ORNL-TM-4047 by Jon Morrow

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MOLTEN SALTS AS BLANKET FLUIDS IN CONTROLLED FUSION REACTORS W. R. Grimes Stanley Cantor

,:. .-

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that i t s use would not infringe privately owned rights.

om-TM-4047

C o n t r a c t N o . W-7405-eng-26 REACTOR CHENISTRY D I V I S I O N

MOLTEN SALTS AS BLANKET F L U I D S I N CONTROLLED F U S I O N REACTORS W . R . G r i m e s and S t a n l e y C a n t o r

DECEMBER 1972

OAK RIDGE NATIONAL LABORATORY O a k R i d g e , Tennessee 37830 operated by UNION CARBIDE CORPORATION for the 1J.S. ATOMIC ENERGY COMMISSION

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. i

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CONTENTS Page

............................. 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Behavior of Li2BeFq in a Eypothetical CTR . . . . . . . . . . . . 3 Effects of Strong Magnetic Fields . . . . . . . . . . . . .5 Effects on Chemical Stability . . . . . . . . . . . . . 5 Effects on Fluid Dynamics . . . . . . . . . . . . . . . 7 Production of Tritium ...................9 Recovery of Tritium . . . . . . . . . . . . . . . . . . . . . 11 Chemical Transmutations . . . . . . . . . . . . . . . . . . .13 Abstract

. .16 Compatibility with Steam. Air. and Liquid Metals . . . . . .17 Choice of Most Promising Salts . . . . . . . . . . . . . . . . . 18 . Molten Salts in Laser-Induced Fusion Reactors . . . . . . . . . . .22 Compatibility of Li2BeF4 with CTR Metals and Moderators

Summary: General Comparison of Molten Salts with Lithium in

Fusion Reactors Acknowledgments References

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MOLTEN SALTS AS BLANKET FLUIDS I N CONTROLLED FUSION REACTORS W. R. Grimes and S t a n l e y Cantor

ABSTRACT The b l a n k e t of a f u s i o n r e a c t o r s e r v e s t o absorb and t r a n s f e r t h e energy of t h e f u s i o n r e a c t i o n products, and t o produce t h e tritium necessary t o r e f u e l t h e r e a c t o r . This r e p o r t o u t l i n e s how t h e s e two f u n c t i o n s a r e performed by l i t h i u m - b e a r i n g molten s a l t s . The s t r o n g magnetic f i e l d s may have a c o n s i d e r a b l e e f f e c t on t h e chemical s t a b i l i t y and a l e s s s i g n i f i c a n t e f f e c t on t h e f l u i d dynamics of a flowing s a l t . A s a l t melt flowing a c r o s s a s t r o n g magnetic f i e l d induces an e l e c t r i c f i e l d , which i n t u r n produces an emf between t h e walls of t h e conduit and t h e a d j a c e n t s a l t . The emf can be lessened t o minor proportions by c a r e f u l design--causing t h e s a l t t o flow p a r a l l e l t o t h e magn e t i c f i e l d wherever p o s s i b l e and using a system of small bore t u b e s where t h e flow must c r o s s t h e magnetic f i e l d . Although flow i n t h e magnetic f i e l d p a r a l l e l t o t h e l i n e s of f o r c e suppresses turbulence (necessary i n a s a l t f o r adequate h e a t t r a n s f e r ) , t h i s e f f e c t on molten s a l t s w i l l be n e g l i g i b l e owing t o t h e i r low e l e c t r i c a l c o n d u c t i v i t i e s . Breeding of tritium i n a m o l t e n - s a l t b l a n k e t i s a t b e s t marginal when t h e l i t h i u m i s i n i t s n a t u r a l i s o t o p i c abundance; however, t h e t r i t i u m - b r e e d i n g r a t i o can be improved by i n c l u d i n g b l a n k e t r e g i o n s of l i t h i u m or of beryllium, or by e n r i c h i n g t h e s a l t i n l i t h i u m - 6 . LiF and i t s mixtures w i t h BeFz are t h e b e s t m o l t e n - s a l t c o o l a n t s i n which t o breed tritium i n q u a n t i t i e s adequate f o r f u e l i n g a r e a c t o r . Molten LiF-BeF2 i s advantageous i n recovering tritium s i n c e , i n c o n t a c t with m e t a l l i c N i , Mo, or W, v i r t u a l l y a l l o f tritium i s p r e s e n t as TF. While f l u o r i d e s a r e adequate h e a t - t r a n s f e r a g e n t s and possess good r a d i a t i o n s t a b i l i t y , n e u t r o n i c transmutation of Be and F i n t h e s a l t c a y leqd t o c o r r o s i o n u n l e s s a redox b u f f e r (analogous t o U3 /U4 i n a f i s s i o n r e a c t o r ) i s included i n the m e l t . I n a b l a n k e t which h a s two c o o l a n t s , one being m e t a l l i c l i t h i u m , s a l t s o t h e r t h a n LiF-BeF6 could be considered. For example, L i C 1 - K C 1 , melting a t 354 C, may be adequate as vacuum w a l l c o o l a n t and as t h e f l u i d t o t r a n s p o r t h e a t t o t h e steam system of t h e r e a c t o r .

INTRODUCTION A c o n t r o l l e d thermonuclear r e a c t o r (CTR) t h a t f u s e s deuterons with

t r i t o n s y i e l d s 17.6 Mev p e r fusion event mostly i n t h e form of very e n e r g e t i c neutrons.

Such a device r e q u i r e s a b l a n k e t system, a more or

l e s s complex composite of s e v e r a l m a t e r i a l s , capable of performing a t These f u n c t i o n s a r e (a) a b s o r p t i o n of t h e energy

l e a s t two f u n c t i o n s .

c a r r i e d by t h e e n e r g e t i c f u s i o n r e a c t i o n products and t r a n s f e r of h e a t generated i n t h e b l a n k e t t o t h e power-producing p o r t i o n of t h e r e a c t o r , and (b) generation of tritium, i n a manner such as t o enable i t s ready

recovery, t o replace t h a t consumed i n t h e f u s i o n r e a c t i o n .

The f i r s t of

these functions c e r t a i n l y requires a suitable heat t r a n s f e r f l u i d .

The

second r e q u i r e s t h a t t h e blanket contain a s u f f i c i e n c y of l i t h i u m , from which tritium can be e f f e c t i v e l y bred. separable i n p r i n c i p l e

Though t h e s e two f u n c t i o n s a r e

t h e r e i s probably a considerable advantage,

o t h e r t h a n elegance, i f t h e coolant f l u i d can be a l i q u i d w i t h s u f f i c i e n t l i t h i u m t o s u s t a i n t h e r e q u i r e d tritium production. The coolant f l u i d must meet s e v e r a l c r i t e r i a .

These a r e g e n e r a l l y

similar t o t h e requirements imposed on molten s a l t s as f u e l s f o r f i s s i o n r e a c t o r f u e l s (1).

It must not adversely i n t e r a c t with neutrons necessary

for breeding of tritium.

It must be a good h e a t t r a n s f e r f l u i d and i t s

h e a t t r a n s f e r and hydrodynamic behavior must ( f o r most a p p l i c a t i o n s ) be adequate i n t h e presence of l a r g e magnetic f i e l d s .

It must be non-

c o r r o s i v e toward metals of c o n s t r u c t i o n i n t h e b l a n k e t region, t h e pumps, and t h e power generation equipment.

It must be s u i t a b l y s t a b l e t o t h e

i n t e n s e r a d i a t i o n f i e l d s within t h e b l a n k e t and it must n o t r e a c t v i o l e n t l y i f , upon f a i l u r e of t h e h e a t t r a n s f e r equipment,

it i s i n a d v e r t e n t l y

mixed with t h e power-generating f l u i d (steam, potassium, e t c . )

It should,

i n a d d i t i o n , possess a r e l a t i v e l y low vapor p r e s s u r e t o minimize s t r e s s e s on t h e blanket s t r u c t u r e , and it should be compatible with a u x i l i a r y b l a n k e t subsystems such as neutron moderators ( g r a p h i t e s ) or neutron multipliers.

F i n a l l y , t h i s f l u i d should a l s o be capable of e f f i c i e n t

i s p o s s i b l e , a t p r e s e n t , t o v i s u a l i z e a b l a n k e t i n which tritium i s bred i n ( e s s e n t i a l l y ) s t a t i o n a r y bodies of l i t h i u m metal, l i t h i u m a l l o y s , o r l i t h i u m salts, with t h e necessary cooling accomplished by another fluid--molten sodium, p r e s s u r i z e d helium, gas, or molten s a l t .

'It

g e n e r a t i o n of tritium and it should be of a n a t u r e such as t o permit easy recovery of t h e tritium f o r r e t u r n t o t h e f u s i o n c y c l e . This paper a t t e m p t s t o a s s e s s t h e p o t e n t i a l of molten s a l t s as b l a n k e t f l u i d s i n c o n t r o l l e d thermonuclear r e a c t o r s .

A s m a t t e r s stand a t

p r e s e n t , s e v e r a l e n t i r e l y d i f f e r e n t t y p e s of CTRs a r e p o t e n t i a l l y f e a s i b l e . This f a c t coupled w i t h t h e p o s s i b i l i t y (even t h e l i k e l i h o o d ) t h a t t h e c o o l a n t and t h e breeding f u n c t i o n s a r e separable makes it impossible t o examine i n a s i n g l e document a l l t h e c r e d i b l e combinations. We have chosen i n s t e a d , i n what we hope w i l l prove t o be a continuing examination of t h e o v e r a l l problem, t o do t h e following: 1. To a s s e s s t h e problems f o r t h e most d i f f i c u l t case, a s i n g l e

molten s a l t c o o l a n t arid breeder b l a n k e t i n a closed magnetic f i e l d device. We w i l l use molten Li2BeF4, probably t h e most s t u d i e d and b e s t understood of t h e p o s s i b l e candidates, f o r t h i s assessment i n a h y p o t h e t i c a l Tokamak;

a S t e l l e r a t o r would be e q u i v a l e n t i n n e a r l y every r e g a r d , 2.

To compare s e v e r a l molten s a l t s f o r t h i s and o t h e r l e s s demanding

p o s s i b l e CTR u s e s , 3.

To c o n s i d e r , b r i e f l y , a p p l i c a t i o n of molten s a l t s f o r a laser-

powered f u s i o n device whose problems a r e q u i t e d i f f e r e n t , and f i n a l l y

To compare and c o n t r a s t t h e s e molten s a l t s w i t h molten l i t h i u m

as t h e b l a n k e t f l u i d .

BEHAVIOR OF L i 2 B e F 4 IN

A HYPOTHETICAL CTR

The most d i f f i c u : l t problems which must be surmounted by a molten s a l t i n a CTR b l a n k e t system a r e , almost c e r t a i n l y , t h o s e imposed i f t h e s a l t must serve as t h e s i n g l e - f l u i d blanket-coolant f o r a closed magnetic f i e l d (and e s s e n t i a l l y steady s t a t e ) CTR.

The p r e c i s e magnitude of t h e s e

problems w i l l depend upon t h e d e t a i l e d design of t h e d e v i c e - - i t s power l e v e l , s i z e , temperature and temperature d i f f e r e n t i a l , and coolant passage p a t t e r n s within t h e b l a n k e t r e g i o n .

To i l l u s t r a t e t h e n a t u r e and g e n e r a l

magnitude of t h e problems we have chosen a t o r o i d a l CTR, blanketed and cooled w i t h molten Li2BeF4, of t h e size and c h a r a c t e r i s t i c s shown i n Table 1.2 The b l a n k e t dimensions a r e e s s e n t i a l l y t h o s e proposed by ~~

2This design i s a hybrid from sources i n d i c a t e d i n t h e t e x t . It i s p r e s e n t e d only f o r i l l c s t r a t i o n of s e v e r a l problems t o be d e s c r i b e d .

F r a a s ( 2 ) f o r a lithium-metal cooled device; t h e magnetic f i e l d s

are t h o s e i n d i c a t e d i n an O a k Ridge National Laboratory study (3); flow

rate and temperature d i f f e r e n t i a l a r e s c a l e d from a proposed 1000 rJrw(e> molten s a l t f i s s i o n r e a c t o r ( 4 ) .

It i s c l e a r from Table 1, t h a t t h e e f f i c i e n c y of t h e device (ca 45%) 0

presupposes temperatures above 700 C f o r t h e coolant o u t l e t and t h a t mean residence time of t h e f l u i d w i t h i n t h e a c t i v e b l a n k e t region i s (since only a small f r a c t i o n of t h e inventory i s i n t h e pumps, piping, and h e a t exchangers) approximately f i v e minutes.

It i s assumed f o r t h i s p a r t i c u l a r

device t h a t t h e Li2BeF4 i s pumped through t h e b l a n k e t region (acd through t h e enormous magnetic f i e l d ) a t 120 cubic f e e t p e r second and d i r e c t l y t o equipment f o r generation of high q u a l i t y steam.

These assumptions, as

t o pumping r a t e s , AT, and steam generation c o m p a t i b i l i t y , a r e not u n l i k e t h o s e proposed f o r molten s a l t breeder ( f i s s i o n ) r e a c t o r s (MSBRS) ( 4 ) . Table 1.

C h a r a c t e r i s t i c s of a Hypothetical

Controlled Thermonuclear Reactor

Major Diameter

21 meters

Minor Diameters: F i r s t Wall Blanket Region Shield Region

7 meters 9 meters 11 meters

Magnetic F i e l d s : Maximum Toroidal F i e l d a t t h e Coils Toroidal F i e l d a t t h e Center of t h e Plasma P o l o i d a l F i e l d (pulsed) i n t h e Plasma

80 kgaus s 37 kgauss 7 kgauss

Blanket C h a r a c t e r i s t i c s : S a l t (Li 2 BeF4 Graphite ( o r Be) Inventory of Li2BeF4 Flow Rate AT

60%

40% 2 x lo6 kg 4 x lo5 kg/min (120 f t 3 / s e c ) 167OC (300째F)

5 W

It i s worthy of note t h a t t h e mean r a d i a t i o n l o a d on t h e Li2EeF4 (ca 1.1 watts/gram) i s more than 1 0 - f o l d below t h a t proposed f o r MSBRs. This comparison i s , however, d e c e p t i v e l y f a v o r a b l e toward MSBRs i n t h a t t h e s e r e a c t o r s can a s s u r e moderately uniform r a d i a t i o n l e v e l s w i t h i n t h e i r f u e l s while CTRs cannot do s o f o r t h e i r b l a n k e t s .

It i s l i k e l y

t h a t r a d i a t i o n d e n s i t i e s i n CTR b l a n k e t n e a r t h e plasma-confinement ( f i r s t ) w a l l w i l l be l a r g e r than those proposed f o r t h e MSBR.

"his CTR

r a d i a t i o n d e n s i t y i s n o t , however, l i k e l y t o approach t h e maximum r a d i a t i o n d e n s i t y a t which molten s a l t s have been t e s t e d (5). Such a device as t h a t d e s c r i b e d above w i l l , on t h e o t h e r hand, pose s e v e r a l problems f o r t h e Li2BeF4.

Some of t h e s e problems a r e similar

and some a r e q u i t e d i f f e r e n t from those posed by use as f u e l s o l v e n t s i n fission reactors.

These problems a r e defined and discussed i n t h e

following s e c t i o n s . E f f e c t s of Strong Magnetic F i e l d s Pumping a conducting f l u i d i n t o ( a c r o s s t h e magnetic f i e l d l i n e s o f ) a closed magnetic f i e l d device poses a problem.

For a l i q u i d metal t h i s

problem m a n i f e s t s i t s e l f as a l a r g e pumping power l o s s due t o magnetic a l l y induced turbulence; f o r molten s a l t s t h e e f f e c t appears as chemical destabilization.

A f t e r t h e f l u i d i s within t h e magnetic f i e l d one can,

i n p r i n c i p l e (and perhaps, with considerable d i f f i c u l t y , i n p r a c t i c e ) make t h e flow channels conform c l o s e l y t o t h e magnetic l i n e s of f o r c e . I n t h a t c a s e t h e magnetic f i e l d may e x e r t a pronounced e f f e c t upon t h e f l u i d dynamics of t h e flowing stream. E f f e c t s on Chemical S t a b i l i t y From electromagnetic t h e o r y it i s known t h a t t h e e l e c t r i c f i e l d induced i n a conducting f l u i d c r o s s i n g a magnetic f i e l d i s given by t h e cross-product of f l u i d v e l o c i t y and magnetic f i e l d :

E = V X B

Molten Li2BeF4 (or any conducting f l u i d ) flowing a t 10 meters/ second i n a pipe of 5 cm diameter w i t h i t s axis a l i g n e d perpendicular t o t h e l i n e s of f o r c e of an 80 kgauss (8 volt-sec/meter2) magnetic f i e l d v

w i l l have induced, a t r i g h t a n g l e s t o both t h e magnetic f i e l d and t h e

flow d i r e c t i o n , a p o t e n t i a l d i f f e r e n c e of 4 v o l t s between t h e s a l t and t h e pipe w a l l .

P o t e n t i a l d i f f e r e n c e s of such magnitudes a r e c l e a r l y

i n t o l e r a b l e ; though LiF and BeF2 are both very s t a b l e compounds (6) an induced v o l t a g e such as t h i s (equivalent t o d e s t a b i l i z a t i o n by 92 k c a l / mole) would make t h e s e compounds q u i t e c o r r o s i v e t o t h e m e t a l l i c tube

walls. Homeyer (7), who seems t o have been t h e f i r s t t o consider such e l e c t r o l y t i c corrosion i n a CTR b l a n k e t system, noted t h a t such corrosion should be a l l e v i a t e d by (a) reducing f l u i d v e l o c i t i e s perpendicular t o t h e magnetic f i e l d , and (b) using a s e r i e s of p a r a l l e l p i p e s t o reduce t h e pipe dimension where flow a c r o s s t h e magnetic f i e l d l i n e s a r e necessary. If, f o r example, t h e 120 f t 3 / s e c flow of Li2BeF' r e q u i r e d of our h y p o t h e t i c a l 1000 MW(e) CTR were supplied a t a flow r a t e of 4 meters/sec through pipes of 4 cm diameter perpendicular t o t h e 25 kgauss f i e l d 3 t h e emf induced i n each pipe would be 0.4 v o l t s ; some 675 p i p e s would be required.

If t h e s e p i p e s p e n e t r a t e d t h e f i e l d a t 30'

t h i s e m f would be reduced t o 0.2 v o l t s . be t o l e r a b l e .

t o the f i e l d l i n e s

These c o n d i t i o n s would seem t o

A l t e r n a t i v e l y , by supplying e x t e r n a l cooling t o each pipe,

as it c r o s s e s t h e magnetic f i e l d l i n e s , so as t o form a poorly conducting l a y e r of frozen s a l t on t h e i n n e r pipe w a l l , it may be p o s s i b l e t o reduce t h e number of p i p e s and t o somewhat i n c r e a s e t h e i r s i z e .

Periodic

replacement of corroded pipe s e c t i o n s might a l s o be considered, s i n c e they a r e l o c a t e d a t t h e periphery of t h e torus.' Plasma s t a b i l i t y i n a r e a c t o r such as t h i s r e q u i r e s a pulsed p o l o i d a l magnetic f i e l d t r a n s v e r s e t o t h e main f i e l d and, accordingly, perpendicu-

l a r t o t h e f l u i d flow p a r a l l e l t o t h e f u e l l i n e s of t h e main ( t o r o i d a l ) field.

Chemical e f f e c t s of t h i s p o l o i d a l f i e l d (which may reach 7 kgauss)

may not be t r i v i a l , b u t they would seem, i n g e n e r a l , t o be t o l e r a b l e . 3This i s roughly t h e maximum f i e l d between t h e c o i l s (3) i n a pipe e n t e r i n g t h e o u t e r edge of t h e t o r u s . 'Other a l t e r n a t i v e s e x i s t . It should be p o s s i b l e t o p e n e t r a t e t h e f i e l d by s h a f t s of mechanical pumps t o permit use of Li2BeF' t o t r a n s f e r h e a t t o ( f o r example) a b o i l i n g potassium cycle w i t h i n t h e magnetic f i e l d . Such a l t e r n a t i v e s are beyond t h e scope of t h i s document.

It i s c l e a r t h a t t h e problems o u t l i n e d above deserve experimental study e s p e c i a l l y i n t h e area of k i n e t i c s of de- and r e - s t a b i l i z a t i o n of r e a l f l u i d s upon passage through i n t e n s e magnetic f i e l d s . E f f e c t s on F l u i d Dynamics To avoid induced e l e c t r i c f i e l d s as discussed above, flow of t h e

b l a n k e t f l u i d w i t h i n t h e t o r u s w i l l be a l i g n e d with t h e magnetic l i n e s of force.

However, i n t h a t case t h e magnetic f i e l d w i l l e x e r t a f o r c e

opposed t o e d d i e s within t h e f l u i d and w i l l tend t o damp t u r b u l e n t flow. Heat loadings i n t h e blanket s t r u c t u r e o f a CTR, and e s p e c i a l l y a t t h e f i r s t (plasma-confining) w a l l , w i l l be very l a r g e , and molten LizBeF4

must develop t u r b u l e n t flow i f it i s t o cool t h i s w a l l e f f e c t i v e l y .

i s important, t h e r e f o r e , t o assess t h i s damping e f f e c t of t h e f i e l d on

t u r b u l e n t flow i n t h e s a l t . No experimental study of magnetic damping i n molten s a l t h a s been

r e p o r t e d , b u t experiments with l i q u i d mercury have been performed (8,9). These experiments with mercury appear t o provide a means of e s t i m a t i n g t h e Reynolds number a t which t h e t r a n s i t i o n from laminar t o t u r b u l e n t flow occurs.

A dimensionless q u a n t i t y which c h a r a c t e r i z e s t h e magnetic

f o r c e s t h a t a f f e c t flow i s c a l l e d t h e Hartmann number (MI, and i s defined: 1

where

BR(o/r))Z

B i s the applied f i e l d , ,t i s a c h a r a c t e r i s t i c l e n g t h , u s u a l l y t h e half-width of t h e flow channel, o i s t h e f l u i d ' s e l e c t r i c a l conductivity, and r) i s t h e v i s c o s i t y

I n t h e absence of a magnetic f i e l d t h e laminar-turbulent t r a n s i t i o n occurs a t Reynolds number (R

of about 2200; i n t h e presence of t h e f i e l d

t h i s t r a n s i t i o n occurs a t a h i g h e r Reynolds number (Rt). (more commonly t h e r a t i o (Rt/Ro)

This i n c r e a s e

i s a f h c t i o n of t h e Hartman number

(MI.

Three such c o r r e l a t i o n f u n c t i o n s have been published (8?9,10) ,.

For Li2BeF4 a t 6OO0C, t h e e l e c t r i c a l conductivity (11) i s 220 (ohm-rneter)-l,

the viscosity i s 8 x

kg/(sec-meter)

Accordingly,

f o r t h i s material i n a 80 kgauss (8 webers/meter2) f i e l d and assuming a 6 cm (3 ern half-width) channel t h e value of t h e Hartman number i s 40. If w e apply each of t h e t h r e e c o r r e l a t i o n s (8,9,10) developed from e x p e r i ments w i t h mercury t o a f l u i d of

8 M

we f i n d t h e t r a n s i t i o n Reynolds number should r i s e from Ro = 2200 t o

= 2720, 3740,

and 2400, r e s p e c t i v e l y .

The e f f e c t of magnetic f i e l d

on t h i s f l u i d i s , t h e r e f o r e , p r e d i c t e d t o be r e l a t i v e l y small. These t h r e e values f o r R

t a r e very much l e s s than values estimated f o r flows i n t h e f i r s t w a l l r e g i o n . A s an approximation l e t us assume t h a t t o cool t h e vacuum w a l l we r e q u i r e 40 f t 3 p e r second of s a l t (one t h i r d t h e q u a n t i t y required t o cool t h e e n t i r e b l a n k e t ) and t h a t t h i s s a l t flows through a 6 cm wide annulus around t h e 7 meter diameter f i r s t The l i n e a r v e l o c i t y of s a l t i s 0.85 meters/sec, t h e d e n s i t y (11)

wall.

( a t 6OO9C) of LizBeF4 i s 1990 kg/meter3 and t h e v i s c o s i t y i s 8 c e n t i p o i s e . The Reynolds number under t h e s e c o n d i t i o n s i s about 13,000. These data s t r o n g l y suggest t h a t molten Li2BeF4 can be made t o flow t u r b u l e n t l y w i t h i n t h e b l a n k e t system, b u t d i r e c t experiments with molten

s a l t s would c e r t a i n l y appear d e s i r a b l e . Any t r a n s v e r s e magnetic f i e l d w i l l a l s o a c t t o suppress t u r b u l e n c e . Hoffman and Carlson (10) propose t h e formula, Rt = 500M for c a l c u l a t i n g t h e t r a n s i t i o n Reynolds number of Mercury flowing t r a n s v e r s e t o t h e magnetic f i e l d .

The same formula a p p l i e d t o Li2EkF4 a t 600 C flowing i n

a 6-cm t h i c k channel t r a n s v e r s e t o 8 kgauss ( t h e p o l o i d a l f i e l d s t r e n g t h ) yields Rt = 500M = 2000.

This r e s u l t suggests t h a t an 8 kgauss p o l o i d a l f i e l d i n a t o r o i d a l r e a c t o r may n o t a f f e c t turbulence i n Li2EeF4; a t most, t h e suppression of turbulence by t h i s f i e l d w i l l be comparable t o t h e e f f e c t s of t h e toroidal field.

5Metallic l i t h i u m i s expected t o be q u i t e d i f f e r e n t . The Hartman number f o r L i i s 12,000 f o r t h e condition where t h a t of Li2BeF4 i s 40; t h e corresponding R t f o r l i t h i u m i s , accordingly, above 700,000. It would appear t h a t L i w i l l be c o n s t r a i n e d t o laminar flow; it seems l i k e l y , however, t h a t (because of i t s good thermal conductivity) it can adequately cool t h e f i r s t w a l l .

Production of T r i t i u m

It i s obviously necessary t o use t h e neutrons produced i n f u s i o n t o breed t h e tritium r e q u i r e d t o f u e l a D-T r e a c t o r .

If t h e only sources of

tritium were t o d a y ' s transmutation f a c i l i t i e s then t h e f u e l c o s t alone would be about 1 . 2 c e n t s p e r k i l o w a t t - h o u r . 6 The only p r a c t i c a , l neutron r e a c t i o n s which w i l l y i e l d tritium s u f f i c i e n t f o r t h e needs of a D-T f u s i o n r e a c t o r a r e 6Li(n,a)T and 7Li(n,an')T. 2 5 MeV.

The l a t t e r i s a high-energy r e a c t i o n w i t h a t h r e s h o l d a t

Neutron-capture c r o s s s e c t i o n s of 6 L i become s i g n i f i c a n t only

a t e n e r g i e s of 0.5 MeV and l e s s .

The 7 L i r e a c t i o n i s p a r t i c u l a r l y

f a v o r a b l e s i n c e t h e product neutron ( n ' ) can r e a c t with 6 L i t o y i e l d a second tritium atom, b u t because t h e b l a n k e t c o n t a i n s elements which s c a t t e r and absorb high-energy neutrons, t h e production of tritium from 7 L i i s n o t very e f f i c i e n t .

When t h e l i t h i u m i n t h e b l a n k e t i s i n

n a t u r a l i s o t o p i c abundance (92.58% 7 L i , 7.42% 6 L i ) , t h e g r e a t e r f r a c t i o n of tritium i s produced from 6 L i . S e v e r a l s t u d i e s have been r e p o r t e d concerning t h e breeding of tritium i n f u s i o n r e a c t o r b l a n k e t s (12-16).

I n c a s e s where t h e l i t h i u m

i s i n n a t u r a l i s o t o p i c abundance, t r i t i u m - b r e e d i n g r a t i o s c l e a r l y g r e a t e r

t h a n u n i t y a r e c a l c u l a t e d f o r l i t h i u m metal b l a n k e t s ; t h e breeding r a t i o s f o r lithium salts a r e d i s t i n c t l y l e s s favorable.

Table 2 p r e s e n t s some

very r e c e n t c a l c u l a t i o n s f o r f o u r s a l t s and f o r l i t h i u m metal a l l i n t h e same b l a n k e t c o n f i g u r a t i o n .

Some of t h e neutron c r o s s s e c t i o n s , p a r t i c -

u l a r l y t h o s e f o r t h e n,a, and n,n'Y r e a c t i o n s of f l u o r i n e (171, are uncertain.

The v a l u e s i n Table 2 a r e , t h e r e f o r e , more u s e f u l f o r com-

p a r i s o n than f o r a c c u r a t e p r e d i c t i o n of tritium production;

uncertain-

t i e s of perhaps 10% i n t h e c a l c u l a t e d breeding r a t i o s a r e p o s s i b l e . Three o p t i o n s , e i t h e r alone o r i n combination, can be considered f o r upgrading tritium production when t h e breeding r a t i o i s marginal as appears t o be t h e case f o r L ~ z E ~ F These ~ , . ~are: 6Based on a tritium c o s t o f 10 c e n t s / c u r i e and 22 MeV/fusion u t i l i z e d i n a p l a n t o p e r a t i n g a t 40% thermal e f f i c i e n c y . 71t should be noted t h a t Blow, e t a l . (14) c a l c u l a t e a tritium breeding r a t i o of 1.027 f o r Li2BeF4 i n a b l a n k e t assembly similar t o t h a t of Table 2 . 8 P o s s i b l e use of LiF, L i C 1 , and L i 2 C O 3 i s discussed b r i e f l y i n a subsequent s e c t i o n of t h i s r e p o r t .

Table 2.

T r i t i u m Breeding CalculationsaJb Breeding Ratio'

Coolant

To t a l Bre e ding Ratio

from

7 ~ i

LiF

(85O0C) e

0.804

0.244

1.05

LizBeF,

(85O0C)

0.785

0 144

0.93

L i 2 CO,

(900OK)

0.642

0.167

0.81

LiCl

(900'K)

0.614

0.132

0.75

(85OoC

0.982

0.45,:

1.44

aD. S t e i n e r , Oak Ridge National Laboratory, personal communication, March 1972. bBlanket Configuration: (1) f i r s t w a l l - 0.5 cm Nb, (2) 94% coolant, 6% Nb - 3 cm, (3) second w a l l - 0.5 cm Nb, (4) 94% coolant, 6% Nb 60 cm, ( 5 ) g r a p h i t e - 30 cm, (6) 94% coolant, 6% Nb - 6 cm. 'Defined as tritium atom produced p e r f u s i o n neutron i n c i d e n t on t h e first w a l l . dLithium i n n a t u r a l i s o t o p i c abundance. e Temperature a t which atom d e n s i t i e s were c a l c u l a t e d .

(a) design of blanket t o include a region of m e t a l l i c l i t h i u m , (b) i n c r e a s i n g Be content of t h e blanket by adding a region of Be

or Be2C t o i n c r e a s e neutron m u l t i p l i c a t i o n and t o provide more 6 L i ZBe(n,d $He

> $ L i , and

(c) modest enrichment of t h e blanket m a t e r i a l i n 6 L i . The second option was b r i e f l y t r e a t e d by B e l l (16) who showed t h a t i f a blanket region (40 cm t h i c k a d j o i n i n g a 1 cm f i r s t w a l l of molybdenum)

were changed from Li2BeF4 t o an equal t h i c k n e s s of Be and LizBeFq, t h e t r i t i u m - b r e e d i n g r a t i o would i n c r e a s e from 0.95 t o 1.50. The t h i r d option h a s a l s o received some a t t e n t i o n .

Impink (13)

r e p o r t e d t h a t small i n c r e a s e s i n 6 L i enrichment of t h e Li2BeFq b l a n k e t l e d t o modest gains i n breeding r a t i o .

For example, i n c r e a s i n g t h e 6 L i

i s o t o p i c f r a c t i o n t o 0.2 i n a 6.25-cm t h i c k coolant region next t o t h e f i r s t w a l l improves t h e t o t a l breeding r a t i o by about 3%. Although

enrichment c o s t s a r e high, t h e s e c o s t s would be p a r t l y o f f s e t by improved s h i e l d i n g of t h e magnet c o i l s and by reduced r a d i a t i o n damage t o t h e f i r s t w a l l through reduced resonance capture (13).

I n l i g h t of p r e s e n t knowledge of t h e p e r t i n e n t c r o s s s e c t i o n s , it appears t h a t t h e breeding c a p a b i l i t y of Li2BeF4 i s marginal i n devices such as our h y p o t h e t i c a l t o r u s .

This m a t e r i a l would, t h e r e f o r e , probably

need t o be augmented by one of t h e methods i n d i c a t e d above, o r by o t h e r means.

It i s c l e a r % h a t b e t t e r c r o s s s e c t i o n d a t a a r e needed s o t h a t

t h i s p o i n t can be decided. Recovery of T r i t i u m Approximately 270 grams of tritium a r e consumed p e r day by f u s i o n i n a 2250 MW(t) D-T r e a c t o r .

S l i g h t l y more than t h i s , o r approximately

300 grams p e r day, must be produced and recovered; t h i s corresponds t o some 50 moles of T2 o r t o 100 moles of TF p e r day.

I n our h y p o t h e t i c a l

CTR t h e mean residence time of t h e f l u i d i n t h e b l a n k e t i s 5 minutes p e r

cycle.

Some 0.174 moles of T2, o r 0.348 moles TF i s , accordingly,

produced i n t h e Li2BeF4 i n t h i s i n t e r v a l .

If t h e f l u i d e n t e r i n g t h e

b l a n k e t contained no tritium s p e c i e s t h e f l u i d emerging from t h e b l a n k e t w i l l c o n t a i n about 1.74 x

moles T2 (or a l t e r n a t i v e l y about 3.48 x

moles TF) p e r l i t e r i f complete homogeneity i s assumed.

The problems i n

recovery and management of t h e tritium depends s i g n i f i c a n t l y on whether t h e m a t e r i a l e x i s t s as T2 o r as TF.

These two s i t u a t i o n s , and t h e e x t e n t

t o which t h e mode of tritium behavior can be c o n t r o l l e d , a r e b r i e f l y described i n t h e following. S o l u b i l i t y of H2 i n molten Li2BeF4 has been shown t o i n c r e a s e 0

l i n e a r l y w i t h p r e s s u r e of H2; a t 1000 K, t h e s o l u b i l i t y should be n e a r

7 x

moles H2 p e r l i t e r of s a l t p e r atmosphere of H2 (18). No

s t u d i e s of t r i t i u m s o l u b i l i t y have been r e p o r t e d .

If t h e bred tritium

occurs as T2, and i f t h e s o l u b i l i t y behavior of T2 and H2 a r e similar, t h e emerging b l a n k e t f l u i d c a r r i e s T2 (generated during i t s p a s s through t h e b l a n k e t ) e q u i v a l e n t t o a s a t u r a t i n g p r e s s u r e of about 2 . 5 x atmospheres.

E q u i l i b r a t i o n of t h e emerging s a l t with a r e l a t i v e l y small

volume of i n e r t gas will r e s u l t i n s t r i p p i n g of a very l a r g e f r a c t i o n of t h i s d i s s o l v e d T2 from t h e s a l t .

It i s c l e a r , however, t h a t t h i s process

(with 120 f t 3 of s a l t and, f o r example, 1 f t 3 of He) w i l l be d i f f i c u l t t o engineer, and, moreover, t h a t d i f f u s i v i t y of T2 a t such e f f e c t i v e p a r t i a l p r e s s u r e s through h o t metal s u r f a c e s w i l l pose problems. The s o l u b i l i t y of HF i n molten Li2BeF4 a l s o depends l i n e a r l y on p r e s s u r e of t h e s o l u t e gas, and i t s Henry's l a w c o n s t a n t i s

HF p e r l i t e r of s a l t p e r atmosphere HF a t 1000째K (19).

l o v 2 moles

The TF produced

during each cycle of coolant through t h e b l a n k e t region w i l l correspond t o about 3.5 x

moles TF p e r l i t e r of Li2BeFq; t h i s i s e q u i v a l e n t

t o a s a t u r a t i o n p r e s s u r e of about 3.5 x lo-* atmospheres of TF.

The TF

w i l l be more d i f f i c u l t t o s t r i p from t h e s a l t than w i l l T2, b u t TF w i l l n o t d i f f u s e through t h e metal walls.

If i t s r e a c t i o n with t h e metal

walls can be s u f f i c i e n t l y minimized, t h e TF c o n c e n t r a t i o n can be allowed

t o i n c r e a s e and t h e r a t e of processing t h e b l a n k e t f l u i d can be c o r r e s pondingly reduced.

If, f o r example, t h e TF can be allowed t o c o n c e n t r a t e

atmospheres, sparging o f perhaps 5 f t 3 / s e c of

u n t i l i t s pressure i s

t h e f l u i d w i t h helium should s u f f i c e f o r e f f e c t i v e recovery of t h e bred

tritium.

It i s , accordingly, worthwhile t o examine whether t h e bred

tritium can reasonably be maintained a s TF. T r i t i u m produced, f o r example, from 6LiF

--f

4He

T+

+ F-

i s , i n p r i n c i p l e , born a s an oxidized s p e c i e s .

The t o l e r a b l e concentra-

t i o n of TF, or of any o t h e r oxidized s p e c i e s , w i l l , of course, be l i m i t e d by t h e e x t e n t t o which c o r r o s i v e r e a c t i o n w i t h t h e CTR metal can occur. I f t h e containment metal i s s u f f i c i e n t l y i n e r t , u s e f u l c o n c e n t r a t i o n s o f TF can be maintained without a p p r e c i a b l e r e a c t i o n .

By way of i l l u s t r a t i o n , l e t u s examine t h e r e a c t i o n of HF w i t h n i c k e l , where ( g ) , ( c ) , and (d) i n d i c a t e , r e s p e c t i v e l y , t h a t t h e s p e c i e s i s gaseous, c r y s t a l l i n e s o l i d , or d i s s o l v e d i n molten LizBeF4. 0

of Table 3 AGO = 10.9 kea1 f o r t h i s r e a c t i o n a t 1000 K . c o n s t a n t i s given by

From t h e data The e q u i l i b r i u m

13 where N i s t h e mole f r a c t i o n of d i s s o l v e d NiF2, a i s t h e a c t i v i t y of n i c k e l ( u n i t y i n t h i s c a s e ) , and P i s t h e p a r t i a l p r e s s u r e of t h e d e s i g - 3.2 x n a t e d gaseous s p e c i e s . If we s e t NNiF (equivalent t o 6 1 ') L

p a r t s p e r m i l l i o n of N i 2 + , a value t h a t seems l i k e l y t o be t o l e r a b l e ) we c a l c u l a t e p r e s s u r e s of H2 of 6 x lo-' atmospheres and 5 x

atmos-

pheres, r e s p e c t i v e l y , i n e q u i l i b r i u m with HF p r e s s u r e s of 3.5 x atmospheres.

and

These r e s u l t s suggest t h a t i f t h e CTR metal were N i

a very l a r g e f r a c t i o n of t h e tritium could be maintained as TF and

s t r i p p e d as such. Examination of Ta,ble 3 suggests t h a t t h e s i t u a t i o n may be even more f a v o r a b l e f o r molybdenum and, perhaps, f o r tungsten as t h e containment metal.

However, i f t h e containment metal were i r o n , chromium, niobium,

tantalum, t i t a n i u m , or, probably, vanadium t h e tritium must, of n e c e s s i t y , be s t r i p p e d and handled as T2.

If one of t h e s e more r e a c t i v e metals

proves necessary as t h e CTR m a t e r i a l , some way of preventing c o r r o s i o n due to xTF must be provided.

--f

MFx

+3 2

This would seem t o be p o s s i b l e by i n c o r p o r a t i o n of a

redox b u f f e r (described i n more d e t a i l i n t h e subsequent s e c t i o n ) i n t h e molten L i 2 BeF4. A t t h i s s t a g e i n t h e technology of f u s i o n r e a c t o r s one should

probably n o t dismiss t h e p o s s i b i l i t y o f using s t a i n l e s s s t e e l or a chromium-containing n i c k e l -based a l l o y a t temperatures a t or below 1000째K. Such m a t e r i a l s can, perhaps, be coated with molybdenum, t u n g s t e n , or n i c k e l , by e l e c t r o d e p o s i t i o n (22) or by plasma spraying (23). Chemical Transmutations S e v e r a l t y p e s of chemical t r a n s m u t a t i o n s w i l l occur i n molten Li,BeF,: i n i t s s e r v i c e as t h e b l a n k e t f l u i d i n a f u s i o n r e a c t o r .

The

most important of t h e s e , and means f o r maintenance o f t h e b l a n k e t t o minimize o r avoid t h e i r d e l e t e r i o u s e f f e c t s , a r e t h e following: Transmutation o f l i t h i u m i s , of course, e s s e n t i a l t o production of

tritium.

The o v e r a l l r e a c t i o n s can be r e p r e s e n t e d as 7LiF 6LiF

+n +n

+ $He + $He

+ +

TF TF.

+ n',

and

14 Table 3 .

Free Energies of Formation of F l u o r i d e s f

" 1 OOOOK (kcal/g-atom of f l u o r i n e )

Ref e renc e

-50.2 -56.8

c-55.3" (21) (21)

-66 -66.2 -66. 5a -72. 5a -75.2 -82.2 -85.4 -125.2; -106.9

(20) (20)

Standard f r e e energy of formation i n molten Li2BeF4.

f f b E s t i m a t e d from t h e r e l a t i o n , AGlo0o = m 2 9 8 - 1000 (C S g g 8 ) t a k i n g m $ 9 8 and most s 9 9 8 from NBS Technical Notes 270-3,4,5 Other S z 9 8 estimated from analogous compounds.

(21).

These r e a c t i o n s a r e n o t i n h e r e n t l y o x i d i z i n g or reducing, though, as described i n t h e previous s e c t i o n , t h e generated TF can o x i d i z e r e a c t i v e s t r u c t u r a l metals t o form metal f l u o r i d e s which w i l l d i s s o l v e i n t h e m e l t . Transmutation of beryllium (as EkF2 i n Li2BeF4) l e a d s t o corrosion of any system metal s i n c e disappearance of Be2+ i s e q u i v a l e n t t o r e l e a s e of f l u o r i n e .

The two r e a c t i o n s may be represented as: BeF2

--f

2$He i- 2F ( o r Fz) , and

BeF2 + n + $He + $He $He 0.8 see h a l f l i f e 2Li

2F, followed by

, gLi,

and

6LiF.

I n our 2250 MW r e a c t o r , t h e s e r e a c t i o n s y i e l d , r e s p e c t i v e l y , t h e e q u i v a l e n t of 500 g and 70 g of f l u o r i n e p e r day.

This problem i s g e n e r a l l y similar

t o t h a t encountered i n f i s s i o n of uranium (as LT4) i n t h e MSRE (1);

15 U

it i s c l e a r l y necessary t o provide a redox b u f f e r i n t h e molten s a l t ( t h e UF3-UF4 couple does t h i s i n f i s s i o n r e a c t o r s ) , capable of o x i d i z i n g

It i s a l s o necessary, if N i , Mo, or W c o n s t i t u t e s t h e c o n t a i n e r

Fo t o F-.

system, t h a t t h i s redox b u f f e r be c o n s i s t e n t with maintenance of t h e

tritium as TF. The couple

e ~e4+ ~e3+ may p o s s i b l y serve t h i s function.

If, f o r example, t h e concentration

of cerium i n t h e melt i s s e t a t tain 6 x

lo3

mole of Ce3+

mole f r a c t i o n t h e b l a n k e t w i l l con-

Ce4+, and t h e Ce3+/Ce4+ r a t i o would r e q u i r e

chemical adjustment on a cycle t i m e of many days.

If, on t h e o t h e r hand,

t h e c o n t a i n e r metal i s Nb (or some o t h e r metal which w i l l reduce TF i n d i l u t i o n s o l u t i o n ) t h e redox couple must be chosen so a s t o be considera b l y more reducing.

It must d e a l with t h e F2 generated by transmutation

of beryllium b u t it must a l s o reduce t h e 100 moles p e r day of TF produced by transmutation i n t h e LiF.

Such a b u f f e r system would r e q u i r e a d j u s t -

ment on a cycle of a few days. I n a d d i t i o n , transmutation of f l u o r i n e occurs upon capture of neutrons of energy above about 3 MeV.

This r e a c t i o n may be represented

bY lZF-

+ n -+ l$N' +

$He,

This n i t r o g e n i s o t o p e decays, with a 7.3 see. h a l f - l i f e , t o an oxygen

isotope 1%-

+ 160

+ p-,

and t h e r e s u l t i s probably, although t h e mechanism may be complex, growi n of 02-.

The a b s o l u t e q u a n t i t y of 1 6 N formed by t h i s r e a c t i o n i s

r e l a t i v e l y u n c e r t a i n ; it i s estimated t o be, within a f a c t o r of t h r e e , 120 grams/day.

The very s h o r t h a l f - l i f e of t h i s i s o t o p e guarantees t h a t

a l l t h e 1 6 N decays w i t h i n t h e CTR b l a n k e t .

The concentration of 1 6 N ,

i n whatever chemical form, within t h e Li2BeF4 cannot exceed 1.1 p a r t s i n loll.

However, some f r a c t i o n of t h i s m a t e r i a l w i l l r e a c t with t h e

CTR containment metal; decay of t h i s i s o t o p e w i l l l e a d t o formation of

metal oxide i n t h e C'I'R metal.

This may, e s p e c i a l l y i f it c o n c e n t r a t e s

w i t h i n t h e g r a i n boundaries, prove troublesome.

If a l l t h e 1 6 N - decayed

w i t h i n t h e blanket sal-t, t h e oxide concentration of our h y p o t h e t i c a l CTR v

would i n c r e a s e about 60 p a r t s p e r b i l l i o n p e r day.

Since 1 0 t o 50

16 p a r t s p e r m i l l i o n of oxide i s almost c e r t a i n l y t o l e r a b l e , a p r o c e s s f o r removal of oxide on a c y c l e time of s e v e r a l months t o s e v e r a l y e a r s should s u f f i c e . F i n a l l y , it should be noted t h a t t h e transmutation r e a c t i o n s

For t h e h y p o t h e t i c a l CTR t h e d a i l y production of helium i s about 125 gram atoms or n e a r l y 100 standard cubic f e e t . H e l i u m i s r e l a t i v e l y i n s o l u b l e i n molten LizBeF4 (24); t h e s o l u b i l i t y shown a l l generate He.

a t 1000째K i s 1 . 7 x

moles He per l i t e r s a l t p e r atmosphere.

Helium

produced p e r pass of b l a n k e t s a l t corresponds t o a s a t u r a t i o n p r e s s u r e of 2.6 x

atmospheres.

If no sparging were attempted t h e helium

p r e s s u r e would reach 1 atmosphere i n about 30 hours. Compatibility of LizBeF4 w i t h CTR Metals and Moderators A s i n d i c a t e d i n Table 3 above, LiF and BeF2 i n molten Li2BeF4 are

very s t a b l e m a t e r i a l s .

Both a r e much more stable than t h e s t r u c t u r a l

metal f l u o r i d e s ; consequently, c o r r o s i o n due t o chemical r e a c t i o n s w i t h t h e s e major b l a n k e t c o n s t i t u e n t s should prove minimal.

Indeed, e x p e r i -

ence w i t h t h e Molten S a l t Reactor Experiment (25) has shown n e g l i g i b l e c o r r o s i o n by t h i s f l u i d on a nickel-base a l l o y (Hastelloy N).

However,

such s a l t s a r e e x c e l l e n t f l u x e s f o r m e t a l l i c oxides and h a l i d e s , and f i l m s of such substances a f f o r d no p r o t e c t i o n a g a i n s t o x i d i z i n g a g e n t s

c a r r i e d by such melts; accordingly, as d e s c r i b e d above, HF (or TF) may r e a c t w i t h t h e containment metal, and impurity i o n s such as N i 2 + w i l l r e a c t w i t h m e t a l l i c i r o n or chromium i n t h e c o n t a i n e r metal (1). Melts such as LizBeF4 a r e chemically i n e r t toward, and do n o t wet, g r a p h i t e (1). However, t h e p o s s i b i l i t y t h a t such s a l t s w i l l t r a n s f e r g r a p h i t e and c a r b u r i z e metals such as Mo or Nb cannot be discounted.

It i s n o t l i k e l y t h a t a system b u i l t of Mo, Nb, or V can use molten LizBeFr, and unclad g r a p h i t e without adverse i n t e r a c t i o n s .

Similarly,

m e t a l l i c Be cannot r e a c t appreciably w i t h LizBeFq (but t h e Be could c e r t a i n l y r e a c t w i t h TF or w i t h t h e Ce3+/Ce4+ couple proposed as a redox b u f f e r i n t h e system).

Any r e a l use of m e t a l l i c Be as a neutron m u l t i -

p l i e r i n t h e b l a n k e t system, t h e r e f o r e , presupposes t h a t t h e Be i s c l a d w i t h an i n e r t metal.

Other processes which could conceivably give r i s e t o corrosion can be dismissed as highly improbable.

D i r e c t d i s s o l u t i o n of s t r u c t u r a l

metals i n LizBeFh has never been observed.

S a l t decomposition caused

by t h e slowing down of e n e r g e t i c p a r t i c l e s should n o t l e a d t o c o r r o s i o n provided t h a t t h e s a l t i s kept a t e l e v a t e d temperatures.

Experience

gained i n t h e Molten S a l t Reactor Experiment (26) and i n a n e x t e n s i v e i n - p i l e r a d i a t i o n t e s t i n g program showed t h a t as long as t h e temperature 0

was g r e a t e r than 150 C (271, r a d i o l y t i c decomposition was of no import a n c e t o c o r r o s i o n of s t r u c t u r a l metals or g r a p h i t e . Compatibility w i t h Steam, A i r , and Liquid Metals I n any system of heat-exchangers and h o t flowing l i q u i d s , t h e r e e x i s t s a r e a l and f i n i t e p r o b a b i l i t y t h a t l e a k s w i l l occur.

In this

s e c t i o n we examine t h e consequences of l e a k s and intermixing of o t h e r f l u i d s and Li2BeF4. The r e a c t i o n of steam with Li2BeF4 y i e l d s HF and Be0 HzO(g) + BeF2 ( a )

BeO(c)

+ 2HJ?(g)

though t h e r e a c t i o n i s n o t p a r t i c u l a r l y exothermic.

Both H2O and HF a r e

l i k e l y t o corrode t h e metal i n c o n t a c t with t h e salt; corrosion-product f l u o r i d e s w i l l d i s s o l v e or be otherwise c a r r i e d by t h e s a l t .

Since Be0

i s only very s l i g h t l y s o l u b l e (125 ppm a t 5OO0C) i n Li2BeF4 (28), a l a r g e in-leakage o f steam would soon l e a d t o t h e p r e c i p i t a t i o n of Be0 i n the salt c i r c u i t .

Leakage of a i r i n t o LiF or LizBeF4 w i l l have t r o u b l e -

some, b u t n o t hazardous, consequences,

D r y a i r w i l l not react directly

with e i t h e r s a l t ; however, a i r o x i d a t i o n of s u r f a c e s i n c o n t a c t w i t h t h e

s a l t w i l l result i n d i s s o l u t i o n by t h e s a l t and, i f continued, i n u l t i m a t e p r e c i p i t a t i o n of BeO. does steam, w i t h Li2BeFq.

Moisture i n t h e a i r w i l l a l s o r e a c t , as

The molten Li2BeF4 can, i f necessary, be

f r e e d of oxide by t r e a t m e n t a t e l e v a t e d temperatures w i t h anhydrous HF (29) I n some CTR d e s i g n s suggested i n a subsequent s e c t i o n of t h i s paper, LizEieF4 ( o r o t h e r s a l t ) could i n a d v e r t e n t l y be mixed w i t h l i q u i d a l k a l i metals.

From Li2E!eFq, m e t a l l i c L i , N a , or K r e a c t t o p r e c i p i t a t e Be

metal, b u t t h e r e a c t i o n i s not h i g h l y exothermic.

I n general, although i n a d v e r t e n t mixing of Li,BeF4 (or most o t h e r molten s a l t s ) with o t h e r CTR f l u i d s would prove troublesome, such mixing would not l e a d t o v i o l e n t or explosive r e a c t i o n s . CHOICE OF MOST PROMISING SALTS

I n t h i s s e c t i o n we attempt t o answer two q u e s t i o n s .

These a r e :

(a> i f tritium must be bred i n t h e blanket-coolant which lithium-bearing s a l t i s b e s t , and (b) i f t h e coolant and breeding f u n c t i o n of t h e blanket can be separated which a r e t h e most promising molten s a l t c o o l a n t s ?

I n answer t o t h e f i r s t question, it must be conceded t h a t o b t a i n i n g breeding r a t i o s g r e a t e r than u n i t y with molten s a l t s alone may pose a

real d i f f i c u l t y .

Table 2 above suggests t h a t LiCl and L i ~ C 0 3show, i n

reasonable (though n o t optimized) b l a n k e t c o n f i g u r a t i o n s , breeding r a t i o s t h a t are unsatisfactory.

Breeding r a t i o s have a l s o been c a l c u l a t e d

f o r LiNO2 (13) and L i N O 3 (15); t h e r e s u l t s tend t o be q u i t e unfavorable. Impink (131, for example, obtained t h e value 0.82 f o r LiN02.'

No c a l c u -

l a t i o n s appear t o have been made f o r Li2SO4, but t h e high c r o s s s e c t i o n s f o r S ( n , d and S(n,p) r e a c t i o n s almost c e r t a i n l y w i l l reduce t h e breedi n g r a t i o below t h a t f o r L i 2 C O 3 .

Moreover, L i N O 2 and LiN03 l a c k t h e

thermal s t a b i l i t y required of t r u l y high temperature coolants, and Li2CO-j and L ~ ~ S OwCi ,l l o x i d i z e many CTR s t r u c t u r a l m a t e r i a l s .

Lithium hydroxide seems t o be eliminated, even i f ( a s i s u n l i k e l y )

i t s p r o p e r t i e s a r e otherwise s a t i s f a c t o r y , because i t s hydrogen would e x c e s s i v e l y d i l u t e t h e bred tritium.

Lithium oxide (Liz01 has a l i t h i u m

d e n s i t y n e a r l y 50% above t h a t of m e t a l l i c l i t h i u m , b u t i t s melting p o i n t of n e a r l y 1470OC (6) e l i m i n a t e s it as a major c o n s t i t u e n t of a blanket fluid.

Lithium c h l o r i d e melts a t 61OoC (6) and should be reasonably

compatible with C T R metals, but i t s breeding r a t i o (see Table 2) appears inferior. The s a l t w i t h t h e most favorable breeding r a t i o i s LiF.

This s a l t

i s i n e r t toward g r a p h i t e and t o metals under c o n s i d e r a t i o n f o r t h e b l a n k e t structure.

The major drawback of LiF i s i t s melting p o i n t of 848OC.

'In t h e same c o n f i g u r a t i o n he c a l c u l a t e d 1.15 f o r LizBeF4.

Because of t h i s high melting temperature, LiF cannot be used t o t r a n s f e r h e a t t o t h e steam system of t h e r e a c t o r .

If t h e blanket region were oper-

a t e d a t very high temperatures (>9OO0C), then LiF could be used i n conjunct i o n with an intermediate heat-exchange medium--liquid Na, a lower melting s a l t , or perhaps a b o i l i n g a l k a l i metal system.

The melting p o i n t o f LiF

can be s u b s t a n t i a l l y lowered by many s o l u t e s ; t h e i d e a l s o l u t e should lower t h e melting p o i n t below 374째C'0

without a f f e c t i n g e i t h e r t h e breeding gain

or t h e g e n e r a l l y favorable heat-removal and chemical p r o p e r t i e s of LiF. We know of no such s o l u t e .

Dissolved Liz0 should i n c r e a s e t h e breeding

r a t i o s l i g h t l y , b u t considering t h e probable l i m i t e d solubili-by of L i z Q , t h e melting temperature (more a c c u r a t e l y , l i q u i d u s temperature) of LiF w i l l n o t drop below 800째C.

Using AlF3 and/or another a l k a l i f l u o r i d e t o lower

t h e melting temperature t o -1700째C should n o t have d i r e chemical consequences, b u t t h e breeding r a t i o w i l l almost c e r t a i n l y s u f f e r . mation t o an i d e a l s o l u t e i n LiF i s probably EkF2.

The n e a r e s t approxiThe phase diagram f o r

LiF-BeF2 ( 3 0 ) , presented i n Fig. 1, shows t h a t a melting temperature as low

as 363OC i s a v a i l a b l e i n t h i s system.

Unfortunately, t h e v i s c o s i t y of t h e

melt i n c r e a s e s with BeF2 concentration, and mixtures with >40 mole have v i s c o s i t i e s g r e a t e r than 50 c e n t i p o i s e a t 45OoC (31).

BeF2

The optimum

s a l t mixture of low melting temperature and acceptable v i s c o s i t y , and w i t h a reasonably good tritium breeding r a t i o i s a t -33 mole

BeF2, correspond-

i n g t o t h e LizBeF4 used f o r i l l u s t r a t i v e purposes i n e a r l i e r s e c t i o n s of t h i s report.

Decreasing t h e BeF2 concentration below 33 mole

% may

have a

modest b e n e f i c i a l e f f e c t upon breeding r a t i o ; t h i s i n c r e a s e might, possibly, o f f s e t disadvantages posed by t h e increased l i q u i d u s temperature and l i k e l y changes i n chemical behavior. I n summary, t h e answer t o t h e f i r s t question posed above--the b e s t b l a n k e t coolant s a l t i n which t o breed tritium i s LiF, b u t i t s melting p o i n t of 848OC l i m i t s i t s u s e f u l n e s s only f o r cooling a b l a n k e t t h a t o p e r a t e s above t h i s temperature,

If t h e b l a n k e t coolant must a l s o t r a n s -

f e r h e a t t o t h e steam system, Li2BeF4, or some modest v a r i a n t of t h i s composition, appears t o be t h e b e s t choice, A p a r t i a l s e p a r a t i o n of breeding and cooling f u n c t i o n s , posed i n t h e

second question above, has been approached by S t e i n e r (12). "The

c r i t i c a l temperature of H20.

He c a l c u l a t e d

ORNL-DWG 71-5:

500

900

X (EUTECTIC) =0.$280+0.0004

= 459.1 ? 0.2

800

-tJ"

X (EUTECTIC= TIC= 0.531f0.002 002

700

Li28e& LlOUlO

400

-P

I I

600

0.30

ri. W

500 458.9

f0 . 2 T

400

0.35

0.40

0.45

0.50

0.55

"r-

r r

3 :

8eF2 (p-QUARTZ TYPE1 t LlOUlD

363.5 f 0 . 5 T

300

200

0.1

0.2

LI28eF4 t LiEeF3 I

0.3

0.4

LiEeF,

EeF, (8-OUARTZ TYPE1

227OC

0.5

0.6

0.7

u 0.8

0.9

XeeF, (mole fraction)

F i g . 1. Phase Diagram of t h e System LiF-EkF2.

1.0

t h e tritium breeding r a t i o f o r a b l a n k e t design i n which Li2BeF4 cooled t h e vacuum w a l l and l i t h i u m metal assumed t h e r e s t of t h e h e a t - t r a n s f e r f u n c t i o n , and showed t h a t t h e breeding r a t i o (1.22) was 8.3% l e s s than t h a t (1-33) f o r t h e same blanket with l i t h i u m as t h e s o l e c o o l a n t .

This

small l o s s i n breeding r a t i o suggests t h a t o t h e r s a l t s , e s p e c i a l l y t h o s e 0

melting below 374 C, might a l s o serve as vacuum-wall c o o l a n t s .

Moreover,

t h e h e a t c a r r i e d by t h e l i t h i u m might then be t r a n s f e r r e d o u t s i d e of t h e b l a n k e t t o a molten s a l t o f t h e same composition as t h e vacuwn-wall c o o l a n t . The s a l t streams from t h e vacuum w a l l and t h e l i t h i u m heat-exchanger would t h e n be combined and pumped t o t h e steam-raising system. mixture of L i C l and KC1, which m e l t s a t 354'C such s e r v i c e .

The e u t e c t i c

(321, might be s u i t a b l e f o r

The a u t h o r s a r e p r e s e n t l y a s s e s s i n g t h e i m p l i c a t i o n s o f

t h i s "double-coolant" concept I n p r i n c i p l e , a complete s e p a r a t i o n of breeding and cooling f u n c t i o n s might be embodied i n a b l a n k e t design i n which a molten s a l t c o o l s t h e vacuum w a l l , a moderately t h i c k r e g i o n o f quiescent l i t h i u m metal, and a graphite moderator-reflector

The c o o l a n t s a l t f o r t h i s a p p l i c a t i o n

must have g r e a t chemical s t a b i l i t y ( t o avoid d e l e t e r i o u s d e s t a b i l i z a t i o n a

i n t h e magnetic f i e l d and t o avoid c o r r o s i o n of t h e CTR m e t a l ) , sound h e a t t r a n s f e r p r o p e r t i e s , and, p r e f e r a b l y , a low f r e e z i n g p o i n t .

These

s p e c i f i c a t i o n s narrow t h e choice of major component t o f l u o r i d e s , c h l o r i d e s , and oxides, of l i g h t e r a l k a l i and a l k a l i n e e a r t h metals which melt below 12OO0C.

The l i s t seems t o c o n t a i n LiF, L i C 1 , NaF, N a C l , Na20, KF, KC1,

BeFz? MgC12, and CaC12 with, perhaps, o t h e r compounds o f t h e s e f a m i l i e s as p o s s i b l e minor c o n s t i t u e n t s of mixtures.

When one adds t h e f u r t h e r

requirement t h a t t h e c o o l a n t n o t lower t h e breeding r a t i o below u n i t y , t h e l i s t of u s e f u l major components becomes s m a l l e r .

The h i g h i n e l a s t i c

s c a t t e r i n g c r o s s s e c t i o n s f o r Mg, f o r example, probably e l i m i n a t e s any s u b s t a n t i a l c o n c e n t r a t i o n of MgCl2 from t h e c o o l a n t .

From c o n s i d e r a t i o n

of t h i s l i s t o f m a t e r i a l s it would appear t h a t LiF i s b e s t except f o r i t s h i g h m e l t i n g p o i n t , t h a t Li2BeF4 may w e l l be t h e b e s t o v e r a l l choice, and IIA p o s s i b l e r a t i o n a l e f o r such a design i s t h a t l i t h i u m , though providing a comfortable breeding r a t i o , cannot be made t o flow t u r b u l e n t l y w i t h i n the blanket and may r e q u i r e excessive power i n being pumped through t h e major magnetic f i e l d .

t h a t , i f subsequent c a l c u l a t i o n s show t h a t t h e breeding r a t i o does n o t s u f f e r unduly, t h e t e r n a r y e u t e c t i c LiF-NaF-KF (melting p o i n t 4 5 4 O C ) and t h e b i n a r y e u t e c t i c L i C 1 - K C 1 may be s u i t a b l e c o o l a n t s . P r a c t i c a l problems with t h e s e m a t e r i a l s w i l l d i f f e r i n d e t a i l from t h o s e described e a r l i e r f o r LizBeF4.

S u p e r f i c i a l examination of t h e s e

problems r e v e a l none t h a t seem insuperable, b u t much experimental study would be necessary before use of t h e s e m a t e r i a l s could be a s s u r e d .

MOLTEN SALTS I N LASER-INDUCED FUSION REACTORS

Two major u n c e r t a i n t i e s i n use o f LizEkF4 i n CTRs such as our hypot h e t i c a l device stem from (a) p o t e n t a i l l y troublesome i n t e r a c t i o n s w i t h t h e l a r g e magnetic f i e l d and (b) t h e f a c t t h a t t h e f i r s t (plasma-containi n g ) w a l l and b l a n k e t s t r u c t u r e degrade t h e neutron spectrum so t h a t t h e 7 L i (n,

a n ' ) T r e a c t i o n i s reduced and tritium breeding becomes marginal.

It i s , accordingly, a m a t t e r o f some i n t e r e s t t o examine b r i e f l y t h e p o t e n t i a l of molten s a l t s i n a CTR device which possesses n e i t h e r a magnetic f i e l d nor a f i r s t w a l l . Lubin and Fraas (33) have described a device i n which p e l l e t s o f deuterium and tritium produce a plasma upon i g n i t i o n by an energy p u l s e from a s u i t a b l e l a s e r .

The blanket-coolant f l u i d (Lubin and Fraas pro-

posed m e t a l l i c l i t h i u m ) i s pumped through t h e r e a c t i o n v e s s e l and through e x t e r n a l power generation equipment.

The l i q u i d i s pumped i n t o t h e

( e s s e n t i a l l y s p h e r i c a l ) r e a c t i o n v e s s e l t a n g e n t i a l l y t o provide a very r a p i d s w i r l ; i g n i t i o n of t h e p e l l e t occurs i n t h e v o r t e x so

formed on t h e v e r t i c a l c e n t e r - l i n e of t h e v e s s e l .

The plasma generated

i n t h i s pulsed device r e q u i r e s no magnetic containment, and t h e b l a n k e t coolant l i q u i d i s exposed d i r e c t l y t o r a d i a t i o n from t h e plasma. I n a d d i t i o n t o i t s c o o l a n t and breeding f u n c t i o n s such a l i q u i d must a l s o provide a t t e n u a t i o n of t h e severe shock waves s u f f i c i e n t t o a s s u r e f e a s i b i l i t y of t h e r e a c t o r v e s s e l .

Lubin and Fraas proposed t o a s s i s t

t h i s f u n c t i o n by i n t r o d u c t i o r of (compressible) gas bubbles i n t o t h e swirling liquid These shock waves a r e caused by (a) p a r t i a l conversion of n e u t r o n i c energy i n t o mechanical energy w i t h i n t h e l i q u i d , and (b) d e p o s i t i o n of x-ray energy i n t h e l i q u i d a t t h e v o r t e x s u r f a c e .

The former i s by f a r

t h e dominant p e r t u r b i n g f o r c e ( 3 4 ) .

According t o an a n a l y s i s by

Dresner ( 3 4 ) , t h e impulse t o t h e v e s s e l w a l l due t o t h e n e u t r o n i c a l l y induced shock i s p r o p o r t i o n a l t o CXpCP-l R1

i s t h e volume e x p a n s i v i t y , p i s t h e s o n i c v e l o c i t y , C i s t h e P s p e c i f i c h e a t , and R, i s a neutron a t t e n u a t i o n d i s t a n c e which depends

where

upon neutron s c a t t e r i n g and a b s o r p t i o n r e a c t i o n s .

The values of t h e s e

f o u r q u a n t i t i e s f o r Li.2BeF4 and f o r L i are:

(Oc-1)

LipBeF,: (6OOOC)

L i (6OOOC)

2.4

2.1

p (cm sec-1)

3.0

2.4

(erg g - l 0 c - l )

(11)

io5â&#x20AC;&#x153; io7 (11)

23 ( 3 4 )

R, (cm)

4.3 x 4.2 x

(35)

io5 io7

(36)

(35)

33 (34)

â&#x20AC;&#x153;Estimated. This a n a l y s i s suggests t h a t t h e walls of a v e s s e l f i l l e d with molten

LizBeF4 w i l l s u f f e r an impulse almost twice t h a t of an i d e n t i c a l v e s s e l f i l l e d with l i t h i u m metal.

This conclusion, coupled w i t h t h e f a c t t h a t

enhanced c e n t r i f u g a l f o r c e s (Li2BeF4 i s n e a r l y f o u r t i m e s as dense as L i )

w i l l make suspension of gas bubbles more d i f f i c u l t i n t h e s a l t , would seem t o p l a c e LizBeFq a t some disadvantage. l 2

It seems apparent, however, t h a t design and c o n s t r u c t i o n of t h i s v e s s e l t o withstand r e p e a t e d shocks over a long l i f e will pose formidable problems.

M e t a l l i c l i t h i u m a t temperatures of 5OO0C and above i s l i k e l y

t o prove compatible w i t h r e l a t i v e l y few (and g e n e r a l l y expensive and exotic) materials.

It i s p o s s i b l e t h a t Li2BeF4 (or o t h e r s a l t s ) , which

a r e compatible w i t h a much wider spectrum of metals may have r e a l

advantages i n e a s i n g t h i s d i f f i c u l t design problem. Problems with chemical transmutations and with recovery and management of tritium seem g e n e r a l l y similar t o , and should be handled by methods l i k e , t h o s e described above f o r t h e h y p o t h e t i c a l t o r o i d a l device.

l 2 D i f f e r e n c e s i n l i q u i d p r o p e r t i e s w i l l probably be r e l a t i v e l y unimportant i n a t t e n u a t i n g t h e shock waves. The e n t r a i n e d bubbles almost c e r t a i n l y w i l l be t h e p r i n c i p a l shock-absorbers.

seems l i k e l y t h a t t h e e a s e of tritium recovery may g i v e t h e molten s a l t s an a d d i t i o n a l advantage. F i n a l l y , it should be noted t h a t t h e absence of t h e f i r s t w a l l l e a d s t o decidedly improved breeding.

M e t a l l i c l i t h i u m w i l l s t i l l prove t o

possess t h e h i g h e s t r a t i o s , b u t it seems c e r t a i n t h a t Li2BeF4 w i l l have v a l u e s markedly above u n i t y .

Indeed, it i s l i k e l y t h a t s e v e r a l l i t h i u m -

b e a r i n g s a l t compositions would be p o s s i b l e b r e e d e r s i n t h i s s o r t of laser-powered CTR.

SUMMARY: GENERAL COMPARISON OF MOLTEN SALTS W I T H LITHIUM I N FUSION REACTORS I n summary, and t o supplement t h e s e v e r a l preceding d i s c u s s i o n s , we b r i e f l y compare l i q u i d l i t h i u m w i t h s a l t s ( e s p e c i a l l y LizEkF4) i n s e v e r a l regards. L i t h i u m m e t a l i s c l e a r l y s u p e r i o r t o any molten s a l t i n breeding of

tritium; t h i s seems c e r t a i n l y t r u e i n any CTR embodiment.

C e r t a i n pro-

posed d e s i g n s , of which t h e laser-powered devices a r e t h e b e s t examples, can c e r t a i n l y breed s u f f i c i e n t tritium using molten s a l t s a l o n e .

However,

t h e i n d i c a t i o n t h a t tritium breeding i s marginal f o r t h e s a l t s i n some ( i f n o t most) designs r e p r e s e n t s t h e worst drawback t o t h e i r use.

Fluo-

r i d e s a l t s are a l s o i n f e r i o r t o l i t h i u m i n t h a t , p r i m a r i l y because of f l u o r i n e ' s r e l a t i v e l y h i g h c r o s s - s e c t i o n for i n e l e a s t i c neutron s c a t t e r i n g , t h e salts a r e more i n t e n s e gamma s o u r c e s and cause i n c r e a s e d gamma h e a t i n g of t h e vacuum w a l l (12).

T r i t i u m recovery should prove considerably simpler i f molten s a l t s a r e used; t h i s i s p a r t i c u l a r l y t r u e i f t h e tritium can be maintained as TF t o minimize d i f f u s i o n through m e t a l l i c walls. S e v e r a l of t h e p h y s i c a l p r o p e r t i e s of l i t h i u m (thermal c o n d u c t i v i t y , s p e c i f i c h e a t , v i s c o s i t y and m e l t i n g p o i n t , f o r example) a r e s u p e r i o r t o t h o s e of t h e molten s a l t .

However, s i n c e t h e magnetic f i e l d w i l l prevent

t u r b u l e n t flow i n t h e b l a n k e t f o r l i t h i u m , b u t n o t for t h e s a l t , it may be t h a t t h e molten s a l t i s a b e t t e r h e a t t r a n s f e r medium f o r such a CTR. Lithium i s compatible with r e l a t i v e l y few s t r u c t u r a l m e t a l s , niobium a l l o y e d with 1% zirconium appears t o be a s u i t a b l e c o n t a i n e r ( 3 5 ) .

More-

over, l i t h i u m r e a c t s w i t h g r a p h i t e , and t h i s m a t e r i a l must c e r t a i n l y be

25 c l a d i f it i s t o serve i n a lithium-cooled b l a n k e t assembly.

Molten

LizBeFA i s compatible w i t h g r a p h i t e and with a wide v a r i e t y of s t r u c t u r a l metals.

Corrosion by t h e s a l t i s p o s s i b l e , through i n t e r a c t i o n with

s t r o n g magnetic f i e l d s , but such corrosion can apparently be avoided by c a r e f u l design.

Transmutations w i t h i n t h e s a l t , which provide p o t e n t i a l

f o r c o r r o s i v e r e a c t i o n s , can be accommodated by r e l a t i v e l y simple means. Reactions of s a l t s with steam or with a i r produce a c c e l e r a t e d corrosion b u t , u n l i k e similar r e a c t i o n s of l i t h i u m , l e a d t o no i n h e r e n t l y hazardous c o n d i t i o n s . It i s c l e a r l y not p o s s i b l e a t t h i s s t a g e of t h e technology t o p r e d i c t

w i t h confidence how t h e problems i n h e r e n t i n use of molten s a l t s (or of l i t h i u m ) w i l l be solved.

It i s e n t i r e l y p o s s i b l e t h a t both l i t h i u m and

molten s a l t s w i l l be u s e f u l .

A t any event, and r e g a r d l e s s of t h e u l t i m a t e

choice, it i s c l e a r t h a t many f a s c i n a t i n g chemical r e s e a r c h and development ventures l i e ahead. ACKNOWLEDGMENTS The a u t h o r s a r e i n d e b t e d 3 0 Don S t e i n e r for h i s c a l c u l a t i o n of t r i t i u m - b r e e d i n g r a t i o s , t o Lawrence Dresner f o r h i s a n a l y s i s of shock a t t e n u a t i o n , and t o R . A. Strehlow and W. K. S a r t o r y f o r much h e l p f u l discussion.

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27 P. E. F i e l d and J. H. Shaffer, "The s o l u b i l i t i e s of HF and DF i n Molten F l u o r i d e s , " J . Phys. Chem. 71, 3218 (1967). 20. C. F, Baes, Jr., "The Chemistry anaThermodynamics of Molten S a l t Reactor Fuels," Nuclear Metallurgy, Vol. 15 (ed., P. C h i o t t i ) , CONF-690801, U. S Atomic Energy Commission (1969), p. 624. D. D. Wagman e t a l . , "Selected Values of Chemical Thermodynamic 21. P r o p e r t i e s , " Technical Notes 270-3, 4 , 5 , U.S. National Bureau of Standards, Washington, D , C . , 1968, 1969, 19'71. 22. S. Senderoff and G. W. Mellors, "Coherent Coating of Refractory Metals," Science 153, 1475 (1966). 23. J. Wischhusen, M a t e r i a l s Engineering 74(1), 35 (1971). 24. G. M. Watson, R. B. Evans 111, W. R. Grimes, and N. V. Smith, " S o l u b i l i t y of Noble Gases i n Molten F l u o r i d e s , " J. Chem. Eng. Data 7, 285 (1962). 25. E. E. Thoma, Chemical Aspects of MSRE Operations, ORNL-4658, (Dec. 1971) pp. 68-71. 26. P. N. Haubenreich and J. R. Engel, "Experience w i t h t h e Molten S a l t Reactor Experiment, Nucl. Appl. Tech. 8 (2), 118 (1970) 27. W. R. Grimes, Chemical Research and Devglopment f o r Molten S a l t Breeder Reactors, O W CF-66 4 - 4 1 (1966), pp. 45-55. 28. B. F. Hitch and C. F. Baes, Jr., Reactor Chemistry Division Annual Progress Report Dec. 31, 1966, ORNL-4076, p. 20. 29. J. H. S h a f f e r , P r e p a r a t i o n and Handling of S a l t Mixtures f o r t h e Molten S a l t Reactor Experiment, ORNL-4616 (Jan. 1971) 30. K. A. Romberger, J . Braunstein, and R. E. Thoma, "New Electrochemical Measurements-of. t h e Liquidus i n t h e LiF-BeF2 System. Congruency of Li2BeF&," J . Phys. Chem. 76, 1154 (1972). 31. S. Cantor, W. T. Ward, a n d C . T. Moynihan, "Viscosity and Density i n Molten BeF2-LiF S o l u t i o n s , " J . Chem. Phys. 50, 2874 (1969). i n Molten 32. E. Adcrust, B. Bjarge, H. Flood, T. F4rland;"Activities S a l t Mixtures of Potassium-Lithium Halide Mixtures: A Preliminary Report," Annals New York Acad. S c i . 79, A r t . 11, 830-837 (1960). 21 33. M. J. Lubin and A. I?. Fraas, " F u s i o n b y L a s e r , " S c i . h e r . g, (1971). 3 4 . L. Dresner, Oak Ridge National Laboratory, personal communication. 35. J. 0. Cowles and A. D. Pasternak, Lithium P r o p e r t i e s Related t o Use as a Nuclear Reactor Coolant, UCRL-50647, Lawrence Livermore Radiation Laboratory (Apr. 18, 1969). 36. I. I. Novikov, Y. S. T r e l i n , T. A. Tsyganova, "Experimental Data on t h e Speed o f Sound i n Lithium up t o llOO째K," High Temperature (Transl a t e d Russian J o u r n a l ) 7 (6), 1140 (1969). 19.

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