule which had f a l l e n i n t o the o p e r a t i o n a l valve a r e a . These r e p a i r s were performed. without t n e spread of airborne contamination or t h e exposure of t h e personnel t o s i g n i f i c a n t r a d i a t i o n l e v e l s . An iiicrease of t h e b u f f e r leakage i n the o p e r a t i o n a l valve w a s determined Lo be caused by p a r t i c l e s which f e l l onto t h e upper seal. surface, and i t w a s found t h a t simple cleaning of t h i s surface was e f f e c t i v e i n reduc-ing t h e leakage. Problems r e s u l t i n g from an i n c r e a s e i n Lhe contamination level. wit'ni-n t h e meclianfsm were solved by a p a r t i a l cleanup of one area, t h e establishment of a contamination c o n t r o l a r e a a t t h e sample withdrawal area, and t h e modification of t h e t r a n s p o r t container t o red.uce contamination of t h e upper p a r t and t o permit irie,xpensive d i s p o s a l of t h e lower part. Changes were made i n t h e sampler-enricher control. c i r c u j - t t o reduce t h e chance of rupturing the manipulator boots. I n a d d i t i o n , a

fuse and voltage suppressor w e r e instal.l.ed t o p r o t e c t t h e e l e c t r i c a l l e a d s froin excessive voltages and c u r r e n t s

A t o t a l of 45 samples, i n c l u d i n g two 50-g samples, have been ta.ken using t h e coolant sampler. One e l e c t r z i c a l r e c e p t a c l e w a s replaced, and t h e leakage of t h e removal valve w a s reduced 'by cleaning. The design o f t h e f u e l processing sampler w a s e s s e n t i a l l y completed, and i n s t a l l a t i o n i s proceeding as c r a f t i s a v a i l a b l e . Tbe e l e c t r i c a l complete, and t h e i n s t a l l a t i o n of and instrument work i s about o t h e r equipment i s over 95% complete.

The o r i g i n a l o f f - g a s f i l t e r i n l i n e 522 w a s replaced wi-Lh one which i s designed t o t r a p organic materia1.s i n a.ddition t o p a r t i c u l a t e m a t t e r . Activated- charcoal w a s chosen as t h e f i l t e r i n g medium, and preliniiriary t e s t s indicated. t h a t it had good e f f i c i e n c y f o r {;he removal of c6 and h e a v i e r molecules. A p r e f i l t e r was insta.ll_ed- t o remove t h e r a d i o a c t i v e p a r t i c u l a t e matter as w e l l as i;hc organic mists which might e x i s - t . Since one of the purposes of t h e p r e f i l t e r w a s t o reduce t h e h e a t l o a d on t h e charcoal t r a p , h e a t d i s s i p a t i o n w a s a l s o a consideration i n t h e design. The ent-ire f i l t e r - c h a r c o a l t r a p i s cool.e(I. 'uy irrunersi.on in water. Since l i t t l e w a s known of t h e c h a r a c t e r of t h e organic mat e r i a l a t t h e time of t h e design of t h e f i l t e r system, one of - t he purposes w-as t o provide a method of diagnosing t h e problem. 'Therefore, t h e p a r t i c l e t r a p w i l l be removed and exmiined to g a i n i n f o m a t i o n need.ed i n t h e design of a more pennanent system. D i f f u s i o n of a c t i v i t y i n t o t h e f u e l pump off-gas l i n e resulted. i n two s h o r t p e r i o d s of high activrity a t tjne o f f - g a s s t a c k . A s m a l l charc o a l t r a p was i n s t a l l e d t o provide holdup times of approximately 2-1/2 days f o r krypton and 30 days for xenon.

S e v e r a l remote maintenance jobs were performed during t h e period, i n which t h e accumulated r e a c t o r power increased. from 35 t o '7822 Mwhr. S e v e r a l ObserTrdtions w e r e made as a r e s u l t of t h e work. Control of a i r borne contamination i s not d i f f i c u l t , and t h e niaintenance techniques and systems prepared f o r t h e MSRE have worked w e l l . The f l e x i b i l i t y of t h e maintenance approach was demonstrated by carrying ou-1; unanticipated t a s k s s u c h as t h e i n s t a l l a t i o n of a thermocouple on a piece of pipe i n t h e r e a c t o r c e l l and t h e thawing out and c l e a r i n g of a plug i n OLE of t h e s e r v i c e gas l i n e s . The major t a s k s completed during t h e r e p o r t i n (1)opening a s e c t i o n of t h e off-gas l i n e , i n s p e c t i n g t h e i n s i d e , clu2te: and r e t u r n i n g t h e l i n e t o operating condition; ( 2 ) removal arid replacernent of both of t h e r e a c t o r - c e l l space cooler:;; (3) i n s t a l l a t i o n of a new thermocouple on a h o r i z o n t a l s e c t i o n of t h e oTf-gas l i n e ; ( 4 ) r e p a i r of the sampler-enricher e l e c t r i c a l receptacle; (5) i n s t a l l a t i o n of temporary p i p i n g i n t h e main off-gas l i n e t o measure p r e s s u r e d i s t r i b u t i o n s ; ( 6 ) removal of t h e g r a p h i t e 4 I a s t e l l o y TJ s u r v e i l l a n c e sampl-es; ( 7 ) removal, r e p a i r , and replacement of two control-rod d r i v e u n i t s ; (8) r e moval of a s a l t plug from a gas-pressure reference l i n e by applying p r e s s u r e whi1.e h e a t i n g t h e l i n e .

-vi 3.

Punip Development

The MSFE prototype f u e l pump w a s operated f o r 2631 h r a'c 1200째F t o o b t a i n d a t a on t h e concentration of undissolved hellum i n t h e c i r c u l a t i n g s a l t and of1 t h e hydrocarbon concentration i n t'ne pump-tank and catchb a s i n purge gases. The spare r o t a r y elements f o r t h e MSRE f u e l and coolant pimp and t h e bK-2 f u e l pump were modified wi.th a s e a l weld between t h e beari.ng housiiig and shte1.d plug t o prevent o i l from l e a k i n g out of t h e leakage catch b a s i n and down t h e outside of t h e s h i e l d plug t o t h e pump-tank gas space. A lower s h a f t seal f a i l u r e w a s experienced during preheat of t h e spare r o t a r y element Tor -1;he MSRE fbel. pwnp in p r e p a r a t i o n f o r hob shakedown. The spare r o t a r y element f o r t h e MSI% coolant pump w a s given cold and hot shakedown b e s t s . The l u b r i c a t i o n pump endurance t e s t w a s continued, and f a b r i c a t i o n of t h e MK-2 f i e 1 purnp t a n k w a s begun. Operation of t h e I'K-P molten-salt pump w a s hal-ted by f a i l u r e of ( I n t h e summayy s e c t i o n of a previous Progress Report, the d r i v e motor. t h e number of opera-tin9 hours was r e p o r t e d i n e r r o r as 22,622. T o t a l f o r f o u r t e s t s i s 23,426 h r . ) The giriibals support, f o r t h e sal.1; bearing O i l t h e molten-salt bearing pump w a s modified, and a new bearring sleeve and j ournal were f abrricated.

Instrument Development

Perfo-rmance of t h e temperature scanning system continues t o be s a t i s f a c t o r y , although some problems were experi.enced with asci-lloscopes and mercury swltches and. some system i n s t a b i l i t y was noted. &cause spare p a r t s f o r t h e mercury swibches used i n t h e scanner can no longer be obtained fi"o:n t h e manufacturer, an e f f o r t i s being made t o f i n d a replacement fox- t h e mercury switch. Further t e s t i n g of t h e c o o l a n t - s a l t system fl.ow transmit-ter which f a i l e d j.n s e r v i c e a t the MSRE confirmed t h a t r e f i l l i n g t'ne t r a n s m i t t e r with s i l i c o n e o i l had s i g n i f i c a n t l y reduced i t s temperature s e n s i t i v i t y . The new NcK-filled d - i f f e r e n t i a l -pressure t r a n s m i t - t e r ordered f o r use a s an MSRF, spare w a s found t o be exce3sivel.y s e n s i t i v e .Lo p ~ e s s u i ~ and temperature v a r i a t i o n s during acceptance t e s t i n g . Perf+oimancc of a l l molten-salt l e v e l d e t e c t o r s instal.l.ed at the

MSRE, on the MSFP Level T e s t F a c i l i t y , and on t h e MSRE Prototype Pumil7 Test Loop contj.riues t o be s a t i s f a c t o r y .

To c o r r e c t excessive frequency d r i f t presen-t i n t h e excita-'iion o s c i l l a t o r supply:-ng t h e u l t r a s o n i c l e v e l probe, a number of minor changes i n components and c i r c u i t r y were made t n e l e c t r o n i c equipment a s s o c i a t e d with t h e probe. Modifrica-tion and/or r e p a i r of two d e f e c t i v e helium c o n t r o l valves was completed. The f e a s i b i l i t y of using sl.iding d i s k valves f o r c o n t r o l of very s m a l l dry-heliim flows i s being i-nvestigated.

Reactor Analysis

Rod drop experiments, performed during MSRE run No. 3, were analyzed and- compared with rod worths determined from o t h e r independent measurements. T h e o r e t i c a l t i m e - i n t e g r a t e d flux t r a j e c t o r i e s following rod scrams were c a l c u l a t e d , based on negative r e a c t i v i t y i n s e r t i o n s obtained by i n t e g r a t i n g d i f f e r e n t i a l worth measurements. These t r a j e c t o r i e s were found t o compare c l o s e l y with experimental records of t h e accumulated count following t h e scram. We have concluded t h a t &n approximate 5$ band of s e l f - c o n s i s t e n c y can be assigned t o t h e c o n t r o l rod r e a c t i v i t y worths i n f e r r e d from t h e s e two independent c a l i b r a t i o n tochiiiques. P a r t 2. 6.

Materials S t u d i e s

MSRP M a t e r i a l s

The grade CGB graphi-be and H a s t e l l o y N specimens Tdere removed from t h e core of t h e MSRE a f t e r 7800 Mwhr of operation. Their macroscopic appearances were e s s e n t i a l l y imclianged by t h i s exposure. Some o f t h e specimens were damaged p h y s i c a l l y as a r e s u l t o f d i f f e r e n c e s i n therma.l e:qansion of p a r t s of t h e assembly. A new core specimen a r r a y w a s assembled with modifications t o c o r r e c t t h e s e d i f f i c u l t i e s . A rnetallu.rgica1 i n v e s t i g a t i o n was conducted t o d e t e m i n e Lhe e f f e c t of alm'-num-zinc a l l o y contamination on t h e 8 a s t e l l o y M t u b i n g of t h e MSRF s a l t - t o - a i r r a d i a t o r . Contamination occurred from a blower f a i l u r e during which shrapnel was blown a c r o s s the h o t r a d i a t o r tubes. Laborat o r y t e s t s showed t h a t , i n general, an aluminum oxide coating contained t h e aluminum, even i n t h e molten state, and i n t e r a c t i o n d i d not occur. When the oxide s k i n was broken from mechanical a.brasion, shock, o r o t h e r reasons, wetting occurred. Moderate i n t e r a c t i o n t o a d-epth of about 0.010 in. occurred. i n n wetted sample h e l d a t 1200째F f o r T h r . '-Thetubes i n t h e r a d i a t o r were inspected, and those which were contaminated were carefbllry cleaned. A s a r e s u - l t of t h e i n v e s t i g a t i o n and cleanup procedure, t h e r a d i a t o r system w a s judged t o be s a t i s f a c t o q f o r f'u-rther ope r a t ion.

Examinations of new grades of' both a n i s o t r o p i c and i s o t r o p i c g r a p h i t e i n d i c a t e t h a t t h e s e do not yet meet t h e requirements of molten-salt breeder r e a c t o r s . ilesults of a. v a r i e t y of' g r a p h i t e creep e-xperiments p e r f o m e d over a w i.de temperature range support a C o t t r e l l model f o r i r r a d i a t i o n creep. U s e of t h i s model w i l l pe-rmit e a s i e r ex%rapolat,ion of d a t a . Lmpl.ied i n t h i s concept i s t h e conclusion t h a t as long 2 s t h e stress a c t i n g on the

g r a p h i t e does not exceed t h e f r a c t u r e stress, the graphi.te w i l l con-time t o absorb t h e creep d-eformation Without loss o f mechanica.1 i r i t e g r i t y

n1e experimental brazing a l l o y 60 Pd-35 ~ i - 5 C r ( w t % ) w a s evaluated. f o r j o i n i n g g r a p h i t e t o metals. ALthou-gh i t e r J i i b i t s r e l a t i v e l y poor w e t t a b i l i t y on high-density g r a p h i t e , i t s marginal behavior i s enhanced. by p r e p l a c i n g it as f o i l i n t h e ,joint Graphite -to-molybdenum j o i n t s brazed with t h i s a l l o y preplaced in t h e j o i n t were .f;hemial.ly cycled between 200 and 700"C, and metallographic i n v e s t i g a t i o n showed t h a t no d e t e r i o r a t i o n had occurred. Two g r a p h i t e -t o-molybdenum-t o -Hastelloy -N

viii ti-ansi-Lion j o i n t s were brazed using a t a p e r e d joini; design. Vlsual examination r2vealed no cracks, a,ild ev-aluation i s contirmTng

A new brazing a l l o y , 35 Ni-60 Fd-5 C r ( w t $), f o r j o i n i n g g r a p h i t e t o molybdenum bad l e s s t h a n 2 m i l s a t t a c k a f t e r exposure t o I,~-F-EeF'~ZrFte-ThF4-UF4 a t 1300째F f o r 5000 h r i n a H a s t e l l o y N coiihainer.

Since zirconium and - t i t a n i u m have been foimd t o improve the r e s i s tance of 1-Ias-Lell.oy N t o e f f e c t s of' neu.tron i r r a d i a t i o n , t h e ri.nfluence of t h e s e elements on t h e w e l d a b i l i t y i s being eval-uated. Titani-urn app e a r s t o have no d e l e t e r i o u s e f f e c t s . Zirconium i n concentrations as low as 0.06 w t $ causes hot cracking. However, reasoilably good. welds have been made by the use of f i l l e r wire t h a t contains d i s s i m i l a r metal.. The l e v e l of zirconium thal; can be t o l e r a t e d has y e t t o be determined. Our studi.ec of t h e behavior of t h e Hastelloy N under neuti-on i r r a d i a t i o n have been concemed with e v a l u a t i n g t h e h e a t s of m a t e r i a l used i n t h e MSRE and i n evaluating s e v e r a l modified heabs of Hastel.l.oy N for use i n an advanced system. I n - r e a c t o r sti-ess-rupture t e s t s on s e v e r a l hea-i;s of m a t e r i a l suggest t h a t tliere may be a s t r e s s below which e s s e n t i a l l y no neutron damage occurs. T e s t s on specimeiis exposed t o vari o u s r a - t i o s of f a s t f l u x t o thermal f l u x i n d i c a t e t h a t t h e damage C O Y r e l a t e s with %he thermal flux. We b e l i z v e t h a t the damage is due t o W e have produced. s e v e r a l helium produced by t h e ( n , a ) r e a c t i o n with "13. h e a t s of m a t e r i a l with very l o w 'Doroil, but have had. t o change from a i r t o vacuum mel-'Ling p r a c t i c e . I f t h e 1-ow-boron m a t e r i a l i s i r r a d i a t e d cold, we f i n d t h a t t h e p r o p e r t i e s a r e s u p e r i o r t o those of the higher boron maberial; i f i r r a d L a t e d hoi;, t h e p r o p e r t i e s a r e as bad o r worse. Taus the p o s t i r r a d i a t i o n p r o p e r t i e 3 are no-L uniquely dependent upon the boron con-tent, and o t h e r f a c t o r s such as t h e d i s t r i b u b i o n o f boron and -the presence of o t h e r i m p u r i t i e s must be ve-ry important. Tne a d d i t i o n of t i t a n i u m t o Hastelloy N has been very e f f e c t i v e ri.n improviix -the properties.

Limited creep-rupture t e s t s have been run on Hasteloy N t o d e t e r mine i t s s u L t a b i l i t y f o r u.se a s a d i s - b i l l a t i o n v e s s e l f o r molten s a l t s a t 982째C. This work has r e s u l t e d i n a determination of the s t r e n g t h p r o p e r t i e s t o times of 1.000 h r . The formation of a second phase w a s observed t h a t may influence t h e d u c t i l i t y a t lower temperatures. T'ne oxidation c h a r a c t e r i s t i c s und.er c y c l i c t e n p e r a t u r e s remain t o be d e t e r mined. Thelma1 convection loops containing i"used s a l t of MSIW composition and fabricated. from Hastelloy N and type 446 s t a i n l e s s s t e e l have continued operation f o r 4.5 and 3.2 years, r e s p e c t i v e l y , with no s i g n of d - i f f i c u l t y . A s l i g h t decrease i n cold-lcg tempera.'Lii.re has been noted i n an N b l $ Zr 3 . 0 0 ~ a f t e r 0.6 year. A Hastelloy N loop has c i r c u l a t e d a secondary coolant s a l t f o r 3000 h r , whereas a Croloy 9 4 loop with t h e same salt plugged i n 1440 h r .

Chemistry

The f i e 1 and coolanl; s a l t have not changed p e r c e p t i b l y i n composition since they were f i r s t c i r c u l a t e d i n t h e reaci;or some 16 months ago. T%e

ix c o n c e n t r a t i o n of c o r r o s i o n products has not i n c r e a s e d appreciably. The average oxide c o n c e n t r a t i o n i n t h e Fuel was 5 4 ppm, which i s r e a s s u r i n g l y low. The v i s c o s i t y and d e n s i t y of molten I3eF2 were measixed; t h e visc o s i t y w a s about 1% g r e a t e r t h a n p r e v i o u s l y reported, and t h e d e n s i t y of t h e l i q u i d i s n o t very d i f f e r e n t from t h a t of t h e s o l i d .

Vapor e q u i l i b r i a t h a t a r e involved i n t h e reprocessing by d i s t i l l a t i o n have been measured. Decontamination f a c t o r s o f t h e order of 1000 f o r r a r e e a r t h s were evfdenced. Thermophysical p r o p e r t i e s have been e s t i m a t e d f o r t h e sodium potassium f l u o r o b o r a t e mixture t h a t is a proposed coolant f o r t h e MSBR. The vapor p r e s s u r e , due t o e v o l u t i o n o f BF3, reaches 229 mm at t h e h i g h e s t opera-ting temperature. I n t e r i m e s t i m a t e s f o r d e n s i t y , s p e c i f i c h e a t , arid v i s c o s i t y of t h e proposed coolant were made a v a i l a b l e e

P o s s i b l e reprocessing methods were s t u d i e d i n g r e a t e r d e t a i l . Fundamental s t u d i e s r e l a t e d t o t h e thermodjmamics of t h e r e d u c t i o n of f i s s i o n product r a r e e a r t h s i n t o a bismuth a l l o y were c a r r i e d o u t . The exceedi n g l y low acti-crjty c o e f f i c i e n t s of r a r e e a r t h s i n t h e bismuth expla,ined t h e f e a s i b i l i t y of t h e process. F u r t h e r a t t e n t i o n w a s p a i d t o t n e r e moval of r a r e e a r t h s by p r e c i p i t a t i o n i n a s o l i d s o l u t i o n with UP,.

The removal of p r o t a c t i n i u m from blaiiket m e l t s was s t u d i e d i n seve r a l ways. 'These included an oxide p r e c i p i t a t i o n with Zr02, a pump loop t o t r a n s f e r p r o t a c t i n i u m i n a bismuth-thorium alloy, and attempts a t e l e c t r o l y t i c r e d u c t i o n from b l a n k e t m e l t s . Moderate success was achieved i n t h e s e experiments, b u t more work i s r e q u i r e d -to a r r i v e a t f i n i s h e d and f u l l y c o n t r o l l e d procedures.

Analyses obtained from sampling assemblies t h a t had been exposed i n t h e pimp bowl of t h e MSRE showed t h a t noble-metal f i s s i o n products were b e i w p a r t i a l l y r e l e a s e d t o t h e gas space, presumably as v o l a t i l e Fluorides. A t t h e same time, plakillp; of noble metals frorri t h e l i q u i d was encountered. These puzzling phenomena w e r e r e f l e c t e d i n r e s u l t s on s u r v e i l l a n c e specimens of g r a p h i t e and. metal which were removed. from t h e IGRE. Some 10 t o 20% of t h e y i e l d of noble-metal f i s s i o n products w a s found t o have e n t e r e d t h e gas space i n t h e g r a p h i t e . Analyses of xenon i s o t o p e r a t i o s i n concentrated samples of o f f - g a s from t h e !ISHE showed t h a t t h e burnup of 135Xe w a s about 8$; t h e remainder escaped. t o t h e cover g a s o r deeayed. This i s i n accord with t h e low j r r e a c t i v i t y behavior. xenon poisoning i n d i c a t e d b Preliminary estimates of xenon poisoning and cesium carbride f o r mation i n t h e MSBR i n d i c a t e t h a t cesium d e p o s i t i o n w i l l probably not be a s e r i o u s problem-, but t h a t s t r i p p i n g f o r i o d i n e removal w i l l probably be r e q u i r e d Go keep poisoning w i t h i n bowids. Oxfde c o n c e n t r a t i o n s of 5C t o 70 ppm were dete-rmined i n f'uel samples t a k e n from t h e r e a c t o r during o p e r a t i o n s a t a l l power l e v e l s without apparent i n t e r f e r e n c e from t h e a c t i v i t i e s of t h e sample:;. Techniques for t h e regeneration. of e l e c t r o l y t i c rnoisture c e l l s w e r e developed to provide dependable repl.acerrients f o r t h e h o t - c e l l oxide a p p a r a t u s and components f o r f u t u r e i n - l i n e applications.

x Measurements d i r e c t e d toward t h e developmen-t ol” i n - l i n e spectropho-torne.tric -methods dri.sclosed addi-tional~wavelengths of p o t e n t i a l a n a l y t ical. value i n the u l t r a v i - o k t a b s o i p t i o n spectrum of U(IJT) and confinned t h e absence of i n t e r f e r e n c e from corrosion products. Iil-vestj-gation of unusu-a1 valence s t a t e s of r a r e - e a r t h f i s s i o n products i n d i c a t e s p o s s i b l e i n t e r f e r e n c e from Sm(TT) but none from E u ( I I ) . A n i n t e n s e absorption peak s u i t a b l e f o r monitoring t r a c e s of uranium i n coolani; sali; has been found i n t h e u l t r a v i o l e t spectmm of T J ( 1 V ) . A modified o p t i c a l system has been ordered which w i l l . improve t h e spectrophotometri-c measurements o f molten Iluori.de sal’is. By voltamne’m5c and chronopotentiometric rfleasu.rement,s, t h e U(ZV) reduction wave w a s found t o correspond ’io a one-electron r e v e r s i b l e r e a c t i o n . Diffusion coeffri.cri.ents and t h e a c t t v a t i o n eneF-7 were measured. Repeated scans of t h i s wave i n qu.j.escent MSFG melts were reproduci.bIc t o about 2% over extended p e r i o d s and b e t t e r Lhan 1% during short-term measurements. A new v o l . t m e t e i - i s being bui.1t t o improvr: the reproduci b i l i t y and make p o s s i b l e measurement of flowing s a l t streams. Desi-gn c r i t e r i a a r e being considered for an in-li.ne t e s t f a c i l i ty f o r evaluating three types of continuous a n a l y t i c a l methods e

Hydrocarboas were measured i n helium from simulated pu.r!ip l e a k experiments, and an apparatus was developed f o r tine conti.mous measurement of hydrocarboas i n MSRE off-gas.

E f f o r t s were continued on t h e development ajld e v a l u a t i o n o f equipment and- procediires for analyzing r a d i o a c t i v e MSFQ? s a l t samples. The remoLe apparatus f o r oxtck determinations was instal.led. i n c e l l 3 of Lhe High-Radiation-Level Analytical. Labora’iory (BuLlding 2026), I n ad.d.i.ti.on t o t h e aiial-yses performed. on line s a l t samples, radiochemical l e a c h solu.tions were prepared on s j l v e r and B a s t e l l o y N wires c o i l e d onto t h e s t a i n l e s s s t e e l cable be-tween t h e l a t c h and l a d l e .

The quality - c o n t r o l program was continued during t h e p z s t period t o e s t a b l i s h more r e a l . i s t i c l i n i i - t s of error f o r t h e methods. P a r t 3.

Molten-Salt Breeder Reactor Studies

Further design changes were incorporated i n t o t h e reference molten-

s a l t breeder r e a c t o r concept. The design of -the pi-irnarry h e a t exchangers w a s a l t e r e d to e l i m i n a t e t h e need f o r expansion bellow:;. Also, the flow

of f l u i d i n t h e primary r e a c t o r c i r c u i t s w a s reversed t o lower t h e operati.ng pressu.re i n t h e r e a c t o r vessel.

The e f f e c t of lowering t h e feedwaker tempera1;ure from 700 t o 580°F w a s evaluated. It was found t h a t t h i s change increased t h e p l a n t thermal e f f i c i e n c y from 44.9 t o 45.4% and. reduced p l a n t c o n s t m c t i o n c o s t s by $465,000 i f t h e r e were no accompanying adverse e f f e c t s . ‘Yhese savings a r e canceled i f t h e coolant used with t h e lower feedwater temperature c o s t s $2.4 mill.i.on more t h a n t h e coolant ii.sed. with 700°F feedwater. Molten-salt r e a c t o r s appear w e l l s u i t e d f o r modular-ty-pe p l a r i t cons t r u c t i o n . Such c o n s t r u c t i o n causes no s i g n i f i c a n t penalty ’io e i t h e r

the power-production c o s t o r t h e iiuclear performance, and it may permit 14SBR's t o have veqy high p l a n t - a v a i l a b i l i t y f a c t o r s .

U s e of d i r e c t - c o n t a c t cooling of molten s a l t s with l e a d s i g i i i f i c a n t l y improves t h e p o t e n t i a l performance of molten-salt r e a c t o r s and ind_icates the v e r s a t i l i t y of molten s a l t s as r e a c t o r f'uels. However, i n o l d e r t o a t t a i n the technology s t a t u s requTred f o r such concepts, 8 developrnent program i s necessary-.

Tne molten-salt r e a c t o r concept t h a t r e q u i r e s t h e l e a s t amount o f development e f f o r t i s t h e MSCR, b u t it i s not a breeder system. Yne e qi!nilibriuQ 'breeding r a t i o and t h e power-production oost of t h e MSCR p l a n t were estimated t o be about 0.96 and 2.9 mills/kw?ir ( e l e e t r i c a l ) , respec-Lively, i n an investor-owned. p l a n t with a load f a c t o r of 0-8. KL-though t h i s r e p r e s e n t s excellent performance as an a.d-vanced converter, the development of MSBR(Pa) o r MSBR p l a n t s appears p r e f e r a b l e because of the lower power-prod.isction costs arid s u p e r i o r iiuclear and fuel-conserm t i o n c h a r a c t e r i s t i c s associated. with t h e breeder r e a c t o r s .

Mol_-t;en-S-zltReactor Processing S t u d i e s

The processing p l a n t f o r an MSBR would use s i d e streams withdrawn from the fuel- and f e r t i l e - s a l t r e c i r c u l a t i n g systems at r a t e s t h a t y i e l d a fuel-sal-t; cycle t i m e of approximately 40 days and f e r t ; i l e - s a l t cycle t i i n e of approximately 20 days. Among the s i g n i f i c a n t sl;eps i n t h e p r e s e n t l y envisioned process are recovery of the uranium by continuous f l u o r i n a t i o n and r e c o v e q of t h e carrlier .piel s a l t by semicontinuous -vacuum d i s t i l l a t i o r r . A l t e r n a t i v e sc'rierrtes a r e ? ~ l . s obeing consid.ered. Semicontinuous D i s t i l l a t i o n . Values of t h e r e l a t i v e v o l a t i l i t i e s of N-3, LaFs, and CeF3 i n 1A.F a r e of t h e order of 0.0007. These a r e from new nieasurements made using a r e c i r c u l a t i n g eqi!lrilj.brium s t i l l . E a r l i e r measu.rements made by a c o l d - f i n g e r technique were a'ooilt 8 f a x t o r of 50 t o o high. Die complexity of stlill design and o p e r a t i o n i s considerably eased by t h e s e lower values. Retention of over 90% of Lhe r a r e e a r t h neutron poisons i n l e s s than 0.55 of the processed. s a l t c a n easily be achieved. Continuous F l u o r i n a t i o n of a Moltlen S a l t . The uranium i n t h e f u e l stream of an MSBR must be removed. by continuous f l u o r i n a t i o n prior -Lo the d i s t i l l a t i o n step. Tlie s i g n i f i c a n - t problems are corrosrion of t h e f l u o r i n a t o r and the p o s s i b l e l o s s of uraniwri. S t u d i e s a r e i n progress con s t rvc-Led. as towers w i t h c ounte r c u r r e n t on (3 ontinuou s fliuorinat o ~ s flow of f l u o r i n e t o s a l t . Recoveries exceeding 99$ have been c o n s i s t e n t l y a t t a i n e d w i - t l ? towers only 42 i n . high. Higher r e c o v e r i e s with longer towers a r e an.l;icipa.ted.. Corrosion p r o t e c t i o n may be efi%cted by t'ne use o r a l a y e r of frozen s a l t on tile wall of t h e f l u o r i n a t o r . F e a s i b i l i t y of t h i s technique i s based on suecessYu1 experiment:; with batch systems and ::i.mpl.e heat, t r a n s f e r c a l c u l a t i o n s . The h e a t g e n e r a t i o n of the fuel salt should be a d e q m t e t o maintain an easily c o n t r o l k d l a y e r of frozen s a l t on t h e cooled metal wall.

A l t e r n a t i v e Chemical Processing Methcd.s f o r an MSBR. 1iecl.u.ct.i.ve cop r e c i p i t a t t o n and l i q u i d - m e t a l e x t r a c t i o n a r e being .studied as p o s s i b l e

xii. methods f o r decontamination of YEBB c a r r i e r s a l t ( L i 2 B e F 4 ) a:â&#x20AC;&#x2122;I;I elâ&#x20AC;&#x2122; urani.um removal by t h e f l u o r i d e v o l a t i l i z a t i o n process. Adequate removal of La aiid Gd ris achieved by treatment writh n e a r - t h e o r e t i c a l q u a n t i t i e s of b e r y l l i u m metal t o form b e r y l l i d e s of t h e type T.n&:13. EiYler excess Ee, up t o 243 times t h e t h e o r e t i c a l amount, or a s t r o n g e r reductant, L i , i s nece s s a r y t o remove z,-i-rconi.um a t t r a c e l e v e l . The zirconium TS removed as f r e e m e t a l from 5 mole $ ZrF4 s o l u t i o n s i n Li2BeF4, b u t from d i l u t e s o l u t i o n s a b e r y l l i d e , Z r B e 2 , has a l s o been i d e n t i f i e d . Lithium- b i s-muth liquid-me t a l e xtraction expe rPilent,s we re a1so c.on tinued.. S i g n i f i c a n t removals were observed f o r La, Sm, M, Sr, and Eu, t h e l a t t e r p r i n c i p a l l y by e x t r a c t i o n i n t o t h e metal phase, the o t h e r s by d e p o s i t i o n as i n t e r f a c e s o l i d s , as previously reported f o r o t h e r metal extmction tests.

........................................................... 1.ilODUCTION ......................................................

Part 1

1.3

1.4

1.5

1.6

1.7 1.8 1.9

.................................. Chronological Accowrt; of Operations and Maintenance ..... 8eacl;ivity Balance ...................................... R e a c t i v i t y Balances a t Power ......................... R e a c t i v i t y Balances a t LOWPower ..................... Xenon Poisoning ......................................... P r e d i c t e d Steady-State 135Xe Poisoning ............... Analysis of Transient 1 3 5 ~ poisoning e ................ Circula-Ling Bubbles ..................................... S a l t Transport .......................................... GT-ad.ua1 T r a n s f e r t o O v e i * f l o w 'F'ank.................... O v e r f i l l ............................................. Power .easuremnen.s ...................................... Beat B l a n c e ......................................... Tiuclear Instruments .................................. Radiator A i r Flow.................................... Radiation Heating ....................................... F'uel-Pump T a n k ....................................... Reactor Vessel ....................................... Thermal S h i e l d ....................................... Reactor Dynamics ........................................ Equipment Performance ................................... Heat T r a n s f e r ........................................ Main B l o w e r s ......................................... 1hd.iator Enclosu-re................................... FIie1 Off-Gas System .................................. Treated Cooling-Water System ......................... Component-Cooling System ............................. Salt-Pump O i l Systems ................................ E k e - t r i c a l System ....................................

.............................. .............................................. Contaiiunent .......................................... Shielding and Radiation .............................. I n s t n u n e n t a t i o n and Controls ............................ Control Rods and Drives

5 ~ ~ 2 e r

1.10

- Process and Kuclerzv ........................................ .......................................... ................................

Operating Experience Instruments D a t a 3jstem Control-System Design

comomNT

DEVEO . PN .T

......................................... xiii

MOLTEN-SALT REACTOR EXPERIMENT

MSRF: OPERATIONS AND ANATiYSIS

1.1 1.2

iii

19 11 12

14 16 22 24

24 2I!. 25 25

26 26 27 27 28

29 29 35 35 39

i+l

43 47 1-8 50 51 53

53 54 56 5

59 61.

xiv 2.1 2.2 2.3 2.4 2.5

2.6 2.7 2.8

2.9 2.10

3.1

3.2

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

n-eeze Va1ves Control Rods Contrvl-Rod Drive Units Radiator Doors S.pler-Enricher Heplacement of Manipulator Roots Replacement of t h e Capsule Latch Repair of an Open E l e c t r i c a l C i r c u i t Kecovery of a Capsule 0pera-t;ional Valve Leakage Contamination of Removal Valve S e a l s Miscellaneous Problems Changes t o t h e Control Cf:rcuit Coo1.an.t Sampler Fuel Processing System Sampler Off-Gas F i l t e r Assembly F i l t e r Medium Heat D i s s i p a t i o n P a r t i c l e Trap Charcoal Trap 524 Charcoal Ped Remote Maintenance

MSRZ YUlli~s Molten-Salt Rmp Operation in t h e Prototype Pump Test F a c i l . i t y . Yurnp Rotary Element Modification Lubrication System MK-2 Fuel PUInp Other Molten-Salt Rmps PK-P Fuel-hmp High-Temperature Endurance Test Pwnp Contarining a Molten-Salt-Lubricated J o u r n a l Ijearing

............................................ 4 . INSTRUMENT DEVELOPMENT ........................................ 4.1 Terrq3eratur.e Scanner ..................................... 4.2 High.Temperature, NaK.Filled. Differential.. P u ..e Transmitter ........................................... 4.3 Molten-Salt Level Detectors ............................. 4.4 Helium Control Valve T r i m Replacemneiiâ&#x20AC;&#x2122;i, ................... 5 . REACTOR Y.ST.S .............................................. 5.1 Analysis of Rod Drop Experiments ........................ Description of Experiments ........................... Analysis Procedures .................................. Re..u-lts ..............................................

65 66 67 70

70 71 71 72 72 72 73

73 73

74 74 74 74 75 76

77 77

81 81 81 82 82 82 82 82 82

84 84 85 85 86 8%

88 88 89 91

. MATERIALS STUDIES 6 . MSIP Materials ................................................ Part 2

..................... 6.1 6.2 ........................... .................................. 6.3 6.4 ................................................ ..................................... 6.5 6.6 ............ 6 .'7 ...................... .......................... ........................................... ................................ 6.8 S 7. . . ..................................................... 7.1 Chemistry of the MSRE ................................... Behavior of FLlel and Coolant Salt.................... P h y s i c a l Chemistry of Fluoride Melt.. .................... 7.2 MSLF: Materials Surveillance T e s t i n g Evaluation of P o s s i b l e MSIIE Radiator Tubing Contamination with A.lminwn Evaluation of Graphite I n t e r n a l S t r e s s Problem i n Graphite Moderator BlockS Brazing of Graphite Corrosion of Graphite-to-Metal Brazed J o i n t s Welding Development of Hastelloy N E f f e c t of I r r a d i a t i o n on t h e Mechanical P r o p e r t i e s of Hastelloy N C h a r a c t e r i z a t i o n of H a s t e l l o y N for Service at 982OC Thermal Convection Loops

. T

V i s c o s i l q and Density of Molten Ek1-ylliu11 Fluoride T r a n s p i r a t i o n Studi-es i n Support of t h e Vacuum D i s t i l l a t i o n Process Estimate6 Themlophysical P r o p e r t i e s of MSBR Coolant S a l t Separa-Lion i n Molten Eliiorides., E x t r a c t i o n of Rare Earths from Molten Fluorides i n t o Molten Metals Rernovzl of Rare E a r t h s Pron. Molten Flu.orides by Simultaneous P r e c i p i t a t i o n with UF3 Removal of Protactinium from Molten Fluorides by Oxide P r e c i p i t a t i o n ExLraction of Protactinium from Molten Flu.ori.d?s i n t o Molten Metals Protactinium Studies in the Bigh-Alpha MoltenSalt Laboratory Radiation Chemistn. Xenon D i f f u s i o n and P o s s i b l e Forrflation of Cesium Carbide i n a n MSBR F i s s i o n Product Behavior i n t h e 1G.W Development and E.valuation of A n a l y t i c a l Methods f o r Molten-Salt Beactors Determination 0:" Oxide i n Radioactive MS%E S.ples Spectrophotometric StucEes of Molten-Salt Reactor . e l s

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

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

7.3

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

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

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

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

'7. Lk

7.5

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

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

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

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

9'7 97

1.03

1(38

110 112 115

117 117

125 130

139

140 1.41 142

14.2

145 1-47 1a8

156 158

156

165

191

1.91

193

xvi VolLammetric and Chronopotentiometric Studies of Ui-ani.um i n Molten ILF-EeF2 .ZrF4 I n - l i n e Test FaeLlj.ty Analysis o f Helium Blanke-t; Gas Development and Evaluation o f Equripment, and Procedures f o r Analyzing Radioacti-ve MSliE S a l t Samples Sample Analyses Qualrity-Coiitrol Program

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

7.6

Part 3

MOI,TEN-S.WT

MOLTTN-SKLT BREEDER REACTOR DESIGN STUDIES

~j.tii

196 199 200 200

BFEEUER FEACTOR STUDIES

.................... 8.1 Design Changzs i n MSEZ P l a n t ............................ 8.2 Modular-Type P l a n t ...................................... 8.3 Steam Cycle Altei-nati.ve Feedwater Temperatirre ...... 8.4 Additional Design Concepts .............................. 9 . MOLTEN-SALT ENACTOR PKOCZSSTNG STUDIES ........................ 9.1 Serriiconti.nuou.s D i s t i l l a t i o n ............................. 9.2 Continuous F l u o r i n a t i o n of a Molten Sal-t;................ 9.3 A l t e r n a t i v e Chemical Processing Methods f o r an MSBR. .... Reductton Prccipitat5.on .............................. L i - B i Alloy E x t m c t i o n ............................... 8

195 196

207

207 212

21.7 223 227 2.28 232 233 2.35 23'1

INTRODUCTION

The Molten-Salt Reactor Program i s concerned wTth research and development f o r nuclear r e a c t o r s t h a t use mobile f u e l s , which a r e solut i o n s of f i s s i l e and f e r t i l e materials i n s u i t a b l e c a r r i e r s a l t s . The program i s an outgrowth of t h e NTP e f f o r t s t o make a molten-salt r e a c t o r power p l a n t f o r a i r c r a f t and i s extending t h e technology o r i g i n a t e d t h e r e t o t h e development of r e a c t o r s for producing low-cost power for c i v i l i a n uses. The major g o a l of t h e program i s -to develop a thermal breeder r e a c t o r . Fuel. for t h i s type of r e a c t o r would be 233UF4. o r 235UE'4 dissolved i n a s a l t of composition near 2LiF-BeF2. The blanket wo1.il~lbe T I S 4 d i s solved i n a c a r r i e r . of s i m i l a r composition. The technology being developed f o r t h e breeder i s a p p l i c a b l e to, and could be expl.oited sooner i n , ad-vanced converter r e a c t o r s o r i n .biui-ners or f i s s i o n a b l e uraniim and plutonium t h a t also u s e fl-uoride fuels, Solidtioris o f uranium, plutonium, and thorium s a l t s i n c h l o r i d e and. f l u o r i d e c a r r i e r salts offer a t t r a c t i v e p o s s i b i l i t i e s f o r mobi3.e fuels f o r interraediate and fast 'oreeiler r e a c t o r s . The P a s t r e a c t o r s a r e of' i n t e r e s t t o o , b u t itre n o t a s i g n i f i c a n t p a r t of t h e program. Our major e f f o r t i s being a p p l i e d t o t h e o p e r a t i o n and t e s t i n g of a Molten-Salt Reactor Experirnen-t 'The purpose of - t h i s experiment is to .tea'i t h e t y p e of fuels and m a t e r i a l s t1ia.t would be used i n t h e thermal breeder and t h e converter r e a c t o r s and t o o'u-Lain s e v e r a l y e a r s of experience w i t h t h e o p e r a t i o n and maintenan.ce of a s m a l l molten-salt power m a c t o r . A s u c c e s s f u l experimen-t w i l l demonstrate on a small sca1.e t h e a t t r a c t i v e f e a t u r e s and t h e - t e c h n i c a l f e a s i b i l i t y of t b e s e systems f o r l a r g e c i v i l i a n power r e a c t o r s . The ?!EKE: operates a t 1200째F sLnd a t atmospheric pressure and was intended t o produce 1.0Mw of h e a t . I n i t i a l l y , t h e fuel c o n t a i n s 0.9 mole $ of UF4, 5 mole $ &FA, 2 9 . 1 mole $ BeF2, and 6 5 mole $ LiF, and t h e uranium i s a h o u . t 30% 235U. The melting p o i n t i s 640째F'. I n l a t e r operation, we expec-L Lo use h i g h l y errriched ux-aniim i n t h e l m e r c o n c e n t r a t i o n t y p i c a l of t h e f u e l f o r t,he core o f a b r e e d e r . 111 each case, the cornposition of %he s o l v e n t easi be adJusted. t o r e t a i r i l i q u i d u s teniperature about t h e scar~e

The f u e l c i r c u l a t e s through a r e a c t o r v e s s e l arid an 2 x t e r n a l pump and heat-exchange system. A l l . t h i o equipment i s constructed of BastelLoy N, a new nickel-molybdemurn-chromiwn a l l o y w i t h exception.al r e s i s t a n c e t o c o r r o s i o n by molten f3-uorides and with high s t r e n g t h a t high. temperat u r e . Tne r e a c t o r core contains an asseubly of g r a p h i t e modera-Lor bars t h a t are i n d i r e c t c o n t a c t w i t h -tile f u e l . The g r a p h i t e i s a new m a t e r i a l 2 of' high d e n s i t y .and s m a l l . gore s i z e . The f u e l salt doe:; noi; wet t h e g r a p h i t e and t h e r e f o r e should not e n t e r t h e pore:;, even a t pre above t h e o p e r a t i n g p r e s s u r e .

'Also Corp.

s o l d cornnlercial1.y as I a c o No. 806. 2Grade CGB, produced by Carbon Prodixcts Division of Union Carbide

Heat pi-oduced i n t h e r e a c t o r i s i;.ra.nsferred t o a coolant s a l t i n

t h e h e a t exchanger, and t h e coolant s a l t i.s pumped through a r a d i a t o r t o d i s s i p a t e t h e h e a t t o the atmosphere. A s m a l l f a c i l i L y i s i n s t a l l e d i n - t h e MSRE -building f o r o c c a s i o n a l l y processing t h e f u e l by treatment

with gaseous HF and F2.

Design of t h e MSIIE was begun e a r l y i n t h e summer of 1960. Orders f o r s p e c i a l m a t e r i a l s were placed i n t’ne spi-ing of 1.961. Major modificai;ions t o Hiiild.ing 7501 at, OKML, i n which t h e reac1;or i s installled, were s t a r t e d i n t h e fall of J-961 and were completed by January 1963. F a b r i c a t i o n of t h e r e a c t o r equipmmt w a s begun e a r l y i n 1962. Some d i f f i c u l t i e s were experienced i n o b t a i n i n g m a t e r i a l s and i n making and i n s t a l l i n g t h e equipment, but; t h e essential i n s t a l l a L i o n s w e r e completed so t h a t prenuclear t e s t i n g could begin i n August of 1964. The prenuclear t e s t i n g w a s completed w i t h only minor d i f f i c u l t i e s i n March of 1965. Some modi f i.c a t ions were m a d e before beginning t he c r i.t ical. experiments i n May, and -the r e a c t o r w a s f i r s t c r i - L i c a l on June 1, 1965. The zeropower experiments w e r e completed. ear1.y ri.n J u l y . Addri.ti.ona1 modifications, maintenance, and sealj.ng and testing of t h e containment were r e q u i r e d bef o r e t h e r e a c t o r began L o operate a t appreciable power. This work w a s completed i n December. 0peral;ion at; a power of 1 bfw w a s begun i n January 1966. A t Lhat power l e v e l , t r o u b l e w a s experienced with plugging of small p o r t s 3.n t h e control. valv-es i n t h e ofr-gas system by heavy l i q u i d and vsrnishl i k e organic materials. Those materia1.s are b e l i e v e d t o be produced from a very s m a l l amount of o i l t h a t leaks through a gasketed s e a l a.nd. inl;o t h e f u e l s a l t i n t h e pump t a n k of t h e fuel circiil.ating pump. ?‘he o i l . vaporizes and a,ccompanies t h e gaseous f i s s i o n products and heI.iwn cover gas purge i n t o t h e off-gas system. There t h e inteiise b e t a i-adlation from t h e k-rypton and xenon. polymerizes some of t h e hydrocarbons, and t h e products plug s m a l l openings. This d i f f i c u l t y w a s l a r g e l y overcome by i n s t a l l i n g an a b s o l u t e f i l t e r i n t h e off-gas l i n e ahead of t h e c o n t r o l va lv-e s

The f u l l power c a p a b i l i t y of t h e r e a c t o r - about 7 . 5 Mw under design conditions - w a s reached i n May. The power w a s l i m i t e d by t h e p e r f o r mance of t h e s a l t - t o - a i r r a d i a t o r heat-dump system. Tne p l a n t w a s opera t e d u n t i l t h e midd.le of J u l y t o t‘ne equivalent of about one monLh a t f u l l power when t r o u b l e s wi’ch ‘ihe blowers i n t h e hea-t-dump systerii required t h a t t h e o p e r a t i o n b e i n t e r r u p t e d f o r maintenance. I n most yespects t h e r e a c t o r has performed very well: t h e fu.el, ha:; been completely s t a b l e ; t h e f u e l and coolant s a l t s have not corroded t h e Hastelloy N c o n t a i n e r material i n s e v e r a l thousand boixrs a t 1200°F; and t h e r e has been no d e t e c t a b l e r e a c t i o n between t h e f u e l s a l t and t h e Mechanical d i f f i c u l t i e s wi.th equipg r a p h i t e i n t h e core of t h e r e a c t o r ment have been l a r g e l y confined t o p e r i p h e r a l s y s t e m and a u x i l i a r i e s .

Because t h e MSRF i s of a new and advanced type, s u b s t a n t i a l r e s e a r c h and development e f f o r t i s pro-crid-ed i n support of the o p e r a t i o n . Included a r e engineering development and testring of r e a c t o r components a n d . sy-st e r n s , m e t a l l u r g i c a l development of materials, and s t u d i e s of t h e chemistry

of t h e s a l t s and t h e i r c o m p a t i b i l i t y with g r a p h i t e and m e t a 1 . s b o t h inp i l e and o u t - o f - p i l e . Work i s a l s o being done on methods f o r purifying t h e f u e l s a l t s and i n preparing p u r i f i e d mixtures f o r t h e r e a c t o r and f o r t h e r e s e a r c h and development stuciies. Some s t u d i e s a r e being 1nad.e of t h e l a r g e power breeder r e a c t o r s f o r which t h i s t e c h n o l o w is being developed

This r e p o r t i s one of a s e r i e s o f p e r i o d i c r e p o r t s i n which we des c r i b e b r i e f l y the progress of Lkie program. ORNL-3708 i s an e s p e c i a l l y usef-ul r e p o r t because it gives a thorough review of 1;he design and cons t r u c t i o n and supporting development work for t h e MSRE. It also des c r i b e s much of t h e g e n e r a l technology f o r molten-salt reactor sys-terns 0-ther r e p o r t s i s s u e d i n t h i s s e r i e s are:

OmL 2474

Perrod Ending January 31, 1958

ORNL-2626

Period Ending October 31, 1958

OmTL- 2684

Period Ending January 31, 1959

ORNL-2723

Period Ending A p r i l 30, 1959

ORNL2799

Period Ending J u l y 31, 1959

ORNL2890

Period Ending October 31, 1959

ORNL2973

Periods Ending January 31 and A p r i l 3G, 1.960

QRNL- 30 14

Period Ending J u l y 31, 1.960

OIWL- 3122 O H V E 32 15

ORnrL-3282 ORIâ&#x20AC;&#x2122;E-3369 ORlTL- 3419

Period Ending February 28, 1961 Period Ending AuLmst 31, 1961

Period Ending F e b r u a q 28, 1962 Period Ending August 31, 1362

Period Ending January 31, 1963

O R N L 3 529

Period Ending J u l y 31, 1963

ORNL- 3626

Feriod Ending January 31, 1964

ORNL-3708

Period Ending J u l y 31, 1964

ORNL-3812

Period Ending February 28, 1965

ORNL-3872

Period Ending August 31, 1965

ORNL- 3936

Period Endring February 28, 1966

Part 1. MOLTEN-SALT REACTOR EXPERIMENT

1. E R E OFFmTIONS Ai'JU AHALYSIS P. N. Bauberireich 1.1 Chronological Account of Operations and Maintenance R . H. Guyrnon J. L. Crowlcy T. L. Hudson P. H. Harley H. R. Payne W. C. U l r i e h

H. C . Roll-er R. C. Steffy

V. i). H o l t A. I . Yirakoviak

13. H. Webster C . K. McGlothlan

R. Rlumberg

A t t h e beginning of t h i s r e p o r t period. t h e r e a c t o r w a s down t o cope with t h e problem of plugging i n s m a l l passages i n t h e f t i e l o f f - g a s system. I n v e s t i g a t i o n showed t h a t t h e material causing t h e t r o u b l e was a mixture or" hjdrocarbons, probs2oLy pump l u b r i c a t i n g oil t h a t had. been a f f e c t e d by heat and r a d i a t i o n i n t h e off-gas l i n e . With this informat i o n , a device t o c l e a n up t h e gas stream w a s designed, b u i l t , and. i n stalled i n t h e off-gas Xine upstream of -Lhe f u e l p r e s s u r e c o n t r o l -valve. it c o n s i s t e d of a. t r a p f o r p a r t i c k s and mist, followed by a charcoalbt'd f o r vapor a d s o r p t i o n . A l s o d.u:ring t h i s shutdown, t h e pressure cont r o l valve and t h e charcoal-bed i n l e t valves vzre replaced. with valves having l a r g e r trim. I

Power o p e r a t i o n was resurtled i n raid-April, and t h e program of i n v e s t i g a t i n g t h e performance iip t o - f u l l power was completed by t h e end of' May. (This perioti oi' o p e r a t i o n was designated run 6 . ) Ixlring t h i s time, observations were made as planned on r a d i a t i o n heating, h e a t t r a n s f e r , xenon poisoning, and r e a c t o r cPjnrmics. With t h e exceptLon of h e a t t r a n s f e r , t h e system behavior was w i t h i n t h e expected l i m i t s , although xenon poisoning w a s somewhat l e s s than p r e d i c t e d . Tlne power e s c a l a t i o n w a s i n t e r r u p t e d twice, once when t h e anomalous behavior of' the control. system l e d to a drain and again hy an e l e c t r i c a l f a i l u r e i n t h e f u e l campler, whose r e p a i r r e q u i r e d t h e f u e l b e drained. T'he approach t o f u l l power also d i s c l o s e d problems i n several areas:

1. A f t e r about s i x weeks o f o p e r a t i o n , p r e s s u r e drop E L C X ' O : ; ~ t h e newly i n s t a l l e d t r a p i n t h e off-gas Line had. ' b u i L t up t o 1.0 p i g , and it seemed it; would have t o be replaced. Eut during f u r t h e r o p e r a t i o n a t high power, the p r e s s u r e drop went down t o less than 1.. p i g . Temperatures i n d i c a t e d considerable r e t e n t i o n of f i s s i o n product 3 in t h e t r a p b u t no evidence of poisoning o r deteriora-Lion.

A f t e r each s t e p up i n power the pressure drop across t h e main charcoal bed i n l e t s i n c r e a s e d , but each time t h i s occiirreit, backblow-ing w i t h helium proved e f f e c t i v e i n r e s t o r i n g t h e pressu.re drop t o an RC

ceptab l e l e v e l .

8 3.

Radioactive gas from t h e f u e l d r a i n tanks d i f f u s e d back i n t o t h e helium supply l i n e s o u t s i d e t h e s h i e l d , r e q u i r i n g a p e r i o d i c purge of t h e s e l i n e s t o keep down r a d i a t i o n i n t h e North E l e c t r i c Ser-vice Area. When t h e power reached 5 MwJ r a d i o l y t i c gas began t o accumulate i n t h e t h e m a l s h i e l d , d i s p l a c i n g p a r t of t h e water. E f f o r t s t o e l i m i n a t e t h e gas by venting {;he s h i e l d s l i d e s and i n c r e a s i n g t h e water flow were unsuccessful..

5. The water c i r c u l a t e d through t h e s h i e l d contained lithium. I i i t r i t e as

c o r r o s i o n i n h i b i t o r , and o x i d a t i o n of t h e n i t r i t e i o n t o n i t r a t e was a l s o observed a t t h e higher power.

6. A discrepancy a r o s e betw-een t h e r e a c t o r power indicated. by t h e heat

balances and by t h e neutron instruments (cal.ibrated a t low power). It w a s found l a t e r t h a t -the neutron instrumen-ts gave erroneously high readings a t high power because of an i n c r e a s e i n t h e temperature of water i n t h e shaft; around t h e instruments.

The climax of t h e power e s c a l a t i o n w a s reached xhen t h e coolant h e a t removal system (air-cooled. r a d i a t o r w i t h a d j u s t a b l e doors , bypass damper, and two blowers) w a s extended t o i t s l i m i t , and t h e c a p a b i l i t y proved t o be only 7.5 MM. The c o e f f i c i e n t f o r h e a t 'Lransfer i n t h e p r i mary h e a t exchanger w a s a l s o below expectations, imposing a lower l i m i t of about 12LO'F on t h e f u e l o u t l e t temperature a t t h e maximum power. I n l a t e May, power o p e r a t i o n w a s hal-ted when i-t became evident t h a t apparent inl-eakage of a i r i n t o t h e r e a c t o r c e l l had begun to exceed the s p e c i f i e d l i m i t , . The c e l l w a s pressizrri.zed t o 20 p s i g f o r l e a k hunting, and no l e a k of any consequence w a s found. It. w a s discovered t h a t t h e apparent c e l l . l e a k was a c t u a l l y n i t r o g e n I-eaking i n t o t h e c e l l from p r e s s u r i z e d thermocouple p e n e t r a t i o n s . When t h i s was t a k e n i n t o account, t h e measured r e a c t o r c e l l . leakage a t 20 p s i g w a s acceptably low. Wnile t h e c e l l l e a k hunt w a s i n progress, attemp-ts were made t o determine t h e source of w a t e r which had appeared i n t h e c e l l atmosphere (1 t o 2 gpd had begun t o condense i n t h e component-coolant p m p domes, t h e c o o l e s t spot exposed t o t h e c e l l atmosphere). 'The source w a s n o t l o c a t e d because e l e v a t e d temperatures i n t h e c e l l prevented meaningful leak r a t e measurements on s e p a r a t e p o r t i o n s of t h e water system. Operation a-t f u l l power was resumed on Jime 13 -to i n v e s t i g a t e t h e chemistry and r e a c t i v i t y behavior of t h e r e a c t o r and t o i n c r e a s e t h e exposure of t h e core specimens b e f o r e t h e i r removal., scheduled a t 10,000 Mwhr T h i s w a s rim 7.

Fuel-salt samples, taken a t a r a t e of three per week, showed no change i n t h e main c o n s t i t u e n t s o f t h e s a l t , very low oxide (about 50 ppm) and. no appreciable g o w t h of corrosion-product cbromium j.n t h e s a l t . The sampler-enricher w a s also used t o expose m e t a l w i r e s b r i e f l y t o t h e gas i n t h e pump bowl, and t h e s e showed more f i s s i o n products t h a n expect ed

R e a c t i v i t y t r a n s i e n t s following changes i n power i n d i c a t e d t h a t t h e 135Xe poisoning w a s only 0.4% Sk/k a t f u l l power. The presence of c i r c u l a t i n g gas bubbles was suggested by t h e low xenon poisoning, and experiments on t h e e f f e c t of pressure on r e a c t i v i - b y confirmed t h a t t,here w a s as much as 1-76 by volume of' bubbles i n the core s a l t . Tine system r e a c t i v i t y showed very l i t t l e n e t change connected with power operation o t h e r t h a n t h a t a t t r i b u t e d t o xenon, ev-en though t h e c a l c u l a t e d samariuni poisoning i n c r e a s e d t o about 0.3% 6k/k. Another anomalous behavior w a s t h e slow, continuous accumulation of f u e l s a l t i n t h e overflow t a n k a t pump-bowl l e v e l s below t h a t a t which accimulation had. been observed. b e f o r e .

lriere w a s some encouragement from t h e treated-wa-ter system. P a r t i a l deaerati.on of water going t o t h e t h e r m a l - s h i e l d s l i d e s s i g n i f i c a n t l y reduced. t h e holdup of r a d i o l y t i c gas, l e a d i n g t o plans for. more e f f e c t i v e d e a e r a t i o n . Decomposition of t h e n i t r i t e c o r r o s i o n i n h r i b i t o r Ikveled o f f a t an acceptable l e v e l . IT

Power operation was i n t e r m p t e d for lr+h r a f t e r 8 s h a f t coupling on one of t h e main blowers f a i l e d . Another i n t e r r u p t i o n , this one f o r f o u r days, r e s u l t e d when an e l e c t r i c a l short, i.n a component-cooling pimp caused t h e f u e l system t o d r a i n . Power o p e r a t i o n ended on Jmly 17, when t h e huh on one of t h e main blowers broke up, reducing 'the air flow arid czusririg p i e c e s of hub mid b l a d e s t o f l y 3.nto t h e r a d i z t o r . The coolant system was immediately drained. and cooled down t o i n s p e c t tine radia-Lor . A f t e r sone experiments a t low power, t h e f u e l was also cbi3iIlerl t o begin t h e planned p r o g r m of maintensnee. I n t e g r a t e d power up t o t h e sliiit~:io:m w a s 7823 Mwkr. Sane of t h e o p e r a t i n g data a r e summarized. i n Ta'Dle 1.1.

The f i r s t s t e p was t o f l u . s h t h e f u e l system with f l u s h sal.? i n p r e p a r a t i o n for t h e specimen removal. Drring an experiment, t o v~er-if'ythe F u e l pm-p overflow p o i n t , fliish s a l t got i n t o some of t h e g z s l i n e s on t h e pijrnp bowl. and. f r o z e then?, adding another jo'o t o t h e shut,down.

The s?ssembly of g r a p h i t e and B a s t e l l o y N specimen:; t h a t had been i n t h e core s i n c e September 1965 w a s removed f o r examination. These showed p r a c t i c a l l y no c o r r o s i o n o r d.eterioration. The samples wzre suis jectetl t o a program of a n a l y s i s and t e s t i n g w i t ' r i emphasis o:n fission product deposition. DTOcontrol-rod d r i v e s were removed and f a u l t y posjhrion i n d i c a t o r s repaired.. Testing showed t h a t t h e water l e a k i n the r e a c t o r cell. was from one of t h e space c o o l e r s , and it was removed and. r e p a i r e d . ,";peerial t o o l s and h e a t e r s were devised, and t h e frozen s a l t was thawed. from t h e plugged gas l i n e s on t h e p-lurip. A l l t h e work i n t h e r e a c t o r c e l l was done through t h e maintenance s h i e l d because of r a d i a t i o n , which ranged from 1 t o 60 r/kr over openings i n t h e t o p s h i e l d . I n s p e c t i o n of the r a d i a t o r showed only i n e o n s e q u e n t i a l damage due t o t h e blower f a i l u r e , b u t cons i d e r a b l e r e p a i r of' t h e enclosure and t h e door c e a l . ~w a s necessary because of heat-induced deformation and f a i l i r e s * Replacement r o t a r y e l e ments with s t r o n g e r hubs and. l i g h t e r blading were procu.red f o r the maLn blowers.

10 Ta.ble 1.1. Sumiiary of Some J$SRE Operatirig Data February 28, 1966

August 31, 1966

Time c r i t i c a l , h r

29 2

1775

I n t e g r a t e d power, MGThr

7823

C i r c u l a t i n g helium C ir e u l a t ing s a l t

1916 2836

2780 4691

C ir c u l a t ing he l i u m

1933 1809

2020 5360

5 5

20 9

Fuel loop time above 900'E', hr

Coolan-t loop time above 900"F, hr Circulating salt Heating cycles Fuel. system Coolant system

Fi11 cyc l e s

Fuel system Coolant system

Power cycles Fuel. system Coolant system

1.2

R e a c t i v i t y Balance

J. R. Engel The r e a c t i v i t y balance, as c a l c u l a t e d for t h e PERZ, i s a summation of a l l terms which a f f e c t t h e system r e a c t i v i t y . It i s r o u t i n e l y computed every 5 min while t h e r e a c t o r i s c r i t i c a l for t h e purpose of r e v e a l i n g any anomalous e f f e c - t s t h a t may be developing. The value of t h e r e a c t i v i t y balance i n r e v e a l i n g unexpecAed. e f f e c t s i s s t r o n g l y dependent on t h e accurate c a l c u l a t i o n of a l l t h e known terms. Very e a r l y i n tile power opera-Lion it became apparent t h a t -the 135Xe poi-soning was much less than expected. Accordingly, t h i s term w a s eliminated fi-om t h e r e a c t i v i t y bal-ance u n t i l t h e xenon e f f e c t could be evaluated and an accur a t e r e p r e s e n t a t i o n programed i n t o t h e computer. (The considerable e f i ' o r t d i r e c t e d toward evaluaLing t h e xenon e f f e c t i s described i n Sect. 1.3. ) I n spi-Le of t h i s omission, consi dera'ole u s e f u l information w a s derived from t h e r e a c t i v i t y balances.

11 R e a c t i v i t v Balances at Power Figure 1.1 shows t h e h i s t o r y of t h e p a r t i a l r e a c t i v i t y balance (no 135Xe c o r r e c t i o n ) during t h e approach t o full power from 1 Mw and steady o p e r a t i o n a t high power. The power h i s t o r y f o r this r e p o r t period i s included for r e f e r e n c e .

Xenon Poisoning. The most prominent f e a t u r e of t,he r e a c t i v i t y balance behavior i s t h e t r a n s i e n t s t h a t accompany s i g n i f i c a n t changes i n power. The d i r e c t i o n s of' the t r a n s i e n t s and t h e i r time dependence ccirrespond t o the expected behavior of 135Xe poisoning, but, they a r e much smaller i n magnitude. We used t h e s e transien-'is f o r a t e r k a t i v e eva1u.a t i o n of' t h e xenon poisoning e f f e c t . Power C o e f f i c i e n t of R e a c t i v i t y . A power. c o e f f i c i e n t of react,ivitjr i s used t o account f o r t h e f a c t t h a t t h e average grap1iii;e temperature i s higher t h a n t h a t of t h e f u e l at high power. I n i t i a l l y we cal.cuiated a i ef:t'ective temperature d i f f e r e n c e of 4A"F a t 10 Mw. T'hls l e a d s t o a O R N L - D W b 6 6 -9 0 8 2

'17

I 19

MAY, 1 9 6 6

..........

........!....i-L

.......... 1l.~

19 23 21 J U N E , 1966

.....!.. 1

J - . i l

.......... ..... 1

F i g . 1.1. Modified R e a c t i v i t y Balance During Power Operation.

12 p r c d i c t e d power c o e f f i c i e n t of -0.006 (% Sk/k)/Mw when tiie r e a c t o r ou’clet temperature i s h e l d constan-t ObservatTons of c o n t r o l - r o d p o s i t i o n s immediately b e f o r e and a f t e r l a r g e power changes i n d i c a t e d a simal.3.er power c o e f f i c l e n t of r e a c t i v i t y . C a r e f u l measurements i n t i m e s that, w e r e s h o r t r e l a t i v e t o t h e larger r e a c t i v i t y e f f e c t s gave a value of -0.001 ri: 0 .OOl(qb Gk/k)/Mw. This val-ue corresporids t o an e f f e c t i v e -Lemperat,ure difference betveen t h e graphi.ie a.nd fuel. o f 30°F a-t 10 Mis. Although t h e c o n t r i b u t i o n of Lhe power c o e f f i c i e n t t o t h e n e t r e a c t i v i t y i s small, a l l the r e a c t i v i t y balances were c o r r e c t e d t o t h e observed value of t h i s parameter.

H e a c t i v i t v Bal.ances a t Low Power

A somewhat less-obvious f z a t u r e of t h e g e n e r a l r e a c t i v i t y behavior w a s a gradual. d r i f t i n t h e p o s i t i v e d i r e c t i o n of balances taken a t very l o w power when xenon poisoning w a s n e g l i g i b l e . By t h e t i m e -the r e a c t o r was shut down i.n July, t h i s d r i f t had r a i s e d -the apparent n e t reac-Livity t o +O.l.% Sk/k. However, t h e r e a c t i v i t y balances do not con-Lain a t e r m t o c o r r e c t f o r c i r c u l a t i n g bubbles, and t h e r e i s some evidence (see S e c t . 1 . 4 ) tha-t the bubble f r a c t i o n i n c r e a s e d from e s s e n t i a l l y zero to about 1% during t h i s period. Since c i r c u l a t i n g voids have a negative efyec-t on t h e r e a c t i v i t y , proper compensation foi- t h e bubbles would rev e a l an even l a r g e r p o s i t i v e d r i f t i n t h e n e t r e a c t i v i t y . If t h e bubble f r a c t i o n d i d i n c r e a s e by l$, t h e n e t p o s i t i v e s h i f t i n r e a c t i v i t y during t h e p e r i o d i n question w a s abou-t 0.3% 6k/k. S e v e r a l of -the major termis i n t h e r e a c t i v i t y balance are a c c u r a t e l y known, as demonstrated by t h e good balances obtained i n t h e i n i L i a l period of low-power o p e r a t i o n . These t e r m s i n c l u d e t h e teniper,atu.re c o e f f i c i e n t of r e a c t i v i t y , compensation f o r t h e o p e r a t i n g 235U concentration, and control-rod poisoning. The t e r m s which were introduced by extended operati-on of t h e r e a c t o r at, high power are poisonjhg by low-cross-section y i s s i o n products, 235U burnup, and samarium poisoning. (Poisoning by 135Xe hac, not ye?, been included because o f t h e d i s c r e p a m y between pred i c t e d and observed behavior. ) One possTble explanation f o r t h e upward d r i f t i n r e a c t i - v i t y i s overcompensation f o r one o r more of t h e s e negative terms

Low-Cyoss-Section F i s s i o n Products. Since t h e yie2.d~ and e f f e c t i v e c r o s s s e c t i o n s f o r -ihese f i s s t o n products a r e reasonably w e l l kllomi, t h i s poTsoiiing t e r m can be a c c u r a t e l y calculatecd. Furthermore, a t t h e burnup a.chieved s o far, t h i s term accounts f o r only -0.004% 6k/k. 235U Burnup. Tlne c r o s s s e c t i o n s f o r 235U were adequately t r e a t e d i n t h e &ERE c a l c u l a t i o n s , as evidenced by t h e p r e d i c t i o n of t h e i n i t l a l . c r i t i c a l concentration and t h e concentration c o e f f i c i e n t of r e a c t i v i t y . Therefore, compensation f o r the buriiup of 235U,which amounted i o -0.128% Sk,/k when t h e r e a c t o r was l a s t shut dorm, i s probably not a major source of e r r o r .

Samarium Poisoning. IT2 es-iiniate t h a t tiie equilibrium samarium poisoning i n t h e MSRE w i l l be about 1% 6k/k. Both I4’Srn and 15’Sm cont r i b u t e t o t h i s e f f e c t , and, s i n c e d i f f e r e n t time c o n s t a n t s a r e a s s o c i a t e d w i t h each i s o t o p e , t h e two components a r e c a l c u l a t e d separate2.y and.

13 t h e n combined t o give the t o t a l r e a c t i v i t y effec.;. The c a l c u l a t e d samarium poisoning when t h e f u e l s a l t w a s drained on Jllly 24 was -0.364$ Sk/k.

Causes of Anomaly. The apparent r e a c t i v i t y anomaly a t low power must r e s u l t from an unknown p o s i t i v e r e a c t i v i t y e f f e c t , ovcrcompcnsation f o r negative e f f e c t s , o r a combination of this two. The magnitude of t h i s anomaly appears t o be at l e a z t 0.1% 8k/k, b u t it may be as Large as 0.3% iik/k. The u n c e r t a i n t y i s r e l a t e d t o t h e uncertairity i n t h e c i r c u l a t i n g void f r a c t i o n during o p e r a t i o n . To date t h e r e has been no evidence, e i t h e r chemical

01'

physical,

that the items which make up t h e negative r e a c t i v i t y ternis a r e behaving d i f f e r e n t l y than w a s assumed i n t h e c a l c u l a t i o n s . However, a d d i t i o n a l d e t a i l e d analyses of f u t u r e operations w i l l be r e q u i r e d t o v e r i f y t h e p r e d i c t i o n s of samarium poisoning and burnup. There h a s a l s o been no o u t s i d e evidence of any unforeseen phenomenon t h a t could have r e a c t i v i t y e f f e c t of th? magnitude observed.

1.3 B. E. Prince

positive

Xenon Poisoning

J. R. Engel

R. J. Ked].

Before t h e M S S was operated a t power, e s t i m a t e s were made of t h e 135Xe poisoning t h a t would be encountered.. These e s t i m a t e s were based on d e - t a i l e d models p o s t u l a t e d f o r t h e xenon behavior i n t h e s a l t , helium, and g r a p h i t e i n t h e r e a c t o r . Values f o r important parameters were obt a i n e d wherever p o s s i b l e from various development; t e s t s arid, i n t h e case of t h e c i r c u l a t i n g bubble f r a c t i o n , from experiments i n t h e MS.RE. (These e a r l y t e s t s i n d i c a t e d p r a c t i c a l l y no On this b a s i s t h e s t e a d y - s t a t e r e a c t i v i t y effect; due t o 135Xe was estimated t o he -l.O$$ 6k/k (poison TractLon = 1.44%) a t 7.5 Wd. The d e t a i l e d equations which describe xenon behavior were a l s o used t o malie p r e d i c t i o n s about t h e time dependence of t h i s phenomenon. 4

When t h e reac-tor w a s operated. a t power, t h e r e a c t i v i t y t r a n s i e n t s t h a t were a t t r i b u t e d t o 135Xe were found t o have time c o n s t a n t s t h a t were c l o s e t o t h e p r e d i c t e d values, b u t t h e magnitudes of t h e t r a n s i e n t s were o n l y about 0.3 t o 0 . 4 of t h e predicted. values. A p o s s i b l e explanation f o r t h e low xenon poisoning appeared when t h e r e began t o be s u b s t a n t i a l , independent evidence t h a t t h e r e were now c i r c u l a t i n g helium bubbles i n t h e f u e l loop ( s e e S e c t . 1 . 4 ) . A s a r e s u l t of t h e s e observations, add i t i o n a l s t u d i e s were performed i n an e f f o r t to o b t a i n b e t t e r c o r r e l a t i o n s between our p r e d i c t i o n s and experience" Two s e p a r a t e s t u d i e s were performed. u s i n g t h e same b a s i c s e t of equations 'out with somewhat difi'erent ob j e c t i v e s The f i r s t of t h e s e was an extensive parameter study of the s t x a d y - s t a t e ""Xe poisoning. The o b j e c t i v e s were (1)t o s e e i f t h e fiSRE experience could be explained with reasonable values of t h e parameters and ( 2 ) t o provide information

about t h e e f f e c t s of various parameters t h a t would be requ-ired f o r t h e extension of t h i s treatment t o o t h e r molt,en-sal.i;-reactor concepts. The second study w a s aimed. p r i m a r i l y a t the time dependence of t h e xenon The ob jecpoisoning with fewer v a r i a t i o n s i n t h e physical parame'iers t i v e here, i n a d d i t i o n t o provfding a b e t t e r i n s i g h t i.nto t h e behavior of xenon i n t h e MSRE, was t h e developmeni; of an adequa-t,e computational model f o r t h e i n c l u s i o n of xenon i n t h e oil-line c a l c u l a t i o n of t h e rea c t i v i t y balance.

P r e d i c t e d Steady-State "35Xe Poisonine: The s t e a d y - s t a t e 135Xe model described previously2 w a s modified t o i n clude t h e e f f e c t s of buhbles of helium c i r c u l a t i n g i n t h e s a l t , and c a k u l a t i o n s were made, The r e s u l t s a r e shown i n Fligs. 1 . 2 and 1.3. S i g n i f i c a n t parameters which were constant f o r t h e s e p l o t s are as follows: Reactor power l e v e l

7.5 Mw

S a l t s t r i p p i n g e f f i c i e n c y = 12%

Mass t r a n s f e r c o e f f i c i e n t t o b u l k g r a p h i t e

0.060 f t / h r

Mass t r a n s f e r c o e f f i c i e n t t o c e n t e r - l i n e graph-ite Diffusion c o e f f i c i e n t of xenon i n g r a p h i t e = 1 x

0.3% f t / h r

lom4 f t 2 / h r

Some of t h e s e parameters have been changed somewhat Trom those r e p o r t e d i.n t h e l a s t semiannual repor-L, b u t t h i s i s an updating and does not change any of t h e concl.i~sions. While t h e c a l c u l a t i o n s included t r a n s f e r o f 135Xe from t h e s a l t t o t h e bubbles, they omitted any t r a n s f e r of bubbles between t h e s a l t and t h e s u r f a c e of t h e g r a p h i t e . There aye ar,pnents t o support t h i s omission, b u t t h e e f f e c t might l a t e r prove t o be s i g n i f i c a n t . Figure l.2 shows t h e r e a c t i v i t y as a f u n c t i o n of c i r c u l a t i n g void f r a c t i o n . 'The band shows -the v a r i a t i o n wheli t h e bii'nble diameter i s f i x e d ah 0.010 i n . and t h e mass t r a n s f e r c o e f f i c i e n t t o t h e bubble covers a range of 3. t o 4 f t / h r . I t al-so shows t h e v a r i a t i o n when 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 i s f i x e d a t 2 f t / h r and t h e bubble diameter covers a range of 0.005 t o 0.020 i n . For thi.s f i g u r e Lhe bubble s t r i p p i n g e f f i c i e n c i s f i x e d a t 10%. The bubble s'iripping e f f i c i e n c y i s t h e f r a c t i o n of 3135Xeenriched bubbles t h a t b u r s t i n going through t h e p n n p bowl and ar? replaced w i t h pure helium bubbles. The a c t u a l value of t h e bubble s t r i p p i n g e f f i c i e n c y i s completely unknown, and 10% was picked only because thj.s i s approximately t h e value derived from some development t e s t s f o r t h e e f f i c i e n c y w i t h which d i s s o l v e d gas wou1.d be s t r i p p e d from t h e sal-t. E'igure 1.2b shows t h e v a r i a t i o n of r e a c t i v i t y with void f r a c t i o n a t v a r i o u s values o f bubble s t r i p p i n g e f f i c i e n c y . F o r t h i s p l o t t h e bubble diameter i s f i x e d a t 0.01.0 i n . and t h e bubble m a s s t r a n s f e r c o e f f i c i e n t i s f i x e d a t 2.0 f t / h r . The conclusion t h a t can be drawn froin t h e s e f i g u r e s i s t h a t c i r c u l a t i n g bubbles certarinly can, and probably do, account f o r t h e discrepancy between measured and p r e d i c t e d values of 135Xe

15 O R N L - D W G 66-11436

-1.5 FIXED PARAMETER:

FIXED PARAMETERS,

BIJBBLE STRIPPING EFFICIENCY = 10%

-$? >

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

b--SEE T E X T FOR DESCRIPTION

> -

I-

= 2 . 0___ f t / h r

-1.0

k -

u a

BUBBLE DIAMETER =0.010in BUBBLE MASS TRANSFER COEFFICIENT

-0.5

BUBBLE STRIPPING EFFICIENCY ( O l d 5 10

0.5

4.0 CIRCULATING

Fig. 1.2.

1.5

20 50

1.0

0.5

1.5

VOID FRACTION (%)

135Xe Poisoning as a Function of C i r c u l a t i n g Void F r a c t i o n

and Other Parameters A s I n d i c a t e d . -4.0

Fig. 1.3.

ORNL-DWG

66-1(437

Contribution of Systems to Total. 135Xe Poisoning.

poisoning. To prove t h i s conclusively, one would have i,o have accurate knowledge of t h e c i r c u l a t i n g void f r a c t i o n , bubble s t r i p p i n g e f f i c i e n c y , and o t h e r factors which a r e u n a v a i l a b l e at t h c p r e s e n t t,Lrnc. Figure 1.3 shows t h e c o n t r i b u t i o n of '"Xe i n e w h phase ( s a l t , g r a p h i t e , and bubblcs) t o t h e t o t a l computed 135Xe r e a c t i v i t y e f f e c t .

16 The various parameters a r e f i x e d as indica-Led. T h i s plo-L shows how c i r c u l a t i n g bubbles work t o decrease t h e loss of r e a c t i v i t y t o 135Xe. A s t h e void f r a c t i o n i s increased, most of t h e dissolved xenon migrates 'to the bubbles, dropping the dissolved xenon concentration g r e a t l y . Tne conc e n t r a t i o n p o t e n t i a l necessary for 1 3 5 ~ et o migrate t o tile g r a p h i t e i s reduced accordi-ngly. Now, s i n c e 135Xe in the g r a p h i t e was t h e l a r g e s t contribu-Lion t o r e a c t i v i t y i n the "no c i r c u l a t i n g bubble" case, t h e overall l o s s i n r e a c t i v i t y drops also.

Analysis of ~ r a i i s i e n t1 3 5 ~ ePoisoning The equatj.on.s given i n ref. 4 were modified to include t h e possib1.e presence of minil-Le helium gas bubbles c i r c u l a t i n g with t h e l i q u i d s a l t . The equations describing t h e t r a n s i e n t concentrations, rnod.ifleri to i n clude mass t r a n s f e r of xenon t o -the gas bubbles, are given below. To si.rflpl.ify t h e d e s c r i p t i o n , we w i l l assume t h a t t h e neutron fl.iix i s f l a t throughout t h e c o r e . The met'nod described. i n r e f . 4 f o r c o r r e c t i n g f o r t h e s p a t i a l dependence of t h e 135Xe poisoning w i t h i n -the graphitemotlesated region 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 modified equations given below. A s in r e f . 4> we have used a one-d-imensional model f o r t h e f u e l channels i n order t o simplify t h e c a l c u l a t i o n s . The d i f f e r e n t i a l equat i o n s governing t h e concentrztions of 135Xe i.n t h e 1iqiii.d s a l t , graphi-te, and c i r c u l a t i n g gas volume a r e as foll.ows:

-dt

V y . P - -C

R hINI >

The .sy-11li3olsused i n t h e s e equations a r c defined as f o i l o w s : ITsa

1,Xe

( t ) = average concentration OS 1351 and 135Xe in t h e l i q u i d f u e l s a l t , atoms per cubic centimeter of l i q u i d ;

Mb (t)

= average coricentration

(x, t )

'ke

of 135xe i n t h e c i r c u l a t i n g gas phase, atoms per cubic centimeter of gas;

local concentration of 135Xe a t p o s i t i o n x w i t h i n the g r a p h i t e stringel-, measured from t h e graphi-cc-salt i n t e r f a c e , atoms per cubic centimeter of g r a p h i t e ;

~ ! ~ (=t average ) concentration OS '35~e over t h e g r a p h i t e volurne a s s o c i a t e d with a s i n g l e f u e l channcl, atoms per cubic centimeter of graphite;

f i s s i o n d e n s i t y i n t h e core s a l t , f i s s i o n s per sccurid per cubic centimeter of l i q u i d ;

= average thermal-neutron

ern-2

YI,Xe %,Xe

sec-l;

f l u x i n reactor

COL'C',

neutrons

= f i s s i o n y i e l d s of 1351 and 135Xe; == r a d i o a c t i v e decay c o n s t a n t s f o r

1351 and I3'Xe,

sec'l;

cross s e c t i o n of 135Xe f o r thermal

= average absorption

Dxe

= d i f f u s i v i t y of xenon i n g r a p h i t e , square centimeters oâ&#x201A;Ź g r a p h i t e per. second;

neutrons i n M S ~em';,

yo = r a t i o of volume of s a l t i n core t o e f f e c t i v e mass t r a n s f e r s u r f a c e a r e a of g r a p h i t e , cm;

y1 = r a t i o of volume of' g r a p h i t e t o mass transf'txr surface a r e a of g r a p h i t e , em; = r a t i o of volume of s a l t w i t h i n r e a c t o r corc t o t o t a l

V /V

volume of c i r c u l a t i n g s a l t ;

h = mass t r a n s f e r c o e f f i c i e n t f o r l i q u i d f i l m at; the g r a p h i t e- s a l t i n t e r f a c e cm/s cc j

% C$

= mass t r a n s f e r c o e f f i c i e n t f o r l i q u i d f i l r r t at l i q u i d -

gas bubble i n t e r f a c e , cm/sec;

= e f f e c t i v e volume f r a c t i o n of h e l i i m bubbles i n c i r c u l a t i n g f luid;

d = bubble diameter, em;

u n i v e r s a l gas constant, ~2.0'7 em3 a t m mole-'

= average temperature,

OK;

("~1-l;

E =

Eenryrs l a w c o e f f i c i e n t , em3 atm mole-';

g r a p h i t e p o r o s i t y , cubic centimeters of void per ciib5.c centimeter of graphite;

= e f f e c t i v e removal constant

l i q u i d , sec-';

:::

i"or s t r i p p i n g of

1 3 5 ~ e from

e f f e c t i v e renioval constant f o r s t r i p p i n g of 1 3 5 ~ efrom gas bubbles, sec-'.

Equations (I) and ( 4 ) a r e i d e n t i c a l i n fori1 wi.th those gri.ven i n ref. 4 , Equation ( 2 ) has been modified by -tile a d d i t i o n of t h e las-t term on t h e right-hand s i d e of ( 2 ) t o r e p r e s e n t t h e n e t m a s s t r a n s f e r of 135Xe from t h e l i q i x i d . t o t h e gas phase. Transfer of bubbles between Lhe l i q u i d m d . t h e s u r f a c e of the g r a p h i t e w a s riot included. Equation (3) governs t h e time dependence of t h e ' 3 5 X e i n t h i s phase. The boundary conditions r e quired i n t h e so.1iition of Eq. (&) are:

Ap roxirnate values of t h e b a s i c parameters governing t h e mass transf e r of '35Xe t o t h e g r a p h i t e were obtained from krypton i n j e c t i o n experiments. N o d i r e c t experimental data a r e a v a i l a b l e fo:c t h e e f f e c t i v 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 the bubbles, hb, o r t h e e f f e c t i v e bubble si zes; however, r e p r e s e n t a t i v e values and probable ranges f o r t h e s e parameters could be estimated. The depen.dence o f the volLune f r a c t i o n of c i r c u l a t i n g bubbles on t h e r z a c t o r o p e r a t i n g conditions ( f u e l pump-bowl. l e v e l , temperature, p r e s s u r e ) i s n o t y e t w e l l understood. In this stuw, w e r e considered. Numerical values volume f r a c t i o n s between zero and 1% f o r 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 , geometric parameters, and g r a p h i t e c h a r a c t e r i s t i c s used i n most of t h e c a l c u l a t i o n s a r e given i n T a h l e 1.2. The g r a p h i t e d i f f u s i v i t y and p o r o s i t y a r e approximate values I"or t h e MSRE graphite; however, i t can be shown t h a t -the c a l c u l a t e d t r a n s i e n t s ar2 r e l a t i v e l y i n s e n s i t i v e t o t h e s e parameters. The e f f e c t i v e removal c o n s t a n t s f o r e x t e r n a l s t r i p p i n g , A, were c a l c u l a t e d i n accordance with t h e fornilla

and Asb,

where Q/Vz i s t h e r a t i o of t h e bypass flow r a t e through t h e xenon-stripping spray r i n g t o t h e volume of t h e c i r c u l a t i n g f l u i d and E i s the

19 Table 1.2.

Numerical Values of Parameters Governing I b s s Transfer of "35Xe i n MSRE

Paraneter YO,

Yl, cm

h, cm/sec

Value Assumed i n This Xtudy1.41

1.38

5 .46 x

hby cm/sec

0.017

d, cm

0.02.54 cm2/sec

~ cm3 ~ , a t m mole-'

2.15

j (

0.33 x

io9

s t r i p p i n g e f f i c i e n c y . Based on t h e krypton i n j e c t i o n experiments, the value of E i s expected t o be about 10%. F o r t h i s study, t h i s parameter w a s v a r i e d i n t h e range OP 10 t o 20%.

R e l a t i v e values of t h e c a l c u l a t e d time c o n s t a n t s in Eq. (3) f o r mass t r a n s f e r , s t r i p p i n g , decay, and neutron absorption i n d i c a t e t h a t the t35Xe i n t h e c i r c u l a t i n g gas phasc should be very n e a r l y i n eqiiilibrium w i t h the 135Xe i n t h e l i q u i d , independentiy of changes i n t h e r e a c t o r power l e v e l . Hence, t h i s approximation [ s e t t i n g t h e right-hand s i d e of Ey. ( 3 ) equal t o zero f o r a l l t i m e s ] w a s made t o s i m p l i f y t h e numerical c a l c u l a t i o n s . Some t y p i c a l t r a n s i e n t r e a c t i v i t y curves c a l c u l s t e d with the preceding formulas a r e given i n F i g s . 1.4 through 1.6. Figure 1 . A corresponds t o a s t e p i n c r e a s e i n power Prom Aero t o 7.2 Mw a t time zero.

The s e p a r a t e curves i n d i c a t e t h e e f f e c t i v e n e s s o f i n c r e d s i n g t h e voLwne of c i r c u l a t i n g ea.; i n reducing t h e n e t L35Xe poisoning. Each of these curves corresponds t o a f i x e d s t r i p p i n g e f f l c i e n e y of 10% for xenon both i n t h e l i q u i d s a l t and t h e c i r c u l a t i n g bubbles. The t r a n s i e n t a t 7.2 bEw w a s chosen, s i n c e a s u s t a i n e d r u n w a s made a t t h i s power l e v e l during run 7 . I n F i g . 1.4, we have also p l o t t e d t h e emoothed experimental d a t a obtained during t h i s run. These d a t a r e p r e s e n t t h e magnitude of the apparen?; 135Xe poisoning, determined by s u b t r a c t i n g a l l o t h e r know^^ power-dependent r e a c t i v i t y ef'fec ts from t h e r e a c t i v i t y rcpresentpd by movement of' t h e c o n t r o l rod. W e should emphasize t h a t the experimental evidence conceriiing the r E p r o d u c i b i l i t y of' t r a n s i e n t s of t h i s type i s a; y e t i n s u f f i c i e n t f o r conclusions t o be &ram concerning the amount of gas bu.bbles which may be i n c i r c u l a t i o n . 'Die data i n Fig. l a 4 suggest t h a t from 0.5 t o 1.0 v o l $ c i r c u l a t i n g gas can account q u a l i t a t i v e l y or t h e observed t r a n s i e n t poisoning. However, t h e experimental curve seems t o e x h i b i t a slower approach t o equilibrium t h a n i s p r e d i c t e d b y t h e t h e o r e t i c a l modc51.

1.4

20 ~~~

.........

ORNL-DWG

12 16 20 24 28 32 rlME AFTER INCREASE IN POWER LFVFl (hr)

66-4'438

Fig. l e 4 . E f f e c t of Voluriie F r a c t i o n of C i r c u l a t i n g G a s on T r a n s i e n t 135Xe R e a c t i v i t y , S t e p change i n power from 0 t o 7.2 Mw; strjp-ptng efPicieiicy, 1

vo,

l I M E AFTEt? I'UCREASE IN DOWEt? LEVtL(hi)

F i g . 1 . 5 . E f f e c t of Bubble S t r i p p i n g E f f i c i e n c y on T r a n s i e n t 1 3 5 X e R e a c t i v i t y . S t e p change i n power from 0 t o 7 . 2 Mw; volume Fraction of bubbles, 0.005.

The i n f l u e n c e of t h e bubble stri-ppi-ng e f f i c i e n c y on tho c a l c u l a t e d t r a n s i e n t s i s shown i n F i g . 1 . 5 . Here, t h e s e p a r a t e curves r e p r e s e n t t h e v a r i a t i o n of t h i s parameter w i t h i n a range of 10 t o 20% f o r a constant bub'ole voI.ii.rne f r a c t i o n . of 0.005. The experimental d a t a of Fig. I , 4 are also p l o t t e d i n t h i s f i g u r e .

Each of t h e transi.eni;s shown i n F i g s . 1.4 and 1..5 may be s e p a r a t e d i.nto components which correspond t o t h e 135Xe con'iained i n t h e l i q u i d , t h e helium bubbles, aiid t h e g r a p h i t e pores. The composition o f a t y p i c a l t r a n s i e n t , corresponding to a c i r c u l a t i n g gas volume f r a c t i o n o f 0.005 and a s t r i p p i i i g e f y i c i e n c y of lo$, i s shown i n F i g . l.6. For t h e poison-

21 0.5

. . . .

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

O R N L - D W G 66-11440

I - . i

TOTAL

'35Ke

0.2

5 0

0.1

0.05

n 3

5 2 k>-

F 4 <> W cr

0.07

0.01

0.005

0.002

0.001

8 16 24 32 1 I M C P F T I I R INCREASE IN P O W E R ILEVFL. ( h r )

Fig. 1.6. Components of Troulsient l"Xe R e a c t i v i t y . Step change i n power from 0 t o 7.2 Mw; volume f m c t i o n of bubbles, 0.005; stri-pping e f f i c i e n c y , LO$.

i n g i n t h e g r a p h i t e , c a l c u l a t i o n s a r e given both for a Ylat-flux approximation (dashed c u r v e ) and t h e weighted poisoning f o r a f l u x d i s t r i b u t i o n approximating t h a t i n t h e a c t u a l core ( s o l i d curve). Figure 1.6 illust r a t e s t h a t n e a r l y a l l t h e 135Xc i; contained i n t h e bubbles and t h e g r a p h i t e pores, t h e bubbles providing t h e a d d i t i o n a l ''sink'' which reduce;., t h e e f f e c t i v e rnass tran:;fer t o t h e g r a p h i t e . It a l s o i l l u s t r a t e s t h e diâ&#x201A;Źfcrence i n the time c o n s t a n t s â&#x201A;Źor buildup of t h e s e corriponents. Tne approach t o equilibrium o f t h e 13'Xe i n t h e g r a p h i t e i s slower than t h a t i n t h e liqAid, owing t o t h e e f f e c t i v e time l a g introduccd by the m a s s t r a n s f e r between t h e l i q u i d and g r a p h i t e .

As more experimental evidence i s accumulated concerning t h e trans i e n t behavior oi' t h e 135Xe poisoning, attempts w i l l be made t o r e f i n e t h e preceding model. T h i s will include attempts t o d e t e r n i n e t h e dependence of t h e volume o f c i r c u l a t i n g gas on t h e r e a c t o r o p e r a t i n g condicions and t h e degree t o which a f i x e d gas volume Inight be e,Cpected during f l i r t h e r o p e r a t i o n of t h c r e a c t o r .

1.4 Circu3.ating Bubbles ..._... _.R . J. Ked1

J. E. Engel

Ear1.y i n t h e d e w l o p e n t of t h e MS,W s a l t pumps, some evid-ence appearcd t h a t t h e c i r c u l a t i n g f u e l s a l t would c o n t a i n a s m a l l b u t rneasurab1.e q u a n t i t y of helium bu.bbI.es introduced. by t h e xenon stripp.j.ng device. This was a s i g n i f i c a a t f i n d i n g because of t h e p o t e n t i a l i n f l u e n c e of t h e s e bubbles on t h e r e a c t o r dynamics (through a preszure c o e f f i c t e n t of r e actri.vj.ty) and on xenon poisoning. T h e o r e t i c a l analyses l e d t o the conc l u s i o n t h a t the dynamic e f f e c t s would n o t be s e r i o u s b u t t h a t bubbles would. s u b s t a n t i a l l y reduce t h e xenon poisoning. Because o f 'ihe i m portance of t h e bubbles, experiments were planned 'io measure t h e c i r c u l a t i n g void f r a c t i o n . The experiment designed t o measure t h e void f r a c t i o n c o n s i s t e d i n s u b j e c t i q t h e fuel. system t o a rapid. p r e s s u r e r e l e a s e . I n t h e s e t e s t s t h e f u e l system would f i r s t be pressui-ized t o about 15 p s i g ( n o m a 1 overpressure i s 5 p s i g ) w i t h heliiim and allowed. i;o e s t a b l i s h a new sieady s t a t e . The excess overpressure would t h e n be r a p i d l y r e l e a s e d by venting t h e gas t o a prev-iously vented, empty d r a i . a tank. Expamion of any gas i n t h e l o o p f o r c e s sal'i. i n t o t h e surge space i n t h e pump bowl, where it can be measu.red by t h e l e v e l instrument. I n a d d i t i o n , t h e expulsion of sa1.t f r o m t h e core reduces r e a c t i v i t y , which can be measured i n tlie c r i t i c a l r e a c t o r by observing c o n t r o l - r o d motion. A t h i r d method or" eval-uating t h e c i r c u l a t i n g voids , a s a l t densitometer wa,s i n s t a l l e d f o r use i n t h e i n i t i a l t e s t s p r i o r t o o p e r a t i o n of the r e a c t o r a t s i g n i f i c a n t power.

'l'hx-ee p r e s s u r e - r e l e a s e t e s t , s were perf o m e d as p a r t of t h e zero-power experiments i n J u l y 1965. Two of t h e s e t e s t s a t normal. system temperat u r e and s a l t l e v e l i n t h e pimp bowl, indicated. t h a t t h e r e w a s essentia.l.3-y no gas i n tile c o r e . However, tlie t h i r d t e s t , which w a s conducted a t an. abnormally low pump-bowl l e v e l (obtained by 1owering t h e o p e r a t i n g temp e r a t u r e t o lO5O0F), showed a void -fraction of 2 t o 3%. It; appeared f r o m t h i s t e s t t h a t bubbl-es d t d not begin to c i r c u l a t e i n t h e loop i m t i l t h e putlip-bowl l e v e l was reduced t o about 50% on t h e bubbler l e v e l elements. Since only one such ex1periment w a s performed, t h e i n d i v i d u a l e f f e c t s of pump-bowl l e v e l and s a l t temperature were no-1; separated.

The r e s u l t s of t h e s e zero-power tests I.ed t o t h e establishment of a mininium pumpbowl o p e r a t i n g l e v e l of 50% t o prevent c i r c u l a t i o n of helium bubbles. I n additlion, t h e bubble term was removed from t h e eqiiations used t o p r e d i c t xen.on poisoning. When t h e r e a c t o r w a s operated a'i, high power, t h e observed xenon t r a n s i e n t s were miich smaller t h a n t h o s e pred i c t e d by t h e "no bubble" equations, implying t h e presence of bubbles. I n a d d i t i o n , a r e a c t i v i t y disturbance occurred on June 19, 1966, which again emphasized t h e i.mportance of bubbles. On t h a t d a t e (see F i g . 1.1) the n e t r e a c t i v i t y began t o decrease sharpl.y, and i t w a s Iioted t h a t t h e lower of two pimp-bowl l e v e l indri.cations had dropped. below 50% because of t h e continuous %ransfex- of sal-i; from t h e pump bowl t o the overflow tan.k. The r e a c t i v i t y recovered r a p i d l y when t h e s a l t w a s r e t u r n e d t o t h e

pump bowl from t h e overflow tank. Following t h i s event, small i n c r e a s e s i n r e a c t i v i t y were noted each time s z l t was returned from t h e overflow t a n k even though the pwnp-bowl l e v e l was kept above 50$.

Several pressure-release experimerits were performed near t h e end of' run 7 (July. 1966) t o determine whether t h e c i r c u l a t i n g void fra,:< t i o n vas higher t h a n t h a t observed a year ago. Since, b y t h i s time, s a l t w8s cont i n u o u s l y t r a n s â&#x201A;Ź e r r i n g t o t h e overflow t a n k a t t h e normal pump-bowl l e v e l , experiments could be performed at d i f f e r e n t pumpbowl l e v e l s with t h e same r e a c t o r o u t l e t temperature. Experiments were perfoniied a t both high and low power l e v e l s , and one was performsd a t an abnormally l o w temperature. Preliminary evaluations have bcen made of t h e void f r a c t i o n s a t each condition, End t h e r e s u l t s are shown i n Table 1.3. Ti-le r e s u l t s of two of t h e e a r l i e r t e s t s (performed July 2, 1965) a r c included f o r r e f e r e m e . Although a d d i t i o n a l experiments a r e necessaiy t G elucidate. the Lituation, some conclusions can be drawn. It appears t h a t t h e c i r c u l a t i n g void f r a c t i o n a t t h e end. of run 7 was s u b s t a n t i a l l y higher than during the zero-power experiments. The r e s u l t s a l s o show a s u b s t a n t i a l dependence

Table 1.3.

Date of Test

C i r c u l a t i n g Void F r a c t i o n Measurements i n IGW Void Fraction ($J)

Conditions Reactor

Power

Reactor Outlet Temperature (OF)

I n i t i a l PumpB o w l Level

($1

From

lump-Bowl.

Ievel R i s e "

From Control-Rod Motion

'7/2/65

io-

1197

59 .6

7/2/65

10-5

1050

50.O

2.69

2 .05

7/8/66

'7.3

1210

53 .O

0.65

0.81

7/12/66

7.2

1210

61.2

0.2443.54.

0.34

7/21/66

0.01

1191

56.2

0.87-1.01

1.94

7/22/66

0.01

1190

51.3

0.50-0.73

1.24

7/23/66

0.01

1189

61.5

0.48-0.62

0.96

7/23/66

0.01

1124

52.8

2.68-2.91

2.39

%ange r e f l e c t s c u r r e n t u n c e r t a i n t y in compen-D a t i n g f o r pressure s e n s i t i v i t y of level. elements.

on s a l t temperature, a t l e a s t ai; pump-bowl l e v e l s above 50%. This dependence may be r e l a t e d 'io Yne e f f e c t of s a l t v i s c o s i - t y on t h e bubble r i s e ve l.oc i t y

There a r e some i n c o n s i s t e n c i e s i.n t h e measured void f r a c t i o n s . These may be due i n p a r t t o t h e uncer-Laiiities i n compensa-timg f o r s i d e e f f e c t s during t h e pressure r e l e a s e , f o r exanple, pressure s e n s i t i v i t y of -the l e v e l - i n d i c a t i n g devices and t r a n s i e n t nuclear periods during control-rod adjustment. There i s a l s o a b a s i c d-ifference between t h r void f r a c t i o n s measured by t h e two methods i n Table 1.3. The pump-bowl l e v e l measurements i n d i c a t e t h e average void f r a c t i o n i n t h e e n t i r e primary loop, while t h e conti-01-rod measurements i n d i c a t e only t h e average void f r a c t i o n i n t h e core. Thus, i f t h e r e were any tendency f o r voids t o conceiltrate i.n a p a r t i c u l a r l o c a t i o n , e i t h e r i n o r o u t s i d e Lhe core, d i f f e r i n g r e s u l t s could be expec-Led. Furthermore, t h e r e may be some dependence on t h e rimmediate p a s t h i s t o r y of t h e reac1;oi". I f , f o r example, t h e bubbles c i r c u l a t i n g a t low pressure a r e very s t a b l e and a r e inefficizn.t.3y stripped., a l e v e l change j u s t p r i o r t o a t e s - t could prodince d i s l e a d i n g r e s u l t s . De'ia:Lled. evaluations of t h e s e and o t h e r e f f e c t s w i l l be i.ncl.uded in f u t u r e analyses.

1.5

S a l t Transport H. B. P i p e r

Gradual Transfer t o Overflow Tank E a r l y operation of t h e r e a c t o r showed t h a t 'uy some unexplained mechanism s a l t grad.uaI..ly accumid.ated i n t h e f u e l pump overflow tank even when -the s a l t l e v e l i n t h e p m p bowl w a s well below t h e overflow p o i n t . The t r a n s f e r r a t e depended on s a l t level., and "ihe t r a n s f a ceased when t h e l e v e l w a s abou-t; 3 i n . below t h e overflow p o i n t . 'This s i t u a t i o n exi s t e d u n t i l about A p r i l 1966, when t r a n s f e r began t o be observed at; lower sa1.t l e v e l s . The r a t e appeared t o i n c r e a s e gradually as time went on u n t i l it l e v e l e d o f f i n June and J u l y a t 0.57 To of s a l t per hour, i n dependent of salt l e v e l as Car down as 4.7 i n . below t h e overfl.ow p o i n t . The change occurred a t t h e -Lime of t h e stepwise i n c r e a s e j.n power, b u t no mechanism connecting t h e two has been i d e n t i f i e d . This t r a n s f e r has no i l l - e f f e c t on operation of t h e r e a c t o r o t h e r than i-mposing t h e r e q u i r e ment -I;iiat t h e overflow tank be emptied t h r e e -Limes a week t o keep t h e l e v e l s i n t h e d e s i r e d operating range.

Ov-erf ill At; t h e conclusion of operctioii i n July, t h e f u e l with f l u s h s a l t t o r i n s e out r e s i d u a l pockets of f u e l ducing t h e r a d i a t i o n l e v e l s f o r scheduled work i n t h e decided t o t r a n s f e r f l u s h s a l t i n t o t h e overflow tank

loop w a s f i l l e d salt, thus rereactor c e l l . W e f o r two reasons:

t o f l u s h out t h e r e s i d u a l f u e l and t o check t h e i n d i c a t e d l e v e l a t t h e

overflow p o i n t . T r a n s f e r began t~hent h e i n d i c a t e d l e v e l vas 9.6 i n . ( I n January 1965 t h e i n d i c a t e d l e v e l a t t h e overflow poiri-t had been 9.2 i n . ) Approximately 0.6 f t 3 of s a l t had been t r a n s f e r r e d when suddenly the f u e l pump l e v e l r o s e s h a r p l y o f f s c a l e . R i s i n g l e v e l i n t h e overflow tank t r i g g e r e d a d r a i n , b u t not b e f o r e s a l t had e n t e r e d some of the l i n e s comec-ked t o t h e t o p of t h e pump bowl. What had happened was t h a t t h e s a l t l e v e l i n t h e f l u s h t a n k had been lowered t o o f a r , allowing t h e press u r i z i n g gas t o e n t e r t h e f i l l l i n e arid pass up i n t o t h e r e a c t o r v e s s e l , The gas expanded r a p i d l y as it r o s e through t h e s a l t , causing s a l t to flood. t h e pump bowl. The pump-bowl bubbler r e f e r e n c e l i n e was plugged with f r o z e n s a l t , and enough s a l t was f r o z e n i n t h e sampler tube t o o b s t r u c t passage of t h e l a t c h . A. thermocouple i n d i c a t e d "chat some s a l t ; a l s o e n t e r e d t h e off-gas l i n e , b u t t h i s l i n e w a s not plugged. S a l t a l s o f r o z e i n the annulus ?round t h e fuel-pump shad%%,preventing i t s r o t a t i o n .

This i n c i d e n t was caused by human e r r o r . The l e v e l 1;o which t h e overflow t a n k w a s t o be f i l l e d i s w i t h i n t h e range e a s i l y a t t a i n a b l e wtth f u e l s a l t . But -the volume of f l u s h s a l t i n t h e r e a c t o r i s l e s s , and, i n order t o r e a c h t h e specrified 2.evel i n t h e overflow tank, i-t was necessary t h a t t h e s a l t temperature be ahout L200Â°F o r above. Thi.s was overlooked when t h e procedure was s p e c i f i e d , and. t h e loop was f i l l e d a t I1IO0F. This tempera-Lure i s w i t h i n t h e range f o r a normal f i l l , and t h e s p e c i a l r e quirement f o r t h i s experiment w a s n o t recognized u n t i l a f k r the i n c i d e n t had occurred. IL?unediatelya f t e r t h i s mishap t h e overflow t a n k was ernptied and t h e %he pump t a n k was heated -Lo 1200OE' and t h e s h a f t was f r e e d . Subsequently e l e c t r i c h e a t e r s were a p p l i e d t o the o u t s i d e of t h e l i n e s t o melt out t h e s a l t i n t h e bubbler r e f e r e n c e l i n e an6 the sampler t u b e . The short f l e x i b l e p o r t i o n of t h e o f f - g a s l i n e was ~ e p l a c e dbecause of u n c e r t a i n t y over t h e p o s s i b l e e f f e c t s of s a l t i n -the l.*onvolutions.

loo;: vJas r e f i l l e d .

1.6

Power Measurements

H. B. P i p e r

C . Iâ&#x201A;Ź. Gabbard

Hea t Balanc e The n u c l e a r power produced i n t'rre E R E i s determined by an o v e r a J l system h e a t balance. During e a r l y o p e r a t i o n a t lot7 power (below -1.0 Mw) u m e r t a i n t i e s i n measuring s m a l l temperature d i f f e r e n c e s yielded. a large percentage e r r o r i n the conputed h e a t balance. ?â&#x201A;Źowever, as t h e power w a s r a i s e d t o i n t e r m e d i a t e l e v e l s , t h e u n c e r t a i n t i e s i n t h e h e a t balance c a l c u l a t i o n became less and good confidence w a s e s t a b l i s h e d i n t h e hra-t; balance power. Since t h e h e a t balance i s t h e primary power standard, a l l n u c l e a r power instrrunents were c a l i b r a t e d t o agree w i t h i t . A s t h e power w a s r a i s e d , t h e c a l i b r a t i o n of t h e n u c l e a r insti-urnelits changed, m d a disagreement i n power i n d i c a t i o n e x i s t e d between t h e n u c l e a r i n s t r u ( T h i s disagreement w i l l b e ' d i s c u s s e d l a t e r ments and t h e h e a t balance. iii t h i s s e c t i o n . )

26 The heat-balance ca!.culation i n t h e computer remains unchanged, but the method f o r obtaining a zero-power base 3 - n e has been modipied. Init i a l l y , a constant "heat l o s s " term along wi.th zero-power temperature b i a s e s were used t o establislh t h e h e a t 'oal.ancr zero power. It was noted, however, t h a t with t h e r e a c t o r producing zero power, t h e cornpilted heat bala,nce might vary from lnm t o run by as much as S O 0 hw. We b e l i e v e t h i s occurs because many thermocouples a m s e n s i t i v e t o h e a t e r s e t t i n g s ant1 the h e a t e r s nay not be s e t e x a c t l y t h e same f o r each :rim. This d i f f e r e n c e r e p r e s e n t s an e r r o r o f only ?2"'7%when we run a t 7 . 5 Nw. Nevertheless, at; t h e beginning of each run, s e v e r a l heat balances a r e taken, t h e value of t h e discrepancy i s determined., and t h i s value i s e n t e r e d i n t h e beat-balance c a l c u l a t i o n as a new value of t h e "heat I.oss" term, thus y i e l d i n g a c o r r e c t e d power f o r t h e remainder of each run.

Nuclear Instruments __.'The agreement between t h e heat-balance power and t h e power indica-Led by t h e nuclear instruments w a s b e t t e r that). k -lo$ from 2 t o about 6 Mw. (Beat balances have a s c a t t e r of + -200 kw, and t h i s i s independent o f power; below 2 Mw t h e percentage s c a t t e r is l a r g e . ) Above t h i s l e v e l t h e t w o power i n d i c a t i o n s began 'io diverge with t h e nuclear rinstrurnents indi.ca.ting 1.5 t o 20% high a t a heat-balance power of 7.5 Mw. A f t e r i n v e s t i g a t i n g , w i t h negative r e s u l t s , s e v e r a l mechanisms which might e x p l a i n t h e disagreement, i t w a s post;ula.ted t h a t t h e e f f e c t might have been caused by a r i s e i n wa.ter temperature i n t h e nuclear rins-ti-unent penet r a t i o n ( N I P ) as t h e power w a s i-ncreased.. This w a s found t o be t h e case. When t h e r a t i o of heat-balance power t o nuclea~-i.nstrument power w a s p l o t t e d vs rJIP temperature, a good c o r r e l a t i o n . w i - t h a negative slope r e sulted., This p l o t showed t h a t an i n c r e a s e of l0"F i n t h e NIP water temp e r a t u r e produced an i n c r e a s e of 450 kw, o r a1mu.i; 6$, i n the powi3r i i i d i c a t i o n from t h e nuclear instruments a t a l e v - e l power of 7.5 Mw. Thri.s anomaly could be caused by teinperature s e n s i t i v i t y of t h e nuclear h s t m ments, b u t we be1.i-eve %he most l i k e l y explanation of t h e temperat-u.re sens-i.tYvity i s t h e change i n t h e a t t e i i u a t i o n c h a r a c t e r i s t i c s of water with temperature. On June 27, a heat exchanger system w a s placed i n operation t o c o o l t h e water i n t h e mP. A s t h e NIP ~rai;ertemperature decreased, tlle rati.0 between heat-balance power and. nuclear-instrument power approached u n i t y . The h e a t exchanger used w a s immediately azrailabl-e, b u t i t does not have t h e capacity t o hold t h e NIP water tetruperatu.re constant a t a l l power l e v e l s . From zero t o f u l l power, t h e r e i s now a temperature r i s e of -16째F as coinpared t o -72째F before the heat exchanger w a s iristal.led. There i s s t i l l a s h i f t of about 5% between t h e two power measurements from z e r o t o f u l l power.

Radiator A i r Flow Because o f t h e l a c k of agreement between the heat-balance power and t h a t i n d i c a t e d by t h e nuclear instriunznts , w e attempted t o verify t h e power by determining t h e m o u n t of heat removed. from t h e rad-iator by t h e a i r . The i n h e r e n t u n c e r t a i n t y i n determining Lhe r e a c t o r power by a heat

27 balance around t h e a i r s i d e of t h e r a d i a t o r i s g r e a t because of d i f f i c u l t i e s i n measurement of b o t h t h e air flow and t h e temperatures. These d i f f i c u l t i e s a r i s e â&#x201A;Źram t h e f a c t t h a t t h e coolant s t a c k i s riot long enough (L/D = 7 ) f o r symmetrical flow t o be e s t a b l i s h e d . Even so, c a l c u l a t i o n s were rnade using t h e b e s t d a t a a v a i l a b l e f o r t h i s evaluation. The heat removed by t h e a i r vas determined f o r r e a c t o r power l e v e l s of 4 , 5.8, snd. 7 MJ, as neasured by t h e o v e r a l l system h e a t balance, and w a s found t o be low, 16% high, and 15% high r e s p e c t i v e l y . This i s considered t o be a reasonable confirmation of t h e system heat-balance niethod.

1.7

Radiation Heating

C. H. Gabbard

H. B. Piper

The e f f e c t s of r a d i a t i o n h e a t i n g on some of t h e MSKF: components were evaluated b o t h during t h e approach t o f u l l power and during s u s t a i n e d o p e r a t i o n a t high power. O f p a r t i c u l a r i n t e r e s t i n t h i s a r e a a r e t h e fuel-pump tank, t h e r e a c t o r v e s s e l , and t h e thermal s h i e l d . (Tne e f f e c t s of f i s s i o n product r a d i a t i o n h e a t i n g i n t h e off-gas piping a r e discussed i n connection with o t h e r observations of t h a t system i n Sect. 2 . 9 , subs e c t i o n e n t i t l e d "Ehel O f f - G a s System").

Fu.e1-mUnp Tank Tie upper p o r t i o n of t h e fuel-pump t a n k i s s u b j e c t t o su'ostantisl h e a t i n g from f i s s i o n products i n t h e gas space above. t h e s a l t . Since t h e u s e f u l l i f e of t h e pump t a n k i s l i i n i t e d by t h e r m a l - s t r e s s considerat i o n s a t t h e j u n c t i o n of t h e v o l u t e support c y l i n d e r with the s p h e r i c a l t o p of t h e tank, c l o s e c o n t r o l w a s maintained over %he t e r n p e r a t u e s i n t h i s region. Design s t u d i e s 7 had i n d i c a t e d t h a t t h e maximum l i f e t i m e would r e s u l t i f t h e j u n c t i o n temperature were kept about 100Â°F below t h e temperature on t h e t a n k s u r f a c e 6 i n . out from t h e j u n c t i o n . Component cooling a i r i s provided t o maintain t h i s temperature d i s t r i b u t i o n . A secondary c o n s i d e r a t i o n i n c o n t r o l l i n g t h e temperatures w a s a d e s i r e t o keep as much of t h e pump t a n k as p o s s i b l e above t h e l i q u i d u s temperature of t h e s a l t .

I n o p e r a t i n g t h e r e a c t o r , i-t would be i d e a l if a fixed flow r a t e of a i r over t h e m p t a n k would provide a s a t i s f a c t o r y temperature d.is-tribuEarly design 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 i s t i o n f o r a l l conciitions c o n d i t i o n could be met with an a i r flow of 200 c f m . However, temperature measurements on t h e pump-test loop and d m i n g the i n i t i a l heat-up of the MSRF: i n d i c a t e d t h a t only about 50 cfm would be requil-ed and t h a t t h e a i r would have t o h e t u r n e d o f f when t h e pump t a n k w a s empty.

To minimize t h e temperature e f f e c - t s when t h e c o o l i a g a i r i s t u r n e d on, a i r flow during power o p e r a t i o n should be t'ne minimum t h a t gives t h e d e s i r e d .terxperatures. It w a s found t h a t an a i r flow of 30 c f h provides a s a t i s f a c t o r y temperature d i s t r i b u t i o n at; a l l power l e v e l s up t o 7 . 5 M,. Figure 1 . 7 shows t h e temperatures i n Lhe two regions of i n - t e r c s t as a furiction of r e a c t o r power l e v e l with t h i s a i r flow. The v a r i a t i o n s i n

F i g - 1 7. V a r i a t i o n of Fuel-Pimp Tank Temperatures with Reactor Power. Cooling-air flow, 30 c3n.

-the i n d i v i d u a l temperatures a r e cav.sed by varia,tions i n pump-bowl l e v e l , s a l t t e m p r a t u r e , and a i r flow. Both t h e indLvidua1 temperatures and t h e temperature d i f f e r e n c e i n c r e a s e l i n e a r l y with power, as expected. Although t h e temperature d i f f e r e n c e would exceed 100째F a t powers much above 7.5 MGJ, t h e r e a c t o r c0ul.d be operated a t 1.0 NIT w i t h t h e 30-cfm a i r flow without s i g n i f i c a n t l y reducing t h e l i f e of t h e pump tank. However, vari.ati.on of t h e a i r flow c o u l d a l s o be employed t o o b t a i n closer c o n t r o l of t h e temperatures I

Reactor Vessel Sirice radiation-prod-uced h e a t i n the r e a c t o r - v e s s e l w a l l s m u s t be t r a n s f e r r e d t o t h e s a l t f o r removal, t h e o u t e r s u r f a c e s of t h e vessel. a r e h o t t e y t h a n t h e adjacent sal-t by an amoun'i t h a t i s p r o p o r t i o n a l t o t h e r e a c t o r power. Any d e p o s i t i o n of solids on t h e i n n e r s u r r a c e s would reduce t h e heat; t r a n s f e r (and i n c r e a s e t h e h e a t production) ar?d lead t o s t i l l higher temperatures a t t h e o u t e r s u r f a c e s . There are two l o c a t i o n s i n the r e a c t o r vessel. where solids would tend. t o accu.mlate i f they were present i n t h e c i r c u l a t i n g s a l - t . These are t h e lower head and t h e lugs, j u s t above t h e i n l & voliite, which support the core matrix. Deviations from t h e normal silxrface temperatu-res might a l s o i n d i c a t e changes i n t h e core flow p a t t e r n .

Although t h e r e has been no evlidence, whatever, of so3.ids i n t h e molten s a l t s , the d i f f e r e n c e s between t h e r e a c t o r - v e s s ? l Lernperatures and t h e s a l t inl.et temperature have been c a r e f u l l y monitored. Since t h e s a l t i n l e t temperature can be measured only a t t h e i n k t l i n e and t h e r e i s some f i s s i o n heat generation i n t h e sal-L as it flows t o t h e areas i n question, t h e observed N " s do not r e p r e s e n t t h e a c t u a l temp e r a t u r e drops across t h e w a l l s . However, t h e p r o p o r t t o n a l i t y -to power should e x i s t , and t h e r e should be no change w i t h t i m e .

Throughout t h e power o p e r a t i o n of t h e r e a c t o r , t h e temperature d i f f e r e n c e between t h e v e s s e l wall a t t h e core-support l u g s and t h e salt i n l e t has been 2.0 t O.l.'F/Mw, and t h a t between t h e lower head and t h e s a l t i n l e t has been 1 . 5 I0.2'F/Mw. There has been no i n d i c a t i o n of d e v i a t i o n from l i n e a r i t y with power o r of' changes with t i m e i n e i t h e r temperature d i f f e r e n c e . T'nermal S h i e l d

The f u n c t i o n of t h e thermal s h i e l d around t h e r e a c t o r vessel- i s t o reduce t h e r a d i a t i o n l e v e l and r a d i a t i o n h e a t i n g i n t h e r e s t of' t h e rea c t o r c e l l . A s a r e s u l t , a s u b s t a n t i a l m o u n t of f a s t - n e u t r o n and g m a energy i s d e p o s i t e d i n t h i s s h i e l d . The c o o l i n g system f o r t h e therrnal s h i e l d was designed t o remove up t o 600 kw t o allow â&#x201A;Źor u n c e r t a i n t i e s in t h e r a t e of h e a t g e n e r a t i o n a t power. Measurements of t h e h e a t l o a d on t h e therrnal s h i e l d gave a zero-poww value of 40 kw due t o h e a t losses from t h e r e a c t o r furnace and an a d d i t i o n a l 17 kv p e r megawatt of r e a c t o r power due t o r a d i a t i o n h e a t i n g .

1.8 Reactor DynamLcs

T. W. K e r l i n

S. J. Ball

The i n h e r e n t s t a b i l i t y of t h e r e a c t o r system was i n v e s t i g a t e d by frequency response t e x t s a t e i g h t power l e v e l s from zero t o full power. The t e s t i n g methods, a n a l y s i s procedu.res, and r e s u l t s of t e s t s a t powers t o 1 Mtur a r e described i n d e t a i l i n t h e last progress r e p o r t . 8 Subsequently, t e s t s were conducted at 2.5, 5.0, 6 . 7 , and. 7.5 M ~ Iu s i n g pseudorand.om b i n a r y r e a c t i v i t y i n s e r t i o n s pulse r e a c t i v i t y i n s e r t i o n s , and step r e a c t i v i t y i n s e r t i o n s . A t each power l e v e l , e s s e n t i a l l y e q u i v a l e n t r e s u l t s were obtained from t h e d i f f e r e n t t e s t s .

A r e a d i l y o b t a i n a b l e r e s u l t i s t h e n a t u r a l p e r i o d of o s c i l l a t i o n of

the r e a c t o r pumr following a distidcxmce i n r e a c t i v i t y . This information can be obtained by simply observing t h e flux t r a n s i e n t i f ' t h e response i s l i g h t l y damped o r by dete-miining the frequency of t h e peak i n t h e m p l i t u d e of t h e frequency response. The experimental results agree very w e l l w i t h previous t h e o r e t i c a l p r e d i c t i o n s , ' as S ~ O ~ L TiSnI F i g . 1.8. The measured frequency resZJonse r e s u l t s f o r power l e v e l s of 2.5 Mw and higher a r e shown i n Figs. 1 . 9 t o 1 . 1 2 along with t h e t h e o r e t i c a l p r e d i c t i o n s . The t h e o r e t i c a l phase p r e d i c t i o n s agree wj-th t h e experimental r e s u l t s w i t h i n t h e experimental s c a t t e r . A l l t h e tests at a given power l e v e l give magnitude r a t i o s having t h e same shape b u t d i f f e r i n g i n t h e i r a h s o l u t e v a l u e s . Furthermore, t h e p o r t i o n s of t h e frequency responses above 0.3 r a d i a n l s e c should be t h e sane f o r al.1 power l e v e l s , sirice feedback e f f e c t s are s m a l l i n t h i s frequency range and t h e zeroThe experimental r e s u l t s for power frequency response should dorainate s

30 various power l e v e l s show ’ L ~ E s a w shape i n this frequ-ency regloxi bui d-iffei-ent absolu.te m p l i t u d e n Both of t h e s e i n c o n s i s t e n c i e s i n d i c a t e a b i a s problem which i s apparently due t o equipmen’; l i m i t a t i o n s .lo These equipment d i f f i c u l t i e s a r e not s u r p r i s i n g , s i n c e we wantsd t o be a b l e p o s i t i o n t h e c o n t r o l rod ~ 5 t han accuracy bette:f: iiiaii 0.050 i n . i n t h e dynam.i.cs tests; t h i s f a r exceeded design s p e c i f i c a t i o n s .

We previously -tho-ught that, a simple arijustinent o f s e v e r a l paramaters i.n t h e t h e o r e t i c a l model c o u l d f o r c e agreement be tween theory and experiment. An adjustment rrlaile to minimize t h e e r r o r a t 1.0 Mw a l s o produced agreem.ent a-t; 0.075 Mw and 0.465 Mw. This now appears t o have been f o r t u i t o u s , since t h e same pararrleter adjustinents i n c r e a s e the d t s c r e p m c i e s a t power 3.evels g r e a t e r .than 1.0 WT. The n e t conclusions a r e t h a t Lhe dynamic c h a r a c t e r i s t i c s of the sy,s.tem a r e quite satis.faci;ory and i n reasonable agreerneiit with p r e d i c t i o n s . The system i s s t a b l e a t a1.l operating power levels, and t h e stabl.l.ity i n c r e a s e s with power l e v e l . The t h e o r e t i c a l model.. appears t o be satisfactory i n Spi-Lc of unfortunate e q u i p e n t l i m i t a t i o n s which prevent det a i l e d parameter f i t t r i n g ”

Flg,

Oscillation.

Compari-son of Predicted and Measured Natural Periods of

FREQUENCY

(radians/sec)

9U ER L E V E L - 5

0 Mw

00 70

127 B I T P R E S - D I R E C T

4NAIYSIS

i z 7 ~ i PRES-INDIRECT r

544 B I T P R B S - D I R E C T A N A L Y S I S

ANALYSIS

10 THEORE TI C A L

-io -20 -3 0 -40

- 30 -60 -70

0004

0002

0005

004

FREQUENCY

Fig. 1..10. Frequency Response: MTIJ (a) and Phase of

00 5

0 O?

EN/%

m for

0 2

0 5

(radians/sec)

Magnitude R a t i o of

5 Mw (b).

bN/No

GK/Ko

f o r No

i IIII

ORNL-DWG 66-1CC39A

POWER LEVEL - 6.7MW STEP T E S T NO. 1 A S T E P T E S T NO. 2 V 511 BIT PRES - INDIRECT ANALYSIS

....

1.O

1 .o

Fig.;, 1.11. 6.7 Nw (a)

Frequency Response: 6W/JYO

Phase ol"

Magnitude R a t i o of 8 K h for Ti,

Tor No = 6.7 ivd (b).

34 2 o STEP T E S T a 12( B I T PRES - D I R E C T ANALYSIS

1o3

A 127 B I T PRES - INDlRECl ANALYSIS

d 511 B I T PRES

21"

- DIRECT A N A L Y S I S

... -.......

0.002

0 005

0 01

0 05

002

F R E Q U E N C Y (rodions/sec)

70 60

50 40 30 20 c

:o Q I

a -10 -20

-3 0 -40

-50 -60

-7

W N O

Fig. I-. 12. Fre yuency Response: Magnihndr Rati o of 0-

7.5 Mw (a) and Phase of

W N O

m for

7.5 Mw (b).

1.9 Heat Transfer

Equipment Performance

C. H. Gabbard, H. B . Piper, and E. J. Ked1

A s t h e r e a c t o r power w a s r a i s e d , t h e h e a t - t r a n s f e r c a p a b i l i t y of t h e a i r - c o o l e d r a d i a t o r w a s found t o be l e s s t h a n expected and, i n f a c t , t o l i m i t t'ne a t t a i n a b l e h e a t removal t o about 7.5 Mw. The o v e r a l l heatt r a n s f e r c o e f f i c i e n t of t h e primary h e a t exchanger w a s a l s o below -Lhe p r e d i c t e d value, r e s u l t i n g i n soraevhat l a r g e r f u e l - c o o l a n t temperature d i f f e r e n c e s than had been planned. A f t e r t h e first, i n d i c a t i o n s of low h e a t t r a n s f e r w e reexamined t h e r e a c t o r data t o de-terrrline heat--transfer c o e f f i c i e n t s a s a c c u r a t e l y as p o s s i b l e and t o s e e i f t h e c o e f f i c i e n t s v a r i e d with power l e v e l o r o p e r a t i n g time. Meanwhile, we reviewed tile o r i g i n a l design work t o see i f Y l e r e were e r r o r s i n t h e c a l c u l a t i o n a l method or p h y s i c a l p r o p e r t i e s t h a t could. account for t h e discrepancy between t h e p r e d i c t e d and observed performance.

Primary Ifeat Exchanger. Because of t h e e l e v a t e d teniperatures and r e l a t i v e l y s m a l l temperature d i f f e r e n c e s i n i;he primary heat exchanger, a proper accounting f o r thermocouple e r r o r s i s e s s e n t i a l t o an a c c u r a t e c a l c u l a t i o n of h e a t - t r a n s f e r c o e f f i c i e n t The performance w a s evaluated by two procedures, which d i f f e r e d mainly i n . t h e method o f handling thermocouple b i a s e s . e

The e s s e n - t i a l f e a t u r e of t h e f i r s t procedure, used r o u t i n e l y a t t h e mHE, i s a s t a t i s t i c a l fit of a t h e o r e t i c a l r e l a t i o n t o a l a r g e nwnbey of temperat,uve measurements a t d i f f e r e n t power l e v e l s . The formulation i s such t h a t b i a s e s i n thermocouples, i f c o n s t a n t , do not s i g n i f i c a n t l y a f f e c t t h e outcome and need not be evaluated. The e f f e c t of random e r r o r i n thermocouple output i s minimized by u s i n g many s e t s of d a t a . The r e l a t i o n used t o e v a l u a t e t h e o v e r a l l h e a t t r a n s f e r c o e f f i c i e n t , U, i s

where

T F

measured s a l t temperatures,

= mass fl.ow rates, =

h e a t capacity;

subscrjpts fuel.,

poolan-t s a l t ;

i. = h e a t exchanger i n l e t ,

h e a t exchanger o u t l - e t .

During operation, t h e t e r m s i n the d e r i v a t i v e on t h e l e f t a r e computed and lozged by -the on-line computer. These values can b e r e t r i e v e d and a s l o p e determined from t h r p l o t of orie a g a i n s t t h e o t h e r . The o t h e r procedure, used as a check on t h e r e s u l t s of t h e f i r s t , A s e t of temperatures i s measu e d , and a va~lueof U is c a l c u l a t e d from tiie conventional heat-transfeie quat i on i s i n some r e s p e c t s more s t r a i g h t f o r w a r d .

where

o v e r a l l h e a t - t r a n s f e r coeffi-cient,

Q = heat t r a n s f e r r e d , computed from balance, A LC

coolafit,-salt heat,

2'/9 f t 2 of iotal. tube s u r f a c e area, i n c l u d i n g t h e r e t u r n bends, based on t h e tube OD,

= l o g mean tenzperaiure d i f f e r e n c e .

Temperatures used i n t h e c a l c u l a t i o n of AT, and Q a r e obtained by add-ing a b i a s c o r r e c t i o n t o each thermocouple i n d i c a t i o n . Biases a r e determined by 1.ogging a complete s e t of thesraocoupl-e readings when t h e r e a c t o r i s o p e r a t i n g a-t a steady, very low power, s o t h a t -the s a l t s shou1.d be i s o thermal throughou-t t h e fue3. and coolant loops. The b i a s f o r each thermocouple i s t h e n taken t o be t h e d i f f e r e n c e between t h e average of a l l t h e thermocouples and t h a t p a r t i c u l a r thermocouple. H e a t - t r a n s f e r c o e f f i c i e n t s c a l c u l a t e d by t h e two methods a r e shown i n Fig. 1.13. The continuous curve f o r tiie " d e r i v a t i v e " Iflethod w a s obt a i n e d by fiLLing d a t a p o h t s taken over Lwo periods of time: t h r e e weeks i n A p r i l and May and seven week.s i n May and June. Tile two s e t s of d a t a gave i d e n t i c a l r e s u l t s . Tlne 'lconventional" p o i n t s were o b t a h e d on May 26. A dependence of h e a t - t r a n s f e r c o e f f i c i e n t s on power Level, as e x h i b i t e d i n t h e r e s u l t s of b o t h methods, i s t o be expected. A s t h e power i s r a i s e d w i t h t h e core o u t l e t temperature h e l d c o n s t a n t , t h e average temp e r a t u r e s of t h e s a l t s i n t h e heat exchanger decrease. According t o conv e n t i o n a l formulas f o r h e a t - t r a n s f e r c o e f f i c i e n t s , -the changes in sa1.t p r o p e r t i e s ( p r i m a r i l y s p e c i f i c h e a t and v i s c o s i . t y ) could account f o r pra3ctical.l.y a l l t h e observed v a r i a t i o n .

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

METHOD OF ANALYSIS (SEE TEXT) : CCNVENTICNAL -.

Fig. 1.13. Observed Ovemll Ileat T r a n s f e r C o e f f i c i e n t s i n %RE Primary Heat Exchanger.

2 z

l'j

"DEEIVATIVE"

700 .-

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

5 600

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

111 W

L---, ~~

4 .........

I%....... .

\ ........

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

.........

...~

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

Design c a l c u l a t i o n s had p r e d i c t e d an o v e r a l l h e a t - t r a n s f e r c o e f f i c i e n t a t l o Mw of 1100 Btu hr-' f t - 2 ("F)-l. (This w a s f o r t h e s t r a i g h t p o r t i o n of t h e t i h e s , i n a c l e a n c o n d i t i o n . ) This i s about a f a c t o r of 2 above t h e c o e f f i c i e n t s observed a t temperatures approximating t h o s e used i n t h e design. I n an e f f o r - t t o r e s o l v e t h e discrepancy, t h e design c a l c u l a t i o n s were c a r e f u l l y reviewed t o s e e i f t h e proper procedures were used and t o check f o r e r r o r s i n t h e c a l c u l a t i o n s . The r e s u l t s of t h i s design review i n d i c a t e d t h a t t h e h e a t exchanger had been properly designed using conventional procedures and t h a t t h e design should have been cons e r v a t i v e by about 20%. References 11 and 1 2 i n d i c a t e t h a t conventional h e a t - t r a n s f e r r e l a t i o n s are v a l i d f o r molten s a l t s , and t h e r e f o r e t h e conven-tional. design procedures should b e a p p l i c a b l e for t h e MSRE h e a t exchanger. The most l i k e l y e x p l a n a t i o n f o r t h e discrepancy appears t o be erroneous v a l u e s of s a l t c o n d u c t i v i t y i n t h e design computations. Recent measurements of a s a l t s i m i l a r i n composition t o t h e MSIB f u e l salt have shoim t h e thermal c o n d u c t i v i t y t o be about o n e - t h i r d of' t h e value t h a t was b e l i e v e d t o be c o r r e c t a t t h e time of t h e h e a t exchanger design ( s e e Chap. 7 ) . No r e c e n t d a t a a r e y e t a v a i l a b l e on t h e c o n d u c t i v i t y of t h e c o o l a n t salt; b u t i f a s i m i l a r discrepancy e x i s t s , t h i s would. e s s e n t i a l l y account for t h e reduced performance of t h e h e a t exchanger e

Radiator. The design and i n s t r u m e n t a t i o n of t h e a i r r a d i a t o r preclude a c a l c u l a t i o n of t h e o v e r a l l h e a t - t r a n s f e r c o e f f i c i e n t a t a l l b u t two power l e v e l s . A t most reduced poT?er c o n d i t i o n s t h e r a d i a t o r doors a r e p a r t i a l l y c l o s e d o r t h e bypass damper is open; t h u s t h e e f f e c t i v e t u b e area, t h e a i r flow through t h e rad.iator, and t h e downstrean a i r ternp e r a t u r e are unknown. Therefore t h e reduced performance was not obvious w n - L i l t h e r e a c t o r w a s raised t o f u l l power. The o v e r a l l c o e f f i c i e n t f o r t h e r a d i a t o r was evaluated. with b o t h main blowers running, the doors f u l l open, and t h e bypass damper f u l l y cl.osed (full-power c o n d i t i o n s ) . The a i r flow measured a t t h e s e cond.itions was e q u a l t o t h e design f l o w r a t e of 200,000 c f x . Another e v a l u a t i o n was made w i t h s i m i l a r r a d i a t o r c o n d i t i o n s except t h a t only One main blower The h e a t - t r a n s f e r c o e f f i c i e n t s were 38.5 a,nd 28.5 Btu hr-l was runnin ft-2 (OF)-' and the power l e v e l s were 7.L+ awl 5.6 Mw f o r t h e s e two conThe observed h e a t - t r a n s f e r c o e f f i c i e n t s v a r i e d with t h e 0.575 ditions

33 pow27 of tile ai.r fl..ow r a t e , agreeing w i t h a t3h.eoretical cxpon2iii; of 0.6. But t h e predicted coeffici.er,t a t full-power cond.i.tri ons w a s 58 3 2 ~ ftm2 ( f a r above t h e observed v a h c . The r a d i a t o r desi.gn w a s roviewed tn detemn:i.ne t h e reason f o r Lhe un.expectedly low perforiiia-oce Tile d e s i p procedures foll.oweci cofiventional pr%ctice except i n two impoi%ani; poj-nts : t h e e v a l u a t i o n of a . i r p r o p e r t i e s and t h e allowance f o r e r r o r i n t h e predic-Lions. In t h e c a l c u l a t i o n of t h e aii--side c o e f f i c i e n t t h e physical. p r o p e r t i e s of a i r were ev-aluated a t the tube s u r f a c e t e n p e n t u r e i n s t w d of :he prescrribed "filrri" temperature, defined as t h e mean of t l i r s u r f a c e S,errperature and t h e Sulk air t,emperature. Iiad t h e "film" temperature bee-n used, t h e o v e r a l l c o e f f i c i e i i t w0u.l.d have been lower by J-4$, U s e of an erroneous vai.ue f o r the conduc.tivi-Ly of t h e s a l t had l i t t l e e f f e c t on t h e o v e r a l l c o e f f i c i e n t , siiice t h e heat'irans€er r e s i s t a n c e on t h e i n s i d e of t h e -tubes i s 3.ess t h a n 5% of tile t o t a l i n any c a s e . Thus, even when t h e a i r - s i d e calculat3,on fol.lowed t h e prescri.hed. formula, t h e observed o v e r a l l coefsloi c i e n t w a s s t i l l only 66$ of t h e p r e d i c t e d value. %h.is i s g r e a t e r t h a n the usual. errol- i n heatt r a n s f e r p r e d i c t i o n s , 'mi; i s pro'bably not unreasonable considering t h e c o n f i g u r a t i o n of t h e r a d i a t o r and -the very l a r g e temperature d i f f e r e n c e between t h e bulk of the alii- and t h e s u r f a c e of t h e tubes. 'The r a d i a t o r w a s designed. when t h e nominal design power for t h e r e a c t o r w a s 5 MW-* The components were designed f o r o p e r a t i o n a t 10 Mw -Lo e m u - r e s u f f i c i e n t capacity; and when it was l a t e r decided. to c a l l t h e MSRE a 10-Mw r e a c t o r , t h i s l e f t them with l i t t l e o r no allowance f o r i m c e r t a i n t y . The actual. tube area i s only 4.$ more t h a n t h e minimum r e q u i r e d f o r 10-Mw o p e r a t i o n according t o t h e o r i g i i i a l calcula1;i-ons.

E f f e c t s of Low IIea-t 'TL'raiisr'er on Reactor OperaLion. In t h e main h e a t exchanger t h e reduced 'neat t r a n s f e r causes a l a r g e r temperature d i r f e r e n c e between t h e f u e l and coolant s a l t s f o r any given power level.. The o r i g i n a l design temperatures f o r lo-Mw o p e r a t i o n were 1.225 and 1175°F f o r the f u e l s a l t e n t e r i n g an.d. l e a v i n g t h e h e a t exchanger and 1025 and 1100°F f o r the coolant s a l t . Actually, o p e r a t i o n at, a max5.mim f u e l temperaturc of 1225°F and a minirn1.m coolant tempera-Lure of 1025°F r e s u . l t s i n a heatt r a n s f e r r a t e of '7.5 Mw. It would be p o s s i b l e t o operate t h e heat exchanger a t higher power l e v e l s by inci-essine; the heat exchanger f u e l i n l e t temperature and/or reducing t h e coola.nt i n l e t temperature. :lowever, f o r long-term o p e r a t i o n t h e hea-t exchanger f i x I f i l l e t temperature i s l i m i t e d t o a. maximiim of 1250°F by thermal s t r e s s and stress rupi;L i x e considerations, and the coolant i n l e t temperature i s limi-Led t o a minimiim temperature of 1000°F by t h e p o s s i b i l i t y of freezj-ng t h e r a d i a t o r . Ope r a t i o n a t t h e s e temperature conditions would approach 10 Mw. 'The heati r a n s f e r r a t e could a l s o be improved by iiicreasing t h e f u e l and coolants a l t flow ra-Les. The f l - o w r a t e s could b e i n c r e a s e d e i t i i e r by i n s t a l l i n g larger-diameter i m p e l l e r s o r by i n c r e a s i n g t h e pmp speeds by 11si.n.g a higher-frequency power supply. The reduced perf'ol.mance of t h e coolant r a d i a t o r , however, imposes a d e f i n i t e 1.5.mj.t 011 t h e heat-removal r a t e from t h e coolant system, and t h e r e i s no cotlvenri.ent method of i n c r e a s i n g t h e heat, removal. The mean t e m p e r a t u r e d i f f e r e n c e between the coolant s a l t and t h e 'uu1.k-air temperature i s 920"F, and t h e c o o l a n t - s a l t tempel-atiire would have t o be increased.

s i g n i f i c a n t l y before a g a i n i n r e a c t o r poxer could be r e a l i z e d . The f u e l i n l e t temperature t o t h e h e a t exchanger would then be pushed t o an unacceptable l e v e l .

I n summary, t h e rnaxirnum reactor. power l e v e l i s l i m i t e d b y the a i r side h e a t t r a n s f e r from t h e c o o l a n t r a d i a t o r . There i s a l s o a l e s s scvei-e r e s t r i c t i o n a t t h e main heat exchanger which could be c i r c m v e n k d by ope r a t i n g t h e r e a c t o r s y s t m a t o f f - d e s i g n temperatures. The r a d i a t o r h e a t t r a n s f e r can be improved only by r e l a t i v e l y e x t e n s i v e modifications. There w i l l be a s m a l l i n c r e a s e i n m a x i r r i u power l e v e l during the w i n t e r months because of t h e lower ambient a i r temperatures. Mairr Elowers

C . 11. Gabbard.

A e r o d p m i c Perfo-smnce e Eie aerodynamic perf"ormance o f t h e maiu hlowers T J a C j s a t i s f a c t o r y . 'The EKE angle OD b o t h blowers had been set a t 20', as o r i g i n a l l y s p e c i f i e d by t h e manufacturer f o r t h e design cond i t i o n s . However, t h i s vane s e t k i n g d i d not f u l l y load t h e d r i v e motors; s o when t h e maxiinum r e a c t o r power w a s found t o b e below t h e expected v-alue, t h e vane angle w a s increaised t o 22.5' t o i n c r e a s e the a i r flow and h e a t removal. A s expected, t h i s s e t t i n g 1-oaded. t h e drive motors t o t h e i r c a p a c i t y and i n c r e a s e d t h e a i r flow about lo$. The e f f e c t was t o r a i s e maximum r e a c t o r power by s l i g h t l y less tkmn 1/2 â&#x201A;Ź4~.

Motors. The bl-otrers are &riven by 25O-hp woimd-rotor i n d u c t i o n 1iiot;ors t h a t have four stages o f e x t e r n a l r o t o r r e s i s t a n c e . Automatic s t e p p i n g switches shu-nt out t h e s e r e s i s t a a c e s i n a timed sequence d u r i n g the s t a r t x p of t h e ?jlower t o l i m i t t h e s t a r t i n g current, of t h e m o t o r s . D.nring t h e e a r l y s t a g e s of power o p e r a t i o n , clifficu.l.vy w a s periodical1.y experienced i n t h e s t a r t of iliain blowel- No. 1. The motor c u r r e n t during the s t a r t s w a s e r r a t i c , and sometimes the c u r r e n t was high enough t o t r i p t h e c i r c u i t breaker. One of t h e c a s t - i r o n r e s i s t a n c e grids i n t h e ext e r n a l r o t o r r e s i s t a n c e on MJ3-1 was found brokeri. A broken grid. was also fou.nd i n t h e ME3-3 s t a r t i n g r e s i s t o r s , b u t t h i s gri.d wss i n a J.Z?..C-u*3 c r i t i c a l l o c a t i o n I n t h e s t a r t i n g s e q u m c e and i t a e f f e c t had not been n o t i c e d . I3ot.h t h e g r i d s were weld-repaired, and no f u r t h e r d i f f i c u 3 - t i e s of this type have been n o t i c e d . b-

Coupling F a i l u r e Thc blowers a r e c o m e c t e d t o t h e i r r e s p e c t i v e cirive motors through s h o r t f l o a t i n g shafts with disk- type - - flexible coupliiigs on each end. On June 16, while tne rewtor wa:: opera-t,ing a t YulL power, t h e couplings on M3-1 f a i l e d . The s h a f t coupling a.t t,he motor end a p p a r e n t l y f a i l e d f i r s t , and. the coupling on The blower end w a s Then t o r n a p a r t by t h e r e s u l t i n g s i m f t whip. The s h a f t destroyed t h e coupling g i a r d and damaged t h e sheet-rnetal nose t h a t coTJered t h e f r o n t b e a r i n g of t h e blower. Debris from t h e two coupJingc w a s scabtered trxoughout -the f a n room, and s c r a t c h e s on t h e f a n b l a d e s i n d i c a t c d thai some of' t n e m a t e r i a l had gone t:hmu& the blowers into t h r~a d i a t o r duct.

The coupling on t h e motor end of t h e s h a f t showed erating i n a p a r t i a l l y f a i l e d c o n d i t i o n for some tirw. -the f l e x i n l c d i s k s were severely worn, i n d i c a t i n g t h a t had been transnlitled from the motor f l a n g e d i r e c t l y t o

evideacG oi' opThe n u t s holding t h e motor torque Lhc! :;hrtl"t l'llangc

by t h e b o l t s r a t h e r t h a n through t h e flexi'ole d i s k s . The i n i t i a l f a i l u r e of t h e disks was attribu-Led t o f a t i g u e where some i n c o r r e c t , flat; washers had. caused high s t r e s s e s . The couplings on MB-1 were r e b u i l t , and n e w f l e x i b l e shims were i i i s t a l . l e d i n t h e MB-3 couplings. Operation was resumed a f t e r t h e r a d i a t o r duct w a s cleaned and inspection of t h e hot; r a d i a t o r tubes showed no damage t o t h e t u b e s . Blade and Hub F a i l u r e . Fower operatLon w a s 'oroueht, t o a premaLure end on J u l y 17 by t h e cat$strophic f a l l u r e of t h e r o t o r hub and t h e b l a d i n g of MI3-I. The ou-Lei- periphery of t h e r o t o r hub d i s i n t e g r a t e d , and a l l t h e blading was destroyed. Most of t h e fragpcnts were contained i n t h e blower housing, b u t numeroius fraguients of the c a s t aluminim-alloy hub and blades en-tered t h e r a d i a t o r duct and some a c t u a l l y passed through t h e r a d i a t o r . The r e a c t o r w a s taken t o verj- low power, and t h e coolant was drained t o determine tlie cause of t h e f a i l u r e , t o i m p e c t t h e o t h e r blower, and t o examine t h e r a d i a t o r f o r p o s s i b l e damage. I n s p e c t i o n of t h e broken p i e c e s of Mu-I revealed numerous "old" cracks i n t h e b l a d e s and i n t h e hub as evidenced by darkened o r d.rirty a r e a s on t h e f r a c t u r e d s u r f a c e s . One b l a d e ii1 p a r t i c u l a r had f a i l e d along a l a r g e "old" crack. The hub had contained s h o r t , 1-1/2 t o 2 i n . , c i r cumferential cracks a t t h e base of % of t h e 16 blade sockets, and t h e f a i l u r e g e n e r a l l y followed t h o s e cracks. Figure 1.14 i s a piece of t h e hub showing t h e darkened a r e a s a t t h e base of t h e b l a d e sockets. Since tile f a i l e d blower had contained t h e s e o l d cracks, t h e top casing was removed from MB-3 t o permit a c a r e f u l i.nspectioil of i-ts hub and b l a d i n g . The f r o n t hub cas-Ling contained a l a r g e , continuous crack whi-ch extended about 35% around t h e circumference. There were a l s o several of the s h o r t cracks s i m i l a r t o those that, had been i n t h e MB-l hub. The blades were dye-penetrant inspected and Po-und t o be s a t i s f a c t o i y . A r e placement blower t h a t had not been i n s e r v i c e a l s o contained some rninor s u r f a c e cracks i n t h e 'nub. There i s no g e n e r a l agreement on t h e cause of t h e f a i l u r e . The o r i g i n a l soundness of t h e hub c a s t i n g s i s i n question because of t h e o l d appearance of p o r t i o n s of t h e f r a c t u r e siirfaces and t h e presence of

Fig. 1.14. Fragment of F a i l e d Impeller Zub from Main Blower N o . 1.

cracks i n t h e other blower hubs. Shock forces produced d1lrin.g the coupling f a i l u r e and v i b r a t i o n due t o s l i g h t imbalances a r e suspected as c o n t r i b u t i n g f a c t o r s .

The t h r e e blowers are being r e b u i l t i n the manufacturer * : p l m t The hubs are being r e i n f o r c e d t o r e l i e v e t h e bending mo:ncnt at the base of t h e b l a d e sockets, and t h e c e n t r i f u g a l b l a d e loading i s being reduced by SubStitUting magnesium a l l o y blades which a r e 35% 1igh'ce:r. Tke t h r e e complete r o t o r assemblies w i l l be given a 304 overspeed test with dyepenetrant i n s p e c t i o n s b e f o r e and a f t e r the t e s t s . I n t h e i n s t a l l a t i o n , e:Lose t o l e r a n c e s w i l l be imposed on alignment, and vi'oration, and i n s t r s mentation w i l l be provid.ed to monitor v i b r a t i o n during opera.l;ion. Ra.diator Enclosure

- T.

L. Hudson, C

H. Gabbard, and M. Richardson

Operation of t h e r e a c t o r a t power yrovided t h e d t i m a t e best of t h e r a d i a t o r enclosure, involving f o r t h e first time t h e o p e r a t i o n of t h e r a d i a t o r a t t h e maximum c a p a b i l i t y w i t h t h e doors fulLy open a d w i t h forced air circulation. Operation a t power l e v e l s up t o 1 . 0 1%~ had been achieved during t h e l a s t r e p o r t period. This operation had inclica,ted t h a t t h e r a d i a t o r door s e a l s had become l e s s e f f e c t i v e during ope r a t i o n . The l o s s in door-seal e f f e c t i v e n e s s continued during this r e p o r t period.

Power Level a t Various Eadiator Conditions. During t h e power e s caial;ion phase of operation, t h e r a d i a t o r conditions were a d j u s t e d t o o b t a i n p r e s e l e c t e d power l e v e l s . Therefore, t h e complete heat-removal c h a r a c t e r i s t i c s of t h e r a d i a t o r are not known because t h e r e a c t o r has operated- a t s t e a d y - s t a t e c o n d i t i o n s a t r e l a t i v e l y few power levels. flotrever, the r e a c t o r power l e v e l s f o r some c;f t h e key s e t t i n g s are l i s t e d in Table 1.4. M.1 intermediate p m e r l e v e l s can be obtained by' t h e proper adjustment of t h e doors o r t h e by-pass damper.

'Table 1.4.

Radiator Conditions and Reactor Power

Radiator Conditions Outlet

Bypass

Closed

Open

None

@en 15 i n .

Open

Closed

Open

Cpen

Closed

I..

Inlet Door

Door

Emper

Pkin Blowers Aunning

%epends on h e a t leakage and h e a t e r s e t t i n g s . bFxact value depends on ambient a i r temperature.

P m e r (MW)

04.05" 2.5

4.1 5" 8 7.2 i 0.2

42 S a l t Frozen i n Tubes, One of t h e m i n consid.erations during t h e design of t h e r a d i a t o r enclosure w a s -Lo avoid t h e f r e e z i n g of s a l t i n t h e r a d i a t o r t u b e s . The expansion of s a l t during tinawing w a s b e l i e v e d capable of r u p t u r i n g a tube i f t h e -l;hming f i r s t occurred i n the c e n t e r s e c t i o n of a tube, s o t h a t t h e molten s a l t was confined between two f r o zen p l u g s . A ''load scram, " which dropped t h e r a d i a h o r doors and. stopped t h e main blowers when the r a d i a t o r s a l t o u t l e t temperature dropped below 900째F, wads provided t o prevent s a l t from being f r o z e n i n t h e radiat o r . However, s a l t w a s f r o z e n i n t h e r a d i a t o r tubes on two occasions and w a s s u . c c e s s f u l l y melted out w i t h no apparent &mge t o t h e radiator. I n both c a s e s , t h e f r e e z i n g occurred as a r e s u l t of a rod and load. scram combined w i t h a stoppage of t h e c o o l a n t pump. The f i r s t freezeup occurred when a d e f e c t i v e r e l a y caused a. "rod scram" from a 5 .O-W power l e v e l . The r a d i a t o r load. w a s s c r m e d m a n i ~ ~ l layt 1000째F because of tine r a p i d l y decreasing temperatures, bul; 'che coolant pump w a s stopped by a low l e v e l i n t h e pump bowl.. which r e s u l t e d from -the reduced temperature. With c i r c u l a t i o n stopped, h e a t losses f r o z e some s a l t i n 30 o r more of t h e 120 t u b e s . The second freezeup occurred as a result of an el.ectrica1. f a i l u r e which caused a stoppage of t h e c o o l a n t pump and a scram of t h e rods and load. I n both c a s e s t h e c o o l a n t system w a s d r a i n e d immediately, but t h e b a i n - t m k weight i n d i c a t e d tha-1; some s a l t had remained i n t h e c o o l a n t sys tem. Recent data i n d i c a t e t h a t t h e volume change during t h e thawing of c o o l a n t s a l t i s r e l a t i v e l y small. T'nis l o w volume change, p l u s t h e f a c t t h a t t h e n o m 1 temperature d i s t r i b u t i o n durLng h e a t i n g of t h e rad i a t o r would cause progressive tha7din.g of t h e tubes from t h e 'top t o t h e bottom, gave confidence t h a t t h e r a d i a t o r could be thawed without damage. I n t h e f i r s t f r e e z i n g i n c i d e n t , t h e r a d i a t o r w a s r e h e a t e d slowly and a l l t h e remaining s a l t w a s recovered i n t h e d r a i n talk. A p r e s s u r e t e s t w a s t h e n conducted on t h e e n t i r e c o o l a n t system t o check f o r rupt u r e d t u b e s . There w a s no i n d i c a t i o n of leakage. Af-Ler t h e second f r e e z i n g i n c i d e n t , i n c r e a s e d h e a t h a k a g e from l;he r a d i a t o r enclosure prevented a p o r t i o n of t h e r a d i a t o r from reaching the melting p o i n t , and some s a l t remained f r o z e n i n t h e t u b e s . However, t h e lowest temp e r a t u r e s were s u f f i c i e n t l y near t h e melting p o i n t t h a t t h e coolant system w a s f i l - l e d and c i r c u l a t e d . The r a d i a t o r temperatures i n d i c a t e d t h a t f o u r o r f i v e of t h e tuises were blocked a t f i r s t , b u t a f t e r s e v e r a l minutes of s a l t c i r c u l a t i o n a l l t h e t u b e s thawed and reached t h e temperat u r e of t h e flowing s a l t . A f t e r t h e f i r s t f r e e z i n g i n c i d e n t , t h e c o n t r o l system w a s r e v i s e d s o t h a t a rod scram would also cause a l o a d scram, The low-temperature s e t p o i n t f o r a l o a d scram was i n c r e a s e d from 900"F, v h i c h i s only 60째F above t h e l i q u i d u s temperature, t o 990째F. Other r e v i s i o n s were made s o t h a t t h e coolant pump would n o t be t u r n e d o f f u n l e s s a b s o l u t e l y necess a r y . A scram t e s t w a s conducted f r o m f u l l power, and t'nese r e v i s i o n s were adequate t o prevent f r e e z i n g of t h e r a d i a t o r as long as t h e coolant pump remained running.

43 Damage and D e t e r i o r a t i o n . The r a d i a t o r w a s s u b j e c t e d t o p o s s i b l e damage on two occasions from mechanical failures of main blower No" 1. P i e c e s of s t a i n l e s s s t e e l shim s t o c k were blown i n t o t h e r a d i a t o r duct

when t h e s h a f t coupling f a i l e d . The r a d i a t o r t u b e s were v i s u a l l y i n s p e c t e d from t h e i n l e t s i d e while salt w a s c i r c u l a t e d a t o p e r a t i n g t e m p e r a t u r e , and no evidence of damage from t h e coupling failure was found. A l o o s e sheet-metal cover from an e l e c t r i c a l c a b l e t r a y was found a g a i n s t t h e tubes and w a s removed. Reactor o p e r a t i o n w a s resumed. a f t e r t h e rad i a t o r duct w a s c l e a n e d t o remove t h e d e b r i s from t h e coupling.

The c o o l a n t system w a s d r a i n e d and t h e r a d i a t o r w a s cooled and thoroughly i n s p e c t e d af%ert h e shutdown t h a t followed t h e hub f a i l u r e of main blower No. 1. S e v e r a l r a d i a t o r tubes were dented, p o s s i b l y by aluminum fragments from t h e blower, and a few small p i e c e s uf aluminum were s t u c k t o t h e t u b e s , These p i e c e s were e a s i l y removed, and t h e t u b e s w e r e c l e a n e d t o remove any adhering aluminum. V i s u a l i n s p e c t i o n and a helium l e a k t e s t a t 20 p s i g i n d i c a t e d t h a t none of t h e t i b e s had been s e r i o u s l y damaged by t h e blower fragments, arid t e s t s were run t h a t i n d i c a t e d t h a t t h e exposure t o aluminmi would not endanger t h e l i f e of tfie r a d i a t o r i f t h e t u b e s were cleaned.

I n a d d i t i o n t o the daraage that had been caused by the 'ulvder failure, t h e r a d i a t o r enclosure was i n need or" o t h e r r e p a i r . Beating t h e empty r a d i a t o r t o a n accepta'ole temperature d i s t r i b u t i o n p r i o r t o a f i l l bad become i n c r e a s i n g l y d i f f i c u l t , and on t h e l a s t f i l l some of t h e Lubes could- not be h e a t e d above t h e melting p o i n t of salt u n t i l t h e r a d i a t o r w a s f i l l e d and c i r c u l a t i o n s t a r t e d . The r a d i a t o r doors had warped EL l i t t l e , and the seal s t r i p s had been s e v e r e l y d i s t o r t e d . 'Die s e a l s t r i p s had a l s o been t o r n l o o s e i n some pLaces by t n e o p e r a t i o n of t h e doors. Numerom sheet-metal screws had broken or had worked loose, allowing sheet-metal c a b l e - t r a y covers and s h e e t metal on t h e i n s i d e s u r f a c e s of the e n c l o s u r e t o come l o o s e . 'There w e r e a l s o numerous broken e l e c t r i c a l insulators. Although t h e r e w a s excessive h e a t leakage from t h e radia,tor enclosize, t h i s was mnainly around t h e doors, and t h e overheatirvj of e l e c t r i c a l l e a d s and the-mocouple leads t h a t had occurred p r e v i o u s l y d i d not r e c w . The r e p a i r of t h e radLator enclosure i s i n progress. Design of t h e seal s t r i p has been improved t o reduce t h e thermal d i s t o r t i o n and t h e o v e r a l l warpage of t h e doors. This seal s t r i p i s segmented and free t o move t o allow f o r d i f f e r e n t i a l Yfiermal expansion, and t h e Tb a r which holds t h e s e segments has been s l o t t e d t o r e l i e v e thermal stresses which w e r e causing t h e door t o warp. The l o o s e s h e e t metal and t h e l o o s e ceramic h e a t e r elements a r e being h e l d i n p l a c e w i t h welded c l i p s r a t n e r t h a n t h e sheet-metal screws, F u e l O f f - G a s System

- A.

N . Smith

The d i f f i c u l t i e s encountered w i t h t h e f u e l off-gas system during t h e i n i t i a l o p e r a t i o n of t h e r e a c t o r a t power, t h e f i n d i n g s and conc l u s i o n s r e l a t i v e t o t h e causes of t h e s d i f f i c u l t i e s , and th.e system m o d i f i c a t i o n s proposed t o prevent t h e recurrence of t h e d i f f i c u l t i e s

were a l l d e s c r i b e d ,j.:ii t h e last; progress report;. The m.odifications, which cons-isted e s s e n t i a l l y i n using v a l v e s w i t h l a r g e r f1.w a r e a s and in.sta,l.ling a p a r L i c l e Lrap and a.n organic-vapor t r a p upstream of t h e p r e s s u r e - c o n t r o l val.vc (PCV-522), were a l l compl-eted before resiming power o p e r a t i o n of t h e r e a c t o r i n A p r i l 1966. Observable p r e s s u r e s and temperatures i n t h e off-gas system were c a r e f u l l y monitored during a11 subsequent o p e r a t i o n s , p a r t l y t o e v a l u a t e t h e e f f e c t i v e n e s s of tile changes b u t p r i m a r i l y t o i d e n t i f j - and. c o r r e c t any undesirabl-e cond3.tions b e f o r e they became unmanageable. Some d i f f i c u l t i e s were encouitered w i t h buil-dup of p r e s s u r e drop, b u t none were s e r i o u s enoygh t o f o r c e a shutdown. I n a d d i t i o n , t h e r e w a s no observable l o s s i n effici-ency of t h e primary funckion of t h e off-gas system, t h e retentiion of gaseous f i s s i o n products e D e t a i l e d anal-ysis of t h e performance of some componenks, p a r t i c u l a r l y t h e partLc1.e tl-ap and t h e organic-vapor t r a p , w a s hampered somewhat by t h e s c a r c i t y of a c c e s s i b l e pressure-measuring devices i n t h e system. This w a s aggravated by t h e f a c t t h a t t h e p r e s s u r e drop a c r o s s the main c h a r c o a l beds o c c a s i o n a l l y exceeded t h e 3 - p s l range of t h e i n s t a l l e a (and inaccess i b l e during o p e r a t i o n ) measuring instrumelit and a l s o by t h e failure of t h i s instrument t e n days before t h e shutdown on J - d y 17. Line 522 Holdup Volume. When plugging occurred a t s e v e r a l p o i n t s i n t h e off-gas system shor%ly aft;er t h e power w a s f i r s t r a i s e d , it was swges-bed t h a t tile dependence on power might be r e l a t e d t o r a d i a t i o n h e a t i n g of tine off-gas holdup vol-iune i n t h e reactor c e l l . Off-gas samples t a k e n while %'ne r e a c t o r was s h u t down i n March w i t h t h e r e a c t o r c e l l a t d i f f e r e n t t e m p e r a t m e s showed more hydrocai-bons a h higher %emp e r a t u r e s , l e n d i r g support t o t h e hypothesis t h a t t h e r e was a r e s e r v o i r of hydrocarbons i n 'ihe holdup volume. 1% w a s not; p r a c t i c a b l e t o c l e a n t h e 68-ft-long, 4 - i n . -&Lam p i p e ; but; t h e off-gas l i n e w a s disconnected a t t h e f u e l pump and i n t h e ven-1; hnixe, and l a r g e q u a n t i t i e s of helium were blown through t h e l i n e i i i t h e forward and r e v e r s e d i r e c t i o n s at v e l o c i t i e s up t o 20 times normal. Very l i t t l e v i s i b l e m a t e r i a l was collected. on f i l t e r s a t t h e ends of khe l i n e , b u t t h e r e were f i s s i o n products, and t h e mouni; doubled when t h e c e l l w a s h e a t e d from 120 t o 175째F. Visual observation showed t h a t t h e head end of t h e hol-dup volume w a s c l e a n except f o r a b a r e l y perceptibl-e d u s t l i k e f T l m . A thermocouple was a t t a c h e d t o t h e holdup pipe n e a r t h e head end f o r monitoring temperatures during power o p e r a t i o n . When t h e power was subsequently r a i s e d , t h e temperature r o s e from c e l l a i r temperature (about 130째F) a t zero power t o about 235째F a t 7.5 Mw. The rise i n ternperat;m*e after a s e t u p from zero power occurred w i t h a time c o n s t a n t o f about 30 min, not i n c o n s i s t e n t w i t h buildup of gaseous f i s s i o n products i n t h e l i n e

Line 522 F i l t e r Assembly. The f i l t e r a.ssernh3-y t h a t was i n s t a l l e d . upstream of t h e f u e l p r e s s u r e c o n t r o l valve (PCV-522) c o n s i s t s of t w o s e p a r a t e u n i t s i n s e r i e s . F i r s t is a, f l l t e r t o remove p a r t i c u l a t e s and mist; next;, a s m a l l . c h a r c o a l bed t o remove organic vapors (See Component Developnient, Chap. 2, f o r a d e t a i l e d d e s c r i p t i o n . ) A s a r e s u l t o f t h e experience during t'nis p e r i o d of operati-on, t h e f i l t e r p a r t of tile assembly will be r e p l a c e d w i t h a new one of t h e s m e design. The o l d u n i t w i l l be exarrrined i n a hot c e l l t o d e t e r n i n e , if p o s s i b l e , t h e cause f o r t h e v a r i a t i o n s i n p r e s s u r e drop t h a t were observed.

I n t h e new condition, t h e pressure drops a c r o s s t h e p a r t i c l e t r a p and charcoal.. bed were c0.05 and 0.'7 p s i r e s p e c t i v e l y . With t h e s e i n s t a l l e d , t h e t o t a l . pressure drop iu t h e f u e l off-gas s stem was about 2.3 p s i a t t h e noxlnal gas flow r a t e of 4.2 s t d l i t e r s min and PCV-522 wide open. Thus when t h e reactor-system overpressure was c o n t r o l l e d a t 5 p s i g , a 2.7-psi pressure drop occurred a t t h e t h r o t t l i n g valve. Because t h e r e were no measurements of p r e s s u r e s a t intermediate p o i n t s between t h e pump bowl and t h e upstream ends of t h e main charcoal be&, n m only t o be below t h e p r e s s u r e drop a c r o s s t h e f i l t e r assernbly w a s k T U s c o n d i t i o n p r e v a i l e d i m t i l m y 9, during operation of t h e 3.4 psi. r e a c t o r a t powers up t o 5 Mw. There w a s no i n d i c a t i o n t h a t t h e pressure drop a c r o s s t h e f i l t e r assembly reached t h e d e t e c t a b l e limit of 3.4 p s i during t h i s t i r n e .

During most of t h e operations a f t e r P k d 9, PCV-522was kept wide open, allowing t h e f u e l overpressure t o follow t h e t o t a l pressure d ~ o p through t h e o t h e r p a r t s of t h e off-gas l i n e . This mode of operation permitted -tine monitoring of t h e pressure drop a c r o s s t h e f i l t e r assembl-y For t h e f i r s t t e n days t h e o v e r a l l t r e n d i.nt h e pressure drop w a s upward, with i n c r e a s e s a f t e r t h e power w a s r a i s e d and decreases a f t e r it was lowered. On May 19, w i t h Vne power a t 5 Mw, t h e pressure drop was up t o 8 psi. The power w a s s h u t down t o r e d i s t r i b u t e t h e e l e c t r i c a l load, but t;he p r e s s u r e drop continued on up, even though tihe gas flow was reduced. On May 20, s h i e l d i n g w a s removed, and a p r e s s u r e gage w a s temporarily a t t a c h e d t o a t a p between t h e p a r t i c l e t r a p and t h e charcoal f i l t e r t o determine which w a s responsible for t h e high flow r e s i s t a n c e . 'The drop measured across t h e t r a p was 9.9 p s i , while t h e drop a c r o s s t h e charcoal was only 0.5 p s i . Thus t h e i n c r e a s e i n r e s i s t a n c e w a s due e n t i r e l y t o t h e p a r t i c l e t r a p . System p r e s s u r e was reduced by venting from t h e d r a i n With t h e r e m L a r k s , and t h e power was r a i s e d t o determine n ~ i , j % power. a c t o r operating a t 7.5 Mw t h e f i l t e r pressure drop decreased t o about 3 p s i . Then when t h e poder was lowered -60 zero, t h e pressure drop c&ne down over a period- of a day t o l e s s t h a n 1 p s i . The p r e s s w e dxop r e mained low until. July 1.2,when it began t o i n c r e a s e g r a d m l l y . The inc r e a s e continued a f t e r t h e shutdown, and t h e u n i t w i l l be repl.aced.

The p a r t i c l e t r a p was immersed i n a tank of water f o r cooling by n a t u r a l convection. Thermocouples on t h e o u t s i d e of t h e t r a p responded t o c h a w e s i n power and gas f l o w , but t h e maximwn temperature r i s e was only about 25째F'.

It was expected t h a t accumulation of organic rmteria.1 i n t h e charc o a l f i l t e r would r e s u l t i n progressive poisoning along t h e l e n g t h of t h e t r a p . Such poisoning would s h i f t t h e l o c a t i o n of ~ i m n u mf i s s i o n product absorption and produce a s h i f t i n t h e temperature profile of kh.. t r a p . Figure l.L5a shows two p l o t s of t h e charcoal temperature p r o f i l e , one on May lo, when about 12C)O M w h r had been accumulated, and one on July 7, when about ?GOO Nwhr had been a c c w n l a t e d . Except f o r t h e upward s h i f t due t o t h e i n c r e a s e d power l e v e l , the b a s i c shape of t h e p r o f i l e i s t h e same for both periods, i n d i c a t i n g t h a t s i g r r i f i c a n t poisonip4 had not occurred during t h i s i n t e r v a l . Figure 1-.15b shows t h e e f f e c t of v a r i a t i o n s i n pump-bowl p r e s s u r e on t h e t r a p tenipel-at u r e p r o f i l e . A s would be p r e d i c t e d , t h e t r a p temperatures, pa.rt;icu l a r l y n e a r t h e i n l e t , vary i n v e r s e l y w i t h system pressure, because

CRNL -DWG

FP POWER

DATE

0 5-40-66

140

7-7 --66

Fig. 1.15.

5 Mw ?.2 M,/i

PRESSURE

4.6psig 5.0 pslg

DATE

FP PRESSURE

POWER

a6--24-66 ?.2 Mw e 7~-7--66 7.2 M M 75 M w CI 5-14 -66

80 100 i20 0 20 40 DISTANCE FROM TRAP I N L E T (In.)

66-11443

3.0 psig 5.0 psig 7.0psig

100

120

Temperature Profi.l.es Along Line 522 Charcoal. 'Yrap.

as t h e p r e s s u r e i n c r e a s e s , t h e residence time o f t h e gas between t h e pimp bawl and t h e t r a p i n c r e a s e s , p e r m i t t i n g a g r e a t e r f r a e t i o n of t h e s h o r t - l i v e d a c t i v i t y t o decay b e f o r e reaching the t r a p .

Main CharcoaJ. R e d s . The fuel off-gas was r o u t e d through bed s e e t i o n s IA and 1 3 f o r t h e e n t i r e p e r i o d of power o p e r a t i o n w i t h .the exc e p t i o n of %hree days a t t h e very end, when s e c t i o n s ZA m c i 2B were used.

The p r e s s w e d~-o-pa c r o s s t h e charcoal. beds shoved a p e r s i s t e n t tendency t o i n c r e a s e during power opera.tion. P r e s s u r i z a t i o n and. eqimll z a t i o n experiments e s t a b l i s h e d t h a t -Lhe restri.ct.iorzs were at, -the i n l e t s t o Yne beds, probably whei-e t h e l / 4 - i n . gas l i n e opens i n t o a packing of s t e e l wool above the c h a r c o a l . It w a s found t h a t $he pressure drop coixld be reduced, u s u a l l y t o n e a r t h e normal l . 0 p s i , by blowi n g helium backward through the bed. This was done w-henever %he p r e s sure drop through t h e two beds i n p a r a l l e l approached 3 p s i . S e c t i o n lE plugged more o f t e n , bat sometimes r e s t r i c t i o n s ' o u i l t , up in both seet i o n s . The plugging of .WE beds occurred each time t h e power w a s r a i s e d during tine approach t o fu1.l. power. The plugging became l e s s f r e q u e n t later, b u t a t t'ne end of power o p e r a t i o n 2% w a s s ? ; i l L necessarj; t o backblow t h e beds about once a week.

Stack monitors i n d i c a t e d no breakthrough of a c t i v i t y o t h e r t h a n ten-year 85Kr at any time. That t h i s w a s s o , d-espite the sometimes unbalanced flow through bkie p a r a l l e l be& and t h e e x t r a v o l w ~ e sof gas introduced by backblowing, is an i n d i c a t i o n of a c a p a c i t y t h a t exceeds expectations Line 524 Charcoal Bed. I n t h e fuel pump, pax% of t h e gas admittied t o t h e s h a f t a.nnulus (about 100 c c / i i n ) flows up along tile shaft t o prevent o i l fumes from d i f f u s i n g down i n t o t h e pump bowl. T h i s gas t h e n

flows out through t h e c a t c h b a s i n and l i n e 524. O r i g i n a l l y t h e l i n e 524 flow joined t h e main off-gas stream just downstream of PCV-522,

whose pressure drop s u p p l i e d t h e d r i v i n g f o r c e for t h e gas f l m through 524. Line 524was r e r o u t e d t o come i n downstream o f t h e main charcoal bed for two reasons: t o g e t more pressure drop when PCV-522 was open and to e l i m i n a t e a p o s s i b l e way t h a t hydrocarbons could en-ter t h e charc o a l bed.;. Some manipulations of t h e system p r e s s u r e caused a c t i v i t y t o g e t ifito l i n e 524, r e s u l t i n g i n c l o s u r e of t h e radiation-block valves a t t h e end o f t h e off-gas Line. Therefore a small. charcoal bed vas added i n l i n e 524 t o h o l d up f i s s i o n gases and prevent s t a c k r e l e a s e s by t h i s r o u t e ( s e e "Component Development, " Chap. 2 ) . P r i o r t o t h e start;u$ on A p r i l 11, d i f A u x i l i a r y Charcoal Bed. f i c u l t y i n venting through t h e a u x i l i a r y c h a r c o a l bed was found t o be due t o a check-valve poppet which had become lod-ged i n t h e bed i n l e t l i n e . Tne poppet had apparently v i b r a t e d loose from a check valve a t one of t h e drain-tank o u t l e t l i n e s and had. been c a r r i e d downstream duri n g subsequent venting o p e r a t i o n s . After removal of t h e poppet, venting operations through t'ne a u x i l i a r y bed were uneventful through most of t'ne power operations. Zmever, an i n t e r m i t t e n t r e s t r i c t i o n was noted e a r l y i n JKiy, and, a f t e r t h e shutdown on J u l y 17, t h e r e s t r i c t i o n becane continuous m d more severe. Furthemiore, t h e s i t m k i o n w a s not r e l i e v e d by r e v e r s i n g t h e gas f l o w (backblowing). Pressure and flaw t e s t s i n d i c a t e d t h a t t h e plug w a s i n the same a r e a as i n t h e main charc o a l beds, namely, a t t h e place where t h e gas header connects t o t h e charcoal bed.

An attempt w i l l be made t o remove t h e r e s t r i c t i o n by l o c a l e x t e r n a l h e a t i n g . A t t h e same time, we a r e designing and b u i l d i n g a replacement bed, p r o t e c t e d by an i n l e t f i l t e r , t h a t can be i n s t a l l e d and connected w i t h a minimum of r e a c t o r shutdown time. Treated Cooling-Water System

- R.

B. Lindauer

Chemical Treatment. During power o p e r a t i o n of t h e r e a c t o r , r a d i o l y t i c decomposition of t r e a t e d cooling water i n t h e tinermal s h i e l d produced hydrogen peroxide i n a concentration of 300 t o 500 ppm. This caused oxidation of the l i t h i u m n i t r i t e c o r r o s i o n iriliZbitor t o l i t h i m n i t r a t e . Additional n i t r i t e w a s added p e r i o d i c a l l y u n t i l equilibrium was reached a t approxima-t;ely equal. concentrations (-700 ppnd o f n i t r i t e and n i t r a t e . This occurred a t about 3000 MsThr, and no adclitioiial n i t r i t e a d d i t i o n w a s r e q u i r e d a f t e r t h a t time. The presence of t h e n i t r a t e ion has no e f f e c t on t h e c o r r o s i o n i n h i b i t i o n . R a d i o l y t i c G a s Forraation. Because of t h e i n l i i b i t i v 4 e f f e c t of t h e corrosion i n h i b i t o r on t h e recombination of r a d i o l y t i c gases, approximately 2 f't3/hr of hydrogen was formed i n t h e thermal s h i e l d during OFe r a t i o n a t f u l l power. A t steady s t a t e , about 8 I"t3of r a d i o l y t i c gas accumulated i n t h e thermal s h i e l d and t h e r m a l - s h i e l d s l i d e s . A ~ Q u %onef o u r t h of t h i s accumulated gas was removed by p a r t i a l l y deaerating, i n a small vented tank, t h e cooling water supplied. t o t h e s l i d e s . A l a r g e r degassing t a l i s being i n s t a U e d t o deaerate t h e e n t i r e thermal s h i e l d f l a w . T h i s i s expected t o keep the r a d i o l y t i c - g a s concentrations below

t h e I . i m i t , s of sol.iibriI.ity and-t h u s prevent ga.s pockets from forming. The gas that i s s t r i p p e d from .i;iie water w i l l be d.il-uted wi%h ni.troge11 t o below t h e explosive l-imit and vented to t h e a r e a s t a c k . A contilluous hydrogen analyzer will be instal.led i n t h e o f f - g a s s-trem a t t h e tank t o ensure adeqiiate dj.J.ution e

In-Cell- Leaks. Beforc full-power operation, while t h e react.or cel.1. w a s open, r e a c t o r c e l l . c o o l e r Eo. 2 w a s observed. t o have a s m a l l water l e a k . The cool.er was removed-, r e p a j r e d , and replaced. Some time after $he c e l l w a s r e s e a l e d , a steacv- accl.unulation i n t h e c e l l o f 1.-1/2gpd w a s observed, T h i s water w a s condensed from $he circula%t:ng air strea,m i n t h e c o o l suctioii. l i n e o f t h e component-cooling pumps. A f L w r e a c t o r shu-tduwn i n July, the v a r i o u s water-containing components i n t h e cellwere isol-ated and I-eak t e s t e d . AJ-1.. components were leak--tigbt except rea.ctor cell c o o l e r N o . 1. It w a s removed, decontaminated, and r e p a i r e d . A s i n RCC-2 e a r l i e r , t h e leak was i i n a brazed- j o i n t be-bween a .tube and 8 header. Treated-Water Cooler

Ahout one week before the reacbor was shut

diiwn, the t o t a l 1.eakage froii.1 t h e t r e a t e d - w a t e r system sudden3.y i-ucreased . I

from -4 gpd t o 3 to 5 gph. Since t h e r e was no vri.sible 2.ea.k or increaseda~ce.~miil.a$j_on i n t h e cel.ls, i t w a s suspected tâ&#x20AC;&#x2122;ilat the water was l e a k i n g t h o u g h t h e treated-wa-ter cooler to the cooling-tover-water system. A f t e r t h e ti-eated--ws-ter sysi;ern w a s s h u t down, t h e cooler w a s o p e ~ dfor i n s p e c t i o n and l e a k checking, A I.arge aiiounrt; of %ray s o l i d s was found i n the shell (tower w a t e r ) s i d e around t h e t u l . 1 2 ~and i n 1-ow-velocity a r e a s , Al.1 tube-to-tube s h e e t j o i n t s were I.eak t e s t e d w j . t h a i r and were l e a k f r e e , b u t a h.yd.ra1LLj-c: t e s t of t h e tubes i n d i c a t e d t h a t 17 o f t h e 360 -Lubes had l e a k s a t -the i n s i d e s u r f a c e o f t h e t u b e s h e e t . A f t e r these tiibes were plugged and t h e gasket on t h e f1.oati.o.g head w a s repla,ced, the hea-t exchanger w a s 1.eak-tight. Ccmpoaent -Cooling Systern

- I?.

1%. Harley

The two component-cooling p m p s (CCP), one o f which i s a standby u n i t , supply c e l l gas t o cool i n - c e l l equipment; c i r c u l a t e gas p a s t a r a d i a t i o n monitor, and discbarge gas t o keep t,he cell a-t a negative p r e s s u r e , C C P - 1 operated f o r 1584 h r and CCP-2 operated- 1-759hi- d u - i n g t h i s report period.

Di~r.i.jzg t h e pl-evious r e p o r t period- t h e rnul-tiple matched bel-ts on each CCP were replaxed by a s i n g l e poly-Vi-be1.t. B l o w e r operation, a l though improved, w a s not completely s a t i s f a c t o r y because .Lhe o u t p u t w a s I.ow at b e s t , t h e r e were times when -the o p e r a t i n g pump f a i l - e d . cornp l e t e l y -tomeet â&#x20AC;&#x153;cie demmnd, and t h e standby u n i t w a s sometrinles slow i n b u i l d i n g up pressure. Drive b e l t s l i p p a g e caused tltze loss of a blower on t h r e e occasions. On CCP-1 t h e b e l t had %o be r e t i g h t e n e d a f t e r 450 hr of o p e r a t i o n and r e p l a c e d af%er 870 h r because of damage due t o s1.j.p-

Ping

poor performance caused. some inconvenience i n r e a c t o r operation, and t h e second l o s s of CCP-1 conbkibuted t o a r e a c t o r dxain. A t t h e t i m e of t h i s f a i l u r e , t h e containment encl.oslx-e of CCP-2 w a s i s o l a t e d ni LCE

49 and undergoing a l e a k t e s t . An attempt was made t o g e t CCP-2 back i n operation, b u t t h e system began t o d r a i n before t h e blower could be started.

A t t h e shutdown i n J u l y t h e b e l t on CCP-1 had operated f o r 1084 h r and t h e one on CCP-2 had operated f o r 2013 h r . Both b e l t s shoved some wear and minor cracking, probably caused by overheating. UoYn had relaxed, s o t h e t e n s i o n w a s s i g n i f i c a n t l y less t h a n t h e o r i g i n a l a d j u s t ment.

Even when t h e b e l t s were not s l i p p i n g , t h e output of t h e blowers was l o w , The output a t t h e speed a t which t h e blowers were operating w a s supposed t o be 590 scfm, but conservative flow c a l c u l a t i o n s i n d i c a t e d only 400 scf'm. Various l e a k s might account f o r t h e d i f f e r e n c e . A r u p t u r e d i s k i s being i n s t a l l e d a t t h e discharge of Yhe pressurer e l i e f valves, which a r e known t o l e a k . The check valves will be i n spected and r e p a i r e d i f necessary. (One of t h e check valves f a i l e d completely i n 1965. ) Leakage through t h e valve which v e n t s excess gas t o t h e r e a c t o r c e l l t o c o n t r o l blower discharge pressure m i g h t a l s o account f o r p a r t of t h e l o s s e s .

I n August new, l a r g e r sheaves were i n s t a l l e d on t h e d r i v e motors t o r a i s e t h e nominal output of each blower .bo '740s c f h . P a r t of Vne i n c r e a s e i n output w i l l be discharged i n t o t h e drain-tank c e l l t o provide b e t t e r m i x i n g of a i r between t h a t c e l l and t h e r e a c t o r c e l l . The modifications should r e s u l t i n extended b e l t l i f e . 'The l a r g e r d r i v e sheaves w i l l lower t h e s t r e s s on t h e b e l t s , and stopping t h e l e a k age through t h e pressure r e l i e f valves should lower the ambient tempera t u r e i n t h e enclosures. Another change being m d e s p e c i f i c a l l y t o lower b e l t temperatures is t h e a d d i t i o n of a simple d e f l e c t o r t o d i r e c t c o o l incoming gas over t n e b e l t s . A f t e r t h e space cooler began t o l e a k water i n t o t h e r e a c t o r c e l l , condensate accumulated i n t h e LO-in. s u c t i o n l i n e t o t h e CCP-1 dome a t a r a t e of 1 t o 2 gpd. (The water w a s vaporizing i n t h e r e a c t o r c e l l and condensing i n t h e s u c t i o n l i n e , t h e c o o l e s t surface exposed t o t h e c e l l atmosphere. ) Simple drains were i n s t a l l e d , b u t t h e s e could be used o n l y when t h e r e a c t o r w a s s u b c r i t i c a l s o t h a t r a d i a t i o n i n t h e coolant d-rain c e l l permitted e n t r y . Handling of t h e drained water was complic a t e d by t h e t r i t i u n (up t o 915 pc/ml) produced from t h e %ii n t h e t r e a t e d - w a t e r c o r r o s i o n i r i t i i b i t o r . During t h e shutdown i n August, pipi n g w a s i n s t a l l e d t o permit Straining t h e domes during power operation should leakage i.n t h e c e l l r e q u i r e it. Water condensed i n t h e s u c t i o n l i n e s now w i l l d r a i n t o a t a n k i n t h e sump room, from whence it can be t r a n s f e r r e d t o t h e 1iqid.d-waste tank. Moisture i n t h e component-cooling domes m%y have c o n t r i b u t e d t o

an e l e c t r i c a l f a i l u r e i n wiring t o t h e CCP-1 motor which happened on June 27. A s h o r t i n a seal on t h e end o f a copper-sheathed magnesiai n s u l a t e d c a b l e destroyed t i e seal and caused a l a r g e breaker t o open,

and t h e f u e l drained before s e r v i c e s could be r e s t o r e d . Breakdown of t h e epoxy p o t t i n g i n t'ne s e a l i s another p o s s i b l e e x p l a r a t i o n for t h e f a i l u r e . The C C P - l wiring w a s replaced a t t h a t time, and during t h e August shutdown CCP-2 was rewired t o elimim-te t h a t epoxy-f L l l e d s e a l

50 S a l . t - b m O i l Svstenis - J, 1,. Crowley and H. B. Piper The performance of t h e salk-pump oil- systems during the period. w a s a c c e p t a b l e although not troiib1.e f r e e . Thc h e a t t r a n s f e r in the c o o l e r s d e t e r i o r a t e d because of cooling-water s@al.e,which had t o be renioved, and the tendency for o i l t o collec-L i n t h e s a l t - p - m p motor housings under c e r t a i n c o n d i t i o n s continued t o be a nuisance. Leakage by t h e s e a l s i n .the 3al.t pumps continued- t o be very low, although t h e r e was some i n c r e a s e i n leakage by .the lower shaft, s e a l i n t h e f u e l pump.

Coolers. The o i l i s cool.ed by cooling-tower water passing t i i r o i g h c o i l s i n t h e two o i l r e s e r v o i r s . Dwing March t h e temperakure of t h e coolant-pump oil. su~qYLyg r a d u a l l y increased. from i t s n o - m l - 134’F t o 140°F. A f t e r inspeckion showed t h e r e w a s s c a l e i n t h e c o i l on t h e cool-ant-pump oil- c o o l e r , it w a s flushed. wit;in a. 1.5 v t $ s o l u t i o n of ace3j.c a c i d . Considerable i n a t e r i a l was removed, and t h e o i l . temperat u r e was reduced 7°F. The fuel-pump o i l c o o l e r w a s given t h e s m e treatmertt and t h e oil temperature w a s reduced 3OF. Du.ring subsequent operaticm t h e tempera-Lure of the fuel-pump o i l g r a d u a l l y r o s e > and i n A u g u s t t h e acetic. a c i d treatment was again given both c o o l e r s ,

Holdup i n Motor Cavitx. Holdup of o i l i n t h e salt-pump motor housi n g s continued t o occur uxder c e r t a i n c o n d i t i o n s o f flow and p r e s s u r e . 1x1 July, during a pressure t e s t of t h e c o o l a n t system, tlne presswe on %he coolant-pump o i l t a n k w a s i n c r e a s e d from 7 t o 20 p s i g . T h i s cadused 58 l i k e r s of oil.. t o accumula.te i n the motor c a v i t y , and i k took f i v e days for a l l of it t o d r a i n back t o t h e t a n k .

Shaft S e a l Leakage. O i l l e a k i n g p a s t t h e lower s h a f t seal i n a s a l t pump d r a i n s through a c a t c h b a s i n i n t h e pump t o a n ex’cernal c a t c h t a n k provided. wi.th a l e v e l i n d i c a t o r . Changes i n t h e coolant-pump o i l . ca-bch tank i n d i c a t e d a s t e a d y accwnulatlion of less t h a n 2 crn3/clay throughout t h e perri.od. U n t i l A p r i l t h e accumulation from %he f u e l puml) w a s also l e s s ,than 2 cm3/day. It increased. t h e n t o about 6 cm3/day and agarin i n mid-June t o about 20 cm3/day. This Tndicates Some d e t e r i o r a t i o n o f t h e pump s h a f t s e a l , b u t tile r a t e i s s t i l l f a r below the 1000 cm3/day considered t o l e r a b l e Leakage p a s t S t a t i c S e a l s , O i l can l e a k p a s t a sta.t,ic, s e a l aroimd t h e shield- plug and i n t o t h e s a l t i n t h e pump ’oowl. This leakage cannot be measured direct,l_y b u t , i n p r i n c i p l e , is d e - k c t a b l e by t h e decrease i n oil. j-nventory. ‘This technique i s l i m i t e d by t h e accuracy of tile tank l e v e l measurements and v a r i a k i o n s i n t h e .amoi.mt of oil. h e l d up i n t n e salt-pump motor holmiixs, which cannot be measured. The l a b t e r e f f e c t J.s canceled when data a r e averaged over a long p e r i o d of time. The expected accixacy of t h e l e v e l measul’ements i s e q u i v a l e n t t o 21.2 l i t e r s . Data f o r t h e four-month p e r i o d f r o m A p r i l -through .July a r e ( I n v e n t o r i e s f o r t h e s e p a r a t e systems were not shown i n Table 1.5. obtained. i n March because of t r a n s f e r s while t h e o i l c o o l e r s were being f l u s h e d , ) The apparenk l o s s e s a r e a’ooilrt one-fourth tine proba’ble e r r o r i n t h e l e v e l measmements l___l_

Oil. Replacement. No d e t e r i o r a t i o n o f %he o i l was observed during operation, b u t a f t e r t h e r e a c t o r w a s shu3 down i n Judy, both systems were b a i n e d and refiLl.ed w i t h f r e s h o i l .

51 Table 1.5.

O i l Systems Inventory Changes, A p r i l J u l y , 1966

Cnange (cm3)

It em

Fue 1 System

Coolant System

Samples removed

8834

Increase i n catch t a n k (shaft s e a l )

1.005

181.

T o t a l accounted f o r

9839

9015

Decrease i n r e s e r v o i r

9536

9450

Apparent 10ss

-303

335

E l e c t r i c a l System

- T.

I;. Hudson and T. F . pr;ullinix

The MSRE p l a n t includes an e l a b o r a t e e l e c t r i c a l subsystem t o provide ac and dc pawer t o t h e various components. F a i l u r e s w i t h i n o r a s s o c i a t e d w i t h t h e e l e c t r i c a l system accounted f o r SLY unscheduled i n t e r r u p t i o n s i n t h e power operation of t h e r e a c t o r during t h i s r e p o r t p e r i o d . These i n t e r r u p t i o n s v a r i e d i n l e n g t h from a few minukes t o s e v e r a l days. Ln a l l cases t h e necessary r e p a i r s or modLfications were made, and no damage t o r e a c t o r equipment w a s i n c u r r e d .

AC Power Supply. Five of t h e six e l e c t r i c a l f a i l u r e s t h a t caused r e a c t o r power i n t e r r u p t i o n s were a s s o c i a t e d w i t h t h e ac supply system: t h r e e were caused by e l e c t r i c a l storms, one by a wiring f a i l u r e a t a component-cooling pump, and one by a simple overload of t h e main processpower breaker. On two occasions while t h e r e a c t o r was operating a t power, momentary e l e c t r i c a l outages during s t o r m caused control-rod scrams by r.mge-switching t h e nuclear power s a f e t y channels because of dips i n t h e fuel-pwnpmotor c u r r e n t . I n both t h e s e cases t h e nuclear power w a s quickly r e s t o r e d t o 'che value t h a t e x i s t e d just p r i o r t o t h e oatage. Since t h e low range of t h e s a f e t y channels i s used only while f i l l i n g t h e r e a c t o r (when t h e f u e l punip i s o f f ) , r a p i d response of t h e range switching i s not required. Therefore, time-delay r e l a y s were incorporated i n t h e s e c i r c u i t s t o prevent t h e i r a c t i v a t i o n on momentary power d i p s . The -t;hird storm-induced f a i l u r e occurred when l i g h t n i n g s t r u c k a power s u b s t a t i o n and p a r t e d one w i r e of t h e main MSBE f e e d e r . I n t h i s case t h e e l e c t r i c a l l o a d was a u t o m a t i c a l l y t r a n s f e r r e d t o an a l t e r n a t e f e e d e r , and a l l e s s e n t i a l equipment was r e s t a r t e d i n time t o prevent d r a i n i n g e i t h e r t h e fuel o r c o o l a n t system. However, operation a t high nuclear power could not be resimed u n t i l s e r v i c e w a s r e s t o r e d on the main f e e d e r . The e n t i r e supply system has s i n c e been reviewed and improved t o make it l e s s s u s c e p t i b l e t o damage by storms. The s h o r t i n t h e component-cooling pwq cable s e a l i s described i n S e c t . 1.9, subsection e n t i t l e d "Component Cooling System. '* When t h i s

52 s h o r t occurred, t h e r e w a s a rmsslve f l o w of cixren-L and. t h e breakelindl7i:'Lduai breaker f o r the supplyri.ng t h e er?lcire bus tl-ipped b e f o r e mot or. During t h e iniLia!. full-powex- operation of t h e re process-power b r e a k z r (breaker R) was loaded -Lo n e a r i v-al-lie Td%.ent h e I.oad on t h e c o o l a n t - r a d i a t o r main -bl.aver motars w a s i n c r e a s e d by i n c r g t h c p i l x h on the blower f a n bla.d.es ( s e e S e c t . @ d "Main Blowers "1, t h e increase& load. on breaker 1..9: s u b s e c t i o n e R caused il; t o t r i p on o v e r c u r r e n t . T h i s condTtion w a s r e l i e v e d by 00 kw of auxiltiary l o a d f r o m t h e main process t r a n s t r a n s f e r r i n g abou f o r x e r t o an e x i s g a u x i l i a r y power transfoxmer The l o a d t r a n s f e p decreased t h e CWreilt ,through breaker R from about 1700 a,mp/pha,se t o cbout 1550.

A f t e r tihe shutdown 5--n J - d y all.. switchgear b r e a k e r s were removed, tested., and c a l i b r a t e d .

DC-AC I n v e r t e r , To improve t h e r e l i a b i l i . t ; y and i n c r e a s e tihe c a paci.ty of t h e reli.ahl-e ac p a r e r suppl.y, mot.or generatAo?Li.i.s a 25-kt-a single-phase r o t a r y i.:nverteer, w a s r e p l a c e d w:i.th a new 62-kva -Lhreephase s t a t i c i n v e r t e r . The total..l o a d on tine r e l i a b l e power supply, ri.nclud.i.ng the o n - l i n e computer, which has some three-phase load, i s 4.0 kva. The s t a t i c i n v e r t e r o f f e r s a iiumber of advan-bages over the o l d r o t a r y j_:n.veri;er, including h i g h e r el"fir,j.ency (increased 35$), s m a l l e r s i z e , no movi-ag p a r t s q u i e t opera-tiion, and e x c e l l e n t voltage and frequency regulakion. Prlior t o tine i n s t a l l a t i o n oâ&#x201A;Ź t'nh e q ~ p m e n t , both t h e c a p a c i t y and t h e voltage r e g u l a t i o n o f t h e relia1il.e power siipply were inadequate for t h e o p e r a t i o n of thc: o n - l i n e computer. Dur7.n.g the checkout and t e s t i n g of t h e sl;at.ic i n v e r t e r i n April, a f t e r t h e i n s t a l l a t i o n had been compl-e-Led, t r o u b l e o c c a s i o n a l l y developed .that blew t h e l o a d f u s e s . Two %Fmes t h e m.niYCacturer's f i e l d eng i n e e r made exhaustive t e s t s and could not f i n d any t r o u b l e , hiit a l l symptoms i n d i c a t e d t h a t t h e t r o u b l e was i n 1;he I-ow-voltage l o g i c power On A p r i l 22 ';he i n v e r t e r supply, which s u p p l i e s 24-v de ~ o ~ i tpower. r ~ l f a i l e d a g a i n while t h e r e a c t o r w a s opei?atlri.g s.t ].ow power, causing a c o n t r o l - r a d scram. The i n v e r t e r load w a s aukoriiati.cal_ly t r a n s f e r r e d to t h e normal ac power supply. A f t e r t h i s fai.l.ux-e a new power-supply mod.i l l e was i n s t a l l e d , and no f i x t h r r JGroukk has occurred.

The i n v e r t e r output v o l t a g e regillakion has been 208 k 1./2 v, andt h e output frequency- b e t - t e r t h a n 60 cps ? O.Ol.$. On one occasion t h e i n v e r t e r was operated. 2-1/4 hr from t h e 250-v baf,tery syskeem withoiut tlie dc g e n e r a t o r o p e r a t i n g . Alihoug'n -tile input .Lo t h e i n v e r t e r v a r i e d 20 v, the output v a r i e d only 0.5 v.

D i e s e l Generators Three diesel-power gmermtors, each wi.Lii a c a p a c i t y of 300 b-, supply emergency ac power t o motors and h e a t e r s i n t h e NSRE. During t h i s r e p o r t p e r i o d t h e r e were tiiree occasions on which t h i s emergency power w a s needed. The d i e s e l g e n e r a t o r s were star-Led and operated wit'nout d i f f i c u l t y except i n Jme, when t h e cornponent-coolankpunp breaker w a s d o s e d a f t e r the f a u l t i n the j u n c t i o n box. This caused. an. overload on DG-3, and it w a s manually shut r1ow:o.. e

53 I n February a crack w a s found i n t h e block of X-3 a t one of t h e b o l t h o l e s . All. attempts a t r e p a i r s were l e s s t h a n completely successful, b u t t h e u n i t w a s operable. D i e s e l generator 3 i s being replaced w i t h a s u r p l u s d i e s e l generator from another i n s t a l l a t i o n . The r e p l a c e ment u n i t i s similar t o t h e o r i g i n a l except t h a t it is s t a r t e d by compressed a i r i n s t e a d of by a s t o r a g e b a t t e r y . Control Rods and Drives

- M.

Richardson and R. H. Guymoa

Tne c o n t r o l rods continued t o operate. r e l i a b l y although t h e r e were f a i l u r e s i n p o s i t i o n instrumentation. During t h i s r e p o r t p e r i o d t h e r e were 16 rod scrams while t h e r e a c t o r Six were caused by power f a i l u r e s , six r e s u l t e d from i n strument malfunctions, two resul"ced from uperator mistakes, and two were I n a d d i t i o n , t h e rods were scrammed 18 t i m e s d e l i b e r a t e experimentz. i n c i r c u i t t e s t s and 42 times t o measure drop times. I n no case did any rod ever f a i l t o scram, nor w a s m y drop time i n excess of the spec i f i e d maxinun.

was critical.

Drop times f o r rods 1 and 2 were c o n s i s t e n t l y below 800 m e c . The drop time on rod 3 i n c r e a s e d from 900 t o 960 msec, s t i l l w e l l below t h e l.3-sec l i m i t s e t by s a f e t y c o n s i d e r a t i o n s .

Measurement of tine f i d u c i a l zeros showed no appreciable change i n rod l e n g t h nor any shift; i n p o s i t i o n i n d i c a t i o n . The coarse posi-tion synchro on r o d &rive 3 f a i l e d on July 2 because of an i n t e r n a l s h o r t , ,and it w a s necessary t h e r e a f t e r t o count t u r n s of: t h e f i n e synchro i n posi'cioning t h i s shim rod. The potentiorneter on rod dxive I, supplying a p o s i t i o n sign81 t o a f i l l - p e n n i t i n t e r l o c k , became i n o p e r a t i v e because of woryl windings. The d e f e c t i v e potentiometer and synchro were replaced i n A L I ~ U S ~ , hplers

- R.

B. Gallaher and R. X. Gqmon

The sampler-enricher was used t o o b t a i n 35 f u e l salt smiples, LO of which were 50-g samples f o r oxide a n a l y s i s . Most cjf t h e s e were taken without i-mident A b r i e f account of d i f f i c u l t i e s follows; d e t a i l s a r e covered i n Chap. 2.

On A p r i l 29 a l a t c h w i t h reduced. d i m - e t e r was i n s t a l l e d t o e l i m i n a t e binding which was encountered a t t h e lower bend i n t h e swnple l i n e . While it w a s being t e s t e d , wires t o t h e d r i v e motor shorted- out i n s i d e t h e sampler. The f u e l w a s drained from tine r e a c t o r , t h e sampler was removed and r e p a i r e d , and o p e r a t i o n ~jsa.8reswned i n t e n days.

Af-i;er t h e l a k h replacement t h e operation of %he safipler went w i t h out a h i t c h except f o r one time ( J u l y GI, when the capQ tule s t u c k for s o r e unexplained reason and no sample w a s oi3tained. Once it w a s necessary t o r e t r i e v e an empty capsule which had been dropped a c c i d e n t a l l y t o t h e o p e r a t i o n a l valve. A magnet on a cable w a s used t o r e t r i e v e t h e magnetic Latch key w i t h capsule a t t a c h e d .

The intexvior of t h e tr-ansf

box (area 3 A ) gradually became con-ia:mi -

naked, and on t w o occasions minor contaminatloil of the outside r e s u - t c ? as the -l;ransport coni;a..:'l.nerw a s 'wing removed throug% t h e top. More s';ringezt procec7iures i.including %he estab1ishrneiY-t of a "coiitamina.S,ri.csn" zone a t t h e saiaple~,were adopted t o preveni recurrence.

On July 2 4 accidcnta1. overf?.l.lirg of t h e pimp w i t h t'lush s a l t f o r e e d s a l t i n t o the sampler t u b e . The %-&e w a s found t o be obstru.c.l;e:d about 2 ft above t h e pump bowl-, preventing sanipliag . External h e a t e r s appl..icd remotel..y wzre u s e d . t o m c l t out t h e sall;. The cool_ant sampler was used wi.i;hoirt difficul-iy t o o b t a i n 18 coo1an.L.sall; smnples. Containmeiit .........- - H . B. P i p e r

Several.. a s p e c t s of containnent axe o f i n t e r e s t i n tine o v e r a l l ope r a t i o n of the MSW. I n a d d i t i o n t o 'che primayy consideration, tlhat of rmintainiLng a low-leakage envelope t o prevent t h e rei-ease of excess i v e a c t i v i t y i n -the u n l i k e l y event oT a reac-boor accident, i'i j.s a l s o necessary t o prevenk a c t i v i t y r e l e a s e s and contaxi:i.nation duri.ng maintenance p z r i o d s , when t h e normal second,ziry containment a.nd even the -fu.e1 loop i t s e l f may be open, The l.atter c o n s i d e r a t i o n i s par%lcul a r l y inqmrtau-l; w i t h . a fLuid-fiiel r e a c t o r , where fissi-oi? product act i v i t y i s dl.stri'uuted tbro-whout t h e fuel? I-oop. The high chemical toxici-?;y o f MSRE s a l t s (due t o t h e i r high beryllium and. fluoride cont e n t ) a l s o requi.res c a r e f u l measures t o prevent t h e r e l e a s e of large q i m n t i t i e c of even nomzd.ioacl;l.ve s a l t s . l)ur:i.ng r e a c t o r opera'iion t h e secondary containment, o r primaryaccidenl; containment, system c o i i s i s t s o f t h e r e a c t o r and drain-ta-nk c e l l s , which are sealed a.nd kept a t -2. pig. The r e a c t o r b u i l d i n g serves as a thi-rd b a r r i e r , s i n c e i t i s kept a t sI.ight1-y subatmospheric press-m-e arid the exhaust a i r goes through. roughing and a b s n l u t e T i l . t e r s before being released from t h e containment s.i;e.ck. When V i e rmain contai-men%b a r r i e r and t b e reac%or m u s t be opened f o r i n - c e l l maintenance, prima,ry a c t i v i t y containment i s provided by d.iver=ti.ng t h e bifilding v e n t i l a t i o n a i r into t h e c e l l opening and out t o t h e s t a c k by way of Lhe a b s o l u t e f i l t e r s . 'The r e a c t o r buL1diri.g t h e n becomes t h e second c o n - b a i i x ~ n b t arrier.

Seconda-ry containment System. The i - n i k i a l t e s t i n g of -the secondary containmenl; system has been covered i n de-iai.1..l 3 'The I-eakage rake from the secondary containme:at h a s been monttored throughout t h e r e p o r t i n g period. The leakage ra-Le of tile coiitainmeni; i s determined by measuring e i t h e r the cha.nge i n inventory ( c e l l atmosphere) o r t n e change i n press i x e as a f u n c t i o n of t h e arid t h e n comectiiig t h i s value for t h e known and measure2 flows both ?.:at0 and out of %'tie sys-bem. A higher t h a i 2 auxeptable leakage r a t e was measured when Llne containment system was re-burned t o s e r v i c e i.n March a f t e r a, period of inc e l l maintenance. A check valve i n t h e air-stea.m l i n e l e a d i n g .bo t h e r e a c t o r - c e l l s m p j e t was found 'GO be leaking. There i s a s r i . m i l a r check

55 valve i n t h e d r a i n - t a n k - c e l l swnp j e t l i n e , and it was suspected of l e a k ing a l s o , s o both l i n e s were p a r t e d and capped t o a s s u r e l e a k - t i g h t n e s s . A f t e r t h i s t h e containment w a s fourid t o be acceptable, with a measured in-leakage r a t e o f 1.9 ft3/day at -2 p s i g . The h i g h e s t acceptable le.&S t a r t i n g i n Late A p r i l age r a t e a t t h i s pressure would be -75 f t 3 / & y . and continuing through k y , it appeared t h a t a l a r g e l e a k had developed i n t h e containment envelope, and a g r e a t d e a l of e f f o r t was made t o f i n d and s t o p t h i s l e a k . It was f i n a , l l y necessary, hoxever, t o p r e s s u r i z e t h e c e l l t o 20 p s i g and do extensive l e a k hunting.

A t -2 p s i g it looked as i f in-leakage had increased by about 100 ft3/day, and a f t e r p r e s s u r i z i n g t o 20 p s i g t h e d&a s t i l l i n d i c a t e d a l e a k i n t o t h e c e l l . !The l e a k w a s found t o be i n one or more of t h e e i g h t p r e s s u r i z e d thermocouple headers. Each header i s constructed as a box, w i t h one w a l l of t h e box Pacing t h e containment e e l - l s ,and t h e o t h e r f a c i n g atmosphere. Themocouple l e a d s coming from t h e containsent p e n e t r a t e f i r s t t h e inner w a l l and t h e n t h e o u t e r wal.1 of t h e box, w i t h t h e space between being pressurized- with n i t r o g e n t o iz pressure g r e a t e r t h a n t h a t of t h e containment. Three of t h e s e headers were found t o be d e f i n i t e l y l e a k i n g . Assurance was obtained t h a t t h e headers were not leaking t o atmosphere by soap -bubble checking all. p e n e t r a t i o n s i n all. headers while they were p r e s s u r i z e d . Mo l e a k s were four-d. A c a l i b r a t e d rotameter w a s placed i n t h e n i t r o g e n l i n e which i s used t o p r e s s u r i z e t h e headers s o t'nat t h e leakage from t h e headei-s t o t h e contaimnent can be continuously monibored and c o r r e c t e d f o r 3.n t h e leakagera-k c a l c u l a t i o n . A f t e r t h i s work was completed, t h e leakage i n t o t h e containment w a s a g a i n measured a t -2 p s i g and found t o be ,-25ft'/ldsty, an acceptable value. The le&age r a t e has been monitored d a i l y s i n c e t h a t time, and, u n t i l the r e a c t o r containmelit was opened for maiiitennnce, t h e containment remained acceptable. Altbo-ugh some l e a k s cEfd occux during e'ne r e p o r t period, none was l a r g e , and a l l were found and renedied.

Containment for In-Cell Mainterlance. Under noma1 c o d i t i o n s , whether t h e r e a c t o r i s operabing or not, t h e r e a c t o r b u i l d i n g (high bay) i s kept a t subatmospheric p r e s s u r e , -43.2 in. 1320. A i r from t h e r e a c t o r b u i l d i n g i s discharged from t h e 1 0 0 - f t containment s t a c k a f t e r p a r t i c u l a t e s have been removed by an "absolute" T i l t e r . Wnen i n - c e l l maintenance i s c a r r i e d on ( t h e r e a c t o r c e l l is open), a l a r g e c e U exhaust l i n e t o t h e f i l t e r s i s opened t o a s s u r e that a i r flows down i n t o t h e contaimnent cell with a v e l o c i t y a t l e a s t 100 f p s through t h e o p e n i q s , taus preventing any urlcoiitrolled r e l e a s e of a i r b o r n e a e t , i v i t y I)

During t h e r e p o r t p e r i o d no d e t e c t a b l e p a r t i c u l a t e a c t i v i t y - w a s r e l e a s e d . There w a s a t o t a l of 97.3 r c of gaseous a c t i v i t y ( i o d i n e ) r e leased, w i t h 74 mc being r e l e a s e d during t h e two weeks t h a t t h e g r a p h i t e s c a p l e s nnd f l e x i b i l e jumper i n t h e 022-gas l i n e were being removed. 'i"he t o t a l m o u t r e l e a s e d i n six months is 0,016 of the t o t a l permissible rel e a s e from t h e f i v e s t a c k s i n t h e OLUL area. F i l t e r s and Stack Fans, In October 1965 t h e f i l t e r p i % wes overhauled, and aew roughiog and absoluke f i l t e r s were i n s t a l l - e d . Effic i e n c i e s measused by %he standard OBdL d i o c t y l plithalate (1301))t e s t

56 w e r e 99.99.4 t o 99 .c~w$ for t h e ttil-ee 'oariks (99.95$ 5.s t h e miniIriwm acc e p t a b l e ) . T'ne f i l - t e r s were a g a i n DOF-tested i n March 1966, and meas u r e d e f f i c i e n c i e s were 99.995 t o 99.999%. Evidently nei.ther t h e abs o l u t e fi-1-ters nor t h e new s i l i c o n e caulking had d e t e r i o r a t e d . From t h e t i m e of i n s t a l l a t i o n through A q u s t , t h e p r e s s u r e &-op a c r o s s tile a b s o l u t e f i l ' c e r s remained w-elzanged, while drop a c r o s s t n e roughing f i l t e r s g r a d u a l l y i.ncreaseci t o 5.5 i.n. H20, causing a decrease i n s t a c k flaw of 15%. The flow remained above -the val.ine assumed in" s a f e t y a n a l y s e s f o r s t a c k d i s p e r s i o n , b u t t h e roughing I"il.ters w i l l be replaced a f t e r i n - c e l l miriLenail~e i s completed. The h e a r i n g s were r e p l a c e d i n t h e west s.i;a,ck fan i n March. Jlndicatior-s were that, i n s u f f i c i e n t l u b r i c a t i o n had contributed. t o t h e f a i l u r e , s o t h e l u b r i c a t i o n system was changed f r o m g r e a s e t o l i g h t o i l . The same l i i b r i c a t i o n r e v i s i o n i s planned. f o r t h e e a s t f a n . 'The f a n s a r c driven through V-belts by an e x t e r n a l motor, which, a s o r i g i n a l l y i n s t a l l e d , These sheaves a p p a r e n t l y cause greatex- t h a n had adjustah1.e sheaves normal bel!; wear, and even thoi@ no b e l t f a i l u r e has occurred, r e placement with a p r o p e r l y s i z e d s o l i d sheave seemed advisa'nI..e * Tjnis was done on t'ne west sLa.ek fm i n JUly and i s a l s o planned f o r the east unit. e

13eryll.im. A i r i s continuously sampled at; 1.5 I-ocations -Liirow;hout t h e MSRE a r e a f o r b e r y l l i u m contamination. T h i s i s done by d r a w ing a i r through paper f i l t e r s upon which the bery3.l_iixn would be c o i l e c t e d and t h e n detem-ining t h e amount of contaminan!; t h a t i s deposited. These s m p 1 . e ~are c o l l e c t e d and analyzed. every- working day. 'i'he Lower limit of detect,i.on i s 0.05 pg p e r sample, and each d a i l y ( 2 4 hr.) sample repr e s e n t s the amount; o f b e r y l l i u m i n 14 m3 of a i r . T h i s r e p r e s e n t s a. lower l i m i t of d e t e c t a b l e c o n c e n t r a t i o n of 0.001;p.g/m3. he m i m u m peniissibl.e conceiitrat,lon of b e r y 1 l i . m for continuous occiqacncy of an area for an 8-hr work day i s 2 pg/m3. There has been no detecLable rel e a s e of berylliwni d - i r i n g t h i s report p e r i o d .

A i r d r a w n from -bile c o o l a i i t - r a d i a t o r s t a c k i s monitored contiuuousI.y while t h e r e a c t o r i s i n operati-on. A b e r y l l i u m d e t e c t o r w h k h samples and analyzes on l i n e i s used f o r t h i s purpose, The L i m i t s of d e t e c t a b i l i t y a r e t h e same as t h o s e described- above. Again, t?nere has been no d e t e c t a b l e r e l e a s e d.iu*ing t h i s r e p o r t p e r i o d .

Sinielding and Radiation - H. B. P i p e r Complete r a d i a t i o n surveys were made of t h e r e a c t o r a r e a as t h e poTwer w a s r a i s e d froui 1 Mw t o full.. power, and wi.'&i? t h e exce,pti.on of t h e a r e a s discussed i n t h e f o l l o w i n g paragraphs, t h e shieldi.ng was found t o be adequate. When t h e r e a c t o r power was f i r s t r a i s e d t o 1. Mw i n A p r i l 2 t h e rad i a t i o n l e v e l iil -the North E l e c t r i c S e r v i c e ! ~ e ah S A ) w a s found t o be h i g h : 20 mr/hr on t h e balcony and 8000 m / h r a t the vest wall.. Ii1v e s t i g a t i o n showed t h a t t h e r e was r a d i o a c t i v e gas i n t h e lines -t;hroi.&i which gas is added *bo t;he d r a i n tanks. Two check v a l v e s i n each l i n e

57 prevented t h e gas from g e t t i n g beyond t h e secondary coniairuneat enclosure, b u t t h e enclosure, of l / 2 - i n . s t e e l , provided l i t t l e gamma. s h i e l d i n g . The p r e s s u r e i n t h e f u e l system a t t h a t t i m e w a s c o n t r o l l e d by t h e newly i n s t a l l e d p r e s s u r e c o n t r o l v a l v e w i t h r a t h e r coarse t r i m , and. t h e p r e s s u r e f l u c t u a t e d around t h e c o r i t r d p o i n t ( n o m l l y 5 p s i g ) by +2$. I'hese p r e s s u r e f l u c t u a t i o n s caused f i s s i o n product gases t o d i f f u s e more rapidl;y i n t o t h e d r a i n tanks and back through t h e l / 4 - i n a l i n e s through t h e s h i e l d i n t o t h e NESA. The r a d i a t i o n l e v e l w a s l e s s e n e d by i n s t a l l i n g a temporary meam of supplying an i n t e r m i t t e r l t purge t o t h e g a s - a d d i t i o n l i n e s t o sweep t h e f i s s i o n product gases back i n t o t h e d r a i n tanks. A t -7.5 %1 on May 24, t h e r a d i a t i o n l e v e l s were 5 mr/hs on t h e balcony and 2000 n r / h r a t t h e west w s l l . bring t h e Jwje shutdown, a permanent purge system w a s i n s t a l l e d t o supply continuolzs i i e l i m purge of 70 cc/min t o each of t h e t h r e e g a s - a d d i t i o n l i n e s . This w a s proved succ e s s f u l by subsequent full-power o p e r a t i o n i n v h i c h t h e general backgrowld i n t h e NESA w a s <l mr/hr

There a r e now t h r e e areas i n which t n e dose r a t e s a t full power m e t o o h i g h f o r continuous occupancy. Lirniting a c c e s s t o t h e s e a r e a s is n o t considered a hindrance t o t h e o r d e r l y o p e r a t i o n of the r e a c t o r and s o no f u r t h e r rernedlal a c t i o n i s planned.

Reactor C e l l TOE. Two v e r y narrow beams, presm.ably coming from c r a c k s between s h i e l d blocks, reading 10 mr/hr gamma and 60 m i l l i r e m / hr fast neutrons, were found on t o p of t h e r e a c t o r c e l l blocks; t h e s e a r e a s were p r o p e r l y marked. Coolant Drain T m k . Cell. Access Ramp. Even though s h i e l d i n g w a s added i n s i d e t h e c o o l a n t d r a i n c e l l door, t h e dose r a t e s o u t s i d e t h e door (700mr/hr gamma, 125 m i l l i r e m / h r fast nei;ct;rons, > 75 rnilLirem/ hr thermal n e u t r o n s ) and halfway up t h e a c c e s s ramp (35 m/hr gama, 2 millirems/hr f a s t neutrons, 25 milliremL;/hr thermal neutrons ) are high d w i n g power o p e r a t i o n . This a r e a i s c l e a r l y rrmrked w i t h radiat i o n zone s i g n s a t t h e e n t r a n c e and halfway down t h e ramp.

Vent House. Stacked c o n c r e t e 'oloclr s h i e l d i n g has been added p e r i o d i c a l s y t o keep dose r a t e s l o w i n this area. E v e n so, t h e background r a d i a t i o n Level i s -7.0 mr/hr a t f u l l power, aiid t h e a r e a i s a condit i o n a l - a c c e s s r a d i a t i o n zone.

1.10

1nstrwnexita;t;ion and Controls

J. E. Tallacksorr

R . L. Moore

The MSRE i n s t r u n e n t a t i o n and c o n t r o l s system continued t o perform w e l l . There w a s t n e normally expec'ced r e d u c t i o n i n b o t h n i a l f u c t i o n s and misoperation of instruments 8 6 instrument and o p e r a t i n g personnel gained experience and developed r o u t i n e s . While t h e r e were many design changes, most of t h e s e were improvements and a d d i t i o n s t o the system r a t h e r t h a n c o r r e c t i v e measures t o the i n s t m m e n t s and c o n t r o l s . A &isappointjngly l a r g e nwnier o f f a u l t y commercial r e l a y s and e l e c t s c n i c swltches were d i s c l o s e d . These faults were i n .the areas of' both r e l a y design arid f a b r i c a t i o n , and c o r r e c t t t i e s t e p s have 'oeen t a k e n

58 Operating Jkperience - Process and Nuclear Instruments E . N . Fray, K. W . Tucker, and G. H. Burger

- C . E.

Mathews,

Control-System Relays. All 12.5 of t h e 48-v dc-operated r e l a y s i n both t h e s a f e t y - and contrh.-grad.e c i r c u i t s w i l l be r e p l a c e d because of h e a t damage t o t h e i r Bakeli-Le frames. T h i s problem w 8 s d i s c u s s e d w i t h t h e manufacturer, who s t a t e d t h a t overhea%ing i s a coumon problem w i t h a l l r e l a y s of t h i s p a r t i c u l a r model. i f t h e y are continuousLy energ i z e d f o r long periods h S R Z r e l a y s have operated for t w o y e a r s ) . It i s a b o r d e r l i n e condition., which he says has been c o r r e c t e d by changing t h e design t o reduce by 20% t h e t o t a l power d i s s i p a t e d i n t h e operating c o t l and t h e s e r i e s - c o - m e c t e d dropping r e s i s t o r . An order w a s placed f o r 139 rela-ys of t h e l a t e s t design.

Four new spare sol-enoid c o i l assemblies were puxchased f o r t h e speApproximately 40 valves have

cial weld-sealed e l e c t r i c s o l e n o i d v a l v e s

been i n s e r v i c e on t h e f u e l - and c o o l a n t - s a l t c i r c u h t i n g pump 3-eve1 measu-ing systems and t h e f u e l sampler-enricher f o r 'iwo y e a r s . The f i r s t a;nd only c o i l f a i l m e occurred r e c e n t l y . P r e s s u r e Transducers A d i f f e r e n t i a l pressme c e l l u s e d . t o o b t a i n p r e s s u r e drop i n t h e heliimi flow through t h e c h a r c o a l bed s h i f t e d i t s range setLing. The c e l l has been removed, b u t t h e cause of tjnis range s h i f t has not y e t been determined. . I

Therrfiocoiiple performance has coni;inued t o be excel'i'hemiocouples le&. Only one thermocouple f a i l u r e occurred duririg t h i s peri.od. This b r i n g s t h e .tubal number OS f a i l u r e s s i n c e t h e s t a r t of MSRE operaLion t o 5 out o f over 1000 couples i n use. e

s ~ ~ f o r alarm El.ectronic Switches, The E l e c t r a Systems s w i - t c l ~ used and control- of teinperatures i n tlne freeze-valve system performed without malfunction during t h i s p e r i o d . This improvement i n performance i s a t t r i b u t e d t o modifications reported. p r e v i 0 u s l y ; l 5 t o t h e establisimei?t and enforcement of more r i g o r o u s test and periodic, checking procedures; Lo t h e stab.i.Lization, by aging, of c r i t i i c a l r e s i s t o r s i n t h e switch modu l e s ; sild 'GO a b e t t e r understanding, by o p e r a t i n g personnel, of t h e i r use i n t h e system. A check showed tAat out of 109 switch s e t p o i n t s , 83% had. s h i f t e d less t h a a 20째F over -the sLx-monLh p e r i o d , No swj-tches w i t h double set poiilts were found, and it i s l.i.ke3-y t h a t t'nis malfwic-bioi1 w i l l not reappear. SporadZc m a l f m c t i o n s i n c o n t r o l loops contaiiiiilg a p a r t i c i n l a r model current-actua-Led- c o m e r c i . a l e l e c t r o n j x switch h a v e been a sou.rce of annoyance. This f a u l t y behavior w a s , a p p a r e n t l y , a s s o c i a t e d rnos-1; f r e q u e n t l y w i t h ambient temperatixe changes brought on by a i r - c o n d i t i o n i n g f a i l i x r e s and w i t h excessive v i b r a t i o n . Thoraigh i n s p e c t i o n , mde p o s s i b l e by a system shutdown, revealed" t h a t oul; of 61. switches i n s e r v i c e , 38 had one o r more faul.ty i n t e r n a l connections Tinese f a u l t y - connections, o r i g i n a t e d during maaufacture, were imperfec-Lly s o l d e r e d j o i n t s o r j o i n t s which had never been sol.dered. Nuclear Instrunienta-tlion Water leakage v i a t h e c a b l e into %be counter-pream$lif i e r assembly caused s e v e r a l f a i l u r e s i n t h e wid-e-raiGe I)

59 counting channels. The cause has been diagnosed a s excessive s t r a i n and f l e x i n g of t h e cable, and a redesigned c a b l e assembly w i l l be i n s t a l l e d . Fersonnel Monitoring System. 'The r e a c t o r b u i l d i n g r a d i a t i o n and contaminaLion warning system was a g a i n r e v i s e d t o c o r r e c t some d e f i c i e n c i e s and improve i t s e f f e c t i v e n e s s . Four a d d i t i o n a l beacon l i g h t s were i n s t a l l e d . These were l o c a t e d i n t h e coolant c e l l , blower house, d i e s e l house, and.motor-generator room. The power c i r c u i t s f o r t h e l i g h t s were r e v i s e d t o improve r e l i a b i l i t y . 'The t e s t procedures f o r t h e system were r e v i s e d t o include morithly t e s t s t h a t a c t u a t e t h e e n t i r e systeni, including t h e air horns, and t o a c t u a t e and t e s t tlie system t r o u b l e alarm f e a t u r e s .

D a t a System

- G.

I-I. Burger and 6. D. ?Jarbin

Several new analog i n p u t signals were added t o t h e data system, bringing t h e t o t a l close t o Yhe r m x h m n c a p a c i t y oâ&#x201A;Ź 350. 'Thesewere added t o o b t a i n more information about t h e o p e r a t i o n o f t h e off-gas system, t o measure t h e r e a c t o r c e l l l e a k r a t e , and t o monitor t h e bearing temperatixes of t h e inain blowers and t h e water -temperatwe i n t h e nuclear instrument p e n e t r a t i o n . New p r o g r m were added t o supply more r e a c t o r operating i n f o m a t i o n and t o r e t r i e v e operating information p r e v i o u s l y s t o r e d on t h e magnetic %apes The two operating i n f o r m t i o n programs c a l c u l a t e an average of t h e f u e l - and c o o l a n t - s a l t o u t l e t temperatures and t h e r e ac-bor e e l 1 l e a k r a t e . The average o u t l e t temperature calcula,tions (OAYOT, OACOT) a r e used e x t e n s i v e l y by t h e o p e r a t o r s as a guide f o r t h e operation and coritrol of t h e r e a c t o r . The d a t a - r e t r i e v a l programs were w r i t t e n t o r e t r i e v e and process t n e s t o r e d informat;ion on l i n e o r at t h e OmL computer c e n t e r . Both p r o g r a m were used r m y times t o l i s t and p l o t old data and were very u s e f u l in helping t o determine th.e time, cause, and e f f e c t of s e v e r a l r e a c t o r shutdomis. These d a t a also provided i n f o m a t i o n which was used t o redesign t h e off-gas system and r e s u l t e d i n changing some of t h e r e a c t o r operating procedures. T h e r e t r i e v a l program f o r t h e computer c e n t e r w a s m i t t e n s o t h a t a , l I stored informxbion including c a l c u l a t i o n r e s u l t s could be processed and l i s t e d o r p l o t t e d . The use of t n i s program i s becoming a r o u t i n e operation, and d a t a - r e t r i e v a l r e q u e s t s are handled by a j& order card. The o n - l i n e r e t r i e v a l programs a r e more s p e c i a U z e d and hizn&Le only c e r t a i n i n p u t s o r c a l c u l a t i o n r e s i d t s . These programs have t o be put i n t o t h e system as t h e y a r e needed and r e q u i r e some operator t i m ? when t h e y a r e executed. 1"re a n a l y s i s groug i s now being t r a i n e d t o handle r e t r i e v a l w i t h t'nese programs. A new general-puspose on-line program similar t o tize computer c e n t e r program i s planned. I

Zieuision of operating programs continued as new requirements were determined- during r e a c t o r operation. The h e a t -balance program was r e v i s e d and is now used t o deterrrine t h e t r u e l e v e l of r e a c t o r power. The r e a c t i v i t y - b a l a n c e program was r e v i s e d b u t is s t i l l nol; e n t i r e l y c o r r e c t due t o uncertai.nties i n some of -the paranzeters used i n t h e calculations.

60 I n addition to t h e routfne and p e r i o d i c c o l l e c k i o n of operating data, t h e data syst-rn was used t o in~-t:cumeci.ta;nd c o i i t r o l f u r t h e r r e a c t o r dynarnics k s t s sirnil-ar t o t h o s e las%reported-.IG ~t w a s a l s o used -to control. %he ?xniperat;ie of a maS,ei:ri.al. s u r v e i l l a n c e test; s.tan& by a prograin which simulated Lhree three-mode analog c o n t r o l l e r s . The

control. program computes t h e s u r v e i l l a n c e specirneli temp-i-ature control. se-t poini; from t h e r e a c t o r power, f u e l oiitl-et ixnigerature, and a:o orfs e t temperature t o match t h e temperstu.rc? proPLl-e of the rmtierial s p e c i mens i n t h e r e a c t o r c o r e , P;o. e r r o r s i g n a l i s generated by using t,hi.s szl; p o i n t a n d . t h e temperature of the t e s t - c t a r d specimens. An output signal. is then generated. by the computer t o coni;rol t h e test-stand.

specimen temperatures by changing -the vel-ttnge t o %he h e a t e r s by means of compressed,-aj.r-actilatea a u t o t r a n s f ormers

5" B

D u r i n g the p e r i o d covered by this report, t h e data system has become a v i r t u a l l y i.nd.ispensable ' t o o l for t h e operators and analys-ks 'The acceptance and- confidence i n this equiprIient wiiich i s now shared by t h e o p e r a t o r s and a n a l y s t s are the resu3-t of t h e systemts a b i l i t y t o supply r e l i a b l e and accurate i n f o r m t i o n 1x1 assis$ t h e o p e r a t o r s i n

"0N"TIMT

MSRE COMPUTER TlMF

100 -

908580-

757065-

60-

E . 55W

2 b

50-

45-

40 -

35-

30-

25 -

2015105-

JAN

AVAILABLE

985

-9-

--_---__-___ <-37 31 %

INTEGRATED 'ON'

1.3

NCF :I

14 2

TIME

15 2.

FEB

~~~

3+vd 6t 3740

FOR MAINTENANCE OF PERIPHERAI. EQUIPMENT

.___

95-

carlL

0 SCHEDULED SHUTDOWNS

SCHEDULED SHUTDOWNS FOR MAIPITENANCE AND MODIFICATIONS

JUNE

JVLY

1966

WEEK BEClNNlNG

FLg. 1.16. MSRE Data System Service Record from Date o f Acceptaice, Oc'wber 1, 1965, t o September 1, 1966.

61 c o n t r o l l i n g t h e r e a c t o r and t o assist t h e a n a l y s t s i n e v a l u a t i n g t h e o p e r a t i o n . During t h i s p e r i o d t h e system continued t o show a s t e a d y improvement i n o v e r a l l r e l i a b i l i t y . F i g u r e 1.16 shows t h e a v a i l a b i l i t y of t h e system on a weekly basis. Some of t h e downtimes i n Yarch and A p r i l w e r e caused by a c power d i f f i c u l t i e s as a r e s u l t of i n s t a l l i n g and g e t t i n g t h e s t a t i c i n v e r t e r power supply o p e r a t i n g . Since A p r i l , a f t e r t h e i n v e r t e r shakedown w a s completed, t h e system has had only one unscheduled downtime. For t h e 11 months t h e system has been i n operation, the a v a i l a b i l i t y i s i n excess of 97$, and f o r t h e p a s t 6 months i s about 98%. The system downtimes t o data t o t a l 19 f o r 220 h r 40 min. The data system has m e t a l l t h e o b j e c t i v e s f o r which it w a s o r i g Most i n a l l y intended, and t'ne o p e r a t i o n is approaching r o u t i n e status of t h e programming i s complete w i t h tile exception of d - a t a - r e t r i e v a l programs and t h e r e a c t i v i t y - b a l a n c e program. It is expected t h a t f u t u r e programming and o t h e r system changes w i l l be minimum and w i l l only r e sult from requirements g e n e r a t e d by continued o p e r a t i o n of t h e r e a c t o r . Control-System Design -A. 3. Anderson, D. G. Davis, and P. G. Berndon Control Instrumentation Additions and Modifications F u r t h e r addit i o n s t o <and m o d i f i c a t i o n s of 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 s systems were made t o provide a d d i t i o n a l p r o t e c t i o n , improve performance, o r prov i d e more information for t h e o p e r a t o r s . One hundred twenty-five r e q u e s t s for changes i n t h e i n s t r u n e n t a t i o n and coritrols system (os i n systems a f f e c t i n g i n s t r u m e n t a t i o n and c o n t r o l s ) were r e c e i v e d and r e viewed during t h e p a s t r e p o r t p e r i o d . Of t h e s e , 52 r e q u e s t s r e s u l t e d i n c h a q e s i n i n s t r u m e n t a t i o n and/or c o n t r o l s , 1 9 were canceled, 8 did not r e q u i r e changes i n i n s t r u m e n t a t i o n o r c o n t r o l s , and 25 are a c t i v e r e q u e s t s f o r which design r e v i s i o n s a r e e i t h e r i n progress o r pending. Prior t o t h e i n i t i a t i o n of d e s i g n changes, t h e r e q u e s t s were reviewed by persons r e s p o n s i b l e f o r o p e r a t i n g tine r e a c t o r and for t,he o r i g i n a l . design. Chapges i n t h e r e a c t o r system were not; made u n t i l . t h e necess a r y approvals had been obtained. Some examples of these changes f o l low. F u e l and Coolant Pumps. The six r e l a y s t h a t monitor t h e fuel-pump motor cu..rent were r e p l a c e d t o prevent unnecessary s h u t d m n s . Relay c h a t t e r was causing s p u r i o u s operatioris of t h e r e a c t o r f l u x scram s e t p o i n t c i r c u i t s . Modifications t o t h e e x i s t i n g r e l a y s and t h e i r c u r r e n t s e t t i n g s d-id n o t c o r r e c t t h i s c o n d i t i o n ; t h e r e f o r e , new r e l a y s were i n s t a l l e d . Some s p u r i o u s operaLl.ons occurred d u i n g t h u n d e r s t o r m . It i s b e l i e v e d t h a t lightning-induced t r a n s i e n t s on tne power d i s t r i b u t i o n system caused t h e very f a s t - a c t i n g c u r r e n t r e l a y s t o drop o u t mid scr;wn t h e r e a c t o r . To prevent t h i s , t h e e x i s t i n g r e l a y s i n t h e r e a c t o r f l u x scram s e t - p o i n t c i r c u i t s were r e p h e e d w i t h . time-delay r e l a y s A f t e r t h e f a i l u r e of a lube o i l flow switch i n t e r l o c k had s h u t down the c o o l a n t - s a l t c i r c u l a t i n g pimp during a l o a d scram, it was proposed t'nat a l l p r o t e c t i o n i n t e r l o c k s be removed from b o t h t h e c o o l a n t - and f u e l - s a l t c i r c u l a t i n g pump c o n t r o l c i r c u i t s . This would prevent unnecessary pump si;oppages and provide a d d i t i o n a l p r o t e c t i o n a g a i n s t f r e e z ing of s a l t i n t h e r a d i a t o r . A f t e r c a r e f u l c o n s i d e r a t i o n it w a s decided

62 t h a t t h e s e intxel-locks should iwfl.3,:i.n S.n t h e c i r c u i t s , because t h e protec .-Lion t h e y provide f o r t h e pumps outxeighs t h e i r disa.d-vani;ages. Hmevei-; new operating c r i t e r i a stipii.I.ate tha-l; preve-nt3.m of p o s s l b l e f r e e z i n g of s a l t i n t h e radiator i s more i.inpo-rtan"i. t h a i l p r o t e c t i n g -Lhe p i n p from possi.bl..e dama,ge x=esu.l'ciiig from l o s s o f lii'oe o i l o r coo1.ing-water f l o v . To s a L i s f y t h e s e new reqiiremeiits, we p r e s e n t l y plan -to i n s t a l l . a, ;nanual switch which ( a f t e r proper a d i n i n i s t r a t i v e approval) rmy be o p e r a t e d to override t h e pump protee-Live i n t e r l o c k s . Since pump shui;dwn may r e s u l t from o t h e r ca,i.ises, such as a c t i o n of overcurrent 4;ri.p i n t h e circui.t, breakers: l o s s of TVA power, e t c . , ad.d.;i-t;iomal. changes i r i the povcr distrib.uhioii and switchgear s y s t e m w i l l be r e q u ~ i r e di f maxij.riurn obtainable pimpiiig r e l i a b i l i - t y i s r e q u i r e d . b'hnual swi-Lch c i r c i , r i t s t h a t wi.1.1. overr i d e a1-7 p r o t c c t i v e i n t e r l o c k s i n t h i s pl.xf*j c o n t r o l c i r c u i t , are now bef.rg designed . A weld-sealed e l e c - t r i c p r c s s u r e t r s n s m i t t e r was i n.sta1.led on the fuel-pump helium su$ply l i n e 51.6 a t a p o i n t h y d r a i i l i c a l l y n e a r t h e f u e l pump. This iueas?.rement wi1.1~be cornpared. to t h e pwnip-bowl. cover-gas p r e s s u r e t o detei-riline the pressure dxop a c r o s s t h e l u b e - o i l s t a t i c s e a l bethreen Liie fuel.-pump s h i e l d and the impeller s h a f t housing. 'i'nis j.nf o r m i t i o n should h e l p t o d-etemine i f t h e r e are p e r i o d s o f c o n d i t i o n s tha-1; shoi1l.d f a v o r leakage of sn abnormal am.ou~nto f o i l i n t o t h e pump bow 1-

Master ConLrol C i r c u i t s . A new juniper a n d associa-Led c i r c u i t r y were i n s t a l l e d t o provide a bypms around t h e f r e e z e valve 111 f r o z e n permissive c o n t a c t i n t h e d r a i n - t a n k he!..ium supply valve c o n t r o l c i r c u i t . The jumper w j - k l make it; more convenient; t o operate -through t h e s a l t - t r a n s f e r f r e e z e vaLves. It w a s p r e v i o u s l y necessary t o f r e e z e a.nd. thaw f r e e z e valve 111 t h r e e times when blowing out tihe t r a n s f e r I.i:nes af.ter a f u e l - s a l t t r a n s f e r .

To prevent r a d i o a c t i v e gas backup int,o t h e drain-tank helium suppl.y l i n e s , a continuous heltum purging system, cornpatibbe w i t h s a f e t y r e qulrements, w a s desigiied and i n s t a l l e d . Each supply l.i.ne i s purged Lhrougb a c a p i l l a r y flow r e s t r i c t o r which is s i z e d t o 1j-mj.t t h e purge flow r a t e t o 0.07 l i t e r / m i n . The c a p i l l a r i e s are s u p p l i e d from l i n e 51-9a t a p o i n t daw-ris-Lream of t h e containment block v a l v e s .

It w a s proposed. t h a t spurious o p e r a t i o n s of in-i;erloc,ks i n the RUN mode, OPEXITI3 mode, matn blower No. I, and main blower No. 3 c o n t r o l c i r c u i - t s t h a t were causing unnecessary shutdowns be prevented by rep l a c i n g t h e e x i s t i n g r e l a y s i n t h e s e c i r c u i t s w i t h time-delay r e l a y s . This proposal was canceled a f t e r i n v e s t i g a t i o n s i n d i c a t e d that the real. cause of t h e t r o u b l e w a s e r r a t i c o_neration of the new 60-kva system power supply. The performance of t h e power supply has been improved considerably, and t h e s e c i . r c u i t s a r e now operating normL1.y. Load Control.. 'To s a t i s f y e s t a b l i s h e d operating c r i t e r i a , add3 t i o n a l c o n t r o l - g a d e c i r c u i t s were designed t o provide automatic load setback a c t i o n when Vine r e a c t o r i s i n t h e manual l o a d c o n t r o l mode. 11%~: i n s t a l l a t i o n o f these c j r c u i t s i s ' u e i r i g delayed pending a complete review of t h c automatic load c o n t r o l system.

63 Additional. safety-grade c i r c u i t s were i n s t a l l e d t o provid-e automatic l o a d scram whenever t h e r e a c t o r c o n t r o l rods are scrammed. The purpose of t h i s r e v i s i o n is t o help prevent salt from f r e e z i n g i n t h e radiat or The design of a system t o measure t h e v i b r a t i o n of t h e r a d i a t o r c o o l i n g - a i r blowers and motors is now i n progress. Surplus v i b r a t i o n instnunents s u i t a b l e f o r t h i s a p p l i c a t i o n are on hand.

Thermocouples. Tlie thermocouple system did not change appreciably, although a few thermocouples were added. ' i i e l v e with i n - c e l l type remote disconnects were i n s t a l l e d on t h e f u e l system off-gas f i l t e r and p a r t i c l e t r a p . These are r e a d on a multipoint record-er l o c a t e d i n t h e vent house. Thermocouples were a l s o added t o t h e new f i l t e r s i n o f f gas l i n e 524, t o t h e gas holdup volume tax& i n l i n e 522, and t o t h e bearings on t h e main blowers. Weigh System. The problem of l e a k i n g pneumatic s e l e c t o r valves i n t h e drain-tank weigh system readout w a s s t u d i e d . Manometer readout i s accomplished by s e l e c t i n g p a r b i c d a r weigh c e l l channels w i t h t h e s e Lector valves. The valves a r e composed of a stacked array of i n d i v i d u a l valves operated by cams on t h e operating handle shaft. Leaks from t h e s e switches cause a s l i g h t e r r o r i n t h e manometer reading. E f f o r t s t o s t o p t h e l e a k s permanently have not been s u c c e s s f u l . Leak tes%s on a quick disconnect device i n d i c a t e t h a t it w o u l d be a s8tisz"ac-l;ory replacement for each valve i n t h e switch assembly. Tne valves were not replaced b e c a u w t h e problem i s n o t Severe enough a t t h i s time t o J u s t i f y t h e expense. A u x i l i a r y Systems A pressure-reducing valve, a f l a m e t i e r , and a containment block valve were i n s t a l l e d i n t h e r e a c t o r c e l l thermocouple n i t r o g e n - p r e s s w i z i n g supply header. The n o r m 1 operating pressure was reducea from 50 t o 5 p s i g because of t h e excessive leak r a t e i n t o t h e reactor c e l l . a

The component -Coolant-pwlp c o n t r o l c i r c u i t s were cross-ic%erlocked t o prevent both p m p s from being energized a t t h e same tfme. T h i s w a s accomplished previously with c o n t a c t s mounted d i r e c t l y on t h e c i r c u i t breaker s t a r t e r , b u t this arrangement would not allow one pump t o ope r a t e normally when t h e breaker â&#x201A;Źor t h e o t h e r pump i s racked out f o r maintenance.

A new design of instrwnents and c o n t r o l s i s under way f o r a 350g a l - c a p a c i t y degassing and surge t a n k which was added t o t h e t r e a t e d w a t e r system t o remove gases generated i n t h e r e a c t o r thermal s h i e l d . A tank l e v e l measurement aod p o s s i b l y some flow c o n t r o l a r e required. An a i r purge system, which includes a pressure r e g u l a t o r , f L o v i n d i c a t o r y arid two solenoid-operated containment block valves, .is also r e q u i r e d. Other minor r e v i s i o n s and a d d i t i o n s were as f o l l m s :

1. m e beryllium monitor w a s r e l o c a t e d from t h e vent home t o t h e highbay a r e a .

The range of helium flow neasuring loop FE-524-B w a s increased.

The range of t h e 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 w a s i n c r e a s e d from 0-3 p s i s t o (2-10p s i g . ALSO, t h e i n d i c a t o r i n t h i s measuring loop w a s replaced w i t h a s t r i p - c h a r t recorder.

A flowmeter w a s i n s t a l l e d i n t r e a t e d - w a t e r I.ine 877.

A new instrumen'c power d i s t r i b u t i o n panel was i n s t a l l - e d t o provide a d d i t i o n a l c j . r c u i t s r e q u i r e d by o t h e r modifications and f o r f u t u r e expansion.

Manual switches were add.& i n t h e main r a d i a t o r blower d m p e r control c i r c u i l ; s o that tSle dampers can be c l o s e d when t h e blowers a r e not running.

R a d i a t o r ducL blower a i r flow switches were added to t h e armmciaLoor circuits.

A time delay w a s provided annunciator

j.0

t h e high-bay a r e a containment p r e s s u r e

References

MSR Program Semiann. Progr. Kept. Feb. 28, 1966, ORNL-3936, pp. 1-0-12, Ibid

-a .

pp. 69-71.

MSK Program Semiam. Pro@. Rept. Aug. 31, 1952, OKlTT~3872, pp. 22-23.

MSR Program Semiarm. Progr. Kept. Feb. 28, 1966, ORT\TL-3936, pp. 87-92,

M=;H Program Semiam. Progr. Bept. Auge;. 31, 1965, ORNTJ-3872, pp. 55-56.

R . 3. Kedl, personal comuricatiion, June 1966.

C . H. Gabbard, Thermal-Stress and S t r a i n - F a t i g u e Analyses o f --tne

8. 9.

N5RE Fuel and Coolant h i p Tanks, ORNL-TM-78 (October 1962). MSB Program Semianil. P m g r . Rept. Feb. 28, 1366, ORNL-3936, pp. 12-23. 13-23.

S. J. B a l l and 'Y. W. K e r l i n , S t a b i l i b y Analysis ot LIE Molten-Salt Reactor Fxperiment, O~WTPTM-1070 (December 19651

of t h e 10. T. W . K e r l i n and S. J. B a l l , Experimental. Dynamic & l y s i s Molten-Salt Reactor Experiment, ORNL-TM-1647 ( t o be published]

__I

11. H. W . Xoffman and S. EI.Cohen, Fused S a l t Heat 'i'raasfcr - P a r t U T ; Forced Convection Heat T r a n s f e r i n C i r c u l a r Tubes Containing t h e S a l t Mixture NaN02 -NaN03-KN03, 0FiNTI-2433 (March 19601

12. R . E . MacFherson and M. M. Yarosh, Development T e s t i n g P e r f o - m a c e Evaluation of Liquid Metal and Molten S a l t Heat Exchangers, OKNLCF-60-3-164 (Mar. 17, 1960); a l s o ANS Meeting i n 1959 (Washington, 13.

D.C.). MSR Program Semiami. Progr. Rept. Feb. 28, 1966, OKNL-3936, pp. 29-34.

14.

l b i d . , pp. 78-79.

15.

MSK Program Semiann. Progr. Hept. Ai%.

16.

MSR Program Semiann. Progr. Rept. Feb. 28, 1966, ORNL-3936, p . 4 9 *

31, 1965, ORlVL-3872, p. 72.

Dunlap S c o t t The development group coniinued t o assist i n t h e o p e r a t i o n and t e s t i n g of t h e r e a c t o r . Much of t h e i r e f f o r t c o n s i s t e d of h e l p i n g i n diagnosing problems and i n d e v i s i n g and i n s t a l l i n g equipncnt used t o s o l v e ;he problems. The o p e r a t i o n a l performance of t h e equipment i s covered i n Chap. 1, b u t t h e d e s c r i p t i o n of problems and t h e i r s o l u t i o n s i s given be low

2.1

Freeze Valves M. Richardson

Operation of the f r e e z e valve s i n c e t h e a d d i t i o n of t h e modulating airr c o n t r o l l e r s has been without i n c i d e n t . Operation of FV-103 wa.s i m proved by d e l e t i n g t h e h y s t e r e s i s f e a t u r e of t h e FV-103-LI1. module, which caused t h e r m a l c y c l i n g of t h e valve b e f o r e t h e valve temperature reached equilibrium. The modu.le FV-103-IA now o p e r a t e s as an off-on switch which alarms a t 1OOOOF. 2.2

C o n t r o l Rods

M. Richardson The t h r e e c o n t r o l rods have operated without d i f f i c u l t y . F i d u c i a l zero p o s i t i o n s a r e l i s t e d below. Cinanges a r e caused by changes i n rod. length. Date -

Rod 1

Rod 2

Rod 3

1.74

1.55

1.40

2/12/66

1.73

1.41

1.49

4/24/66 7/14/66

1.78

1.57

1.52

(startup)

Rod-drop times for 51-in. f a l l f o r rods 1 and 2 remain a t < 0.8 s e e . Drop time f o r replacement rod 3 remains between 0.9 and 0.95 sec sfnce installation.

2.3

Control-Hod Drive Units

M. Richardson

5. R . Tallackson

The control-rod d r i v e u n i t s were operated Prom i n s t a l l a t i o n i n February u n t i l shutdown i n August with t h e f o U o w i n g d i f f i c u l t i e s . 1. The c o a r s e - p o s i t i o n synchro torque trmsmitter of t h e No. 3 d r i v e f a i l e d . The t r a n s m i t t e r w a s deenergized, a n d t h e d r i v e u n i t cont i n u e d operation u s i n g t h e f i n e - p o s i t i o n synchro t r a n s m i t t e r and t h e potentiometer t o i n d i c a t e p o s i t i o n .

2 . The " F i l l Permit" p o s i t i o n potentiometer 07 t h e No. 1 d r i v e began t o trarisrnit e r r a t i c readings. 'The potentiometer was jumpered out of' t h e c i r c u i t , and t h e d r i v e continiied t o o p e r a t e s a t i s f a c t o r i l y .

3. The high-tempera-Lure (200째F) switches which are mounted 6 i n . from t h e bottom of t h e d r i v e - u n i t housings went i n t o a l a r m on No. 1 d r i v e and remained i n a l a r m under normal o p e r a t i n g conditj.ons. The switches c l e a r e d when t h e r e a c t o r was drained a n d t h e c e l l teiiiperature w a s lovered. The potentiometer and SyiTchro were r e p l a c e d during t h e curren-L shutdowli. Examination showed t h a t t h e potentiometer had developed. a r e g i o n of open wiper c o n t a c t . 'The synchro, mildly r a d i o a c t i v e , has n o t y e t been disassembl.ed t o determine t h e exact cause of fal.I.in-e. Resistance rneasurements i n d i c a t e a c o i l - t o - c o i l s h o r t c i r c u i t in t h e s t a t o r windings, and t h e p a r t i a l l y melted p l a s t i c end cap i s p o s i t i v e evidence of excessive temperature. The t h e r m o s t a t i c temperature switches' i n t h e lower end of t h e d r i v e housiilg a r e inteuded -Lo t n d i c a t e t h e approach of high-temperature cond i t i o n s which would damage t h e motor and gear box assembly a t t h e upper end of t h e housing. The switches a r e i n a c c e s s i b l e , arid i t w a s n o t p o s s i b l e t o determine a b s o l u t e l y i.f t h e high-temperature i n d i c a t i o n from Lhe No. 1 d r i v e was c o r r e c t or i f one o r b o t h of t h e switches had misoperated. Since n e i t h e r of t h e o t h e r d r i v e u n i t s showed a s i m i l a r i n d i c a t i o n , t h e r e was room f o r doubt. Measu.rernents were taken of t h e winding resistarices of t h e d r i v e motor, -the f a n motor, and t h e tachometer g e n e r a t s r and compared t o those of sj-milar uni-tsa t room temperature and i n t h e o t h e r two r o d d r i v e u n i t s . These i n d i c a t e d t h a t temperatures of t h e s e n s i t i v e p a r t s of t h e questionable wit weye normal. Operation w a s continued with t h e switches bypassed b u t w i t h p e r i o d i c checks of -these winding r e s i s t a n c e s . I n s p e c t i o n o f the No. 1 and N o . 3 rod d r i v e u n i t s i n Augxst r e v e a l e d t h a t t h e switches on t h e No. l u n i t were o p e r a t i n g c o r r e c t l y , and t h e y showed evidence ( d i s c o l o r a t i o n ) t h a t they had been exposed t o high t e m p e r a t u r e . Motors, gear boxes, and o t h e r p a r t s of t h e d r i v e u n i t s showed no evidence of overheating or mechanica.1 d i f f i c u l t y . The gear c a s e s were opened and were i n e x c e l l e n t condi-tion. The APL grease was s o f t and adhering t o t h e worm and wolLirlg e a r . The l u b r i c a n t bad darkened s l i g h t l y , but t h e r e was no evidence of t a r r i n g or lumping of t h e grease. The wire i n s u l a t i o n w a s i n good c o n d i t i o n .

67 It i s reasonable -Lo conclude . t h a t t h e a i r stream introduced a t t h e upper end of t h e No. 1. rod d r i v e housing, while s - u f f i c i e n t t o keep t h e gear-box components cooled., w a s not l a r g e enough t o prevent t h e development of t h e high tempersLure a t t h e lower end of t h e housing caused by a p a r t of t h e heated gas stream r i s i n g from t h e thinlule. The temperature switches on rod d r i v e s 2 and 3 went i n t o alarm during p e r i o d s when t h e r e a c t o r c e l l w a s operated above l.50째F. T h i s ind-icates t h a t t h e a i r flow t o all t h r e e rod d r i v e s i s marginal. The good c o n d i t i o n of t h e gears, motors, arid l.ubricant makes illmediate a c t i o n unnecessa-0, b u t a study wi1.1. be made of methods of i n c r e a s i n g t h e a i r flow t o t h e d r i v e housings.

2.4

Ra,diator Doors -

M. Richardson

sin pei-mit t e d Modi .fi.c a t ion s t o the r a d i a t o r do o r operating mec ha.n.?:. SatisfaCtOYy o p e r a t i o n a l perf ormancx of t h e doors through t h e l a s t run. However, excessive leakage of a i r i n t o t h 2 r a d i a t o r enclosure du.e t o poor s e a l s became e v i d e n t a f t e r t h e doors had been thermally cycled s e v e r a l ti_mnes during o p e r a t i o n . Ex'wiination of t h e doors a f t e r slriutdown m v e a l c d t h a t the metal s e a l s u r f a c e s had been s e v e r e l y damaged. The metal s e a l s , i n t u r n , damaged t h e mating s o f t s e a l mounted- i n the f a c e of t h e r a d i a t o r . The m e t a l s t r i p s had buckled between weld p o i n t s , broken a t some poinLs, and been t o r n aTJa,y corple-Lely a t t h e "cop of t h e o u t l e t door. Some 0.t t h i s darnage i s 8ho:m. i n F i g s . 2 . 1 and. 2.2. The door s-tructme and i n s u l a t i o n boxes 1Jei-e i n good c o n d i t i o n exc e p t f o r bowing of t h e 4-in. H-beam s - t r u c t u r a l . members. The amximum bow, vhich w a s a-t t h e t o p of t h e o u t l e t door, was 5/16 i n .

l a b o r a t o r y t e s t s were conducted on s e v e r a l arrangements of t h e metal s u r f a c e s . A method of thermal c y c l i n g t h e test s e c t i o n s was devised s e a l s t r i p s on t h e doors which wou1.d d u p l i c a t e tine d i s t o r t i o n found i n a f t e r t h e previous o p e r a t i o n . Figure 2.3 shows t h r e e of t h e s t r i p a r rangements that, were t e s t e d ; t h e s t r i p support inerrher ( o r T-bar) w a s t h e scam i n each c a s e . I n t h e c a s e of s e c t i o n s 1 and 2 of Fig. 2.3, t h e s e s t r i p s were welded t o the T-bar at i n t e r v a l s of 2 t o 4 i n . Because of t h e h e a t l o s s through t h e door, t h e s e s t r i p s were operated ahou-t 500'F ahove t h e temperature of t h e su.pport b a r , r e s u l t i n g i n s e v e ~ ed i s t o r t i o n of s t r i p s between t h e welds. I n some p l a c e s t h e welds had broken, perm i t t i n g t h e seal. s t r i p s t o protrude away f r o m t h e plane of t h e s e a l surf a c e . A s i m i l a r t e s t w a s run on a t h i r d arraagement OS t h i s s e a l which c o n s i s t e d of 2 - i n . segments of t h e s e a l h e l d i n p l a c e ai; one end by a plug weld and a t t h e o t h e r end by an overlapping t a b t h a t interlocked. w:ith t h e a d j a c e n t segment. This arrangement i s shown as s e c t i o n 3 i n It w a s found t h a t thermal c y c l i n g d i d not a f f e c t t h e alignment Fig. 2.3. of t h e s e segmen-ts. The segments were spaced 0.031 i n . along t h e T-bar.

68 PHOTO 854!6 -SEAL

STRIP SUPPORT MEMBER, S E A L S T R I P T O R N AWAY

INSULATION BOXES

BUCKLED METAL SEAL STRIP

-SEAL

S E A L S T R I P I-.

STRIP SUPPORT

(T-BAR)

Fig. 2.1. Radiator O u t l e t Door Showing Buckled, Broken, and T o r n S e a l S t r i p (a ) and Top Seal, North Side (b). PHOTO 854t7

RADIATOR FACE

Fig. 2.2. S o f t S e a l and R e t a i n e r Outlet Side o f Radiator, Showing Buckled and Broken S o f t S e a l Retaining S t r i p .

PLUG

PHOTO 7 3 6 t 2

WELDS

SECTION 1

-BROKEN

PLUG

WELD

LUG

WELDS

, SECTION 3

Fig. 2.3.

Seal Strip Tests

- Radiator Door.

It w a s e v i d e n t throughout a l l t h e t e s t program t h a t t h e s e a l - s t r i p support member bowed about 3/16 i n . along t h e 32-in. l e n g t h of t e s t s e c t i o n . It seemed reasonable t o assume t h a t bowing of t h i s member would a l s o occur along t h e s o l i d 1 0 - f t 4-1/2-in. l e n g t h of t h e T-bar i n t h e r a d i a t o r door and c o n t r i b u t e t o t h e s t r e s s i n g of t h e door s t r u c t u r e . The door r e p a i r work included c u t t i n g t h e T-bar i n t o segments; when t h i s w a s done, t h e bowing of t h e door s t r u c t u r e was reduced from 5/16 i n . t o l/8 i n . C o r r e c t i v e measures t o t h e s e a l s and T-bar are p r e s e n t l y i n progress. These include:

1. Modification of t h e T-bar t o minimize bowing by i n s t a l l a t i o n of expansion j o i n t s i n t h e b a r .

I n s t a l l a t i o n of a new hard s e a l which i s composed of 3-1/4-in.-long overlapping l i n k s . The s h o r t l i n k s w i l l be plug welded t o t h e T-bar by a s i n g l e weld p e r l i n k with a 1/32-in. expansion j o i n t between overlapping segments.

The e x i s t i n g s o f t - s e a l r e t a i n e r , which i s mounted on t h e f a c e of t h e r a d i a t o r , i s b e i n g modified t o permit thermal expansion of t h e m e t a l retainer.

It i s not a n t i c i p a t e d t h a t bowing of t h e T-bar w i l l be completely e l i m i n a t e d . Thermal expansion of t h e r a d i a t o r f a c e may a l s o cont r i b u t e t o t h e a i r leakage. An a d d i t i o n a l s e a l i n t h e form of a r e s i l i e n t , s o f t s e a l i s being proposed as backup t o t h e e x i s t i n g s e a l s . This s e a l would form a c l o s u r e a t t h o s e p o i n t s along t h e hard seal which a r e n o t i n c o n t a c t with t h e e x i s t i n g s o f t s e a l .

2.5

Satmler-Enricher R. B. Gallaher

During runs 6 and 7, 35 samples were i s o l a t e d w i t h t h e sampler-enr i c h e r , 10 of which were 50-g oxide samples. To d a t e 119 10-g and 20 50-g samples have been taken, and 87 enrichments made t o t h e f u e l system. I n the past equipment. They placement of t h e and ( 4 ) recovery e r a t i o n a l valve.

s i x months, f o u r major maintenance jobs were done on t h e were (1)replacement of t h e manipulator b o o t s , ( 2 ) r e d r i v e u n i t l a t c h , ( 3 ) r e p a i r of open e l e c t r i c a l c i r c u i t s , of a capsule which had f a l l e n onto t h e g a t e of t h e opA b r i e f d i s c u s s i o n of each job follows.

Redacement of M a n i m l a t o r Boots A 12-psi p r e s s u r e d i f f e r e n c e which w a s a c c i d e n t a l l y placed a c r o s s t h e manipulator b o o t s caused a s m a l l puncture i n t h e i n n e r boot. To r e place t h e b o o t s t h e manipulator assembly w a s removed from t h e sampler. The r a d i a t i o n l e v e l 3 i n . from t h e hand w a s 10 r/hr a s removed, b u t t h i s

w a s reduced t o 1 r/lnr by seriibbin-g with soap and w a t e r . Aboui; 2 hr w a s r e q u i r e d for t h e job of r e p l a c i n g both boo-ts. The boots had been used during t h e 48 sampling c y c l e s s i n c e t h e o p e r a t i o n a t power w a s s t a r t e d . Replacement of t h e Capsule Latch

Just a f t e r t h e boots were replaced, t h e d r i v e - u n i t motor s t a l l e d as t h e l a t c h which holds t h e sample capsule t o t h e cable w a s being r e t r i e v e d through t h e lower bend i n t h e t r a n s f e r tube. A f t e r s e v e r a l t r i e s t h e l a t c h w a s completely withdrawn. T e s t i n g showed t h e l a t c h w a s jamming i n t h e t r a n s f e r tube near t h e t o p of t h e lover bend. The design was changed t o provide ad-ditional 1/8 i n . clearance between t h e tube w a l l and. t h e l a t c h . The o l d l a t c h and p a r t OT t h e cable were p u l l e d through t h e access p o r t and t h e removal valve with t h e r e a c t o r o p e r a t i n g a t less t h a n 100 kw. The o l d l a t c h w a s p u l l e d i n t o t h e sample t r a n s p o r t cask bo reduce t h e r a d i a t i o n level. i.n t h e vork a r e a . It was disconnected from the d r i v e unj-t c a b l e and t h e new 1at;ch vas i n s t a l l e d . Repais of an Open E l e c t r i c a l C i r c u i t Tdhile o p e r a t i n g -the d r i v e u n i t t o b e eel-tain t h a t t h e new l a t c h would pass around t h e lower bend without jamming, t h e cable posiâ&#x20AC;&#x2122;iion i n d i c a t o r stopped at 15 f t 2 i n . from f u l l withdrawn p o s i t i o n , and the upper l i m i t switch a c t i v a t e d . E l e c t r i c a l - c o n t i n u i t y checks showed open c i r c u i t s t o both i n s e r t and withdraw windings of t h e d r i v e - u n i t motor and t o t h e upper l i m i t switch. A l l t h r e e of t h e s e leâ&#x20AC;&#x2122;ads p e n e t r a t e d t h e containment w a l l through a common 8-pin r e c e p t a c l e .

When t h e d r i v e motor stopped, t h e c a b l e extended almost t o t h e pump bowl, preventing c l o s i n g of t h e o p e r a t i o n a l and maintenance valves. Therefore, t h e r e a c t o r had t o be drained b e f o r e maintenance work could be s t a , r t e d . A f t e r t h e r e a c t o r w a s drained, t h e 15 f t 2 i n . of c a b l e w a s p u l l e d out of t h e t r a n s f e r tube without exposing t h e f u e l system t o a i r by using t h e one-hand manipulator t o p u l l and t h e t r a n s p o r t c o n t a i n e r and access p o r t o p e r a t o r s to hold t h e c a b l e . Then t h e o p e r a t i o n a l and maintenance valves were c l o s e d t o provide t h e containment b a r r i e r t o allow t h e motor assembly t o be removed f o r r e p a i r .

The assembly, which c o n t a i n s t h e d r i v e - u n i t motor, w a s removed from t h e sampler-enricher and placed i n t h e equipment s t o r a g e c e l l for decontamination and r e p a i r . Shadow s h i e l d i n g and p a r k i a l decontamination were used t o reduce t h e r a d i a t i o n l e v e l enough t o permit d i r e c t maintenance. P a r t i a l disassembly revealed that, t h r e e connector p i n s had burned o f f one %pin receptacle. The damaged r e c e p t a c l e w a s removed and 8 new oiie w a s welded i n i t s place. A l l s i x r e c e p t a c l e s i n t h i s l o c a t i o n were f i l l e d with epoxy r e s i n t o provide a d d i t i o n a l e l e c t r i c a l i n s u l a t i o n and mechanical s t r e n g t h t o t h e connector p i n s .

A s t h e d r i v e - u n i t cable was being p u l l e d from t h e t r a n s f e r tube it was ben-t i n s e v e r a l p l a c e s and needed t o be s t r a i g h t e n e d . The cable w a s

72 scrubbed w i t h soap and water u n t i l t h e r a d i a t i o n l e v e l w a s l.ess t h a n 5 Then most of t h e kinks were s t r a i g h t e n e d . The remaining bends i n t h e c a b l e d.id n o t appear t o adversely a f f e c t t h e o p e r a t i o n s of t h e d:rive u n i t when it was operated p r j o r t o r e i n s t a l l a t i o n . r/hr a t 3 i n .

The p a r t s were reassembled. A l l e l e c t r i c c i r c u i t s were checked for conLinuity and f o r grounds, and a l l gas l i n e s were l e a k checked. The assembly w a s t h e n r e i n s t a l l e d i n t h e sampler-enricher and. t h e normal smpl-ing w a s resumed. Recovery of a Capsule A s a capsule key was being i n s e r t e d i n t o bile l a t c h , -Lhe manipulator s l i p p e d and t h e capsule w a s jerked through t h e access p o r t and fel.1. onLo t h e g a t e of t h e o p e r a t i o n a l valve i n t h e t r a n s f e r l i n e . A magnet w a s lowered i n t o t h e t r a n s f e r l i n e ; t h e m i l d s t e e l key3 011 t h e capsule w a s picked up by t h e magnet, a:nd t h e capsule assembly w a s removed. as t h e magnet w a s withdrawn. The r a d i a t i o n l e v e l of t h e magnet a f t e r t h i s ope r a t i o n was 10 r/hr a t 2 f t .

These four maintenance jobs involved handling equipment t h a t had been i n c o n t a c t with fuel salt,. A11 work w a s done i n coiltamination control. zones. Contamination was found o u t s i d e t h e s e zones only twice, and bo-Lh times it was f r o m conâ&#x20AC;&#x2122;hninated shoes. Apparently t h i s type contamina.tion i s n o t r e a d i l y a i r b o r n e . Personnel exposures did not exceed a dose of 40 m i l l i r a d s / d a y f o r any one i n d i v i d u a l .

Operational

Valve Leakage

While t h e assembly w a s removed f o r replacement o f the e l e c t r l c a l r e c e p t a c l e , t h e upper face of t h e o p e r a t i o n a l valve g a t e w a s cleaned as much as p o s s i b l e with t h e valve closed. Several s m a l l , d.ark p a r t i c l e s were observed on t h e g a t e p r i o r t o cleaning. A f t e r cleaning, t h e l e a k r a t e of helium -ihrough t h e t o p sea.1 decreased f o r a while. A f t e r â&#x20AC;&#x2122;che capsule had been dropped on-Lo t h e gate, t h e l e a k r a t e suddenly i n c r e a s e d again, indicatTng t h a t another p a r t i c l e had lodged i n t h e s e a l i n g a r e a . Contamination of t h e Removal Valve S e a l s The s u r f a c e o f t h e t:ransport, c o n t a i n e r used during t h e withdrawing of t h e cable wiLh t h e manipulator became very contaminated from c o n t a c t wi.th t h e c a b l e . When t h e t r a n s p o r t c o n t a i n e r w a s reiiloved, p a r t oP t h i s contamination w a s t r a n s f e r r e d t o t h e removal a r e a s e a l . During subsequent sampling procedures particul..ate contamination w a s spread t o the t o p of t h e sampler-enricher. Since t h e removal a r e a w a s cleaned using damp r a g s and t h e t o p of the sampler-enricher w a s made a contam.ination c o n t r o l zoiie during s m p l i n g operations, t h e r e have been no f u r t h e r problems w i t h contaminat i on.

Miscellaiieous Problem DurLng one sampling sequence as t h e .COP of t h e transport, c o n t a i n e r was being lowered over t h e botcorn p a r t , which contained a 50-g s a l t saxple, t h e s t e e l wire connecting t h e capsule t o t h e key c a ~ g h ton t h e edge or’ .tile t r a n s p o r t c o n t a i n e r cop and vas p a l l e d d.oiWA irito t h e t l i r e a d a . !hen t h e two pieces :.rere tllreadeii togekher, he wii-e caused tile threads L o g a l l h e r o r e t h e p i e c e s scaled. The sz,.nple and the ti-ansport conttZj.iFti* iqcz-e ruined. Si.nce t h e n a long p l a s t i c s l e e v e has been placed i n the bottom of t h c t r z n s p o r t c o n t a i n e r t o hold t h e srirc out of’ t h e w3y. The s l e e v e also reduces t h e m o u n t of contamination tramFerr’c-.csl f i , o m the sample t o t h e i n s i d e O? t h e top piece of the t r a n s p o r t coricainei-. About 4 hr i s p r e s e n t l y r e q u i r e d ‘io decontaminate a t r a n s p o r t cont a i n e r sufficien;.ly to be r e t u r n e d f o r use. Mild s t e c l bottom pieces have been f a b r i c a t e d vhich v i 1 1 be used Olie time and i;’nr-oT~navzy without deconta:iinating

Changes t o t h e Control C i r c u i t Three changes were made t o t h e c o n t r o l c i r c u i t .

1. The annunciator, which alarmed when capsule a r e a p r e s s u r e was g r e a t e r t h a n manipulator a r e a pressure, w a s removed. A permLssive l i g h t was i n s t a l l e d t o i n d i c a t e when capsule a r e a p r e s s u r e w a s eqiial t o o r less t h a n manipulator area pressure. This c o n d i t i o n i s necessary b e f o r e t h e access p o r t can be opened b u t i s not necessary a t o t h e r times.

2 . A f u s e w a s added t o t h e d r i v e - u n i t motor c i r c u i t t o p r o t e c t t h e motor an.d t h e e l e c t r i c r e c e p t a c l e s from excessive c u r r e n t s . The f u s e i s l o c a t e d on one of t h e panelboards. 3 . Voltage suppressors were placed a c r o s s t h e two motor Twindings t o l i m i t any high v o l t a g e peaks during s t a r t i n g and stopping of the motor.

2.6

Coolant Sampler

R. B. Gallaher During runs 6 and 7 , t e n 10-g s a l t samples were i s o l a t e d from t h e coolant pump bowl. A t o t a l of 45 samples inel-uding two 50-g samples have been taken using t h e coolant s m p l e r . One p i n on an e l e c t r i c a l r e c e p t a c l e s h o r t e d during a sampling cycle. This p i n w a s i n t h e c i r c u i t t o t h e i n d i c a t o r l i g h t which showed vhen t h e capsule had been withdrawn 18 i n . from the pmp bowl. The r e c e p t a c l e w a s removed and a new one welded i n place.

A l e a k r a t e from t h e lower s e a l of t h e removal valve Increased. The valve w a s disassembled, cleaned, and reassembled. The valve t h e n s e a l e d properly.

2.7

Fuel. Processing System Sampler R. B. Gallaher

Design of t h e fuel processing system sampler has been compl.eted exc e p t f o r t h e s h i e l d i n g . The sampler-enricher mockup equipmeni; w~as modif i e d t o conform with t h e design. A l l p a r t s were received, and t h e r e v i s i o n s t o t h e mockup parielboards were completed. The equipmelit i s being ins-Lalled a t Building 7503 whenever c r a f t are avaiIl.ab2.e. The tubing i n s t a l l a t i o n i s 95% complete, and t h e e l e c t r i c a l and instrument work i s about 50% complete. The f i n a l . assembly and l e a k checking reniaio 'GO be done. 2.8

O f f - G a s F i l t e r Asserfrilv

A. N . Smith

The off-gas f i l t e r i n l i n e 522 was o r i g i n a l l y provided t o p r o t e c t t h e very f i n e t r i m of t h e r e a c t o r pressure c o n t r o l valve, X V 522, from becoming fouled by p a r t i c u l a t e m a t t e r . Following t h e a n a l y s i s o f plugging d i f f i c u l t i e s i n February and March 1966, e f f o r t s were d i r e c t e d toward t h e design of a f i l t e r which a l s o would t r a p organic 1mLerials. Primary cons i d e r a t i o n s were (1)choice of f i l t e r medj.wn and ( 2 ) heat d i s s i p a t i o n .

FiI t e r Me d i m The organic m a t e r i a l w a s presumed to e x i s t in a. x-ange of forms extending from ~ o w - m o l e c u l a ~ - ~ vapors ~ei~~~ t ot suspensions of d r o p l e t s and polymerized. s o l i d s . Charcoal w a s s e l e c t e d as t h e b e s t a v a i l a b l e medium f o r t h e remov-a1 of the heavier organics. Preliminary- t e s t s repoi-ted i n Chap. 7 confirmed t h a t the charcoal would have good e f f i c i e n c y for removal. of c6 and.heavi-er molecules. It w a s a,ssutned t h a t .l.fghter molecules would pass through -the main charcoal beds without adverse e f f e c t s I

Heat D i s s i p a t i o n The heal; l o a d a t t h e f i l t e r comes p r i m a r i l y from b e t a decay of krypton, xenon, and t h e i r daughter product,s. The c o n t r i b u t i o n due t o krypton and xenon alone i s es-Lirnated. at 0.I kw/liter. The c o n t r i b u t i o n duz t o t h e daughter products would depend on t h e assumed physical. model. For purposes of t h e f i l t e r design, t h e most p e s s i m i s t i c viewpoint w a s adopted, namely, t h a t a l l daughters formed between t h e pump bowl and t h e f i l t e r rema7.n i n suspeiision and a r e t r a n s p o r t e d t o t h e f i l t e r . Since t h e e f f i c i e n c y of t h e charcoal t r a p would vary i n v e r s e l y with temperature, a p r e f i l t e r o r p a r t i c l e t r a p was added for removal of s o l l d daughters and t h e e n t i r e assembly w a s water cooled.

P a r t i c l e Trap The design of t h e p a r t i c l e t r a p i s i l l u s t r a t e d i n Fig. 2 . 4 * G a s from t h e r e a c t o r m p bow1 e n t e r s a t t h e bottom of t h e u n i t through a c e n t r a l pipe, r e v e r s e s d i r e c t i o n , and passes i n succession through two c o n c e n t r i c c y l i n d e r s of porous m e t a l ( f e l t m e t a l ) , t h e f i r s t somewhat c o a r s e r t h a n t h e second, and a bed of i n o r g a n i c ( F i b e r f r a x ) f i b e r s . A l a y e r of s t a i n l e s s s t e e l wool i s i n s e r t e d a t t h e bottom of t h e u n i t t o s e r v e as an impingement s u r f a c e f o r m a t e r i a l which m i @ t b e thrown out of t h e stream by centrif'ugal a c t i o n . A bellows s e c t i o n i s provided i n t h e f e l t - m e t a l zone f o r thermal expansion. The F i b e r f r a x (a poor cond u c t o r ) i s compartmented between p e r f o r a t e d m e t a l p l a t e s to provide f o r b e t t e r t r a n s m i s s i o n of h e a t t o t h e walls of t h e f i l t e r housing. Three theymocouples a r e a t t a c h e d t o t h e o u t s i d e of t h e f i l t e r housing one near t h e top, one a d j a c e n t t o t h e lower end of t h e F i b e r f r a x s e c t i o n , and one a d j a c e n t t o t h e middle of t h e f e l t - m e t a l s e c t i o n .

S p e c i f i c design daSa a r e a s follows: F e l t -Metal Seet ion Coarse

Fine

Material

Stainless s t e e l

Manufacturer s type (Xuyck Metals Go., Milford, Conn. )

FM 225

FM 204

Element s i z e

2-5/8 i n . dim x 9 i n . long

3-5/8 i n . dim x 9 i n . long

F i l t e r area

0.5 P t 2

0.7 f t 2

Removal r a t i n g

98% > 1.4 IJ98% > 0.1 p 1-1/4i n . I320

Clean p r e s s u r e drop a t 4.2 l i t e r s / m i n f o r coarse and f i n e i n series Fiberfrax Section Material

Carborundum Co. F i b e r f r a x , long s t a p l e fi'oers, 5 p, mean diameter

Packing d e a s i t y

8-1/2 to 9 1 b / f t 3

T o t a l weight Geometry

189 g

Nine annular compartments, 4.05 i n . OD x 0.84 i n . I D , w i t h t h i c k n e s s of two each a t 1/4 i n . , t x o each a t 1/2 i n . , f o u r each a t 1 i n . , and one a t 1-1/4i n .

76 ORNL-DWG

FINE METAILLIC FILTER

-,,

NICKEL SPACER (TYP)

FIBERFRAX

COARSE ME-lALLlC FILTER-,,,

66-11444

( LONG F I B ER )

\-THERMOCOUPLE

"\,

(TYP)

LSIAINLESS

STEEL MEjl-1

NICKEL BAFFLE

STAINLESS STEEL flAFFLE-

F i g . 2.4.

(e)-'

STAIN1 ESS S T E E L BAFFLE

P a r t i c l e Trap of Line 522 F i l t e r Assembly.

D i a c t y l p h t h a l a t e (DOP) e f f i c i e n c y t e s t s 4 were run on tile f e l t metal (coarse and f i n e i n s e r i e s ) and on t h e F i b e r f r a x w i i h t h e following res u l ts :

Material

Ge omet r y

Aero s ol 'Type _I__.

Av P a r t ic l e

.--

Size

($1

96.7

F e l t metal

Coarse and f i n e i n s e r i e s , L+ in. d i m

Polydisperse

0.8

Fiberfrax

4 i n . diam x

Monodisperse

0.3 iJ-

7-1/4i n .

Kf'ficiency

99 ./!

long, bed d e n s i t y 9-l_/2 lb/ft3 The e f f i c i e n c y of the assembled p a r t i c l e t r a p u s i n g the polydisperse a e r o s o l w a s determined t o be 99.9%. Charcoal Tran

The c h a r c o a l t r a p c o n s i s t s of W ft of 1 - i n . IPS staijl-less s t e e l pipe, arranged i n t h r e e h a i r p i n s e c t i o n s of approximately e q u a l l e n g t h . The ti-ap was loaded with 1-092 g of Pi-LLsburgh PCB c h a r c o a l t o g i v e an average bed d e n s i t y of 0 . 5 g/crn3. S i x thermocouples were i n s t a l l - e d a t 5, 1 2 , 51, 59, 105, and 113 i n . , r e s p e c t i v e l y , from t h e bed i n l e t . The

77 e n t i r e c h a r c o a l t r a p i s enclosed i n a s e a l e d t a n k through which water i s c i r c u l a t e d a t a r a t e of 10 gpm and an.in1e-L temperature of 6 5 t o 70째F. The diameter of t h e t r a p p i p i n g was s e l e c t e d on t h e basis of t h e o r e t i c a l temperature p r o f i l e c a l c u l a t i o n s . One-inch I F 5 w a s s e l e c t e d as t h e s i z e which would permit t h e lowest t r a p opera-Ling temperature c o n s i s t e n t with an a c c e p t a b l e p r e s s u r e drop. Flow pressure-drop t e s t s gave t h e following r e s u l t s a t t h e normal r e a c t o r off-gas flow of 4.2 l i t e r s / m i n : psi Felt material

Fibe rf rax

0.04 0.004

Total particle t r a p

0.06

Charcoal t r a p

0.85

T o t a l f i l t e r assembly

0.95

The performance of t h e o f f - g a s system a f t e r t'ne i n s t a l l a t i o n of t h i s

f i l t e r i s described i n Chap. 1.

2.9

S 2 4 Chaxoa.1 Bed A. N. Smith

Diffusion of a c t i v i t y i n t o t h e f u e l pump upper off-gas l i n e ( l i n e 5 2 4 ) r e s u l t e d i n high s t a c k ac-Livity on two occasions during t h e r e p o r t pe:riod and d i c t a t e d t h e need f o r a s m a l l c h a r c o a l bed i n l i n e 524 ( s e e Chap. 1).

A s m a l l upfl.ow of gas (about 100 cm3/min) i s maintained a t t h e f u e l pwnp s h a f t t o i n h i b i t b a c k - d i f f u s i o n of o i l vapors i n t o t1.w pmp bowl. 1in.e 524 s e r v e s t o t r a n s p o r t t h i s flow t o t h e off-gas system.

The bed c o n s i s t s of 9 f t of 3 - i n . sched .lo pipe arranged i n h a i r p i n shape and loaded with 15.8 lb of ;Pit-tsburgh PCB c h a r c o a l . Bulk d e n s i t y of t h e bed i s O.L+7 g/cm3. Holdup time a t 100 cm3/nlin heliixn flow i s e s t i m a t e d as 2-1/2 days f o r krypton o r 30 days f o r xenon. The bed was placed i n s e r v i c e on June 9, 1966.

2.10

Remote Maintenance R . Blumberg

A t t h e s t a r t of t h i s r e p o r t i n g period, r a d i a e i o n 1eve.l.a encountered by rnaintenance crews were mild due t o t h e small accumulated power-hours produced. T h i s low r a d i a t i o n l e v e l p e r m i t t e d t h e use of temporary, and

a t times c a s u a l , s h i e l d i n g , and i n - c e l l manipulatrions were t h u s unhampered by t h e r e s t r i c t i o n s of t h e s h i e l d i n g , s o t h a t t h e L-irne r e q u i r e d f o r comHowever, by t h e middle of p l e t i o n of Lhese e a r l y jobs w a s shortened.. July, when t h e r e a c t o r w a s s h u t down f o r maintenance a f t e r having produced some 7800 Mwhr, ‘the r a d i a t i o n l e v e l w a s an important f a c t o r , adding t o t h e d i f f i c u l t y , time, and expense of t h e work. A s 3 consequence t h e p o r t a b l e maintenance s h i e l d had t o be s e t up f o r each job, and extensive h e a l t h pliy-sics precautions , e s p e c i a l l y i n t h e a r e a of contamination c o n t r o l (housekeeping), had t o be employed. A s o f t h i s w r i t i n g , t h e remote maintenance work of t h e shutdown i s about 60% complete.

Based on t h e experience gained Lo d a t e one may make t h e following We (1)Contamhation control. i.s not a major d i f f i c u l t y observations. have handled s e v e r a l p i e c e s of equipment t h a t had much wipable and transf erab le contamination wi.thou’t. spreading contanin%Lion t hroug’nout the working a r e a . The contam.i-nation does riot become a i r b o r n e r e a d i l y . Nevert h e l e s s , the p r a c t i c e has been t o use conservative handling measures; t h e s e involve t h e use of p l a s t i c bag coverings, b1.otter paper, gas masks, e t c . ( 2 ) An encouraging s i g n i s t h e ease of executing some of t h e routiiile maintenance jobs. There have been many i-nstances where removal and replacement of i . n - c e l l compone:nts have gorie very smoothly and with minimum s u p e r v i s i o n . I n general, t h e s e are i t e m s which have standard e l e c t r i c a l and piping discomec’is and supports, such as t h e space cooler, and which r e p r e s e n t a considerable percentage of t h e equipment Lhat must be main(3) Thus far, almost a l l of t h e mai-ntenmce techniqucs t a i n e d remotely. o r s y s t e m have been t r i e d and have worked w e l l - . These a r e t h e p o r t a b l e maintenance s h i e l d , g r a p h i t e sample sys Lem, vent house s h i e l d i n g , t h e remote maintenance c o n t r o l room, and r e p a i r techniques i n t h e decontamin a t i o n cel.1.. The remote maintenance t a s k s where we do not y e t have experience a r e i n g e n e r a l a s s o c i a t e d with t h e handling of t h e l a r g e corripon r n t s . The sliielding provided f o r maintenance has ’oeen q u i t e adequate.

The following i s a summary of t h e tasks per.€omed dui-ing t h e l a s t period. Yne accumulated hours of power operation, toge”Lirer w i t h an i n d i c a t i o n of the r a d i a ~ t i o nl e v e l i n the immediate a r e a j u s t below Lhe work s h i e l d , a r e given f o r each t a s k . I n general, t h e work shi.eld w a s e f f e c t i v e i n reducing t h e background radialiion level. above it t o l e s s t h a n 5 n r / h except while a t o o l p e n e t r a t i o n was p a r t i a l l y open, and theri t h e T h e maxi-jmm acr a d i a t i o n l e v e l a t t h e hands woxld b e n e a r 200 mi-/&. cumulated dosage t o any one worker w a s less t h a n 1/4 of t h e maximum perm i s s i b l e level. over t h e period.

Removed t h e f l e x t b l e jumper which connects t h e off-gas 31ne of t h e pimp bowl t o t h e permanent i n - c e l l p a r t o-f l i n e 522, inspected t h e f l a n g e f a c e s and i n s i d e of -the piping with a borescope and b i n o c u l a r s , obtained specimen oi” a r e s i d u e from t h e p i p i n g for chemical ana.lysis, and r e s t o r e d t h e system. T h i s t a s k was p a r t of t h e e f f o r t t o di-agnose t h e r e s t r i c t i o n problem i n t h e off-gas system. The r a d i a t i o n l e v e l was 200 mr/hr a t floor level.

79 March 10

35 Mwhr

Removed and r e p l a c e d t h e r e a c t o r c e l l e a s t space c o o l e r . This o p e r a t i o n was accomplished mostly by t h e c r a f t f o r c e s . Readings were 500 mr/hr a t f l o o r l e v e l . March 1 2

35 Mwhr

I n s t a l l e d a therrnocouple on a h o r i z o n t a l s e c t i o n of o f f gas l i n e 522. A C-clamp was modified t o provide t h e c o n t a c t i n g f o r c e t o hold t h e couple onto t h e & i n . p i p e . The thermocouple l e a d s were connected t o a s p a r e -Lhermocouple lead-out box. Radiation was 500 mr/w a t f l o o r l e v e l .

March 31 - 35 k h r

The r e v i s e d E V 522 valve and f l l t e r u n i t described above were i n s t a l l e d i n t h e vent house area. Changes i n t h e s h i e l d i n g

and containment arrangement were done t o make p o s s i b l e t h e r e mote replacement of any one of t h r e e component; p a r t s , t h a t i s , t h e valve, t h e p a r t i c l e t r a p , o r t h e carbon bed, r a t h e r t h a n havjng t o remove t h e e n t i r e assembly. The new i n s t a l l a t i o n req u i r e d l a r g e r maintenance s h i e l d i n g and s t r o n g e r s t r u c t u r a l support f o r t h e s h i e l d i n g .

Repaired t h e sampler-enricher A l a r g e subassembly of -Lhe equipment was removed t o t h e decontamination c e l l , where it was cleaned and r e p a i r e d u s i n g l o c a l s h i e l d i n g . This was t h e f i r s t r e a l use of t h e decontamination c e l l , which had. been prepared f o r t h i s t y p e of work, and it was found t o work q u i t e w e l l . There were c o n t a c t r e a d i n g s of above 100 r/hi-, b u t t h e r a d i a t i o n was s o f t enough t h a t a l i t t l e s h i e l d i n g reduced t h e f i e l d t o acceptable l e v e l s .

Mav 20 - 7.932 Mvihr I n s t a l l e d temporary instrurnentatiori p i p i n g a t t h e PCV 522 a r e a f o r p a r t i c l e t r a p , carbon bed, and valve p r e s s u r e drop measurements. Tubing connections were made up remotely; t h i s w a s a new maintenance procedure. Readings were 109 r/hr a t f l o o r l e v e l and 10 r/hr throu.gh an open t o o l p e n e t r a t i o n . J u l y 27

7822 Mw'lr

This was t h e s t a r t of t h e shutdown which has extended t o The r e a c t o r was s h u t down on J u l y 17, and t h e graphite-INOR-8 s u r v e i l l a n c e samples were removed from t h e r e a c t o r core on J u l y 28, 11 days l a t e r . The work r e q u i r e d t h r e e days. The e s t i m a t e d r a d i a t i o n level while t h e sample was being t r a n s p o r t e d w a s 1500 r/hr a t 1 f t . 'Yiie remote c o n t r o l room f o r t h e crane was used f o r t h e f i r s t time and performed s a t i s f a c t o r i l y . The t o o l s used f o r t h e o p e r a t i o n vere contaminated t o a l e v e l g r e a t e r t h a n 1.00r / h r . Yfle end of t h i s r e p o r t period.

Removed, r e p a i r e d , and r e p l a c e d t h e Nos. 1 and 3 c o n t r o l rod d r i v e s . The d e t a i l s o f Lhe r e p a i r work a r e described i n S e c t . 2.3. The remote handling o p e r a t i o n of t h e removal and replacement went smoothly. Ziadiation wa.s ,500 m / h r a t f l o o r ].eve L a

Aumst 15

7822 Mwhr

Rerno-v-ed and replaced t h e r e a c t o r c e l l w e s t space c o o l e r . The job went roii.tinely and was accorflplished most1.y by t h e c r a f t f o r c e s . Radltztion was 1. 'LO 6 r / h r a t f l o o r I.evel.

August 17 - 7822 Mwir

A gas p r e s s u r e r e f e r e n c e l i n e which became T i l l e d wi.1;h a s a l t p l u g w a s cleared by anpl.ying p r e s s u r e while h e a t i n g t h e l i n e . This t a s k was u n a n t i c i p a t e d and r e q u i r e d some des i g n , fal-xication, and t e s t i n g p r i o r t o instal..ling a h e a t e r on a long-handled t o o l a n d s a f e l y o p e r a t i n g ri.t, remotely. Readings were SO r / h r a t floor level and 10 r/hr through a t 00 1. p e n e t r a t i o n I

References 1. MSR Program Semiann. Progr. Rept. Eeb. 28] 1966, ORNL-3936, p . 54.

Ihid.,

pp. 54-56.

Ibid.,

p. 5 8 .

E . C . l a r r i s h and H. W. Schneider, T e s t s of High E f f i c l e n c y F i l t e r s and Filter I n s t a l l - a t i o n a t OmL, OHNL-3442 (May 17, 1963). I _

Personal communication from S. J. B a l l and J. R . Engel.

P. G. Smith

A. G. G r i n d e l l

3.1 Molten-Salt Pump Operation i n t h e Prototype Pump T e s t F a c i l i t y

The prototy-pe pump w a s operated f o r 2631 h r , c i r c u l a t i n g t h e s a l t LS-BeFz-ZrF4-ThF4-UF4 (68.4-24.6-5.0-1.14.9 mole $1 i2t 1200째F. The f u e l - s a l t pump i m p e l l e r of 11-1/2 i n . OD ( s i z e i r s s t a l l e d i n t h e MSHE fuel pump) was used. Measurements were made of t h e c o n c e n t r a t i o n of helium bubbles i n t h e c i r c u l a t i n g s a l t , and v a r i o u s t e s t s were conducted on t h e pump-tank and t h e c a t c h - b a s i n purge gas l i n e s , 1 Tlie r a d i a t i o n densitometer++was used t o determine t h e c o n c e n t r a t i o n of helium bubbles c i r c u l a t i n g i n 1200째F s a l t during o p e r a t i o n a t normal pump-tank l i q u i d l e v e l and wiYiz a fuel-pump i m p e l l e r of 11-1/2 i n . dim e t e r running a t 1170 rpm. The helium c o n c e n t r 8 t i o n i n t h e s a l t w a s 0.1% by volume. This value c o n t r a s t s w i t h 4.676 by volume measured prev i o u s l y 2 i n t h e prototype f a c i l i t y using a 1 3 - i n . d i a m f'uel i m p e l l e r , and compares f a v o r a b l y t o a bareljr d e t e c t a b l e c o n c e n t r a t i o n i n t h e MSFB fuel circuit.

Tests were performed which i n c l u d e d a n a l y s e s t o dete-&ne the hydrocarbon c o n t e n t of t h e pump-tank, and c a t c h - b a s i n purge gas strews and t h e composition of hydrocarbons. 'Bey were done as part of t h e efI"or*t t o establish whether t h e fuel pump was t n e l i k e l y source of hydrocarbons i n t h e off-gas system o f t h e lSs?F,. During t h e s e t e s t s the flow of gas down t h e s h a f t annulus a t c o n s t a n t supply p r e s s u r e decreased, and t h i s w a s t a k e n as a n i n d i c a t i o n of a p a r t i a l plug i n %he arLnuLus. The p a r t i a l plug i n c r e a s e d t h e p r e s s u r e &Lfferenee a c r o s s t h e gasketed j o i n t between the s h i e l d plug and t h e b e a r i r g housing from 0 t o 5 p s i a t t h e design purge f l o w of 4. l i t e r s / m i n . Under t h e s e circwnstances -the off-gas from tlne pump tank contained s e v e r a l hundred p a r t s p e r m i l l i o n of hydrocarbons. This i n d i c a t e d that t h e p r e s s u r e differer-ce w a s f o r c i n g o i l from t h e c a t c h b a s i n through the gasketed s e a l , dawn t h e o u t s i d e of t h e s h i e l d pLug, and i n t o t h e pump t a n k . The p a r t i a l plug could be removed t e m p o r a r i l y by s t o p p i r g t h e pump l o r a s h o r t time o r by r a i s i n g t h e 'cemperatue of t h e c i r c u l a t i n g salt from 12GO t o 1250째F. When t h e plug w a s not p r e s e n t , t h e c o n c e n t r a t i o n 01' hydrocarbons i n t h e o f f - g a s stream from t h e pump t a n k w a s very low. Samples of t h e plug m a t e r i a l were obtained when $he pump w a s d i s m n t l e d . Exm i r i a t i o n showed them t o be s a l t of t h e composition t h a t w a s k i ~ g circwlated by t h e pump. The mechanism by which t h e s a l t reached t h e s h a f t antiulus i s being i n v e s t i g a t e d . Other t e s t s were run. i n which o i l w a s i n j e c t e d i n t o t h e pump t a n k through khe sampler-enricher nozzlf: R e s u l t s of t h e ctmlyses and o t h e r information about b o t h t y p e s of t e s t s are r e p o r t e d i n ore d e t a i l i n S e c t . 7.5, s u b s e c t i o n e n t i t l e d "Analysis of I l e l i u m Blanket Gas e I' e

"Densitometer w a s provided and o p e r a t e d by V. A. McKay of t h e Ins t r u m e n t a t i o n and ControLs D i v i s i c n .

82 Pump Rotary Element Modification The modification3 that r e p l a c e s t h e gasketed seal between t h e s h i e l d plug and t h e b e a r i n g housing w i t h a s e a l weld, which should e l i m i n a t e t h e oil leakage i n t o t h e pump bowl, w a s compkted on t h e s p a r e r o t a i y elements f o r -the MSRE f u e l and- cool.ai1t pumps and on t h e r o t a r y element f o r -the MK-2 fuel- pump. The s p a r e elernent for Yne f u e l pump w a s t e s t e d i n the cold. shakedown s t a n d and i n s t a l l e d i n t h e p r o t o t y p e hot t e s t s t a n d f o r shakedown. Drring p r e h e a t of t h e system and pump, approximately 1 q t of o i l . passed thyough t h e lower r o t a r y s e a l i n t o t‘ne c a t c h b a s i n . ‘The cause of t h e poor performance of t h e s e a l i s being i n v e s t i g a t e d , and t h e r o t a r y e l e m a i t i s being c1ea:ned and r e as semble d. Cold and hot shakedown t e s t s of t h e s p a r e r o t a r y element f o r t h e

MSRE coolan--1;pump were completed. The hydrocarbon content i n t h e pump t a n k off-gas w a s not more than 15 ppm, Lubrication System

Yne l u b r i c a t i o n pump endurance t e s t 3 w a s continued., and t h e pump has now run for 27,000 hr, c i r c u l a t i n g o i l a t 160°F and 70 gpm. MK-2 Fuel Puim The pump tank3 i s being Pahricated, and, when completed, it wi1-7. be i n s t a l l e d i n t h e prototype pump tes.1; f a c i l i t y . Then t h e MK-2 f u e l pump will be t e s t e d a t o p e r a t i n g c o n d i t i o n s sirnulati-ng t h o s e required by t h e MSRE.

3.2

Other Molten-Salt Pumps

YK-P Fue 1-Pwiip iiigh -Teiiip e rat m e Endurance Test Endurance operation3 was h a l t e d as a result of a f a i l u r e of t h e d r i v e motor. The P L U I Ihad ~ operated continuously f o r 7830 h r , c i r c u 1.ating t h e s a l t LiF-BeF2-ThF4-W4 (65-30-4-1 mole %) at, 1200°F, 800 gpm, and 1650 q m e The r o t o r windings o f t h e wound r o t o r motor had s e i z e d a g a i n s t t h e s t a t o r . The pump has operated f o r a t o t a l of 23,426 hr in four t e s t s .

Pump Containil?G a Molten-Salt -Lubricated tJourL?al Bearing ‘The ginfjal-s support f o r t h e sal%b e a r i n g 4 w a s modified, and a new bearing and j o u r n a l were f a b r i c a t e d . Performance o f t h e s a l t b e a r i w w i l l be i n v e s t i g a t e d w i t h an o i l l u b r i c a n t p r i o r t o molten-salt I.ubrication e

References 1. MSR Program Semiann. Progr. Rept. Feb. 28, 1966, ORNL-3936, 75.

2. MSR Program Semia.m. Progr. Kept;. A%. 65

pp. 74-

31, 1965, Oâ&#x201A;ŹUL-3872, pp. 62-

MSR Program Semiann. Progr. Rept. Feb. 28, 1966, OIXNL-3936, p. 75. Lbid., -

p. 76.

R . L. Moore

G. 8. Burger

ir7. Krewson

4*1 Tenlperatuse -~ Scanner Performance of t h e temperature scanning syskem' continued -Lo be g e n e r a l l y s a t i s f a c t o r y , although some problems were experienced w i t h t h e o s c i l l o s c o p e s and mercury switches a n d some system i n s t a b i l i t y was noted. The problems w i t h t h e o s c i l l o s c o p e s were only c o n t i n u a t i o n s of t'nose p r e v i o u s l y experienced due $0 the age and design of t h e scopes, The scopes a r e about 1.2 t o 1.5 y e a r s o l d and have been a conLinuing source of t r o u b l e . h n u f a c t u r e of %he scopes w a s discontimied, s o iio s p a r e p a A s were a v a i l a b l e . Two new s o l i d - s t a t e - c i r c u i t scopes The new scopes have a p p a r e n t l y e l i m i were ordered a,nd instal.3.ed. n a t e d t h a t problem, al-tflough more tjme is required. t o e v a l u a t e t h e i r p e r f omance

Although t h e mercury swi'khes have contia.ii.ed t o g i v e rfluch b e t t e r s e r v i c e than expected, some problems due -to n o r m 1 wear developed. Upon ordering replacement p a r t s for t h e switches, it was discovered t h a t t h e switches were no l o n g e r manufactured a n a :no s p a r e p a r t s e x i s t e d . Some s p a r e p a r t s and switches were obtained from the OKNL Reactor Division, b u t it was apparent -that a replacement switch w a s needed. A p o s s i b l e replacement was found a t Union Ca-sloide Corporat i o n , Olefins Division, i n South Charleston, West V i r g i n i a . The Olefins Division h a s developed a s o l i d - s t a t e m u l t i p l e x e r as a d i r e c t replacergent Tor t h e mercury- switch a,nd has agreed- t o s e l l one t o OXNL f o r t,es-t and e v a l u a t i o n . An o r a e r has been p l a c e d f o r one u n i t , w i t h d e l i v e r y expected about January 1967. In t h e meantime t h e Reactor Div-ision wil.1- continue t o supply mercury switch s p a r e p a r t s as long a s t h e y a r e a v a i l a b l e and can be r e l e a s e d f o r o u r use. The scanner i n s t a b i l i t y problems mos'cly resulbed from operatiing t h e system o u t s i d e i t s design r a a g e , The systeiu was a d j u s t e d to obtain more d i s p l a y r e s o l u t i o n and t o provide e a s i e r readout f o r -tile o p e r a t o r s . I n order t o d-o t h i s t h e al.am d i s c r i m i n a t o r w a s reqiii.red t o o p e r a t e o u t s i d e i t s design range, causing alarm se-t p o i n t i n s t a b i l i t y . To e l i m i n a t e t h i s problem while continuing t h i s mode of ope r a t i o n would r e q u i r e r e d e s i g n of the cliacrimina,tor, s o o p e r a t i o n of t h e system w a s changed back t o comply w i t h t h e o r i g i n a l design. A c a l i b r a t i o n and t e s t u n i t i s being designed and w i l - l be i n s t a l l e d . s h o r t l y t o provide t h e o p e r a t o r s wi-t'n an e a s y method of c a l . i b r a t i n g t h e system and of checking i t s s t a b i l i t y . This t e s t u n i t will provide a v a r i a b l e , a c c u r a t e l y c a l i b r a t e d s i g n a l t o one p o i n t on any of t h e s e l e c t e d scanners mid- w i l l all-ow t h e o p e r a t o r s t o check t h e scaiin e r c a l i b r a t i o n and alarm s e t p o i n t s during r o u t i n e o p e r a t i o n of t h e scanner system.

4.2

High-Temperatwe NaK-Filled D i f f e r e n t i a l - P r e s s u r e Transmitter

T e s t i n g of t h e c o o l a n t - s a l t system f l a w t r a n s m i t t e r which f a i l e d i n s e r v i c e a t t h e MSRF and which w a s subsequently r e f i l l e d w i t h s i l i cone oil2 w a s continued. F u r t h e r t e s t i n g a t temperatures over t h e range f r o m roonitemperatme to 1200째F confirmed t h a t t h e temperature s e n s i t i v i t y had been s i g n i f i c a n t l y reduced by t h e r e f i l l i n g o p e r a t i o n but was; s t i l l excessive. Before r e f i l l i n g , t h e z e r o s h i f t s observed were of t h e order of 15 t o 20 i n . (water column) p e r degree Fahrenheit change i n body temperature. A f t e r r e f i l l i n g t h e s h i f t s were of t h e order of 1 i n . HzO p e r degree Fahxenheit. Zero s h i f t s of t h e order of 0.1 i n . H20 p e r degree Fahrenheit o r less are r e q u i r e d Lo o b t a i n t h e accuracy d e s i r e d i n measurement of MSRE c o o l a n t - s a l t flow. I n a l l - c a s e s the temperature-induced shifts observed were zero s h i f t s . No s h i f t s of spa,n c a l i b r a t i o n were observed. Also, t h e instrument did n o t e x h i b i t a, s e n s i t i v i t y t o s t a t i c p r e s s u r e changes e i t h e r b e f o r e o r after r e f i l l ing. The remaining s h i f t s a r e p r e s e n t l y b e l i e v e d t o be due t o the cont i n u e d presence of some gas v o i d i n t h e s i l i c o n e - o i l - f i l l e d c a v i t i e s . Attempts t o e l i m i n a t e t h e s e voids w i l l . be made by r e p e a t i n g t h c filling o p e r a t i o n s . To assure that a l l remaining gas has been removed, a t tempts w i l l be made t o o b t a i n a "harder" vacuum t h a n t h e 28 i n , HE vacuum p r e v i o u s l y obtained. A f t e r r e f i l l i n g , t h e temperature s e n s i t i v i t y t e s t s will.. be r e p e a t e d . The new NaK-filled d j 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 ordered f o r use as a n MSRE s p a r e w a s received; however, acceptance t e s t s showed t h a t t h e instrument w a s extremely s e n s i t i v e t o temperature and s t a t i c p r e s s u r e v a r i a t i o n s and would, t h e r e f o r e , n o t m e e t s p e c i f i c a t i o m Negotiations w i t h t h e mariufacturer f o r r e p a i r o r replacement of tihe t r a n s m i t t e r a r e i n progress. a

4.3

Molten-Salt Level Detectors

Perf ormarice of a l l m o l t e n - s a l t l e v e l d e t e c t o r s i n s t a l l e d at the KSXE, on t h e JKEW Level. Test F a c i l i t y , and on t h e MSF3 Prototype Pump Test Loop continues t o be s a t i s f a c t o r y . 2 1 3 No f a i l u r e s have occurred i n ;my of t h e l e v e l devices during t h e p a s t r e p o r t period, and, except f o r t h e changes made i n e l e c t r o n i c equipment a s s o c i a t e d w i t h tine ultras o n i c l e v e l probes r e p o r t e d below, no m o d i f i c a t i o n s have been r e q u i r e d . The c o r r e c t i o n s made i n t h e c a d l i b r a t i o n of t h e b a l l - f l o a t - t y p e t r a n s m i t t e r i n s t a l l e d on t h e MF3 c o o l a n t - s a l t p m p 4 were a p p a r e n t l y a,&q u i t e , and no f u r t h e r adjustments have been necessary.

To c o r r e c t t h e excessive frequency d r i f t p r e s e n t i n t h e e x c i t a t i o n

oscillator supplytng the u l t r a s o n i c level probe, r 6 a nuniber of minor changes were made i n t h e components and c i r c u i t r y of t h e o s c i l l a t o r and

d e t e c t o r a m p l i f i e r c i r c u i t s . I n g e n e r a l , t h e s e changes involved t h e r e placement of a nwriber of c r i t i c a l components w i t h high-grade coraponents having very small temperature c o e f f i c i e n t s , i n c r e a s i n g t h e s i z e of

86 coupJ.irg c a p a c i t o r s s o that they would. have small-er reactance a t t h e 25-kilohertz o p e r a t i n g frequencies, and making s e v e r a l minor c i r c u i t r e v h i o n s t o i n c r e a s e t h e s t a b i l i t y of t h e B+ supply. 'These changes r e s u l t e d i n a c o n s i d e r a b l e improvemerit i n t h e frequency s-t;abil_ity. Before t h e changes were made t h e o s c i l l a t o r d r i f t e d randomly, wi-th a m i m u m d e v i a t i o n from t h e cenker o r resonan-t frequency of 300 h . e r t z e s . T'nis d e v i a t i o n w a s s u f f i c i e n t t o cause t'ne instrument; t o become I n o p e r a t i v e When t h e changes were made, t h e maximim d r i f t observed a f t e r wamup w a s 5 hertzes These drifts were observed i n a n a i r - c o n d i t i o n e d l a b o r a t o r y and are expected t o be g r e a t e r i n t h e f i e l d ; however, it i s expected t h a t t h e i n c r e a s e d s t a b i l i t y obtained w i l l be aaequate, A complete check on t h e opera'oiliLy of t'ne u l t r a s o n i c l e v e l probe r e q u i r e s an a.ctual_ v a r i a t i o n of t h e l e v e l of molten s a l t i n t h e f u e l s t o r a g e tank of t h e MSRF:. No salt has been t r a n s f e r r e d to o r froiii t'nis -Lank s i n c e t'ne probe c i r c u i t r y w a s modified, and f i e l d checks on t h e e f f e c t i v e n e s s of t h e modifications have not been made a t t h i s time. These checks wlllbe made when s a l t t r a n s f e r s can be made without i n t e r f e r e n c e w i t h MSRX operations. e

4.4

Helium ConLrol Valve T r i m Replacement

Mod-ifications and/or r e p a i r of two weld-sealed helium c o n t r o l v a l v e s which f a i l e d i n MSRE s e r v i c e during t h e previous r e p o r t period7 have been completed.. The s p l i n e - t y p e t r i m p r e v i o u s l y used i n t h e inain heliuii supply c o n t r o l valve, which had f a i l e d tawice, was r e p l a c e d w i t h a t a p e r t r i m . The use of t a p e r . b r i m w a s permissible and desirahlk because of t n e r e l a t i v e l y high flow r a t e s involved.

There have been no f u r t h e r f a i l u r e s of helium contiwl. valves during t'ne p a s t six months.

Yo determine t h e f e a s i b i l i t y of c o n t r o l l f n g v e r y l o w flows of dry helium w j - t h s l i d i n g d i s k valves, a mockup of such a valve was c o n s t r u c t e d and tested. The a c t i v e member of t h e s l i d i - n g disk valve i s a f l a t d i s k a t t a c h e d t o tlne valve stem and h e l d a g a i n s t a s e a t i n g s u r f a c e by s p r i n g and p r e s s m e act1.on. The s u r f a c e between t h e disk and s e a t is lapped t o 1-ight band flatness to a s s u r e t i g h t shutoff. T h r o t t l i n g c o n t r o l of helium Plow i s accomplished by means of a t a p e r e d V-notch i n t h e d i s k , which connects a por-i; i n t h e disk t o a p o r t i n .the valve s e a t . Xotat i o n of t h e d i s k causes t h e e f f e c t t v e c r o s s - s e c t i o n a l a r e a of t h e passage between t h e p o r t s t o v a r y fn p r o p o r t i o n to t h e degree of r o k a t i o n . This type of c o n s t r u c t i o n offers promise i n t h e c o n t r o l of dry-helium flow because of an i n h e r e n t self-wiping a,ckion and because of tlne poss i b i l i t y t h a t t h e valve might be operated wi-thout t h e use of l u b r i c a n t s . P r e l i m i m r y results of bench t e s t s were inconclusive because of excessive l e a k r a t e s between t h e lapped s u r f a c e s of tile disk and s e a t . The t e s t s w i l l be r e p e a t e d a f t e r a d d i t i o n a l lappiiag, c l e a n i n g , and r e assembly of t h e valve a r e completed.

References 1. MSR Program Semiann. Progr. Hept. Feb. 28, 1966, ORJTL-3936, p . 80. 2.

I b i d . , pp. 77-78.

IGR P r o g r m Semiarm. Progr. Rept. Feb. 28, 1965, ORIYL-3812, pp. 42-43.

MSIi Program Semiann. Progr. Rept. Feb. 28, 1966, OREL-3936, p. 78.

5. Ibia., p. 77. I

6. MSR h o g r a m Semiann. Progr

. Rept . Aw . 31,

1965, ORNL-3872, pp. 66-70,

MSR Program Semiann. Prcgr. Rept. Feb. 28, 1966, ORNL-3936, p. 79.

REACTOR ANALYSIS 73. E.

5.1

Prince

Analysis of Rod Drop Experiments

D e s c r i a t i o n of FxDeriments The s e r i e s of zero-power nuclear experiments made during MSKE run No. 3 included s e v e r a l rod drop experiments as p a r t of t h e c o n t r o l rod c a l i b r a t i o n program. The piirpose of t h e s e experiments w a s t o provide an a l t e r n a t i v e and independent measurement of t h e control. rod r e a c t i v i t y worth, which could be compared with worths determined by o t h e r methods (rod-bump period measurements and equivalent 235U a d d i t i o n ) . Three s e t s of rod drop experiments were performed, af-Ler a d d i t i o n s of 30, 65, and 87 capsules o f excess 235U had been made. Each s e t of experiments iseluded rod drops b o t h with t h e f u e l c i r c u l a t i n g and with c i r c u l a t i o n stopped. W e have analyzed -the experiments made with t h e f u e l pimp stopped, and Lhe r e s u l t s a r e summarized beI.ow. The r o d drop experiment c o n s i s t s of t h e i n t e n t i o n a l scram o f a rod, or rod group, from an i n i t i a l l y c r i t i c a l c o n f i g u r a t i o n , and t h e recording of t h e decay of t h e neutron f l u x as a funcLion of t i m e fol-lowing -the scram. One t h e n determines t h e amomt of nega-Live r e a c t i v i t y r e q u i r e d

t o produce t h i s f l u x decay t r a j e c t o r y . The t r a j e c t o r y i s c h a r a c t e r i z e d by a sharp drop trt t h e flux immed.iately following t h e scram, which corresponds c l o s e l y w i t h t h e actual. f a l l of t h e rod. TThe curve r a p i d l y and continuously evoI.ves i n t o one with a nuch slower r a t e of f l u x decrease, governed by t h e decay of t h e i n i t i a l d i s t r i b u t i o n of delayed-neutron precursors.

Due t o t h e requireiiient imposed by t h i s experLmeat of a c c u r a t e l y recording t h e f l u x while it i s r a p i d l y f a l l i n g by about t w o decades, t h e g r a p h i c a l r e c o r d obtained Prom t h e t r a c e of a l o g n racorder i s of I l m i t e d u s e f u l n e s s . ?"ne corn'oined reqix.remelits of f a s t i-enponse, good counking s t a t i s t i c s , and r e p r o d u c i b i l i t y can be served, however, by recording -the rintegrated count as a f u n c t i o n of time following t h e drop.

I n o r d e r t h a t t h e i n t e g r a t e d flux-time curve could b e recorded withou-i; r e q u i r i n g s c a l a r s with s p e c i a l a c c u r a t e l y timed c y c l e s f o r count accumulation and recording, t h r e e s c a l a r s , t o g e t h e r w i t h a photographic techniqiie of r a p i d recording, were employed i n t h e following way. One of t h e s c a l a r s w a s driven by one of t h e fission-chamber channels. The o t h e r two were operated as 60-cps tirning devices. One of t h e s e t i m e r s was synchronized. t o s t a r t w i t h t h e scram o f the r o d , while t h e other timzr and t h e count-accumulating s c a l a r w e r e synchronized and s t a r t e d a few seconds b e f o r e t h e scram w a s i n i t i a t e d . The t h r e e s c a l a r s were stacked t o g e t h e r i n a v e r t i c a l a r r a y , and a yapid-action camera w a s used .Lo simultaneously photograph the r e c o r d s on t h e three s c a l a r s approximately once every second, starl;ing a f e w seconds b e f o r e t h e scram and ending about 30 see a f t e r t h e scram. From t h e s e photographs, t h e count

r a t e a t t h e i n i t i a l - c r i t i c a l condition, t h e time of t h e scram s i g n a l , and t h e i n t e g r a l of t h e f l u x , o r count r a t e , as a f u n c t i o n of t i m e f o l lowing t h e scram could be a c c u r a t e l y determined. I n t h e s e experiments, t h e p o s i t i o n of t h e f i s s i o n chambers was a d j u s t e d -to o b t a i n an i n i t i a l count r a t e a t c r i t i c a l i t y of approximately 30,000 counts/sec, which was low enough t o r e s u l t i n q u i t e s m a l l counting r a t e losses due t o dead-time c o r r e c t i o n s . Also, t h e remote p o s i t i o n of t h e MSRE instrixnent s h a f t , r e l a t i v e t o t h e r e a c t o r c o r e , would h e expected t o minimize e r r o r s due t o changes i n t h e s p a t i a l f l u x shape during t h e rod drop experiment. Analy s i s Proc e dur e s The method used t o analyze t h e experiments performed wi-th t h e f u e l pwnp stopped w a s t h a t of comparison wi-tn t h e o r e t i c a l f l u x decay curves. These l a t t e r curves corresponded t o a negative r e a c t i v i t y i n s e r t i o n with magnitude determined from t h e i n t e g r a l worth vs p o s i t i o n curves a l r e a d y obtained from p e r i o d measurements and c r i t i c a l p o s i t i o n compsrison techniques,â&#x20AC;&#x2122; and with rate of i n s e r t i o n corresponding t o t h e f a l l of the rod from its i n i t i a l c r i t i c a l p o s i t i o n . The t h e o r e t i c a l t i m e - i n t e g r a t e d f l u x decay curves were c a l c u l a t e d u s i n g t h e MATEXF program2 t o i n t e g r a t e t h e s t a n d a r d space-independent r e a c t o r k i n e t i c s e q u a t i o n s . Since t h i s program i s designed t o i n t e g r a t e a g e n e r a l system of f i r s t - o r d e r d i f f e r e n t i a l equations, t h e t h e o r e t i c a l t i m e - i n t e g r a t e d flux following t h e scram could be obtained by s o l v i n g t h e system:

where Q ( t ) = t i m e - i n t e g r a t e d count r a t e following t h e scram,

n ( t ) = d e t e c t o r count rate following scram, C i (t ) = delayed-neutron p r e c u r s o r c o n c e n t r a t i o n s , normaltzed t o d e t e c t o r count r a t e ,

+ ( t ) = r e a c t i v i t y a d d i t i o n vs time following scram, f3-i = production f r a c t i o n f o r i t h

group of delayed neutrons,

r a d i o a c t i v e decay c o n s t a n t for i t h group precursors,

A = prompt neutron g e n e r a t i o n tine,

The i n i t i a l conditions f o r performing t h e i n t e g r a t i o n s of E q s . and ( 3 ) a r e

$(O)

(l), (2),

( 41

n ( 0 ) = i n i t i a l count r a t e a t c r i t i c a l c o n d i t i o n

(51

The 'Lime v a r i a t i o n of t h e r e a c t i v i t y i s governed i m p l i c i t l y by the equations

&(t)

=yo .-

- 22

Ys >

= P(Y0)

at2

p[y(t)l

(rl>

S t S t e + t x n ,

t t t e

s t ,

where y

r o d posiLLon, inches withdrawn (0 5 y 5 5 1 i n . ) ; ini-Lial

p o s i t i o n , yo; scram p o s i t i o n , y ; S

t o yod p o s i t i o n y, normalized t o zero r e a c t i v i t y a t f u l l y withdrawn p o s i t i.on ;

p ( y ) = magnitude of reactivi.t;y worth corresponding

= e f f e c t i . v e l a g time between scram s i g n a l and s t a r t of rod

drop (-20 msec);

a = a c c e l e r a t i o n during f a l l (-15 f t / s e c 2 ) ; m

= time t o fa.11 t o scram p o s i t i o n .

A s discussed previously, t h e value of p ( y ) used i n t h i s a n a l y s i s w a s dete:cm:i.ned. by i n t e g r a t i o n of period d i f f eren-Lial-worth measurements We have also used an a l g e b r a i c r e p r e s e n t a t i o n of t h e s e experimental curves, obtained by a l e a s t - s q u a r e s c u r v e - f i t t i n g procedure.

i n applying t h e above ana3.ysj.s t o t h e experiments i n whlch rod groups were dropped, the magnitude of t h e t o t a l negative r e a c t i v i t y i n s e r t i o n was determined by comb:i.ning t h e c a l i b r a t i o n curve f o r t h e s i n g l e rod with t h e r e s u l t s of rod-shadowing experiments (comparisons of c r i t i c a l p o s i t f o n s o f s i n g l e rod and rod groups), I Typical rod-group drop experiments cons i s t e d of t h e simultaneous scram OB -the r e g u l a t i n g rod (rod N o , 1) from i t s i n i t i a l c r i t i c a l p o s i t i o n and one o r both of t h e shim rods from t h e

91 m l l y withdrawn posi-Lion. The normalized shape of t h e r e a c t i v i t y ins e r t i o n curve f o r t h e rod group w a s approximated by t h a t corresponding t o a s i n g l e rod, r a l l i n g from t h e f u l l y t.rithdrawn p o s i t i o n . Results The r e s u l t s of t h e rod drop experiments made a f t e r a d d i t i o n s of 30, 6 5 , and 87 capsules of e n r i c h i n g s a l t a r e shown i n F i g s . 5.1, 5.2, and 5.3 r e s p e c t i v e l y . In all t'hree s e t s of experiments, t h e a n a l y s i s of t h e s i n g l e r o d drops shows very good c o n s i s t e n c y with t h e rod wor'ch c a l i b r a t i o n obtained by i n t e g r a t i o n of t h e d i f f e r e n t i a l worth measurements. A s i m i l a r c o n s i s t e n c y w a s obtained from t h e experiments involving t h e scram of a l l t h r e e rods. I n t h e c a s e of t h e two-rod experimerrts, r e s u l t s obtained a f t e r 65 and 87 capsules appear t o be s l i g h t l j anomalous with r e s p e c t t o t h e experiment with t h e same r o d group a f t e r 30 c a p s u l e s . M u l t i p l i c a t i o n of t h e magnitude of t h e negative r e a c t l i v i t y insen-Lion by a f a c t o r of about 1.05 b r i n g s t h e c a l c u l a t e d and experimental curves f o r t h e s e experiments i n t o b e t t e r agreement. However, another source of t h i s discrepsncy could be i n t h e approximation of t h e shape of r e a c t i v i t y i n s e r t i o n vs time for t h e tandem fall of t h e rods by t h a t corresponding t o a s i n g l e rod. This source wou.ld be expected t o have i t s greates-1; i n f l u e n c e on t h e two-rod experiments. The s e n s i t i v i t y of t h e s e experiments t o v a r i a t i o n s i n %he magnitude of t h e r e a c t i v i t y i n s e r t i o n i s i l l u s t r a t e d i n Fig. 5.4. Here t h e a n a l y s i s of t h e experiment where rod No. 1 w a s scrammed a f t e r a d d i t i o n of 30 caps u l e s i s reproduced from Fig. 5.1; t h e t h e o r e t i c a l curves a r c added which correspond t o an i n c r e a s e and a d-ecrease of 5% of t h e t o t a l magnit,ude oti' negative r e a c t i v i t y i n s e r t i o n . For t h i s p a r t i c u l a r experiment, t h i s corresponds t o an increment of 0.007$ 6B/k i n t h e magnitude of r e a c t i v i t y . With t h e exception of t h e apparent anomaly i n t h e cxperirnents involving t h e scram of two rods, t h e resul-Ls of all t h e s e experiments were well w i t h i n t h e 5$ band of s e l f - c o n s i s t e n c y w i t h t h e rod c a l i b r a t i o n r e s u l t s oi).Lained from t h e d i f f e r e n t i a l worth raeasurements 1

Work w i l l continue on t h e a n a l y s i s af t h e s e experimein-Ls and sirnil-ar ones performed w i t h t h e f u e l c i r c u l a t i n g , i n an e f f o r t t o a s s e s s -the full p o t e i i t i a l of t h e rod &op experiment as a ro-utine method f o r r a p i d p e r i o d i c redetermination of t h e shutdoTrm worth of t h e MSRE c o n t r o l rods.

92 ORNL-CWG 66-11445

EXPERIME”ITAL POlN-rS BY INTEGRATION OF R E K T O R KINETICS EOUATION; RE4CTIVITY DETERPAINED F W W INDEPENDENT CALIBRATION MEASUREMENTS

- CALCULATED 0

F i g . 5.1. Results of Sod Drop Experlmen-ts After 30 Capsule A d d i tions.

io 15 TIME AFTER SCRAM (secl

ORNL- D‘NG 66 - 1 < 4 L

(X1O41

3,o.n . I

EXPERIMEUTAL POINTS CALCUL ATFD BY INTEGRATION Oc REACTOR KINETICS EQUATIONS, REACTIVITY DETERMINED FROM INDEPENDENT CALIBRAl~lOh

ROD NO I SCRAMMED I

Fl.g. 5.2. Results o f Rod Drop Experiments After 65 Capsule Addi-

tions.

2.9

u 0

n 4 0

TIME AFTER SCRAM (secl

!/I

ROO NO I SCRAMMED

1 Fig. 5.3. Resu.l.ts of Rod Drop Experiments A f t e r 37 Capsule AdditLons.

RODS 1 AND 2 SCRAMME13

_SCRAMMED

t/i

~CNCUL,ATED

BY IbIUf~GRArlOkOF REACTOR K I NET1C S EOUlTl O h S ; R C n C T l V l T Y DETERMINED FROM

INDEPENDENT CALIBRATION

MEASUREMENTS.

IO j5 TIME AFTER SCRAM lsecl

ORNL-DWG 66-11448

EXPERIMENTAL POINTS CALCULATED BY INTf.6fIATION OF RFACTOR KINETICS IQUATIONS

s III

$ 4

A NEG4TIVE HEACWIIY INSERTION,ilp, DETERMINFO rROM INTEGHArION OF DIFFEREbI rlA1 'WORTH HEASUHFMFN IS B NEGATIVt HLACTIVITY INSERTION,I 0 5 Ap C NEGATIVE KIIACTIVITY INSERTION, 0 9 5 A p

0 0

I-I--/

10 45 TIME AFTEH SCRAM lsec)

F i g . 5.4. Sensitivity of Rod Drop Experiment to Changes i n MaLgnitude of R e a c t i v i t y Insertion.

Heferences 1.

P. N. Haubenrei-ch et a l . , E R E : Zero Power Pnysics Experiments, ORNL report i n preparation.

S. J. B a l l and R. K. A b ~ n s , MATEXP A General Purpose l j i g i t a l Computer Program f o r Solving Nonlinear Ordinary D i f f e r e n t i a l Equations by t h e Matrix Exponential Method, O R N E T T 4 r e p o r t i n preparation.

MSR Program Scmiann. Progr

. Rept . Feb . 28,

I _

1966, ONKL-3936, pp. 82--87.

Part 2.

MATERIALS STUDIES

6 .I MSRE Ma-terials Surveil.lance T e s t i n g T/J.

H. Cook

Specimens of grade CGB g r a p h i t e and Iias-telloy N (INOR-8) vere remoyed from t h e c o r e o f t h e MSL% a f t e r '7800W a r of o p e r a t i o n as part; of t h e m a t e r i a l s s u r v e i l l a n c e progr~m.' The v i s u a l appearance of t h e meLal and g r a p h i t e w a s good. The e x t e r n a l surfaces were virtua1J.y f r e e of s a l t , The metal w8s d u l l gray, and- t h e g r a p h i t e appeared unchanged by %lie exposure * The Reaxtior Chemistry D i v i s i o n was s u p p l i e d w i . t h graphj%e spt3ci11ie11sf o r f i s s i o n product a n a l y s e s f r o m t h e t o p , middle, and- bottom of t h e assembl.y. The r e s u l t s of , t h e i r analpes a r e r e p o r t e d i n Chap. 7 . M,her examinatiions s c h e d d e d for tlne grxphilx and iuetal. a r e i n progress

The o b j e c t i v e a t t h i s sf;a,ge of s m p l i n g was t o remove one s t r i n g e r ( o n e - t h i r d ) of the assembly a;nd return %he ot;$ers, plus R replacement, Bowever, a p p r o x h a t e l y one-seventh of t h e assernbI.y in to t h e r e a c t o r a zone just above t h e mid.$il.ane of t h e r e a c t o r was s e v e r e l y d - ~ m g e d . Graphite specimens were buckled and broken., and the t e n s l l e rods were bent. Apparently, .the assembly had been locked t o g e t h e r by f r o z e n s a l t during the r e a c t o r cooldown, and t h e l a r g e rlifferenccs j.n t h e c a e f f i cients of thermal expansion of t h e graphlibe and iiietal. c:r.eated. high s t y e s s e s which l e d t o t h e mechanleal W g e . The cl,zma.gc i n t h i s ::one occurred i n all. Three I I a s t e l l o y N and g r a p h i t e s t r i n g e r s , r e q u i r i n g %ha$ all. t h r e e be r e p l a c e d . The g r a p h i t e and fias.l;elloy N i n t h e o t b e r port i o r i s of t n e a r r a y were suita'ole for t h e intend-ed p r o p e r t y e v a l u a t i o n e

i;L.> L,:'. t.S .

A s l i g h t l y modified replacement for -f;he damaged. reactor core specim e n s has been i n s t a l l e d i n t h e MSRF. The modifications were made t o r e duce mechanical stresses i n .the assemn'd.y by r e a c t o r h e a t i n g and cooling c y c l e s , The Ilastelloy N tensi.2-e specimen rods i n t h e new s e t are made fran r e a c t o r v e s s e l wall and head material-s plus two modified alloys of IIastel..l.oy N, one c o n t a i n i n g 0.52 w t '$ T i and t h e o t h e r 0.43 w-b $ Zr. These a d d i t i o n s were made for t h e purpose of reducing tllc e f f e c t s of r a d i a t i o n on -the alloy,

I n g e n e r a l , t h e molten salts d r a i n e d w e l l from t h e g r a p h i t e and t h e metal specimeiis, as shown i n P i g s . 6.1 and 6-2. The near absence of salt a i d e d t h e disassembly.

The o v e r a l l mechanical damage i n t h e r e a c t o r core specimens i.s shown i n F i g . 6.2 and i n more d e t a i l i n F i g . 6.3. A r e g i o n of minor danm,ge n e a r t h e bottom o f t h e assembly i s shown i n F i g . 6.3a, and t h e r e g i o n of mrrui.murn. &image i s shown i n F i g . 6 , 3 b . Approximately 25% of the g r a p h i t e specimens were broken i n each of t h e tlaree stringers. The g e n e r a l a p p e a r a c e of t h e g r a p h i t e was t h e same as it was when it was machined. Note the r e f l e c t i o n of t h e cross p i n i n t h e sixface of t h e graphite i n F i g . 6.3a.

IR-30975

6.1, Basket of tor Core Spec 0 Mwhr of Operation.

Fig. 6.2.

from Basket. + .

Overall View of t h e Reactor Core Specimens A f t e r Removal

SLEEVE 15.

R-31013

Fig. 6.3. Det Is of t h e Mechanical Damage t o t h e Graphite and Hastelloy N Specimens i n Zones of ( a ) Moderate and ( b ) Severe Damage. a p h i t e specimens had been assembled so t h a t t h e y formed tongueand-groove j o i n t s t h a t were bound together by Hastelloy N s t r a p s , as s h a m i n Figs. 6.2 and 6.3. S l i p - f i t sleeves had been spot-welded t o t h e metal s t r a p s t h a t hold t h e rods of t e n s i l e specimens i n p o s i t i o n . The graphite w a s h e l d w i t h i n t h e cage of t e n s i l e specimen r o d s by cross pinning through t h e shoulders of t h e t e n s i l e specimens (Fig. 6.3a). The t o t a l assembled l e n g t h of t h e g r a p h i t e s t r i n g e r s at room temperature w a s 62 i n . A t t h e r e a c t o r operating temperature, 1210째F, t h e graphite and Hastelloy N had expanded approximately 0.06 and

100 pectively. A t the f r e e z i n f l u s h salt, t h e Hastelloy N w a s approx t h e g r a p h i t e . During any h e a t i n g or c elloy N tensile s expansion of t h e shoulders s l i d e n the sleeves, t h a t bind t h e g r a p h i t e specimens.

t h e assembly, t h e g r e a t e r

rods r e q u i r e s t h a t t h e i r

spot-welded t o t h e s t r a p s

On disassembly, it w a s found t h a t most of t h e g r a p h i t e tongue-andgroove j o i n t s had separated during t h e heatup a l k w e d salt $0 become entrapped i n t h e j o i n t s . As t h e r e a c t o r cooled, t h e s a l t had frozen i n small r e c t a n g u l a r p l a t e l e t s shown i n F i g - 6 = 4 * These ranged from 0.022 t o 0.065 i n . i n t h i c s - Their t y p i c a l t h i c k m s s e r a t u r e l e n g t h of each stri which means t h a t t h e room and s a l t w a s approximately 62.21 r a t h e r t h a n t h e normal 62.00 i n . The t h i r d item found was t h a t some of t h e s l e e v e s were locked t o t h e shoulders of t e n s i l e specimens by frozen s a l t . The most s t r o n g l y bonded s l e e v e s were a t t h e ends of t h e s e v e r e s t ge

II I _

I I I

101 We conclude t h a t t h e Hastelloy X t e n s i l e specimen rods sought t o r e t u r n t o t h e i r o r i g i n a l room-temperature l e n g t h during t h e r e a c t o r cooldown, b u t t h e y were o b s t r u c t e d by t h e s l e e v e s t h a t were a t t a c h e d t o t h e rods w i t h f r o z e n s a l t and by t h e i n c r e a s e i n room-temperature length of t h e g r a p h i t e columns c r e a t e d by t h e f r o z e n salt trapped i n t h e j o i n t s . The g r a p h i t e specimens were end loaded, and t h e y buckled and broke i n t h e manner of s l e n d e r columns. Calculations based on 45,000 p s i , t h e lowest value, f o r t h e y i e l d s t r e n g t h of b s t e l l o y N, showed t h a t t h e end loading would be s u f f i c i e n t t o buckle such s l e n d e r columns of g r a p h i t e , assuming t h a t t h e ends were f i x e d and t h e loads were axial. A s one might expect, t h e t h i n n e s t specimens were broken more f r e q u e n t l y t h a n t h e t h i c k e r ones. We b e l i e v e t h a t t h e damage w a s unavoidably magnified during t h e r e moval of t h e assembly from t h e p e r f o r a t e d b a s k e t . W e assume t h a t a broken piece of g r a p h i t e became t i l t e d i n t h e region t h a t showed t h e s e v e r e s t damage, and t h i s t i l t e d piece of g r a p h i t e a c t e d as a yoke t o b i n d t h e assembly i n t h e basket when approximately one-third of t h e assembly had been withdrawn from t h e b a s k e t . The a d d i t i o n a l damage w a s probably c r e a t e d by t h i s yoke when t h e assembly was f o r c i b l y e x t r a c t e d t h e r e s t of t h e way out of t h e basket. Because many f i n i s h e d specimens were a v a i l a b l e f o r use i n a replacement assembly and time w a s s h o r t , we decided not t o make major r e v i s i o n s i n t h e design of t h e assembly. We did, however, make t h r e e minor modif i c a t i o n s t o t h e b a s i c design t o a l l e v i a t e t h e s e problems. 1. To avoid t h e entrapment o f s a l t w i t h i n t h e tongue-and-groove j o i n t s , O.O4O-in.-diam p i n s of Hastelloy N were used t o p i n t h e j o i n t s s o t h a t t h e g r a p h i t e would not s e p a r a t e during t h e heatup.

To minimize t h e d i s t a n c e s t h a t t h e shoulders of t h e t e n s i l e rods m u s t s l i d e w i t h i n t h e i r s l e e v e s , t h e middles of t h e g r a p h i t e s t r i n g e r s were pinned t o t h e middles of t h e t e n s i l e specimen rods. Since expansion i s now forced t o work both ways from t h e pinned middles, t h e d i f f e r e n t i a l movements a r e halved. However, t h e maximum movement, f o r t h e s l e e v e s and shoulders f a r t h e s t from t h e middle, is s t i l l as much a s 0.2 i n .

To minimize f r i c t i o n , misalignment, and s a l t entrapment, t h e sleeves were shortened and s p l i t l o n g i t u d i n a l l y . Compare those of F i g s . 6.3a and 6.5.

The weakest p o i n t i n t h e modifications i s t h a t s a l t may f r e e z e i n some of t h e annular spaces between s l e e v e s and shoulders and t h a t t h e p i n s i n t h e tongue-and-groove j o i n t s may s h e a r . The g r a p h i t e specimens i n t h e modLfied assembly were made from grade

CGB g r a p h i t e t h a t i s i n f e r i o r t o t h e g r a p h i t e i n t h e f i r s t assembly i n t h a t it has more c r a c k s .

The Hastelloy N t e n s i l e specimen rods of t h i s second assembly were made from t h e r e a c t o r v e s s e l w a l l and head m a t e r i a l s , h e a t Nos. 5085 and 5065, r e s p e c t i v e l y , p l u s two Hastelloy N a l l o y s modif i e d with 0.52 w t % T i and 0.43 wt % Zr, h e a t Nos. 21545 and 21554 r e s p e c t i v e l y . The modified a l l o y s a r e attempts t o reduce t h e damaging

102 Y-750 11

Fig. 6.5. Shortened and S l i t Sleeves t o Provide B e t t e r S a l t Drainage and t o A l l e v i a t e Binding, e f f e c t s of i r r a d i a t i o n . The specimens a r e included i n the s e r i e s i n order t o study t h e e f f e c t s of t h e a l l o y i n g a d d i t i o n s on damage by i r r a d i a t i o n and c o r r o s i o n by molten s a l t .

F l m monitors of 0.020-in.-diam w i r e s of type 302 s t a i n l e s s s t e e l and pure i r o n and n i c k e l had been s e a l e d under vacuum i n a p r o t e c t i v e 6.3a. In t h e postirras h e a t h of H a s t e l l o y N as shown i n F i g s . 6.6

d i a t i o n exambation, t h e s t a i n l e s s s t e e l and i r o n w i r e s were r e a d i l y s e p a r a t e d f r o m t h e sheath, although t h e s t a i n l e s s s t e e l showed some s i g n s of bonding t o it. The n i c k e l wire had solid-phase-bonded throughout i t s length t o t h e sheath. The new set of flux monitors i n s t a l l e d i n t h e w i t h t h e new r e a c t o r core specimens are of t h e same materials. However, t o guard a g a i n s t a r e p e t i t i o n of t h e s o l i d - p h a s e bonding, t h e flux monitor w i r e s and t h e i n s i d e of t h e sheath were h e a t t r e a t e d i n air t o produce t h i n oxide c o a t ings on them. To minimize v a p o r i z a t i o n of oxide, t h e s h e a t h w a s s e a l e d w i t h 1 a t m of a i r a t room temperature.

103 ORNL-OWG

66-11449

0.100-in-DlAM x 3/16-in. LONG PLUG, I N O R - 8

T I G WELD

0 . 1 2 5 - i n - O D x 0.020-in.-WALL

INOR-8

In.

I RON DETAIL OF END WELDS

NICKEL

TYPE 302 STAINLESS STEEL

0 0 2 0 - i n - D l A M F L U X MONITOR WIRES NOTE:

WIRES ARE FOLDED BACK AT ONE END AS I L L U S T R A T E D ABOVE TO FACILITATE THEIR IDENTIFICATION. THE B E N T ENDS ARE AT THE TOP OF T H E SHEATH.

PINCH CLAMP MARK ( P I N C H CLAMP HELD VACUUM WITHIN T H E SHEATH DURING THE SEALING OF T H E F I N A L END WELD.) SHEATH

BOTTOM

TOP

* THE

F L U X MONITORING WIRES E X T E N D ALONG T H I S SPACE OR DIMENSION

Fig. 6.6.

6.2

E R E Flux Monitoring Wires and P r o t e c t i v e Sheath.

Evaluation of P o s s i b l e MSRE: Radiator Tubing Contamination w i t h Aluminum D. A. Canonico

D. M. Haseltine

On Sunday, July 17, a c a s t Al-5 w t '$ Zn a l l o y blower f a i l e d a t t h e MSRE s i t e , throwing small s h r a p n e l a c r o s s t h e Hastelloy N t u b i n g of t h e s a l t - t o - a i r r a d i a t o r . The f a i l u r e occurred a t about 10:00, while t h e r a d i a t o r w a s o p e r a t i n g a t 1070째F. The p r o t e c t i v e doors were closed while t h e s a l t w a s s t i l l c i r c u l a t i n g ; t h e temperature t h e n rose t o approximately 1200'F. This temperature w a s maintained u n t i l 14330, a t which

104 time t h e salt w a s drained and t h e h e a t w a s t u r n e d o f f . A t 19:00, t h e temperature had decreased t o 250°F. The doors were opened and t h e temp e r a t u r e dropped f u r t h e r t o 150°F a t 2 0 : O O .

A m e t a l l u r g i c a l i n v e s t i g a t i o n w a s conducted t o determine t h e e f f e c t of t h e aluminum-zinc a l l o y on t h e r a d i a t o r tubing. Since t h e a c t u a l tubing could not be removed and s e c t i o n e d metallographically, only specimens simulating t h e exposure could be prepared and evaluated. Small segments of t h e f a i l e d blower were t e s t e d i n c o m p a t i b i l i t y experiments with r e p r e s e n t a t i v e samples of t h e tubing. Laboratory experiments were conducted t o determine t h e influence of temperature and time upon t h e Hastelloy-N-luminum-alloy i n t e r a c t i o n . Temp e r a t u r e s of U50, 1175, 1190, 1200, 1225, and 1250°F were i n v e s t i g a t e d , Y-74029

4150°F

4200°F

1175 O F

1190°F

4225OF

1250°F

INCH

Fig. 6.7.

i 5 M I N U T E S AT TEMPERATURE Hastelloy FAlWninum Alloy Compatibility Test Specimens.

105 t o 5 hr. Figure 6.7 shows t h e samples and times a t temperat o r 15 min. F i v e 6.8 shms t h e samples a f t e r being h e l d a t t with t h e aluminum removed from t h e tubing. The r e f r a c t o r y aluminum oxide c o a t i n g had contained t h e aluminum, even i n t h e molten s t a t e , and intera c t i o n d i d n o t occur. The rounded corners i n d i c a t e t h a t a l i q u i d phase i c examination v e r i f i e d t h i s . e n t a t 1175"F and ab ion, shock, o r When t h e oxide s k i n w a s b r o from mechanical t i n g occurred. Figures 6.9a and 6 how t h e appearwhere an angular drop of aluminum a l l o y k i n and become a t t a c h e d t o t h e Hastelloy N t u b imen w a s h e l d f o r 5 h r a t 1200"F. A metallographic s e c t i o n through t h e cone and tube revealed t h e moderate i n t e r a c t i o n shown i n F i g . 6 . 9 ~ . A t t e l y 0.010 i n . had occurred. t a c k t o a depth o f approx iments i n d i c a t e d some p o s s i b i l i t y of p e n e t r a t i o n Since t h e s e e of aluminum i n t o t h e WRE r a d i a t o r tubes, t h e y were inspected c a r e f u l l y apnel. The d i f f i c u l t y of t h i s task can f o r both d e n t s and a t t a c 6.10, a photograph of t h e f a c e of t h e radiator. The cing of t h e tubes ma& t h e use of mirrors and e l a b o r a t e ry. It i s estimated t h a t 80% of t h e s u r f a c e t h e t u b i n g w a s examined. Y-74028

120OOF

1225OF

1175OF

Ji90째F

1250째F

INCH

15 MINUTES AT TEMPERATURE

Fig. 6.8.

Hastelloy N--Alwninum Alloy Compatibility Test Specimens.

106 Y-74027

IY -74080

Fig. 6.9. ( a ) Specimen Where an Angular Drop of Aluminum Had Broken Through Its Skin and Become Attached t o a Hastelloy-N Tube. ( b ) Closeup of drop (lox); ( c ) metallographic s e c t i o n through cone and tube ( 5 O X ) .

A s polished.

Eight smears of aluminum were found on t h e air-inlet s i d e of t h e a t o r , none on t h e o u t l e t s i d e . No cone-shaped deposits of aluminum were discovered, although one small angular piece w a s found wedged between a lower tube and a h e a t e r . Three dents were n o t i c e d i n t h e o u t e r

107

Fig. 6.10.

Face of MSRE Radiator, Showing Close Packing of Tubes.

t u b i n g on t h e a i r - i n l e t s i d e , b u t no aluminum w a s d e t e c t e d i n t h e s e areas. It i s thought t h a t t h e dents r e s u l t e d f r o m small rocks , e t c which t h e blowers had dram i n a t an e a r l i e r d a t e .

The t u b e s on which aluminum w a s found were marked and subsequentlji cleaned. S t a i n l e s s s t e e l w o o l w a s used t o remove most of t h e aluminum from a d e p o s i t a r e a ; t h e n emery paper w a s employed. The r a d i a t o r w a s t h e n brushed thoroughly t o dislodge any p i e c e s of aluminum t h a t might have been missed during i n s p e c t i o n . A s a r e s u l t of t h i s i n v e s t i g a t i o n and cleanup procedure, it appears t h a t t h e r a d i a t o r system i s s a t i s f a c t o r y f o r f u r t h e r o p e r a t i o n . Actual adherence of t h e aluminum t o t h e t u b i n g w a s observed i n only a few c a s e s . I n s p e c t i o n and c l e a n i n g o f a c c e s s i b l e t u b e s a s s u r e d t h a t aluminum w a s r e moved from t h o s e most l i k e l y t o be contaminated. If i n t i m a t e c o n t a c t occurred i n s c a t t e r e d a r e a s , i n t e r a c t i o n does not appear t o be r a p i d . Longer time e f f e c t s a r e being s t u d i e d by v i s u a l and metallographic a n a l y s i s of specimens from t e s t s of d u r a t i o n up t o 1000 h r .

108 6.3

Evaluation of Graphite W . H. Cook

Work has continued on t h e e v a l u a t i o n of a n i s o t r o p i c and i s o t r o p i c grades of g r a p h i t e as p o t e n t i a l m a t e r i a l s f o r molten-salt breeder r e a c t o r s . 2 The MSRE g r a p h i t e p r o p e r t i e s a r e being used as a b a s i s f o r comparison. The needle-coke, a n i s o t r o p i c g r a p h i t e has t h e more d e s i r a b l e p r o p e r t i e s f o r excluding molten salts and gases b u t i s l e s s s t a b l e under i r r a d i a t i o n . Some i s o t r o p i c m a t e r i a l s show promise, b u t many of t h e i s o t r o p i c grades of g r a p h i t e t e n d t o be t o o amorphous f o r nuclear u s e . I s o t r o p i c grades of g r a p h i t e a r e new, and p a s t development has not been d i r e c t e d toward t h e production of m a t e r i a l having t h e low gas p e r m e a b i l i t i e s and small pore entrance diameters r e q u i r e d of g r a p h i t e f o r molten-salt breeder r e a c t o r s . Table 6 . 1 is a comparison of t h e p h y s i c a l p r o p e r t i e s of t h e various grades of g r a p h i t e . The s p e c i f i c r e s i s t a n c e s o f t h e s e i n d i c a t e t h a t grades CGB, CGB-LEI, 1425-64-1, and H-315 a r e f a i r l y w e l l g r a p h i t i z e d ; t h e r e s t a r e t o o amorphous. For i s o t r o p i c g r a p h i t e , we d e s i r e s p e c i f i c r e s i s tance l e s s t h a n 900 microhms em2 em-â&#x20AC;&#x2122;. The gas p e r m e a b i l i t i e s a r e a l l very high. We a r e seeking p e r m e a b i l i t i e s approaching lT7 cm2/sec. The pore entrance diameters a r e important i n t h a t (1)t h e y must be small enough t o prevent p e n e t r a t i o n by t h e nonwetting f l u o r i d e s a l t s and ( 2 ) t h e y must be grouped t o minimize t h e number of impregnations necessary t o f a b r i c a t e t h e base s t o c k i n t o a low-permeability g r a p h i t e . For t h e l a t t e r , it has been r e p o r t e d t h a t pore entrance diameters should The grades be l e s s t h a n 1 IJ- and be concentrated i n a narrow of g r a p h i t e shown i n Fig. 6.11 are f i n i s h e d grades r a t h e r t h a n base stocks, but only grades CGB, CGB-LB, and EP1924-1 appear amenable t o improvement by impregnation t r e a t m e n t s . The t h i r d grade had been a l ready r i l e d out because of i t s amorphous n a t u r e . The standard s a l t screening t e s t w a s made i n which 0.500-in.-diam by 1.500-in.-long specimens were exposed f o r 100 h r t o molten salt a t 1300Â°F under a 150-psig pressure. The r e s u l t s a r e shown i n Table 6.1. The MSRE grades CGB and CGB-LB a r e included f o r reference purposes. O f t h e new grades, only grade 1425-64-1 showed a pore s t r u c t u r e approaching t h e q u a l i t y of t h e MSRE g r a p h i t e . Work is i n progress t o o b t a i n a d d i t i o n a l a n i s o t r o p i c and i s o t r o p i c grades of g r a p h i t e with p r o p e r t i e s s u p e r i o r t o t h o s e of t h e MSRE g r a p h i t e and approaching t h o s e r e q u i r e d f o r t h e molten-salt breeder r e a c t o r s .

Table 6.1. Ccmparlson of various Physical Properties of Anisotropic Needle-Coke md Isotropic Grades of Graphite

Grade

%ape

Cross-section Dimensioiis (in.)

BuLk

Type

Density (g/cm3)

Helim Density

(g/cm3 1

Accessible

Porosity ($)a

Surface Psea

(n2/gP

Specific Resistarce (microim cmz ea-l)

I Ib

-c IC

Pemeability t o Eelim (cm’/sec )

E - d k Volme cf Graphite Filled with S a l t

($ Id

x 1cr4 CGB CG3-a

Bar ijar

1425-64-1 Pipe ii-315A Ps2e

EP-1924-1 Cylinder 2020 Block IICTE-sI12

Cylinjer

2x2

Neeae-coke

1 X 1.6

Needle-coke

3.6 OD X 2.5 ID 4.7 03 x 3.5 E

Needle-coke Isotropic

4.1 dim

Isotropic

4.1 X 4.1

Isotropic

1.83 1.90 1.71

Isotropic

1.8K

7.5 &Lam

1.84

2.03

1.86

2.12

1.83

1.31

13.7

Z2.4 9.2

2.04 2 .I4 2.02

11.7

1.35

0.462 0.171

0.2

613

1230

690

1215

4500 89 2600 24-30

0.5 7.I 13.5 14.6

04G0

4.0

535

0.4 (0.070.8)e

1130

L5.8 17.2

0.145 G .332 0.316

1760

$80 1395 1960

4.4

0.946

13C3

1813

8‘70

“‘The measurenents were made on C.250-in.-diam X l.c@O-in.-lorg specimens. bMeasure8 i n the direction of t h e ao a e s f o r needle-coke, anisotropic graphite; no s p e c i f i c directions indicated for isotropic graphite except tha-t Lreaswements were mxtually perpenac ular CMeasured in the a r e c - t i o n perpen&cular t o t h e ao axes f o r needle-coke, m i s o t r o p i c graphite; no specific direction i n a c a t e d for isotropic graph ‘ t e except that tvo measmements were mde %imtwere m . ~ t m l l yperpendicdar , ‘Evacuted specimens, 0,500 i n . dim X 1.500 hi. long, exposed f o r 100 hr t o molten salt a t 1300’F ard a pressure of 150 psig; E star:&:$ screexirg t e s t . e-b p r e g r a t i o n was not unifom; the v d ~ e sL i parefittheses ifidicate t h e r a g e o-bserved.

110

20 9

I O

0 30

005

003

0 0 2 001

PORE ENTRANCE DIAMETER ( p )

Fig, 6.11.* Comparison of t'ne D t s t r i b u t i o n s of t h e Pore Entrance Diameters â&#x201A;Źor Va.rious Grades of Graphite.

6.4 'The I n t e r n a l S t r e s s Problem i n Graphite Moderator Blocks C . R. Kennedy

One of -the major coilcerns i n t h e use of graphite-moderated r e a c t o r s i s the stress g e n e r a t i o n caused- by d i f f e r e r i t i a l growth. The s t r e s s gene r a t i o n i s moderated considerably and g e n e r a l l y maintained a t s a f e l e v e l s by the a b i l i t y of t h e g r a p h i t e t o creep under i r r a a a t i o n . The problem r e s o l v e s i t s e l f t o a determination o f the balance between t h e d . i f f e r e n t i a l growth r a t e t h a t produces s t r e s s and 51ne creep %hat red.uces s t r e s s . KLthough t h e c r e e p - r a t e coefficj-en%m y be such t h a t t h e stress J-eveI does n o t exceed t h e f r a c t u r e s t s e n o h , a second concern i s t h e a b i l i t y of the g r a p h i t e t o absorb t h e creep s t r a i n i n d e f i n i t e l y without f a i l u r e . C e r t a i n l y , a f a i l u r e c r i t e r i o n based- iupon t h e f r a c t u r e s t r e s s o f t h e m t e r i a l i s a c c u r a t e . Therefore, it i s o f g r e a t importance t o know Both t h e r e s t r a i n e d grow-l;h r a t e and t h e creep c o e f f i x i e n t f o r t h e m a t e r i a l under tlne opera-Ling conditions. Our purpose has been t o de'cemine t h e g e n e r a l creep behavior of g r a p h i t e under i r r a d i a t i o n . Creep experiments were performed ai; 700 and 1000Â°C f o r comparisoi? with t h e previous &&a5 ob-tained a t lower temperatures. The high-temp e r a t u r e experiments were again s i m i l a r t o tlie previous experiments i n

111 ORNL-DWG G G - 1 1 4 5 1

F i g . 6.12. E f f e c t of Tempera t u r e on the Creep C o e f f i c i e n t of Graphite Under I r r a d i a t i o n .

R-TYPE AGOT

200

600

400

800

1000

1200

1400

TEMPERATURE ("C)

t h a t cantilevered parabolic-hem ence was i n t h e use of four-zone a t u r e s . The number of specimens of t h e space requirements of t'ne

specimens were used.. The m i n d i f f e r furnaces t o o b t a i n t h e d e s i r e d temperw a s reduced from nine t o six because furnaces.

K e s u l t s from a l l c r e e p experiments performed from 150 t o 1000째C do demonstrate a g e n e r a l i z e d c r e e p behavior, as shown i n F i g . 6.12. This t y p e of behavior s t r o n g l y supports a C o t t r e l l model f o r i r r a d i a t i o n creep, which allows e x t r a p o l a t i o n of t h e s e data t o most r e a c t o r grades of g r a p h i t e . The C o t t r e l l model_ for i r r a d i a t i o n creep, as given by Anderson and Bishop,' i s

= Aj/C

Y '

where K = creep c o e f f i c i e n t ,

A = accomuiodation f a c t o r ,

7 cr

= s h e a r rate due t o a n i s o t r o p i c growth (G = y i e l d s t r e n g t h of t h e c r y s t a l l i t e s ,

- GalJ

and G a r e t'ne growth r a t e s i n t h e c and a d i r e c t i o n s . a

The s h e a r r a t e 7 of g r a p h i t e can be derived. from measurements r i d e on p y r o l y t i c g r a p h i t e s through e s t i m a t e s of p o l y c r y s t a l l i n e g r a p h i t e growth rates. The accommodation f a c t o r A p r i m a r i l y r e f l e c t i s t h e degree of accommodztion by microcracks and-,i n g e n e r a l , t h e v o i d volume i n t h e g r a p h i t e . It i s not n e c e s s a r i l y c o n s t a n t and is expected t o vary w i t h temperature and neutron exposure. The v a r i a t i o n of A w i t h temperature should not be v e r y l a r g e ; however, A should. e x h i b i t a r a t h e r s i g n i f i c a n t Increase as microcrack c l o s u r e occurs e The c l o s u r e of microcracks r e q u i r e s a dose of a p p r a x i m t e l y neutrons/cm2; t h u s tine value of A w i l l be e s s e n t i a l l y c o n s t a n t f o r a t least h a l f this dose. The value of

112 of t h e c r y s t a l l i t e s w i l l undoubtt h e y i e l d strengiih o r flow stress, rn YP The valine e d l y vary under i r r a d i a t i o n and wi.th iri*ad&,t;ion teinperatixe of cry, l i k e t h a t of A, w i l l not vary- w i t h temperakure, however, as sign i f i c a n t l y as 4, t h e shear rate a

'Yne c r e e p - r a t e c o e f f i c i e n t should t h e r e f o r e s t r o ~ i g l yreflect t h e v a r i a t i o n of 4 w i t h temperat8ure, This i s demonstratied i n F i g . 6.12, where t h e c r e e p - r a t e e o e f f i c i e x t exhib.j.ts a minimum around. 350째C. The c r e e p - r a t e c o e f f i c j - e n t K i s not exsckly p r o p o r t i o n a l t o -Lhe shear r a t e 7 because o f the v a r i a t i o n s of A and cry. 'Thevalue of A would be e s s e n t i a l l y independent o f t h e g r a p h i t e grade; t h u s t h e e f f e c t of cry on t h e c r e e p - r a t e c o e f f i c i e n t c a be ~ demonstxa'ced. by a camparison o f v-ari o u s grades a t t h e same temperature. This w a s demonstrated previously5 by comparing t h e modu?.m of e l a s t i c i t y of six grades of g r a p h i t e t o t h e i r c r e e p - r a t e c o e f f i c i e n t s a t LJlO"C. AlLhough "cis c o r r e l a t i o n strongly supports Eq. (l), or the C o t t r e l l model, f o r t h e creep o f g r a p h i t r , one g l a r i n g discrepancy i n t h e c o r r e l a t i o n i s tlie tes-t. :resu.lt, a t 1000째C f o r ,the CGB grade o f g r a p h i t e . It should be noted t h a t this pa.l-,icul.a.r m a t e r i a l demons-Lrated a oize-thlrd decrease i n i t s modulus of e l a s t i c i t y , which i s a l s o u n l i k e t h e behavior of p r e v i o u s l y tested. grades. This p a r t i c u l a r t e s t result r e q u i r e s conf-iming data. before s p e c i f i c conclus i o n s can be reached. One shoid-d recognize t h a t t h e C o t k r e l l model for c r e e p does not sugg e s t an ac'cual mechanism by which t h e g r a p h i t e defoxms pl.astical.1.y. It does d e s c r i b e t h e creep as a process o f continuous yiel.d.ing, which i s n o t thenmI.Ly a c t i v a t e d as the term creep g e n e r a l l y implies. &so, t h e m a n i f e s t a t i o n o f t h e c r e e p d e f o r m t i o n i s a c t u a l l y nothing more t h a n a s t r e s s -induced imbalance o f t h e i n t e r n a l s t r a i n i n g occurring i n all polyc r y s t a l l i n e g r a p h i t e s due t o a n i s o t r o p i c growth. This implies that; tile limit o f c r e e p deforiilation can be a s l a r g e as t h e internal- s t r a i n s t h a t musl; occ1.x 5.n p o l y c r y s t a l l i n e g r a p h i t e s i r r a d i a t e d without s t r e s s . Polyc r y s t a l l i n e g r a p h i t e c8n accommodate l6$ s h e a r s t r a i n and p o l y c r y s t a l l i n e carbons 160% s h e a r s t r a i n ' without a, 1.0s~of mc:hani.cal i n t e g r i t y . The obvious conclusion i s that, as long as t n e s t r e s s a c t i n g on t h e g r a p h i t e does not exceed t h e f r a c t u r e stress, toe g r a p h i t e wi1.l. continue t o absorb t h e creep d e f o m t i o n without loss o f mechani-cal i a t e g r i . t y .

6.5

Brazing of Graphite

S. M. Jones

. . I I .

J. Werner

The j o i n i n g of graphite t o s t r u c t - m a l me.ta1.s such as Hastel-1-oy N i s of prime i n t e r e s t i n advanced m o l t e n - s a l t r e a c t o r concepts. S t u d i e s a r e under way 'ca develop methods f o r jotni.-ng l a r g e graphite pipes t o Hastelloy N t u b e s h e e t s . Such j o i n t s w i l l be needed f o r t e s t assemblies and f o r t h e r e a c t o r c o r e .

The c u r r e n t studies have t w o primary o b j e c t i v e s : (I) t o devel-op a c o r r o s i o n - r e s i s t a n t b r a z i n g alloy for g r a p h i t e which does u o t s u f : f e r frc3m

113

t h e transmutation problem a s s o c i a t e d with t h e gold-containing a l l o y s and ing t r a n s i t i o n j o i n t s w i t h one or more m a ( 2 ) t o develop means f o r t e r i a l s having expansion f f i c i e n t s intermediate between those of t h e g r a p h i t e and t h e Hastelloy N .

Work w a s focused on t h e e v a l u a t i o n of an experimental precious-metali o n 60 Pd-35 Ni-5 C r (wt $1. T h i s a l l o y base a l l o y hav appears t o hav on for j o i n i n g g r a p h i t e t o t h e r e f r a c t o r y metal p o r t i o n s i t i o n p i e c e . Unfortunately, it e x h i b i t s r e l a e (Fig. 6.13a); however, t i v e l y poor f l i t s marginal b it as f o i l i n t h e j o i n t s of such a j o i n t a t low a t high mag(Fig. 6.1%). n i f i c a t i o n are 6.14a and 6.14b. The nee - l i k e carbides of F i g . 6.14a are c l e a r l y evident i n F i g . 6.L4b. The extensive d i f f u s i o n zone along t h e molybdenum+razing-alloy i n t e r f a c e i n F i g . 6.14a suggests t h a t considerable molybdenum w a s t a k e n i n t o s o l u t i o n i n t h e brazing a l l o y .

A s e r i e s of hite-to-molybdenum j o i n t s brazed w i t h t h i s palladiumnickel-chromium a l l o y preplaced i n t h e j o i n t were thermally c y c l e d t e n times between 200 and 700째C. Metallographic i n v e s t i g a t i o n i n d i c a t e d t h a t no d e t e r i o r a t i o n had occurred.

Small arc-melted b u t t o n s of o t h e r a l l o y s i n t h i s t e r n a r y b u t w i t h higher chromium c o n t e n t s , a r e being prepared i n a n e f f o r t t o improve wetting of g r a p h i t e without reducing t h e o v e r a l l j o i n t propert i e s . Alloys containing o t h e r c o r r o s i o n - r e s i s t a n t carbide formers, t h a t i s , niobium and molybdenum, are a l s o being prepared.

Two graphite-to-molybdenum-to-Hastelloy-Nt r a n s i t i o n j o i n t s w o i n t design reported previously. 8 s u c c e s s f u l l y brazed using t h e t a p e r e The 1-1/4-in. -OD b 3/16-in. - w a l l g r i t e tubing w a s joined t o t h e mo$) a l l o y preplaced i n t h e j o i n t ; lybdenum w i t h t h e Pd-35 N i - 5 C r copper was used t o braze t h e molybdenum t o t h e Hastelloy N. V i s u a l examination revealed no cracks, and m e t a l 1 i c examination t o f u r t h e r evaluate t h e j o i n t s .

Fig. 6. W . Graphite-to-Molybdenum J o i n t s Brazed w i t h 60 Pd-35 Ni-5 Cr (wt $) a t 1250째C i n Vacuum.

INCH

Y-75420

EEEOL-A

3 - ' i

115 6.6

Corrosion of Graphite-to-Metal Brazed J o i n t s

W. H. Cook

A s w a s d i s c u s s e d i n t h e previous s e c t i o n , some success has been obtained i n j o i n i n g small p i e c e s of g r a p h i t e t o metal by brazing t h e g r a p h i t e t o molybdenum and, i n t u r n , b r a z i n g t h e molybdenum t o H a s t e l l o y N.9J10 I n a d d i t i o n t o making a good j o i n t , t h e braze m u s t be resistant t o c o r r o s i o n by molten f l u o r i d e s a l t s . Corrosion of t h e b r a z i n g a l l o y i s being i n v e s t i g a t e d by exposing j o i n t s of grade CGB g r a p h i t e b r a z e d t o molybdenum t o s t a t i c LiF-BeF2 -ZrF4-ThF4-UF4s a l t s f o r 100, 1000, 5000, 10,000, and 20,000 h r a t 1300째F i n H a s t e l l o y N c a p s u l e s . The b r a z i n g a l l o y , 35 Ni-60 Pd-5 C r ( w t $1, w a s n o t a t t a c k e d by t h e s a l t during exposures f o r as long as 5000 hr. However, l a y e r s of m e t a l l i c - l i k e c r y s t a l s appeared p r e f e r e n t i a l l y on t h e brazing a l l o y i n t h e 1000- and 5000-hr t e s t s . The 10,000- and 20,000-hr exposures are s t i l l i n p r o g r e s s .

The method of f a b r i c a t i o n of t e s t specimens i s shown i n F i g . 6.15. The l a t e r a l s u r f a c e s of t h e machined p i e c e s were p o l i s h e d p r i o r t o c u t t i n g t h e p i e c e s i n t o 0.62-in.-long specimens. The m i c r o s t r u c t u r e s of t h e l e f t and r i g h t edges of t h e s i d e s ( t h e s i d e s a r e perpendicular t o t h e plane shown) of an untested b r a z e i n F i g . 6.16a show t h a t t h i s produces s t r a i g h t , smooth s i d e s s u i t a b l e f o r r e f e r e n c e s f o r determining t h e 66-11452

(b)

CGB GRAPH1

INCHES.

F i g . 6.15. Grade CGB Graphite Brazed t o Molybdenum with 35 Ni-60 Pd-5 C r (wt % ) . (a) A s brazed; (b) as machined i n t o t h r e e t e s t specimens. The l a t e r a l s u r f a c e s a r e polished.

116 PHOTO85277

(a)

0 hr

Fig. 6.16. Microstructures of the 35 Ni-65 Pd-5 Cr ( w t %) Brazing A l l o y Used to Join Grade CGB Graphite to Molybdenum. (a) A s brazed and (b, e , d) After Exposures to LiF-BeF2-ZrFq-ThF4-UF4 (70-23.6-5-1-0.4 m o l e % ) at l-300'~. The gr te was tilted during the brazing which produced the different thicknesses of braze in the sets of photomicrographs that show both edges of a specimen. Etch: 10% oxalic acid. 1 O O x .

Fig. 6.1'7. Microstructure of a Metallic-Like Deposit on the Graphite of the Graphite-Molybdenum Joint Exposed for 5000 hr to LiF-BeF2-ZrF4T1?F4-UF4 at 1

117 e x t e n t o f a t t a c k . For t h e metallographic examination, t h i s specimen and a l l o t h e r s were c u t i n t o halves perpendicular t o t h e i r 0.62-in. dimension, and t h e s e c u t s u r f a c e s were p o l i s h e d and photographed. This technique w a s used t o compare t h e c o n t r o l specimen w i t h t h o s e t e s t e d f o r 100, 1000, and 5000 h r (Fig. 6.16). There i s no microscopic e v i dence of a t t a c k on t h e b r a z e . Deposits approximately 0.5 and l m i l t h i c k are e v i d e n t on t h e s i d e s of t h e b r a z e s exposed f o r lOC0 and 5000 h r r e s p e c t i v e l y . These l a y e r s are c r y s t a l l i n e and m e t a l l i c i n appearance. They have not been i d e n t i f i e d . The chemical analyses of t h e s a l t from t h e 1000-hr t e s t d i d not d e t e c t any c o r r o s i o n products; t h e a n a l y s e s for t h e 5000-hr t e s t a r e i n p r o g r e s s .

I n t e r p r e t a t i o n of t h e 5000-hr t e s t i s f u r t h e r complicated by a t h i n m e t a l l i c - l i k e d e p o s i t on t h e g r a p h i t e . It i s u n l i k e t h e l a y e r s on t h e b r a z e a l l o y i n t h a t it does not e x h i b i t c r y s t a l l i n e f a c e s . The d e p o s i t w a s h e a v i e s t on t h e s i d e of t h e g r a p h i t e p a r a l l e l w i t h t h e brazed j o i n t . I t s m i c r o s t r u c t u r e i s shown i n F i g . 6.17. The i d e n t i f i c a t i o n of t h i s l a y e r i s being sought. It i s s u s p e c t e d that t h i s m y be C r 3 C 2 . I n previous t e s t s t h a t involved only s a l t , H a s t e l l o y N, and g r a p h i t e , t h e r e were no d e p o s i t s on t h e g r a p h i t e . The l o n g e r - t e r n t e s t s appear necessary t o e x p l a i n t h e cause of t h e s e d e p o s i t s . 6.7

Welding Development of Hastelloy N

H. E . McCoy

D. A. Canonico

Titanium and zirconium a d d i t i o n s t o H a s t e l l o y N appear t o improve t h e r e s i s t a n c e of t h e a l l o y t o high-temperature embrittlement i n a n i r radiation field. W e have made welds i n s e v e r a l experimental h e a t s t o e v a l u a t e t h e i n f l u e n c e of t h e s e a l l o y a d d i t i o n s on t h e w e l d a b i l i t y . Welds have been made i n 1/2-in. p l a t e s of Ni-12 Mo-7 ' Cr-0.05 C ( w t '$1 w i t h t i t a n i u m c o n t e n t s of 0.15, 0.27, 0.33, 0.45, and 0.55 w t $. These w e l d s appear t o be sound,. and t e s t specimens have been made f o r e v a l u a t i o n . Alloys c o n t a i n i n g Ni-12 Mo-'7 Cr-3.05 C (wt %) and e i t h e r 0.06 o r 0.43 w t % zirconium have a l s o been s t u d i e d . The a l l o y containing 0.06 w t % zirconium e x h i b i t e d e x t e n s i v e weld cracking. It was impossible t o g e t a complete pass i n t h e a l l o y c o n t a i n i n g 0.43% zirconium without a c r a c k propagating t h e e n t i r e l e n g t h of t h e p a s s . Some attempts have been made t o weld t h e s e h e a t s w i t h d i s s i m i l a r weld m e t a l . E f f e c t of I r r a d i a t i o n on t h e Mechanical P r o p e r t i e s of H a s t e l l o y N H. E. McCoy

The foremost o b j e c t i v e of t h i s e f f o r t has been t o determine t h e i n f l u e n c e of neutron i r r a d i a t i o n on t h e mechanical properties of t h e Hast e l l o y N used i n c o n s t r u c t i n g t h e MSm. We have u t i l i z e d p o s t i r r a d i a t i o n t e n s i l e t e s t s , i n - r e a c t o r creep-rupture t e s t s , and p o s t i r r a d i a t i o n creepr u p t u r e t e s t s t o e v a l u a t e t h e performance of s e v e r a l r e p r e s e n t a t i v e h e a t s of m a t e r i a l used i n t h e MSRE. P o r t i o n s of t h i s study have been r e p o r t e d previouslyl1-l4 and have been used i n s e t t i n g a minimum s a f e o p e r a t i n g

118 ORNL-OWG 66-5779R

-0

30 20

vroO

10'

102

RUPTURE LIFE (hr)

5065.

Fig. 6.18. Creep-Rupture P r o p e r t i e s of Hastelloy N a t 65OoC, Heat Numbers i n d i c a t e f r a c t u r e elongations.

l i f e f o r t h e MSM. One of t h e most i n t e r e s t i n g f i n d i n g s i n t h i s study i s i l l u s t r a t e d by t h e data i n F i g . 6.18. Although t h e rupture l i f e and d u c t i l i t y a r e both reduced by i r r a d i a t i o n , t h e data i n d i c a t e t h a t t h e r e may be a s t r e s s below which e s s e n t i a l l y no i r r a d i a t i o n damage OCCUTS. One of t h e c u r r e n t t h e o r i e s of high-temperature i r r a d i a t i o n damage p r e d i c t s t h i s type of behavior, s i n c e some minimum s t r e s s i s r e q u i r e d The t o allow t h e bubbles of transmuted helium t o grow without l i m i t . 1 5 existence of a s t r e s s below which one could design without concern f o r gross reductions i n d u c t i l i t y due t o neutron damage i s of extreme importance and needs t o be s t u d i e d f u r t h e r . The s u r v e i l l a n c e specimens were removed from t h e core of t h e MSRE a f t e r '7800 M w h r w i t h an e f f e c t i v e i n t e g r a t e d dose of about '7 X lo1'. So f a r a s neutron dose i s concerned, t h e s e specimens s h o u l d b e r e p r e s e n t a t i v e of t h e pressure v e s s e l a f t e r t h e r e a c t o r has operated about 150,000 Mwhr (equivalent t o 15,000 h r a t a power l e v e l of 10 Mw) The specimens have been disassembled, b u t t e s t i n g w i l l not begin u n t i l a f t e r examination with an o p t i c a l comparator t o s e p a r a t e t h e bent ones. Limited creep and t e n s i l e t e s t s w i l l be run t o determine whether t h e p r o p e r t i e s f a l l i n l i n e with those determined previously f o r material i r r a d i a t e d t o t h e same dose.

The second o b j e c t i v e of t h i s program has been t o understand t h e mechanism of t h e damage i n Hastelloy N and t o determine a means of making a b a s i c improvement i n i t s r e s i s t a n c e t o i r r a d i a t i o n damage. We have found t h a t t h e damage i s dependent on t h e thermal-neutron f l u x . T h i s i s i l l u s t r a t e d by t h e data i n Table 6.2. Specimens were exposed t o neutron environments of various energies, and it was found t h a t t h e damage w a s f a i r l y independent of fast dose and depended p r i m a r i l y on t h e thermal dose. It i s b e l i e v e d that t h e s p e c i f i c thermal-neutron r e a c t i o n i s that of t h e transmutation of '% t o helium.

119 Table 6.2.

T e n s i l e DuctLLity of H a s t e l l o y N (Heat 5045) a t 760째C

I-

7.1

0.002 min-'

6.2

12.0

Hence, t h e f i r s t approach t o t h e problem has been that of r e d u c i q F i g u r e 6.19 shows t h e p o s t i r r a d i a t i o n creep-rupture properbies of s e v e r a l a i r - m e l t e d h e a t s of Has-belloy N . The m a t e r i a l s contain between 20 and 40 ppm boron. The r u p t u r e d u c t i l . i t j . e s a r e given i n p a r e n t h e s e s . There seems t o bz l i t t l e e f f e c t of rirrad-iation tempera t u r e on the r u p t i x e l i f e or d u c t i l i t y , E'iguxe 6.20 shows t h e propert i e s of two vacu.imi-meL-Led h e a t s c o n t a i n i n g 7 ppm (247'7) anii 9 ppm. 51o:ron (65-552). When t h e m a t e r i a l s a r e i r r a d i a t e d a t a low temperature, t h e i r p r o p e r t i e s e x c e l t h o s e of t h e a i r - m e l t e d heats. When .these same heats are irradiated hot, t h e y e x h i b i t p r o p e r t i e s comparable w i t h t h o s e of t h e air-melted heats. Yhe boron l e v e l .

ORNL-DWG 66-(1453

Ln W Ln

HCAT NO,

ALLOY ING ELFIMFNT

0 21541

0 0.1

0 21546 A71542 A 21545 0 21543 m 65-551

W AND No TI Nb -

}

ANNEALED 100 h r AT 874OC PRIOR TO IRRADIATION

WORKED AT 871째C

IRRADIATED ar 650-c Q,h=3 5X1OZ0 nvf

1 I

1000

10,000

RUPTURE L I F E ( h r )

Fig. 6.19. I'ostirradj.a.1;rion Creep o f S e v e r a l Alloys a t 650째C. bers indica,te f r a c t u r e e l o n g a t i o n s .

Num-

120 ORNL-DWG

66-10882

II)

W m

E m

100 RUPTURE LIFE

1000

10,000

(hr)

Fig. 6.20. P o s t i r r a d i a t i o n Creep-3upture P r o p e r t i e s oY S e v e r a l Vacuum-Melted Heats o f H a s t e l l o y N a t 650°C Numbers i n d i c a t e f r a c t u r e elongations. I

S e v e r a l of t h e a l l o y s were i r r a d i a t e d to v a r i o u s Cioses, and t h e helium c o n t e n t w a s c a l c u l a t e d from tine dose and t h e o r i g i n a l boron cont e n t of t h e a l l o y . F i g u r e 6.21- shows t h e m p t v x e d u c t i l i t y i n a t e n s i l e t e s t a t 650°C and 0.002 in./min as a f u n c t i o n of helium c o n t e n t . There i s considerable d e v i a t i o n about t h e l i n e drawn, with some of it probably being s i g n i f i c a n t . The two vacimm-melted h e a t s (65-552 and 2477) a g a i n show lower d u c t i l i t i . e s when i r r a d i a t e d h o t . The two 101~ points f o r heat 4065 indj-cate a p o s s i b l e infl-uence of high i r r a d i a t i o n Leniperature on t h i s h e a t . However, t h e most important obse-rvation i s that, f o r a r e a sonable ’OB content and a reasonable l i f e t h e , t h e helium content will and LOs6 atom f r a c t i o n . The v a r i a t i o n i n d u c t i l i t y over be between this range of helium c o n t e n t s j.s only about 25%, a s s v m i w t h a t t n e l i n e drawn i s reasonably c o r r e c t A s i m i l a r p l o t i s shown i n F i g . 6.22 which r e l a t e s t h e helium p r o duced i n t h e a l l o y to t h e f r a c t u r e d u c t i l i t y . The l i n e drawn s e e m t o be r e p r e s e n t a t i v e of t h e higher-boron a i r - m e l t e d h e a t s (5065 e t c ) The vacuim-melted low-boron h e a t s (65-552 and 2477) e x h i b i t b e t t e r duct i l i t y if tiney a r e i r r a d i a t e d c o l d b u t a c t i m l l y have lower d u c t i l i t y when i r r a d i a t e d h o t . Sence, t h e r o l e of boron i n t h e s e a l l o y s i s not a t a l l c l e a r . We have not prepared a s e r i e s of a l l o y s where evei-ytlning e l s e has been h e l d c o n s t a n t except the boron c o n t e n t . It seems t h a t t h e v a r i a t i o n s i n composition and melting p r a c t i c e m u s t i n f l u e n c e t h e

121

0 -1 m9

ANNEALED 1 hr AT 1177'C PRIOR ro IRRADIATION TESTE0 AT 650 'C, 0002 m n - ' CLOSE0 POINTS COLD lRRAOlATlON OPEN POINT5 HOT IRRADIATION

U',

I ! l l l l ' l 10-8

lo-'

10-6

IO-^

He CONTENT ( a t o m f r a c t i o n )

!?rig. 6.21. Variakion of t h e P o s t i r r a d i a t i o n Tensi1.e Properties of S e v e r a l Heats of H a s t e l l o y N w i t h Heliim Content.

Id8

ORNL-DWG 6 6 - 1 0 8 8 0

I1 1

C L O S E D P O I N T S COLD IRRADIATION O P E N POINTS H O T 1,RRADIATION

-~ He C O N T E N T

(atom fraction)

V a r i a t i o n of P o s t i r r a d - i a t i o n Creep Ducti.1.ity o f H a s t e l l o y Fig. 6.22. w i t h Helium Content. Numbers indicate stress in ksi.

122 d i s t r i b u t i o n of boron o r t h e e f f e c t t h a t the transmuted helium has on t h e p r o p e r t i e s s o g r e a t l y t h a t t h e r o l e of boron p e r s e i s masked. The g r e a t 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 propert i e s of t h e vacuum-melted a l l o y s supports t h i s supposition. Although we have known for some time t h a t t h e d u c t i l i t y of a n irr a d i a t e d t e s t specimen v a r i e s g r e a t l y w i t h temperature, we have made e x t e n s i v e use of p o s t i r r a d i a t i o n t e n s i l e tests for screening purposes even when we were i n t e r e s t e d i n long-term a p p l i c a h i o n s F i g u r e 6.23 shows haw misleading t h i s approach can b e . e

The r u p t u r e d u c t i l i t y i n p o s t i r r a d i a t i o n t e n s i l e and c r e e p t e s t s

i s p l o t t e d t o i l l u s t r a t e t h e i n f l u e n c e of zirconium c o n t e n t on the

p r o p e r t i e s . '-me two sets of p o i n t s a t t h e l e f t were obtained by t e n s i l e 'The t r e n d t e s t s at, two d i f f e r e n t s t r a i n r a t e s (0.05 and 0.002 in./min). i s evident that t h e ductxLlity improves w i t h i n c r e a s i n g zirconium c o n t e n t a However, t h e d u c t i l i t y i n t h e c r e e p tests ( r e p r e s e n t e d by t h e p o i n t s a t t h e r i g h t ) shows no systematic dependence on t h e zirconium c o n t e n t . This mterial contained extremely high boron (approximately 200 ppm), and w e b e l i e v e t h a t t h e data do not warrant t h e conclusion t h a t zirconium 'has no b e n e f i c i a l i n f l u e n c e . The important p o i n t i s that t e n s i l e t e s t s may not be adequate even for screening purposes i n nickel-base alloys. The more expensive c r e e p t e s t nay be necessary.

46 44 12

-1

5i w e z

' 1 1

/ '

s w

0 0.01

0.4

4 io RUPTURE LUFE (hr)

400

4000

Fig. 6.23. I n f l u e n c e of Zirconi-m Content on .the P o s t i r r a d i a t i o n D u c t i l i t y of H a s t e l l o y N.

123 S e v e r a l small commercial melts have been procured and evaluated. The b a s i c a l l o y I s Ni-12 Mo-7 Cr-C).05 C , t h e red-uction in molybdenum c o n t e n t being made t o suppress second-phase formation. The aLloy ad.d.it i o n s i n v e s t i g a t e d include niobium, tw-gsten, and t i t a n i u m . To d a t e t h e s e all-oys liave been i n v e s t i g a t e d i n only one m e t a l l u r g i c a l state, LI.O$ c o l d working followed by 100 h r a t 871째C. This t r e a t m e n t produces a very f i n e g r a i n s i z e and probably does not result i n t h e optimum p r o p e r t i e s . F i g u r e 6.24 shows the 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 of s e v e r a l of t h e s e a,lloys a t 650째C. The very encouraging a l l o y i s No. 21545, which c o n t a i n s 0.5 w t $ t i t a n i u m . The r u p t u r e l i f e i s b e t t e r -tiian t h e o t h e r a l l o y s , b u t Yle r u p t u r e d u c t i l i t y i s far s u p e r i o r .

Figure 6.25 shows a compilation of a l l t h e i n - r e a c t o r c r e e p t e s t s

run on v a r i o u s h e a t s . All t h e data a r e contained i n a s c a t t e r band bounded by h e a t s 5065 and 5085. With few exceptions, a l l t h e h e a t s exh i b i t f r a c t u r e d u c t i l i t i e s of L t o 35, w i t h no systematic h e a t - t o - h e a t

v a r i a t i o n e v i d e n t . Three of t h e h e a t s l e n d support t o t h e i d e a t h a t t h e r e may be souie c r i t i c a l s t r e s s below which i r r a d i a t i o n clama,ge becomes minimal. One must f a c e t h e q u e s t i o n of why h e a t 21545 looks exc e p t i o n a l l y good i n p o s t i r r a d i a t i o n creep t e s t s (Fig. 6.24) and not i n i n - r e a c t o r creep t e s t s (Fig. 6 . 2 5 ) . With a c l o s e r exa,minatton, one s e e s t h a t t h e t e s t a t 21,000 p s i (Fig. 6.25) d i d n o t f a i l during t h e e x p e r i ment. 'This p o i n t i n d i c a t e s tha.1; t h e t h r e s h o l d s t r e s s for diwzage i n t h i s a l l o y may be h i g h e r t h a n t h a t f o r t h e o t h e r a l l o y s (approximately 15,000 p s i ) . Tnus t h e i n - r e a c t o r creep t e s t s do suggest t h a t t n e t i t a n i w n bearing alloy m y be s u p e r i o r . ORNL-DWG 66-1087

0.04

Fig. 6.24.

0.4

4 io RUPTURE TIME (hr)

400

P o s t i r r a d i a t i o n D u c t i l i t y of S e v e r a l All.oys a t 650째C.

124 ORNL-DWG

6 6 - 1 1473

1000

100

10,000

RUPTURE ILIFE ( h r )

Fig. 6.25. Comparison of In- pad Ex-Pile Creep Rupture P r o p e r t i e s of Eiastelloy N a-t 650"C

1800

LLJ

I-

1 01

ORNL-DWG 66-40878

P~~

IRRADIATION TEMPERATURF=650"C5 x 10'0nvf

UN I R RAD IATF D, STD H A S l t L L O Y N

01 0

-r

TEST TEM PERATUR E-650째C STRLSS=32,350 psi

04 05 06 07 TI CONTENT ( w t % )

- 1

Fig. 6.26. Influence of Titanium on t h e P o s - t i r r a d i a t i o n Creep Prope r t i e s of Hi-12 M o - 7 Cr-O.05 C. Numbers i n d i c a t e fracture elongations.

125 F i g u r e 6.26 shows t h e r e s u l t s of p o s t i r r a d i a t i o n c r e e p t e s t s on severa,l l a b o r a t o r y h e a t s c o n t a i n i n g v a r i o u s amounts of -Li-f;ani?un. All t h e a l l o y s are s u p e r i o r t o i r r a d i a t e d s t a n d a r d H a s t e l l o y N w i t h r e s p e c t t o both r u p t u r e ILfe and d u c t i l i t y . S e v e r a l of t h e a l l o y s e x h i b i t r u p t u r e l i v e s i n excess O S t h a t of uiirradia-Led I i a s t e l l o y N and ductil.i.t;i.es as high a s 10%. C h a r a c t e r i z a t i o n of J l a s t e l l o y N for S e r v i c e a t 982°C

- H.

E. McCoy

Since HasteLloy N i s being considered as t h e s t r u c t u r a l m a t e r i a l foi: a m o l t e n - s a l t d i s t i l l a t i o n v e s s e l , t h e Mechanical P r o p e r t i e s Group w a s asked to determine t h e c r e e p p r o p e r t i e s of t h i s a l l o y a t 982°C. The results of -this b r i e f s t u d y a r e presented, and s e v e r a l p o t e n t i a l . problems a s s o c i a t e d w i t h t h e use of H a s t e l l o y N at; such ai? eleva-Led Although t h e v e s s e l p r e s e n t l y being b u i l t temperature are p o i n t e d out w i l l be used only w i t h nonactive salts, i t ; i s anticiLpated t h a t a similar d i s t i l l a - t i o n a p p a r a t u s w i l l be an i n t e g r a l p a r t of a Molten-Salt Breeder Reactor. For t h i s reason t h e q u e s t i o n s concerning t h e use of Has-telloy N f o r t h i s a p p l i c a t i o n should b e resolved.. The creep-rupture p r o p e r t i e s of H a s t e l l o y N a r e w e l l docuniented'6 ' I 7 over tine temperature r a q e of 600 t o 800°C where it i s comrnonly used. Bowever, data a t 982°C were n o n e x i s t e n t , s i n c e tni.s is above t h e normal-

s e r v i c e temperature f o r t h i s a l l o y . The r e s i f i t s of a b r i e f creep-ruptuTe program imdertaken t o supply data at 982°C a r e shown i n Table 6.3. P l o t s of t h e s e scme data are shown i n F i g s . 6.27 t o 6.29. These data were obtained.. on t e c t specimens of a t y p i c a l h e a t of a i r - m e l t e d H a s t e l l o y N (heat 5065). The t e s t specimens were srm11. rods having a gage s e c t i o n 1. i n . long X 0.1.25 i n . i n diameter. All t e s t s were c a r r i e d out i n dead-weight c r e e p machines i u a i r . The creep p r o p e r t i e s shown i n F i g . 6.27 i n d i c a t e t h a t t h e s t r e s s e s t o produce r u p t u r e and- 5% s t r a i n i n 1000 h r a r e reasonably w e l l defined. Ifowever, t h e s t r e s s e s f o r l and 2% s t r a i n i n 1000 'hr a r e not d e f i n e d s u f f i c i e n t l y by experimental &-La. The minimum creep rake data i n F i g . 6.28 c o r r e l a t e v e r y w e l l , but t h e s e numbers a r e n o t v e r y useful f o r design purposes, s i n c e t h e minimmi creep r a t e only a p p l i e s dxring a smal-1 f r a c t i o n of t h e l i f e a-t a given s t r e s s . 'Pne p l o t of t h e d u c t i l i t y shown i n Fig. 6.29 e x h i b i t s a d u c t i l i t y minimum for t e s t specimens having r u p t u r e l i v e s over t h e approximate range o f 50 t o 200 hr. However, t h e minimum d u c t i l - i t y observed s t i l l i s s l i g h t l y i n excess of 20'$. The r e d u c t i o n i n area decreases r a p i d l y w i t h i n c r e a s i n g r u p t u r e l i f e t o a value of about 15%. 'The i n c r e a s e i n t'ne elongakion f o r l o n g r u p t u r e l i v e s i s t'nough-t, t o be a s s o c i a t e d w i t i i t h e v e r y e x t e n s i v e i n t e r g r a n u l a r cracking t h a t o c c u ~ s

T'ne specimen from t e s - t 5768 w a s examhied m e t a l l o g r a p h i c a l l y . The It w a s e x t e n t o f i n t e r g r a n u l a r cracking i s i l l u s t r a t e d by F i g . 6.30. a l s o noted t h a t t h e quankity of p r e c i p i t a t e p r e s e n t a f t e r t e s t i n g w a s much g r e a t e r t h a n t h a t p r e s e n t b e f o r e t e s t i n g . Figure 6.31 shows a t y p i c a l a r e a of t h i s h e a t of H a s t e l l o y N prior t o t e s t j - n g . Figure 6.32 shows t h e t e s t e d specimen. The p r e c i p i t a t e marked 'h" i s believed- t o be t h a t p r e s e n t i n t'ne s t a r t l i n g m a t e r i a l . Ti?e l a r g e r p r e c i p i t a t e , marked ''I3 I ' i s though-1; t o be induced. by t'ne the-rmal and mechanical h i s t o r y .

Table 6.3.

Creep P r o p e r t i e s of Xastelloy IY a t 982’C”

5768

5765b 5762b 5761 5763

5867 5868

2,000

3,000 4,000 6 , GOO

10,000 1,880

3,000

35 1

0.7 0.75 <0.1 35

‘7.6 2.0 1.3 0.2

72 25

185

33 11

3.2 0.5

165

495

117

10.5

1.9

407 154

644.9

0.0276

123.9 51.5

0.123 0.282

16.15 2.95

50.0

37.86

0.026

52.0

Heat 5065 t e s t e d i n t h e as-received condition (1/2 G r a t 1176°C m i 1 1 & m e a l ) . bTemperatme c o n t r o l not a d e q m t e a t start of t e s t .

13.4 15.4’7

48.44

0.031

157.9

16.22

22.36 21.88

1.65 9.0

520.8

41.50

22.22

36.57

15.6 15.6

fz,

127 20,000

10,000

5000

Fig. 6.27.

Creep-HupLure Prop-

erties of H a s t e l l o y N at, 982°C.

W U>

+ Tc

2000

1000

500 0.1

10 TlPAE ( h r )

io0

4000

i0,ooo

ORNL-DWG G G - 111155

5000 I

F i g . 6.2.8. M i n i m u m Creep Rate

vs Stress f o r H a s t e l l o y N at 982°C.

a “3

Ln W

+ Ln

2000

f000

0.01

O R U L DflG 66-11457

$? 40

a n

Ti Ill

k 30

30 g

w LT 3 n i-

0 t

20 F HASTELLO

10 100 RUPTURE TIME ( h r l

0 1000

0.1 1 MIN CREEP RATE ( % / h r )

128

Fig. 6.30. Photomicrograph of Hastelloy N Tested at 982째C and

2000 p s i .

Fig. 6.31. Photomicrograph of Hastelloy N, Heat 5065, in the AsReceived Condition.

129

Fig. 6.32. Photomicrographs of Hastelloy N Tested at 982째C and.

2000 p s i .

130 S t a i n i n g w i t h a KMnOh-NaOH s o l u t i o n i n d i c a t e d that t h e p r e c i p i t a t e s were of two d i f f e r e n t compositions. Although t h i s p r e c i p i t a t i o n does not appear t o impair t h e d u c t i l i t y a t 982OC, it remains t o be e s t a b l i s h e d whether t h e low-temperature d u c t i l i t y i s a f f e c t e d . Since Yne v e s s e l w5l.l be exposed t o numerous thermal c y c l e s , t h e high- and low-temperature d u c t i l i t i e s a r e botb of i n t e r e s t . The results of t h i s study are h a r d l y adequate f o r t h e design of a d i s t i l l a t i o n system that i s t o be a n i n t e g r a l p a r t of a r e a c t o r system. has shown t h e need for (1)s t r e n g t h data extending t o longer times, 2 t e s t s t o evaluate t h e i n f l u e n c e of t h e p r e c i p i t a t i o n on t'ne d u c t i l i t y , and ( 3 ) o x i d a t i o n data under c o n d i t i o n s of c o n s t a n t and c y c l i c temperatures *

st??

6.8

'Thermal Convection Loops

A. P. Litman

G. M. ToLson

We are continuing t o s t u d y t h e c o m p a t i b i l i t y of s t r u c t u r a l materials with f u e l s and c o o l a n t s of i n t e r e s t t o t h e Molten-Salt Reactor Program. N a t u r a l - c i r c u l a t i o n loops d e s c r i b e d previously" a r e used as t h e s t a n d a r d test in these studies. Currently, four loops a r e i n o p e r a t i o n . Three thermal-convection c i r c u i t s c o n t a i n i n g simulated MSIW f u e l s a l t and f a b r i c a t e d from e i t h e r Hast e l l o y N, t y p e 304 s t a i n l e s s steel, or Nb-l$ Z r a l l o y w i t h type 4.46 s t a i n less s t e e l e x t e r n a l cladding have operated f o r approximatel-y 4.5> 3.2, and 0.6 y e a r s r e s p e c t i v e l y . Operating c o n d i t i o n s f o r t h e loops a r e det a i l e d i n Table 6.4. The H a s t e l l o y N and type 304 stainless s t e e l loops have continued t o circulate s a l t without i n c i d e n t . Bowever, t h e r e f r a c t o r y - a l l o y c i r c u i t has shown some degradation of l a t e . This w a s e v i denced by t h e c o l d l e g g r a d u a l l y l o s i n g temperature d e s p i t e t h e a d d i t i o n of i n s u l a t i o n . It i s suspected that t h e s m a l l e r i n t e r n a l diameter of t h i s loop (0.3 i n . ) has c o n t r i b u t e d t o t h e o p e r a t i o n a l problems. The f o u r t h o p e r a t i n g loop (loop 10) i s f a b r i c a t e d from I h s t e l l o y N and c o n t a i n s a proposed secondary c o o l a n t (NdF-KF-BF3,48-3-40 mole 5 ) for t h e reference-design MSBR. This c i r c u i t has operated for over 3000 inr w i t h t h e h o t l e g a t 1125째F and a temperature d i f f e r e n t i a l of 265OF. During t h i s r e p o r t i n g period, a Croloy 9M loop (Loop 1 2 ) c i r c u l a t e d t h e proposed secondary MSBR coolant f o r 14-40hr, a f t e r which time it w a s s h u t down due t o plugging. X rays taken of t h e Loop d i s c l o s e d s p o t t y high-density regions i n t h e c o l d l e g . A few s u s p i c i o u s a r e a s were a l s o seen i n t h e h o t l e g . The l o o p p i p i n g and h e a t - t r a n s f e r f l u i d w i l l be s u b j e c t e d t o complete chemical and m e t a l l u r g i c a l a n a l y s i s .

A Croloy 9M (loop 8 ) n a t u r a l - c i r c u l a t i o n loop c o n t a i n i n g l e a d w i t h 230 ppm magnesium as an i n h i b i t o r plugged a f t e r o p e r a t i o n f o r 2950 h r . A s e c t i o n through t h e c o l d l e g i n t h e plugged region i s shown i n F i g . 6.33,. Examination of t h e loop components i s proceeding.

Table 6.4. T h e m l Convection Loop Operation Through September 3C, 1966

Hot - k g Specimens

Loop Material Hastelloy N Type 304 s t a i n l e s s s t e e l

None

T n e 446 s t a i n l e s s - s t e e l -

None

Hastelloy N

None

Croloy 9M

Croloy 9X

Croloy 9M

clad m - ~ $ Zr

Loop plugged on 9/26/66. b L o q plugged on 6/9/66.

iieat Transfer Medium LiF-BeF2 -ZrF4-W4-TkiF4 ('70-23-5-1-1 mole $1 Lir'-BeF 2 -ZrF 4-TJF4-'ThF4 (70-23-5-1-1 mole $1 LS-SeFz -ZrFq-ii.4

(65-29.1-5-0.9mole

NaF -KF -BF 3 (48-3-49mole %) pb 3 230 PPX %1

INaximwn

Time

(T1

Operated

1300

160

39,430

1250

180

28,125

1403

330

5,235

1125

265

3,110

1125

260

1,440a

1100

20G

2,950b

(hr1

P w P

132 PHOTO 73481

Fig. 6.33. Matching Halves of P o r t i o n of Cold Leg from a Croloy 9 M Loop Which C i r c u l a t e d Lead witin 230 ppm Magnesium its I n h i b i t o r for 2950 h r at 1100째F.

To date, a l l u n i n h i b i t e d l e a d systems c o n s t r u c t e d o f carbon, lowalloy, and s t a i n l e s s s t e e l s have tended t o plug due t o t h e formation of d e n d r i t i c c r y s t a l s of i r o n and chromium i n t h e c o l d regions of t h e loops. The h o t - l e g a t t a c k has c o n s i s t e d of uniform s u r f a c e removal w i t h i s o l a t e d p i t s extending t o a g r e a t e r depth. While Nb-l$ Z r a l l o y has e x h i b i t e d

no measurable h o t - l e g c o r r o s i o n during t e s t , niobium c r y s t a l s have been found i n the c o l d l e g of a loop which operated for 5000 'rrr a t 1400"F, All t h e s e f i n d i n g s a r e d i s c u s s e d i n d e t a i l i n a r e p o r t swnmarizing results t o d a t e on t h e c i r c - d a t i n g - l e a d loop program.20

Re f ereiic e s 1. M 87-92.

E ORNL-3872, pp.

G ORNL-3936, pp.

W. P. E t h e r l y e t a l . , Proc. U.N. I n t e r n . Conf. P e a c e f u l Uses A t . Energy, a d , Geneva, 1958, 3 389-401.

10743.

-9 89 1 10-11 4 . W . Watt, R. L, Bickerman, and L. W . G r a h a m , Engineering 1 (January 1960) 5. C . 3 . Kennedy, Metals and Ceramics Div. Ann. Progr. Rept. June 30,

-1965 ,

OXiL-3870, pp. 1 9 4 4 7 .

133

6. R . G. Anderson and J. F. I d . Bishop, " f i e g f f c c t of Neu-bran Irradiat i o n and 'I'herrzal- Cycling on Permanent Deformations i n Uranium Undcr Load, " pp 17-23 i n Uranium and Graphite, Monograph 27, The L n s t i t u t e of Metals, London, 1962.

7. J. C. Bokros and R. J. P r i c e , Radiation-Induced Dimensional Changes GA-6736 (November 1965). To be published i n t h e Journal of Applied Physics. 8" MsIi Program Semiann. Progr. Rept. Feb. 28, 1-966,ORNL-3936, p. 104* 41(51, 461-63 (1962). 9. R. G. Donnelly and G. M. Slaughter, Welding J-. -

10,

MSH Program Semiam. Progr. Rept. Feb. 28, 1366, OKNL-3936,pp.

101-4.

11. W. ii. I k r t i n and J. R . Weir, E f f e c t of Elevated Temperature Irradiat i o n on t h e S t r e n g t h and D u c t i l i t y of t h e Nickel-Base Alloy, Hastell o y N, ORNL-TM-1005 (February 1965). 12. 13.

W . R. MarLin and J. R. Weir, P o s t i r r a d i a t i o n Creep and S t r e s s Rupture P r o p e r t i e s of I a s t e l l o y N, ORYL-'TM-1515 (June 1966).

MSR Pr0gra.m Semiam. Progr. Rept. A u g . 31, 1965, ORNL-3872, pp. 94-

105.

14- MSR Program Semiann. Progr. Rept. Feb. 28, l.966, ORNL-3936, pp. 11121.

-(1>,74 (January 1966). 15 D. 13. Harries, J . B r i t . Nucl. Energy Soc 5 16. J. T. Venard, T e n s i l e and Creep P r o p e r t i e s of INOH-8 for the MoltenSalt Reactor Ekperiment, ORNL-TM-101'7 (February 1965). a

17.

R . W Svindeman, The Mechanical P r o p e r t i e s of INOR-8, (Jan. 10, 1961).

OEIIUL-2780

18. G. M. Adamson, Jr., et al., I n t e r i m Report on Corrosion by Zirconium Base F l u o r i d e s

, OKNL-2338 (Jan

3, 1961

19. MSR Program Semiann. Progr. Rept. A x . 31, 1965, OWL-3872, pp. $187. 20.

G . M. Tolson and A. Taboada, A Study of t h e Lead and Lead-Salt Corr o s i o n i n Thermal-Convection Loops, ORNL-TM-1437 ( A p r i l 1.966).

7.1

Chemistry of the MSRE

Behavior of Fuel and Coolant S a l t

- R.

E . Thoma

S e v e r a l refinements of a n a l y t i c a l rriethods were made during t h e lowpower o p e r a t i n g period of the MSRE which l e d u s t o b e l i e v e that, t h e composition and p u r i t y of t h e r e a c t o r s a l t s can be ascer-Lained a c c u r a t e l y and economically on a r o u t i n e basis.' Within t h e l a s t few months we have attempted t o confirm t h i s b e l i e f by demonstrating t h a t samples of t h e r e a c t o r s a l t s could be obtained and aual.yzed on a r o u t i n e b a s i s with t h e r e a c t o r operating a t f u l l power. I n a d d i t i o n we have sought t o e s t a b l i s h from t h e r e s u l t s a p r a c t i c a l optimal frequency of sampling. Comparisons of t h e c u r r e n t d a t a wi-Lii previous resul.ts i n d i c a t e t h a t t h e f u e l and coolant s a l t s have not undergone p e r c e p t i b l e composition change s i n c e they were f i r s t c i r c u l a t e d i n t h e r e a c t o r some 16 months ago. The conc e n t r a t i o n of corrosion products has not; increased appreciably i n these s a , l t s w i t h i n -LIE r e p o r t period. Fuel Salk Composition and P u r i t y . 'PJenty-five s c m p l e s of f u e l s a l t were removed from t h e MSIIE during full-power runs FP-5, -6, and -7 Tor composition a n a l y s i s . The r e s u l t s of t h e s e analyses, l i s t e d i n Tables 7.1 and 7.2, show c l e a r l y t h e chemical. s t a b i l i t y of t h e f u e l solution; it has maintained cons-Lant composition s i n c e it was c o n s t i t u t e d i n t h e r e a c t o r i n 1965. Structural-Metal I m p u r i t i e s . The Concentrations of s t r u c t u r a l - m e t a l c o r r o s i o n products found i n the MSRE: f u e l s a l t i n t h e period January t o August 1966 a r e compared with previous assays i n Table '7.3. Since chrom i u m i s t h e most chemically a c t i v e c o n s t i t u e n t of Hastelloy, a l l COTr o s i o n r e a c t i o n s should, on proceeding t o equilibrium, r e s u l t i n t h e production of C r F 2 . The e x t e n t of corrosion i n t h e MSR.5 i s c u r r e n t l y monitored by analyzing f o r t h e chromium content of t h e s a l t s . In i t s full-power operation during t h e period February t o J u l y 1966, t h e MS-, has behaved w e l l with r e s p e c t t o c o r r o s i o n chemistry; no appaLwit corr o s i o n has occurred within t h e fuel 01' coolant sys-kerns. We have concluded i n t h e p a s t t h a t corrosion might be influenced by t h e presence of a s m a l l . amount (perhaps approximate1.y 1%) of UF3 formed i n t h e LiFUF4 enriching s a l t during preparation. When present, W3 i s r e a d i l y oxidized t o UF4 i n r e a c t i o n with CrF2:

The presence of MoF4 o r MoF5 i n t h e fuel. s a l t , as i n f e r r e d from t h e r e s u l t s of r e c e n t exanljnations of s u r v e i l l a n c e specimens removed from t h e r e a c t o r core,3 i s puzzling i n connectton with t h e l i k e l i h o o d t h a t UF3 s t i l l remains i n t h e f u e l s a l t . The notable freedom from c o r r o s i o n during t h i s period t h e r e f o r e i s r e a s s u r i n g .

134

135

Results of MSRE Fuel S a l t Analyses, Runs FP-5, -6, and -7

Table 7.1.

Sample No.

Mwhr

FP5-1

26.5

FP6-2 FP6-5 FPG-6

FF6-7

180

FP6-8 FP6-9

FP6-10

FP6-3-1 FP6-13 FP6-14 FP6-15 FP6-16 FP6-17 FP6-19 FP7-1 FP7-3 FP'7-Lp FP7-6 FP7-7 FP7-8 FP7-10 FP7-11 FP7-12 FP7-14 FP7-16

1000

Concentration (wt Li

10.65 1.1 .43 10.45 10.45 10. 32 10.43 10.48 10.30 10.30 10.50 1.0"50 10.55 10.55 1-1-

2920

1 0 40 1.0.60 10 55 7-0.50 LO .60 10.55 1.0e 60 10.63 10.45 1-0.50 10.55 10.55 e

&626

6900 7823

6.53 6.22 6.37 6.46 6.41 6.49 6.66 6 .76 6.42 6.41 6.45 6.86 6.58 6.64. 6.88 6 .78 6.56 6.40 6.63 6.65 6.59 6.91. 7.00 6.65 6.50 6.71

11.45 10. 80 11.12 11.32 11.42 11.29 11.52

11.54

11.28 11.06 11.33 11.35 11.31 11.05 11.72 11.16

11.44

11.61 11.35 11"13 11.67 11.21 IS"22 11.04 11.26 11.60

4.622 4.605 4.625 4.647 4.655 4.684. 4.595 4.612 4.628 4.617 4.601 4.629 4.652 4.667 4.647 4.656 4.640 4.614 4 641 4.663 4.609 4.630 4.640 4.660 4.638

68 .18 68.97 69.85 68.56 69.6'7 68.90 68.92 68.81. '70.09 66.79 G8.18 68.1.8 67.88 68.26 69.1-0 69.26 68.24 67.82 69.22 69.60 67.8'7 68.20 69.48 68.44 68 .79 67.59

4.625

c 101.44 102.04 102.40 101.52 102.47 101.77 102.26 102 00 102.70 99.38 101.08 101.54 100.90 102.04 102.77 102.45 1 0 1.45 100.97 102.41 102.57 101.39 101.56 102 .78 101.27 1-01 .?6 101.08

aAS 237.003~.

The average concerltrations of the s t r u c t u r a l - m e t a l impuri.ties which have been found i n t h e MSFZ f u e l s a l t s i n c e t h e beginning of r e a c t o r operatrions a r e given i n Table 7.3. A n i n t e r e s t i n g t r e n d i s evident i n the above r e s u l t s . A s i m p u r i t i e s , i r o n and n i c k e l a r e presumed t o e x i s t as c o l l o i d a l l y dispersed m e t a l l i c p a r t i c l e s . The concentration of Tron has decreased slowly b u t s t e a d i l y during reactor operation, while n i c k e l analyses remained e s s e n t i a l l y cons t an.t

Oxide Analyses. Eight samples of MSRE f u e l were anal-yzed f o r oxide content, during t h e r e c e n t full-power o p e r a t i o n s . Detaj-ls of t h e procedures employed are given elsewhere.4 The average value of oxide concent r a t i o n w a s found to be 5 4 ppm, s i g n i f i c a n t l y lower t h a n t h a t found i n

136 Simmry of PEiU Fuel Composition Analyses

Table 7.2. -

__I_

Book

Component; Nominal.

FP4

YP5-7

FP4-7

63.36 i 0.567 30.65 k 0.583 5.15 i 0.116 0.825 0.011

62.20 i- Oe764 30.76 i 0.746 5.22 i. 0.129 0.822 f 0.0llb

63,29 2 0.721. 30.70 i 0.695 5.19 k 0.126 0.824 0,011

10.57. L 0.137 6.55 0.161 11,U 0.295

1 0 e S 4 i. 0.017 6.60 + 0.183 11.33 0.220 4.635 f 0.022b

10.52

Mole Percent

LiF

65 -00 29,17 5.00

BeF2 ZrF4

0.83

uF4

64.88 29.26 5.04 0.

Weight; Percent

1.0.95 6.32 10.97 4.73

Td i

Be Zr

a b

10.93 6.34 11.06 4. 64Ga

237.003 = 33,241

4.642 k 0.028

5 0.J-78 6.57 k Oa179 U.24 0.271 4-638 i 0.02.5

$ 235U. $ 235U.

'~7t

237.009 = 33.06 wt

Table 7.3.

Concentration of C r , %e, and N i i n MSRE Fuel S a l t

RUn

Number o f Sanipl-es

. I

Concentratioii (ppm3

FP-3

FP-4

FP-5,6

48 50

FP-7

154

131

-t

108

* 44 79 * 38

+- 6

19 20

5 4 i. 25

48 i 23

t h e zero-power experimen-Ls (95 ppni). Since f l u o r i n e can be evolved from frozen i r r a d i a t e d fuel., it was necessary t o consider t h e p o s s i b i l i t y t h a t oxide i s r e l e a s e d by the r e a c t i o n -1-

02-

22 00, +

2Irp'

Sample specimens were analyzed i n one i n s t a n c e af1;er minimum delay (approximately a 7-hi- i n t e r v a l between samp1.e removal t o â&#x201A;Źâ&#x201A;ŹFpurge) and i n another i n s t a n c e a f t e r a 48-hr delay. R e s u l t s of t h e two analyses were coincident w i t h i n experimental e r r o r . Although t h e minimum delay period i s probably not sui"ficient1y long t o allow any of t h e oxide t o be conv e r t e d t o oxygen, plans a r e under way t o t e s t t h e i n t r i n s i c c a p a b i l i t y of t h e method by standard a d d i t i o n s of oxides t o f u t u r e samples.4

137 Ta'ole 7.4. I s o t o p i c Composition of Uranium i-i? MSRE Fuel S a l t Specimens Sample

No *

FP2-10-13

F1 ' 6 14 FP6-19 Fp7 8 FP7-12 FP7-15

Mwhr

0 1000 2900

5000

7000

7600

I s o t o p i c composi-l;ion OS

235u

2 3 6 ~

0.356

33.716

0.145

0.345

33 "44.4.

0.352

33a 400

234u

0.352

0.349

0.347

33.534

33.329 33.161

0.144 0.151 0.163 0.174 0.177

( T J ~$)

2 3 8 ~

65.783

65 970 66.060 66 085 66 148 I

66 315 e

I s o t o p i c Analysis o f U r a i i i i i n . Variations i i 7 t h e r e l a t i v e concent r a t i o n s of uranium i s o t o p e s i n t h e MSRE fuel. a r e d.etermined on a regul.ai: b z s i s by m a s s spectrometric a n a l y s i s . 5 A surmary of t h e i s o t o p i c analyses of t h e MSIU f u e l i s given i n Table 7.4, which shows q u a l i t a t i v e evidence of 235U burnup and ingrowth of 236U. The l i m i t of experimental accuracy (kc). 1% of i n d i v i d u a l v a l u e s ) ;znd tile low bur1iu.p f r a c t i o n (approxi:m.a,tel~I$) render t h e c u r r e n t values o f l i t b l e use for a c c u r a t e cal.culat;ion of K5RE power l e v e l s a t p r e s e n t . It i s a n t i c i p a t e d 'cha-i; a s a grea-ter f m c t i o n of 2 3 5 ~i s consimed., such det,erminations wi1.1. assume g r e a t e r s i g n i f i c a n c e i n corroborating burnup coiriputa-Lioizs which a r e based on performance data.

Coolant S a l t Composi-tion. Coolan-t sal-'i w a s c i r c u l a t e d i - n t h e MSHE f o r some 1200 hr during t h e prenuclear t e s t period. Since f l u s h and coolant s a l t s were siip-plj-etl from t h e s a m e r e s e r v o i r , t h e coolant s a l t w a s analyzed. c h i r h g t h i s per?-od only f o r i m p u r i t i e s . A t t h e end of prenuclear t e s t i n g , concentrations of t h e stru-ctural-jizetal i m p u r i t i e s , C r , Fe, and N i , were e s t a b l i s h e d t o be approximate1.y 30, 90, and 7 ppn, i-espectivel.y, wh.ich a r e remarkably low considering that t h e c i r c u i t had no-t been f l u s h e d prevliousIIy w i t h molten salt The :resulLs of spectroc?nemri.cal.ana!,yse s made a t t h a t tirne showed t h a t no s i gnifi.cant amounts of' add.itiona?_i m p u r i t i e s were iiitrodii.ced during t h i s period. As t h e r e a c t o r was brought t o f - u l l power e a r l y i n 1956, coolant sal.%was again circul.ateil, sampled r e g u l a r l y , and s u b j e c t e d t o compositional and i m pu,r.i-t,y aiialysis %he r e s u l t s obtained from t h e s e analyses a r e given i n Table 7.5. I

I n a d d i t i o n t o t h e components, c o o l a d c salt w a s analyzed for., arid found f r e e o f , zirconium by wet chemical and spectrochemical methods. The intention was t o confirm t h a t no firel.. s a l t had been transfemed. t o t h e coolant c i - r c u i t

Analyses of coolant salts a r e conducted i n t h e General Analysis h.horatory of t h e ORNL Anal.yt,ical Chemistry Division, w h i l e those f o r t h e fuel. are obtained from t h e General. Hot Analyses 12.bor'atory of tha-t;

138

CP4-1 CP4-2 CP4-3 CP4-4 CP4-5 CP4-6 CP5-1 CP5-2 CP5-3

CP5-4 CP5-5 CP5-6 CP5-7

CP5- 8 CP5-9 CP5-10 CP5- 1.1 CP5-12 CP5-13 CP6-1 CP6-2 CPb-3 CP6-4 CP6-5 CP6-6 CP7-I" CP7-2 CP7-3 CP7-4

Average

1.1 59

67 180 229

855

8.91

76.70

99.37

14,.20

8.87

76.80

99.87

53 50

8.85 13 86 8.55 13.82 12.76 10 51 13.00 9.17 9.15 12.60 13 01 10.06 13.17 9.49 12.70 10 22 9.43 12"77 9.59 12 97 9,GI. 12.92 9.74 12.75 13.10 9.98 13,09 9.73 12.76 9.56 9.13 12.82 9.63 12.76 1-2.70 9.79 9.65 13.64 8.72 9.88 12.16 12.39 1.0.24

76.7 76.6 76.04 '16. 8 76.7 'I?.2 76.4 77.2 76.7 76.9 76.4 '76.4 76.2 76.1 76.4 76.8 76.0 74.8 74.1 74.65

99.441

13.03 0.46 13.94

76.16 98.69 0.83 '76,82 100.00

1358

3135 3462

1-3.78

Standard deviation Nomiiml %rFc,

9.46 0.49 9.24

74.5 74.8

98.97

99.31 98.97 98.45 100.27 99.06 loo.12 98.90 99.46 98 93 38.89 99,38 98.92 98.64 98.75 98.39 97.29 97.01 96.54 97.43

83 41 46

5 <2

46 57 35 119 42 87 20 100 24 112 29 36 32 4.4, 33 31 36 47 44 57 32 73 30 43 38 28 45 76 57 68 20 57 28 37 32 60 31 51 51 80 36

58 27

<5 <5 37 24 20 <lo <lo 64 14

28 8 <2

130 1-85

38 150 110 6.5 <20 1.20 260 1-71 7135

<2 53 8

<20 < 20

<20

9 47

<20

1-62

< 20

15 6 6 <2 <2

210 210 135 <40 <20 300 <145

16 17

107 79

method.

division. It is apparent from the contrast of material balances shown in Tables 7.1 and 7.5 that minor differences in analytical. procedures are employed. These differences were appraised with respect to their possible influence on compositional analysis and were found to be insignificant, since compositional analysis is computed f r o m cation assays without; use of the â&#x201A;Ź l u o r i d e values.

139 On t h e b a s i s of t h e a n a l y t i c a l data l i s t e d i n Table 7.5, t h e p r e s e n t composition of t h e c o o l a n t sal-t i s 7LiF-BeF2 (63.93-36.07 mole $), p r a c t i c a l l y i d e n t i c a l w i t h values obtained i n e a r l i e r anal.yses6 of tine The unresolved d i s p a r l t y between the f l u s h s a l t (63.80-36.20 mole $) design composition (66.0 L 0.25-34.0 rtr. 0.25 mole $) and t h a t found by chemical. a n a l y s i s continued t o be a puzzl.i.ng m a t t e r . %ne e x c e l l e n t r e p r o d i i c i b i l i t y o r chemical analyses throughout t h e o p e r a t i o n a l p e r i o d of t h e &!ERE i s , how-ever,of s i g n i f i c a n c e i n a f f o r d i n g t h e opportunity f o r chemical t r e n d s t o be observed.

7.2

P h v s i c a l Chemistry- o f F l u o r i d e Melts

V i s c o s i t y and Density of Molten Be??yllium F l u o r i d e

Tlie v i s c o s i t y of molten BeF2 5'73 t o 985'C usiilg Brookfield LVT p e r a t u r e range, t h e v i s c o s i t y , 7 , about 10% g r e a t e r t h a n previously

S. Cantor and

. T.

M0yniha.n.x-

was measured over the temperature r m g e and IBFSX viscometers. I n t h i s temv a r i e d from l o t o l o 6 p o i s e s and was reported.'

'The p l o t of log '1 vs l/T("K) showed oiily s l i g h t c u r v a t u r e . A l e a s t squares f i t of t h e d a t a t o an equation q u a d r a t i c i n l / T y i e l d e d t h e foll.owing:

l o g 7 ( p o i s e s ) = -8.119

1.1.494 x 1 0'' T( O K )

6.39 x LO5 p.

s t a n d a r d e r r o r i n log 7 = 0.013. This corresponds t o an apparent i n c r e a s e i n t h e a c t i v a t i o n energy f o r viscous flow from 57.3 kcal/mole a t 985째C -Lo 59.6 kcal./mol.e a t 575째C. These a r e r e l a t i v e l y s m a l l activa.t;ioii energy changes, and t h u s t h e temperature dependence of .tile v i s c o s i t y o f BeF2 i s b a s i c a l l y Arrhenius over t h e range (10 t o LO6 p o i s e s ) covered i n t h i s i n v e s t i g a t Ton. Density measurernents were attempted v i a t h e Archimedean. method, by determining t h e apparent l o s s of weight of a platinum s i n k e r when i m mersed i n iiiolten Be?'*. I n such. viscous m e l t s , t h e balance i s extremely slow i n coiiij.ng t o eqiiilibrium; hence, t h e method8 o f e x t r a p o l a t i n g t o zero v e l o c i t y t h e plots o f rate of ascent or descent of t h e s i n k e r under v a r i o u s balance loads (measured by timing t h e t r a v e l . of t h e balance p o i n t e r ) was used t o determine t h e equilibriui1i weight of t h e s i n k e r i n t h e me2.t. I n none o f t h e f o u r attemp-ts t o measure t h e BeFz d e n s i t y w a s it p o s s i b l e t o e l i m i n a t e t h e few sinal1 bubbles t h a t adhered t o t h e s i n k e r . 'The lsiioyant e f f e c t of tine bubbles l e a d s t o low va.Sues of t h e apparent weigh-t of t h e s i n k e r and, hence, t o high values OT the d e n s i t y . *Chemistry Oepartment, California, S t a t e College a t Los Angeles; summer p a r t i c i p a n t , 1966.

140 I f a surface t e n s i o n o f 200 dynes/cm. i s assixned foi- BeFz, t h e besl; of oix- d e n s i t y r e s u i t s y i e l d e d a value of l.96 i- 0.01 g/cm3 f o r BeF2 a t 850째C. This r e s u l t , ~ilustbe considered only as an upper l i m i - t ; to t h e real.. BeF2 density, b u t -it may be compared t o t h e value of 1.95 1- 0.01 g/cm3 a-L 800째C r e p o r t e d by MacKenzieg and to a va1.w of 1.963 g/cm3 measured f o r t h e Bey2 glass a t room temperature. These resul'is suggest t h a t t h e the.nfla1. expansion c o e f f i c i e n t of liquid. ReF2 i s q u i t e s m a l l .

T r a n s p i r a t i o n Studies in S u n ~ o r tof t h e Vacinrm D i s t i l l a t i o n Process S. Cantor

To determine t h e equilibrium vapor s e p a r a t i o n of r a r e - e a r t h f i s s i o n producks from N3;R c a r r i e r s a l t s , a series of vapor. pressures have been meas-ured by t h e trstnspira-Lioii ( i.e gas-entrainment ) me-Lhod. The melts These concentrations were composed of 87.5-11.9-0.6mole $ -IiF-BeFz-IaF3. of ELF and BeF2 a r e approximately those expected i n t h e sti7.1 pot of t h e vacuun d i s t i l l a t i o n process, b u t t h e lanthmum c o n e e n t m t i o n i s many tlmes g r e a t e r t h a n would be permitted. as -todial r a r e - e a r t h concentration i n t h e stil.l-a This high concentration of lanthanum i n t h e me1.t w a s r e q p i r e d i n order t o give lanthanum concentrations i n t h e vapor t h a t were high enough t o analyze.

Measurements were c a r r i e d out i n t h e temperature in-Lervsl 1000 t o 1062OC;; d r y ar on, t h e e n t r a i n i n g gas, f7.owed over each melt a t t h e r a t e S a l t vapor, condensing i n a nickel tube, w a s anao f about 30 ern /inin.

lyzed by spectrochemical an3 neutron a c t i v a t i o n methods. 'The l a t t e r method gave higher, more c o n s i s t e n t , and probably more r e l i a b l e lanthanuxi analyses. To date, t h e more c o n s i s t e n t r e s u l t s have been obtained a t only two temperatures: Temperatu-re

("c)

Decontamination Factor" f o r Lanthanum

1000

910

1.028

1150

Defined as (mole f r a c t i o n o f lanthanum i n liquid)/(mole f r a c t i o n of lanthanum i n condensed vapor). A t s i x o-Lher ternperatures, t r a n s p i r a t i o n p r e s s u r e measurements y i e l d e d much higher (up t o 7 3 0 0 ) decontamination f a c t o r s ; however, t h e s e d e t e r minations e i t h e r were based on i n s u f f i c i e n t sample for proper a n a l y s i s o r e l s e du-plicate analyses gave widely d i f f e r e n t r e s u l t s . It did appear t h a t the higher t h e temperature, t h e higher t h e decontamination f a c t o r s .

Although much more study i s r e q u i r e d b e f o r e t h e vacuum d i s t i l l a t i o n process can be show1 t o be p r a c t i c a l , it seems t h a t decontamination fac'tors close t o 1000 can probably be demonstrated.

1.41 Estimated Thermophysical P r o p e r t i e s or MSECR Coolarit S a l t

S. Cantor

Prel.iminary phase equ.i.1ibriu.m s t u d i e s have i n d i c a t e d t h a t a mixture c o n t a i n i n g 4-’7.5 mole % NaF, 48 mole $ EF3, and 4.5 mole $ KF (melting p o i n t , 365°C) i s s u f f i c i e n t l y l o w melting f o r use as t h e second-ary coolant oi” tlie M,iSRR. To a i d i n v e s t i g a t i o n s (such a,r, h e a t - t r a n s f e r s t u d i e s ) that w i l l l i k e l y be c a r r i e d out i n t h e near f u t u r e , e s t i m a t e s a r e given below f o r some thermophysical p r o p e r t i e s o f t h i s mixture. It i s a n t i c i p a t e d t h a t c e r t a i n thei-mophysical p r o p e r t i e s w i . 1 1 soon be measured. The e s t i rriates given h e r e i n a r e meant t o s e m e u n t i l such measu-rements can be made. Measurements of d i s s o c i a t i o n e q u i l i b r i a have shown t h a t XU?,+1o i s much more stab3.e t h a n NaBF4.I’ The composition given i n t h e first paragraph can be r e c a s t as a mixture of Pluoroborates whose conqosition i s ( i n mole %): NaIBF,:, 83.65; K3F4, 8.65; and NaF, ‘7.7. Thri.s r e c a s t f o r m i s u s e f u l because it permits e s t i m a t e s of p r o p e r t i e s -iobe made i n ternis of components which a r e a l l molten ( o r supercooled I.iquids) i n . t h e ternp e r a t u r e range of i n t e r e s t (UF3 .i.s a gas i n t h i s temperature r a n g e ) .

Vapor Pressures. These were estlirnakd by assuming (I) t h a t t h e f1,uoroborate mixture behaves i n accordance with Rao1LI.t’~l a w and ( 2 ) t h a t t h e only vapor s p e c i e s i s RF3. Since t h e d i s s o c i a t i o n p r e s s u r e of NaBF4 11 i s many ?;i.%iies g r e a t e r t h a n t h a t of ISBFL~,” then, given t h e two assixnpt i o n s , t h e t o t a l vapor pressiire P may be expressed a s

i s t h e d i s s o c i a t i o n p r e s s u r e ( i n mill.irneters) of pure N a W 4 . where F0 N a m /+ From t h e log P vs l / T equation for pure NaBF/,,”- the temperature dependence of t h e proposed lGi3R coolant i s e a s i l y derived and i s gjvcn by log P ( m )

6 . 5 1 - 3650/T(”K)

By a p p r o p r i a t e s u b s t i t u t i o n i n E q . Table 7 .G.

(2)

(2), Table 1;7.6 w a s generated.

Estimated Vapor Pressure of Proposed MSBR Cool.ant S a l t

370 (lowest p o s s i b l e txinperature i n coolant c i r c u i t )

454 (mean temperature o f cool.ant going t o h e a t exchanger)

607 ( h i g h e s t normal o p e r a t i n g temperature )

6.8

27 229

142 Density. The l i q u i d d e n s i t i e s of t h e fluoroboratus have no-t as y e t -~ been ineasll?-ed.. For an e s t i m a t e of t h e d e n s i t y at 4 5 4 ! , " C , t h e following assuinp-Lioiis were made : 1. The f l u o r o b o m t e !i,Ixti~rei s additrive with r e s p e c t t o l i q u i d moI.ar ' 7

volumes of t h e components.

The i-noI.ar volumes of 3.iquid NaYF4"" and TKBF412 are l . 2 times t h e x-ray molar volumes of t h e r e s p e c t l v e s o l i d s .

The mol-a.1- v-olune o f supercooled l i q u i d NaF a t 4-5A째C can be obt a i n e d by extrapol.ntion of the sta1)I.e liquid- val.ues a-3

~ r o i i ithese tliree assumptions a value of 2 . 1 g/cm3 i s c a l c u l a t e i l as the density of -the c o o l a u t a-L454째C. T11j.s d e n s i t y is probably u n c e r t a i n

by 10%. Because expami-on c o e f f i c i e n t s of f l u o r o b o r a t e s a r e unknowj, estimations o f t h e temperature c o e f f i c i e n t of densri'iy woiild be p:remature a-Lthis time

-.S p e c i f i c Heat. By u s i n g the n11.e14' t h a t each gram-atom of' a fluo r i d e mixture c o n t r i b u t e s about 8 cal/OC to t h e molar hea.t* capac:i.ty, t h e But molar heat c a p a c i t y of t h e coolant equals approximately 4% cal/"C. s i n c e t h e coolant contains the complex i o n [BF4]lcy some of t h e oscli.11.ational degrees of freedom of t h e i n d i v i d u a l atonis a r e l o s t ; ny gpess i s tlia"i t h i s l o s s amounts t o about 7 cal./"C. Thus, t h e estimatc?il s p e c i f i c heat i s 4 1 cal/"C divided by t h e molar weight of t h e c o o l a n t , 2-06 g, or about 0.4 c a l g-' ("C)"". This e s t i m a t e i s probably good to +25$.

Viscosity. The v i s c o s i t y of NaBFr, w a s measured'* somewhat crudely a t two temperatures. The r e s u l t s were 7 f. 2 c e n t i p- o i s e s at 466째C and. 14 rf 3 c e n t i p o i s e s a t /+36"C. Since t h e coolant i s predoninantly NaBF4, t h e s e rough values can serve as a guic1.e Lo viscostty u.n-til finthe-*.experimental values become a v a i l a b l e .

7.3.

Separation i n Molten Fluorides

E x t r a c t i o n of Rare Earths from Molten F h o r i d e s intm Molten Metals J. H. Shaffer, F. PI. Blankeflship, and W. R . Crimes

This experimental program envisions a 1iquid-liqu.id e x t r a c t i o n process f o r removing r a r e - e a r t h f i s s i o n products from t h e f u e l solvent

of t h e reference-design MSBR and a s i m i l a r back-extract,lon process f o r coucen-ti-a'iing them i n a second salt nzi..xtu>-e f o r di-sposal or fu.rther u t i l i z a t i o n . This process i s ari al.termative t o d i s t i l l a - t i o n and l i k e t h e d i s t i l l a t i o n process would follow removal of t h e uranium by t h e f I-uoride v o l a t i l i t y process. The resul.ts of grevious experiments have showri t h a t a mixture of bismuth containing 0.02 mole f r a c t i o n of l i t h i u m m e t a l s u f f i c e d f o r removing e s s e n t i a l l y a l l cerium, lanthanum, and neodymium and s u b s t a n t i a l q u a n t i t i e s of samarium and europium from a mixture of LiF-BeF2 (66-34 mole $I) .16 'The second phase of the reprocessing

143 method v o u l d t h e n involve t h e back e x t r a c t i o n of r a r e e a r t h s from t h e molten m e t a l inixtisre i n t o another s a l t mixture. Hydrofluorination of such a two-liquid-phase mixture should be very e f f e c t i v e f o r t h i s s t e p , b u t -the o v e r a l l proccss wo11l.d a l s o r e s u l t i n t h e removal of Some l i t h i u m from t h e fuel. Si-nce i s o t o p i c a l l y pure 7Li.. i s used i n t h e Yuel, the cons e r v a t i o n of t h i s m a t e r i a l i s of economic importance. According t o t h e experimental data, t h e removal of 1 g of neodymium would r e s u l t i n t h e l o s s of about 2.2 g of l i t h i u m . However, material balances on experiments i n which l i t h i u m w a s used as t h e reducing agent showed t h a t only 25 t o 50% of t h e l i t h i u m added to the e x t r a c t i o n system was found as a rlissolved component; of t h e mctal phase The qii.anti.ty of l i t l i i u r r r e q u i r e d f o r t h e s t o i c h i o m e t r i c reduction o f rare-ea]-th f l u o r i d e s was n e g l i g i b l e by cornpaxison. Thei-efore, a d d . i t i o n a l s t u d i e s of t h e behavior of l i t h i u m metal i n t h e e x t r a c t i o n system have been conducted. e

Duplicate experiments dea1.t with t h e m a t e r i a l balance o f lithiurn i n bismuth i n the ahsence of a s a l t phase. A s i n previous experiments, aboiit 2.35 kg of b i s m t h was contained i n ].ow-carbon s t e e l at 600°C. F i l t e r e d samples of t h e moliien metal were taken a f t e r each incremental. a d d i t i o n of 1 i t h j . m m e t a l t o t h e systems and during p r o l ~ m g e deqiuilibration periods (1-00h r ) during which one mixture wa.s maintained under s - t a t i c helium am1 t h e second vas sparged with dry helium. ‘Foe r e s u l t s OY spect r o g r a p h i c analyses of t h e s e sxmpl-es showed t h a . t , as 1j.thiii.m was added, its concentration i n each v e s s e l i n c r e a s e d i n amounts which corresponded t o abou-t ‘15 t o 80% of t h e amou.nt, added t o each system. Zowever, upon standing: t h e concentration of l i - t h r i u t n in each v e s s e l bec.<ameconstant a t values which corresponded, very n e a r l y , ’io tile amoiint of l i t h i u m added. These expel-imen-t,s iI.l.ustrate d the s t a b i l i t y of l i t h i u r n - b i smrtut’n mixtures coi-1-tained i n low-carbon s t e e l equipment and ind5.cated that, t h e rate of d i s s o l u t i o n of l i t h i u m i n t o bisoiuti? i n t h e e x t r a c Lion syst,ems was somewhat slower than a n t i c i p a t e d . The foregoing r e s u l t s showed t h a t the unexplained li.th.iurn l o s s e s were not a t t r i b u t a b l e -to t h e a n a l y t i c a l procedure nor t o the behavior of l i t h i u m i n the molten metal phase o f t h e extrac-Lion systems. Accordingly, t h e next phase of tln.i.s experimeiitial s e r i e s was a.n examination or t h e e f f e c t of t h e salt phase on t h e c o n c e n t r a t i o n of l i - t h i u m Ln t h e metal phase. A previously p u r i f i e d mixture of LiF-BeF2 (66-34 mole $) was now aci6.ed t o each of t h e above mixtures of l i t h i u m and bismuth i n t h r e e succ e s s i v e tared increments of about 1 kg. FiI.tered samples of t h e metal phases were taken disring 24-hr eq1xilibriu.m periods a f t e r each s a l t add i t i o n . The r e s u l t s o f spectrographic analyses of t h e s e samples showed l o s s e s of lithium from t h e metal phase a f t e r each s a l t a d d i t i o n . A s shown by F i g . 7.1, t h i s l o s s corresponded t o about 0.11 mole of l i t h i i m per kilogram of t h e s a l t mixture and was independent of the concentratioil of l i t h i u m i n t h e metal phase. Although t h i s l o s s may be nttribil‘ied t o a n.imber of p o s s i b l e circumstances, it should n o t material.3y a f f e c t t h e econoinics of t h e r a r e - e a r t h e x t r a c t i o n process.

I n e a r l i e r experiments, t h e e x t r a c t i o n of rare e a r t h s from a s a l t phase into molten bismuth was achieved by t h e a d d i t i o n of beryllium metal t o t h e sys-tem. This reduction process a l s o r e s u l t e d i n an i n c r e a s e of t h e l i t h i u m concentration of t h e ino.l.t,en metal. phase. Accordingly, fiurtlier

i n t h e Lwo-phase e x t r a c t i o n system has been i : o i t i a t e d . Tne f i r s t expei-iment of -tk.s s e r i e s ?was conducted 'ny ad.d.ing c l e a n beryllium m e t a l turIli.ngs mole $) and t o a. two-liquid-phase system of 3.1.7 kg o f UF-EeF2 (66-34~ 2.30 kg of bismuth contained i n low-ca:ibon s t e e l a-t 600°C. FiI.tered samples o r t h e metal. phase were w i t h d r a w n at 4- a n d 24-hr i n t e r v - a h al-'teieach incremen-tal additi.oa or about 1 g of bery.l.Ilum metal. These sanp1-e~ were analyzed s p e c t r o g r a p h i c a l l y f o r t h e i r l i t h i u m and h e l y l l i u r n c o n i e u t by groups a f t e r 5 g of Eeo had been added t o t h e system. As shown by Fig, 7.2, t h e 1 i t h i i : m concen-Lration j.n bismllth increased a f t e r e a c h add i t i o n of beryllium u n t i l a value of about 0.16 mole f r a c t i o i i I.j.thium w a s a t t a i n e d . Beryllium concentraLioas i n bismuth remained bel.ow the l i m i t of d e t e c t i o n ( l e s s than 0.0001 w-t; 8) of t h e a n a l y t i c a l . method.. T h i s , t h e a n a l y t d c a l r e s u l t s f o r I.ithiurn i n bisnmth should. r e f l e c t dissol.vied l i t i i i i m metal concentrations r a t h e r t h a n t h e d i s s o l u t i o n or suspension or s a l t i n t h e molten metal- phase. Since -t;h.e d i s t r i b u t i o n of rase e a r t h s between t h e two l i q u i d phe.ses of t h e extracLion system w a s found dependent upoil tile l i t h i u m concentration i n b i sfmth, t h e s e r e sul-Ls provide ex-Lrapolati o n . l i m i t s f o r e s t i m a t i n g e x t r a c t i o n parameters. If t h i s limi-Liiig value of 0.16 molk f r a c t i o n of li.t,hium i L i bismuth i s assumed t o be i n eqiiilibrium with beryllium metal a-t unit a c t i v - i t y , t h e a c t i v i t y c o e f f i c i e n t s y of

ORNL-DWG 65-1!458 - I

o EXPT LI-6

Fig. 7.1. Rate of L i t h i u r n Loss from Molten Bismuth i n t o EiF-BeF2 ( 6 6 - 3 4 Mole '$) a t 600°C.

002

0.04

0.06

000

0 10

LIT! ilUM CONCrNTRATlON IN UI',MUTH (mole frnrtion)

ORNL-DWG

66 11459

WEIG'IT OF SALTPHASF 317kg OF MCTAI. PHASE 2 30 kg I

:012

F i g . 7.2. Reduction by B e r y l l i u m Metal o€ I;ik'-BeF2 (66-34 Mole $) i n Contact wikh Molten l3ismuth a t 600°C.

_-L

0 2

04 05 08 10 12 BERYLLILM ADDED TO SYSTEM h o l e s )

1.1

145 I.ithium and some rare e a r t h s i n molten bismuth can be es-Limated. On t h e b a s i s of t h i s l i t h i u m c o n c e n t r a t i o n and thern1odynami.c d a t a , H i l l t h e following a c t i v i t y c o e f f i c i e n t s of metals d i s s o l v e d i n molten bismuth a-L 600째C:

Metal

8 x io+

La Ce Nd

1.2 x IO--=*

2.9 x 10-l~

8 x

10-l~

Comparable r e s u l t s a t 500째C which d i f f e r by no more t h a n a f a c t o r of 10 have been r e p o r t e d . 19' 2 o Additional experiments a r e i n progress t o b c t k e r d e f i n e the e q u i l i b r i u m reactiori. Xenioval of Rare Earths from Mol-ten F l u o r i d e s by Sirmil-taneous P r e c i p i t a t i o n w i t h UT3 - J. 11. Shaffey and H. F. McDurfie Tine r e l a t i v e l y low s o l . u b i l i t y of UF3 i.n f l u o r i d e mixtures of i n t e r e s t t o t h e MSR P r ~ g r a n t, o~g~ e t h e r w i t h t h e known. s i m i l a r i t i e s of t h e c r y s t a l s t r u c t u r e of r a r e - e a r t h t r i f l u o r i d e s w i t h UF3, 2 2 provides a b a s i s f o r st,udies of t h e p r e c i p i t a t i o n of s o l i d solutri.ons of t h e s e compounds from f l u o r i d e melts. E'ission product rase e a r t h s r e p r e s e n t n major porkion of the poison f r a c t i o n i n t h e fuel of a molten-salt wc.I.ear r e a c t o r ; -this stud-y has been o r i e n t e d toward t h e development of s u i t a b l e reprocessing methods f o r r a r e - e a r t h removal. I n i t i a l - experlrnents conrhicted i n t h i s program considered t h e reduction of UF4 contained i n t h e r e a c t o r fuel. mixture t o UF3 and t h e simultaneous p r e c i p i t a t i o n of r a r e - e a r t h t r i f l u o r i d e s with UF3 a s t h e temperature of t h e f u e l mix-Lure was reduced. A second s e r i e s of experiments is i n progress t o examine t h e p r e c i p i t a t i o n of rare e a r t h s from a simulated f u e l soI.vent upon addi-tLon of so1.j.d UF3. If a l l t h e UFt, contained. i n t h e c u r r e n t MSRE f u e l mix-Lure, LiF-ReF2ZrF4-UF4 (65.0-29.1-5.O-0.9 mole '$ r e s p e c t i v e l y ) w e r e reduced t o UT3, the solu-Lion would. be s a t u r a t e d with UF3 a t approximately 725째C. By lowering t h e melt temperature t o 550째C, approximately 83.576 of t h e uranium would be p r e c i p i t a t , e d from s o l u t l o n . Resirl.ts of preliminary experiments designed to inves-Ligate t1ii.s r e p r o c e s s i n g method demonstrated t h a t k F 3 CeF3, and N d Y 3 could b e p r e c i p i t a t e d w i t h UF3. Europium and samarium were probably reduced i o t h e i r d.ivalen-t s t a t e s by t h e i n s i t u reduction of uranium w i t h a d d e d zirc0nj.m m e t a l and. showed l i t t l e o r no loss from s o l u t i o n duri.ng t h e precipi-Lation o f UF3. Subsequent experiments w i t h excess reducing agent showed that ceriuui removal could be reI.ated t o t h e u3' c o n c e n t r a t i o n i n s o l u t i o n 'oy -tile equat;ion

where N and N 3.j- are res13ectTi.w inole frac-Lions of rare e a r t h and -trj.RE u v a l e n t uranium. A s i l l u s t r a t e d i n Fig. 7.3, a value of about 0.55 was

obtained f o r k i n Ey. (3) f o r t h e simultaneous p r e c i p i t a t i o n of CeF3. Further i n v e s t i g a t i o n would be needed t o v e r i f y t h i s experimental r e l a t i o n s h i p f o r o t h e r r a r e e a r t h s of i n t e r e s t t o t h e program.

A more r e c e n t experimental program has been concerned wiLh t h e ret e n t i o n of r a r e - e a r t h t r i f l u o r i d e s on a bed of s o l i d UF3 as an a l t e r n a t i v e reprocessing technique. I n t h i s experiment, UF3 w a s added i n 30-g i n c r e ments t o approximately 2.2 kg of LiF-BeF2 (66-34 mole that initially contained mole f r a c t i o n of CeF3 with about 1. mc of 144'Ce as a radiot r a c e r . F i l t e r e d samples of t h e s a l t mixture were taken approximately 48 h r a f t e r each a d d i t i o n of: UF3 and analyzed radiochemically f o r cerium. A s shown by F i g . 7 . 4 , t h e s e r e s u l t s i l l u s t r a t e a somewhat l i n e a r decrease i n cerium concentration a s UF3 w a s added which corresponds t o a s o l i d phase which contained about 1 mole $ CeF3.

$ 5

7.0

6.0

ORNL-DWC 66-14460

8.0

Fig. 7.3. Simultaneous Precipi t a t i o n of CeFS and UF3 from Simul a t e d . MSRE Fuel Mixture.

5.0

5- 4.0

3 +

3.0

INITIAL U CONCENTRATION

$ 2.0

; I

1.5

5wt%

I l l

4 5 6 8 40 45 URANIUM FOUND IN SOLUTION (mole fraction x 1 0 3 )

Fig. 7.4. Removal of CeF3 from LiF-BeF;! (66-34 Mole $) by Exchmge w i t h S o l i d UF3 a t 550째C.

0.4 0.6 UF3 ADDED (moles1

0.8

147 Removal of Protactinium from Molten F l u o r i d e s by Oxide P r e c i p i t a t i o n J. H. S h a f f e r , F. F. Blarikenship, and W. R . Grimes I n a previous experiment, protactinium w a s removed from s o l u t i o n i n a s o l v e n t mixture of LiF-BeF;! (66-34 mole $), c o n t a i n i n g ZrF4 (0.5 mole p e r kg of s a l t ) , by t h e a d d i t i o n of Z r O 2 a t 600°C.23 Ax i n t e r p r e t a t i o n of t h e experirnerital d a t a according t o -the equation

= fraction of Pa i n t h e salt, and W = Fpa weight of t h e designated phase, showed. t h a t t h e d i s t r i b u t i o n o f protactiniimi between t h e t w o phases remained constant over t h e pro-Lac1;iniw-n concentration range of -the experiment. Tnese resiilts could be i n t e r p r e t e d as t h e form%tion of l a b i l e oxide s o l i d s o l u t i o n s o r as suxface absorption of 233Pa on khe s o l i d Zr02. F u r t h e r studies of t h i s oxide p r e c i p i t a t i o n behavior vere conducted i n t h e same f l u o r i d e s o l v e n t with Zr02 powders having v a r i e d siirface areas

where D = (Pa)oxide/(Pa)s%l.t,

Zirconium dioxide used i n t h e o r i g i n a l experiment w a s purchased commercially axid had. a s u r f a c e area of about 19.6 m 2 / g . Matterial having higher s u r f a c e areas was prepared from Z r ( O € I ) A by dehych-ation. 2 4 Suff i c i e n t Z r 0 2 for t h i s experiineii1;al s e r i e s w a s f i r e d . a t 600, 700, and .lOOO"C i n s e p a r a t e batches t h a t y i e l d e d average s u r f a c e areas of 80, 50, auld. 1.32 m2/g r e s p e c t i v e l y . About 3.55 kg of a s a l t mixture having a nominal composition of LiF-BeF2-ZrF4 (64.8-33.6-1.6 mole $) w i t h about 1. me of 233Pa (as i r r a d i a t e d Th02) was prepared i n a n i c k e l v e s s e l by our u s u a l KF-H;! treatmerit a t 600°C, followed by B;? sparging at 'I00"C f o r f u r t h e r p u r i f i c a t l o n and dissol-dtion of protactinium as i t s f l u o r i d e s a l t . S e l e c t e d Z r 0 2 was added t o t h e sa1-k mixture i n 10-g increments; t h e mixture w a s t h e n sparged w i t h helium a t 8, r a t e of about 1 li'cer/miri during 24-hr e q u i l i b r a t i o n p e r i o d s . F i l t e r e d sa,mpl.es of t h e s a l t mixture were taken a f t e r each e q u i l i b r a , t i o n p e r i o d and analyzed radiochemically f o r 233Pa by counting i t s 31.0-kv photopeak on a single-charmel gamma spectrometer. A t t h e conclusion of t h e Pxperiment, t h e mixture w a s h y d r o f l u o r i n a t e d t o converi a d d e d Zr02 t o i t s f l u o r i d e s a l t and. t o r e s t o r e "'Pa, a c t i v i t y i n t h e molten-salt phase. This experimental procedure w a s repeated w i t h t h e same s a l t mixture f o r a l l three lots of Z:rOZ.

I n each experiment t h e addfirition or Z r O 2 t o t h e 7luol-i.de mixture res u l t e d i n t h e loss o f p>?otactiniux from s o l u t i o n . Ilowever, as shown by F i g . '7.5, a p l o t of tlie r e c i p r o c a ~ f. r a c t i o n of 2 3 3 ~ ian s o l u t i o n v s ZXQ added, according t o Eq. ( d ) , y i e l d e d 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 233Pa between t h e two phases whrich v a r i e d conti-nuously as the p r e c i p i t a t l o n r e a c t i o n approached completion. These ex:peri.mental results are cori-Lrary t o those ob-Lained previously with respec-t -io t h e constancy of the 233P, d i s t r i b u t i o n coel'ficj-ents; t h e y i n d i c a t e -ti.iat 2331% removal from t h e salt mrixtiire i s not proporti.onal t o t h e surface area of t h e a.dded oxide pa.rtic l e s and a l s o does not conform t o 811 e q u i l i b r i u m s o l i d sol.u.ti.on. Fxperiments i n progress wi1.1. attempt t o f u r t h e r e l u c i d a t e t h e c h a r a c t e r i s t i c s o.f t h e oxide p r e c i p i - t a t i o n process.

14% 1

1 - 7

SURFACE AREA Zr02=80 m2/q

0 A

SURFACF AREA Zr02 - 5 0 SURFACE AREA Z r 0 2 - 1 3 2

GSNL -DWG 66-11462

m7/q

m2/q

WEIGHT OF SALT MIXTURC' 3 55 kg

WI-ICRC Fp, = FRACTION OF 233Pa IN LIQUID W - WEIGHT OF UESlGNATfD P H A S E . CGNC OF PO ird SOLID P i i A x CGNC OF Pa IN I IQUID PHASE

-1 t

Z r 0 2 N l D f D (g)

Fig. 7.5. E f f e c t of Surface Area of ZrO, on t'ne Removal of 233Pa from LiF-BeF,-ZrFs (64.8-33.6-1.6 Mole %) at 600OC. E x t r a c t i o n of IProtactinium from Molten Fluorides i n t o Molten Metals J-. H. Shaffer, F. F. Blankenship, and W . R. Grimes

The removal- of protactinium from s o l u t i o n i n ZiF-ReF2-ThF4 ('73-2-25 mole $) by adding thorium metal d i r e c t l y i n t h e s a l t mixture o r by cont a c t i n g t h e s a l t with molten l e a d o r bismuth lin which -thorium had been dissolved has been demonstrated i n s e v e r a l experiments. 2 5 More r e c e n t experiments h.ave examined methods which could be used f o r recovering protactinium from t h e f e r t i l e blanket of t h e reference-design MSBR. The r e s u l t s of s e v e r a l batch-type l a b o r a t o r y experifmiits led -to t h e design and operation of a s m a l l pump loop which has demonstrated, i n p r i n c i p l e , t h e removal of protactinium from molten f l u o r i d e s by a l i q u i d - l i q u i d ext r a c t i o n technique. I n e a r l y experiments a molten f l u o r i d e mixture containing dissolved

233Pa and m o l t e n bismuth containing dissolved t h o r i u n metal were k f t i n

contact i n low-carbon-steel c o n t a i n e r s under s t a t i c condi-tions. Subsequent examinations of t h e c o n t a i n e r i n d i c a t e d t h a t most of t h e p r o t actinium had deposited on t h e v e s s e l walls t h a t were is c o n t a c t with the salt phase. The d-isappointing f a i l u r e of t h e protactinium t o c r o s s t h e boundary- of t h e two l i q u i d phases may have r e s u l t e d from nonwetting behavior. The e f f e c t s of such behavior could be g r e a t l y reduced by t h e i m proved c o n t a c t i n g obtainable i n a pump-loop system.

I n o t h e r experiments i n which no sal-L phase w a s used, s o l u t i o n s of 233Pa i n molten l e a d and bismuth were obtained by t h e a d d i t i o n of i r r a d i -

a t e d thorium metal -to t h e l i q i i i d metals i n s t e e l c o n t a i n e r s . Radiochemical analyses of f i l t e r e d samples taken from t h e s e v e s s e l s showed-

149 that; 233Pa d i d not form s t a b l e s o l u t i o n s i n e i t h e r l i q u i d m e t a l . About 40$ of 'che 2331'a a c t i v i t y w a s r e t a i n e d i n bismuth, and less t h a n 5$ was r e t a i n e d i n l e a d during 4.8-hr c o n t a c t p e r i o d s . Much of t h e 233Pa was on t h e walls of t h e v e s s e l s , w i t h t h e d i s t r i b u t i o n shown i n F i g . 7.6. The I-arger m o u n t near t h e bottom of each v e s s e l implies l o s s of 233Pa. vi.a sedimentary deposi-Ls of i n s o l u b l e materials r a t h e r t h a n by surface ads o r p t i o n . It i s of i n t e r e s t t h a t t h e c o n c e n t r a t i o n s of thorium i n b i s m u - L h were found, s p e c t r o g r a p h i c a l l y , t o be less t h a n t h e 1000 ppm added and well. below r e p o r t e d s o l u b i l i t y v a l u e s of 3000 t o 4000 ppm.27 The f r a c t i o n s of 233Pa arid thorium found i n s o l u t i o n i i l aisrnuth were roughly e q u a l . The c o n c e n t r a t i o n s of b o t h i n c r e a s e d for about 5 h r a f t e r t h e irradiated. thoriwn w a s added t o t h e liyu.id 'uismuth and t h e n decreased w i t h time. The behavior i n lead. appeared t o be considerably d i f f e r e n t . Although as much as 80% of t h e thorium d.issolved i n t h e lead, t h e f r a c t i o n of protactinium i n s o l u t i o n remained very small.

We concluded from t h e s e d a t a t h a t bismuth i s t h e p r e f e r a b l e e x t r a c t a n t and. t h a t formation of s l i g h t l y solu.hle co:mpounds can complicate t h e ext r a c Lion of prot,actiriiwn from f l u o r i d e s a l t s by c a u s h g t h e effec-Li-v-es o l u b i l i t y of protactinium i n l i q u i d bismuth t o be low. Although a high solub i l i t y seems d e s i r a b l e , t h e l i q u i d - m e t a l phase i n t h e process a c t s o:nIy as a c a r r i e r t o t r a n s f e r t h e protactinium from one s a l t t o another. High s o l v b i l i t y of protactiniuiu i n the l i q u i d metal i s n o t an e s s e n t i a l . condit i o n -Cor a t t a i n i n g adequate t r a n s f e r rates. Thus, a pump-loop expertmeni was t r i e d i n an e f f o r t t o achieve t r a n s p o r t oâ&#x201A;Ź protactinium f r o m a. b l a n k e t salt while maintaining a low c o n c e n t r a t i o n i n t h e l i q u i d bismuth.

An experimental loop, showrt schematically ii? F i 7.7, w a s designed t o c o n t a c t a f l u o r i d e mixture c o n t a i n i n g d i s s o l v e d 2"Pa w i t h 5 r e c i r c u l a t i n g s t r e a m of molten bismuth c o n t a i n i n g thoriuii. The -thorium was i-ntroduced by passing t h e bismuth over thorium c h i p s j u s t b e f o r e i'is e n t r y i n t o omi

400

BISMLJTL1

LEAD

-DWG 66-14463

Fig. 7.6. D i s t r i b u t i o n of 233Pa, i n Low-Carbon S t e e l U s e d t o Contain Bismuth and Lead at 600Â°C.

z 0

AVERAGE HEIGHT ABOVE BOTTOM O r CONTAINFR (In )

ORNL D W G 66 $1464

HELlUhl SUPPLY

Eâ&#x20AC;&#x2122;Q. 7.7.

EXkiAUSl

I)i.agraun of 233pa

E x t r a c t i o n Pump Loop.

t h e e x t r a c t i o n v e s s e l . Thus, a t low flow r a k s thorium would be introduced a t a r a k r e g u l a t e d by i t s s o l u b i l i t y i n bismuth. The al.loy w a s t h e n sprayed i n t o t h e sal-t mixture so t h e protactinium would be e x t r a c t e d at t h e su.rfaces of f r e e - f a l l i n g d r o p l e t s of bisniiith. A pseudo-first-order r a t e of e x t r a c t i o n was expected.

Although t h e blanket reprocessing method involves s t r i p p i n g the p r o t acâ&#x20AC;&#x2122;iin7.m from molten bi-smuth i n t o a second s a l t mixture by iiydrofluorination, t h i s f e a t u r e was not included i n the i n i t i a l . pi,u~ip-loog design. Instead, t h e r e c i r c u l a t i i i g molten-metal stream w a s pumped through a bed. of s t e e l wool t o provide f o r t h e c o l l e c t i o n of protactinium by absorpbion on t h e iron s u r f a c e s o r by f i l t r a t i o n of suspended p a r t i c l e s . This expedient was based on r e s u l t s of t h e experiments described above and on another i n which thorium m e t a l w a s added t o a b l a n k e - t - s a l t mixture t h a t contained 233Pa. The protactinium w a s found uniformly dis-Lributcd on s t e e l wool t h a t had been immersed i n t h e s a l t . Accordingly, the s t e e l wool. coliumn was designed t o provide a l a r g e s u r f a c e a r e a of i r o n r e l a t i v e t o iron surfaces exposed t o t h e l i q u i d phases elsewhere i n t h e system without unduly r e s t r i c t i n g t h e flow of bismuth. The e x t r a c t i o n v e s s e l was a l s o f i t t e d wi-th an open c y l i n d e r of niobium for primary contairment of t h e s a l t mixture. The c e n t r i f u g a l pump was t h e same as t h a t designed and operated by E. S. B e t t i s , Reactor Division, i n s i m i l a r molten-salt-molten-lead systems.

Pump-Loop Operation. S e v e r a l r e l a t e d experiments were c a r r i e d out i n t h e pimp l o o p . The loop w a s f i r s t charged w i t h 13.5 kg of bisnmth t h a t

151 had been previoiisly t r e a t e d w i t h hydrogen a t 600째C f o r oxide removal.. This m a t e r i a l was c i r c u l a t e d through the system to ascer-Lain o p e r a t i o n a l procedures and pimp performance c h a r a c t e r i s t i c s . The s t e e l wool coluuul was t h e n prepared on i t s f i x t - u r e , i n s e y t e d i n t o t,he system, and f i r e d w i t 1 1 hydrogen a t 700째C i n s i t u w h i l e bismu-th was s t a t i c , and t h e balance o f t h e system w a s protect,ed. f r o m oxide contamination by flowing lielivm. The c o l m contained 12.5 g of grade 1 steel- wool having a t o t a l s u r f a c e area oi" 0.49 m2 o r about t e n times that o f the georne-tric s u r f a c e of i r o n t h a t was elsewhere exposed t o bi.s-m?i.t,hi n t h e c i r c u l a t i n g s y s t c m . The sa1.t mixtu.re LiF-ReFz-ThF4. (73-2-25 mole $) w a s spiked w i t h a'oout 1 me of 233Pa from i r r a d i a t e d Tho2 by our u s u a l HF-Hz treatment i n n i c k e l a t 600째C and w i t h Hz alone a t '700째C. Approximately 6 . 7 kg of this materi.aL was t r a n s f e r r e d i n t o t h e niobium-lined e x % r a c t i o n v e s s e l .

Bismuth w a s at f i r s t c i r c u l a t e d without a reducing agent, t o estahlish he s t a b i l i t y of 233Pa i n the s a l t mixture. Then thorium m e t a l w a s introduced i n s m a l l amounts by submerging a b a s k e t of thorium chips i n t h e bismuth stream a-t the oiit,I.et of t h e column. Five successive a d d i t i o n s of thoriurm were made i n t h i s mamer d u r i n g t h i s phase of t h e experiment. The radiochemical r e s v l t s obtained f r o m fT1-tered sarrp?.f::; o-f t h e two l i q u i d pha.ses dining sone 30 h r of pump o p e r a t i o n are shown i n F i g . '7.8. it is i n t e r e s t i n g 'GO n o t e t h a t t h e 233Pa a c t i v i t y i n t h e s a l t phase was extremely s t a b l e during -the f i r s t 1.7 hr of loop opera%ion and t h e f i r s t t h r e e a d d i t i o n s of thorium. A f t e r t h e f o u r t h a d d i t i o n of thorium, t h e 233Pa a c t i v i t y i n t h e s a l t phase decreased a-L a, measuraln1.e r a t e u n t i l apparent exhaustion of t h e thorium metal and continued 3ftt.r t h e f i f t h thorium a d d i t i o n u n t i l 3'7% of t h e 233Pa w a s removed. A s shown by F i g .

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

120

----T------T

ORMl

- D W C 66-11465 ........

100

-s

Fehavior of 233Pa i n Fig. 7.8. Pump Loop D u r i n g First E x t i e a c t i o n Exper:-merit (Tho Added t o Bismuth A s

2 *

Noted)

L U 0

a 0

N m

10 45 20 LOOP OPERATING TIME (hr)

3.52

of 2 3 3 ~from a LiF-BeF2-ThF~(73-2-25 Mole %) by ~ i g .7.9.

LOSS

Reduction wi.th Thorium i n Bismuth as a Pseudo-First-Order Reaction.

1 6 EXTRACTION TIME (hr)

7.9, thi.s removal r a t e reasonably agreed with a f i r s t - o r d e r r a t e r e l a t i o n postula-Led. f o r t h e reduction of protactinium by bismuth d r o p l e t s of cons t a n t thorium concentration while f a l l i n g through t h e s a l t phase. The run was i n t e r r u p t e d al; t h i s p o i n t t o c o r r e c t a mal-function i n t h e pump. Tine apparent c o l l e c t i o n of s o l i d s about t h e pump roLor r e s u l t e d i n a s e i z u r e which could not be overcome by t h e low-torque 1/3-hp motor.

A compilation of m a t e r i a l balance d a t a on thorium ad-ded t o t h e syst e r n i s shown i n Table 7.7. Since t h e thorium b a s k e t s were coated h2avil.y with bismuth, t h e actual. q u a n t i t y of thorium introduced i n t o t h e system w a s estimated by volume l o s s r a t h e r t h a n by weight; balance. Spectro-

graphic analyses of samples taken p r i o r t o each. thorium a d d i t i o n showed t h a t very l i t t l e t h o r i i m o r reduced l i t h i u m w a s r e t a i n e d as a soluble component of t h e metal phase. Chemical analyses of s a l t s,mpl.es from corresponding periods showed t h a t t h e chromiuii concentration of the s a l t phase w a s reduced from 164 t o l e s s t h a n 2 ppin after t h e f i r s t thorium ad-dition a a d remained a t tha"i. l e v e l T o r t h e duration of t h e experimen-t. Concentrations of i r o n and nickel. were v i r t u a l l y unchanged a t about 125 and 30 ppm r e s p e c t i v e l y .

During the i n t e r r u p t i o n , t h e columi of s t e e l . wool w a s removed from t h e system f o r examinatton. Althou.gh t h e column had gained considerable weig?it, only t h e head-end s e c t i o n s ( t h e bottom of t h e column) contained appreciahle q u a n t i t i e s of s o l i d s . A q u a n t i t a t i v e a n a l y s i s for 233Pa i n t h e columrn was nlade by E. 1. Wyatt, A n a l y t i c a l Chemistry Div-isioa, by d i s s o l v i n g the e n t i r e assembly i n t o an aqueous s o l u t i o n . Radiochemical analyses of a l i q i i o t s of t h i s s o l u t i o n were r e l a t e d t o t h e t o t a l volume of s o l u t i o n and t h e qiiantity of 233Pa p r e s e n t o r i g i n a l l y i n t h e s a l t sysOn t h i s b a s i s , t h e col1.m accounted f o r ahout 14% of tile 233Pa. tem. Since 43% of -the 233Pa a c t i v i t y remained i n t h e s a l t and 3% remained i n 'Pa w a s apparently deposited elsewhere i n t h e metal, ahout 39% of t h e " t h e system.

Table 7.7. & A e r i a l Balance of T h o r i m Metal Added t o 233Pa Extraction Loop

9.37

2.0

6.3

468

936

1856 2169 2836 3579

2 3

â&#x201A;Ź3.39

6.4

943

5.9

4.4

1.5

1055

5.9

1.0

4.9

1419 1790

5 .o

5 .0

0.45

114

127

0.13

< 30

17 17

171 216

0.17

0.11

0.09

154 The second s t e e l wool column w a s assembled with c o a r s e r grades o f s t e e l wool i n t h e i n l e t s e c t i o n i n an attempt t o r e t a i n more o f t h e s o l i d s , I n t h e previous column t h e f i l t e r a b l e s o l i d s were stopped by Lhe f i r s t t h r e e of e i g h t s e c t i o n s of s t e e l . wool. It seems p o s s i b l e t h a t s o l i d s h e l d by i n e r t i a on t h e head end of t h e column s e t t l e d i n t h e pump bowl when t h e pump w a s stopped. The s t e e l wool on t h e new column ha.d. a n e t weight o-f 18.2 g and a s u r f a c e a r e a of 0.87 m2.

The r e s u l - t s o f radiochemical analyses of f i l t e r e d samples from -the two l i q u i d pha,ses taken during t h i s second e x t r a c t i o n experiment a r e summaxized i n F i g . 7.10. 'Two a d d i t i o n s of thorium during 15 h r of pumping made no change i n t h e 233Pa concentration i n t h e s a l t phase. Because t h e piimp w a s operating pooiqly and t h e flow r a t e of bismuth w a s i r r e g u l a r , subsequent thorium a d d i t i o n s were made through t h e sampEng p o r t d i r e c - t l y t o t b e s a l t phase. Three 1-g a d d i t i o n s of thorium reduced t h e 233Pa cont e n t of t h e s a l t phase t o abollt 27% of i-ts orLgiiial value b e f o r e the r u n was i n t e r r u p t e d t o change o u t t h e s t e e l wool colimn. During t h i s ope r a t i o n a l i n t e r v a l , 16% of t h e 233Pa w a s removed from t h e s a l t phase, 4% w a s i n -the metal phase, and about 7% was found on the column. The s t e e l wool colurrm f o r t h e f i n a l e x t r a c t i o n experiment w a s patt e r n e d a f t e r the preceding one. A t o t a l of 28.7 g of s t e e l wool from gyades 3 through 0 provided a s u r f a c e of 1.4 m2. Thorium metal w a s added i n three 2-g increments during 1 2 . 5 h r of pump o p e r a t i o n . Radiochemical analyses of f i l t e r e d samples of t h e l i q u i d phases a r e shown i n Fig. 7.11. Protactinium w a s removed from t h e s a l t phase u n - t i l about L+$ of t h e 233Pa remained a t apparent equilibrium. During t h i s period t h e pump was ope r a t e d a t i t s maxirnum allowa.ble speed i n an attempt t o wash protactinium from t h e w a l l s of t h e extractj.on v e s s e l and t o b e t t e r suspend any p r o t actinium-bearing s o l i d s i n t h e molten bismuth. Material-balance calcul a t i o n s show t h a t 23% of the o r i g i n a l q u a n t i t y of 233Pa was removed from

MOSl-LY S1.ATlC OPERATION WHII. F PUMP ,/VIAS

100

SEIZED PRIOR i 0 t - 5

Fig. 7.10. Behavior of 233Pa i n Pump Looy During Second E x t r a c t i o n Expertmen% (Tho Added t o B i Except

Where Noted).

c 2

a 40 0

n. N 10

0 0

10 15 LOOP OPERATING TIME (hr)

155 ORFIL-Dn9

Fig. 7.11. Behavior of 233Pa i n Punp Loop During Third Extract i o n Experiment (Tho Added t o S a l t ~nase).

66 44168

4 ,

+ N" -'

2.5

5.0

7.5

10.0

12.5

LOOP OPERATING TIME (hr)

t h e s a l t phase. About 194 of t h e 233Pa was on t h e colurnn, g i v i n g ari 82.6% recovery f o r t h i s t h i r d . experiment. Chemical analyses were obtained on s a l t samples taken during the second and t h i r d e x t r a c - t i o n experiments. Concentrations of i r o n ranged raadomly from 100 t o 170 ppm, while chromium and n i c k e l were v i r t u a l l y absent a t r e p o r t e d values of l e s s thLm lo ppm. The niobium content of t h e s a l t phase w a s c o n s i s t e n t l y below t h e d e t e c t a b l e l e v e l of 4 p p . Values for t h e concentration of bismuth i n t h e s a l t mixture ranged from 67 t o 264 plxa i.n a random manner; the a r i t h m e t i c average concentration Prom a l l samples was 119 ppm. However, i t w a s not p o s s i b l e , under t h e experimental conditions, t o a s c e r t a i n whether t h e s e values represented dissolved bismuth o r d r o p l e t s suspended i n t h e salt m k t u r e . The value:: d i d not, however, r e f l e c t the pumping speed of t h e bismuth o r a dependence on time. Discussion and Conclusions. The protactinium balance f o r t h e comp l e t e experiment shows t h a t 96% of t h e 233Pa original-1.y i n t h e s a l t phase w a s removed by thorium metal a d d i t i o n s . A t l e a s t 43% w a s pumped a s a sol u t i o n o r suspension i n molten bismuth and deposited on r a t h e r s-ma1.l volumes of s t e e l wool. Since an a d d i t i o n a l 476 of the 233Pa remained i n each of t h e two l i q u i d phases, w e can account f o r a.bOQt 51% of the p r o t actinium. RlLhough l a r g e moixits o f thorium were added t o Lhe system, t h e conc e n t r a t i o n i n bisrnuth rernarined very l o w . Consid.erable thorium had t o be a2ded i n the f i r s t experiraen-i; 'oefore any p r o t a c t i n i i m w a s extracted. from the s a l t . Additional thorium was consumed without e x t r a c t i o n o f protactinium a t the beginning of t h e second experiment, which foIlowed the changeout of t h e s t e e l W O O 1 column. Reduction of some metal f l u o r i d e i m p u r i t i e s from t h e s a l t was evid.ent, b u t t h e m o u n t w a s not s u f f i c i e n t

t o account f o r a l l t h e -thorium l o s s e s . Some high-melting m e t a l l i c plugs were taken Brom t h e system, and t h e spectrographic analyses showed them t o c o n t a i n high c o n c e n t r a t i o n s of thorium a o c i a t e d w:i.th i r o n and chromium. The c o l l e c t i o n oi" protactinium on 'the s t e e l wool.. colwms appeared t o be p r i m a r i l y a fil'ii-a.t;ion process, although some s u r f a c e absorption a l s o was apparent. We expected some mass t r a n s f e r of i.ron i n 'die polythermal loop system, b u t it appears t h a t t h e t r a n s f e r was aggravated by -LIE presence of thorium. We b e l i e v e t h a t i r o n , chromium, and thorium, accompanied by some of t h e protactj.niurn, formed compounds of low solub i l i t y i n bismuth a t t h e operatri-ng temperature. P r e c i p i t a t e s formed, some of them c o l l e c t e d on t h e f i l t e r , but t h e remainder c o l l e c t e d i n o t h e r p a r t s of t h e system t o account f o r t h e thorium aad protactinium 3.osses. This suggests t h a t a m0i-e r e s i s t a n t material, such as iliobium, would be d.esi.rable f o r use i n t h e e x t r a c t i o n equipment. The pump-loop experiments w i l l be continued. 'The next one i s planned t o demonstrate recovery of prol;actir*ium from t h e l i q u i d - m e t a l stream by c o n t a c t i n g the bismuth w i t h a molten s a l t that i s s a t u r a t e d with a mix-Lure of â&#x201A;ŹE and H2. Frotac'iinium S t u d i e s i n t h e High-Alpha Molteri-SaIt, Taboratory - C . J. Barton II^

An experiment on t h e removal of protactinium from a breeder-blanket mixture LiF-ThFA (73-27mole $1 having an i n i t i a l c o n c e n t r a t i o n of 25 ppm of 231Pa w a s described i n t h e previous r e p o r t . 2 7 l3edu.ction OS pro1;actiniwri w a s e f f e c t e d by metall.5.c t'norium i n t h e presence of l e a d a t about 625Â°C. The f a c t t h a t o n l y a small- f r a c t i o n of the reduced protactinium w a s found i n t h e l i q u i d l e a d . encouraged study of o t h e r r e d u c t i o n techniques.

Reduction ~ - _ w-i t h S o l i d Thorium. S e v e r a l experiments were performed t o study t h e reduction of pro-tactinium i n T.iF-ThF4 (73-27 mole $) by so1j.d thorium i n t h e form of a rod or t u r n i n g s . Three d i f f e r e n t c o n t a i n e r mate:eials were used: n i c k e l , copper, and g r a p h i t e . The f i r s t experiment was conducted i n a nickel. c o n t a i n e r with a 3/8-in.-OD thorium rod. The 231Pa content o f t h e sa1.t mixture, based on a n a l y s i s of f i l t e r e d samples, dropped from 11.1t o 9.09 mg during t h e i n i t t a l 65-min exposure of t h e rod t o t h e molten f l u o r i d e mixture a'i 625'C. A f u r t h e r 5 - i ? ~exposure a t the sane teiiiperature produced an apparent i n c r e a s e i n 231Pa content t o O . S + m g . A l a r g e f r a c t i o n (approximate1.y 70$, o r 28 g) of t h e p a r t of tlhe rod t h a t w a s immersed i n t h e molten-sal-L mixture was l o s t during t h e experiment. We b e l i e v e t h a t t h e thorium r o d w a s i n con-tac'i with t h e bottom of t h e n i c k e l pot rhirri.ng t h i s experiment, causing a c u r r e n t flow t h a t corroded t h e r o d electyolytical1.y. The s a l t mixture removed from t h e n i c k e l pot contained a l a r g e amount of b l a c k m a t e r i a l , p a r t of which w a s magnetic. 'The a n a l y s i s of t h e magnetic p a r t showed 45% N i , 30% Th, and O.Ol.5% '"Pa. The black, nomiagnetic material contained 22% N i , 50% Tln, and 0.027% 231Pa.

157 A second experiment, performed under conditions described above exc e p t t h a t c a r e w a s e x e r t e d t o avoid c o n t a c t of t h e thorium rod writh t h e n i c k e l pot, gave more r e a d i l y understandable r e s u l t s . The 231Pa concen-t.ration of a f i l t e r e d sample of t h e s a l t dropped t o 30% of t h e j - n i t i a l concentration ( 3 2 pprn) a f t e r a 1 - h r exposure and t o 19% a f t e r t h e second hour of exposure. A ground s.m-pleof t h e u.nfili;ered. salt, removed from t h e pot a t t h e conclusion of t h e experinieent had a highe:r coilcentration of 231Pa t h a n t h e i n i t i a l f i l t e r e d sample. This may have been due, i n p a r t , t o t h e f a c t t h a t t'ne p r e c i p i t a t e d protactiniim? was r e d i s s o l v e d by HF-H2 treatment i n a smaller volume of fused s a l t than was p r e s e n t ai:, t h e beginning of t h e experiment because of t h e removal of a s i g n i f i c a n t f r a c t i o n (about 2 . 5 $ ) o f t h e s a l t i n each f i l t e r e d sample. The next experiment was similar t o t h e previous one except t h a t thorium t u r n i n g s supported i n a n i c k e l - p l a t e d copper screen were exposed t o t h e melt for 65 min and t h e 23LPa, concentration of f i l - b e r e d s a l t decre&c'p ,>-d t o '3% of the i n i t i a l value. The screen came loose from. i t s supp o r t i n g rod when we attempted t o remove it from t h e pot, and i t rzmained i n t h e molten mixture. Consequently, it was necessary t o d i s s o l v e t h e thorium metal- by p:rolonged treatment w i t h a i HF-Hz mixture i n order t o r e d i s s o l v e t h e p r e c i p i t a t e d . protactinium. The 2 3 ' - ~concentration a of a f i l t e r e d sample was 92$ of tine i l r i t i a l concentration a f t e r a 170-min W - H z treatment, and, a f t e r an a d d i t i o n a l 43-min. treatment, an imfiI.te:red sample showed a content e q u a l t o 96$ of the i n i t i a l value.

I n t h e four-Lh thorium redirction experiment , we again exposed t h e melt c o n t a i n i n g 19 ppm of 23'Pa t o thorium t u r n i n g s h e l d i n a nickelp l a t e d copper screen and found t h a t a 120-min exposure removed 97.5% o f t h e protactinium f r o m s o l u t i o n , as determined i n a f i l t e r e d sample. This time, however, we removed the basket and t u r n i n g s from t h e melt, cooled. t o room temperature w i t h R helium atm.osphere i n t h e poi;, and disassembled t h e apparatus t o dcterrrrine the d i s t r i b u t i o n of reduced protactinium. The recovered s a l t contained 51% of t h e anroi~~i-l; of 231Pa p r e s e n t a t t h e hegrinning of t h e experirnent, t h e basket and contents had 20$, t h e wall had 7$, while the d i p l e g and magnetic m a t e r k l removed from t h e s a l t ( p l u s p a r t i c l e s prod-uced i n sawing throu.gh t h e n i c k e l p o t ) each contatnet3 a700u.i; l$. About 16% of t h e protactinium was unaccounted for. Experiments very much l i k e t h a t described i n t h e previous paragraph

were conducted i n copper and g r a p h i t e c o n t a i n e r s t o study t h e e f f e c t or" c o n t a i n e r materia.1 on d i s t r i b u t i o n of reduced protactinium. I n both cases, approximately 60% of t h e recovered protactinium vas found i n t h e groimd, u n f i l t e r e d . s a l t ( m d u n t r e a t e d with iIFi and H 2 ) , although only 5% of t h e i n i t i a l protactinium concentration was p r e s e n t i n t h e final filtered sample of reduced s a l t i n t h e g r a p h i t e c o n t a i n e r experirnent and 29% i n t h e copper c o n t a i n e r . It appears, t h e r e f o r e , tha-t a I.a~:ge f r a c t i o n of re&uced protactinium rem.ains suspended i n t h e molten LTF-TMY'4 mixture r e g a r d l e s s of t h e c o n t a i n e r m a t e r i a l .

E l e c t r o l y t i c Reduction of .Protactinium i n LiF-ThF4 (73-2'7 Mole $I). A s e r i e s of e x p l o r a t o r y experiments on t h e e l e c t r o l y t i c reduction of protactinium i n molten LiF-TkF'4 (73-27 m c j l e $) has been condiicted w i t h a v a r i e t y of e l e c t r o d e arrangements. None of t h e s e arrangenient:; has been explored i n d e t a i l , and the preliminary r e s u l t s obtained i n some cases

3-58 a r e more confusing t h a n e n l i g h t e n i n g . w i l l be suminarized very 'oriei"l.y.

Consequently, t h e s e experiments

Graphite anode - n i c k e l v e s s e l cathode - 3.0 v and 0.5 amp: The protactinium contenl; decreased during t h e f i r s t hour of e l e c t r o l y s i s and t h e n rincreased dur:i.ng t h e second ana t h i r d hours f o r reasons t h a t ai-e not a1.3. c l e a r . S i l v e r anode - g r a p h i t e l i n e r o r nick21 d i p l e g as cathode - 3.0 v and about 1 amp: About, 20$ reduction i n 231Pa c o n c e n t r a t i o n af'ier e l e c t r o l y z i n g f o r 2 hr.

Thorium rod anode - thorium rod cathode - g r a p h i t e I.iner - 3.0 v Hemoved 95% of 231pa during 70-min e l e c t r o l y s i s ( f i l t e r e d sample), b u t 95% of t h e i n i t i a l . 231Pa c o n c e n t r a t i o n was found i n the unfiltered salt. asiil about 1.6 amp:

Nickel r o d immersed i n bismuth connected t o negative s i d e of 6.0-v baLtery - n i c k e l rod immersed i n t h e molten f l u o r i d e connected t o p o s i t i v e p o l e o f b a t t e r y - 5 . 0 v and abou-t 2.7 amp: N o r e d u c t i o n i n protactinium content of s a l t , and only a t r a c e amount w a s found i n t h e bismuth. Another c o n s t r u c t i o n of t h e previous experiment w i t h bismuth cathode n i c k e l d i p l e g c o n t a c t i n g b o t h s a l t and bismuth) - g r a p h i t e anode c o n t a c t i n g f l u o r i d e mixture oniy - g r a p h i t e l i n e r - 5.0 v and 0 . 5 amp: Again, t h e r e was no s i g n i f icarit r e d u c t i o n i n t h e protac,Linium content of -the s a l t . About 0.02% of t h e protactinium w a s found i n t h e l a s t f i l t e r e d sample of bismubh as compared t o 0.4% i n t h e unâ&#x201A;Źil_tered bismuth. The 2-attei' also contained 6.3% n i c k e l . (t.e.,

Conclusions. Protactinium d i s s o l v e d i n molten ILF-ThF4 can be reduced t o a form that does not pass through a s i n t e r e d copper f i l t e r , b u t a l a r g e p a r t ol" t h e p r e c i p i t a t e d protactj-nium remains suspended i n t h e mol-Lea mixture. Exploratory experiments on e l e c t r o l y t i c r e d u c t i o n of' protactj.nium have not produced encouraging r e s u l k s t o d a t e , b u t we are continuing t o pursue t h i s approach t o t h e protactinium removal problem because of i t s p o t e n t i a l sirnplicrity.

7.4

Radiation Cherni-stry

Xenon Diffusion and P o s s i b l e Formation of Cesium Carbide i n an MSBK C . F. Baes, J r . , arid R. B. Evans I11 Previously, s e v e r a l i n v e s t i g a t o r s have considered t h e neutron poisoni n g elffect caused by d i f f u s i o n of 135Xe i n t o t h e g r a p h i t e moderator oT a molten-salt reactorr 28-32 It i s t h e present purpose 'LO consider as w e l l t h e e r f e c t s of t h e cesium which is born w i t h i n t h e g r a p h i t e by decay of the various f i s s i o n pi-oduct xenon n u c l i d e s which have d i f f u s e d t h e r e . I n

159 p a r t i c u l a r , it i s of i n t e r e s t t o estimate whether o r not s u f f i c i e n t conc e n t r a t i o n s of cesium might occur t o form ( l a m e l l a r ) cesium. ca:rbri.des, as by Cso(g) t nc(s)

;=t

cscn(s)

and whether o r not a s u - f f i c i e n t m o u n t of CsC, t h e g r a p h i t e i n a f u l l - s c a l e MSBR.

could be formed to damage

I n an attempt t o answer t h e s e questions, t h e p a r t i a l pressure of cesiinii within t h e g r a p h i t e void spaces w a s c a l c u l a t e d u s i n g Lhe f o l l o w i i i g node1 and assumptions :

1. Diffusion of gaseous xenon i n t o t h e g r a p h i t e void spaces arid d i f f u s i o n of' gaseous cesium out of t h e grapliite were approximated as one dirnensional; t h a t i s , t h e moderator w a s represented as a s l a b of g r a p h i t e infini-Le i n two dimensions, wi.th a specified. thickness (221, immersed i n t h e f i x 1 sa1.t).

Al3. cesium born i n t h e g r a p h i t e w a s assumed t o be i n t h e gaseous eleinental form. Cesium bora i n t h e f u e l salt, o r reaching {;he fuel. s a l t by d i f f u s i o n from t h e g r a p h i t e wzs asswned t o be oxid-ized t o Cs+ and t o remain i n t h e s n l t t .

S t e a d y - s t a t e c o n d i t i o n s were assumed.

The r e s u l t i n g expressions and the parameters employed (which correspond approximately t o -the present IGBR r e f e r e n c e design33) a r e s i m a r i z e d i n Table '7.8. The s t e a d y - s t a t e p a r t i a l p r e s s u r e of each cesium nuclide (PCcs)w a s a func-Lion of t h e depth in-Lo t h e g r a p h i t e (x), t h e p o r o s i t y of t h e g r a p h i t e ( E ) , t h e p a r t i a l p r e s s u r e of t h e parent xenon. a t t h e s a l t g r a p h i t e i n t e r f a c e (Po ), t h e d i f f u s i o n c o e f f i c i e n t s of cesium and xenon , (D, assumed t o be t h eX$uJm? f o r bot,b), and- t h e appropriat,e decrzjr c o n s t a n t s The xenon p a r t i a l . p r e s s u r e ( A ) a n d neutron capture c r o s s sectioris (cr). a t t h e s a l t - g r a p h i t e i n t e r f a c e (Po 1 was, i n turri, a f u n c t i o n of several. Xe terms: Y corresponds t o t h e xenon production r a t e ; S r e f l e c t s t h e xenon loss f r o m t h e fiuel s a l t by deca,y, s t r i p p i n g , and burnup; G r e f l e c t s d i f f u s i o n of xenon i n t o t h e g r a p h i t e ; and, final.ly, E' i s a f a c t o r r e f l e c t i n g t h e e f f e c t of t h e f i l m c o e f f i c i e n t H a t the sall;-gi%phite i n t e r f a c e . (This film c o e f f i c i e n t i s defined. by t h e r e l a t i o n s h i p f a r the f l u x J Xe'

i s t h e concentration of t h e nuclide i n t h e b u l k o f s a l t and Xe C g e i s t h e c o n c e n t r a t i o n i.n equilibrium with Po a t t h e i n t e r f a c e . ) The

wherein C

t e r m S, F, and G also appear i n t h e 135Xe poison fa,ctor, which i s t h e r a t i o of t h e 135Xe poison f r a c t i o n under t h e conditions s p e c i f i e d t o t h e maximum p o s s i b l e poison fraction, approximately 0.005.

The r a t h e r cumbersome expressions i n Table 7.8 were evaluated. with a computer. The e f f e c t s of v a r i a t i o n s i n t h e gas s t r i p p i n g r a t e ( A ),

160

.........

Table 7.8. Parameters

Ca,LciA.ation of Cso P a r t i a l . P r e s s i x e a n d of 13*Xe Poisoniilg ....._

MSW

Assrigned

Values

1.5 x 1013

Avern e t h e r m a l - n e u t r o n flux, cm-3 sec-l

2 3 5 ~ concentration i n f u e l ,

2 x 10-4

L.8 x 10-4

873

6000

3 a t i o of -totalf u e l volume t o f u e l volurne i n f l u x

4.37

4.9

Rxtio of g r a p h i t e area t o f u e l volume i n flux, cm-'.

2.0

2.5

Half t h i c k n e s s of g r a p h i t e s l a b , cm

0.5

P o r o s i t y of g r a p h i t e

0.05

0.09

F r a c - t i o n of f u e l s t r i p p e d p e r

0.001-0.1

0.000~k4,002

Effective di-ffusion c o e f f i c i e n t f o r bot? X e and C s , cm2/sec

1.0-~-~1.0-~ 1.3 X

moles/cm3

Temperature of c o r e ,

Henry's law d i s t r i b u t i o n c o e f f i c i e n t for xenon

second, sec-'-

Fi-lm c o e f f i c i e n t a.t s a l t - g m p h i t e i n t e r f a c e , cm/sec

1014

0.002-0.02

ltj-"'l

0.0004.5

135Xe Poj-son F a c t o r

a y, ci, and A denote, as u s u a l , t h e yield, 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 decay c o n s t a n t uf a g i v e n nucl isle

161 D R N L - D Y G 66-41469

..........

Fig. 7.12. Calculated SteadyS t a t e Pressure of C e s i u m at Center o f Graphite S l a b as a Function or“ t h e G a s S t r i p p i n g Rate (AsT the Diffusion C o e f f i c i e n t (D), and the Film C o e f f i c i e n t (H) Other condit i o n s a r e s p e c i f i e d i n Table 5.8. The upper curves show t h e corresponding v a r i a t i o n i n t h e 135Xe poison f a c t o r .

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

.....

IO+

,--

Bw 10-3 E

v) 3

n W CL

(o-~ c

A,,

the dil”fusion c o e f f i c i e n t s ( U ) , m-Fne d.

0.01

(sec-j)

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

0.001

and t h e f i h c o e f f i c i e n t ( H ) were de.ter-

Cesium Car’nFde Formation. The lnaxirnwn t o t a l press-ure o f ce:;ium ( a t {;he c e n t e r of t h e g r a p h i t e slab) was found t o i n c r e a s e a:; D wa:; decreased ( F i . g . 7.12). T h i s i s a paradoxical remit since it i s usual.ly thought d e s i r a b h ? t h a t t h e g r a p h i t e posses:; t h e l O t 7 e s t possi’~I.e D values. In the

range of D values t e s t e d here, however, t h e r a t e - c o n t r o l l i n g s t e p i n t h e ciiI’fi.ision of parent xenon into t h e g r a p h i t e appearEir3. .to be a t -tile s a l t g r a . p h i t e i n t e r f a c e ( s e e below) and d i d not depend s i g n i f i c a n t l y upon D,

A s a r e s u l t , lowering D f o r xenon and cesium appreciably decreased only t h e d i f f u s i o n of cesium out of t h e g r a p h i t e , causing t h e s t e a d y - s t a t e acculmilation of cesium (p)to b e h i g h e r .

Included f o r cortiparison i n Fig. 7.12 i s t h e p a r t i a l pressure of cesium a t which carbide formation might be expected a t 6oo°C, based on an estimate by man ow it^.^^ It appears t h a t i n a l l c a s e s t e s t e d the cesium p a y t i a l pressure i n t h e g r a p h i t e was high enough t o produce c a r b i d e f o r mation. A s a consequence, it i s l i k e l y t h a t t h e a c t u a l q u a n t i t i e s of cesium which could accumulate wi.tbin t h e g r a p h i t e w i l l be higher than estimated i n t h e p r e s e n t c a l c u l a t i o n s . WTile no d e t a i l e d calcul.ation of this e f f e c t w a s attempted, considerable corni”ort may be found i n t h e f o l lowing observations.

By t h e p r e s e n t c a l c u l a t i o n s t h e amount of cesium accumulation i n the graphi.te i s very s m a l l ; even wi-ti? a xenon p a r t i a l p r e s s u r e as high as 0.01 a t m , f o r example, t h e r e would b e only I atom of cesium present f o r every 25,000,000 atoras of carbon. A t acceptably low 1’5Xe poisoni n g l e v e l s , t h e c a l c u l a t e d maximum cesium concentrati.on would be approximately 100-fold (lo-‘ atmm) lower t h a n t h i s . Thus, although -the present, estimates of cesium accurnulation would probably b e i n c r e a s e d i f ‘ eai-’oi.de formation occurs, an enormous i n c r e a s e ( e . g . , 7.05-fold) i n t h e accumulation could occur b e f o r e it would become a m a t t e r of concern.

Even i f it were assumed t h a t a l l t h e cesium born i n t h e g r a p h i t e were -to remain t h e r e , t h e r a t e of ac_cumu.lation would be low. Thus, under t h e most unfavorable c o n d i t i o n s t e s t e d (H = 0.02 cm/sec, AST = 0.001

sec-I, and D = cm2/sec, which gave a “35Xe poison f a c t o r of 0.9), t h e t o t a l of a l l xenon n u c l i d e s e n t e r e d t h e g r a p h i t e ai; a, r a t e

V s o low t h a t even 3.f i t a l l were t o decay t o cesium, 150 days would be r e q u i r e d t o produce a cesium-to-carbon r a t i o of 3_:1000. With more r e a l i s t i c c a l c u l a t i o n s and a more r e a l i s t i c c a l c u l a t i o n of t h e accumulation r a t e - i n p a r t i c u l a r , a calcul.ation which i n c l u d e s t h e d i f r u s i o n of CsC as w e l l as gaseous cesium out of t h e sl3.h - much n lower accurnula-Lion r a t e s undoubtedly would r e s u l t .

135Xe Poisoning. For most, of ilie v a l u e s of D and H chosen here, t h e rate-determiming sLep w a s t h e t r a n s f e r of xenon across t h e f i l m a t t h e s a l t - g r a p h i t e i n t e r f a c e ( i . e . , F >> 1 and G/F -+ AH/VcC+). Hence

t h e poison f r a c t i o n w a s not very dependent upon D, b u t r a t h e r was d e t e r mined almost e n t i r e l y by t h e magnitude o f 11 and A (Figs. 7.32 and 7.1A).

This r e s u l t , it should be noted, i s compatible w i t h . t h e assumption of onedimensi-onal d i f f u s i o n i n t h e g r a p h i t e ; t h a t i.s, i f t h e r a t e s t e p i n s t e a d had been i n t h e g r a p h i t e , such a cru.de model would have been more questionable.

163 O R N L - D W G 66-11470

0.5 ...................

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

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

0.2 E

2 u 2

s2 z

0.t

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

0.05

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

~ _ .._ ... ...................

0.02

0.0 1 10.6

10-

10."

D (crn'/sec)

F i g . 7.13. Coefficient.

Dependence of t h e Xenon Poison Factor on t h e Diffusion

The 135Xe poison factor, a s well as the cesium p a r t i a l p r e s s u r e s , could of course h e reduced. either by i n c r e a s i n g A or decreasing I3 (Fig.

ST 7.14.);however, it seems unlikely t h a t ; in prac-i;ice t h e s t , r i p p i n g rate cou.ld greatly exceeci. O .On. (corresponding t o a rzrnoval ~ s a ~ . f - t i m eof ap-

proximately 1 min) or Lhat 1-1 wou1.d normally b e kept below 0.01.crn/sec. Approxirilately these c o n d i t i o n s e v i d e n t p i must be inet i f ' the poir;on factor is to be h e l d below 0 .I (poison f r a c t i o n approxima1;el.y 0.095).

ORNL--DWG 66-14471

0.01

0 005

- 0.002 " -r: 5 ._ D

0.001

0 0005

0 0002

0 000 1 0001

0002

001

0005

002

005

iST (sec-'~

Fig. 7.14, Approximate Boundary Values of t h e S t r i p p i n g Xate and t h e Film C o e f f i c i e n t Calculated f o r Various Xenon Poisoning L i m i t s i n t h e Absence of Iodine S t r i p p i n g .

Iodine Removal. Removal of iodine (as HI) by I F sparging of t h e s a l t s would be an e f f e c t i v e way of reducing t h e 135Xe poison f r a c t i o n , provided t h e o v e r a l l removal r a t e i s l a r g e compared w i t h t h e decay rate of 1351 (2.89 X l r 5see-'-, t1/2 = 6.7 h r ) - and it seems l i k e l y t h a t this could be done.35 The anrount of t h e r e d u c t i o n i n t h e case of 233U fissioni n g could be as much as a f a c t o r of 5, I.imited by -the 18 t 3% of t h e 135Xe being produced d i r e c t l y from f i s s i o n . T h i s treatment i s rela-Lively i n e f f e c t i v e i n reduci-ng t h e cesium partial pressure, however, 'oecaiise t h e p y i n c i p a l c o n t r i b u t o r s t o i.t are mass numbers 1.37 and L38, which have s h o r t - l i v e d i o d i n e precursors (A 0.03 and 0.12 sec-' r e s p e c t i v e l y ) .

S a l t Impregnation. Impregnation of t h e g r a p h i t e t o a l i r n i t e d depth w i t h t h e fuel. s a l t would be an e f f e c t i v e means 'io recluxe t h e rate of xenon d i f f u s i o n i n t o t h e g r a p h i t e by v i r t u e of t h e f a c t t h a t both t h e xenon c l i f f i s i o n c o e f f i c i e n t and t h e xenon c o n c e n t r a t i o n would be roughly f o u r o r d e r s of magnitude lower i n an i n t e r s t i t i a l sal-t phase t h a n i n an i n t e r s t i t i a l gas phase e

This s i t u a t i o n can be represented w i t h i n t h e fmmework of t h e present, c a l c u l a t i o n s by -the simple procedure of considering t h e i n t e r p e n e t r a t i o n salt-graphite b a r r i e r as t h e f i l m t o which Ii r e f e r s . Comparison of t h e equation which d e f i n e s H i n a normal film>

= â&#x201A;ŹI

(c -

CO)

165 w i t h t h e equation which would define 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 s a l t graphite b a r r i e r ,

shows t h a t it i s reasonable t o approximate H f o r such a b a r r i e l . by

where t i s t h e depth of salt p e n e t r a t i o n . The e f f e c t i v e D f o r t h i s s a l t g r a p h i t e b a r r i e r should be i n t h e range t o lom8 crn2/sec f o r MSREtype g r a p h i t e ( i . e . , D f o r xenon i n t h e molten s a l t timer, t h e p o r o s i t y / t o r t u o s i t y f a c t o r ) . Assuming a p e n e t r a t i o n depth of 0.1 ern, we can then pla.ce H i n . t h e range to which i s a t l e a s - t t h r e e orders of magnitude below t h e minimum film f a c t o r csLirnated f o r an MSBR. The consequences of such a small film c o e f f i c i e n t a r e t h a t d i f f u s i o n of xeiion i n t o t h e g r a p h i t e i s no longer s i g n i f i c a n t i n determining t h e 135Xe poison f a c t o r ( i . e . , th.e terms contaii-ii.ng F i n t h e expression f o r t h e poison f a c t o r beccme n e g l i g i b l e ) . The 135Xe poisoning i s t h e n d e t e r mined only by A

P.F. ==

(vT/v c

Dl35 (A135 4- hST) + c13fi0 '

Swmnary Tlne p r e s e n t c a l c u l a t i o n s i n d i c a t e t h a t cesium carbide f o r mation can be expected t o occur ri.n an MSBR, b u t i n su-ch sma1.l amoun-Ls as t o be of l i t t l e concern. In a d d i t i o n , t h e s e calcul-ations i n d i c a t e t h a t i n t h e absence of i o d i n e removal, xenon poisoning i n a f u l l - s c a l e MSER w i l l be c o n t r o l l e d p r i m a r i l y by a f i l m c o e f f i c i e n t H and will be reduced. most e f f e c t i v e l y e i t h e r by i o d i n e removal o r by some iiiethod which i n e f f e c t reduces t h i s f i l m c o e f f i c i e n t . F i s s i o n Product Behavior i n t h e FERE - S. S. Kirslis The behavior of f i s s i o n products i n t h e E R E : i s b e i n g s-tudied t o d e r i v e information b e a r i n g on the p r a c t i c a l concerns of c o r r o s i o n and. neutron poisoning. S i g n i f i c a n t c l u e s t o t h e b a s i c n a t u r e of Hastelloy N c o r r o s i o n i n a f i s s i o n i n g m o l t e n - s a l t environment a r e provided by observ a t i o n of t h e v o l a t i l i z a t i o n and.p l a t i n g behavior of f i s s i o n products whose o x i d a t i o n s t a t e s are rela-Lively e a s i l y changed. The chemica.1 f a t e of a number of P i s s i o n product poisons i s important i n detei*rnining t h e i r c o n t r i b u t i o n s t o t h e o v e r a l l poisoning of a r e a c t o r . Thus, f o r example, it i s of i n t e r e s t t o determine .&tat Yraction o f t h e 135Xe procluced by f i s s i o n i n t h e melt i s r e l e a s e d t o t h e cover gas b e f o r e it becomes '"Xe by neutron captu.re Likewise, it i s importarit t o determine wh.e-the% noble-meta.1 f i s s l o n prodlucts which a r e moderate neutron poisons (Mo, Ru, T e , Nb, Pd, and Rh) remain i n t h e c i r c u l a t i n g Yuel, vol.atilize, o r deposit

166 on g r a p h i t e or Ilastelloy N. The r a r e - e a r t h f i s s i o n product poisons, because of t h e chemical. s t a b i l i t y of t h e i r nonvolatil-e f l u o r i d e s , are expected 'GO remain i n -the c i r c u l a t i n g f u e l . There are unique advan-tages i n c a r r y i n g o i i t f i s s i o n prorliict s t u d i e s i n an operatri.ng r e a c t o r r a t h e r t h a n ri.n s m a l l - s c a k 1.a'oorator-y or i n - p i l e t e s t s . F i r s t , i n small-scale t e s t s i t i s d i f f i c u l t t o mock up r e a l i s t i c a l l y t h e geometry, t h e f u e l c i r c i d a t i o n conditions and o t h e r p o s s i b l y s i g n i f i c a n t factors of t h e r e a c t o r environment. Second, although tiie PGW w a s not p r i m a r i l y designed f o r t h e chemist's convenience, s e v e r a l r e a t u r e s make i t rather w e l l adapted t o chemri.cal s t u d i e s . Most importantly, a f a c i l i t y e x i s t s f o r t a k i n g s i z a b l e samples of f u e l s a l t from t h e pump bowl during r e a c t o r o p e r a t i o n . I n -tile same f a c i l i t y it i s possib1.e t o expose s e l e c t e d metal samples t o b o t h t h e covei- gas and t h e f u e l m e l t i n t h e punp bowl. Provrisions exis-i; for t a k i n g samples of t h e r e a c t o r cover gas and are b e i n g improved t o permit continuous monii;orring and t h e t a k i n g of concentrated samples. F i n a l l y , provisioiis were m a d e f o r inser-Ling r e movab1.e 1-ong-term s i n v e i l l a n c e specimens of Iiastelloy N and g r a p h i t e i n t h e r e a c t o r core of t h e MSRE. These f a c l . U . t i e s and advantages are a v a i l able only wiLi.1 g r e a t d i f f l i c u l t y i n small-scale i n - p i l e t e s t s . The p r i n cipal. l a c k s from t h e chemist's viewpoint a r e f a c i 1 . i t i e s f o r d i r e c t samp l i n g of t h e pimp bowl cover gas and f o r exposing m e t a l and g r a p h i t e samp l e s t o .the pump bowl abmosphere and f u e l phase f o r longer periods of Lime. This r e p o r t on f i s s i o n product behavior w i l l cover t h e i n i t i a l r e s u l t s from f u e l s a l t sampling, from t h e exposuxe of m e t a l samples t o t h e pump bowl gas and liqirid. phases, from the f i r s t examination of the 1-ongterm s u r v e i l l a n c e specimens of g r a p h i t e and Kastelloy N, and from t h e a n a l y s i s of t h e f i r s t sample of r e a c t o r cover gas taken during r e a c t o r operation. f i e 1 S a l t Samples. Usiilg t h e pump bowl sampling f a c i l i t y , a l a r g e number of 10- and 5 0 - g f u e l sal.%samples were taken during reactor ope r a t i o n t o monitor changes i n t h e concentrations of oxide, b u l k f u e l components, and c o r r o s i o n products. Metal sampl-es were a t t a c h e d t o -the 10-g sampling assemb1.y f o r observati.on of t h e v o l a t i l i z a t i o n and pl-ating behavior of f i s s i o n prodircts during f i v e of' t h e s a l t samplings. ii'iiese f i v e s a l t samples were d e l i v e r e d t o t h e a n a l y t i c a l hot c e l l s w i t h i n a f e w hours of sampling and were rapi.dly powdered, weighed, dissolved, and analyzed radiochemically f o r tiie 15 iso.topes l i s t e d i n Table 7.9. The stisontiurn and cerium i s o t o p e s were determined as f i s s i o n monitors, s i n c e t h e s e elements have convenient h a l f - l i v e s and s t a b l e f l u o r i d e s which should remain i n t h e m e l - t . The rutheniuai and molybdenum i s o t o p e s were r e p r e s e n t a t i v e of noble rnetals. The t e l l u r i u m and i o d i n e i s o t o p e s were of i n t e r e s t f o r t h e i r v o l a t i l i z a t i o n and p l a t i n g p r q e r t i e s as precursors of 135Xc. The 239Np and 239Pu i s o t o p e s were measured as i n d i c a t o r s of ihe epithermal f l u x i n t h e MSRE.

The data l i s t e d i n Table '7.9 show t h a t t h e sti-oiitiim and c e r i m i s o t o p e s behaved i n a r e g u l a r and expected manner. The "Sr a n d 143Ce iso-topes appear t o be t h e most r e l i a b l e f i s s i o n momi.tors f o r i n t e r r u p t e d poTrrer o p e r a t i o n . The average of t h e four values f o r "Sr a t t h e norninal

F i s s i o n Products i n

Table 7.9.

hrm3 S a l t

Saqles

Sanple

FP6-17

FP6-19

p’P7-7

Date

s m p l i a g time a . 3perat ing t i n e , a q s

5-23, 0430

5-26> 0400

6-27, 0243

2.3

2.5

13.3

Nominal pover, Ivlw

5.6

‘7.3

7.2

Fission Yield

5.81 5.3

1.08 x 101’

4.75

1.80 x 1310 2.65 x 1910

5.7

9.8 x 10‘Q

lolo

6.06

4.68

3.0

1.81

0.9

4.5 x 1o1o

0.35

4.7 3.1 6.9

6.1

FP7-12 7-13, 0336

4.2

11.9

7.2

Disintegrations per PXnu%e per Cram of S a l tb

($1

6.0

PP7-10 7-6, 0238

IO8

3.12 X 101*

2.45

10” 1.08 x 10’1 X

9.5 x

loLo

1.20 x

1.16 X 10‘l

1.19 x L o l l

2.23

1.45

10”

2.96

6.10

10’‘

1.5 x lo1’

3.51 X 10” ? 7.05 x 1s9 2.47 X 10’‘

4.21

x 131°

4.20

1.31

1.50

10”

9.70

10” 10”

9.51

2.42 x

10” 10” 10’’

lo9

1.31

lo1’

1.51 x lo1’ 2.93 X 13‘’

6.69

1.43 X

1.10 x

lolo

3.96

X lolo

lo1’

3.50 x 1010

9.67

5.15 x 10’0 5.0 x 1o1o 1.35 X 10” 1.17 X loL1 5.35 x 10” 7.50 x 105

3.64 x 1o1O

1Olo

10’’ 10”

6.88 X 10“

1.32

6.02 X 10’ X

1.32 1.49

3.15 X 1O1O

7.14 x l o 9 3.76 X

2.13 x

4.50 1.40

10”

X 10’l

1.0 x 10’2

8.77 x 105

3.81 X 10”

5.36 x 13’0

1.45 x

1.11 x

lo1’

1.08 x 1012

1.20 x 106 c

aCofiSin-J.om operating time s l n c e previcus s k ~ u t & o ~ of m iiiore t h a n 12 hr duration or change i n p w e r level. bCalculat;ted a t sampling time. C

Alpha c o u n t s p e r minute per g r a ~ .

'TabLC:

7.1.0. Surrunary of Pump Bowl 'Yest K e n u l t s Averages of f i v e runs

9gMo

^...._._ Sal-t, 5 o.i t h e o r e t i c a l ~

Latch h i ) Silver

BastelLoy N

Liquid phase ( s s )

run.

~2~~

.._. ..__. 30

i 0 . 5 ~ ~ .

i 0 3 ~ ~ a

1 0 6 ~ 1351 ~

>lo0

lox

0.5x

3x -+ lx 25X -' 0.3X 40x ;x

2x 1X

3x 5x

-9

1311

1 1 1

8Xb 2x

1331

.....__....._I

103

0 2 x 0 1x 0 2 x 0

98 1.5X 0.9x 0.5X 0.8X

%ercent l o 3 R u deposited on metal.. samples uniformly decreased f r o m f i r s t t o f i f t h

b~ = ctisintegrations p e r mii1l;ite of given isotope p e r %ram o f s a l t ,

(1-25x 1.0'-'d - i s rnin-l g - l ) x (4.68 x

lo6

x (200 M e v / f i s s i o a ) x

i>]+

f i s s i o n y i e l d of "Sr)

[(fractional

x (60 s e c / m i n ) ]

'che c a l c u l a t e d f i s s i o n power d e n s i k y i s 5.4 MW, o r about 75% of t h e nominal t o t a l power density. Using t'Lle average of t h e four L43Ce v a l . 1 ~ ~ a t t h e nominal 7.2-Mw power, t h e c a l c u l a t e d power i s 6.3 Mw, o r 8'7% of the noniiiial v a l u e . For molybdenum and ruthenium i s o t o p e s , t h e c o n c e n t r a t i o n s found i n sal-t s m p l e s showed much more s c a t t e r , which. may w e l l h e r e a l . The f i r s t row of data i n Table 7.10 shows t h e a v e r a g e s of t h e amoimts of these i-sotopes found. compared t o t h e amounts c a l c u l a t e d t o bc formed usirig "Sr ( a r b i t r a r i l y ) a:; t h e f i s s i o n monitor J.n e a c h r u n . The r e a s o n f o r t h e i m p o s s i b l y h i g h values f o r lo5Ru i s b e i n g s o u g h t . The 132'Te v a l u e s v a r i e d l i t t l e Lmong t h e 7.2-Mw ruils b u t r e p r e s e n t e d low f r a c t i o n s of the t o t a l amount formed (Table 7.10). The i o d i n e i s o t o p e s showed r e l a t , i v e l y li.t-ile s c a t t e r , and t h e m o u n t s tound corresponded w e l l w i t h t h e amounts c a l c u l a t e d from the "Sr v a l u e s .

The epithermal. flux i n t h e MSRE has n o t y e t been ca,lcula-ted from t h e neptunium and. pliltonium va?.iies i n Table 7.9.

Pump Bowl V o l a t i l i z a t i o n and P l a t i n g T e s t s . Advantage w a s t a k e n of t h e e x p e r i m e n t a l p o s s i b i l i t i e s of t h e pump bowl s a l t sarrtpl.ing f a c i l i t y t o c a r r y o u t some q u a l i t a t i v e t e s t s t o d e t e c t t h e p r e s e n c e of chemically r e a c t i v e f i s s j - o n p r o d u c t s p e c i e s in t h e pump bowl cover gas and to d e t e r mine which f i s s i o n p r o d u c t s would pla,%e on c l e a n metal. s u r f a c e s from t h e fuel s a l t phase.

169 ‘%Ecopper. f u e l salt sai:ipling ladle is a t t a c h e d by a double s t a i n less steel c a b l e to a nick-el-plated i r o n .latch which fli-Ls Lnto a mecha1 i j . m . f o r 1oweriIig and raising t h e assembly i n a. p i p e l e a d i n g frorri the p1uil-p b c j w l t o t h e sampling cubicle above t h e r e a c t o r . To de-tee-t t h e presence of chemical-ly reactive f i s s i o n products i n the gas phase, c o i l s of O.OlS-in.-diaa slilver and H a s t e l l o y N wire were wound oa t h e small stainless s t e e l c a b l e s for a d i s t a n c e of 2 in.. below the bot;i;om of t h e 1-atcb. Die l a t c h and t h e wlre cot]-s were l.%-terleached and analyzeti for gasL?ou.a fission products. The lower 2 - i n . l e n g t h s of -Lhe stainless s t e e l ca7jl-e~,just above t h e copper ladle we1-e leached and. aimlyzed s i ~ i G l a r l ~ ~ t o d.eterinine vhich fission prod1.ncts p l a t e d from. t h e fuel melt. F i g u r e 7 1.5 shows t h e :sampling asserflb1.y with wire coils attached.. The swapling device was su.inmergeci i n the pump bowl- for t i m e s va.rying from 1. min. t o 10 min. It was t h e n r a i s e d 2 ft and al1.owed -to cool for 10 min and. then rai.sed t o the smtpling ci~’oic1.e The metal axid s a l t samples were delivered T i l a c a r r i e r t o the hot i m a l y - t i c a l laboratory, u s u a l l y - w i - L h i i i 3 hr of tbe s:xripling time. The s a l t sample was prepared for. analysis by the proc5diire ~ 1 ~ ~ 1 1 1 . a rri?;ove. ized The stainless :;tee1 cables were cl-ipped. to provide s e p s r a t e samples of the l a . t c h , Lhe siI.ver coil, t h e Ha:;telloy P3 coil-, a n d tbe s t a h l e s s s-beel. cable exposed to the F u e l melt. The m & a l smipLes were leached first with a n a l k a l i n e mixture o f Versene, b o r i c a c i d , and. c i t . r i c ;zcid t o remove iodirie witno!it vol.atiJ.j.zai;ion. Then they were leached.with 8. warin m i x t u r e o f WJ03 and.H C I u n t i l t h e r a d - i o a c t i v i t y wa,s 1 . e ~ than ~ 1% of the o r i g i n a l . read.ing ( u s . u a ~ yg r e a t e r than 500 rf’ilr a t con-tact1 Sjil-iitions OP -tile origina,:~.1.eac-h s o l u t i o n s were: sent t o t,he rad.iocherxical se:pa.ra.tions group fox- o v - w a l l gamia scans and estirrtations of :several i n d i v i d u a l . isot,opes e

The overall g~~~mm:a scan.s showed t h n t the principal. a c t i v i t i e s in t h e m e t a l samples exposed t o t ~ i r ? pimp -t:oisrl gas phase were ‘ 3 2 ~a;nd~ ,’.321~ w i t h smal.ler mmounts of 1311: and 99Mo. T h e 14,0Ba-”40ik and 95Z1:-95M1 pesks wtiicli were pro~n.inenti n t h e gamrra r;:pectra of -file 1. s a l t s a r r i ~ ~ l . ~ : ~ , vpy(2 mu.ch lower i n t h e r w t a l samples Tnis i n d i c a t e s -t:kiat t h e observed activities were riot due to cond.ensation of fuel s a l t mist on t h e me.tal :;j?eciriielns S i m i l a r l y , t b e gamma sisec t m of t h e sihmerged st;air:d s : u ~ ~ ~ j :.rere l e : ~ qi!jTite d . i f f e r e n - 1 ; from t h o s e of x?el s a l t Co:rrespon no a d h e r i n g pa.r‘cicr:les of fuel s a l t w e r e v i s i b l e on m y of’ the rrietal s:s)ecciIt was l a t e r found. {Table 7.lo) t h a t t h e amomits of t e l l i x - i u m , enri.i.m, an (1In0 lyb dei i i ~ idepo s 1.te d. on t b.e .meta 1 sample ;3 c ori-e spolzd e d. t o t h e mi!mnts in :;ever&!. gram:; of f u e l s a l t

The g,anm.a 6c a m i n d i c a - te d. t h a t q1.i.ian.t:ita-t;ive radiochemical..e s t ima’iions ~ o : r132’~l’e - 7 13’1 and 9 9 ~ , 1w~o i i . ~’oe u s e f u l . 111 aiiditri.on, estirna-tion:; were made of 1331, 1551, 1 0 3 m , ~ ~ j and ~ 1~ 0 6 ~ i1 2 . ~ . ~11e , 1-esij.l-t;sof these sna1.y-

ses are sm.mar.izctd i n Ta11I.e 7.10. Althoi.i,g;ii !;he exposure t-imes f o r .the were I, 2 , 5, 3.0, a.ri,d. 10 min, there was no corresponding v a r i a t i o c of :imoun%s of the several i s o t o p e s d e p o s i t e d .Prom ei’cher t h e gas o r t h e liquid phases. ‘The s e a - t t e r of resu1.t:; for a g i v e n iso-tope between o f t e n a factor of 2 and. some-times a f’eictor. of 5 or more ms, t h e averaged results given in Tab1.e ‘7. 10 a r e 11~ore easitly in?;erpretecl t h a n a t a b u l a t i o n of t h e indi.vid.u.a.1 :results As in t,he c a s e of’ some of i;he s a l t arla,lyses, t h e obsersrecl scat-Ler i s :n-ucb grcciter thari the aormal e r r o r of rad3.ocherillica.l amalyses ar?d und.oi.ibi;eciljr five? r u n s

170

Fig. 7.15. Pump Bowl Deposition Testing Assembly. represents real large variations in the mounts deposited. for these variations are as yet un

The causes

The results in Table 7.10 reveal a striking degree of volatili and plating olybdenum rut i m , and tellurium on clean metal faces. Lar ounts of 4 9 ~ 0 e found on the metal samples in both onding*, only the gas phase and fuel phase of the pump bowl. Corr about 60% of the theoretical yield of "Mo was found in the fuel salt

samples. The r e s u l t s f o r ruthenium were s i m i l a r l y s p e c t a c u l a r . The f r a c t i o n s of t h e t h r e e ruthenium i s o t o p e s remaining i n t h e s a l t decreased with i n c r e a s i n g h a l f - l i f e , suggesting t h a t slow r e a c t i o n s a r e removing ruthenium from t h e melt. I n successive runs, t h e amount of 41-day lo3Ru t h a t deposited on metals s t e a d i l y decreased from t h e f i r s t run t o t h e l a s t (although t h e exposure time of t h e samples increased from 1 t o 10 min), as i f t h e amount i n s o l u t i o n were decreasing with time. This behavior i s not explained

For 132Te t h e amount remaining i n t h e melt i s a l s o low ( 3 0 $ ) , and t h e corresponding gas- and liquid-phase depositions a r e high. For 1311 1331, and 'j51 most of t h e element remains i n t h e melt, although high a c t i v i t i e s of i321were observed on t h e gas-phase specimens. The s h o r t i s , however, a daughter of t h e r e l a t i v e l y long-lived 132Te, l i v e d 1321 which w a s shown t o v o l a t i l i z e r e a d i l y . Rather l e s s 1331 and ' " I was found on t h e metal specimens t h a n of molybdenum, ruthenium, and t e l l u r i u m . However, no 1351 a t a l l w a s d e t e c t e d on t h e metal specimens. Correspondingly, t h e t e l l u r i u m precursor of 1351 has a h a l f - l i f e of only 0.4 min, while 133Te and 13'Te have h a l f - l i v e s of 63 and 24 min. Apparently very l i t t l e t e l l u r i u m can v o l a t i l i z e o r p l a t e i n 0 . 4 min. It t h u s appears t h a t t h e v o l a t i l i z a t i o n and p l a t i n g c h a r a c t e r i s t i c s of i o d i n e a r e determined by t h e behavior of t h e precursor t e l l u r i u m .

Tellurium and i o d i n e had been d e t e c t e d i n t h e gas l i n e s of previous i n - p i l e t e s t s , b u t t h e v o l a t i l i z a t i o n of molybdenum and ruthenium w a s s u r p r i s i n g . The only v o l a t i l e compounds of molybdenum and ruthenium a r e t h o s e of valence 4 o r g r e a t e r . The p l a t i n g behavior of t e l l u r i u m , molybdenum, and ruthenium a l s o i n d i c a t e s t h a t t h e s e elements a r e present w i t h valences g r e a t e r t h a n zero. However, a l l p o s i t i v e l y charged ions of t h e s e elements should be reduced t o t h e m e t a l l i c s t a t e by t h e m e t a l l i c chromium i n Hastelloy N. These c o n s i d e r a t i o n s suggest t h a t t h e Hastelloy N c o n t a i n e r v e s s e l and piping of t h e MSRE may be p r o t e c t e d by a l a y e r of noble-metal f i s s i o n products, p e r m i t t i n g t h e e x i s t e n c e of higher oxidat i o n s t a t e s i n t h e melt. If i t i s assumed t h a t 30% of t h e noble metals produced by f i s s i o n i n t h e MSRE o p e r a t i n g a t 7.2 Mw a r e deposited on an estimated metal s u r f a c e a r e a of lo6 em2, it may be c a l c u l a t e d t h a t t h e metal f i l m would grow a t t h e rate of about 0.3 A/hr. It i s t h u s not unl i k e l y t h a t a l l t h e metal s u r f a c e s exposed t o f u e l i n t h e MSRE a r e p r e s e n t l y coated with s e v e r a l hundred angstroms of noble metals.

It i s n o t a simple matter, however, t o produce adherent pinhole-free e l e c t r o p l a t e s , so t h a t a p l a t e hundreds of atoms t h i c k might not p r o t e c t a g a i n s t t h e reducing a c t i o n of t h e base metal. Furthermore, it has been c a l c u l a t e d on a very reasonable b a s i s t h a t approximately 1% of t h e uranium i n t h e f u e l i n t h e MSRE should e x i s t i n t h e t r i v a l e n t condition. Noblemetal i o n concentrations should be i n f i n i t e s i m a l i n t h e presence of t h i s concentration of t h e s t r o n g l y reducing U3+. These very b a s i c puzzles i n e l u c i d a t i n g noble-metal f i s s i o n product behavior i n t h e MSRE have not y e t been solved. Future pump bowl experiments w i l l involve looking a t t h e behavior of s e v e r a l more elements (noble metals, o t h e r c a t i o n s with v o l a t i l e f l u o r i d e s , neutron-activated Hastelloy N c o r r o s i o n products, e t c . ) and attempts t o

172 take small samples of the pump bowl cover gas. The determination of the reducing power of the fuel salt would also be helpful in explaining fission :,,-educt behavior. Examination of the Graphite Surveillance Specimens. A package of MSRE graphite and Hastelloy N surveillance specimens has been exposed to

a fissioning molten-salt environment along the central axis of the MSRF: for 7800 Mwhr of power operation. After the reactor shutdown of July 17, 1966, the package was removed from the reactor and disassembled in a hot cell. Rectangular bars of graphite, 5 to 9 in. long, 0.66 in. wide, and 0.47 in. thick, from the bottom (inlet), middle, and top (outlet) of the reactor core were made available for detailed examination. The surveillance specimens were contained in a perforated cylindrical tube of Hastelloy N, 5-1/2 ft long, 2 in. in diameter, and 0.030 in. thick. Rings of this tube approximately 11/16 in. in height and 10 g in weight were sawed out of the bottom, middle, and top regions of the tube to provide Hastelloy N specimens for fission product deposition studies.

The graphite bars were first sectioned transversely with a thin Carborundum saw to provide specimens for photographic, metallographic, autoradiographic, x-radiographic, and surface x-ray examination. Specimens were saved for other possible tests (spark spectroscopy or electron probe). The remainders of the bars, 7 in. long for the middle specimen, 2-5/8 in. long for the bottom sample, and 2-7/8 in. long for the top sample, were used for milling off successive surface layers for fission product deposition studies.

(a) Visual, Autoradiographic, and X-Radiographic Examinations. The graphite specimens showed no visible signs of corrosion or chemical change. No metallic or salt films were discernible under low-power magnification, which revealed the original machining grooves on the graphite. The middle sample (Y-2) was known to have a crack near one end before insertion into the reactor. The crack was still visible after removal but had not propagated further. Some of the graphite specimens in one region of the package had cracked due to mechanical stresses caused by the uneven thermal expansion and contraction of the tightly packed Hastelloy N and graphite specimens. A small piece of the bottom sample (VA-1) had cracked off during the disassembly of the package. These cracks should not reflect on the overall integrity of the irradiated graphite specimens. Prints of an autoradiograph and an x radiograph of each of the three graphite specimens are shown in Figs. 7.16 to 7.18. The x radiographs were taken on thin (0.020-to 0.060-in.) transverse slices of the graphite bars. The autoradiographs were taken on adjacent transverse slices after mounting in epoxy resin and polishing for metallographic examination. The x radiographs show no general deposition of fuel salt nor of heavy elements on the surface of the graphite. A hint of penetration or deposition is visible near one corner each of the bottom and top graphite samples. The crack in the middle sample is clearly penetrated by fuel salt. The edge of the cracked bottom sample shows no foreign material, indicating that the crack occurred after removal from the reactor.

173

(Y-2).

F i g . 7.16.

Autoradiograph (a) a i d X Radiograph ( b ) o f Middle Graphite

The autoi-adri.ographs i n d i c a t e a t h i n f i l m of h i g h l y r a d i o a , c t i v e mat e r i a l on tiie exposed s u r f a c e s a? t h e graphl.te and c o n f l m t h e presence of sa2.t i n t h e crack of tiie middle specimen. These p i c t u r e s a l s o show t h a t t h e pene-Lral;ion of t h e r a d i o a c t i v e materi-a1 i n t o the i n t e r i o r of t h e g i - a p h i t e i s by no means uniform. The nonuniform n a t u r e of t h e p o r o s i t y of g r a p h i t e h a s been demonst:rat,ed i n gas p e r m e a b i l i t y t e s t s . The o b s e r v a t i o n s d e s c r i b e d h e r e a r e g e n e r a l l y i n acco-rd w i t h t h o s e from previous i n - p i l e tests. The g r a p h i t e i s n o t v i s i b l y a f f e c t e d , and m e r e a r e no s i g n s of chemical a t t a c k , f i l m f o r m a t i o n , or s a l t p e n e t r a t i o n .

(b ) M e t a l l o g r a p h i c Examination. Metal-lographs of t r a i i s v s r s e secâ&#x20AC;&#x2122;cions of t h e t h r e e g r a p h i t e b a r s are shovm i n F i g s . 7.1â&#x20AC;&#x2122;3 t o 7.21.. The s t x i i c t u r e of t h e graphi-Le i n all c a s e s appeared normal and undamaged under bo-th b r i g h t - f i e l d and p o l a r i z e d- l i g h t i l l w n i n a t i on. No met a l l i e, c a r b i de, o r sa1.t films were v i s i b l e on t h e surfaces of b h e speciirieiis. No s i g n of s a l t p e r l e t r a t i o n w a s observed e x c e p t i n t h e case of t h e cracked middle spec1.men. Here v0id.s were observed which probably had been f i l l e d w i t h sa1.t b e f o r e p o l i s h i n g w i t h a w a t e r suspensi-on of t h e p o l i s h i n g co!ripound. The o t h e r g r a p h i t e speciirnens were p o l i s h e d u n d e r CC14 t o a v o i d d i s s o l u t i o n of f u e l salt.

3-74

Fig. 7.17. Autoradiograph ( a) and X Radiozraph (b) of Top Gra-phiLe

(VH-5).

Fig.

(VA-I.)

7.18. Autoradiograph (a) and X Radiograph (b) of Bo.t;tom Graphite

175

Fig, 7.19. Metallographs of Midd1.e C m p h i t e ( Y - 2 ) . (b) p o l a r t z e d light.

Cield;

(a) B~Q12.f;

Fig. 7.20. Metallographs of Top Gi-aphite (VH-5). (b) polarized light.

(a) Bright f i e

Fig. 7.21. Metallographs of RoLtorri G r a q h i t c (VA-1) â&#x201A;Źield; (b) pol. arized li p;lnt.

(a) B r i g h t

178 A fuel-sal-t-exposed s u r f a c e of t h e middle g r a p h i t e 'oar w a s iiiounted f o r h o t - c e l l x-ray examination of t h e s u r f a c e Tor m e t a l l i c f i l m s o r o t h e r contamination. Only g r a p h i t e l i i i e s were observed. Because of t h e negat i v e r e s u l t of t h i s t e s t , t h e o t h e r g r a p h i t e specimens were not. examined by t h e x-ray technique.

( e > Mill.ing of Surface Layers of Graphite. The va1uabl.e coiltributI.ons of J'. G. Morgan., M. F . Osborne, and. H. E. Ho'nertson i n planning, developing h o t - c e l l me.ti1od.s f o r , and s t a r t i n g the work on t h e sampl.ing of t h e g r a p h i t e specirnens a r e g r a t e f u l l y acknowledged. A very ingenious "planer" w a s designed and b u i l t by t h e Hot C e l l s Operation Group f o r m i l l i n g t h i n l a y e r s from t h e f o u r long s i r f a c e s of each of t h e g r a p h i t e ' o a r s . The c u t t e r and t h e c o l l e c t i o n system lwere s o designed t h a t a l a r g e f r a c t i o n of t h e g r a p h i t e dust removed w a s c o l l e c t e d . By comparing t h e c o l l e c t e d weights of the g r a p h i t e samples with t h e weight loss c a l c u l a t e d from t h e i n i t i a l and f i n a l dimensions of t h e g r a p h i t e b a r s an.d t h e i r known dens i b i e o , t h e average sampling losses were 4.55 f o r t h e middle bar, 1.8.9% f o r t h e t o p b a r , and 9.1$ f o r t h e bottom b a r .

The pai;terns of sampling of t h e g r a p h i t e s u r f m e l a y e r s a r e shown i n Fig. 7.22. An i d e n t i f y i n g groove w a s c u t along t h e length of t h e middle of t h e grapliri.t,e s u r f a c e which w a s pressed a g a i n s t another g r a p h i t e surf a c e i n t h e o r i g i n a l siirveI.llance package. The o t h e r t h r e e s u r f a c e s were exposed t o c i r c u l a t i n g f u e l s a l t . The numbers of t h e l a y e r s i n Fig. 7.22 i n d i c a t e t h e order i n which t h e l a y e r s were c u t from t h e g r a p h i t e b a r s . A f t e r each l a y e r w a s cut, from a b a r , t h e m i l l i n g apparatus and t h e bar were vacuumed t o avoid c r o s s contami.natrioii of samples. Each powdered g r a p h i t e sample was placed i n a s m a l l capped p l a s t i c b o t t l e and weighed. The middle b a r w a s measured with a micrometer t o determine t h e depth of each c u t . Tlnis time-consuming operation vas omi.Lted f o r t h e o t h e r t w o b a r s , s h c e j.t became evident t h a t t h e depth of c u t could be more a c c u r a t e l y c a l c u l a t e d from t h e weight of t h e sam,p,l.e removed. The average depth of c u t w a s 0.0075 i n . f o r t h e middle b a r and 0 . 0 1 1 i n . f o r t h e o t h e r two b a r s . A c l e a n unirradiated.MSl3E g r a p h i t e specimen w a s sampled with t h e m i l l i n g device I.n t h e standard manner a f t e r t h e n i n t h c u t and a.l"ter t h e l a s t c u t on t h e middle g r a p h i t e b a r t o provide comparison samp l e s t o i n d i c a t e t h e l e v e l of c r o s s contamination i n t h e h o t - c e l l m i l l i n g operation. A s seen i n Fig. '7.22, t h e salt-exposed s u r f a c e s of t h e middle b a r were sampled t o a depth of s i x or seven l a y e r s , or about 0.050 i n . The s u r f a c e s i n c o n t a c t wit'n g r a p h i t e were more thoroughly sampled i n t h e ol;her b a r s .

( d ) F i s s i o n Product Analyses i n Graphite Samples. The powdered g r a p h i t e samples were d e l i v e r e d t o t h e Radiochemi.ca1 Separations Group, and weighed portion? were dissolved i n a hot mixture of iIN03 and II2S04. The gases evolved were passed through a condenser, a charcoal t r a p , and an a l k a l i n e s o l u t i o n t o recover any v o l a t i l i z e d i o d i n e o r ruthenium. Aliquots of t h e s e s o l u t i o n s were analyzed radiochemically f o r t h e i s o t o p e s l i s t e d i n Table '7.11. The f i r s t m i l l e d sample of each g r a p h i t e s u r f a c e w a s a l s o analyzed f o r uranium by t h e fluorometric method. No uranium w a s detected with a s e n s i t i v i t y l l r n i t of about 30 pg of uranium per square centimeter of g r a p h i t e su.rface. This f i n d i n g will be confirmed. by more s e n s i t i v e neutron a c t i v a t i o n methods.

179 CWG 66 11378

GRAPH1i E

IDENTIFYING GROOVE

MIDDLE GRAPHITE

L ~

4.. .......

0660in

BOTTOM CRADHITE

Fig

7.22.

Sciierne f o r M i l l i n g G r a p h i t e Samples.

The radiochemical. d a t a s o f a r r e p o r t e d are given i n T a b l e s 7.1.1 t o 7 . W f o r -the middle, t o p , and bottom g r a p h i t e b a r s r e s p e c t i - v e l y . The d a t a a r e g e n e r a l l y in'cernal-ly cons?-stent f o r a griven b a r , and t h e a g r e e ment between b a r s ts good. Very f e w i n d i v i d u a l values are out of l i n e , which i s t o t h e c r e d i t of t h o s e ri.nvolved i n -the sampling and i n t h e a n a l y s i s of t h e samples.

From t h e n e u t r o n poj-son stand.point, t h e r e s u l t s of n o s t t n t z r e s t are t h o s e for. "Mo, 103:iu, a n d 95Nb. It i s s e e n j.n ':Cables 7.12 t o 7 . W t h a t t h e c o n c e n t r a t i o n s of t h e s e i s o t o p e s a r e c o n s i d z r a b l e i n t h e f i r s t l a y z r and t h a t t h e a c t i v i t i e s f a l l o f f by a f a c t o r of about 100 i n t h e second l a y e r . Tellurium-W2, which i s a3.so noble i n t h e s e n s e of p o s s e s s i n g f l u o r i d e s of o n l y moderate stabi.U:t;y behaves r a t h e r s i m i l a r l y , b u t i t s c o n c e n t r a t i o n drops o f f less r a p i d l y with peneti'a1,ion d i s t a n c e . Beyond a p e n e t r a t i o n d e p t h of about f o u r c u t s t h e a c t i v i L i e s of molybdeiiim,

180 ruthen3.urnY and niobium approach 'che contamlnation background ( s m p l e s 10 and 2 4 i n Table 7.11.)>while t h a t of 132Te i s d i s t i n c t l y - higher. It i s p r e s e n t l y thought t h a t t h e deposition of molybdenum, ruthenium, and probably ni0bi.m i n t h e g r a p h i t e may be due t o the r e a c t i o n of v o l a t i l e hexaf l u o r i d e s or pentaf l u o r i d e s with g r a p h i t e , depositing lower f l u o r i d e s or carbides. There i s iicl chemical. reason t o expect t h e lower f l u o r i d e s of molybdemm o r ruthenium t o p l a t e on g r a p h i k . On t h e o t h e r hand, t h e pump bowl experiments d e f i n i t e l y e s t a b l i s h e d t h e v o l a t i l i t y of molybdenum and ruthenium, pro'nably i n t h e forms of MoF6 and RuF5.

The behavior of 14'Ba Y 8 9 S r , "41Ce 144Ce, sild 137Cs, a l l of which have xenon o r krypton precursors, i s distinct1.y d i f f e r e n t . The g r a d i e n t of a c t i v - i t y with p e n e t r a t i o n d i s t a n c e i s much less, and it appears t o b e a r a r e l a t i o n s h i p t o t h e h a l f - l i f e of t h e rare-gas precursor involved. Thus with a 16-see ""Xe precursor i s much s t e e p e r t h a n t h e g r a d i e n t f o r '"'Ba t h a t f o r 89Sr, which has a 3.2-min 89Kr p r e c n r s o r . Apparentl.y, t h e l o n g e r - h a l f - l i f e r a r e gases can achieve a f l a - k t e r g r a d i e n t by d i f f u s i o n before they decay t o t h e observed isotope, vhich i s sssumed t o remain where deposited. l'he p e n e t r a t i o n data f o r 14'Ba and 89Sr f i t t e d w e l l a simple d i f f u s i o n model which l e d -Lo xenon and kryptoil d i f f u s i o n c o e f f i c i e n t s of about I X f t 2 / h r i n MSRE g r a p h i t e . To explain why ""Cs Y which has a 3.8-min '"'Xe precursor, has a much f l a t t e r profi3.e Ynan 89Sr i n Table 7.11, it may f u r t h e r be p o s t u l a t e d that; 137Cs i t s e l f d i f f u s e s , r a t h e r than remainjng where it w a s born. T'ne i n t e r n a l "'Cs concentration of 2 X l.or' dis min-' g-", or about 1 atom of 137Cs per lo8 a1;oms of graphi t e , should have negl-igi'ole chemical e f f e c t on t h e i n t e g r i t y of t h e graphi t e s t r i x t u r e . Only a few values have y e t been obtained f o r 95%r. il'h-is element i s expec-Led t o remain i.n t h e f u e l s a l t , with l i t t l e -tendency t o v o l a t i l i z e o r p l a t e . Thus t h e m o u n t found. i n t h e g r a p h i t e should repres e n t only i n j e c t i o n by f i s s i o n r e c o i l . Correspondingly, t h e amoiint i n t h e g r a p h i t e i s low compai-ed to t h e noble meta1.s.

The concentratLon of 13'1 i n t h e g r a p h i t e i.s a l s o low a t t h e surface, and i t s radieiit i s similar t o t h a t of 132Te. 1.t i s p o s s i b l e t h a t t h e 24-min ""Te d i f f u s e d i n t o t h e g r a p h i t e as TeF6 o r TeF4 and then decayed to 1.711 However, it i s d i f f i c u l t t o s e e why t h e i o d i n e d i d not di.ffuse back out of t h e g r a p h i t e , u n l e s s it formed a n o n v o l a t i l e compound with o t h e r f i s s i o n product atoms i.n t h e g r a p h i t e . While it i s not p o s s i b l e a-t t h i s time t o account s a t i s f a c - L o r i l y f o r t h e f a c t t h a t t h e todine concent r a t i o n s i n g r a p h i t e a r e low, t h e i m p l i c a t i o n of t h e l o w 13'1 concentrat i o n s i s t h a t t h e 135i concentrations w i l l be s i m i l a r l y low. Thus l i t t l e 135Xe w i l l be born i n g r a p h i t e due t o t h e previous immigration of 1351.

Since t h e depths of c u t of t h e many g r a p h i t e samples were not t h e same, e s p e c i a l l y f o r differen-t; ba.rs, it i s not easy t o compare t h e amounts of t h e various i s o t o p e s i n t h e f i r s t l a y e r from the d a t a i n Tables 7.11 t o 7.1.3. Since, a l s o , t h e main p r a c t i c a l i n t e r e s t i s i n t h e noble-metal f i s s i o n products, t h e b u l k of which were deposited i n t h e f i r s t l a y e r , Table 7.14 was prepared, giving t h e amount of each i s o t o p e i n t h e f i r s t l a y e r i n d i s i n t e g r a t i o n s per minuke per square centimeter of g r a p h i t e s u r f a c e . The values i n Table 7.1A were obtained by multiplying t h e values i n Ta'oles 7 . 1 1 t o 7.13 ( d i s i n t e g r a t i o n s per minute per gram) by t h e weight of sample analyzed ( c o r r e c t e d f o r weight l o s s i n sampling) and d i v i d i n g by t h e measured a r e a of t h e s u r f a c e from which t h e sample w a s c u t . The

Table

Sample

Weight

Depth of Cut

(9)

(mils)

7.11.

Radiochemical Analyses o f Middle Graphite Bar

(Y-2)

D i s i n t e g r a t i o n s p e r Minute p e r Gram of G r a p h i t e 9 9 ~ 0

1 3 2 ~ e

IQ3R1l

95zr

1311

95Nb

" ~ r

144~e

I4OBa

141ce

137cs

Wide F a c e Exposed to Circulating F u e l

0.9145

6.94

5.53

0.8962

6.98

1.20 x

8.60 x 1 0 9

10" 2.40 x 109 4.24 X 10' 1.52 X 108 3.17 X 10'

1.13

8.27 x 1 0 9

108

10'

0.8463

6.02

1.88

1.2737

9.27

1.28

0.9814

7.50

2.35 x

17 23

1.0372 0.8176

8.25 6.64

10l2

loiG

io9

x lo8

ioq x io9

1.12 x 109

i.09 x 10" 5.19 X 10" 2.33 X 10" 1.07 X 10"

8.76 x 10'

2.57

2.18 1.73

6.93

9.16

10" IO9

7.76 X10' 2.94

4.28

3.16

10'

lo8 X lo9

1.28 X 10'' 9.45 X IO'

1.12 X 10"

4.17 X10'

1.77 X 10'

3.18 X 10'

1.79 X lo8

3.08 x 10'

1.28 x 10;'

8.43 x

1.10 x 10'

3.80

2.22

lo7 lo7

lo7

7.65 X 10" 7.08

1 0 '

1.44

10"

6.57 x lolo 2.75

1.65

4.07 x 1 0 7

4.55 x i o 1 0

9.71 x

2.46 X 10'

4.30 X 10"

7.60

10" 10"

io9

lo'

3.17 x 1.43

7.33

lo9

0.7583

7.68

0.9720

10.10

0.5139

5.43

1.40 2.70

X X

10" 10"

3.73 x 1 0 9

10"

1.04 X 10"

4.62 X 10"

2.41 X l 0 l o

lolo

2.14

1011

5.92 x 1 0 8 6.33

lo8

8.33 x 10'1

1.52 x i 0 ' O

2.48 x

2.79

3.00 x 107

10'

0.3395

3.65

2.44

4.55 x 109

1.36

0.6976

7.61

4.66 x 109

1.11 X l O l O

7.38 x 10'

2.75

x 10'

0.3737

4.15

2.41 X 1 0 "

3.05 X 10"

4.76 x 109

6.62

3.79 x

1.41 X 1 0 " 3.86 X I O ~ O 2.99

1.52

2.29

2.45 X 10' 2.18 x107

2.54 X I O 7

lo8

10'

1.86 x 1 0 7

3.90

1.96

3.38

10"

2.50 XIO'

10"

8.39

108

10"

1.75

10"

3.35

lo1'

7.18

10''

4.28

10''

Other S i d e Face Exposed to Circulating F u e l

0.6135

6.21

1.73

x x

10''

;0l2

1.09 x 1 O l 2

2.60

1o1O

7.01 X 1 O ' O

8.55 x 1 0 9

3.7543

7.84

5.94

0.6198

6.55

8.53 x 10'

1.1652

12.53

6.26 X 1 0 9

8.70 x

0.8469

9.24

5.61 x 109

0.940b

10.45

5.08 x 109

8.02 X I O y 5.65 x 109

1.96 X 10"

lo9

6.36 X

lo1'

2.89 x l o 1 0

1.61 X lo1' 1.21 ~ 1 0 '

5.52 X l O '

1.79

1.15 x 109

2.05

7.25

6.89 x

108

los

1.41 X 1 0 8

10'

io8

2.04 X

3.02 X

lo'

3.77 x

lo8

1.00 x 1 o ' O

lo7

4.98 x 109

6.99 x 1 0 7

4.23

10'

8.96

10"

F a c e i n Contact with Graphite

1.1381

9.23

3.22

x 10"

5.82

10"

7.88

10"

1.04 X 10"

1.36

1G'O

6.68

IO'

1.65

lo9

2.15 X 10"

Unexposed Graphite Blanks

4.63

6.47

NOTES:

loa lo8

2.62 X I O s

7.18 x107

2.46 x

3.22

8.11 x107

3.28

10'

lo8 10'

3.26 x l o s 1.26

10'

4.48 x 105 1.31

10'

1.07 x 105

8.06 X lo5

2.03 x 105

1. T h e s a m p l e s a r e a r r a n g e d i n order of s u c c e s s i v e c u t s on e a c h f a c e (see F i g . 7.22).

The s a m p l e w e i g h t s given h e r e h a v e b e e n c o r r e c t e d for t h e a v e r a g e 4.5% l o s s d u r i n g milling.

3. T h e d e p t h s of c u t w e r e c a l c u l a t e d from t h e s a m p l e w e i g h t s , a r e a s , a n d t h e known g r a p h i t e d e n s i t y .

4. A d d i t i o n a l a n a l y t i c a l r e s u l t s a r e forthcoming on s e l e c t e d s a m p l e s for 95Nb, 89Sr, 9 y T c : 9 5 Z r , i 4 7 X d , 136Cs, 5.

T h e a c t i v i t i e s t a b u l a t e d a r e c o r r e c t e d t o t h e t i m e of s h u t d o w n , 11:OO AM, J u l y 17, 1966.

s , "Y, 137c

Low

3.21

6 3 N i , a n d 59Fe.

lo7

1.98

5.55 x 10'

7.68 X 1 0 "

8:98 x108

lo9

1.20 x 1010

2.02 x 2.17

Side F a c e Exposed to Circulating F u e l

lo7 lo7 X lo' X lo7

8.39 x

IO'

7.74 x 109

2.43 X 1 0 '

ioio

6.53 x 10'

1.41 x 105 6.38 X

lo6

lo7

182

Table

Sample

Weight

Depth of

(gj

C u t (mils)

7.72.

R a d i o c h e m i c a l A n a l y s e s of T o p Graphite Bar

(VH-5)

Dislntegrations per M i n u t e per Gram of Graphite 9

1 3ZTe

5Nb

1 03*u

1 4 4 ~ e

89~r

4.40 x 108

1.19 x 10"

1.04 x 10'1

4.92 x lo7

5.74 x IO'*

1.60 x 10"

6.54 x

6.19 X 10''

1.98

3.95 x 10"

7.19 x 10'

1.5i x 10"

1311

952,

14lCe

137cs

Wide F a c e Exposed t o C i i c u l G t i n g F u e i

0.3602

6.23

1.54 x 1@12

9.89 x 10"

4.02

0.4355

7.93

5.45 x I O 9

9.24 x lo9

6.30 x

0.5260

9.94

5.95 x l o 9

9.39 x 109

7.76 x

lo6 io8

0.2916

5.51

1.73 x

3.95

io9

1.64 x

ioa

1.0783

20.38

1.63 x

lo9

7.96 x 10'

lo9

6.22 x l D s

1011

i.56

10"

1.06 x 10' 9.54 x

ios

4.87 x

3.38 x 1.34

lo9

1.28 x la9

io7 lo7 lo7

10"

8.60

IO9

1.22 1.87

10'

1.67 x I O '

3.54

IO7

4.94

lo9

Side F a c e Exposed to C i r c u l a t i n g F u e i

0.4615

11.41

4.94 x 1 0 l i

0.4564

11.88

2.24

lo9

4.38 x 10"

1.37 x I O ' '

2.37 x 109

2.59 x 10'

4.96

9.06

2.82

lo8

7.26 x 1 0 7

6.11 x I O 6

1.45 x l o 1 0

2.13 x 1oS

2.69

6.38

5.38

IO9

10"

Other Side F a c e Exposed to C i r c u l a t i n g F u e l

0.6703

17.11

6.10 x l o L 1

5.71 x 10l1

0.5404

14.43

2.20

5.39

10'

IO9

7.81 x 10"

3.44 x 109

lo8

3.01 x 107

2.32

10'

10"

lo9

8.27 x 10'

Wide f a c e in C o n t a c t w i t h Graphite

0.6422

11.32

3.86 x 10"

2.80 x 10"

5.14 x I 0 l o

0.5375

9.95

1.96 x 109

1.03 x I O I O

1.91 x

0.3154

5.96

1.81 x

1.24 x 10"

2.01 x I O s

0.5835

11.03

9.17 x lo8

3.95 x

0.7310

13.82

6.08 X 10'

2.41

NOTES:

1. 2. 3. 4.

lo9

10'

lo8

1.17 x lo8 8.16

lo7

5.59 x

loxi

3.07 x

2.28 x

los

9.26 x

log lo7

6.25 x lo8

7.31 x

lo7

1.24 x 10'

2.74 x IO8

3.29 x 10"

8.51 x i o 9 8.75 x I O 9

1.86 x lo7

2.76 x 109

i.1; x 107

1.58 x 109

The sampies a r e arranged in order of s u c c e s s i v e c u t s on e a c h face ( s e e Fig. 7.22). T h e sample weights given have beer, corrected for the everage 18.9% weight i o s s during milling. The depths of c u t were calculated from the sample weights, a r e a s , and tine known graphite density. Additional analytical results are forthcoming on s e l e c t e d samples for 9sI\:b, 89Sr, "Tc,

5. T h e a c t i v i t i e s tabulated are corrected to the time of shutdown, i 1 : O O AM, July 17, 1966.

"Zr,

147R:d, ' 3 6 C s , 13'Cs, "Y,

63Ni, a n d "Fe.

2.24

4.03 x 10' 2.56 x 10'

2.17 x 107

lo7 10'

183

Table

Sample

Weigh: (9)

7.13.

Radiochemical Analyses of Bottom Graphite Bar (VA-1)

Depth of

D i s i n t e g r a t i o n s p e r Minute p e r Gram of Griiphite

Cut 9

(mils)

1 3 2T

103RU

95Nb

952,

131,

144ce

"sr

"3a

4.17 X 10"

3.34 X 10"

3.86 X 10"

1.65 X 10"

3.52 X 10"

1.05

3.62 X 10"

1.13 X

141

137,5

Wide F a c e Exposed to Circulating F u e l

8.30 X lo1'

3.34 X l o i 1

4.25 X 10'

3.26 X 10"

8.22 X 10'

2.49 X 10'

4.44 X 10'

1.91 x10"

9.76 X

3.12 X 10'

2.63 X

los

1.91 x 1010

1.20 x l o 8

1.40 X 10'

lo8

1.06 X 10"

5.14 x 107

SAI

0.8032

15.04

5.39 x 10'1

4.39 x

0.5979

11.64

5.67 X IO9

0.2323

4.68

9.5

x lo9

0.3i20

6.28

8.65 X

0.7183

14.49

3.39 x

loll

lo7

2.40 X l o 9

6.39 X

lo8

xio7

3.08 x

ioi9

10"

8.11 x 1 0 9

1.09 x 6.92 X 10'

lo1'

5.87 x 109

1.84 X 10'

Side F a c e Exposed t o Circulating F u e l

0.3904

10.70

6.62 X 1011

0.4480

12.98

7.56 x

io9

lolo

5.31 X 10"

9.44 x

4.12 X 10"

5.86 X 10'

7.09 x

lo9

108

5.44

8.32 X 10'

4.18

10"

1.04 X 10"

2.21 x 1 0 "

Other Side F a c e Exposed to Circulating Fuel

0.5480

15.39

0.3520

9.62

io9

10'1

3.64 X 10"

5.11 X l O "

4.58 x

3.95 x

lo9

1.81 X 1 0 "

4.95 x 108

1.43 X 10'

4.38

6.19 X 1 0 8

lo9

6.12 X 10"

9.19 x

1.38 X 10"

7.25 x i o 8

4.48 X 10"

1.07

10"

1.10

108

1.03 X

lo8

Wide Foce i n Conyact with Graphite

1.00 x

ioll

4.20 x

3.70 x 1010

1.06

lo9

2.50 X 10'

5.01 X 10'

2.04 X 10"

io9

2.44 X 10"

1.74 X 1 0 8

3.07 X 1 0 8

4.31 X 1 0 8

1.48 X

1.83 x 109

2.15 X 10"

1.48 x 1 0 8

1.31 X 1 0 8

1.24 X 10"

2.66 X 10'

6.90 X 10'

3.83 X 1 0 '

4.96 x

0.4810

9.12

0.5936

11.77

0.4756

9.58

1.57 x

0.4025

8.10

0.6260

12.61

NOTES:

9.31

10"

8.23 x 109

5.97 x

loll

6.01 x 109

3.47 x

lo9

9.49 x

lo8

io7

4.50 X 10'

1. T h e s a m p l e s a r e a r r a n g e d i n order of s u c c e s s i v e c u t s on e a c h f a c e ( s e e F i g . 7.22). 2.

T h e s a m p l e w e i g h t s g i v e n h a v e b e e n c o r r e c t e d for t h e a v e r a g e 9.1% w e i g h t l o s s d u r i n g milling.

T h e d e p t h s of c u t w e r e c a l c u l a t e d f r o m t h e s a m p l e w e i g h t s , a r e a s , a n d t h e known g r a p h i t e d e n s i t y .

4. A d d i t i o n a l a n a l y t i c a l r e s l i l t s a r e forthcoming on se:ected s a m p l e s for "Nb, 5.

"Sr,

"Tc,

T h e a c t i v i t i e s t a b u l a t e d a r e c o r r e c t e d to t h e time of shutdown, 11:OO AM, J u l y 17, 1966.

"Zr,

lola

147Kd,

1 3 6 -L S ,

137Cs, 'lY,

6 3 N i , a n d 59Fe.

2.80 x 1 0 7

lo7

Table 7.14.

Fission

Producr Deposition on S u r f a c e ' o f MSRE Graphite Midble Giaphite

Top Graphite

Disinte gra?ion s per

Isotope

Minute per Square

Sottom Graphite ~..

Disintegrations pe: P e r c e n t of Total"

Winute per Square

Centimeter

D s i n t e g a t i o n s per Percen: of T o t a l b

Centimeter

Minute per Square

P e r c e n t of Total'

Centimeter

3.97 x 10'O

13.36

5.14 x 10"

17.24

3.42 x 10"

11.5

132Te

3.22 Y 10"

13.84

3.26 x 10"

13.60

2.78 x 10"

12.0

103Ru

8.34

109

11.40

7.53

io5

10.32

4.75

9SNj

4.62 x IS9

12.00

2.28 x 1 O 1 O

59.2

2.40 x 10"

'Mo

1311

io9

6.30 62.4

0.328

0.252

3.14 x 10'

3.27 x 10'

0.270

1.72 x 10'

0.148

0.0516

8.26

0.268

4.36 x 1 0 7

0.142

3.52 x I O 9

3.24

3.58 x I O 9

3.30

2.99 x IO9

2.74

I4OEa

3.56 x I O 9

1.38

4.76

109

1.85

2.93 x l G g

1.14

14 Ice

3.16 x

lo6

0.494

1.03 x

lo9

0.532

5.53 x :os

0.356

:3?cs

6.62 x

lo5

0.070

2.35 x IO6

0.248

2.01 x

2.09 x IDy

0.162

4.22

"2,

3.78 x I O 7

0.326

144ce

1.58

89~r

10'

108

io7

lo6

0.212

6 0 ~ in o adjacent

Hastelloy PI, d i s min-'

4.37

lo9

1.57 x l o ' *

6.69 x 109

g-l

aAveiage on the three salt-exposed surfaces for f i r s t milled cut. "Percent of t o t a l amoun; of isozoge in reactor system which is deposited in t h e 2 X I O 6 cm2 of giaphite surface that is in :he reactor,

185 d a t a were cc)ndeiisc?d by averaging t h e usually well-agreeing amounts fol.xnd

the -three salt-exposed surfaces. The runguiits found. ors otller g r a p h i t e - c o n t a c t i n g s u r f a c e s were, on t h e average, -38% lower, Tne J.atter f i g u r e i n d i c a t e s r a t h e r f r * e e c i r c u l a t i o n of salt, between tile contncting g r a p h i t e surfaces, S a l t may be expected. t o circulate e q ~ l a l l yw e l l i n tlle i n k e r s t i c e s between t’ne g r z p h i t e strin.gers of t h e K9RE. On.

1% is seen f r o n Table 7.3-4 t h a t t h e amounts of r1obI.e metals in -Li.le top, middle, and bottom swaples of t h e g r a p h i t e agree ra-Lher y e l l , with perhaps u s u a l l y somewhat l a r g e r v a l u e s f o r t h e m i d c i l e g r a p h i t e . For f;he o t h e r i s o t o p e s , also, th.e midcile graphite u s u a l l y hoI.ds the higlleat SILTf a w e concentrations, th0ug1-i ~eldorni n the r a t t o of t ; h ~ ! prevailiiig neutron f.luxes. T h e l a s t row i n Table 7.14 g.i.ves Lhe “Co a c t i v i t i e s i i l t l ~ e RaStellOy N Sanples ad-jaccnt t o the t h r e e graphite sainl:@es. Tlj.e:;e nubei-s a r e prOpOrtiOnal t o the thermal-neutron fluxes The 1a;tter have :not; yc?’t be21i caJcula-Led s i n c e t h e chemical. c ( ~ b a l t anal.yscs ; ;lave uot y e t been rec e i v e d.

Also l i s t e d i n Table 7.1.4a r e t h e percentages of t h e total j.so?,opc? produced. by Tissiori f o ? ~ n d011 the graphi Le su.rfrzce, on t h e ass~u!~p-t;ion tllat a l l 2 X lo6 c m 2 of g r a p h i t e h e l d the su:cface coaceiit-r.a.1;ions l i s t e d to the-ir l e f t i n t h e t a b l e . !The t o t a l :mount of’ each isoto-pe was c a l c u l a t z d f o r a f i s s i o n r a t e based on t h e “Sr a c t j - v i t y (1.32 x 10’’ d i s min-” g-‘) In t h e last s a l t m n p l e t a l e ~ l r i on Jiil~13, 1966. Tlie percentages in Table ‘ 7 . 1 4 woL1.l.d be 8.bou-t 20% l o v e r i f t h e nomliial power hi.s-toq of t11.e reactor wej?e used to calculatr- the total <%nountof each isol,ope produced by f i s slon. It shoij.l.c?i be ~ e c o g n j . d. t h a t t h e percentages given. actu.a.l.1.y represent t h e behavior of each Tsotope only dixring a f e w hali‘-Iiver, of -LhaS, i s o t o p e . ~ ~ i i nt ~ s i er ~ g i r e sfor‘ 46-w ‘%o e~iaracterizeon1.y a pel-ioti of a week or s o before t h e J u l y 17, 1966, sliu.tdovn. I-t is q u i t e conceL?able that t h e d e p o s i t i o n behavior of {;he various isotopes i s cha-riging w-il;jz tj.m.e. Several. sets of surveil1ance s~?ecTme~s must be examlned b e f o r e firm c o n c l u s i o n s may be drawn.

Sizable percentages of t h e total 93Mo, 132Te, ”03Ru, and 95Nb were found. on the g r a p h i t e s u r f a c e s . i%ny of ihe .values were c l o s e t o l.376, but two of 3 5 ~ i ~values J were near 60%. ~ u . c t i~.owerpercentages of t h e nther iscitopes de o s i k d on t h e graphite, t h e h l g b e s t being 3.2% f o r *’Sr and. l..g$ for 14Ga.

An attempt w a s made t o oinalyze two of thy s u r f a c e g:raphite samples f o r al.1- f i s s i o n product i s o t o p e s of moll-y’od.eiiwn by inass spectrometry, a f t e r spikzing t h e s a a p l e s wLth 9 2 1 0 o r ‘No. The remits i n d i c a t e d somewliat more molybdenum d e p o s i t i o n (20 and 32$ of t h e t o t a l . ) ttiari was mea:-;i-irc?d radiochernical.1.y w-i-th 9 3 M ~ . However, confidence i n tliese rcsu1-L~was l e s s e n e d by the f a c t t h a t d i s t i n c t l y d i f f e r e n t combinations of .f’i.ssion product molybdenum, n a t u r a l rnolybdenLm, and.n a t u r a l zirconiwn (u c a r r i e r ) had t o lie used t o f i t ttie mass analyses of the two samples. ( e ) F i s s i o n P r o d u ~ tDeposition on Hastelloy- N. It i s il?t;eresting t o compare t h e d,e;oosition of f i s s i o n p r o d i ~ t son grapi-lite with -that on t h e a d j a c e n t HasteLloy N. The samples of t h e perforated Hastelloy N obt a i n e d as described above were weighed. and d i s s o l v e d in a warm mixtiire of IfNO, and HCl. F’ron t h e P~io;sn dimensions and d e n s i t y or Iiastelloy N, i t was c a l c u l a t e d t h a t the surface-to-weight ratio of t h e perforated. r u e t a l

T a b l e 7.15.

D e p o s i l i o n of Fission P r o d u c t s on H a s t e l l o y

Disintegrations P e r c e n t of

per S q u a r e

Totala

2.12 x I O 1 '

9Mo I32

5.08 x 10l1

133Ru

I l l s i n ;e g r a t i o n s

D i s hte g r a t i o n s

p e r Minute Centimeter

Mirlu<.e

G r a a h i te

5.3

131

Total

p e r Square r L. e n t i m e t e r

____~______ 42.8

percent

- . . -~ .

3.4 1 x

2er Einuye

Graph1le

p e r Square

5.3

2.04 x l o 1 '

10. 4

11.27 x l a '

3.4

2 . 3 2 x 10:'

1.84

9.4

5.24 x

55.6

x 19''

3.82

39.4

3.97

lo9

1.8s x 109

0. 96

48.9

1.84 x IO9

0.95

5.9

2.58

I4'ce

5.22

lo7

0.019

0.14

2 . 2 4 x IO8

0.07;

0.22

1.50 x 10E

144,

1.07

lo7

0.020

0.68

8.05 x 10'

0.175

1.1

3.51 x

8.24 x IO9

9 5 ~ r

e ,

4 L.2

5.9 15.3

ll9

2.55

29.3

Crraphi ' E

- _

~~~~

4.3

3.55 x l o l a

i3I1

Total

C e n urn e t er .-

2.76 x 10'

15.8

Has:elloy N

____-

19. :.

io9 lo9

:a5

4.9

2.44

i5.3

1.32

15.0

3.055

0.26

0.368

0.8:

'Oca :n adjacent Hasteiloy d i s m:n

-1

4.37 x

I$, g

io9

i.57

loio

6.69

:O9

-1

~~_

___

a P e r c e n t of t o t a l I s o t o p e p r o d u c e d by l i s s l o n In t r e r e a c t o r w n i c h w d s c e p o s l t e d o n 1 . 2 x : G 6 c m 2 of 1:astelloy N sLi-face c e p o s i n o n o n a:. s u r f a - e s is the barne a s 07 Haste1:oy N :n t h e core. b R a i l o of r h e d i s m1n-l c - K 2 o f e a c h i s c b p e on X a s t e l l o y h ;o h a : i n Tie firs* m i l l e d c u t of t h e a d l a c e n graphite.

lfl

__._ ~~

h e r e d ( tor, a s ~ u l l l l n g

187 w a s 4.30 cm2/g. Using thi:; f i g x r e t h e analytica.1 results ( i n d i s min-' g-'.) cou3.d be converted t o d i s rn2n-l ern-'. Table 7.15 gi?r?s t h e radiochemical results obtained. 'io d a t e from the solirtions of t h e Hastelloy PJ specimens. It 1s seen t h a t large percentages of -the total. 991/10, 132Te, and. I o 3 R u deposited on t h e H a s i e l l o y N . Also given i n Table 7.1.5 a r e tile. ratios of t h e surface concentration:; of each j . s O t G p e on -the Hastelloy N and on t h e g r a p h i t e . Between 3 and ll+ times a& iiiiuch mc~,ly"odenim, t e l l u r i u m , arid ru.thenium deposi.t;ed. on metal as on graphite. It i.s i n t e r e s t i n g t h a t a fair m a i ; t i : r i a l balance i s o?itai.nerl f o r 93Mo by adding t h e percerltages o f t,ke t o t a l produced found i n t h e salt (app~oxi.m.atelyGO$, Table '7.101, F n t h e g r a p h i t e (approxirnately 14$, Table 7.14), and on the 1hS-l;ellOy11 (approximate1.y 45%) Table '7.15). The agreement for t h . e o t h e r i s o t o p e s i.s not s o good.

filch lower percentages of t h e t o t a l deposi-t; 0x1 t h e : - ~ a s t e . ~ - .N, ~oy b i u t t h e m o u n t compared -to t h a t on graphite i s h i g h . The. data s ~ ~ g g e s t t h a t t h e precursor te.lluriurri d e p o s i t s on t h e m e t a l . and that not a l l of' t h e 1311 i s able t o leave when the t e l l u r i u m decays. The mznloimt of 95Z1. on t h e metal. was low bul; hipher t,han t h e su?*faceconceritration on. graphi t e . Very I.littl.e I4'-Ce a;nd I C 4 C e w ~ found ~ e on t,lze metal, i n fact, l e s e t h e i n on g r a p h i t e e The : f i : o . d i n g of more C F L - ~ W JiI s o t o p z i n graplzite my be &u.e t o .thei:r s h o r t - l i v e d xenon precursors.

G e n e r a l Discussion of t h e Depositiori Hesiults The princi-pal- p r a c - t i c a l in-Lerest i n {;he z"ir,si.on product depos:it,ion r e s u l t s l i e s i n t h e i r implicat i o n s x g a r d . i n g nev.trori poisoniag by noble metals in t h e graphite cores o f molten-salt r e a c t o r s . I n most s t u d i e s of the physicss of reactors :;uch as t h e MSBR, it; has been assumed. that; .the noble-metal f i s s i o n prod.ucts would eithei- pl.a.?,e out i n s t a n t a n e o u s l y on metal surfaces 01- 'be remo~red p e r i o d i c a l l y STo:rn t h e fl.uoi-ide f u e l by t h e f l u o r i d e v o l a t i l i t y p~ocessing IJnder t h e s e coxid-itions, the poisoning e f f e c t of no7iI.e metals would Le of minor practical concern. However, j.t has been c a l c u l a t e d 3 6 that if all of t h e elemeilts Se, Br, N'o, Mo2 Tc, 'Te, and I ren-mined i n t h e c o r e of t h e MS3RJ the iieiitrcjxi poison f r a c t i o n . (capture by t h e s e el.enients per ~ b s o r p t i o n i n fissile rtia-terial) would be 0.0363 in two years.;, 0.1652 i n five years, 0.2104 in t e n y e a r s , a r i . ( ~0.2585 a t equili1riix-n. If IO$ of t h e s e materials rermint3d i n t h e core, the r e s p e c t i v e poison f r a c t i o n s would be 0 .O.lO6, 0.131.79, 0.0226, and 0.0275. I f t h i s g:roup of elements rcrliained. 5.n t h e fuel and w a s p e r i o d i c a l l y . rcrnoved by f Iuoride vola,ti.l..i.ty processing, the average poiso1i i'x-action would remain con;;tan.t a t 0.0015. me i s o t o p e s of inol.ybc?en-m and- '?Tc account f o r a b o u t 30% of t h e poisoning erfecl; of t h i s grou-p of elements. T'ne riiiclearc breeding ratio for Lhe K5BIi i s expected to be 1.05 t o 1..07i n t h e absence of d e p o s i t s of noble inetals in t h e core. The number:; above i n d i c a t e that t h e ac-txal.breeding r a t i o or t h e time t h a t t h e g r a p h i t e can h e l e f t i l l t h e c o r e of a breeder caii be corisiderably influenced by t h e deposition of t h i s group of elements. a

It vas also r e p o r t e d above t h a t five ,to s i x times rii.oi-e 9 9 ~ 4 0was de011 Hastelloy N surfaces t h a n on a d j a c e n t g;r.n.phite s u r f a c e s . In t h e MSRE t h e r e i s approximately 2 x .lo6 cm2 of g r a p h i t e surface (aboirt, h a l f i n t h e F u e l channels and half in the f l a t s p r e s s i n g a g a i n s t adjacent f 1 3 . t ~ )a n d . 1..2 x 1 0 6 cm2 of 1Iastel.loy N s u r f a c e exposed t o the circu1atiri.g ruel- I n t h e c u r r e n t MSBR design t h e r a t i o of metal su.rface 'co g r a p h i t e

posited

188

s u r f a c c cxposec! t o c i r c u l z oui 5 It s e e m 1.7.kei.y tha-L .inon of molybdei?il;:- dep & on t h e gra.piii.i;e iis t h e lGH3 c0i-e ~ 0 u l . 6 respoiidingly lower thari i n 'die I G R E . The r a t j o of nie-ial to g!;r-aphitc: s u r f a c e a r e a cour1.d b c f u - t h e r i n c r e a s z a , but. a t t h c e x p e m e of fuel irLveniory by c i r c u l a i g t h e fuel tiirough a. ;.h.a.rther packed wi'Lh f i n e l y d i v i d e d rnei;a.?.

Anotiiler approach t o t h e p r o b k m o f molybden-mz d e p o s i t i o n

ri s suggzsied by c o n s i d e r a t l o n s of t h e p r o b a b l e zhemi-stry i nvolved.

T'i?? volati-I.:i.t,y of 99Mo der*Lons'i,rated i.n t h e pump ijow7. t e s t s su.gg;ests t h e p r e s e n c e of M o ? ' ~ o r MoF5 ir, the c i r c u l a t i n g f u e l . The gaseous f ' o m of niolybdenrfl uou1.d e x p l a i n i ts ohservcd pcne i i > a t i o n i o a p p r e c i a b l e d e p ~ i l s i n t o t h e g r a p h i ~ t es u r f a c c . On t h e basi.s of a v a i i a k l l e t h e r m o c h c z i c a l Lr.Yorlilat:ionJ i.t i s n o t c l e a r what chemica.1.. rea.cti.on occi:rs 'LO f i x t h e molybdenum t o t h e g r a p h i i e . For example, t h e free e n e r g i e s of ilie rea.ct i o n s of MoP'6 w i t h grapiii-te t o forrri CF4 and im1ybdemm o r Moil2 a.re posit i v e by a fcw k i l o c a i o r i e s . The same i s t r u e f o r Ruli'5 ai?d NbF5. Only i n t h e case of t e l l u r i u m i s t h e r e a d e f i n i t e l y n e g a z i v e f r e e , - . e n f o r t h e r e a c t t o r , of t h e f l u o r i d e w i t h g r a p h i t e . Possi.7-iIe c h e m i c a l EXp l a n a t i o n s of Llie observed deposi-Lions arp t h e formatj.im of s t a b l e n i x e d a l l o y s of t h e n o b l . e - m ' i b l fissri-on p r o d u c i s o r t h e r e a c t i o n s of' ihe f h o r i d e s w i t h reduci-ng i.mpuritic.s p r e s e i i t i n t h e g r a p h i t e . In any case, Lhese r e a c t i o n s -take pla.ce h s i d e t h e gyaphi-te p o r e s nearr t h e a v r f a c e . The p e n e t r a t i o n of v o l a k i l e mol.ybdenum c o u l d be d e c r e a s e d by ma,.kj.ng the g r a p h i t e s u r f a c e less permeable. I-ti.s hoped thaL g r a p h t t e specimcns whose su.rfaces have been ~ m d e.less permeable by i m p r e g n a i i o n trextments c a n bc i n c l u d e d i.n f u t u r c survei3.l.ance specimen packages t o t e s t whe'iizer rnolybdcnurn d e p o s i t i o n i.n g r a p h i t e ca.n b e d e c r e s s c d i n t h i s way. If the d e p o s i t i o n of n o b l e - m e t a l f i s s i o n pro&xts i n g r a p h i t e does i n d e e d r e q - o i r e t h e i r p r i o r c o n v e r s i o n t o h i g h - v a l e n t f l u o r i d c s a third me-thod of d e p o s i t i o n c o i i t r o l sugg:ests i - ' i s e l f : t h e fu2-l m e l i ; riiay- b e made more r e d u c i n g by i.ncrea,sing t h e u3"/U4* r a t i o . l3:xistL:o.g thermochemical. d a h i n d i c a t e t h a t a s i z a b l k p e r c e n t a g e of t h e t e t r a v a l e n t u r a n i i m could b e conver-Led. t o t h e U3+ s t a t e w i t h o u t c a u s i n g ura.ni.um c a r b i d e I'or'matiojT. A srna3-1 p e r c e n t a g e of t h e uranium c o u l d b e made t r i v n l e n - i by a d d i n g a few p e r c e n t o f H2 t o t h e helium c o v e r gas oi" a r e a c t o r . A l t e r n a t i . v e l y , when f r e s h r'uc.1 i s added. t o compensate f o r hurnup, t h e added. uranium c o u l d b e partly trivalent. One o r b o t h of t h e s e procedures may b e f e a s i b l e i n t h e E R E . The e f f e c t s on volat,ri.I.i.zation and pla-Ljxg b e h a v i o r c o u l d be easri ly o b s e r v e d by pimp bowl t e a t s w i L h metal. and g r a p h i t e speci.rnens

The second major area in which i l l u m i n a t i o n 5s d e s i r e d frora frissi-on product behav-ioi- is H a s t e l l o y N corrosion. A s i n d i c a t e d . above, it i s

d i f f i c u l t t o r e c o n c i l e a l l the observations w i t h a s i n g l e consistent, chemica,l. p i c t u r e . The p r i n c i p a l . . d i f f i c u l t y i s t h a t t h e h i g h - v a l e n t forms of moI.ybdenum, rutheni.u;n: and tellurri.um h d i c a t c d by t h e i r v o l a t i l i t y and p l a t i n g b e h a v i o r may not e x i s t i n e q u i l i b r i u m . w:i.th t h e a p p r e c i a b l e conc e n t r a t i o n s of 1J3+ e s t i m a t e d 'LO b e pi-esent i n the MSRE f u e l s a l t . The oxi.di.zing e f f e c t of burning up about 400 g of 235U t o dat,e i s cquivalent. 'io 0ilI.y o n e - t e n t h of t h e 1J3+ o r i g i n a l l y p r e s e n t i n t h e fuel.

I f it i s a s s u e d t h a t t h e U3+ c o n c e n t r a t i o n w a s a c . i u a l l y much lower t h a n e s t i m a t e d , t h e p r e s e n c e o f h i g h - v a l e n t n o b l e metals i n t h e f u e l i.mp l i e s that t h e HasteIUoy Tu' s u r f a c e s have b e e n p r o t e c t i v e l y p l a t e d w-i-th

189 noble m e t a l s . Experimental observations of such p l a t i n g s were r e p o r t e d above. 'Riis p r o t e c t i o n would. e x p l a i n t h e observed low corrosion r a t e of Ilastelloy- N as i n d i c a t e d by chromium analyses of t h e f u e l . However, t h e absence Of i o d i n e v o l a t i . l i z a t i o n i s t h e n d i f f i c u l t t o explairl. I n t h e presence of MoE'6, RuFs, and TeF6, i t i s expected t h a t i o d i d e s would be oxidized t o 12. It i s not expected t h a t t h e sol.ubility of 12 i n t h e f u e l i s high enough t o preveat i t s v o l a t i l i z a t i o n . These problems of consistency Wake it; c l e a r t h a t -the n a t u r e of Haatelloy N c o r r o s i o n r e a c t i o n s i n an operating r e a c t o r i s not understood as w e l l as would be d e s i r a b l e . O f g r e a t h e l p i n s o l v i n g some of t h e s e problems would be t h e development of a method t o measure t h e U3+ c o n c e n t r a t i o n i n r a d i o a c t i v e f u e l salt s m ~ p l e s

&ERE Cover-Gas Analyses. Samples of K7F3 cover gas were i s o l a t e d on June 23, 2366, during steady '7.2-Mw operakion in t h e t h r e e s h i e l d e d gas-sampling bombs provided. f o r t h i s purpose. The t h r e e smiples (500, 500, and 1500 cm3) represented pump bowl cover g a s which had. passed through t h e f i r s t holdup v o l u ~ z e (68 f t of & i n . s t a i n l e s s s t e e l p i p e ) , t h e p a r t i c l e t r a p , arid ijhe c h a r c o a l f i l t e r . The l a t t e r should have removed. all. heavy hydrocarbons and o t h e r i m p u r i t i e s more easily- adsorbed than xenon. The gas a n a l y s i s of prime i n t e r e s t was t h a t f o r t h e '''Xe/l"Xe r a t i o , from which t h e f r a c t i o n a l burmip of 135Xe i n t h e !GEE could be determined. To o b t a i n high- s e n s i t i v l t y xiass spectrometric aiialy:;es f o r 13'Xe and I3'Xe, it w a s necessary t o concentrate t h e sampled g a s by a f a c t o r of a t l e a s t 5 0 . The concerrtxation was accomplished by adsorbing t h e irnpuriLies i n a helium. cover-gas sample on a small 7ro.Lum.e of molecular s i e v e sorbent a t l i q u i d - n i t r o g e n temperature, t h e n warming t h e sorbent t o 500'F, and f l u s h i n g t h e l i b e r a t e d i r x p u r i t i e s w i t h helium i n t o a :mall (20an3) sample bottle. In this way, one 500-crn3 sanple was concentrated by a f a c t o r of 25 and t h e 1500-cm3 sanple by a f a c t o r of 75. A-L the same time s m a l l unconcentrated samples of %tie cover gas were taken f o r gamma spectrometry (1em3) arid f o r m a s s :;pectrometry ( 2 era') t o d e t e c t irapurit i e s such as H20 which a r e not r e a d i l y l i b e r a t e d from the warmed molecular s i e v e sorbent. The l a , t t e r s m p l e also provided. more r e l i a b l e anal;rses f o r very low-boiling i r q x i r i t i e s l i k e H2, which would not be coniplete1.y sorbed by the molecular s i e v e . A f t e r cooling f o r more t h a n two months, t h e r a d i o a c t i v i t y of t h e gas sanples was low, and no a c t i v i t y problems wer-e encountered i n t h e d i r e c t The activi-by i n t h e gamnia spectrosampling an6 c o n c e n t r a t i o n procedure:;. metric sample, taken in a thin-walled l-cm3 g l a s s bulb, was preponderantly The observed coun-Lirrg r a t e inclicated a coiicentratiolz of 5.27-day- ''%e. about 7 ppm. of 133iZe i n the cover gas a t t h e time of' sampling. l i n u t e t r a c e s were also d e t e c t e d of EL 0.16-Mev a c t i v i t y which might be 12-day l 3 l r n X e and of a 0.5-I"lev a c t i v i t y which might be lO.3-year "xi", Li-O-day '*~Ru, o r l.O-year l o h ~ u . The results of t h e mass analyses of t h e iinconceotrated sarriple, t h e concentrated 500-cm3 sample, and t h e concentrated. l.%O-cm3 sample a r e From t h e r a t i o of t h e analyses f o r 136Xe a.nd 134Xe shoTm i n 'Table 7.16. f o r t h e concentrated 500-cm3 sample, it w a s c a l c u l a t e d t h a t 7.'7$ of -the

190 135Xe produced i n t h e fuel m e l t c a p t u r e d n e u t r o n s t o become 136Xe. The corresponding more a c c u r a t e r e s u l t from t h e 1.500-cm3 sample was 7.9$ 135Xe b u r m p , w i t h a s t a n d a r d devriatri.0-n of about; 0.576 calcula-Led f i m n t h e estrimated a n a l y t i c a l . accuracy. It s h o u l d be emphasized t h a t t h i s method 017 determining 135Xe burnup i s not a f f e c t e d by sample contamination o r by t h e e x a c t v a l u e of t h e c o n c e n t r a t i o n fa.ci;or, provided t h e c o n c e n t r a t e d Table 7.16. Mass S p e c t r o m e t r i c Analyses of K5lU Cover G a s Sample No.

OG- 8

OG- 5

OG-7

Concentration f a c t o r

constituent,

% 0.022

99.71

CH4 H2O

Hydrocarbons N2

+ CO

< 0.005 < 0.005 < 0.005 0.19

0.81

0.49

93 -65

95.27

0.4L+

0.23

0.058

0.021

0.010

0.004

3 .%7

2 .â&#x20AC;&#x2DC;IO

0.066

0.49

0.26

0.003

0 .043

0.028

0.006

0.53

< 0.005 < 0.01

0.018

0.54 0.083

0.078

0.38

Tbeor.

OG-5

OG- 6

g3Kr

I4.1

1.4.0

14.05

8%cr

25.93

26.8

26.52

co2

I s o t o p i c Analyses Sample N o . Constituent, $

85Kr

7.60

7.6

8 6p3,

52.37

l3 1Xe

W .42

51.6

l3 2

~ e

1 3â&#x20AC;&#x153;e

6 ~ e

7 .4-7 51.96

36.92

8.8 14.7 41.1

40.90

29.59

35.4-

35.30

20.06

9.08

14.72

sample contains s u f f i c i e n t xenon f o r a good measurement of i s o t o p i c r a t i o s . The low 135Xe burnup values a r e c o n s i s t e n t with i n d i c a t i o n s f r o m MSBE rea c t i v i t y measurements a n d . a r e much lower t h a n values p r e d i c t e d t h e o r e t i c a l l y for t h e case of no helium bubbles c i r c u l a t i n g with t h e f u e l s a l t through t h e &ERE core. Recent measurements indicated. an appreciable bubble volume f r a c t i o n i n t h e c i r c u l a t i n g f u e l .

'"Xe

From Table 7.16 it i s seen t h a t t'ne observed f r a c t i o n s of 1 3 1 X e and

were much lower than t h e f r a c t i o n s calculated. from t h e f i s s i o n y i e l d s . I n t h e case of 13'Xe, t h i s i s w e l l accounted f o r by t h e f a c t t h a t tlie precursor $.05-day 13'1 had not y e t reached i t s e q u i l i b r i i m conceritrat i o n when t h e sample was taken. For 132Xe, t h e observed value was somewha-l; lower than i s i n d i c a t e d by a similar explanation involving t h e 7'7-hr 132Te precursor. The observed krypton i s o t o p i c percentages matched c l o s e l y those calcu.lated. from F i s s i o n y i e l d s (Table 7.16). The observed r a t i o s of t o t a l xenon t o t o t a l krypton were lower than t h e t h e o r e t i c a l 5.7, probably because of t h e xenon precursor e f f e c t s mentioned above. It may be noted t h a t t h e t o t a l xenon and t o t a l krypton concentrations were a f a c t o r of n e a r l y 5 higher for t h e 1500-cm3 sample t,han f o r t h e 500-cm3 sample, whereas a. f a c t o r of 3 was expected. The concentrations of a1.l i m p u r i t i e s i n t h e t h r e e analjrzed samples sh0ul.d have been i n t h e r a t i o s of t'fieir r e s p e c t i v e concentration f a c t o r s . This was g e n e r a l l y not t r u e . Except f o r t o t a l xenon and t o t a l Irryp-Lon, t h e impurity concentration in tlie 500-cm3 sample w a s considerably more than t h e expected o n e - t h i r d of t h e 1500-cm3 sample concentration. Most analyses f o r i m p u r i t i e s a r e t h e r e f o r e u n c e r t a i n by a f a c t o r of 2 o r more.

Yne analyses f o r a i r (Nz, 0 2 , and A r ) w e r e higher than expected f o r t h e thoroughly leak-checked sampling and concentration system. A pure i-i.elium sample i s being concentrated i n t h e system t o provide a quantitat;ive blank f o r the a i r values. T'ne analyses i n d i c a t e more t h a n 60 ppm of 132 and C02 and more than 30 ppin of C H 4 i n t h e NYRE off-gas. fiesumably, t h e s e gases wese generated from t h e thermal and r a d i o l y t i c decomposition of t h e orgLmlc iila,terials

which caused plugging i n t h e off-gas system. The l o w concentrations of higher hydrocarbons i n d i c a t e t h a t tine p a r t i c l e t r a p and charcoa,l f i l t e r were s t i l l e f f e c t i v e on Jwie 23, 1966.

7.5

Development and E v d u a t i o n of A n a l y t i c a l Methods for Molten- S a l t Reactors

Determination of Oxide i n Racdioactive b E F 3 Samples D a l e , and A. S. Meyer

- R.

F. Apple, S. M.

'The equipment f o r t h e deterrrrination of oxide3 i n highly raclioactive K9RE salts has been t r a n s f e r r e d t o t h e E~gh-LevelA l p h a Radiation L3bor a t u r y arid i n s t a l l e d t h e r e i n . Since i n s t a l l a t i o n , one coolan-t s a l t and

192 Tab7 e 7.Y7. Oxide C o n c e n t r a t i o n s of Coolaill; and F u e l S a l t f r o m t h e MSRE Sample

Code

Coolant s a l t

C;P-&L,

Fuel s a l t

FP-6- 1 Fp-6 - I , E’P-6- l2 FP-6- 18 FP-’7-5 FP-7-9 FP-’7- l3

FP-7-16

Oxide C o n c e n t r a t i o n (P P )

49 53 50 47

66 59 66 56

e i g h t f u e l sampl-es have beer1 analyzed f o r o x i d e . The 50-g f u e l sa1.i; saznp3.e~ were t a k e n a t l e v e l s from zero- t o fiill-power r e a c t o r o p e r a t i o n s . With a n in-cel.3. r a d - i a t i o n moni-tor, t h e initial sample read 30 r a-t 1 F-t. T h i s a c t i v i t y - i n c r e a s e d t o 1000 r a t 1 Y t a-t t h e fu’u.l.-power l e v e l . Res u l t s of t h e oxide a n a l y s e s a r e g i v e n i n Table 7.17. The oxide i n t h e c o o l a n t s a l t s m p l - e , 25 ppm, i s comparable t o a v a l u e of 38 ppm o b t a i n e d f o r a cool.ant. s a l t samp1.e t a k e n on January 25, 1966, and anal-yzed i n t h e l a b o r a - t o r y a f t e r t h r e e weeks’ s t o r a g e . The file1 a n a l y s e s are i n reasonab1.e agreement with t h e samples analyzed on the bench t o p b e f o r e t h e r e a c t o r wzs o p e r a t e d a t power. The oxide i n t h e s e n o n r a d i o a c t i v e samples g r a d u a l l y deer?ased from 106 t o 65 ppm. Between the F’P-6 and FP-7 s e r i e s t h e s a n p l e r - e n r i c h e r s t a t i o n w a s opened f o r maintenance, and t h e a p p a r e n t i n c r e a s e i n oxide c o n c e n t r a t i o n ( c a . 15 ppm) may r e p r e s e n t contamination of t h e samples by r e s i d u a l moisture-& t h e sampling system; however, t h e rimiber of determina-Lions has n o t been s u f f l c i e n t t o e s t a i ; l i s h t h e p r e c i s i o n of t h e meLhod a t t h e s e low concen-bration levels. I n an a t t e m p t t o determine whether r a d i o l y t i c f l u o r i n e i s removing oxide f r o m t h e f u e l s a u p l e s , sample FP-7-9 w a s removed from t h e t r a n s p o r t c o n t a i n e r and d o r e d i n a d e s i c c a t o r f o r 24 hr p r i o r t o a n a l y s i s . S i n c e t h e oxide c o n t e n t , 59 ppm,, i s comparable -to t h a t of t h e remaiming samples for which a n a l y s e s were s t a r t e d 6 t o 10 hr a f t e r sampl.ing, no s i g n i f i c a n t l o s s of oxygen i s i n d i c a t e d . A more d i r e c t method of e s t a b l i s h i n g t h e v a l i d i t y of t h e s e r e s u l t s by measuring t h e r e c o v e r y of a s t a n d a r d a d d i t i o n of oxide w i l l be a t t e m p t e d when r e a c t o r o p e r a t i o n s are resimed. A method f o r v e r i f y i n g t h e performance of t h e c a p i l l a r y g a s stream s p l i t t e r and t h e water e l e c t r o l y s i s ce1.7. in t h e remote oxide a p p a r a t u s w a s developed. A t i n c a p s u l e c o n t a i n i n g a know11 amount of SnO;! i s h e a t e d -Lo 55OoC i n t h e hydrof111.orinator as hydrogen i s p a s s e d t’hrough t h e system.

193 The SnOz i s reduced t o t h e metal, and t h e water formed passes on to t h e e l e et r ol-ysi s c e l l . Two standard samples of SnO2 were analyzed with a four-month interim, and oxide r e c o v e r i e s of 96 .l% and 95.6% were obtained.

It i s probable t h a t t h i s s l i g h t negative b i a s i s due t o momentary i n t e r r u p t i o n s i n t h e flow of t h e h y d r o f l u o r i n a t o r e f f l u e n t gas through t h e water e l e c t r o l y s i s c e l l . D i f f i c u l t y w i t h c e l l plugging w a s encountered throughout t h e period of development of t h e oxide method. A s a:n attempt t o e l i m i n a t e t h e negative bias and also t o provide a replacement c e l l f o r t h e remote oxide apparatus, it iwas deemed necessazy t o f i n d a method of r e g e n e r a t i n g t h e e l e c t r o l y s i s c e l l which wo1i.l.d permit a steady gas flow a t r e l a t i v e l y low flow r a t e s . The water e l e c t r o l y s i s c e l l c o n t a i n s p a r t i a l l y hydrated PzO5 i n t h e form of a t h i n viscous f i l m i n c o n t a c t with two s p i r a l l y vound 5-mil rhodium e l e c t r o d e wires. The wires are r e t a i n e d on t h e i n s i d e of an i n e r t p l a s t i c tube forrning a. 20-mil c a p i l l a r y through which t h e sample p a s s e s . The 2-ft-long t u b i n g element i s c o i l e d i n a h e l i x i n s i d e of a 5 / 8 - i n . - d i m pipe and p o t t e d i n p l a s t i c f o r permanence.

During t h e course of t h e i n v e s t i g a , t i o n of t h e c e l l , it was found t h a t a wet gas stream i n i t s e l f d i d not cause t h e e l e c t r o l y s i s c e l l t o p l u g . It w a s a l s o necessary f o r curren-L -to be flowing through t h e c e l l f o r flow i n t e r r u p t i o n s t o occur. This i n d i c a t e d t h a t t h e hydrogen and oxygen evolving from t h e e l e c t r o d e s c r e a t e bubbles i n %he p a r t i a l l y hydrated P205 film, which t h e n grow i n s i z e s u f f i c i e n l ; t o b r i d g e -the c a p i l l a r y and form an obstru.cting f i l m .

A f t e r many unsuccessful approaches, an acceptable answer t o t h e problem w a s obtained by means of a s p e c i a l r e g e n e r a t i n g teclmique using d i l u t e acetone s o l u t i o n s of H3FO4 as t h e regenera-Ling s o l u t i o n s . 'This provides a d e s i c c a n t c o a t i n g s u f f i c i e n t t o absoi-b t h e water i n t h e gas stream and gives a minimal amount of flow i n t e r r u p t i o n s during e l e c t r o l y s i s . The c e l l s which have been s u c c e s s f u l l y regenerated i n tliis manner have y i e l d e d oxide r e c o v e r i e s of 99.6 + 1.3%from staridard Sn02 samples.

Spectrophotometric S t u d i e s o f Molten-Salt Reactor Fuels - J. I?.

Young

Studies p e r t a i n i n g t o a continuous s p e c t r ophot o m - tr i c de-te m i n a t ion of U(II1) i n c i r c u l a t i n g IGBR f u e l s have continued. A g e n e r a l d e s c r i p t i o n of t h e o p t i c a l design of a f a c i l i t y f o r performing - t h i s d.eterInination has been The f a c i l i t y w i l l be used i n conjunction with :t coinm e r c i a l instrument a Cary modcl 1411 recording spectrophotometer. During t h i s p e r i o d f u r t h e r and more d e t a i l e d d i s c u s s i o n s of t h e o p t i c a l p r o b l e m involved have been c a r r i e d o u t with t h e designer of t h i s spectrophotometer and have culrniriated i n a purchase order i s s u e d t o them f o r t h e development of s u i t a b l e sample-space o p t i c s . The apparatus which w i l l r e s u l - t from t h i s r e q u i s i t i o n i s t o be d e l i v e r e d i n s i x months and w i l l provide optimum l i g h t g a t h e r i n g power and o p t i c a l design f o r use with a double convex lens-shaped drop of l i q u i d . The apparatus w i l l be used. with e x i s t i n g instrumentation and w i l l be compatible w i t h t h e o p t i c a l p a t h extension which w i l l be r e q u i r e d i n t h e f i n a l proposed r e a c t o r i n s t a l l a t i o n .

194 More d e t a i l e d s t u d i e s of t h e s p e c t r a of U(II1) T i l molten 2J,i.F.Beii12 havz provi-ded b e t t e r r e s o l u t i o n of t h e v a r i o u s a b s o r p t i o n s i n -the complex u ? . t r a v i o l e t a'osorptj-on peaks of U(II1). A s r e p o r t e d b e f o r e , t h e maxinium a b s o r p t i o n i s 360 run, b u t s h o u l d e r s are observed a t a p p r o x i m a k l y 310, 41.5, and. 508 nm. These s h o u l d e r s iilight be of a n a l y t i c a l - v a l u e i f as y e t u ~ i b o w ni n t e r f e r e n c e s p r e v e n t t h e use of t h e a b s o r p t i o n ai; 360 nm. On t h e b a s i s of c a l c u l a t i o n s made t o e s t i m a t x t h e proba'ri!..e valence s t a t e o f f i s s i o n pj-oducts, i t i s expected t h a t dl.ssolved f i s s i o n products w i l l be i n one of t1iel.r more normal v a l e n c e s t a t e s and t h e r e f o r e w i l l cause no l n t e r f e r e n c e at. the c o n c e n t r a t i o n s expected. Concerning 11mrsual o x i d a t i o n s t a t e s of r a r e - e a r - t h ffri.ssion p r o d u c t s , c u r s o q y s p e c t r a l . stud.i.es have been c a r r i e d o u t with S m ( 1 1 ) i n molten 2L31F-BeE'2. T h i s lower v a l e n c e s t a t e of samarium e x h i b i t s a s t r o n g , b r o a d a b s o r p t i o n peak w i t h a maximum a b s o r p t i o n a t 325 mi w i t h a shou.ldar a t approxiit1ate.l.y 1+?0 urn. The mol.arr a b s o r p t i v i t y i s n o t y e t knob^, b u t i.t i s be1.i.eved to be g r e a t e r t h a n 200. If c o n d i t i o n s a r e such t h a t Sm(l1) i s present;, possi-ble i n t e r f e r e n c e w i t h a d e t e r m i n a t i o n of U(II1) a t 360 m may b e encountered, depending on conc e n t r a t i o n s present. I n t e r f e r e n c e of lower-valent r a r e e a r t h s w i l l - not be a g e n e r a l problem, but only a problem w i t h s p e c i f i c i o n s ; f o r exampl.e, E u ( I 1 ) e x h i b i t s iio absorbance a t wa-vel-engths above 300 mn. Althougli i t has been assumed from o t h e r spec.tyal s t u d i e s , mainly i n t h e solven-i LiF-NaF-KF, t h a t c o r r o s i o n product i o n s would n o t i n t e r f e r e w i t h t h e proposed d e t e r m i n a t i o n , e x p e r i m e n t a l v e r i f i c a t i o n has n o t been ava-iI.able u n t i l t h i s p e r i o d . The molar a b s o r p t i v i t y o f F e ( l I ) , Cr(II), and Ni(TI) a t t h e i r wavelengths of maximxn absorbance i s 5 a t 103.0 nm, 6 a t 7bo nm, and 10 a-t 432 nm r e s p e c t i v e l y . None of t h e s e dissolved s p e c i e s will i n t e r f e r e a t c o n c e n t y a t i o n l e v e l s of 10 t o 100 t i m e s that expected i n t h e f u e l s a l t . I n g e n e r a l , t h e s p e c t r a of t h e s e 3d i o n s can be i n t e r p r e t e d as a r i s i n g f r o m e s s e n t i a l l y o c t a h e d r a l c o o r d i n a t i o n i n t h e ca.se of N i ( 1 1 ) and Cr(1I) and d t s t o r t e d o c t a h e d r a l symmetry i n -the c a s e of Fe(1I). A c u r s o r y s p e c t r a l s t u d y of C y ( P I 1 ) w a s made. The molar absorp-tj-vity ai; i t s wavelength of maximum absorbaace, 706 nm, i s approximately 7; C r ( 1 I I ) i s n o t expected t o b e p r e s e n t i n t h e fuel salt.

I n a s t u d y 0.P t h e a b s o r p t i o n spectrum of F e ( I 1 ) i n s e v e r a l difPerent; LiF-DeP2 s o l u t i o n s , a n ex-Lraiieous peak w a s n o t e d a t 432 nm. 'The p o s i t i o n of t h e peak suggested an N i ( 1 I ) j-rflpurity i n t h e mel-t. Based on a subsequent s p e c t r a l s t u d y of N i ( 1 I ) s p e c t r a i n t h e s e m e l t s , a mol-ten-sa1.i; s p e c t r o p h o t o m e t r i c a n a l y s i s of N i (11) c o n c e n t r x t i o n w a s p o s s i b l e . The comparison of t h i s d e t e r m i n a t i o n t o we.L chemical a n a l y s i s o-i" t h e same samples i s g i v e n below.

Sample

N i ( I 1 ) ($J w/w) Molten- S a l t S p e c t r a ---..

0.21 0.18

W e t C h e m i c a1 . X I -

0.19 0.22

195 These melts were made i n g r a p h i t e c o n t a i n e r s b u t were s t i r r e d w i t h a n i c k e l s t i r r e r . It would seem t h a t t h i s high n i c k e l contamina-tion, found o r i g i n a l l y by t h e molten-salt s p e c t r a , may have a r i s e n from t h e stirrer.

An extremely s e n s i t i v e a;bsorpl;ion peak a t t r i b u t e d t o U ( I V ) which causes total a b s o r p t i o n of most u l t r a v i o l e t l i g h t has been 2ound a t 235 nm. The molar absorptivity of t h i s peak i s approximately 1500. The peak has been observed i n aqueous a b s o r p t i o n s p e c t r a a t 207 nm,39 b u t has not been r e p o r t e d previously in any molten-salt s o l v e n t . A p o s s i b l e a n a l y t i c a l a p p l i c a t i o n of t h i s absorption would be a continuous spectrophotometric monitoring of coolant s a l t f o r leakage of uranium-bearing f u e l sa1.t

V o l t a m e t r i c and Chronopoteniiometric S t u d i e s of Uranium i n Molten IS'BeFz-ZrFq - 1). L. Warming and Gleb iMmiantov* Electrochemical r e d u c t i o n and o x i d a t i o n of U ( 1 V ) i n L,iF-BeF2-ZrF, (64-34-1.8and 65.6-29.4-5.O mole $1 was i n v e s t i g a t e d by rapid-scan v o l t ' m et r y and c llronopot e n t iome-try Well- de f i n e d and r e p r oduci b l e

c u r r e n t - v o l t a g e curves and p o t e n t i a l - t i m e c~.xrves were obtained a t concent r a t i o n s of uranium as high as 0.8 mole $ (MS'EIE f u e l ) . From t h e d a t a obtained s o far, t h e r e s u l t s are -very encou.raging from t h e standpoint of u t i l i z i n g t h e v o l t m e t r i c appr.oach as a means f o r i n - l i n e monitoring of uranium i n molten f l u o r i d e systems of i n t e r e s t t o t h e molten-salt r e a c t o r program. U t i l i z i n g a platinum i n d i c a t o r e l e c t r o d e , t h e r e l a t i v e standard d e v i a t i o n of peak current; f o r 4 1 runs over a p e r i o d of 36 days was Z.O$; eon.siderubly b e t t e r p r e c i s i o n ( s t a n d a r d d e v i a t i o n 0.76$ f o r 8 r u n s ) was obtained over a period. o f 2 hr. Other i n d i c a t o r electyodes t e s t e d i n cluded p y r o l y t i c g r a p h i t e , moly'od.enutn, tungsten, and tantalum. O S t h e e l e c t r o d e s tested-, b e t t e r r e p r o d u c i b i l i t y was obtained a t platiiiutn or platiiiixn-lO$ rhodium.

~t 500"~t h e r e d u c t i o n of U(IV) a t p1attnwrl i s i?. r e v e r s i b l e onee l e c t r o n process, as determined from Flernstian l o g p l o t s and t h e diagn o s t i c c r i t e r i a of l i n e a r sweep voltamnetry. Also from chronopoten'tiornetry, a p l o t of t h e current-density-ti-ansitiori-time product ( L O T ) vs ( t r a n s i t i o n time )I/' y i e l d e d a s t r a i g h t l i n e , which i s i n agreement with theory- f o r a r e v e r s i b l e e1ectrod.e p r o c e s s . From t h e slope of t h e l i n e , t h e d i f f u s i o n c o e f f i c i e n t f o r uranium w a s calculated. t o be about 1 . 5 x IO-' cni2/sec, i n good agreement with t h e value obtained by v o l t m m e t r y em2/sec). The e f f e c t of temperature on t h e d i f f u s i o n (1.5 t o 2.0 x c o e f f i c i e n t w a s determined. over t h e range 480 t o 600째C; arid from it plot o f l o g D vs l / T t h e a c t i v a t i o n energgy which corrcsporids t,o t h e redu.ction of IJ(1V) t o U ( I I 1 ) w a s found t o be approximizte1.y 1.1kcal/mole.

Additional data. a r e being c o l l e c t e d t o eva'luate f u r t h e r t h e p r e c i s i o n and r e p r o d u c i b i l i t y of t h e v o l t a m e t r i c measurements a t d i f f e r e n t l e v e l s

-*CoIisu.ltant, Department of Chemistry, University of Tennessee, 'Knoxville.

196 of u r a n i i m c o n c e n t r a t i o n s , from which i - t i s hoped t o o b t a i n a b e t t e r a.asessment of t h i s approach as a n a n a l y t i c a i method f o r i n - l i n e d e t e r minaLioii of U(IV) i n moltea f l u o r i r l e s .

A new voltammeter i s b e i n g b u i l t t h a t ~1-11 measure a 2 0 - f o l d h i g h e r c u r r e n - t (100 ma> t h a n e x i s t i - n g equi.pment s o t h a t e l e c t r o d e s with more r e p r o d u c i b l e a r e a can be u s e d . With p r e s e n t equipment -the e l e c t r o d e I s l i m i t e d t o a 20-gage p1,ztlnum wire i n s e r t e d only 5 urn i n t o t h e fuel., s o t h a t s l i g h t changes i n m e l t I.evel i n t r o d u c e a s i g n i f i c a n t change i n red u c t i o n c u r r e n - t . The new i n s t r u m e n t w i l l a l s o prov-Id2 a more r a p i d v o l k g e scan, up t o 500 v/sec, t o minimi-ze f l o x e f f e c t s i n a n i n - l i n e cell.

I n - l i n e T e s t F a c i l i t y - R . ii’. Meyer

Apple, J. M. Dale: J. P. Young, and A. S.

I n view of the v a l u e and p o t e n t i a l . s u c c e s s of methods f o r t h e contri.nuous a n a l y s i s of circulating sa1.t streams a f a c i l i h y t o p r o v i d e s a l t streams of knowil composition i s b e i n g c o n s i d e r e d t o provide a tes-t of equipment under s i m u l a t e d i n - l i n e measiuremen’is. The m o s t p r a c t i c a l f a c i l i t y comrliensurate w i t h tlhe a v a i l a b l e space i n a C a l . i f o r n i a hood cons i s t s of a 20-kg s a l t r e s e r v o i r fitted. w i t h a s t i r r e r , p o r t s f o r sa.mpl.i.ng and f o r t h e a d d i t i o n of soI.id and m o l t e a c o n s t i t u e n t s , purge s-treams and e l e c t r o d e s for p u r i f i c a t i o n , and a helium g a s l i f t t o c o n t i n u o u s l y t r a n s f e r a stream of s a l t t o a n e l e v a t e d c o n s t a n t - l e v e l v e s s e l . From t h e c o n s t a n t level. vessel, s a l t streams c a n be g r a v i - t y - f e d t o a p p a r a t u s e s f o r t e s t t h g e l e c l;rometric and s p e c t r o p h o t o m e t r i c t e c h n i q u e s of a n a l y s i s and for de-termining parameters f o r t h e continuous d e t e r m i n a t i o n o f oxide by c o u n t e r c u r r e n t e q i s i l i b r a t i - o n of a s a l t stream w i t h anhydrous hydrogen f l u o r i d e . T’ne analyzed s a l t s t r e a m s w i l l t h e n be r e t u r n e d t o t h e reservoir. Tnis f a c i l i t y w i l l a l s o b e used t o t e s t c a p i l l a r y and o r i f i c e t e c h n j q u e s f o r t h e c o n t r o l of low s a l t flohrs and t o d e s i g n s m a l l f r e e z e val-ves. TCesks o f v a r i o u s gas l i f - t d-esigns are b e i n g c a r r i e d o u t w i t h s i m u l a t e d molten f u e l (aqueous z i n c c h l o r i d e s o l u t i o n s ) bo cieterinine whether a 6- t o 8-ft l i f t i s practical.. Anal-ysis of Helium Blanket G a s and A. S. Meyer

C . M. Boyd, C . A. Iiorton, A. D. Hor‘co:i,

The Ana.I-ytica1 Chemistry Divrision, t o g e t h e r w i t h members of t h e Zea c t o r and Reactor Chemistry D i v i s i o n s , p a r t i c i p a t e d i n v a r i o u s experi.ments t o determine possible soiirces of t h e o r g a n i c d e p o s i t s which have caused plugging of v a l v e s and f i l - t e r s i.n t h e MSRE o f f - g a s system. The a n a l y t i c a l s u p p o r t i n c hided : 1. t h e i n s t a l . l a t i o n of a continuous hydrocarbon a n a l y z e r to monitor gas streams from R e a c t o r Chemistry e ~ p e r j m e n - t ts o~ ~simul-ate o i l 1eak.s i n t o t h e MSRE pump and t o evaluate t r a p p i n g sys-kerns for r e d u c i n g hydrocarbon concentra;t;i.on, and t o monitor hydrocarbons i n t h e o f f 41 gas from t h e Y - 1 2 pimp -Lest, loop;

197 2.

t h e determination by gas chromatographic a n a l y s i s and by s e l e c t i v e chemical r e a c t i o n s of i n d i v i d u a l hydrocarbons i n "grab" samples from t h e above experiments and i n a t r a p p e d sample Srom 8. nonradioa c t i v e PERE purge ~ . i n e ; ' ~

t h e development of a technique t o measure t h e concentration of hydrocarbons c o l l e c t e d on an experimental c h a r c o a l trap by p y r o l y s i s of a sample of t h e charcoal followed by gas ckiromatographic a n a l y s i s of t h e pyrolyzate. By sampling the c h a r c o a l bed a t various depths, it i s p o s s i b l e to determine t h e d i s t r i b u t i o n of i n d i v i d u a l hydrocarbons as a f u n c t i o n of t r a p length.

The continuous hydrocarbon monitor proved t o be t h e most u s e f u l of t h e s e techniques, p a r t i c u l a r l y i n measurements performed a t t h e Y - 1 2 t e s t loop with P. G. Smi-th, of t h e Reactor Division, and R . G. Ross, of t h e Reactor Chemistry Division. F i b m e '7.23 i s a flow schematic o f t h e inexperiment was designed t o measure t h e j e c t i o n experiment. Although t i . ~ e f f e c t s of d e l i b e r a t e i n j e c t i o n of o i l i n t o t h e p u p tarik, the i n i t i a l r e s u l t s revealed an a c t u a l o i l l e a k i n t h e pump. The experiment t h e r e f o r e a f f o r d e d an opportunity -Lo study t h e o i l l e a k and c o r r e l a t e t h e hydrocarbon l e v e l i n t h e pump t a n k off-gas with an operating v a r i a b l e (Ap a c r o s s t h e s h a f t annulus) and t h u s d i s t i n g u i s h between p o s s i b l e l e a k l o c a t i o n s . A t y p i c a l plot of t h e hydrocarbon c o n c e n t r a t i o n i n t h e pump t a n k off-gas i s shorn i n Fig. '7.24. When t h e p u p r o t a t i o n was stopped, t h e s h a f t annulus Ap decreased from 3 t o 0 . 5 p s i , and t h e hydrocarbon l e v e l i n t h e off-gas dropped. immediately -to less t h m 1.0ppm methane e q u i v a l e n t . A f t e r about 25 l-ir t h e Ap began t o recover, axid t h e hydrocarbon level s t a r t e d t o umdergo a series of r e p i d excursions that are suggestive of d i s c r e t e drops of o i l e n t e r i n g t h e hot regioiis of t h e pump -Lank. The average hydrocarbon c o n c e n t r a t i o n gradually returned. t o a l e v e l ORNI.

DWG. 66-b877A

SAMPLE

POINT 1

ig. 7.23.

n r' .

Flow Sehema-Lfc of O i l I n j e c t i o n Experimerrt.

600

- 1

210

220

230

-I_

240 250 T E S r TIME (hr)

260

27c

280

F i g . 7.24. J3ydrocarbons i n Y - 1 2 Pump Tank O f f - G a s . of about 300 ppm, i n p a r a l l e l w i t h i n c r e a s i n g Ap. S i m i l a r f l u c t u a t i o n s i n hydrocarbon c o n c e n t r a t i o n s were observed d u r i n g - t h r e e a d d i t i o n a l changes i n p u p o p e r a t i o n t o reduce t h e Ap, which. w a s u l t i m a t e l y shown t o be caused by a s a l t p l u g a t t h e bottom of t h e s h a f t a n n u l u s . Because t h i s d i f f e r e n t i a l . p r e s s u r e i s e x e r t e d a c r o s s t h e seals be-iween t h e s h i e l d plug and t h e c a t c h b a s i n , t h e p o s i t i o n o f t h e l e a k w a s d e f i n e d as -through t h e s e seals r a t h e r t h a n down t h e s h a f t a n n u l u s . ‘Thisw a s confirmed, on disassembly, by a n o i l fi..h and p y r o l y s i s s t a i n on t h e o u t s i d e of -the s h i e l d plug. I n j e c t l o n of o i l , Gulf S p i n 3 5 , i n t o t h e pump -tank showed t h a t ess e n t i a l l y a l l t h e o i l e n t e r i n g t h e t a n k a.ppeared as hydrocarbons i n tile off-gas. Table 7.18 shows gas chromatographic a n a l y s e s ol” t h e oyf-gas t o g e t h e r w i t h t h o s e from helium e f f l u e n t s from R e a c t o r Chemistry e x p e r i ments i n which t h e o i l . w a s i n j e c t e d i.nto a heliwri strean e n t e r i n g an empty n i c k e l p o t a t 600°C. These r e s u l t s r e v e a l e d t h a t , a t ?.east i n the absence of r a d l o a c t i v i t y , o i l e n t e r i n g t h e pump t a n k i s predoniinantly c r a c k e d t o l i g h t hydrocarbons, metheme, ethane, and u n s a t u r a t e s l i g h t e r t h a n C 5 , which are t r a p p e d i n e f f e c t i v e l y on c h a r c o a l t r a p s a t 100°C. Conversely, i.n t h e Reactor Chemis‘wy experiments t h e c r a c k i n g w a s incornp l e t e t o y i e l d a s u b s t a n t i a l f r a c t i o n of > c6 hydrocarbons, whri.ch a r e trapped w i t h high e f f i c i e n c y . A t h e r m a l c o n d u c t i v i t y method ,tomeasure t h e t o - t a l hydrocar’oon conc e n t r a t i o n i n t h e r a d i o a c t i v e off-gas of t h e E R E c o n t i n u o u s l y has been developed w i t h t h e R e a c t o r Chemistry D i v i s i o n . I n this method t h e o f f gas sample i s passed over copper oxide a t ‘700°C t o c o n v e r t hydrocarbons t o C02 and H20. This oxidized stream i s passed t h r o u g h one s i d e of a t h e r m a l c o n d u c t i v i t y d e t e c t o r and t h e n c e t o a t r a p containi-ng A s c a r i t e and Mg(C104)2 t o y i e l d a strewn of i n e r t g a s e s which i s d i r e c t e d through t h e r e f e r e n c e s i d e of the t h e r m a l c o n d u c t i v i t y ce1.l. I n bench-top t e s t s t h e response of t h i s a p p a r a t u s w a s l i n e a r t o t o t a l . hydrocarbon c o n c e n t r a t i o n of 1000 ppm w i t h a l i m i t of d e t e c t i o n below 10 pprn. A s i m i l a r syst e m w i t h t h e t r a p and copper oxide f u r n a c e designed f o r one y e a r of r e a c t o r o p e r a t i o n w i l l be i n s t a l l e d i n t h e gas-sanip2.i-ng s t a t i o n of t h e MSHE.

199 Table ' I . 18. HydrocaYuoiis Produced by O i l I n jec1;ion

I n j e c t i o n r a t e , 16 cm3/day

EIydrocarbon Concentr a t i o n [ppm methane e c@.valents )

Hydrocarbon

Y-12 Tes-t; LOOP

Reactor Chemistry Simulated Leak

'rests

Before

Trap

20 h r A f t e r

2 hr A f k r Start o f I n j e c t i o n

After Trap

Before Trap

S t a r t of I n j e c t i o n

After Trap

Before !-rap 1 1

After

T1-ap

CH/,

2 10

210

310

250

2H6

k4.

c 2%

140

600

590

700

c3H6

3-00

120

170

230

Unsatd. CL,

158

40 690

130

160

Unsatd. C S

and

Aromatics

2 10

204

300

Total

'1.6

703

400

1290

1010

1666

1354

Development and E m h i a t i o n of E q u i p m m t and F'rocediirr3; for Analyzing Radioactive IGRE Salt, Samples

E'. K. Heacker

E:. TaJrnb

L. T. Corbiri

17he remote apparatus f o r detc2rmining t h e oxide content of M S F E sall; samples was i n s t a l l e d i n c e l l 3 of the Eli~h-Radiation-:~Yel Analytical. F l i m r i d e s a l t smple:? and t i n oxide h b o r a t o l y (HLIIIAI,) (Building 2026 ) standards were a n a l y z e d l;o check t h e apparatus arid fm.i.liarize t h e EELAL personnel with the method. T h e results w e r e sztisfacto.ry, a n d the physi c a l rnanipulations required. were performed. adequ.ately Eight 50-g fue1.s a l t sariples have been analyzed remott::l;r.

The t i m e requ-ired. t o d.econt;arnina-te t h e t r a n s p o r t c o n t a i n e r s was g r e a t l ; y reduced by iising disposable m i l d s t e e l plugs for each s8~1iple submitked

200

Sample A.na1.y ses

From January 1, 1966, through June 30, 1966, 43 MEXE f u e l - s a l t saxtip l e c were s u b m i t t e d f o r a n a l y s i s . The samples were a n a l y z e d as shown b e l ow. AnaZys i s

Numb e r of D e t e mi n a t ions

Uraniim Zirconium

35 35 35 35 35 35 35

Chromium

Bery-lliim Fluorine Iroil Nickel Molybdenum L?thium RCA Prep. MSA B.ep. Oxide Ca r b on

‘i

35 22 5 6 3

O f t h e 43 samples submitted, iwo 50-g oxide samples were n o t analyzed due -to contaminated l a d l e s . Three s a n p l e s were analyzed for caybon and found t o c o n t a i n <50 ppm.

S e v e r a l of t h e samples were recei-v-ed w i t h a s i l v e r and a H a s t e l l o y

N w i r e c o i l e d onto the s t a i n l e s s s t e e l c a b l e between the l a t c h and l a d l e . The l a t c h , w i r e s ,

analyses.

and. ca1)I.e w e r e s e p a r a t e d . arid p r e p a r e d f o r radiocheniical

The qiia!.ity - c o n t r o l program was c o n t i n u e d d u r i n g t h e first; and secolid q u a r t e r s of 1966. A composite of t h e v a l u e s o b t a i n e d by f o u r d i f f e r e n t groups of s h i f t p e r s o n n e l i s shorn? 1x1 Tables 7.19 and 7.20. MoI.ybde:mm v-alues a r e n o t showil s i n c e it was not added t o t h e s y n t h e t i c s o l u t i o n s .

It T ~ %esv i d e n t from t h e s e c o n d - q u a r t e r c o n t r o l data t,hat a posil;ive b i a s of app:roximately 3$ e x i s t e d i n t h e ampei-ometric zirconium method. The b i a s w a s a t - t r i b u t z d t o polyiiierizat;.i.on of t h e zi.rconilm i n t h e s t a n d a r d s o l u t i o n s used t o s t a n d a r d i z e t h e cupf’erron t i t r a n t ; . Although t h e b i a s appears to have been e l i m i n a t e d by t h e p r e p a r a t i o n of new zirconium s t a n d a r d s , more da-ta a r e needed t o c0nfij-m i.t.

The p o s i t i v e bia,s e x i s t i n g i n the s p e c t r o p h o t o m e t r i c n i c k e l method. has been reduced t o approximately 8% by changing t h e c o l o r f i l t e r i n t h e f i l t e r photometer and c o n s t r u c t i n g a new c a l i b r a t i o n cu.rve. F u r t h e r eff o r t s a r e b e i n g made t o e l i m i n a t e t h e bias comple’iely.

201 Table 7.19. Swnmary of Control Results, January Through February 1966

Determination

. f

Method.

Xumber of Determinations

L i m i t of Error-

(%)

Fixed

Iron

-o- Phenant h r o l i n e

27 25 34

Nickel

15.0

U ra n i m

Dimet hy lglyoxime

Coulometric (high sen. )

1.0

Zirconium

Amper ornet r ic

5.0

Beryllium

Phot oneutron

Chromium

hperometric

Found

15 .o

15.0

2.43 7-95 7.93 12.74

5.0

l.16

5.74-

Table 7.20. Summary of Control H e s u l t , ~ , A p r i l Through June 1966

L i m i t of Error

Determination

Method

($1

Number of

De-terniinations

Fixed

Found

Beryl-1.iurfl

Phot oncut ron

5.0

2.60

Chromium

Amperornetric

15.0

Iron

-0-Plienant h r o l i n e

15.0

12.46 7.54

15.0

'1.67

127

1.0

1.. 04

5.0

5.48

Nickel

D i m e thylglyoximc:

Uranium

C ou l o m e - tr ic (high s e n . )

Zirconium

Amperometric

202 References 1. MSR Program - Semiann. Frogr. Rept. Fzb. -. 3 8 , 1966, CdNTI-3936, p . 123.

T'nc o p e r a t i o n a l h i s t o r y of these runs is d e s c r i b e d i n s e c t . 1.1 of

S. S. Kirslis, t h i s repoi%, s e c t . 7.4> s u b s e c t i o n e n t i t l e d " F i s s i o n Product Behavior i n t h e PEliE."

this report.

R . F . Apple, J. M. D a l e , and A . S. Meyer, t h i s r e p o r t , s e c t . 7 . 5 , s u b s e c t i o n e n t i t l e d "Determi.nation of Oxide i n R a d i o a c t i v e MSRE Sanp l e s "

H. E . Eby, OTIDJI, I s o t o p e s D i v i s i o n .

6. R . E . Thorna t o P. N. Hainbenreich, "Chemical Analysis of MSRE F l u s h and Coolani; S a l t s i n Preriuclear T e s t P e r i o d , " MSH-65-19 (March 19, 1965) ( i n t e r n a l correspondence). S. Cantor and W. T . Ward, Reac-tor Chem. Div-. Ann. R o g r . Rept. Dee. 31, 1965, OWL-392.3, pp. 27-28,

8. L. S h a r t s i s and S . Spinner, J . R e s . N a t l . Bur. S t d . 46, 176 (1951.). 9. J .

1).

MacKenzie, J. Chem. Phys. 32, 1150 (1960).

10. J . H. DeBoer and J . A. M. Van Liempt, Rec. Trav. C'nim. 46, 124 (1927). 56, 36 (193'7). 11. L. J . Kinkenberg, Rec. Trav. Chim. 12.

S t r u c t u r e Re,ports, v o l . X I I I , p. 342.

l3. J . D. Edwards et al., J. Electrochem. S O C . 100, 508 (3953).

14. e

S. Cantor, Reactor Chem. Div.

ORNL-39l3,

24-32.

Ann. â&#x201A;Ź'rogr. Rcpt. Eec. 31, 1365,

1.5. S . Cantor and 'id. T . Ward, i h i d . , p . 27.

16. MSR Program Semiann. Progr. licpt. Feb. 28, 7-966, CRNL-3936, pp.

141-45.

1.7.

D. G . H i l l t o

19.

W. S. G i n e l l . , Nucl. Tech. 51, 185 (1959).

18. 20

21.

22. 23. 24. 25.

W, R. Grimes, p r i v a t e communication, June 29, 1966.

D. G. H i l l to W. R . G r i m e s , p r i v a t e con-munica,tion, J i l y 1, 1966. J. J. Egan and I?.

N . Wiswall, Nucleonics 15, 104 (1957).

Reactor Chem. Div. h n .

Rept. Jan. 31, 1964, OFNL-3591, p. 50.

Reactor Chem. Div. Ann. Progr. Rept. Jan. 31, 1965, ORNL-3789,

p. 16.

MSR Program Semisnn. Progr. Hept. Feb. 28, 1966, ORNL-3936, p. 145.

ZrO2 w a s prepared by H. H. Stone, Reactor Chemistry D i v i s i o n .

MSR Program Semiam. Pi-ogr. Rept. E'eb. 28, 1966, ORT\TL-3936, p .

14-j.

203

26. R . P. E l l i o t t , C o n s t i t u t i o n of Binary Alloys, F i r s t Supplement, p. 203, McGraw-Hill, New Yorlr, 1965.

27.

MSR Program Semi-.

Progr. Rept. Feb. 28, 1966, ORNE3936, p. 148.

28. W. D. Burch, G. M. Watson, a n d H. 0. Weeren, Xenon Control i n F l u i d 29. 30.

31.

Fueled Reactors, ORIX-LCF-60-2-2 ( J u l y 6, 1960).

I . Spiewak, "Xenon Transport i n lGF% Graphite," MSR-60-28 (Nov. 2, 1960) ( i n t e r n a l correspondence). G. M. Watson and K. B. %Vans 111, Xenon Diffusion i n Graphite: Effect,s of Xenon Absorption i n Molten S a l t Reactors Containing GraphORNLCF-61-2-59 (F'eb. 15, 1961).

J. W. M i l l e r , Xenon Poisoning i n Molten S a l t Reactors, OEl\TL-CF-Ql5-62 (May 3, 1961).

32.

R . B. Evans 111, "Xenon Poisoning i n Molten S a l t Reactors Containi n g Graphite," Reactor Chem. Div. bn. Progr. Rept. Jan. 31, 1961, Oâ&#x201A;ŹU'U,-312r7, pp. 15-16.

33.

F. R . Kasten, E. S. B e t t i s , and R . C . Robertson, Design Studies of lOOO-Mw(e) Molten-Salt Breeder Reactors, ORIK-3996 (August 1966).

34.

B. Manowitz, quoted by P. G. Salgado i n Nuclear Reactor MagnetoEiydrodynamics Power Generation, 11-3368, p. 23.

35. 36.

3'1

38.

35.

40.

MSR Program Semiann. Progr. H q t . Aug. 31, 1965, ORNL-3872,

p. 12'7.

A. M. Perry, i n t e r r i a l mcmoraadwn, Juljr 30, 1966. MLSi? Program Serriiann. Progr

I _

. Hept . F P .~28,

1966, ORI'JL3936,

p. 154.

MSR Program Semiann. Yrogr. Rept. Alug. 31, 1965, O R N L 3 8 7 2 , p . 145.

Donald Cohen and W. T. C a m a l l , J. Phys. Chem. 64, 1933 (1960).

B. F. Hitch, R . G. Ross, and H. F. McDuffie, T e s t s of Various P a r t i c l e F i l t e r s - f o r Removal'of O i l Mists and Hybrocarbon Vapors, O i W L TM-1623 ( t o be i s s u e d ) .

4l. A. S. Meyer, I n v e s t i g a t i o n of Hydrocarbons i n t h e O f f - G a s f r o m t h e Y-12 Test Loop, ORNLCF-66-8-30

42.

(September 1966).

A. S. Meyer, "Hydrocarbons i n S e a l Purge of WRE Pwnps," PER-66-10 (May 1966) ( i n t e r n a l correspondence).

Part 3.

MOLTEN-SALT BREEDER IiEACTOR STUDIES

MOLTEN-SALT BEUIEDER RFACTQR DESIGN STUDIES

Paul R. Kasten J. H. Westsik

E. S. B e t t i s H. 3'. Bauman

Roy C. Robertson H. T. Kerr

The MSBR reference design concept w a s presented p r e v i o u s l y , l and i s a two-region, two-fluid system, with f u e l s a l t separated Yrom t h e blanket s a l t by g r a p h i t e tubes. On-site f u e l recycle i s employed, using I n a d d i t ion, f l u o r i d e - v o l a t i l i t y and vacuum- d i s t i l l a t i o n processing r e s u l t s were gjven for t h e case o f d i r e c t removal oP protactinium from t h e blanket region; t h e s s s o c i a t e d concept was ternlied MSBR(Ya). Since t'nese s t u d i e s , a d d i t i o n a l design conditions were i n v e s t i g a t e d and evaluated, and t h e s e a r e discussed below.

8.1 Desim. Changes i n VSBR P l a n t I n r e a c t o r design s t u d i e s it o f t e n occurs t h a t certaim f e a t u r e s of th.e d e t a i l e d d e s i @ imdergo changes as more understanding i s obtained of t h e o v e r a l l problems and a s new ways a r e discovered t o solve a given design problem. Such changes have taken place during t h e MSBI? design s t u d i e s ; t h e most i m p o r t m t a r e those associ.ated with t h e primary h e a t exchanger designs and t h e pressures t h a t e x i s t i n t h e varLous c i r c u l a t i n g s a l t systems. An objectionable feabure of t h e MSBR. h e a t exchanger design considered previously was t h e use of expramion bellows a t t h e bottom o f t h e exchanger. These bellows permit tubes i n t h e c e n t r a l p o r t i o n of t h e exchanger t o change i n l e n g t h r e l a t i v e t o those i n t h e annular region due t o thermal conditions. Since such bellows may be i m p r a c t i c a l t o use under r e a c t o r operatring conditions, a new desi@ w a s developed t h a t eliml.nated them.

Figure 8.1 shows t h e r e v i s e d h e a t exchfmger d.esign. The expcmsion bellows were eliminated, and changes i n t h e tinbe l e n g t h s clue to thernial conditions a r e accommodated by t h e use of sine-wave ty-pe of construction, vkich permits each tube t o a d j u s t to thermal changes. I n addition, t h e coolant s a l t now e n t e r s t h e h e a t exchanger through an mnu.lar v o l u t e a t t h e top and passes downward through a b a f f l e d o u t e r annular region. The cool.mt s a l t then passes upward through a 'oaf f l e d i m e r annular region and e x i t s throu,@. a c e n t r a l pipe.

I n Fig. 8.1 t h e flow of f u e l salt through t'ne pump i s reversed from t h a t given previously1 i n order to reduce t h e pressure in t h e graphite f u e l t u b e s . Fuel s a l t e n t e r s t h e h e a t exc'rianger i n t h e i n n e r annular region, passes downward through t h e tubes, and t h e n flows upward through t h e tubes i n t h e o u t e r annular region before e n t e r i n g t h e r e a c t o r . The b l a n k e t - s a l t heat exchanger w a s a l s o r e v i s e d t o give a design s i m i l a r t o t h a t of Fig. 8.1. The general f e a t u r e s of t h e s e exchangers and t h e i r placement i n t h e r e a c t o r c e l l are shown i n Fig. 8.2, The

207

208 OBXL DWG.

66-7136,

FUEL L E V E L (OPEKATiYG)

-//.,<>7

,,-

FUEI- SALT PUMP

COOLANT SALT FROM STEAM HEAT EXCHANGFRS

COOL4NT PASS SFPPRATiNG GAFFLE

FLOW ARRANGFMENT FUEL s A L r IN -IJBE SIDE COOLANT S A L i iN SHELL SIDE

L TO kUFL

nHAlN TANKS I

-COOLANT SALT TO BLANKFT IHEAT tXCIiANGER

Fige 8.1. Revised Fuel Hcai ExchaRger for PLYRR.

209 OFU'G DWG. FUEI.. PUMP MOTOR

66-7109

BLANKET PUlvlP

FAOTCR

Fig. 8.2. MSRR C e l l Elevation Showing Prlmaly Heat Excliarigers a n d Their Placement.

210 b l a n k e t - s a l t pump w a s a l s o a l t e r e d s o tha-t; blanket sa1.f; l e a v i n g t h e r e a c t o r now e n t e r s t h e s u c t i o n s i d e of tine purcp,

From t h e vi-ewpoint of r e a c t o r s a f e t y , i-t i s important tiiat the blanket s a l t be a t a higher p r e s s u r e t h a n Gie fuel. Under such circu;mstan.ces, rupture of a finel tube trould r e s u l t i n leakage of fertile s a l t i n t o .tile fuel and. a reduction i n r e a c t i v i t y . 111order t o achieve ‘chis condition w i t h a minimum operating p r e s s u r e ri.n the reactor v e s s e l , the f l u i d f l o ~ was reversed from thah j.n t h e i n i t i a l PEBR design as s t a t e d above. The r e s u l t l n g flow diagram i s shown i n Fig. 8.3. I n ad-dition, it i s desrjrable t h a t any leakage between t h e reac’cor f l u i d and c o o l a n t - s a l t systems be from t h e coolant system i n t o t h e f u e l o r blanke’c system. In order t o achieve -these conditions, the MSBR o p e r a t i n s p r e s s u r e s were r e v t s e d t o .t;hose shown i n Table 8.1. Table 8.1. Pressures i n Various P a r t s of Revised. MSBR Salk C i r c u i t s

Flow diagram given in Fig. 8.3

Nominal

Location -..

Fuel.- salt sys-tern Core Core Pump Pump Heat

entrance exkt suction outlet exchanger o u t l e t

Pressure (psig) -50 25 10 150 60

Rlajnket-salt system

Blanket entrance Blanke-t ex-i~t

P1mp s u c t i o n Pump o u t l e t Heat exchanger out1e.t;

66 65

155 67

Coolant- s a l t system

Pump s u c t i o n before b o i l e r - s u p e r h e a t e r s Pimp o u t l e t before b o i l e r - s u p e r h e a t e r s I n l e t t o fuel he& exchmgers O u t l e t from fuel. h e a t exchangers O u t l e t - i n l e t t o blanket h e a t exchangers Pump s u c t i o n before r e h e a t e r s Pump o u t l e t before r e h e a t e r s Rehe a.t e r out let

130 280 220 160 142 130

240 220

REACTOR VESSEL IO. 067--__--_ if r------

j 5 5 0 p - IO00"F

150 f+%ec

3 6 0 0 ~ I0OO"F -

!O ft Vsec

-7 ; 1424 h-3515 p - 1000'

, j I424 h

TURBINE

REHEATERS,

1323.5h ---_-___ 570 p-65O'F

,+ BLANKET --7SALT ( DRAIN TANKS 1I

------A

[DRAIN

Fig. 8.3.

TANKS

Revised &E32 Flow Diagram.

F CONDENSER 8

1307.8 h

Gross

GEN.

3 5 0 0 ~ 5- 5 0 . 9 O

Gross

FEEDWATER + 1,

SYSTEMS

BOOSTER PUMPS LEGEND

I I

A + '

REHEAT STEAM PREHEATERS '69.2h

6 0 0 ~ -1

f ,A

j"5O"F

j 1518.5h-540p-1000"

7.152 X --__-

MIXING T E E PER FOR MANCE NET OUTPUT GROSS GENERATION BF BOOSTER PUMPS STATION AUXlLiARiES REACTOR HEAT INPUT NET HEAT RATE NET EFFICIENCY

1,000 Mwe 1,034.9 Mwe 9.2 Mwe 25.7 Mwe 2,225 M w t 7,60i B t u / k w h 44.9 x

2 12 A s given i n Table 8.1, t h e minimum pressure d i f f e r e n c e between the core and blanket regions i s about 1 5 p s i plus t h e s t a t i c head d i f f e r e n t l a l , o r a minimum tot;a,l d i f f e r e n c e of about 30 p s i . If it i s d e s i r a b l e t o i n crease t h i s pressure d i f f e r e n t i a l , t h e blanke-l; s a l t pump coul-d. be changed s o t'nat it discharges i n t o 'che r e a c t o r blanket region, g i v i n g a minil-num d i f f e r e n t i a l p r e s s u r e between the coTe md blanket f l u i d s of about 1.20 p s i , Whether t h i s change i s necessaiy o r whether i t would i n c r e a s e t h e r e a c t o r v e s s e l design pressure i s dependent, upon t h e s a f e t y c r i t e r i a t h a t need t o be s a t i s f i e d . A design p r e s s u r e of 150 p s i a w a s used i n determining Yne t h i c k n e s s of t h e YSBR r e a c t o r v e s s e l .

8.2

Modular-Type P l a n t

A n j-mportant f a c t o r ii? a t t a i n i n g low power c o s t s i s t h e a b i l i - t y t o maintain a high p l a n t - a v a i l a b i l i t y f a c t o r ; design f e a t u r e s t h a t improve t h i s f a c t o r a r e d e s i r a b l e i f t h e s e f e a t u r e s do not themselves introduce c ornpensat i n g d . i s advajit ages

l i l t'he MSBR pl.ant, use i s made of f o u r h e a t exchanger c i r c u i t s 5.n conjunction with one r e a c t o r v e s s e l i n such a riianner t h a t i f one pump i n t h e f u e l c i r c u i t s t o p s , t h e r e a c t o r i s e f f e c t i v e l y s h u t d-own. I f , on t h e o t h e r hand, it were p r a c t i c a b l e t o have f o u r separat,e r e a c t o r c i r cii.i.ts, with each connected to one of t h e f o u r h e a t exchanger cj.rcui-Ls, stoppage of a Puel pump would s h u t dowfl only one-quarter o f t h e s t a t i o n c a p a c i t y , l e a v i n g 75% a v a i l a b l e f o r power production. In order t o determine t h e p r a c t i c a l i t y of using a number of r e a c t o r s i n a s i n g l e 1000Mw ( e l e c t r i c a l ) s t a t i o n , t h e design f e a t u r e s of a m o d u l a r - t n e PEBR plant, termed bWSBR, were j-nvestigated.

The ? W B R design concept; considers f o u r s e p a r a t e and i d e n t i c a l rea c t o r s , a l o n s with their- s e p a r a t e s a l t ci.rcui-Ls. The only connections of t h e f o u r r e a c t o r s a r e through "ihe f u e l - r e c y c l e p l a t ; . The desi.gns of -the heat exchangers, t h e c o o l a n t - s a l t c i r c u i t s , and t h e steam-power cycle remain e s s e n t i a l l y as f o r t h e MSBR. Each r e a c t o r niod.ule gene r a t e s t h e thermal power requi-red f o r producing 250 Mw ( e l e c t r i c a l ) net.

The flow d . i a g r m given previously f o r t h e MSSX (Fig. 8.3) a l s o i s e s s e n t i a l l y vaJ-id f o r t h e MMSBE. S a l t flow r a t e s a i d capaciti.es of t h e varloiis components remain as i n -the E B H design. F i s u r e s 8.4 and 8.5 give plan and e l e v a t i o n views of t h e f o u r d i s t i n c t r e a c t o r c e l l s , along with t h e i r adjacent steam-generating c e l l s . Any r e a c t o r module can be shut down and s e r v i c e d whi1.e t h e o t h e r t'nree remain operating. The r e a c t o r core c o n s i s t s of 210 g r a p h i t e f u e l c e l l s operating i n p a r a l l e l within t h e r e a c t o r -tank.. The design of t h e g r a p h i t e tubes s e p a r a t i n g t h e fuel- and blanket s a l t s i s s i m i l a r t o t h a t used i n t h e MSBR. The r e a c t o r core region i s c y l i n d r l . c a l with a d i a n e t z r of about 6.3 f t and a height of about 7.9 f - L . The r e a c t o r v e s s e l i s approximately

v, K

a W

213

214

0 0-

' /

215 1 2 f t i n diameter and about 14 f t high. Except f o r t h e use of f o u r rea c t o r v e s s e l s i n s t e a d of one, a l l design f e a t u r e s of t h e MMSBR are similar t o those of t h e MSBR. The design conditions for one r e a c t o r module are summarized i n Table 8.2.

Table 8.2.

MMSBR D e s i p g Conditions for One Modde

Power generation, M~NT Thermal E l e ct r ic a l Thermal e f f i c i e n c y , 5

556 250 45

Plant factor Dimensions, f t Core

0.80

IIeight I)im e t er B l u e t thickness Radial Axial R e f l e c t o r thickness Reactor volumes, f t 3 Core Blavllre t salt volumes,

Fix1

7.87 6.3 2 2

0.5

26 5

1000

ft3

Core BILmket Plena Piping Heat exchanger and pump Processing Totd Fertile Core

Elanket

Heat exchcmger and piping Processing Total S a l t compositions, mole

Fuel 7

BeF2 U F ~( f i s s i l e ) Perbile

7LiF

BeF2

TI-LF,

Average power d e n s i t y i n core f u e l s a l t , k > r / l i t e r

41-5 7 22 25

7.5

185 12

1000 25 24

1061 63.6 36.2 0.2% 71 2 27 l+73

21.6 The nuclear a a d f u e l - c y c l e performance of a four-module plant gene r a t i n s 1000 Mw ( e l e c t r i c a l ) was stildied bo-i;h foi: pro‘mctinium removal from t’ne S l a n k e t stream and f o r t h e case of no d i r e c t prota,ctinLum renzoval. The saxe methods and bases as those f o r t‘ne MSRR s t u d i e s were employed. Ana’l.ogous t o previous teiTLinology, t h e s e cases a r e termed WfHi(P3) and MMSBR. Tile resu3-ts obtained a r e smmfiarizec? i n Table 8.3.. CompaPison w i t h -t‘ne r e s u l t s obtained f o r the MSBR(Pa) and thc MSBK i n d i c a t e s t h a t t h e n u c l e a r and f u e l - c y c l e r,erfor.mance of a modular-type p l a n t compares favoralbl-y with t h a t o f a sj.ngle-reac-i;or-type plan-6; t h e modular p l a n t tends t o have slri.ghtly hlghey breeding rati.o, fissile i n ventory, and f u e l - c y c l e c o s t .

Table 8.3. Nominal Nucl-ear and. FueJ_-Cycle Perforiumce of 1000-Mw ( e l e c t r i c a l ) ModvJ.ar Plan-Ls Investor-owned plant:

0.8 l o a d f a c t o r

_.-

_ I

MM,SBR(Pa)

~ u z l .y i e l d , $/year

Breeding r a t i o Spccri-fic f i s s i l e inventory, kS/Mw ( elec’crical) S p e c i f i c f e r t i l e in-veritory, kg/Mw ( e l e c t r i c a l ) P’iiel-cycle c o s t , mi.lls/kwhr ( e l e c t r i c a l ) a Doubling time y e a r s b P o ~ t ~ edoubling r time, y e a r s

7 3

1.073 0.76

125

0.3% 13.7

9.5

M%R( pa)

WBR *I.-

5.0 1.053 0.80 31.0

0.4% 20 13.9

7.95

1.071

0.68 105 0.35 12.6

8.7

Inverse of f r a c t i o n a l f u e l y i e l d p e r y e a r . ’Based. on continuoils inves.trnent of b r e d fuel i n r e a c t o r power p l a n t s . C a p i t a l cos% e s t i m a t e s were a l s o made Bar t h e modular p l a n t . The prri.mary d i f f e r e n c e between t h e W B R - aitd PERR-type pl.<ants i s t h e use of f o u r r e a c t o r v e s s e l s m d cells i n t h e modular p l a n t rakher t h a n t h e one j-n t h e MSBR. However, t h e r e a c i n r v e s s e l s i n t h e mod-iilar p l a n t a r e smaller, s o t h a t t h e i r combined i n s t a l l e d COS’Li s only about $1 mil.l_ion more than tna-L of t h e s i n g l e I.arge v e s s e l . A t Yne same t r i m e , t’ie moduI.ar p l a n t perinits b e t - t e r placement of c e l l s and a reductlion i n b u i l d i n g volume. The r e s u l t a n t c a p i t a l c o s t e s t i m a t e for t h e modular p l a n t w a s about $li4/kw ( e l e c t r i c a l ) f o r a p r i v a t e l y owned p l a n t , which i s about t h e same as that; estimated f o r the s i n g l e - r e a c t o r p l a n t . Using t h i s c o s t estimate, along with t h e IGBR estima’ce f o r operation arid maintenance c o s t s , and t h e f u e l - c y c l e c o s t s from Ta’01.e 8.3, gives t h e power-senerat-ion cos-ts summarized i n Table 8.4* T’nese COS’GS a r e nzarcly t h e same as those for t h e NyBR-type p l a n t s and t h u s i n d i c a t e b h e d e s i r a b i l i t y of a modular-type p l a n t i f t h e p l a n t a v a i l a b i l i - t y f a c t o r i s improved by its use

2 17

Table 8.4.

Power-Production Costs f o r Modular-Type Molten-Salt Breeder Reactors

Investor-ovner p l a n t :

0.8 p l a n t f a c t o r Cost [ m i l l s / kwhr (electric&)] W B R ( Pa)

MMSBH

Fixed charges

1.95

Operation and maintenance c o s t s a Fuel-cycle c o s t s

0.34-

0.34

0.38

0.48

2.7

2.8

Total. power-produc t i o n c o s t s a costs.

C a p i t a l charges of processing p l a n t a r e included i n fuel-cycle

8.3

Steam Cycle with A l t e r n a t i v e Feedwater Temperature

I n t h e above molten-salt breeder r e a c t o r concepts, t h e feedwater temperature e n t e r i n g t h e once-through s u p e r c r i t i c a l b o i l e r s w a s 700"F, and t h e temperature of t h e "cold." s t e m t o t h e r e h e a t e r w a s 650°F. These temperatures were s p e c i f i e d i n order t o avoid any f r e e z i n g o f t h e i - n t e m e d i a t e - c o o l a n t s a l t L , and involved d i v e r s i o n of prime steam. It would be a s i g n i f i c a n t advantage i f it were n o t necessaiy -to d i v e r t almost 3@/0 of t h e t h r o t t l e s-Leam f o r . h e a t i n g of t h e feedwater and r e h e a t steam, s i n c e t h i s d i v e r s i o n l e a d s to 8 loss of a v a i l a b l e e n e r w . A n even more s i g n i f i c a n t saving could be achieved i f t'ne 9.2 Mw ( e l e c t r i c a l ) of power r e q u i r e d t o d r i v e t h e feedwater pressure-booster pumps could be eliminated; a l s o , removal of t h e reheat-steam pi-eheaters and t h e b o o s t e r purnps would reduce c a p i t a l investment requirements. Thus, savings can be achieved by I.owering t h e temperature of t h e steam-cycle f l u i d e n t e r i n g t h e b o i l e r s ,and r e h e a t e r s . To determine t h e i n c e n t i v e f o r d-eveloping a coolant s a l t having a low l i q u i d u s temperature, t h e MSSR stem-power cycle was s t u d i e d with conditions of 580°F feedwater temp e r a t u r e and 550°F r e h e a t steam. I n o r d e r t o d i f f e r e n t i a i ; e and compare cases, use of 700°F feedwater and 650°F r e h e a t s t e m i s designated case A, while ca.se R r e p r e s e n t s t h e a l t e r n a t i v e conditions

The cycle arrangement f o r t h e case B conditions i s shown i n Fig. $.6. I n this c y c l e t h e 552°F steam f r o m t h e high-pressure t u r b i n e exhaust i s introduced i n t o t h e r e h e a t e r s without preheating. The feedwater i s heated from 550 t o 580°F by t h e a d d i t i o n of one more s t a g e of feedwater heating; steam e x t r a c t e d from t h e high-pressure t u r b i n e i s used. The condensate from this new h e a t e r i s cascad-ed back through t h e f e e d w a k r h e a t e r s t o t h e d e a e r a t i n g h e a t e r i n t h e usual. manner. The h e a t balances and t'ne a i a l - y s i s of t h e steam cycle with case B cond-itions were performed i n t h e same manner as f o r case A conditions. Table 8.5 compares t h e desi.gn data f o r "ciie two cases.

r-4

M c\1

r I

I I I

I I Is, 0

41 I

I I I

I I I L,

il d

I I i-----

---

2 13

Table 8.5.

WBR Steam System Design and Performance Data for Case A and Case B Conditions Case A

MSBR Steam Cycle wi.th 700째F Feedwate r

General performam e

Case B MSBE? Alternative Steam Cycle with 580째F Feedwater.

Reactor h e a t input, Mw N e t e l e c t r i c a l output, M ~ J Gross e l e c t r i c a l generation,

2225 1000 1034.9

2225 1009.7 1035. L,

S t a t i o n a u x i l i a r y load, m (electrica) B o i l e r - f eedwater prc ssurebooster pump load, Mw (electrical) Boiler-feedwater pump steamt u r b i n e power output, Mw Flow t o t u r b i n e t h r o t t l e , lb/hr Flow from superheater, l b / h r Gross e f f i c i e n c y , $, Gross heat r a t e , Btu/kwhr Net efficiency, $ Net heat r a t e , Btu/l<whr

25.7

9.2

None

29.3

30.6

Boiler-superheaters Number of units Total duty, Mw (thermal) Total steam capacity, l b / h r Temperature of i n l e t feedwater, O F Enthalpy of i n l e t feedwater, Btu/lb Pressure of i n l e t feedwater, psia Temperature of e x i t steam, "F Pressure of e x i t stecm, poia, Enthalpy of e x i t stem-, Stu/lb Temperature of i n l e t coolant s a l t , OF Temperature of e x i t coolant salt, "F Average s p e c i f i c lieat of coolant salt, Btu lb-x OF" T o t a l c o o l a t - s a l t flow Ib/hr CfS

a m

7.152

x 10'

10.068 x 106 47.83

7136 M.9 7601

'7.L60

lo6

7.460 x 106 4r7.91

7124 45.4 7518

1931.5 10.068 x LO6 700

'769.2

583.6

-3800

1003

-3600

14%. 0

1125

112.5

850

0.41 58.468 x 106

129.93 58,316

0.L + l 55.608 x

123.57 55,463

loG

Table 8.5.

.....

( continued.)

Case A MSBH S-kearn Cycle wi.th 700째F Feedwater

S'ceam r e h e a t e r s

........______

__l_l.*?

I ^

-....

Case B -

MSRR Alternatj-ve Steam Cycle w i t h 580"F Feed?dater ..-.-

8 388.0

Muxiher of u n i t s ,To.Lal duty, P h r (thermal) T o t a l steam capacity, Lb/hr Tempera-Lure of i n l e t s t e m ,

8 293.5

Pressure of i n l e i ; steam, p s i Enthalpy of i n l e t steam, B-Lu/ lb Temperature of e x i t steam,

-570 1323.5

400 1256.7

1000

Pressure of e x i t s t e m , pia Enthalpy of e x i t steam,

-51:-0

-54-0

1518.5

1125

850

0.41

Btu/lb Temperature of i n l e t coolant s a l t , "E' Temperature of e x i t coolant

salt, "F Average specifi-c heat o f coolant s a l t , Btu lb-1 OF-" 'Total c o o l a n t - s a l t f l o w I.b/hr cf s

%Pm

Cool.ant- s a l t pressure drop, i n l e t -to o u t l e t , p s i Reheat- steam preheater Numberr of u n i t s T o t a l duty, MI< ( t h e r m a l ) To-La1 heated steam capacity, lb/br

I n l e t temperature of heated steam, "F E x i t temperature of heated steam, "F I n l e t pressure of heated steam, p s i a Exi-i; pressinre of heated steam, p s i a I n l e t enthalpy of heated stewn, Btu/lb Ex%-i;enthalpy o f heated s t e m , Btu/l.b T o t a l h e a t i n g steam, I h / h r I n l e t temperature of h e a t i n g s%ea.in, OF

5.13Lt 650

8.884 x 19.742 88634 0

100.45 5.134 x

lo6

None

lo6

650 -580 -570 1256.7 1323.5 X

lo6

1.1.744 x 26.098 11.714

4 0

551.7

2.915 1000

5.056 x 551.7

lo6

221.

Table 8.5.

( continued)

Case A MSBR Steam Cycle with 700째F Feedwater E x i t temperature of h e a t i n g steam, "F I n l e t p r e s s u r e of h e a t i n g steam, psia E x i t p r e s s u r e of h e a t i n g steam, p s i a Boiler-feedwater p u p s Number of units C e n t r i f u g a l pwnps Number of stages Feedwater flow rate, lb/br t o t a l Required c a p a c i t y , g p m Head, f t Speed, i-=pm Water i n l e t temperature, "F Water i n l e t enthalpy, Btu/lb Water i n l e t s p e c i f i c volunie,

ft3/1b

Steam-turbine d r i v e Power r e q u i r e d a t r a t e d flow, Nw ( e a c h ) Power, nominal hp ( e a c h ) T h r o t t l e steam conditions, psia/'F T h r o t t l e flow, lb/hr ( e a c h ) Exhaust p r e s s u r e , p s i a Number of s t a g e s Number o f e x t r a c t i o n p o i n t s

866

3515

6 7152 x 106

6 741.60 x

8060 -9380 5000 357.5 329.5 4.0l808

lo6

$408

-9380 5000 357.5

329.5 -0,01808

14.66

15.30

20,000 1070/'700

20,000 10'70/?00

413,610 -r?7 8

431,400 4'7

None

Boiler-f eedwater p r e s sure-

b o o s t e r pump Number of u n i t s C e n t r i f u g a l pump Feedwater flow r a t e , lb/hr t o t a l Required c a p a c i t y , gpm ( e a c h ) Head, f t Water i n l e t temperature, "F Water i n l e t p r e s s u r e , p s i a Water i n l e t s p e c i f i c volume, f t 3 /ib Water o u t l e t temperzture, "E' EL?c t r i c -motor d r i v e Power r e q u i r e d a t r a t e flow, MW ( e a c h )

Case 13 MSBER A l t e r n a t i v e S t e m Cycle with 580째F Feedwater

10.067 x 9500 -1413 695 -3 500

-0.03020

400 4.587 6150

lo6

222 T'ne e l i m i n a t i o n of t'ne feedwater p r e s s u r e - b o o s t e r pumps r e q u i r e d i n c a s e A s a v e s &oil$ 9 . 2 Mw ( e l e c t r i c a l ) of auxri.liary power, which, t o g e t h e r w i t h t h e improverneil'i i n the c y c l e thermal. e f f i c i e n c y dine t o -the a d d i t i o n a l s t a g e of feedwater r e g e n e r a t i o n , makes ab0u.t 9.7 blw ( e l e c t r i c a l - ) a d d j - t i o n a l power avari.l.ab1-e from t h e c a s e B c y c l e . The ovei.al.1 n e t t h e i m a l e f f i c i e n c y i s t h u s improved from t h e U . 9 $ o b t a i n e d f r o m case A t o 1+5.4$ i n c a s e B. To complete t h e d i s c u s s i o n of c a s e A v s c a s e B c o n d i t i o n s , t h e cos.t; e s t i m a - t e s f o r t h e a f f e c t e d i t e m s of equipment were cornpa-red; -the r e s u l t s a r e s i m a r i z e d i n Tab1.e 8.6. A s shown, t h e c a s e B arrangemeat reqi.J.j.??es about $465,000 l e s s c a p i t a l e x p e n d i t u r e , p r i m a r i l y due t o removal. o f the p r e s s u r e - b o o s t e r pimps. [ I n t h i s c o s t s t u d y i.t was assumed tihat, t h e 580째F l i q u i - d u s - t e m p e r a t u r e cool.aat s a l t has t h e same c o s t ( a b o u t $1-.00/lb) 2,s t h e MSBR coolant s a l t . ] The lower c o n s t r u c t i o n c o s t reduces power c o s t s by about 0.008 m.Tl.1./kTJjhr ( e l e c t r i c a l ) wkile t h e i n c r e a s e d e f f i c i e n c y lowers power c o s t by about 0.026,mi11/kwhr ( e l e c t r i c a l ) (pl-j-vate financi n g ) , t o g i v e a t o t a l saviiig of about 0.034 mill/kwhr ( e l e c . t r i c a l . ) [0.021.

Table 8.6.

Cost Cornparison of 700"E'and 580째F Feedwater Cycl.es for MSU!I Nilmbe r

Fe e dwat e I- p re s3 u ~ b e DO st e r Pumps Reheat-steam p r e h e a t e r s S p e c i a l mixing t e e b Feedwater h e a t e r No. 0 Charge f o r ex'ira e x t r a c t i o n n o z z l e on t u r b i n e f o r hea'ier No. 0 Boiler- superheaters Reheaters

U i i i ts

2 8

Case

- 700째F

Feedwate r

None

180,000 5,000

None None 150,000

6;300,000; 2,720,000

,%,305,000 Cost dif'fe r e n t i a l DJ.rect constm.ct5.on c os-6 I Total construction cost

Case R - 580'1' Peedwate r

400,000

Hone None

45,000

d 5 ,900,000 2,880,000

-000-

$330,000 $165 ,000

a Table shows o n l y t h o s e cos-ts d.ifferenl; i n t h e two c y c l e ari-angements and i s no-t a complete l i s t i n g of t h e 'curbi~neplm-i; c o s t s . "The h i g h - p r e s s u r e feedwater h e a t e r added i n c a s e B w a s designated.

"No. 0" ri.n order not t o d i s t u r b the heater numbers used i n c a s e A. C

E s t i m a t e d on b a s i s of $130/ft2.

'Estimated 0

on b a s i s of $lLkO/f.L2.

LEstimated- on b a s i s of $ 1 2 5 / f t 2 . fJ-ndirec'c c o s t s were assu1:ied t o be 41% of t h e d i r e c t , c o s t s .

223 mill/ksqhr ( e l e c t r i c a l ) f o r p u b l i c f i n a n c i n g ] . This saving i n a 1000blw ( e l e c t r i caL) p l m t (0.8 l o a d f a c t o r ) corresponds t o about $238,000 pel- y e a r . The p r e s e n t worth (6% discount f a c t o r ) of t h i s saving over a 25-year p e r i o d i s about $1.5 m i l l i o n . For s e v e r d MSBR power p l a n t s , t h e sa-fing would be p r o p o r t i o n a l l y g r e a t e r . Thus, t h e r e i s an econornie i n c e n t i v e â&#x201A;Źor developing a coolant s a l t with a l o w l i q u i d u s temper!iture, s o long as i t s 'Lnventory c o s t does n o t outweigh Lhe p o t e n t i a l saving. If the inventory c o s t of t h e coolant salt f o r case B were about $2.4 m i l l i o n more than Ynat f o r case A, t h e po-terrtial saving would be canceled by t h e increased c o o l a n t - s a l t inventory c o s t ( f o r a p r i v a t e l y owned p1:wt).

8.4

Add.i.tiona1 Design Concepts

Other m o l t e n - s a l t r e a c t o r desi-gps we2.e s t u d i e d b r i e f l y . I n general t h e techno lo^ r e q u i r e d f o r t h e s e a l t e r n a t i v e designs i s r e l a t i v e l y mdeveloped, although t h e r e a r e experfmental data t h a t suppcrt t h e f e a s i b i l i t y of each concept. An exception i s t h e molten-salt converter r e a c t o r (designated E C R ) whose a p p l i c a t i o n e s s e n t i a l l y r e q u i r e s only scaleup of &ISRE and a s s o c i a t e d f u e l - p r o c e s s i n g technology. However, t h e PECR i s n o t a breed-er, although it approaches bre<&-even breed-er operation. The add i t i o n a l concepts a r e termed M,YER(Pa-Pb), SSCE( Pa), MOSEIL( Pa-Pb), and MSCR. The MSBR(Pa-Pb) designation r e f e r s t o t h e MSBR(Pa) modified by USE of d i r e c t - c o n t a c t cooling of t h e molten-salt f u e l wi-t'n molten. l e a d . Lead i s Girtniscible wikh mol-ten salt; and car1 be used as a h e a t exchange medium within t h e r e a c t o r vessel t o s i g n i f i c a n t l y lower the f i s s i l e inventory e x t e r n a l t o t h e r e a c t o r . The l e a d a l s o s e r v e s as a h e a t t r a n s p o r t medium be'cveen t h e r e a c t o r and t h e steam generators.

The SSm(Pa) d e s i g n a t i o n r e f e r s t o a Single-Strewn-Core Breeder with d i r e c t protactinium removal. f r o m t h e f u e l s t r e a m T h i s is e s s e n t i a l l y a s i n g l e - r e g i o n r e a c t o r having f i s s i l e and f e r t i l e rnateriAl. i n t h e f u e l stream, with protactinium removal from t h i s stream; i n a d d i t i o n , t h e core region i s enclosed w i t h i n a t h i n metal membrane and i s siirrowded by a blanket of thorium-containing s c a t . Nearly aKL the breeding t a k e s place i n t h e l a r g e core, and t h e b l a n k e t "catches" only t h e r e l a t i v e l y small f r a c t i o n of neutrons tha-t "leak" from t'ne core (t'nis concept i s PJSO ref'erred t o as t h e one-and-one-hal-f region r e a c t o r ) . The MOsEL( Pa.-Pb) d e s i g n a t i o n refers t o a Molten-Salt Epi.tl.ierTn& b r e e d k r having an i n t e r n e d - i a t e - t o - f a s t e n e r a - G e c t r u l , wixh directp r o t a c t h i m removal f r o x t h e f u e l stream a n d d i r e c t - c o n t a c t cooling of t h e f u e l region by molten l e a d . N o g r a p h i t e i s p r e s e n t i n t h e core of

this r e a c t o r .

The MSCEI refers t o a Molten-Salt Conver-be? Reactor t h a t has t h e .ferl;ile a n d f i - s s i l e m z t e r i a l i r i a s i n g l e stream. N o bl-atiket region i s employed, although a. g r a p h i t e r e f l e c t o r surrounds t'ne J.argt? core.

'The f u e l cycle pe rforrmnc 13 c2ian-ct e ri s ti c s for t h e s e r e a c t o r s are :mrmarizc?d i n Table 8.7; i n all cases t h e methods, a n a l y s i s procedures,

Table 8.7.

Svmmary of Design Contiitions and F J e i - C y c l e Performaace f o r R e a c t o r Designs Studied R e a c t o r ~ ei gsa t c o n a

Design C o n n i t i o n s

E B R ( Pa)

PEBR

NMSBR( Pa)

MSBR( Pa-Pb)

SSCB(Pa)

NOSEL( Pa-Pb)

VGCR

Dimensions, f t

Corn

Height Diamt e r Blake.:- t h i c k n e s s RaCial Axial

Volxne f r a c t i o n s , c o r e

Fuel

Fertile

Moderator

S a l t volmes, ft3 Fuel

Core

Ex;? r n a l

Total Fe i"ti l e , t o t a1

12.5 10.0

12.5 io. 0

1.5 2.3

i.5 2.0

3.169 0.073 0.758

0.169

166

551

b 7.9b 6.3

12.5 10.0

15.3

3.3: 6 5

2.0 2.0

1.5 2.0

1.2 0.0

3.0

3.074

0.757

0.17 3.35 0.78

0.169 0.0'76 3.755

0.193 0.0 3.837

0.5 0.0

0.105 0.0 0.'395

166 547

166 574

166

230 6OC

276 1324

830

476 6 54

740 1570

63.5 0.7 64.2 '758

63.6 36.2

71.0

73.3

0.23

8.68 0.23

71.0 0.3 5.3

0.45

41.5 5520

37.7 6280

717 1317

713 3383 63.6 36.2

U F ~(fissile)

63.6 36.2 0.0 0.22

0.23

63.6 36.2 3.0 0. 21

Core a'zorn r a t i o s ni/V

41.7

39.7 5440

28.4 5980

F c e l - s a l t cornpositlion, mole

LiF

BeF2 T1;Fq

c/u

5800

0.0

:L1@

0.0

9.8

985

20.1

0.0

24.0 4.76 0.0

20.8

16.6

1130 0,0

15.3

15.55

36.7 6525

T d 1 e 8.7. (continued)

Destgn ConBi"son;: P o m r dcnsit.j, k,v-/liter Gross

pje;

&EBZ( Pa)

iw3R

~ ~ M S Epa) S(

ze signat i o n a

MER( pa-%)

NOSEL(m-n)

SSCE(Pa)

core average,

s&7-t

3e:Jtroi-i flux, core werage, neutrons c w 2 seL-b ~Blern&l FiLS t

Fast, cvcr 100 kev f & n t ~ c nprcduction per f i s s i l e a'mx-pticn ( ? e ) :juclea.r ai& fuel-cycle perfoimmce y u e l y i e l d , %/yszr Ereedlrig r a t i o

_~ual-cycle cost, rrLlls/kvhr Specific T i s . ile invmtory, kgjMi,i ( e l e c t r i c & ) 1

Re a c t o r

80 L73

80 473

4:s

80 L.73

66 341

7.3 x 2 - c ~ ~ 6.8 x 1014 11.7 x 1 0 ~ 4 12.1 x i W

10.0 x 1014

2.227

2.229

2.226

17.3

6.63 l.06d

3.1

7.95 1.07 0.35 0.68

loi4

3.1

2* 221

4.86 10.5 0.16

0.7'7

loi4

3.0

7.31

1.07

0.3s 0.76

lCi4

3.1

1.08

11.25 0.34

LOi4

618

0.3 10iA 72.2 x 1014 23.3 x 1014 2* 280

1.9 x 1014 2.7 1014 0.7 x 1014

1236

7.2 x 1014 6.7 x 12.1 x 1 0 ~ 12.1 ~ x 1014

6.1

1014

2.6

1014

10.3 1.14 0.13

0 . 37d

0.68

0.99

MSCR

165

2.20;

0.96

3.57 1.63

"See telri; f o r e x p l m a t i o r of r e s c t o r designations.

'%e

core diqensioris f o r this case refer t o o x module of a four-module s t a t i o n .

b o r t h i s case, t h e core had c n l d a r geometry; t h e f u e l mnulus i n s i d e d i a n e t e r was 3 f t , and t h e outside diameter was 6.5 ft.

%se of direct-contact lesd cooling would lower the f u d - c y c l e c o s t t o about 0.32 mill/kwhr ( e l e c t r i c a l ) and t h e specific f i s s i l e imeritoqf to a b u t 0.41 kg/!&r ( e l e c t r i c a l )

2 26 and. economic conditrions employed were ana!-ogoiis -to t h o s e used i n o b t a i n i n g Lhe r e f e r e n c e MSBR d e s i g n d a t a . I n g e n e r a l , f u e l r e c y c l i n g was based. on f l u o r i d e - v o l a t i l i t y and vaciiwn-dist,j.llatioii processi-ng; d i r e c t p r o t a c t i n i u m removal from Lhe r e a c t o r system was a l s o c o n s i d e r e d i n s p e c i f i e d cases.

The r e s u l t s i n d i c a t e t h e p o t e n t i a l perfomnarice of f l . u o r i d e - s d t systems u t i l i z i n g a direct-coiltac-L c o o l a n t such as molten l e a d and t h e v e r s a t i l i t y of molten s a l t s as r e a c t o r f u e l s . They a l s o i l l u s t r a t e t h a t s i n g l e - r e g i o n r e a c t o r s based on MSIW â&#x20AC;&#x2DC;cecâ&#x20AC;&#x2122;mology have good performance characteristics. S i n c e Yne capital., operati-ng, and mainLenance c o s t s of t h e MSCR should be comparable w i t h t h o s e of t h e FSER, t h e power-product i o n c o s t of an inves-tor-owned MSCK p l a n t should be about 2.9 mills/ kwhr ( e l e c t r i c a l ) , based on a l o a d f a c t o r of 0.8. However, -Eie lower power c o s t s of t h e MSBR(Pa) and MSUR p l a n t s and t h e i r superri.or n u c l e a r and f u e l - c o n s e r v a t l o n c h a r a c t e r i s - L i e s make deveI-opment of t h e b r e e d e r reactors preferable. :ieferences 1. K5R Prog-cam Semimn. Progr. Rept. -. Feb. ..-28, 1966, 0;9NJ;-3936, p. 172.

P. :i. Kasten, E . S. B e t t i s , and R. C. Robertson, Design. S t u d i e s of e ) Molten-Salt Breeder .R e a c t o r s , ORNI,-399nA<gust 1966).

.-_I-_ lOOO-Mw(

P. X. Kasten, Sa.fety Program f o r N o l t e n - S a l t Breeder R e a c t o r s , unp u b l i s h e d i n t e r n a l r e p o r t (July 29, 1 9 6 6 ) .

9. MOLTEN-SALT REACTOR PROCESSING STUDIES M. E. Whatley

A close-coupled f a c i l i t y f o r processing t h e f u e l and f e r t i l e streams of a moltten-salt breeder r e a c t o r (MSBR) will be an i n t e g r a l p a r t of t h e r e a c t o r system. Studies are i n progress f o r obtaining d a t a r e l e v a n t t o t h e engineering design of such a processing f a c i l i t y . Tile processing p l a n t w i l l operate on a s i d e stream withdrawn from t h e f u e l stream, which c i r c u l a t e s through t h e r e a c t o r core and t h e primary heat exchanger. For a 1.OOO-Mw ( e l e c t r i c a l ) MSBK approximately 14 f t 3 of salt w i l l be processed p e r day, which w i l l r e s u l t i n a fuel-salt cycle t i n e of approxirnately 40 &ys.l

The probable method f o r fuel-stream and f e r t i l e - s t r e a m processing is shown i n Fig. 9.1. The s a l t w i l l f i r s t be contacted w i t h 3'2 f o r removal of U as v o l a t i l e uF6. P u r i f i e d m(, will be obtained frorn line fluo r i n a t o r off-gas ( c o n s i s t i n g of m6, excess F2, and v o l a t i l e f i s s i o n product f l u o r i d e s ) by use of NE$ s o r p t i o n . It niay be necessary t o d i s c a r d as much as 5$ of t h e s a l t l e a v i n g t h e f l u o r i m t o r f o r renoval of fission products such as Z r , Rb, and C s . A seraicontinuoils vacuum dist i l l a t i o n w i l l t h e n be c a r r i e d out on t h e remaining s a l t f o r t h e removal ORNL- DWG 65 - tR01R2A

...............~.

SPENT NcF t MgF2

SPENT.. NaF t MgrZ

>WASr E FEHl It E SALT O i 6 ft3/ay

W A S T F = 0 0 5 3 ft3/doy 'I 1 = 0i H kg/day FP'S

Fig. 9.1. KSBR Fuel and F e r t i l e S t r e w Trocessing. 227 F

228 o f t h e r a r e e a r t h s , Ray Sr, and Y. These F i s s i o n products w.i.1J.. be r e moved from the s t i l l i n a salt volume equivalrn% Lo O.S$ o f t h e stream, The barren s a l t , the p u r i f i e d UFh, axid- the makeup salt w i l l t h e n be re-combined. This s t e p invol-ves reduc-bion of UFg to UF4, m h i n g aB t h e s e stl-ems, and. sparging t h e resultant, m a t e r i a l w i t h an H2-m stream. F i n a l l y , Lhe salt mixture m y be f i l k r e d before retixm t o t h e r e a c t o r .

9 .l Semicontimxous Disti1l.at:i.o.n J. R. Hightower

L. E . McNeese

New measuremen-Ls of -the r e l a t i v e v o l a t i l i t i e s o f N d F 3 and Lali'3 i n LiF have been made iisimg a, r e c i r c u l a t i n g equilibrium s - t i l l These values are lower t h a n earlier &La by a factor of about 50 and a r e i n a range (around 0.0007) where t h e proposed d i s ~ b i l l a t i o ns t e p in. t h e NYBR proce s s i n g p l a n t should work very w e l l

...

The present concept of t h e d i s i x i l l a t i o n s t e p i n t h e MSBR processing p l a n t uses a con%i.a.uous feed stream and vapor removal for separa5ing ra,re-ear-t;h f i s s i o n products (FP s1 from the f u e l s a l t ; tine less volatiibe r a r e - e a r t h F P ' s w i l l . accumulate i n t h e still pot and w i l l be discharged periodically A measure o f t h e decontamination achieved in t h i s s t e p is t h e r e l a b i v e vola-tK!-ity of t h e less v o l a t i l e F P s s compared. t o the c a r r i e r salt. The rela-Live volat.i.l.ity of component A compared -Lo component B i s defined as

where

aA-B

.-- r e l a t i v - e

= E

v o l a L i l i t y of A compared t o B,

va,por-phase mole f r a c t i o n ,

X z liquid-phase mole f r a c k i o n . F o r s y s t e m i n which t h e concentration of cornpouent A is sml..l..and X 13 i s n e a r l y unity, t h e r e l a t i v e volatli.l..i.ty can be approximated by cr, A -B

Y*/XA

( 21

To achi-eve good decontamination from t h e less volztile f issri.om products t h e i r r e l a t i v e volatil_it:i.es m u s t be s m a l l

Since t h e major constLtuent o f t h e s t i l l pot w i l . 1 'oe LiF, experimental measixements have been made w i t h mixtures 04 rare-earth.f l u o r i d e s i n LW, A cold-finger technique gave approximate values f o r %he r e l a t i v e v o l a t i l i t i e s of six rare-eal-th f l u o r i d e s w i t h r e s p e c t t o LiF (975 t o 1075째C) r m g i n g from 0.01 t o 0.05.2 These were high enough t o s e r i o u s l y l i m i t t h e e f f e c t i v e n e s s of t h e proposed simple d i s t i l l a t i o n scheme. More accurate measurements of tine r e l a t i v e v o l a t i l i t i e s were c a l l e d for.

229 OANL-DWG 66-3933

2-in. NICKEL PIPE---,

.-,

BO1 LI NG LI QU I D

1 .

TH ERMOW ELL,-

r'NICKEL TUB1 N G

Fig. 9.2.

Diagram of Recirerulating Equilibrium S t i l l .

A diagram of t h e r e c i r c u l a t i n g equilibri-wn s t i l l used i n r e c e n t

work i s shown i n F i g . 9.2.

The b o i l i n g s e c t i o n i s a 12-in. l e n g t h of 2-in.-diczm n i c k e l pipe. The condensing s e c t i o n is nude Prom 1 - i n . n i c k e l pipe wrapped with cooling c o i l s of 1/4-in. n i c k e l tubing. I n the bottom of t h e condenser i s a condensate t r a p where l i q u i d c o l l e c t s and overflows a weir t o return t o t h e s t i l l p o t . The vacuim pump i s conriected near t h e bottom of t h e condenser s e c t i o n . A f t e r chargiiy: s a l t of known composition, t h e s t i l l i s wclded shut and purged w i t h argon. The d e s i r e d p r e s s u r e i s set, and t h e still i s heated t o the d e s i r e d temperature while cooling t h e condenser. A f t e r o p e r a t i n g t h e s t i l l f o r a p e r i o d of time a t t h e s e l e c t e d conditions, the s t i l l i s p r e s s u r i z e d w i t h argon, cooled t o room temperature, and c u t a p a r t for examination and sampling. The concentrations of t h e r a r e - e a r t h f l u o r i d e s i n t h e condensate t r a p and i n t h e s t i l l p o t a r e used t o calcul a t e r e l a t i v e v o l a t i L i t i e s according t o Eq. (2).

230 T i ?

these experirflen-bs the d-etemri.natAon of abso1u.k values f o r

rele-,

t i v e volatilities has been hampered because t h e vapor samples have r z r e e a r t h concentrations below t h e ainalflical. l i r 7 l i t of d-etec-tion-. ljowever, upper and. 1.0wer limi-ts of t h e rel.ative v o l a t i l i t i e s f o r 0.01 $0 0.02 mole f r a c t i o n ceF3J N d F 3 , and M'3 i n Li%' a t lO0O"C and 0.5 rmn Hg were d.etermi.ned and a r e given below:

0.0013 <

CXceF,

aLaF3-LW

< 0.0029 -T:,I."F' .. N

0.00069.

These values a r e s u b s t a n k i a l l y Lower than those previous1.y r e p o r t e d , The samples have been submitted for a n a l y s i s by a more s e n s i t i v e anal.3rt,ical. method (neutron a c t i v a t i o n ) Higher concentrations of rare-earth f l u o r i d e will be used i n t h e still pot 7.n future work in order t'nat r a r e ear-th f l u o r i d e concentrations i n t h e vapor phase w i l l be higher than t h e I-lmit of d e t e c t i o n .

'rine importance of r e l a k i v c vol-ati 1 - I . t ~i n determining t h e 0peratin.g characterl.stAcs of t h e d i s t i l l a t i o n system i s shown by -i;he fiill.rJwI.ng ca.1cillation. Consider t h e re'ooiler oâ&#x201A;Ź a s i n g l e - s t a g e d i s t i l l a t i o n system which contains V moles of L i F at any t h e and a q i i m t i t y of BeF2 such t h a t vapor i n equilibrium w i t h t h e l i q u i d has t h e composi"con of NSBR finel s a l t . Assume t h a t MSBR f u e l salt, containing Xo moles of r a r e - e a r t h f l u o r i d e s (REF) per mole of L i F i s fed to t h e sti.l.1.. p o t 8% a rate of F moles of LiF p e r wit time where it mixes w i t h t h e l i q u i d i n t h e system. k t t h e i n i t i a l - REF c o n c m t r a l i o n in the liquid- be Xo moles of REF p e r mole of L1E, axid Let the concentration a t any time L' be X moles of REP per mole o f L i F . From a material hal-ance on REJ?,

where

= s t i l l l i q u i d hol-dup, moles o f L i F ,

X = R.EF concentration i n s t i l l l i q u i d , moles of HXli' per mole of

F XO

= =

CX =

LiF , 1,iF f e e d r a t e t o s t i l l , moles per m i i t time, REF concentration i n feed, moles of REF per mole of LiF, r e l a t i v e v o l a t i l i t y of EEF referred- t o ILF.

This equation -has t h e s o l u t i o n

The t o t a l quanti-ty of REF f e d t o t h e system at time t i s ( F t

-t

V)Xo,

and

231 t h e quantity of REF r e r r m i n i r g in the Liquid at tha% time i s VX. not vaporized a t time t is the fraction of the

Thus

Values f o r the f r a c t i o n of KEF r e t a i c e d in %he still 8,s a function of dimcnsioriLess througilput (Ft/V) are given i n ~ i g 9.3 . for various values of C X . Approximately 9174 of t h e REF w i l l be retairied i n the s t i l l when 99.5$ of t h e LiT' has been recovered if the r e l a t i v e v o l a t i l i t y of the F;EF i s 0.001; a retentioil of g r e a t e r than %$I can be obtained f o r t h e same L i F recovery i f CX has a value of 9.0005.

ORNL-DWG 66-1 i472

Ft/V,

100

DIMENSIONLESS

150

200

250

STILL. 7HROLJGHPI.J~r

232

9.2

C 0 i i t i i u . u x . S F l u o r i n a t i o n of a Mol%een S a l t

L. E. McNeese Uraniinm present i.n t h e f u e l stream of an MSBR m1Js-b be removed p r i o r t o t h e d i s t i l l a t i o n s t e p s i n c e TJF), present i n t h e st211 would not 'ore completely volati.li.zed and would i n p a r t be discharged t o waste when -the stj-ll. contenri;s are dumped p e r i o d i c a l l y Equipment i s b e i r g developed f o r t h e continuous removal OS UF'4 from t h e fuel stream of an _PEER by con-Lacting t h e s a l t w i t h F2 i n a salt-phase-continuous system. This equipment w i l l be p r o t e c t e d from c o r r o s i o n by f r e e z i n g a l a y e r of salt on t h e v e s s e l w a l l ; t h e heat, necessai-y for maintaining mol%en s a l t adjacent t o frozen sa.lt will be provld-ed by t h e decay of f i s s i o n products i n t h e fuel stream. Present dzvelopment work c o n s i s t s of two p a r t s : (1.) s t u d i e s i n a continuous fl.lxorinator not p r o t e c t e d by a frozen wal..L, and ( 2 ) study o f a frozen-wall system s u t t a b l e f o r continuous f l u o r i n a t i o n but w i t h which an i n e r t gas is used. Experimental w o r k on t h e nonprotected system i s w e l l under way; t h e p r o t e c t e d system i s being designed.

The nonprotected system c o n s i s t s of a 1-in.-dia;m nickel f l u o r i n a t o r 72 i n , long and a u x i l i a r y equipment (Fig. 9.4) which allows the co-cmterc u r r e n t contact of a molten sal% wit11 F2. Ex,eriments can be carried. out; w i t d l i o l t e i i - s a l t flow rates oT 3 t o 50 crn /min with fl-uorinator s a l t depths of 1 2 t o 54 i n . The system i s constructed o f n i c k e l w i t h the exc e p t i o n of molten-salt transfer l i n e s , which a r e Hastelloy N . The fluorinaLor off-gas passes through a 400째C NaE' 'bed f o r removal. of chromium

3 . .

oRriL DWG 6 5 - 9 3 5 4 ~

CHROMATOGRAPH FOR U G , F2 AND N2 4NALYSES

METERED Np FOR SALT DISPLACEM EPIT

SAiLT RECEIVER

SAL

NICKEL FLUORINATOR 1 in. DlAM 72 in. LONG

Fig. 9.4. Equipment f o r Removal of U r a n i u m from Molten S a l t by Continuous Fluor rinat i on

233

f l u o r i d e s , a ~ O O O CM ~ ; Ft r a p f o r removal of m6, and a, soda-lime bed f o r F2 disposal. h l y s i s f o r F2, UF6, and I\J% i s rmde p r i o r t o t h e 100째C NaF bed w i t h a gas chromatograph.

Experiments have been c a r r i e d out a t 600 t o 650째C using ari Nu-LiFZrF4 m i x t u r e containing 0.2 t o 0.5 w t $ UF4 and having a m e l t i n g p o i n t of 4 5 O ' C . S a l t f e e d rates of 5 t o 21 c m 3 ~ and n F2 rates of 75 t o 250 cm3/min (STP) have been used w i t h molten-salt depths of LkO t o 52 i n . Uranium removal during one pass through t h e f l u o r i n a t o r has v a r i e d from 9.5% t o 99.6% as determined from s a l t samples. Eqw-pmerit operation has beel?_smooth altnough several. pl-u.s have developed i n s a l t transfer l i n e s and i n t h e f l u o r i n a t o r off-gas.

b w i n g t h e b e s t r'un t o dxte ( C F - I O ) , a m o l t ab n - s a l t feed r a t e 01 20.7 cm3/min and an F2 f e e d rate of 250 cm3/mixl (STP) were m i n t a i n e d for a 2.5-hr period. The concentration of U i n t h e f e e d s a l t was 0.33 wt, $, and the f l u o r i n a t o r was operated at 650째C w i t h a. s a l t depth of 48 i l l , The U concentration i n t h e s a l t discharged from t h e f l u o r i n a t o r during Yhe l a s t hour of operation w a s 0.0020 r r i t $I as detemiincd from four salt saniples taken a t 1 5 - m i n i n t e r v a l s . Rased on i.nlet axid e x i t U eonceritrations i n the s a l t , 99,4$ of t h e U w a s removed by t h e fluo r i r f i t o r . The equipment operated smoobhly during t h e run, s a l t and gas Peed rates were constant, and t h e systern appeared t o have reached s t e a d y s t a t e during t h e l a s t hour of operation. Continuous fl.uorinatiofi of t h e f u e l stream of m YLSBE. w i t h equipment of the t y p e s t u d i e d is considered f e a s i b l e . Study of contirmous f l u o r i n a t i o n w i l l be continued, and. t h e use of a. f r o z e n w ~ t L 1$GI" c o r r o s i o n prot e c t i o n w i l l - be demonstrated.

9.3

U t e r n a t i v e Chemical Proeessrins Methods for a n MSBR

(2. I. Cathers

Schilling

Liquid-metal e x t r a c t i o n was s t u d i e d i n a previous search fo-r a s a l t reprocessing method t o replace vacuum d i s t i l l a t i o n These t e s - t s v i t h Li2Ee%r, sa2t showed t h a t t h e larMianides were removed i n most cases by- a reductive c o p r e c i p i e a t i o n with Be t o y i e l d r e f r a c t o r y insoluble beryll i d e s deposited a t t h e shl.t-metal i n t e r f a c e The present prol-hm was -to develop a reductive p r e c i p i t a t i o n w i n g m i n i m u m qumntities of %i o r Be as reduc%ant and involving sinple p k j s i c a l s e p a r a t i o n of t h e p r e c i p i t a t e d m e t a l s by z"il.tration or s e t t l . i n g Ceconta-uination f a c t o r s were determined i m h g i n i t i a l ccjncerLl;ra'cions of' 30 t o 1000 ppm of Zs, Nd, I;z, SUI, Eu, Gd, and Sr e i t h e r s i n g l y o r i n various combirratbjon.~. a

F I L I W I . ~studies ~ On t h e liqUi.d-uL&al eXtX'YLCtiGr1 DEthOd Were X0Ad.e i n ' L i - B i a l l o y s t o L e s t removal. of t h e scme e k m n t s with the exception of

Zr and Nd.

~ i ~ q

T3ble 9.1.

Reductive P r e c i p i t a t i o n of T\Tev;tron Poisons from Li~Ber'r,

Initial coxentrations:

a p e riment Number

Beduct mt

F a c t o r of Excess Reducta n t

Temperature

Z r = '70 ppm; Kd = 400 ppm; o t r e r s 600-900 2pii;

DF =

103

5 6

121

104

7 8

1000

55G75

234"

162 1.28

105

55M0

4.1

4.2 (Nd) 243 ( Z r )

4.4

553-606 55M0

ppm s p i k e ir, o r 5 g i m l s a l t ppm s p i k e i n t r e a t e d s a l t Nd

2.1

E:: Cu (from f i l k e r ) + ~ _ q ' d euni~i .~- -e"d~ lines

1.3

1.1

1.43

I n i t i a l concentration = 490 pprn Zr. b I n i t i a l concentration = 11.7$ Z r . c Separation by settling.

&Be13 a d Be ( t r a c e )

U-Zr, ZrBe2, Be, and kiBe13

39ga 11

Be, a - Z r ( t r a c e ) , End M e 1 3 ( t r a c e )

Not exazined

8.0

9.0

550

Process r e q u i r e d 3F * s

c-i!

2.3

2.4

550-95 55C-80

55340 803

Species I d e n t i f i e d i n Netal P r e c i p i - t a t e s by X-Ray Analysis

1.7

1.05

Sot examined U-Zr; LiF + Li2BeAF4 i n s a l t cu (from f i l t e r ) Be, k B e l 3 , F&e5

(from c r u c i b l e ! C

235 Reduction P r e c i p i t a t i o n The reduction-coprecipitations t u d i e s were made on 15-g (7.5-cc) samples of LizBeF4 spiked w i t h c o l d neutron poisons as t h e fl.uorides; t h e samples were contained i n mild s t e e l under a p r o t e c t i v e atmosphere of argon. A ty-pical t e s t coiisisted o f : p r e p a r a t i o n and sarr1plir-g of t h e o r i g i m l s a l t while molten; reduction w i t h between l and 243 times t h e t l i e o r e t i c a l asnowzt of L i o r Be a t temperatures i n t i e range 500 t o 1.00~3"C for about 90 min with s t i r r i n g by an argon sparge; f i l t r a t i o n through a s l n t e r e d Cu f i l t e r s t i c k ; recovery of f r o z e n samples of treated s a l t from t h e f i l t e r and, when p o s s i b l e , p r e c i p i t a t e d metals from %he bodtom of the r e a c t o r . Salt samples were analyzed f o r lantnanides and zirconium by neut r o n a c t i v a t i o n a n a l y s i s , spark source mass spectrometry, or emission spectrometry. The metal p r e c i p i t a t e s were examined 'by x-ray d i f f r a c t i o n . Zlze decorxtamination f a c t o r s DF (I&) and DF (Gd) shown i n Table g e l . , when compared w i - t h t h e i n d i c a t e d process requirement at the bottom of each c o l m , show t h a t adequate removals could be achieved w i t h both L i and Be using excess reductant i n t h e range of 1. t o 4 times t h e t h e o r e t i c a l requirement f o r LnlBel3 deposition. The low values obtained in experiment 8 r e f l e c t t h e incomplete removal. of Zr, present i n t h i s one experiment as a major component (U,'7'$). In this case t h e final concentration of Z r (500 ppm) was comparable t o the inLtiaL concenta%,tLons of La and Gd, mid t h e r e f o r e s u f f i c i e n t t o i n h i b i t t h e i r reduction. The species ident i f i e d i n the m e t a l p r e c i p i t a t e s recovered (see Table 9.12 experiments 1, 3, and 10) i n d i c a t e t h a t reduction of LanthaxLdes in Li213eE'~with e i t h e r L i o r Be Leads e x c l u s i v e l y t o b e r y l l i d e s of t h e type LnWe13. 'Tile x-ray i c k n t i f i c a t i o n s l i s t e d i n Table '3 .SA r e c r e s e n t only t h e :rmst l i k e l y s p e c i f i c b e r y l l i d e s i n c e a l l t h e I;riBe13 compozlnds of t h e lanitbanidle s e r i e s are i s o s t r u c t u r a l , w i t h very n e a r l y i d e n t i c a l l a t t i c e parameters, and theref ore are i n d i s t i n g u i s h a b l e from each other when codeposited fl-om a mixture.

ExaJnination of z i r c o a i m DFTs shown i n Table 9.1 slim 3.t t o be removed easily from s o l u t i o n s i n Li2BeF4 over it broad range of e m c e n t r a ti.on by treatment with e i t h e r L i or B e . It is deposited e i t h e r as f r e e metal or from very dilurte s o l u t i o n s (70 p p d as ZrBe2 (Table 9.1, experiThe value c;f :DF ( Z r ) = 11 obtaiiied at 1000째C 3.n experiment 7 ment 4 ) is of s p e c i a l i n t e r e s t s i n c e it suggests a sol-ukion to t h e high v o l a t i l i t y of ZrF4, u major pro-blem encountered a t t h i s banperature i i i t h e ~acuumd i s t i l l a . t i o n s a l t recovery method. Lithium 0% beq-lliwn could b e used t o r e t a i n Z r i n t h e s t i l l pot as n o n v o l a t i l e f r e e metal. I n experiment 4 , d-ue -to t h e low zirconium concentration (70 ppm), ZrBe2 w a s i d e n t i f i e d along w i t h U-Zr. e

In a d d i t i o n t o t h e elements l i s t e d in Ta'de 9.1, Sm, ELI., mud Sr were s t u d i e d as parts 02 t h e nlixtures used i n experiments 1, 3 , and 8 p l u s o t h e r t e s t s not l i s t e d . Aside from a DF (Sin) = 2 owe-med i n experiment 3 and a DF (Sr) = 1.14, i n an u n l i s t e d t e s t using L i ;a% 550", ncl encouraging results were obtained by t h i s method f o r t h e s e elements.

236

237

L i - B i Alloy Extraction

Liquid-metal e x t r a c t i o n t e s t s with s o l u t i o n s of L i i n B i were made i n t h e same equipment but without f i l t r a t i o n of e i t h e r phase. Samples were recovered a f t e r settling, quenching t o room temperature, and sacr i f i c i n g t h e c r u c i b l e . Both s a l t and m e t a l slugs were cleaned of surface deposits before sampling f o r a n a l y s i s . The decontamination f a c t o r s (DF's) and d i s t r i b u t i o n c o e f f i c i e n t s obtained i n liquid-metal e x t r a c t i o n s of spiked c a r r i e r salt using L i - B i a l l o y s are summarized i n Table 9.2. For t h e spectrum of spikes present (La, Sm, Eu, Gd, and S r ) adequate decontamination w a s achieved f o r a l l but Sm. The g e n e r a l l y high DF's cannoi; be explained i n most cases by a true e x t r a c t i o n mechanism, a f a c t i n d i c a t e d b y t h e low dist r i b u t i o n c o e f f i c i e n t s shown i n Table 9.2. Also, poor material balances were obtained through use of a n a l y t i c a l r e s u l t s from samples of t h e salt and metal phases. The explanation f o r removal of t h e elements i n question i s p r e c i p i t a t i o n as i n t e r f a c i a l . s o l i d s which were l a t e r i d e n t i f i e d by x-ray a n a l y s i s t o be b e r y l l i d e s of t h e LriBe13 type. The high KD observed f o r E u i n d i c a t e s t h a t t h i s element w a s removed almost exclusively by ext r a c t i o n when using 30 a t . % L i - B i a l l o y .

(K,)

References

1. C . D. S c o t t and W. L. C a d e r , Preliminary Design Study of a Continuous Fluorination Vacuum-Distillation -System f o r Regenerating Fuel and Breeder Reactor, ORNL-3791---EEzFry Fertlile Streams i n a Molten 1'3661.

salt

msH Program Serriiann. Progr. Rept. Feb. 28, 1966, ORNL-3936, p. 199.

239

OAK RIDGE NATIONAL LABORATORY

MOLTEN-SALT REACTOR PROGRAM

F: 8 BRIGGS, DIRtCTOQ

P R KASTEN, DEPUTY DIRECTOR

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C. H. GABBARD'*

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R R R R

INSTRUMENTATION AND CONTROLS

J R R G. C C. R.

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96. R. S. Livingston 97. M. I. 1,uxxdi.n 98. R. 11. Lyon 99, H. G. MaePherson 100. I<. E. MacPherson 101. F. C . Maienscbein 1-02. W. R. Martin 103. C. E. Matbews 1134. H. E. McCoy

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1.39. \.I. 140 1. 1.41.. R. 142. C . 143 C.

F. Spencer Spiewak Steffy E. S’cevenson D. Susano l44 J. R. Tallackson 145. E. €ITaylor . 146 R. E. Thoma 147. G. M. Tolson 148 1). B. Traiiger 1-45!. R. W. Tucker 150. w. c US.rj.c$ 1.51. D. C. T/Jatkin 152 G. M. Watson 153. B. H. Webslxr 1.54* A. M. Weinberg 155. J. R. Weir 1.56.M. E. Wha’cley 157 G. C . W i l l i a m s 158. J. C . White 1.59. I,. V. Wilson 160. G. J. Young 161. Biology Lribrary 162-3.63. Reactor Division L i b r a r y 164-168 OIWZ - Y-12 Technical L i b r a r y Document Reference Section 169-171.. C e n t r a l Research L i b r a r y 172-207- Laboratory Records Department 208. Laboratory Records OiaL K. I: 0

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XXTEiRNAL DTSTRTBW ION D. 3’. Cope, Atoiiiic Energy Commission, RDT S i t e Office (OIWL) A. Giambusso, Atomic Energy Cormission, Washlngton W. J. Larkin, A-tcsm-ic- Energy Commission, OR0 W. R. McDonald, B a t t e l l e - P a c i f i c Nor‘clwes’i. Laboratory, Hanford Washington 213. T. W. McIntosh, Atomic Energy Cornmission, Washington 214. M. Shaw, Atomic Energy Commission, Washington 215. E. E. S i n c l a i r , A-i;omic Energy Commission, Washington 216. W. L. Smalley, Atomic Energy Commission, OR0 217. J. A. Swartout, 270 Park Avenue, N e w York 1.7,New York 218. R. F. Sweek, Atomic Energy Commission, Washington 219. M. J. Whitman, Atomic Energy Conmission, Washington 220. Research mil Development Division AEC OR0 22 s.-492. Gi.ven d i s t r i b u t i o n as shown j.n TID-4500 under Reactor Technology category (25 copies - CFSTI)

209. 210. 211. 212