Metal Bonding and Interactions in High ... - ACS Publications

33 Use of Lithium in Fusion Reactors J. A . B L I N K

and O . H. K R I K O R I A N

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 11, 2016 | http://pubs.acs.org Publication Date: March 8, 1982 | doi: 10.1021/bk-1982-0179.ch033

Lawrence Livermore National Laboratory, Livermore, CA 94550 N . J. H O F F M A N Energy Technology Engineering Center, Canoga Park, CA

The use of lithium as a solid compound, a pure melt, or a molten alloy is required for tritium breeding in at least the first generation of fusion reactors. Three fusion reactor concepts are discussed with emphasis on material selection and material compatibility with lithium. Engi neering details designed to safely handle molten lithium are described for one of the example con cepts. Tritium recovery from the various breeding materials is reviewed. Finally, two aspects of the use of molten Li-Pb alloys are discussed: the solubility of hydrogen isotopes, and the influence of the alloy vapor on heavy ion beam propagation. Fusion research o f f e r s the p o t e n t i a l to use the nuclear binding energy of l i g h t elements such as hydrogen. Release o f fusion energy requires heating the n u c l e i to about 10 keV (10** K) and c o n f i n i n g the plasma f o r s u f f i c i e n t time f o r f u s i o n to occur i n a reasonable f r a c t i o n of the n u c l e i . The q u a l i t y o f confinement ( d e n s i t y - confinement time product) and the plasma temperature are the figures of merit f o r the f u s i o n process. There are two approaches to achieve an acceptable q u a l i t y o f confinement. In magnetic confinement f u s i o n (MCF), a plasma with d e n s i t y o f about 1 0 ^ n u c l e i per cm-* (10~5 times the density of a i r ) must be confined f o r periods of many seconds. In i n e r t i a l confinement f u s i o n (ICF), the plasma con finement time i s determined by the i n e r t i a of the heated n u c l e i ( ^ 3 x 1 0 " ^ seconds); the corresponding d e n s i t y i s about one thousand times the normal l i q u i d d e n s i t y of the f u e l or 12 times the d e n s i t y o f lead. * Work p a r t i a l l y performed under the auspices o f the U. S. Department of Energy by Lawrence Livermore N a t i o n a l Laboratory under contract number W-7405-ENG-48. 0097-6156/82/0179-0497$11.50/0 © 1982 A m e r i c a n Chemical Society

In Metal Bonding and Interactions in High Temperature Systems; Gole, James L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


498

METAL BONDING AND INTERACTIONS

The f u s i o n r e a c t i o n l e a s t d i f f i c u l t to i n i t i a t e i s the deuterium-tritium (DT) r e a c t i o n which releases a 14.1 MeV neutron and a 3.5 MeV alpha p a r t i c l e . However, because neutrons a c t i v a t e the reactor s t r u c t u r e , other f u s i o n reactions have been considered. These r e a c t i o n s are e i t h e r neutron f r e e , or they produce fewer and l e s s energetic neutrons. The required q u a l i t y of confinement f o r these more d e s i r a b l e fusion r e a c t i o n s i s much higher than f o r DT, and i t i s not yet c l e a r i f i t w i l l be achieved. Hence, f u s i o n r e a c t o r designers have concentrated on the DT r e a c t i o n f o r at l e a s t the f i r s t generation of f u s i o n plants. Deuterium i s present i n o r d i n a r y sea water at a concentrat i o n o f one atom per 3300 water molecules, and i t can be inexpensively e x t r a c t e d . T r i t i u m i s r a d i o a c t i v e with a 12.3 y h a l f l i f e , and there i s no abundant n a t u r a l source. However, t r i t i u m can be produced i n a f u s i o n r e a c t o r by absorbing the neutrons i n l i t h i u m (Figure 1). N a t u r a l L i i s 92.5% L i and 7.5% L i . The L i nucleus can absorb a f a s t (above 3 MeV) neutron to produce a t r i t i u m nucleus, an alpha p a r t i c l e , and a slower neut r o n . A moderated neutron can be absorbed by a ^ L i nucleus to produce a t r i t i u m and an alpha. Neutronic c a l c u l a t i o n s i n d i c a t e that a t h i c k sphere o f n a t u r a l l i t h i u m could breed about 1.8 t r i t i u m atoms f o r each t r i t i u m atom burned i n a f u s i o n r e a c t i o n (O. Structure and portions o f the volume l e f t open for f u e l i n g or d r i v e r beams reduce the 1.8 t r i t i u m breeding r a t i o . I f the r a t i o f a l l s below 1.0, i t may be increased by a d d i t i o n o f a neutron m u l t i p l i e r such as Be or Pb, and by i s o t o p i c a l l y e n r i c h i n g the L i i n °Li. 7

6

7

L i t h i u m and i t s compounds may be used i n f u s i o n r e a c t o r s i n e i t h e r l i q u i d or s o l i d form. L i q u i d L i i s an e x c e l l e n t coolant with low d e n s i t y and v i s c o s i t y , and with high heat c a p a c i t y and thermal c o n d u c t i v i t y (Table 1). Consequently, i t i s used i n many designs as a combined breeding m a t e r i a l and coolant. However, hot molten L i can react v i o l e n t l y with water or a i r under certain conditions. Hence, e i t h e r s t r i c t engineering design must preclude large s c a l e L i - a i r or water r e a c t i o n s , or another form o f L i must be used. Both approaches have been studied. Molten Li-Pb s o l u t i o n s o f s e v e r a l compositions have been suggested for f u s i o n r e a c t o r s . These include LiggPb^ which is pure L i contaminated with 1 a/o Pb from ICF target d e b r i s , and Pbg3Li].7 which i s a eu tec t i c composition with chemical p r o p e r t i e s s i m i l a r to Pb. A phase diagram of the Li-Pb system is shown i n Figure 2. S o l i d phase l i t h i u m compounds such as L i 2 0 , LiA102> Li2Zr03, or Li4Si04 have been proposed for f u s i o n r e a c t o r s . An example i s the STARFIRE Tokamak blanket conceptual design i n which a packed bed o f h i g h l y porous alpha-LiA102 i s used to absorb neutron energy and breed t r i t i u m (4) (Figure 3).


BLINK ET AL.

Lithium

in Fusion

Reactors


33.


499

500

METAL

BONDING AND

INTERACTIONS

Atomic percent Pb in Pb-Li system


0

150' 0

0.5

i

I 10

L_J 20

1

1.5

i

2

77

I

, I I

I

30

40

99.0

80

i

I 99.2

85

i

90

95

100

I i I i I i 99.4 99.6 99.8 100

Weight percent Pb in Pb-Li system Figure 2.

Figure 3.

Phase diagram oj the LiPb system.

The STARFIRE

tritium breeding blanket (A).


33.

BLINK ET AL.

Lithium

Table I .

in Fusion

Comparison of

Coolant P r o p e r t i e s

Li

3

Na

H0 2

480

830

840

0.36

0.24

0.12

M e l t i n g p o i n t , °C

181

98

0

B o i l i n g p o i n t , °C

1347

883

100

4170

1260

4570

50

67

Density,

kg/m

V i s c o s i t y , MPa-s


501

Reactors

Heat c a p a c i t y , J/(kg

K) #

Thermal c o n d u c t i v i t y , W/(m K)

0.65

• Temperature dependent L i and Na p r o p e r t i e s evaluated at 500°C (Ref.2).

• Temperature dependent water p r o p e r t i e s evaluated at 13.7

MPa

(2000 p s i ) and 230°C (440°F) (from Ref. 3.).

The t r i t i u m d i f f u s e s to the g r a i n boundaries, migrates through the g r a i n boundaries to the p a r t i c l e s u r f a c e , and then percol a t e s through the packed bed to low pressure helium purge channels. Heat i s removed by p r e s s u r i z e d water flowing i n a s t a i n l e s s s t e e l tube network i n the packed bed. The next s e c t i o n s d e s c r i b e three r e a c t o r studies with emphasis on the l i t h i u m - s t r u c t u r e c o m p a t i b i l i t y . HYLIFE i s a l i q u i d metal w a l l (LMW) ICF reactor considered here f o r e l e c t r i c i t y production. I t has also been adapted to f i s s i l e f u e l production (5). The Tandem M i r r o r Reactor (TMR) Cauldron Blanket Module i s an MCF concept designed to produce hydrogen. The TMR Heat Pipe Blanket Module i s designed to produce e i t h e r hydrogen or e l e c t r i c i t y . A l l three studies emphasize m a t e r i a l s compatib i l i t y with l i t h i u m . T r i t i u m recovery techniques and two aspects of l e a d - l i t h i u m l i q u i d s are also d i s c u s s e d . The HYLIFE Design (6,_7) Design Concept. The High Y i e l d L i t h i u m I n j e c t i o n Fusion Energy chamber design (HYLIFE) uses 175 j e t s of 0.2 m diameter to absorb the energy from 1800 MJ - 1.5 Hz ICF pulses



502

METAL BONDING AND

INTERACTIONS

(Figure 4). The free f a l l i n g j e t s are grouped i n t o an annular 50% packing f r a c t i o n array with a 0.5-m inner radius (Figure 5). The array has an e f f e c t i v e thickness of 0.74 m, and i t s h i e l d s the 5-m-radius f i r s t s t r u c t u r a l wall from x-rays, debris and 95% of the neutron energy. Due to t h i s s h i e l d i n g , the s t r u c t u r a l wall i s predicted to survive f o r 30 years without replacement. The j e t s are arranged to allow two-sided i l l u m i n a t i o n of the target by two-36 m^ arrays of mirrors set back 60 m from the chamber center (Figure 6 ) . The j e t array is comp l e t e l y disassembled and r e e s t a b l i s h e d between f u s i o n pulses (Figure 7). -.Only ^ 4% of the 1800-MJ fusion y i e l d i s converted to k i n e t i c energy of l i q u i d or gas; hence, the w a l l can be designed to survive the fatigue loading of the 10^ pulses that occur i n a 30-year l i f e t i m e . Several other ICF reactor concepts use l i q u i d metal w a l l s (UMW). These include the Los Alamos N a t i o n a l Laboratory (LANL) wetted wall concept, the Bechtel concept c a l l e d EAGLE (which uses a l i t h i u m spray i n the chamber), the Lawrence Livermore N a t i o n a l Laboratory (LLNL) concept c a l l e d JADE (which uses a fiber-metal s t r u c t u r e to c o n t r o l l i q u i d metal flow), and the German/University of Wisconsin concept c a l l e d HIBALL (which uses carbide "socks" to c o n t r o l l i q u i d metal flow). HYLIFE Lithium Flow. The l i t h i u m j e t s are i n j e c t e d i n t o the 8-m-high HYLIFE chamber with 9.5 m/s i n i t i a l v e l o c i t y (72.2 m /s flow r a t e ) . A d d i t i o n a l coolant i n the neutron r e f l e c t o r increases the flow to 86.2 m /s. The mixed-mean temperature r i s e i n the l i t h i u m i s 18 K, and the peak l i t h i u m temperature i s 500°C Eleven r e c i r c u l a t i o n pumps, each wi th 7.8 m / sec (124,000 gpm) capacity, return the l i t h i u m to the top of the v e s s e l . About 9.8 m /s i s d i v e r t e d from the flow loop to four Li-Na intermediate heat exchangers which i n turn d r i v e twelve steam generators. The plant gross e l e c t r i c power i s 1236 MW; 135 MW i s used to d r i v e the 4.5 MJ - 5 % e f f i c i e n t l a s e r , 95 MW is used elsewhere i n the p l a n t , and 1006 MW is the net power. 3

3

3

3

e

Lithium-Structure C o m p a t i b i l i t y . One of the c r i t i c a l chemi s t r y problems of HYLIFE i s the c o m p a t i b i l i t y of s t r u c t u r a l a l l o y s with the molten l i q u i d of the j e t array. Two candidate l i q u i d metals are l i t h i u m and Pbg3Lii7. High-Z metal (such as lead from target debris) w i l l enter the l i q u i d metal and may a f f e c t the c o m p a t i b i l i t y . The s t r u c t u r a l a l l o y s e l e c t e d i n the HYLIFE study i s 2h Cr-1 Mo, a f e r r i t i c s t e e l . The carbides u s u a l l y present i n t h i s s t e e l are M3C (cementite) and M2C, where M is p r i m a r i l y Fe. Both of these carbides are unstable i n l i t h i u m . M3C i s u s u a l l y present as p l a t e l e t s w i t h i n p e a r l i t e , the eutectoid s t r u c t u r e i n p e a r l i t i c s t e e l . The most common microstrueture for the 2h Cr-1 Mo s t e e l i s large grains of f e r r i t e with small i s l a n d s of p e a r l i t e . M2C i s present as a f i n e spray of p r e c i p i t a t e w i t h i n large f e r r i t e g r a i n s . Lithium



BLINK ET AL.

Lithium

in Fusion

Reactors

503

hi

s



504


Figure 5.

HYLIFE

midplane cross section.



BLINK ET A L .

Lithium

Figure 6.

in Fusion

Reactors

H YLIFE driver-beam port protection.


505


:o

o 7 rows of jets ( ~ 175 total) 25 jus 40 ms

-&P/iS

Figure 7.

HYLIFE

jet array response to a fusion pulse.

Cavitated liquid V - 70 m/s

X-ray pulse has spalled the inner jets

Two phase mixture converging on center

Thermal radiation being absorbed, producing more two phase material

10 ns

(

Expanding hot vapor radiating to the

Jets exploding from neutron energy, V ~ 100 m/s

Ablated vapor

Hot vapor moving through jets V > 1000 m/s

Debris front

Neutron front


Wall

Neutron energy has increased the internal pressure of all jets

2

O

O H

H W

3

o g 3 o > o

w

> r

w H

o


33.

BLINK ET

AL.

Lithium

in Fusion

507

Reactors

w i l l attack the f i n e spray of exposed M2C and the p l a t e l e t s of M3C which i n t e r s e c t the s u r f a c e . Heat treatments have been developed which convert the unstable M3C and M2C to M7C3, M23C5, and M5C which are C r - r i c h carbides that are s t a b l e i n l i t h i u m (Figure 8) (8). I f 2h Cr-1 Mo s t e e l i s welded, a region of s t e e l near the molten weld is heated high enough to convert the pear l i t e plus f e r r i t e to a u s t e n i t e . A continuous f i l m of M3C can form around the austenite g r a i n s (Figure 9). As t h i s hot heataffected-zone (HAZ) c o o l s , the austenite decomposes to f e r r i t e and pear l i t e , but a ghost of the p r i o r austenite g r a i n boundary remains. This ghost boundary i s made up of the f i l m of M3C and p o s s i b l y other impurities deposited i n the austenite boundary. Since such a f i l m may be continuous i n a weld HAZ, lithium r e a c t i o n along the f i l m can be c a t a s t r o p h i c ; t h e r e f o r e , post weld heat treatment could be r e q u i r e d . The M3C and M2C carbides are s t a b l e i n bg31.^7 melt; however, t h i s high lead melt may create l i q u i d metal embrittlement problems. Indeed, crack propagation of 2h Cr-1 Mo s t e e l could p o s s i b l y be accelerated by e i t h e r l i q u i d . Since f a t i g u e damage i s a major concern to the HYLIFE concept, studies have begun r e l a t i n g the number of c y c l e s required to propagate a crack a c e r t a i n d i s t a n c e to both temperature and s t r a i n r a t e . The general trends of such a r e l a t i o n s h i p are shown i n F i g u r e 10. The s t r e s s l e v e l i n an a l l o y may also a f f e c t the c o r r o s i o n rate i n l i t h i u m . F a i l u r e s of bellows and sharp cornered channels have o f t e n been noted i n l i t h i u m systems. This i s contrary to considerable experience i n sodium and to recent experiments at the Colorado School of Mines (Figure 8), and the subject i s s t i l l c o n t r o v e r s i a l . High n i t r o g e n content (> 100 ppm) i n l i t h ium c e r t a i n l y increases the c o r r o s i o n rate and might be a prereq u i s i t e f o r s t r e s s - r e l a t e d increases i n the c o r r o s i o n r a t e . In a d d i t i o n , the r o l e o f hydrogen i n l i t h i u m i s b e l i e v e d to be c r i t i c a l i n a l l these c o m p a t i b i l i t y s t u d i e s , but no research has yet begun on t h i s t o p i c . L i q u i d metal w a l l s i n ICF r e a c t o r s w i l l become contaminated with target d e b r i s . In a d d i t i o n to posing c o m p a t i b i l i t y problems, these contaminants a f f e c t pumping power, pump l i f e , and radioactive inventory. Thus, methods of removing contaminants, p a r t i c u l a r l y high-Z elements, from l i q u i d l i t h i u m are r e q u i r e d . For example, no economical method to remove Pb to below 1 a/o (23 w/o) i n L i has been devised. p

HYLIFE Safety Engineering. In order f o r an accident i n a l i q u i d l i t h i u m cooled fusion r e a c t o r to endanger the general p u b l i c , the accident must i n v o l v e l a r g e s c a l e r e a c t i o n of hot molten l i t h i u m with a i r , water, or concrete. F u r t h e r , the r e a c t i o n heat must be coupled to r a d i o a c t i v e components e i t h e r d i r e c t l y i n the flame, or i n d i r e c t l y v i a heated gas. Therefore, f u s i o n reactor designers t r y to preclude even a remote p o s s i b i l i t y that such r e a c t i o n s and heat t r a n s f e r can take p l a c e .


BONDING AND

INTERACTIONS


METAL

(uiiu) 3N0Z Q 3 1 0 3 d d V l V 3 H NI NOIlVHJL3N3d aVlflNVaOU31NI ΙΛΙΠΙΑΙΙΧνίΑΙ

Ε ΐ



33.

BLINK ET AL.

Lithium in Fusion Reactors

509

Figure 9. Microstructure oj 2 ¥4 Cr-1 Mo steel. Key.C , ferrite grain peppered with M C;£, pearlite (platelets of alternating M C and ferrite) and?;- , ghost boundary of prior austenite grain boundary. 2

3

Figure 10. Relationship of crack propagation resistance to strain rate and temperature. Thermally stabilized 2V4 Cr-1 Mo in high-N Li. Stress intensity factor, K = 20.0; and fatigue load ratio, R — 0.0\



510


As an example of i n t r i n s i c s a f e t y f e a t u r e s , consider the HYLIFE design. The HYLIFE r e a c t o r room has no e x t e r n a l w a l l s or roof; i t i s surrounded by other rooms and covered with a crane loft. The r e a c t o r room contains an i n e r t gas (no a i r ) . The e n t i r e L i inventory can be drained i n minutes i n case of an a i r leak i n t o the room; such a leak would require hours before l i t h ium combustion i s p o s s i b l e . There are no water or steam components i n the r e a c t o r room, and a l l concrete i s s t e e l l i n e d . The l i t h i u m loop is everywhere sub-atmospheric pressure (1 Pa to 80 kPa or 10~2 to 620 T o r r ) ; hence, small leaks w i l l be inward. Large leaks w i l l f a l l on a sloped f l o o r that drains to t a l l narrow tanks c o n t a i n i n g hollow graphite spheres that would f l o a t above s p i l l e d l i t h i u m . A d d i t i o n a l i n e r t gas i n j e c t i o n c a p a b i l i t y w i l l be a v a i l a b l e i n these areas. These design features e l i m i n a t e almost a l l pathways to a s e r i o u s accident, but e l i m i n a t i o n of the l i t h i u m chemical energy would be even b e t t e r . Hence, the i d e a l DT f u s i o n reactor would u t i l i z e l i t h i u m that i s combined with other elements to produce a f l u i d that i s not r e a c t i v e with a i r or water, but s t i l l r e t a i n s the low d e n s i t y and high heat c a p a c i t y of pure l i t h i u m . Various l e a d - l i t h i u m s o l u t i o n s have been considered, but none f u l l y s a t i s f y these c r i t e r i a . The

TMR

Cauldron Blanket

Module

Design Concept. Thermochemical c y c l e s f o r hydrogen product i o n lend themselves w e l l to use of a Tandem M i r r o r Reactor (TMR) heat source with a l i q u i d L i blanket design. This linkage of a thermochemical hydrogen c y c l e to a TMR i s favorable f o r s e v e r a l reasons: (9) • the c e n t r a l c e l l o f the TMR allows the design of r e l a t i v e l y simple and r e a d i l y a c c e s s i b l e blanket modules, • the process heat and maximum temperature requirements for a thermochemical cycle are w i t h i n the performance a v a i l a b l e from l i q u i d L i blankets, and • advanced TMR designs provide high e f f i c i e n c y e l e c t r i c a l power (through d i r e c t c o n v e r t e r s ) , which i s d e s i r able i n some thermochemical c y c l e s . A c r o s s - s e c t i o n a l view of the lithium-sodium Cauldron Blanket Module that has been under study at LLNL and the U n i v e r s i t y of Washington i s shown i n Figure 11. Although the module resembles a pool b o i l e r , i t i s s u b s t a n t i a l l y more complicated due to the non-symmetric geometry, the exponential energy generation i n the f l u i d contained w i t h i n the module, and a l s o due to MHD e f f e c t s on the convective mixing of the l i q u i d pool. The Li-Na l i q u i d metal i n the Cauldron Blanket Module acts as a neutron moderator, heat t r a n s f e r f l u i d , and t r i t i u m producer. Heat i s removed by v a p o r i z i n g the sodium. The v o i d f r a c t i o n


BLINK ET A L .

Lithium

in Fusion

Reactors


The cauldron concept-housing a hot fluid in a cool container

Figure 11.

TMR cauldron blanket module.



512

METAL BONDING AND

INTERACTIONS

created i n the l i q u i d pool by the v a p o r i z i n g sodium i s an inherent l i m i t a t i o n of the Cauldron concept. The Na vapor, t r a v e l i n g at vapor v e l o c i t i e s of roughly 8-10 m/s at 1200 K, condenses on the heat exchanger tubes i n the dome (the condensing vapor heat exchanger, CVHX) and returns as l i q u i d droplets to the pool, thus completing the c y c l e . In the dome, the CVHX t r a n s f e r s the thermal energy out of the module to various chemical processors located some d i s t a n c e from the reactor. L i t h i u m and Na are b e l i e v e d to be m i s c i b l e under the operat i n g c o n d i t i o n s , and t r i t i u m production with a 50-50 Li-Na atomic mixture i s c a l c u l a t e d to be greater than 1.0. Lithiumpotassium mixtures are a l s o of i n t e r e s t f o r the Cauldron concept. Success of the Cauldron concept depends i n part upon containment of the very hot f l u i d (1200 K) i n a c o o l c o n t a i n e r . This i s accomplished by e s t a b l i s h i n g a steep temperature g r a d i ent across a thickness of i n s u l a t o r m a t e r i a l i n t e r v e n i n g between the hot f l u i d and the s t r u c t u r a l container i t s e l f . Satisfactory i n s u l a t i o n can be obtained from a f i b e r - m e t a l , such as the commercial product c a l l e d F e l t m e t a l , which can be f a b r i c a t e d from a number of m e t a l l i c m a t e r i a l s to give an e f f e c t i v e thermal c o n d u c t i v i t y , k , t a i l o r e d to the needs of the problem. In t h i s p a r t i c u l a r case, k i s about 0.175 W/m K. Two important features of fiber-metal are i t s s u b s t a n t i a l compressive strength and i t s low shear s t r e n g t h . The Cauldron a p p l i c a t i o n loads the m a t e r i a l i n compression, due to the h y d r o s t a t i c head of f l u i d and due to the sodium vapor pressure. The 500 K temperature gradient across the i n s u l a t o r m a t e r i a l , with the d i f f e r e n t i a l expansion i t creates, is accommodated by a l l o w i n g the f i b e r metal f i b e r s to s l i d e on one another. To e s t a b l i s h the temperature gradient and to c o n t r o l the f i b e r - m e t a l c o n d u c t i v i t y , the coolant flow i s c o n t r o l l e d i n the f i r s t w a l l heat exchanger (FWHX). The FWHX i s i n t e g r a l with the f i r s t w a l l s t r u c t u r e , as may be seen from the i n s e t i n F i g u r e 11. e

#

e

M a t e r i a l S e l e c t i o n . I n i t i a l s e l e c t i o n s of m a t e r i a l s have been made f o r the most c r i t i c a l elements i n the Cauldron design: • Cooled f i r s t w a l l p o r t i o n of the s t r u c t u r a l envelope • Fiber-metal i n s u l a t o r • Cauldron w a l l (membrane) • Condensing vapor heat exchanger • T r i t i u m permeation membranes In s e l e c t i n g the m a t e r i a l s (10), major emphasis i s given to neutron a c t i v a t i o n and r a d i a t i o n damage e f f e c t s i n m a t e r i a l s c l o s e to the plasma and f u r t h e r c o n s i d e r a t i o n s are given to other f a c t o r s such as c o r r o s i o n , long-term creep s t r e n g t h , f a b r i c a t i o n technology, and c o s t . From the standpoint of low neutron a c t i v a t i o n combined with good r a d i a t i o n damage r e s i s t a n c e , V and T i a l l o y s present the best m a t e r i a l s prospects f o r the region near the plasma. The



33.

BLINK ET A L .

Lithium

in Fusion

Reactors

513

current choices f o r the f i r s t w a l l are V-10% T i and V-20% T i , since both of these a l l o y s have been shown to suppress helium gas bubble formation. F u r t h e r , t r i t o n impact should not cause problems of l o c a l i z e d t r i t i u m buildup and b l i s t e r i n g , since t r i tium i s known to permeate very r a p i d l y through V and i t s alloys. The technologies o f producing V a l l o y sheet and tubing and o f f a b r i c a t i o n by e l e c t r o n beam welding are w e l l e s t a b l i s h e d and present no problems as long as i n t e r s t i t i a l 0, N, and H are kept at low l e v e l s . The current cost o f V i s high (^$440/kg), but V resources are extensive and cost reductions can be expected f o r q u a n t i t y use. Even at $440/kg, the cost i s not excessive f o r the TMR f i r s t w a l l (^$10M). Corrosion should not be a problem i f l i q u i d Na or helium i s used as a coolant. I f organic l i q u i d s (polyphenyIs) are used, the coolant would need to be continuously p u r i f i e d to avoid carbon d e p o s i t i o n i n the tube passages due to r a d i a t i o n damage. Beta-Ti a l l o y s are under c o n s i d e r a t i o n as a backup m a t e r i a l for the f i r s t w a l l . Although r a d i a t i o n damage information i s sparse on these a l l o y s , i t i s encouraging that hydrogen d i f f u s i v i t y has been shown to be s u b s t a n t i a l l y higher than i n the a l p h a - T i a l l o y s . For the cooled s t r u c t u r a l w a l l outside o f the f i r s t w a l l region, a broad range o f conventional low-cost a l l o y s (e.g., Fe-Ni based a l l o y s ) are a v a i l a b l e , but have not yet been s p e c i f i e d i n the i n i t i a l scoping study. For the f i b e r - m e t a l i n s u l a t o r , the b e t a - T i a l l o y s , T i - 1 3 V - l l C r - 3 A l , Ti-2.5A1-16V, and Ti-7Al-4Mo are the current s e l e c t i o n s , based on e x i s t i n g commercial a l l o y s . Improved T i a l l o y s or use of a Nb a l l o y l a y e r next to the Cauldron w a l l may be necessary to avoid creep at the highest temperatures. A helium sweep gas would be used to remove t r i t i u m from the porous f i b e r - m e t a l channel. For the m a t e r i a l o f the Cauldron w a l l which i s near the plasma, and i n contact with the l i q u i d Li-Na pool and the r e s u l tant vapors, neutron a c t i v a t i o n remains o f major importance, and r a d i a t i o n damage e f f e c t s are somewhat reduced (no t r i t o n impact). Corrosion r e s i s t a n c e i s a c r i t i c a l concern throughout the Cauldron w a l l , and long-term creep ( i n s p i t e of the low loading s t r e s s e s ) needs to be considered. The same commercial b e t a - T i a l l o y s were s e l e c t e d f o r the Cauldron w a l l as f o r the f i b e r - m e t a l i n s u l a t o r . The c o r r o s i o n r e s i s t a n c e o f pure T i and of a l l the a l l o y i n g c o n s t i t u e n t s except A l are expected to be adequate i n high temperature l i q u i d L i , and the c o r r o s i o n o f A l i s b e l i e v e d to be n e g l i g i b l e because of i t s low d i f f u s i o n rate through T i . A l s o , l i q u i d L i i s u s u a l l y more c o r r o s i v e than Na, so that the b e t a - T i a l l o y s are expected to have good c o r r o s i o n r e s i s t a n c e i n the Li-Na mixture. A d e f i n i t i v e statement cannot be given on the long-term creep strengths o f b e t a - T i a l l o y s , due to lack of any d i r e c t data under the low-stress, high-temperature c o n d i t i o n s encountered here. The LLNL workers are o p t i m i s t i c , however, i n view o f the f a c t that short-term t e n s i l e



514

METAL BONDING AND

INTERACTIONS

y i e l d strengths (0.2% deformation) are quite high (225 MPa or 33 k s i ) at 1200 K f o r the MST-881 T i a l l o y , Ti-8Al-8Zr-l(Nb+Ta). F a b r i c a t i o n and welding of both alpha and beta-Ti a l l o y s i n t o large complex structures u s i n g e l e c t r o n beam welding techniques i s a w e l l - e s t a b l i s h e d technology i n the aerospace i n d u s t r y . T r i t i u m r e t e n t i o n i n the titanium a l l o y s i s not expected to be a problem because of the high temperatures involved. The condensing vapor heat exchanger i s s u f f i c i e n t l y removed from the plasma region that neutron a c t i v a t i o n and r a d i a t i o n damage are no longer s i g n i f i c a n t . The important m a t e r i a l s cons i d e r a t i o n s here are long-term creep r e s i s t a n c e , high thermal c o n d u c t i v i t y , c o r r o s i o n r e s i s t a n c e to the Cauldron vapors and c i r c u l a t i n g heat exchange f l u i d s , and ease of f a b r i c a t i o n . The molybdenum a l l o y , TZM, has been s e l e c t e d because of i t s outstanding behavior for the f i r s t three c r i t e r i a above. Smallscale (up to ^ 3 cm d i a . ) welding of TZM f o r heat pipes and laboratory test capsules i s well e s t a b l i s h e d and should be d i r e c t l y t r a n s l a t a b l e to heat exchanger f a b r i c a t i o n , although a l a r g e r scale technology has not yet been e s t a b l i s h e d . Certain developmental grades of Nb and Ta a l l o y s would a l s o be s u i t a b l e for the heat exchanger. In-800 and In-800H also become acceptable i f temperatures are held below 1100 K. T r i t i u m permeation membranes can be applied i n s e v e r a l places depending upon the design s p e c i f i c s of the Cauldron and the heat transport loop, i . e . , t r i t i u m may be removed d i r e c t l y from the Cauldron dome, from a processing s l i p - s t r e a m o f f the Cauldron dome, from the f i b e r - m e t a l channel, and from a l i q u i d Na, l i q u i d K, or gaseous helium heat transport loop. The V, Nb, and beta-Ti a l l o y s have been selected as the p r e f e r r e d membrane m a t e r i a l s because of a combination of high hydrogen p e r m e a b i l i t y and good c o r r o s i o n r e s i s t a n c e to a Li-Na environment. Nb a l l o y s are p r e f e r r e d at the highest temperatures where high strengths and low creep rates are r e q u i r e d . A summary of the m a t e r i a l s e l e c t i o n considerations i s presented i n Table 2. The TMR

Heat Pipe Blanket Module

A conceptual design study i s c u r r e n t l y underway (11) at LLNL and the U n i v e r s i t y of Washington on a Heat Pipe Blanket Module (Figure 12) to provide process heat at temperatures of about 800-1000 K. Since work on t h i s concept has only r e c e n t l y begun, d e t a i l s cannot yet be provided on operating parameters. Process heat provided by t h i s blanket design should have u t i l i t y for e i t h e r hydrogen production by thermochemical c y c l e s or e l e c t r i c a l power p r o d u c t i o n . Both l i q u i d Li-Pb and pure l i q u i d L i are under c o n s i d e r a t i o n for the breeder-moderator r e g i o n , which is about 1 m t h i c k . G r a v i t y - a s s i s t e d heat pipes *\* 5-cm diameter and ^ 3-m long remove heat and e x t r a c t t r i t i u m from the l i q u i d metal. The heat pipe enclosure w i l l probably use two



Figure 12.

TMR heat pipe blanket module.


516


Table


Material

II.

I n i t i a l M a t e r i a l s Selections f o r the C a u l d r o n B l a n k e t Module

Application

Pros and Cons

V alloys

• First wall • Feltmetal insulator • T permeation membrane

• • • •

Nb alloys

• T permeation membrane

• Good corrosion resistance to liquid Li, Na, K • High T permeation rates

j3-Ti alloys and Ti-V alloys

• First wall • Feltmetal insulator • Cauldron wall

• • • •

Resistance to radiation damage is probably good Low activation Good corrosion resistance to liquid Li, Na, K High T diffusion rates

Mo alloys (TZM)

• Heat pipes • Heat exchangers

• • • • •

Very high strength Excellent heat conductivity Excellent corrosion resistance to liquid Li, Na, K Good small-scale fabricability Problems in large-scale fabrications

ln-800

• Transport piping for

• Good creep strength to 1100 K • Good corrosion resistance to liquid Na, K

liquid Na, K

Good resistance to radiation damage Low activation Good corrosion resistance to liquid Li, Na, K High T permeation rates

m e t a l s , w i t h TZM a l l o y p r o v i d i n g f o r t h e m a i n s t r u c t u r e and w i t h a m e t a l s u c h as Nb p r o v i d i n g f o r t r i t i u m p e r m e a t i o n . The w o r k i n g f l u i d w o u l d b e e i t h e r K o r Na d e p e n d i n g upon o p e r a t i n g temperature. The h e a t p i p e s a r e c u r v e d t o p r e v e n t n e u t r o n streaming. LLNL a n t i c i p a t e s r e m o v i n g p r o c e s s h e a t f r o m t h e h e a t p i p e u s i n g h i g h p r e s s u r e h e l i u m as a h e a t t r a n s p o r t f l u i d . Tritium e n t e r s the heat p i p e by permeation through t h e heat p i p e w a l l , i s c o n c e n t r a t e d a t t h e c o n d e n s e r end o f t h e h e a t p i p e due t o t h e h e a t p i p e pumping a c t i o n , and i s removed by p e r m e a t i o n t h r o u g h a membrane i n t o a m a n i f o l d . One o f t h e i m p o r t a n t m a t e r i a l s p r o b l e m s i n t h i s d e s i g n i s t h e c o r r o s i o n o f m e t a l a l l o y s when L i - P b i s u s e d as t h e b r e e d e r moderator. The d u a l w a l l s t r u c t u r e u s e d i n t h e C a u l d r o n B l a n k e t M o d u l e s h o u l d a p p l y e q u a l l y w e l l h e r e , so t h a t V c a n be u s e d f o r the plasma f i r s t w a l l to p r o v i d e s t r u c t u r a l s t r e n g t h w i t h m i n i mum a c t i v a t i o n . The c h o i c e o f a m a t e r i a l f o r t h e w a l l membrane i n c o n t a c t w i t h l i q u i d L i - P b becomes d i f f i c u l t . T i alloys cann o t be u s e d b e c a u s e o f r e a c t i o n w i t h P b . P u r e i r o n and i r o n - r i c h a l l o y s appear m a r g i n a l because o f a s o l u b i l i t y o f Fe i n Pb o f M 0 - 5 atom f r a c t i o n a t 900 K (12). Use o f N i o r C r as a l l o y i n g c o n s t i t u e n t s i n i r o n do n o t i m p r o v e t h e s i t u a t i o n , s i n c e N i and C r have s o l u b i l i t i e s i n Pb o f 0 . 0 3 and ^ 10"^ atom f r a c t i o n a t 900 K (JL3). The r e f r a c t o r y m e t a l s N b , T a , M o ,



33.

BLINK ET AL.

Lithium

in Fusion

517

Reactors

and W should r e s i s t c o r r o s i o n i n Li-Pb, and although Nb and Mo are good candidates f o r both the wall membrane and the heat pipe, they present a c t i v a t i o n problems i f used i n the v i c i n i t y of the f i r s t w a l l . Further work i s needed to make a proper s e l e c t i o n for the w a l l membrane i n contact with L i - P b . I f pure L i i s used as the breeder-moderator, -Ti and a number o f other m a t e r i a l s can be used, as discussed f o r the Cauldron Blanket Module. However, the t r i t i u m a c t i v i t y i n L i drops markedly i n the absence o f Pb, and the blanket temperature w i l l need to be r a i s e d to a l l e v i a t e the t r i t i u m removal problem. Tritium Extraction One o f the key chemical problems associated with l i t h i u m i n f u s i o n reactors i s e x t r a c t i o n of the t r i t i u m that has been e i t h e r generated i n or trapped by l i t h i u m . A f i g u r e of merit f o r t r i t i u m e x t r a c t i o n i s the blanket t r i t i u m i n v e n t o r y . Very large i n v e n t o r i e s r e q u i r e excessive start-up inventory and are a p o t e n t i a l l y large r a d i o a c t i v e e f f l u e n t i n the event of a c a t a s trophic accident. For s o l i d blankets such as the STARFIRE concept discussed i n the i n t r o d u c t i o n , d i f f u s i o n of t r i t i u m through the s o l i d i s the l i m i t i n g f a c t o r . A blanket t r i t i u m inventory of 0.7 to 8.2 kg i n a new blanket has been estimated ( 4 ) . However, r a d i a t i o n could cause s t o i c h i o m e t r y changes, g r a i n growth, t r i t i u m trapping, and s i n t e r i n g ; these e f f e c t s could i n c r e a s e the b l a n ket t r i t i u m inventory to hundreds of kilograms ( 4 ) . I f the t r i t i u m breeding medium i s not i n d i r e c t contact with the plasma exhaust ( i . e . , i n a l l but some LMW ICF r e a c t o r concepts), t r i t i u m must be recovered from the plasma exhaust, a gas. In a d d i t i o n , s o l i d breeders, and some l i q u i d breeders, use a gas to remove t r i t i u m from the breeder, and then process the gas. The p r a c t i c a l prospects o f using a vapor phase s l i p stream to e x t r a c t t r i t i u m from a l i q u i d L i breeder were s i g n i f i c a n t l y enhanced due to the d i s c o v e r y by I h l e and Wu (14) i n mass spectrometer studies that high concentrations of t r i t i u m bearing species are expected i n the vapor phase. I h l e and Wu's work was a c t u a l l y on deuterium, but some 30% higher gas-phase concentrations are expected with t r i t i u m . When I h l e and Wu s r e s u l t s are extrapolated to a somewhat higher temperature o f 850°C and assumed to be a p p l i c a b l e to t r i t i u m at an atom f r a c t i o n o f x-j = 10~5, the L i T and I ^ T pressures are of comparable magnitude at 2.6 mPa (2 x 10"5 T o r r ) , and exceed the T2 p a r t i a l pressure by a f a c t o r o f 40. Thus, the vapor phase t r i t i u m concentration i s s u b s t a n t i a l l y increased over T2 alone, and e x t r a c t i o n of the t r i t i u m compounds through permeation membranes may be p r a c t i c a l . I h l e and Wu, i n e x t r a p o l a t i n g t h e i r r e s u l t s , a l s o found that the concentration o f t r i t i u m i n the gas phase should exceed f



518


that i n l i q u i d L i at temperatures above ^ 1200 K, reaching a value o f x-jCgas p h a s e l i q u i d phase) ~ 6 at 1600 K. This led them to suggest d i s t i l l a t i o n as a means of t r i t i u m recovery. Several methods have been proposed to e x t r a c t t r i t i u m from molten L i or molten L i a l l o y s . These i n c l u d e : • Fractional d i s t i l l a t i o n • Cold trapping • Gettering • D i f f u s i o n through a l a r g e permeable window • D i f f u s i o n i n t o heat pipes • Molten s a l t e x t r a c t i o n In a l l of these methods, concurrent removal of c o r r o s i o n products could increase the corrosiveness o f the l i q u i d metal downstream from the e x t r a c t i o n equipment. This f a c t o r has not been evaluated f o r most schemes, but i t has caused problems i n some l i t h i u m loops that use g e t t e r s . D i s t i l l a t i o n . An azeotrope has been reported i n the l i t h i u m - t r i t i u m phase diagram at ^ 1000°C (Figure 13). Reference 15 estimates the azeotrope concentration at 2,000 wppm t r i t i u m while Reference 14 estimates 3 wppm of deuterium (corresponding to ^ 4 wppm t r i t i u m ) . I f the high value i s c o r r e c t , a d i l u t e t r i t i u m s o l u t i o n w i l l have a vapor that i s less r i c h i n t r i t i u m than i s the melt. As the vapor i s removed, both the vapor and the melt would increase i n t r i t i u m concentrat i o n u n t i l a constant b o i l i n g point mixture at the azeotrope concentration i s achieved. I f the lower azeotrope concentration is c o r r e c t , f r a c t i o n a l d i s t i l l a t i o n could be e f f e c t i v e . However, these arguments are complicated by the presence o f other t r i t i u m vapor phases such as L i T . Cold Trapping. There i s considerable u n c e r t a i n t y i n the concentration to which t r i t i u m can be c o l d trapped from L i (Figure 14). The work of Natesan and Smith (Figures 8 and 9 of Reference 16) can be used to estimate concentrations o f 1800 wppm protium and 2700 wppm t r i t i u m at a c o l d trap temperature o f 195°C. Katsuta (17) estimates a protium concentration of 200 wppm at a c o l d trap temperature o f 203°C. V e l e c k i s (18) estimates protium and deuterium concentrations o f 75 and 135 wppm at a c o l d trap temperature o f 195°C. The corresponding t r i t i u m concentration would be *\* 200 wppm. Thus, V e l e c k i s (200 wppm t r i t i u m ) and Natesan (2700 wppm) bracket the a v a i l a b l e estimates. In a 1630 m L i blanket (such as HYLIFE), 200 wppm and 2700 wppm t r i t i u m concentrations r e s u l t i n 160 and 2200 kg blanket t r i t i u m i n v e n t o r i e s , r e s p e c t i v e l y . (The a c t u a l t r i t i u m inventory may be reduced by about 25% due to the presence o f deuterium, but t h i s e f f e c t has been ignored here.) 3

G e t t e r i n g . The g e t t e r i n g approach to t r i t i u m e x t r a c t i o n applies to processing o f e i t h e r l i q u i d metals or gas streams



33.

BLINK E T A L .

Lithium

in Fusion

519

Reactors

FINAL COMPOSITION, BOTH MELT AND VAPOR

COMPOSITION OF VAPOR WHEN MELT IS A T C

O

CO UJ

cc D

CO CO 111

oc Q_

8 cc Ul

VAPOR COMPOSITION OVER INITIAL MELT

D

UJ

cc Q.

INITIAL MELT COMPOSITION

PURE SOLVENT

MELT COMPOSITION A F T E R SOME DISTILLATION

FINAL (AZEOTROPE) C

ppm SOLUTE Figure 13. Phase diagram for a dilute solution with an azeotrope. Diagram can be used qualitatively to predict the distillation behavior of T (solute) in Li (solvent).



520


ATOM RATIO H ISOTOPE/Li Figure 14. Concentrations to which H isotopes can be cold trapped from Li. Key: A, cold trapped at 195°C (16); •, cold trapped at 203°C (11); O , cold trapped at 195° (IS); and O , estimated value if cold trapped at 195°C (IS).


33.

Lithium

BLINK ET AL.

in Fusion

521

Reactors


containing t r i t i u m . The stream to be processed i s passed through a bed o f porous metal that serves as the g e t t e r . A f t e r s u f f i c i e n t exposure, the g e t t e r bed i s regenerated by heating under vacuum or i n a c a r r i e r flow stream to recover the t r i tium. There i s very l i t t l e information on the use o f g e t t e r s for t r i t i u m e x t r a c t i o n . Y t t r i u m (19) and cerium (20) have shown a l i m i t e d degree o f success as g e t t e r s , and then only at r e l a t i v e l y low temperatures ( i . e . , below 350°C). D i f f u s i o n Through the Primary Heat T r a n s f e r Loop. An equation f o r the permeation o f a gas through a metal i s F = C A A/F/t

(1)

where F i s the gas f l u x , C i s the p e r m e a b i l i t y constant, and is the d i f f e r e n c e of the square roots of the t r i t i u m pressures on the high and low pressure sides o f the d i f f u s i n g medium which has area, A, and thickness, t . For l i t h i u m temperatures o f ^500°C, the l i q u i d metal heat exchanger r e q u i r e s ^ 3.3 to 8.0 m o f area per MW (10,600 to 25,600 m f o r a l-GW p l a n t ) . The w a l l thickness w i l l be about 0.65 mm to 1.3 mm f o r a 2h Cr-1 Mo heat exchanger. For a 30% t r i t i u m burn f r a c t i o n and a 1.75 t r i t i u m breeding r a t i o , 19.5 mg/sec o f t r i t i u m are added to a l-GW HYLIFE p l a n t ' s l i q u i d metal w a l l , and the same amount must d i f fuse out. The p e r m e a b i l i t y constant f o r t r i t i u m d i f f u s i n g through 2h Cr-1 Mo s t e e l i s (^1) 2

t

2

e

e

C

=

2

=

0

8

.

6

x

1

0

~

exp[-4706/T(K)]

4

cm (STP)-mm 3

8

1

h-cm

e x p [

_4 o6/T(K)] 7

•/atm 7

At T = 773 K, C = 4.68 x 10" mg/(s-m-/Pa) = (0.20 cm^ mm/h cm /atra). For the range o f heat thicknesses and areas, -

#

2

exchanger

1.1 < A/F < 5.1*/Pa" (0.092 - 0.44/Torr) If the low pressure side i s considered zero t r i t i u m pressure,

(2)

to have e s s e n t i a l l y a

1.1 < P < 27 Pa (0.0084 - 0.20 Torr)

(3)

These pressures correspond to t r i t i u m concentrations o f 2900 and 14,000 wppm (Figure 15) or to a t r i t i u m inventory i n a 1630 m l i q u i d l i t h i u m blanket o f 2300 to 11,000 kg. (The pressure-concentration r e l a t i o n s h i p shown i n F i g u r e 15 i s that of Ref. 16.) I f the low pressure side i s l i q u i d sodium c o l d trapped to 4 mPa (3 x 10~* T o r r ) , the high pressure side 3


522


ranges from 1.3 to 27 Pa (0.0095 to 0.20 T o r r ) , i . e . , 3100 to 14,000 wppm, or 2400 to 11,000 kg i n a 1630 m l i q u i d l i t h i u m blanket. Therefore, u s i n g a secondary f l u i d that can be c o l d trapped to a lower pressure than Na (such as NaK which can be cold trapped to 30 nPa or 2 x 1 0 ~ T o r r ) does not s i g n i f i c a n t l y improve the s i t u a t i o n . I f a much l a r g e r area heat exchanger i s used, c o n s i d e r a b l e improvement i s p o s s i b l e . For example, i f the 25,600 m heat exchanger has i t s tubes reduced i n radius and c o i l e d , perhaps 100 times more area could r e s u l t . Using the 0.65 mm t h i c k 2h Cr-1 Mo, and cold trapped NaK on the secondary side r e s u l t s i n a primary t r i t i u m pressure o f 0.12 mPa or 8.7 x 1 0 ~ Torr (29 wppm or 23 kg i n a 1630 m l i q u i d l i t h i u m b l a n k e t ) . An a l t e r n a t e method o f reducing the blanket t r i t i u m inventory i s to use a more permeable heat exchanger m a t e r i a l such as Nb which has a p e r m e a b i l i t y constant (27) o f 2.6 x 10"^ m g / ( s - m » / P a ) = 110 cm (STP) -mm/(h.cm ./atm) at 500°C (Figure 16). For the o r i g i n a l heat exchanger areas and t h i c k nesses, and for a cold trapped NaK secondary, t r i t i u m pressure ranges from 4.4 to 89- yPa (3.3 x 1 0 " to 6.7 x 1 0 ~ T o r r ) , i . e . , 6 to 26 wppm, or 5 to 20 kg inventory for a 1630 m liquid lithium blanket). These c a l c u l a t i o n s are u n c e r t a i n , however. The permeation equation may pass through a regime p r o p o r t i o n a l to pressure rather than root pressure. A d d i t i o n a l l y , the rate c o n t r o l l i n g f a c t o r may not be permeation, but rather the rate at which t r i tium atoms skating about on the low pressure surface f i n d other atoms and leave the surface as gaseous molecules. 3

1 0


2

7

3

3

2

8

7

3

Heat Pipe Scheme. The p r i n c i p l e involved i n t r i t i u m removal with heat pipes has been described by Lee and Werner (2^,24). The method i s a p p l i c a b l e mainly to l i q u i d metal breeder-moderators. T r i t i u m at the ppm l e v e l i n the l i q u i d metal breeder enters the heat pipe through a permeation membrane ( i . e . , a metal such as Nb or V that permits r a p i d transport o f t r i t i u m through the l a t t i c e ) . The t r i t i u m i s then picked up by the rapid sweeping a c t i o n o f the heat pipe vapor (e.g., Na or K), and i s c a r r i e d to the heat r e j e c t i o n end o f the heat pipe where the t r i t i u m i s entrapped and compressed by the continuous impingement o f the heat pipe vapor. With a t r i t i u m concentrat i o n o f a few ppm i n the l i q u i d metal breeder (corresponding to ^ 1 yPa or 1 0 ~ Torr i n 500°C L i ) , t r i t i u m concentrations up to ^ 130 Pa (1 T o r r ) are expected i n the heat r e j e c t i o n end o f the heat pipe, where the t r i t i u m can then be extracted through a metal permeation membrane. Because o f the s e l e c t i v e sweeping and c o n c e n t r a t i n g a c t i o n o f heat pipes for the non-condensible hydrogen isotope c o n t a i n i n g gases (when metal membranes are used), heat pipes present a very s i g n i f i c a n t p o t e n t i a l as a t r i t i u m recovery method. Development o f f u r t h e r designs and m a t e r i a l s f o r t h i s a p p l i c a t i o n would be very u s e f u l . 8



BLINK

ET

Lithium

AL.

in Fusion

1

10

Reactors

100 1000

10,000

Parts per million (wppm) tritium Figure 15.

E

Relationship of T pressure to T concentration in 500°C

Li.

250

+•» cp CM

E o SI

E cT o o c

n CO CO

E

VQ.

450

500

600

a>

700

800

900

1000

Temperature (°C) Figure 16.

Permeability of Nb to T.



524


Molten S a l t E x t r a c t i o n . Molten l i t h i u m or l i t h i u m a l l o y i s placed i n contact with a molten s o l u t i o n o f L i F - L i C l - L i B r . This l i t h i u m h a l i d e s o l u t i o n i s 22 mol % L i F , 31 mol % L i C l and 47 mol % L i B r , melting at 445°C. Hydrogen isotopes are p r e f e r e n t i a l l y e x t r a c t e d from the m e t a l l i c s o l u t i o n i n t o the l i t h i u m h a l i d e melt. The immiscible s o l u t i o n s o f molten h a l i d e and molten metal are separated, with the m e t a l l i c l i q u i d , c a r r y i n g less than 1 wppm t o t a l hydrogen isotope burden, r e t u r n i n g to the l i q u i d metal c i r c u i t s o f the f u s i o n r e a c t o r . The h a l i d e melt i s processed to remove hydrogen i s o t o p e s , probably by electrochemi c a l e v o l u t i o n . This technique has been developed (25) by Calaway and co-workers at Argonne. The hydrogen isotopes released at the anode of the c e l l are swept away i n molecular form by argon gas emerging from a bubbler-shaped anode. This technique could remove t r i t i u m to 0.5 wppm (a 0.4 kg inventory i n a 1630 m b l a n k e t ) . 3

S o l u b i l i t y o f Hydrogen Isotopes i n Lead-Lithium L i q u i d s L i q u i d Metal Wall ICF r e a c t o r s are d i s t i n c t from other f u s i o n r e a c t o r s i n that the l i t h i u m breeding blanket i s i n d i r e c t contact with the plasma exhaust. Thus, the s o l u b i l i t y of hydrogen isotopes i n the l i q u i d metal w i l l determine whether t r i t i u m must be recovered from e i t h e r the l i q u i d loop or the vacuum system, r a t h e r than both systems. Hydrogen Pressure Ranges f o r Liquid-Only or Vapor-Only T r i tium Recovery f o r UMW ICF Reactors. For a 2700-MWf ICF r e a c t o r with a 600-m chamber, a 30% t r i t i u m b u m f r a c t i o n and a 1.75 t r i t i u m breeding r a t i o , 19.5 mg/s of t r i t i u m are added to the r e a c t i o n chamber. I f t r i t i u m i s to be recovered from only the l i q u i d , a maximum l o s s through the vacuum system of 1% (0.2 mg/s) i s assumed to be acceptable. With a l a s e r d r i v e r (26), the vacuum system might operate at ^ 1.3 Pa ( 1 0 ~ Torr) with about 10% of the vapor being pumped per second. Then, about 3.5 mPa (2.6 x 10"^ T o r r ) o f t r i t i u m , or 10 times the pressure associated with 0.2 mg t r i t i u m , i s allowable. With a heavy-ion-beam d r i v e r (26), the vacuum system might operate around 0.13 Pa ( 1 0 ~ T o r r ) , with about 50% o f the vapor being pumped per second. Then, about 0.7 mPa (5 x 10~6 Torr) o f t r i t i u m , or twice the pressure a s s o c i a t e d with 0.2 mg t r i t i u m , i s allowable i f only the l i q u i d i s to be processed. For vapor-only t r i t i u m recovery, 99% of the t r i t i u m product i o n ( o r 19.3 mg/s) must be processed by the vacuum system, and the r e q u i r e d pressure i s ^ 100 times the allowable pressure f o r l i q u i d - o n l y recovery. Therefore, with a l a s e r d r i v e r , t r i t i u m vapor pressure between 3.5 and 350 mPa (2.6 x 10"^ and 2.6 x l O " Torr) r e q u i r e s t r i t i u m recovery from both the l i q u i d - c i r c u l a t i o n and the vacuum systems. For the heavy-ion3

2

3

-3


33.

BLINK ET AL.

Lithium

in Fusion

525

Reactors

beam d r i v e r , the corresponding pressure range i s 0.7 to 70 mPa (5 x 10~6 to 5 x 10"^ T o r r ) . The a c t u a l t r i t i u m vapor pressure w i l l depend on both the vacuum system design and the s o l u b i l i t y o f t r i t i u m i n the LMW. Startup Inventory i n a LMW ICF Reactor. E f f i c i e n t t r i t i u m recovery cannot begin u n t i l the t r i t i u m c o n c e n t r a t i o n b u i l d s up i n the l i q u i d . For a 30% burn f r a c t i o n , a s t a r t - u p t r i t i u m i n ventory of about 1.4 kg i s required f o r each day o f s t a r t up. For a 1630-m system o f L i o ^ P b i about 14 hours i s required to reach 1 wppm (1 kg) t r i t i u m . For a 900-m system o f Pbg3Lii7, about 5 days are r e q u i r e d to reach 1 wppm (7 kg tritium).


3

3

Hydrogen S o l u b i l i t y . As o f December 1980, no data have been generated that d i r e c t l y give the hydrogen isotope pressure above Pb33Li^7 l i q u i d i n the 400 to 500°C temperature range. However, data at other temperatures and concentrations can be extrapolated to the needed temperatures and composit i o n s . At a given composition, S i e v e r t ' s constant ( K ) i s r e l a t e d to temperature by s

log K

s

= m/T + b

(4)

where m and b are composition-dependent constants. I f K vs composition i s known at two temperatures, the constants m and b can be c a l c u l a t e d at each composition and K can be estimated f o r a l l temperatures and compositions. The data points o f I h l e , Neubert, and Wu (27), f o r the s o l u b i l i t y of deuterium i n s e v e r a l Pb-Li compositions are shown i n Figure 17. The s o l i d l i n e s at temperatures o f 677 and 767°C are i n t e r p o l a t i o n s between data p o i n t s . The gap i n the 677°C curve i s due to the presence o f a s o l i d phase. The data have been extended to the d e u t e r i u m - i n - l i t h i u m data from Argonne (28) and the hydrogen-in-lead data from Opie and Grant (29). The hydrogen-in-lead data were converted to deuterium-in-lead data by assuming that the r a t i o o f S i e v e r t ' s constants for hydrogen and deuterium i s constant (independent of the Pb-Li composition) and by using the Argonne data for hydrogen and deuterium i n pure l i t h i u m . The adjustment was r e l a t i v e l y small, with a 9% increase at 767°C and a 20% increase at 477°C. Using the curves at 677 and 767°C and Eq. (4), curves were constructed at 477 and 577°C. However, at Pb concentrations above 50 a/o, the 677°C curve i s quite u n c e r t a i n . Figure 18 presents a second p l a u s i b l e 677°C curve and the r e s u l t i n g lower-temperature curves. For a "pure l i t h i u m " LMW, Pb target debris can b u i l d up to ^ 1 a/o before c o l d trapping o f b i n a r y P b - L i compounds i s e f f e c tive. I f deuterium i s removed from t h i s l i q u i d to a concentrat i o n o f 1 wppm (4.5 x 10*-6 atom f r a c t i o n o f deuterium i n s

s



Figure 17.

Sievert's constant for solubility of D in Pb-Li.

Figure 18.

A second possible extrapolation solubility data of D in Pb-Li.

Atom % Pb in Pb-Li


of the

33.

BLINK ET AL.

Lithium

in Fusion

527

Reactors

a l l o y ) , the diatomic deuterium pressure at 477°C i s ^ 70 nPa (5 x 10~10 T o r r ) , and hydrogen isotopes need not be recovered i n the vacuum system f o r e i t h e r l a s e r or heavy-ion-beam d r i v e r s . For the Pbg3L.i17 LMW, no c o n c l u s i o n can be reached from the data. The e x t r a p o l a t i o n o f F i g u r e 17, and l i q u i d recovery of hydrogen isotopes down to 1 wppm each (8.7 x 10"^ atom f r a c t i o n of deuterium i n a l l o y ) produce a diatomic deuterium pressure at 477°C o f ^ 4 yPa (3 x 1 0 ~ T o r r ) , and no vacuumsystem hydrogen-isotope recovery i s r e q u i r e d . However, i f the Figure 18 e x t r a p o l a t i o n i s used, and i f deuterium i s extracted from the vapor to a pressure o f 350 mPa (2.6 x 1 0 ~ Torr) f o r a l a s e r d r i v e r or 70 mPa (5 x 10"^ T o r r ) f o r a heavy-ion-beam d r i v e r , the corresponding deuterium concentrations i n the l i q u i d are 0.034 and 0.015 wppm, r e s p e c t i v e l y , and no l i q u i d recovery of hydrogen isotopes i s r e q u i r e d . To r e s o l v e t h i s i s s u e , researchers at Argonne N a t i o n a l Laboratory (ANL) and elsewhere are conducting appropriate experiments. I n i t i a l ANL data i n d i cate that t r i t i u m recovery w i l l only be r e q u i r e d from the vapor phase over Pb33Li^7 (30).


8

3

Heavy Ion Beam Propagation

i n Pb-Li LMW ICF

Reactors

For a heavy-ion-beam d r i v e n , l i q u i d - m e t a l - w a l l ICF r e a c t o r , the l i q u i d metal w a l l (LMW) composition and temperature must not preclude transport and focus o f the heavy ion beam on the t a r get. For a near-vacuum system, (^ 1 0 ^ cm"") both the vapor pressure and the s t r i p p i n g e f f e c t i v e n e s s o f the chamber gas must be known before i t can be determined i f b a l l i s t i c propagation o f the beam i s p o s s i b l e . These c o n d i t i o n s have been considered f o r L i o ^ P b i and f o r Pb33Li^7 l i q u i d metal w a l l s (31). 3

L i and Pb P a r t i a l Pressures. Pb-Li s o l u t i o n i s p

The vapor pressure above a

p

5

= Y L i N L i L i + Yp Np Ppb b

( )

b

where and Np^ are the atom f r a c t i o n s of l i t h i u m and lead i n the l i q u i d , and P L £ and Pp^ are the vapor pressures of the pure elements at the given temperature. The temperatureand-composition dependent f u n c t i o n s , Y L ^ and Yp > are a c t i v i t y c o e f f i c i e n t s ; they d e s c r i b e the i d e a l i t y o f the solution. I f the a c t i v i t y c o e f f i c i e n t s are 1.0, the s o l u t i o n i s "ideal (Raoult's Law). I f they are greater than 1.0, the s o l u t i o n has " p o s i t i v e d e v i a t i o n from i d e a l i t y " and a higher than expected vapor pressure. I f they are l e s s than 1.0, there is a "negative d e v i a t i o n " and lowered vapor pressure. In the case of the Pb-Li system, experimental data (32,33,34) i n d i c a t e a profound negative d e v i a t i o n from i d e a l i t y , probably due to conversion from m e t a l l i c to i o n i c bonding. The n o n i d e a l i t y o f the Pb-Li system i s d r a m a t i c a l l y shown i n a p l o t o f e l e c t r i c a l r e s i s t i v i t y (35) as a f u n c t i o n o f composition (Figure 19). D

1 1



528

METAL BONDING AND

INTERACTIONS

The vapor pressures of pure Pb and L i are shown as a funct i o n of temperature i n Figure 20 and Tables 3 and 4. Vapor pressure of the pure lead i s s e v e r a l hundred times l e s s than that of pure l i t h i u m i n the 400-500°C temperature range. (Higher temperatures are discouraged by a decrease i n mechanical p r o p e r t i e s of f e r r i t i c s t e e l s and by L i c o r r o s i o n ; lower temperatures are discouraged by b r i t t l e n e s s of f e r r i t i c s t e e l s and by thermal e f f i c i e n c y c o n s i d e r a t i o n s , ) For L i o ^ P b i , the L i a c t i v i t y c o e f f i c i e n t , Y L £ , i s about u n i t y . However, data (32,40) at 527 and 659°C i n d i c a t e that the lead a c t i v i t y c o e f f i c i e n t i s less than 2 x 10"^, so that the Pb-component p a r t i a l pressure i s ten orders of magnitude less than that of the L i component f o r L i o ^ P b i . For h i g h - c o n c e n t r a t i o n Pb s o l u t i o n s , such as Pb33Li^7, the a c t i v i t y c o e f f i c i e n t s must be c a r e f u l l y evaluated. Demidov's Yp^ data (40) at 527°C were used to determine a c t i v i t y c o e f f i c i e n t values which ranged from 0.932 at 77 a/o Pb to 1.0 above 88.3 a/o Pb. I f YLi ^ again of order 1, the Li-vapor component would dominate the Pb vapor by a f a c t o r of 50. However, as i s shown below, YLi *- ^ than 10"* at temperatures below 500°C, and the Pb component dominates the vapor. The Li-component a c t i v i t y c o e f f i c i e n t , Y L £ , can be d e t e r mined from e l e c t r o m o t i v e f o r c e (emf) data taken by Saboungi (32) at temperatures of 497, 539, 596, and 659°C i n Pb-Li mixtures with Pb atom f r a c t i o n s above 45%. In Figure 21, Y L i *as a f u n c t i o n of (1/T) at f i v e l i q u i d compositions. The l i n e s i n Figure 21 are least-square f i t s to allow e x t r a p o l a t i o n to the temperature region of i n t e r e s t to ICF r e a c t o r designers, 400 to 500°C. Since the emf data d i d not i n v o l v e d i r e c t pressure measurements, experimental v e r i f i c a t i o n i n v o l v i n g a d i r e c t or i n d i r e c t pressure reading of L i and Pb above a b i n a r y s o l u t i o n was sought. Knudsen c e l l work by I h l e , Neubert, and Wu (33) provide data that are also shown i n Figure 21. A d d i t i o n a l Knudsen c e l l work by Neubert, I h l e , and G i n g e r i c h (34) i s shown i n Figure 22 which p l o t s the Pb and L i p a r t i a l pressures above Pb5QLi5Q l i q u i d as a f u n c t i o n of (1/T). Figure 22 a l s o shows the e a r l i e r Knudsen c e l l work f o r L i , the emf data, and least-square f i t s to the emf data. The emf data f o r Pb uses, at a l l temperatures, the Ypb value of 0.4 shown i n F i g . 3 of Reference 32 f o r a temperature of 659°C. I f a value of 1.0 i s used f o r Ypb a l l temperatures, the emf e x t r a p o l a t i o n f a l l s i n the middle o f the higher temperature Knudsen c e l l Pb data. The t o t a l Pb and L i vapor pressure over 497°C Pb-Li l i q u i d i s shown i n Figure 23 as a f u n c t i o n of Pb c o n c e n t r a t i o n . The pressure above Pb33Li^7 (1.6 mPa or 1.2 x 10"^ Torr) is a f a c t o r of ^ 5 0 lower than i d e a l and a f a c t o r of ^ 270 lower than the pressure o f pure L i at the same temperature (0.43 Pa or s

s

e s s

3

s

s

n

o

w

n

a t


BLINK E T A L .


33.

Lithium

in Fusion

20 a

Figure 19.

Reactors

60

529

100

/ o Pb in Pb-Li

Electrical resistivity of Pb-Li alloys at

800°C.

Temperature (°C) Figure 20.

Vapor pressure of pure Pb and pure Li as a function of temperature.



530

METAL

1.05

1.1

1.2

1.3

BONDING AND

1.4

INTERACTIONS

1.5

1000/T (°K) 650

600

550

500

450

400

T(°C) Figure 21. Ratio oj actual to ideal Li partial pressure above Pb-Li liquids (y ) as a junction of liquid temperature. "Actual' refers to pressures inferred from electromotive force data, while "ideal" is the product of the Li atom fraction and the vapor pressure of pure Li. At 500°C, the actual Li partial pressure above high-Pb eutectic liquid is a factor of 1400 lower than the ideal solution prediction. Key: O, EMF data; and , fit to EMF data; Knudsen cell data: A, 80% Pb; and 90% Pb. Li

•,


BLINK ET AL.

Lithium

in Fusion

531

Reactors


33.

Figure 22. Partial pressures of Li and Pb above Pb Li liquid from EMF and Knudsen cell data. Key for EMF data (2): | , Li; #, Pb; and , fit to EMF data; and for Knudsen cell data: •, Li (4); O, Pb (4); and A , Li (3). 50

50


532

METAL

BONDING AND

INTERACTIONS

Table I I I . Range o f Vapor Pressures i n the L i t e r a t u r e for Pure Lithium

Temperature (°C)


Source

500

400

Cowles & Pasternak (36)

13.6 mPa

473. mPa

Ne smeyanov (37)

12.1

433.

Hultgren (38)

11.4

423.

JANAF (39)

11.2

392.

Fit

11.4 mPa

to average o f Refs. 37,38,39

401. mPa

5

3

(8.57 x 10 " Torr) (3.02 x 10 " Torr)

Notes:

ft

1) An equation f i t to the Douglas" curve ( F i g . 6 o f Ref. 36) was used i n t h i s a r t i c l e . *n P

L i

(Pa)

23.111 -

18,444

2) The data from Hultgren, Nesmeyanov, and JANAF were averaged a t several temperatures between 327 and 627°C. An equation f i t to the averages i s in

P

L i

(Pa) = 23.054 -

3

3.2 x 1 0 ~ T o r r ) . The vapor i s almost pure Pb (^96 a/o Pb) compared to almost pure l i t h i u m (^ 2 a/o Pb) f o r an i d e a l solution. T o t a l Pressure i n the Chamber. The vapor species are L i , L i 2 , Pb, Pb2, L i P b , He, hydrogen i s o t o p e molecules, and gaseous l i t h i u m hydride ( i n c l u d i n g deuteride and t r i t i d e ) . The s i g n i f i c a n t species are L i , Pb, He, and hydrogen isotope molecules. For the LiggPb^ Uffl, the t o t a l chamber pressure ranges between 0.03 and 0.9 Pa (2 x 10"^ Torr and 7 x 1 0 ~ T o r r ) as l i q u i d temperature increases from 400 to 500°C (Figure 24). Monatomic L i i s the primary condensible vapor. Diatomic L i part i a l pressure i s small compared to monatomic L i pressure. The Pb p a r t i a l pressure i s a t l e a s t a f a c t o r o f 600,000 lower than 3



33.

BLINK ET A L .

Lithium

76

in Fusion

80

84

533

Reactors

88

92

96

100

Pb in Pb-Li a/o Figure 23.

Vapor pressure and composition as a junction oj liquid composition at 497°C.

400

420

440

460

480

500

Temperature of 99% Li-1% Pb liquid (°C) Figure 24. Partial pressures oj vapor constituents above Li Pb liquid. He pressure is assumed to equal the sum oj the Li, Pb, and H pressures because detailed vacuum system design has not been addressed. Monatomic Li and He are the primary constituents. Hydrogen isotopes and Pb, r e s p e c t i v e l y , each pressure i s converted to e q u i v a l e n t (monatomic) L i pressure. Figure 26 shows the r e s u l t s f o r both fluids. For LiggPb^, the e q u i v a l e n t pressure f o r s t r i p p i n g is dominated by L i and He; these components are shown w i t h dashed l i n e s . Two cases are shown f o r Pbg3Lii7; the lower l i n e uses the minimum He pressure set by the Pb-Li vapor p r e s sure, and the upper l i n e uses the higher He pressure c a l c u l a t e d f o r the other f l u i d . The higher He pressure seems more l i k e l y based on vacuum pumping design c o n s i d e r a t i o n s . Figure 26 can be used to compare three cases: L i c ^ P b j , Pbg3Lii7 with high He pressure, and Pbg3Li^7 with low He pressure. To make the comparison, draw a h o r i z o n t a l l i n e at the maximum allowable l i t h i u m pressure. (This value w i l l e v e n t u a l l y be provided by the beam propagation community; current estimates range from 13 to 130 mPa or 10"^ to 10~ T o r r . ) Then, compare the l i q u i d metal temperatures f o r the three cases. For example, at 66 mPa (5 x 10"^ Torr) allowable, the maximum l i q u i d metal temperatures are 431, 450, and 472°C f o r the three cases. Recently, i t has been suggested (42) that beam s t r i p p i n g might be s i g n i f i c a n t l y decreased i f the beam i o n and background gas species were i d e n t i c a l . I f so, Pb would make an e x c e l l e n t candidate f o r a heavy i o n beam. As shown e a r l i e r , the vapor above Pbg3Li^7 i s ^ 9 6 a/o Pb ( c o n s i d e r i n g only the Pb and Li). I f the s t r i p p i n g e f f e c t i v e n e s s of l e a d i s much l e s s than 100, He w i l l be the dominant component of the background gas with respect to beam propagation. In a d d i t i o n , a 208 heavy ion beam has h i g h mass, Pb may also be a target m a t e r i a l , and Pb has a very low neutron a c t i v a t i o n p r o b a b i l i t y . However, i s o t o p e s e p a r a t i o n w i l l be r e q u i r e d to separate 208 from n a t u r a l lead. 3

P b

P b


536

METAL

i

10-

1

i '

BONDING A N D INTERACTIONS

r

Case 1 Extrapolate H data to high solubility Case 2 Extrapolate H data to low solubility

10 -3


£ 10-

Hydrogen, helium (case 2) Total (either case)Helium (case 1) -

£ 10-5

10

Lithium -

-6

10i-7 400

420

440

460

480

500

Temperature of 83% Pb-17% Li liquid (°C) Figure 25. Partial pressures oj vapor constituents above Pb Li liquid. H solubility is still undetermined, both extremes are plotted. Pb and He are primary constituents. 83

17

Liquid metal temperature (°C) Figure 26.

Equivalent Li pressures for heavy ion beam stripping above LigoPbt and Pb Li liquids. 83

17


33.

BLINK ET AL.

Lithium

in Fusion

537

Reactors

The lead s t r i p p i n g m u l t i p l i e r o f 113 that was used i n Figure 26 i s the maximum p r e d i c t e d t h e o r e t i c a l l y , and a value o f one-half that i s not u n l i k e l y , according to the t h e o r e t i c i a n s . However, German experimental work (43) using U 8 ions i n t e r acting with n i t r o g e n background gas i n d i c a t e s that the theore t i c a l maximum cross s e c t i o n p r e d i c t i o n s may be too low. I f these s u r p r i s i n g experimental r e s u l t s are confirmed, the Pb-stripping m u l t i p l i e r f o r U l could be as high as 400. The data of Figure 26 are cross p l o t t e d i n Figure 27 as a f u n c t i o n of the P b - s t r i p p i n g m u l t i p l i e r . C l e a r l y , the allowable equival e n t l i q u i d metal temperature i s most s e n s i t i v e to the allowable l i t h i u m vapor pressure, even though the pressure range p l o t t e d is l e s s than one-haIf the range of estimates made by the beam propagation community. The l e a d - s t r i p p i n g m u l t i p l i e r i s also very u n c e r t a i n , but i t i s of secondary importance i n determining the maximum allowable temperatures f o r the two l i q u i d metals. +


+

Comparison o f Pbg^Li^y and Li^gPbj as L i q u i d Metal Walls" A comparison o f Pbg3Li^7 with Li^gPhj can be made by using the d i f f e r e n c e i n allowable temperature based on heavy i o n beam propagation. I f the Pbg3Li^7 has a 30°C higher l i q u i d temperature, the net plant e f f i c i e n c y i s increased by about 0.5% and about 20 MW a d d i t i o n a l power i s produced (44). In a d d i t i o n , the higher neutron energy m u l t i p l i c a t i o n associated with l e a d - l i t h i u m could produce about 150 MW a d d i t i o n a l power i n a 1000 MW -net power plant (45). However, the higher density and lower heat capacity o f Pbg3Lii7 require about 130 MW a d d i t i o n a l pumping power (46) f o r the LMW and about 100 MW f o r the primary loop (47). Hence, from a rough power flow viewpoint, using Pbg3Lij7 r e s u l t s i n a loss o f 60 MW net power. A f u l l e v a l u a t i o n o f Pbg3Li]j must a l s o consider, on the negative s i d e , increased flow loop s t r u c t u r a l requirements, increased f l u i d r a d i o a c t i v i t y , p l a t i n g of a c t i v a t e d lead on plant surfaces a f t e r a s p i l l , and l a r g e r primary heat exchangers; and, on the p o s i t i v e s i d e , a d d i t i o n a l recovered pump heat and e l i m i n a t i o n of l i q u i d metal f i r e hazards. At t h i s point, both f l u i d s are o f i n t e r e s t to LMW f u s i o n reactor designers. e

e

e

e

e

e

Summary The use o f l i t h i u m i n f u s i o n r e a c t o r designs has been described with emphasis on materials c o m p a t i b i l i t y , s a f e t y , and tritium extraction. Several chemical issues remain unresolved, including: • C o m p a t i b i l i t y o f s t r u c t u r a l a l l o y s with Li-Pb l i q u i d s • E x t r a c t i o n o f high-Z target debris from L i ft Chemical physics o f heavy i o n beams and background gas • T r i t i u m g e t t e r i n g from the gas phase



0

017

3

4

5

A

Pb . 3

0

6

0

Figure 27. Maximum allowable LMW temperature is more sensitive to allowable equivalent Li pressure than to the stripping effectiveness of Pb. The shaded band is the range predicted by theory. Key: , 10 Torr Li allowable; , 2 X lO Torr Li allowable; A, Li .oo Pbo.ou B, Pb ss Li , He ~ 10 - 10 torr; and C, Li .n, He ~ 10~ torr. 0 8

Relative stripping effectiveness of lead compared to lithium


„ 3

>

oo

w >

33.

BLINK ET AL.

• • • •

Lithium

in Fusion

Reactors

539

E f f e c t s o f r a d i a t i o n on t r i t i u m inventory i n s o l i d breeders Accurate hydrogen concentration measurement i n Li-Pb liquids S i e v e r t s constant as a f u n c t i o n o f temperature and Pb concentration i n Li-Pb l i q u i d s E f f e c t s o f intense magnetic f i e l d s on b o i l i n g and heat pipes.


Literature Cited

1. 2. 3. 4.

5.

6. 7. 8.

9.

10.

11. 12. 13.

Meier, W. R. Nucl. Tech. 1981, 52, 170. Meier, W. R.; Maniscalco, J . A. "Liquid Metal Requirements for Inertial Confinement Fusion"; Lawrence Livermore National Laboratory: Livermore, CA, UCRL-80424, 1977. El-Wakil, M. M. "Nucl. Power Eng."; McGraw-Hill: New York, NY, 1962; p 534. Smith, D. L . ; Clemmer, R. G.; Jankus, V. Z.; Rest, J . "Analysis of In Situ Tritium Recovery From Solid Fusion-Reactor Blankets"; Proc. 4th ANS Top. Mtg. Tech. Controlled Nucl. Fusion: King of Prussia, PA, 1980. Maniscalco, J . A.; Berwald, D. H.; Engdahl, J . C ; McKone, T. E . ; Whitley, R. H.; Allen, W. O.; Massey, J . V.; McGrath, R. T. "Laser Fusion Driven Breeder Design Study Final Report"; U.S.DOE Contract DE-AC08-79DP40-11; TRW, Inc.: Redondo Beach, CA, 1980. "Laser Program Annual Report—19 78";. Lawrence Livermore National Laboratory: Livermore, CA; UCRL-50021-78, 1979; pp 9-1 to 9-75. "Laser Program Annual Report—1979"; Lawrence Livermore National Laboratory: Livermore, CA; UCRL-50021-79, 1980; pp 8-1 to 8-118. Anderson, T. "An Evaluation of the Corrosion Resistance of 2¼Cr-1 Mo Steel in a Lithium-Lead Liquid"; M.S. Thesis, Dept. of Metallurgical Engineering, Colorado School of Mines: Golden, CO, 1980. Werner, R. W "The Fusion-Synfuel Tie Producing Hydrogen With the Tandem Mirror Reactor"; presented at 15th Intersociety Energy Conversion Engineering Conference: Seattle, WA, 1980. Krikorian, O. H. "Materials Considerations for the Coupling of Thermochemical Hydrogen Cycles to Tandem Mirror Reactors"; Proc. 4th ANS Top. Mtg. Tech. Controlled Nucl. Fusion: King of Prussia, PA, 1980. Werner, R. W.; private communication: Lawrence Livermore National Laboratory; Jan. 1981. Shunk, F. A. "Constitution of Binary Alloys, Second Supplement"; McGraw-Hill: New York, NY, 1969. Elliott, R. P. "Constitution of Binary Alloys, First Supplement"; McGraw-Hill: New York, NY, 1965.


540

METAL

BONDING AND

INTERACTIONS

14.

Ihle, H. R.; Wu, C. H. "Experimental Determination of the Partial Pressures of D , LiD, and Li D in Equilibrium With Dilute Solutions of Deuterium in Liquid Lithium"; Proc. 8th Symp. Fusion Tech.; Leeuwenhorst Congress Centre: Noordwijkerhout (The Netherlands), 1974: published by Commission of European Communities Directorate General; Scientific and Tech. Information and Information Management; Luxembourg, 1974. 15. Watson, J . S. "Evaluation of Methods for Recovering Tritium From the Blankets or Coolant Systems of Fusion Reactors"; Oak Ridge National Laboratory: Oak Ridge, TN, ORNL-TM-3794, 1972. 16. Natesan, K.; Smith, D. "Effectiveness of Tritium Removal From a Lithium Blanket by Cold Trapping Secondary Liquids, Na, K, and NaK"; Nucl. Tech. 1974, 22. 17. Katsuta, H.; Ishigai, T.; Furukuwa, K. "Equilibrium Pressure and Solubility of Hydrogen in Liquid Lithium"; Nucl. Tech. 1977, 32. 18. Veleckis, E . ; Yonco, R. M.; Maroni, V. A. "Solubility of Lithium Deuteride in Liquid Lithium"; J . Less-Common Metals, 1977, 55. 19. Buxbaum, R. E . ; Johnson, E. F. "The Use of Yttrium for the Recovery of Tritium From Lithium at Low Concentrations"; Princeton Plasma Physics Laboratory, Princeton University: Princeton, NJ, PPPL-1548, 1979. 20. Singleton, M. F . ; Folkers, C. I.; Griffith, C. M. "Assessment of Uranium and Cerium as Hydriding Materials for Hydrogen Isotopes in Flowing Argon"; ANS Annual Meeting: New York, NY, 1977. 21. Selle, J . E . ; Personal Communication, Oak Ridge National Laboratory: Oak Ridge, TN, 1977. 22. Webb, R. W. "Permeation of Hydrogen Through Metals"; Atomics International: Canoga Park, CA, NAA-SR-10462, 1965. 23. Lee, J . D.; Werner, R. W. "Concept for a Gas-Buffered Annular Heat Pipe Fuel Irradiation Capsule"; Lawrence Livermore National Laboratory: Livermore, CA, UCRL-50510, 1968. 24. Werner, R. W. "The Generation and Recovery of Tritium in Thermonuclear Reactor Blankets;" Lawrence Livermore National Laboratory: Livermore, CA, UCID-15390, 1968. 25. Calaway, W. F. "Electrochemical Extraction of Hydrogen From Molten LiF-LiCl-LiBr and its Application to Liquid-Lithium Fusion Reactor Blanket Processing"; Nucl. Tech., 1978, 39, 63. 26. "Laser Program Annual Report—1979"; Lawrence Livermore National Laboratory: Livermore, CA, UCRL-50021-79, 1980, p 8-68. 27. Ihle, H. R.; Neubert, A.; Wu, C. H. "The Activity of Lithium, and the Solubility of Deuterium in Lithium-Lead Alloys"; Proc. 10th Symp. Fusion Tech.: Padova, Italy, 1978, p 639.


2

2


33.

BLINK ET AL.

Lithium

in Fusion

Reactors


28.

541

Veleckis, E . ; Yonco, R. M.; Maroni, V. A. "The Current Status of Fusion Reactor Blanket Thermodynamics;" Argonne National Laboratory: Argonne, IL, ANL-78-109, 1979. 29. Opie, W. R.; Grant, N. J . "Solubility of Hydrogen in Molten Lead"; J . Metals 1951, p 244. 30. Cafasso, F . ; Veleckis, E . ; Private Communications, Argonne National Laboratory, Argonne, IL, 1980 and 1981. 31. Hoffman, N. J.; Blink, J . A.; Darnell, A. "Properties of Lead-Lithium Solutions"; Proc. 4th ANS Top. Mtg. Tech. of Controlled Nucl. Fusion: King of Prussia, PA, 1980. 32. Saboungi, Marie Louise; Marr, Jane; Blander, Milton. "Thermodynamic Properties of a Quasi-ionic Alloy From Electromotive Force Measurements: The Li-Pb System," J . of Chem. Phys. 1978. 33. Ihle, H. R.; Neubert, A.; Wu, C. H. "The Activity of Lithium, and the Solubility of Deuterium in Lithium-Lead Alloys"; Proc. 10th Symp. Fusion Tech.: Padova, Italy, 1978, p 639. 34. Neubert, A.; Ihle, H. R.; Gingerich, K. A. "Thermodynamic Study of the Molecules BiLi and PbLi by Knudsen Effusion Mass Spectroscopy," J . Chem. Phys. 1978. 35. Nguyen, V. T.; Enderby, J . E. "The Electronic Structure of Lithium-Based Liquid Semiconducting Alloys"; Philisophical Mag. 1977, 35, 4, p 1013-1019. 36. Cowles, J . O.; Pasternak, A. D. "Lithium Properties Related to Use as a Nuclear Reactor Coolant"; Lawrence Livermore National Laboratory: Livermore, CA, UCRL-50647, 1969. 37. Nesmeyanov, A. N. "Vapor Pressure of the Elements"; Academic Press: New York, NY, 1963. 38. Hultgren, R.: et al. "Selected Values of Thermodynamic Properties of Metals and Alloys"; John Wiley and Sons Inc.: New York, NY, 1963. 39. Stull, D. R.; Prophet, H. "JANAF Thermodynamic Tables, Second Edition"; National Bureau of Standards: Washington, D.C., 1971. 40. Demidov, A. I.; Morachevskii, A. G.; Gerasimenko, L. N. "The Thermodynamic Properties of Liquid Li-Pb Alloys;" Translated from Elektrokhimiya, 9, #6, 848-851, (translation, June 1973; original October 1972). 41. Gillespie, G.; private communication: Physical Dynamics, 1980. For convenience, uranium was used as the heavy ion beam in these calculations although a non-fissionable ion will almost certainly be the eventual choice for a HIB fusion reactor. 42. Kim, Yon-Ki; private communication: Argonne National Laboratory; Jan. 1981. Kim said that for identical beam and background species, the beam stripping cross section will decrease to an extent difficult to theoretically predict.


542

43. 44. 45.


Mueller, R.; private communication; Gesellschaft fur Schwerionenforschung, Darmstadt, West Germany; Nov. 7, 1980. "Laser Program Annual Report-1979;" Lawrence Livermore National Laboratory: Livermore, CA, UCRL-50021-79, 1980, 8-78 to.8-83. Steam cycle III in Fig. 8-79 was used. Meier, W.; private communication; Lawrence Livermore National Laboratory, 1980. The ratio of thermal to fusion power for an 80 v/o Pb Li - 20 v/o steel liquid metal wall is 1.29 (1-D calculation) as compared to 1.16 for the original HYLIFE (2-D calculation). Monsler, M. J.; Meier, W. R. "A Conceptual Design Strategy for Liquid-Metal-Wall Inertial Fusion Reactors; Lawrence Livermore National Laboratory: Livermore, CA, UCRL-84881, 1980, 28. Ref. 44; Figs. 8-82 and 8-84.


4

46.

47.

RECEIVED August 26,

1981.


Metal Bonding and Interactions in High ... - ACS Publications

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