THE CHEMISTRY AND THERMODYNAMICS OF MOLTEN

SALT REACTOR FLUORIDE SOLUTIONS( 1)

C. F. Baes, Jr. Sr. Research Staff Member

Oak Ridge National Laboratory Oak Ridge, Tennessee

ABSTRACT

A solvent of lithium and beryllium fluorides (about 2 moles

of LiF per mole of BeF,) is used in the fuel salt, the coolant

salt, and the flush salt of the Molten Salt Reactor Experiment.

As a result of the chemical development work done for this reactor

concept, considerable chemical and thermodynamic information has

been acquired concerning this solvent and its solutions with

actinide,, lanthanide, and structural metal fluorides. It is the

purpose' 'of this paper to review this information, much of which

is not yet generally available.

The data were obtained mainly by measurements of heterogeneous

' equilibria; i.e., by equilibration of melts with gaseous mixtures

containing hydrogen, hydrogen fluoride, or water and by deter-

minations of solid-liquid phase equilibria.

The results of these measurements gave direct information

about such important chemical problems as: (1) The corrodibility

of structural metals and the reducibility of the structural metal . . I . '

(1); Research sponsored by t contract with the Union Carbide Corporation. ,

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of 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. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

PO\IS, Ni2+, ~e,+, crZ+; (2) reactions with water vapor to form

oxide and hydroxide ions, and the removal of these ions; (3)

the precipitation and solubility of the oxides of beryllium,

uranium, zirconium, thorium and the rare earths; (4) the stability

of uranium(1V) toward reduction to the trivalent state and pos-

sible 'subsequent disproportionation; and (5) the solubilities

and solid solution formation of rare earth fluorides. Equally

important has been the wider usefulness of this information when

the methods of thermodynamics are brought to bear. Thus the data

obtained could be used to: (1) correlate, revise, and extend

existing thermochemical data on fluorides and oxides; (2) deter-

mine activity coefficients of the components LiF,, BeFz , UF4 , and NiF, in these molten salt solutions; (3) calculate electrode

potentials involving a variety of solute ions; and (4) estimate

solubilities and reactivities of compounds not directly investi-

gated.

Thus the chemical development program for the Molten Salt

Reactor concept provides a number of interesting examples of the

interrelationship between thermodynamics and problems in reactor

chemistry and engineering.

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,THE CHEMISTRY AND THERMODYNAMICS OF MOLTEN I

I

1 SALT REACTOR FLUORIDE SOLUTIONS( ? . .

C. F. Baes, Jr. I

S r . Research S t a f f Member I Oak Ridge Nat iona l Laboratory

Oak Ridge, Tennessee

1. . I n t r o d u c t i o n

The Molten S a l t Reactor .Exper iment (MSRE), which went

c r i t i ca l a t ORNL i n June , 1965, is f u e l e d by a molten LiF-BeF2-

ZrF4-UF4 mix ture and moderated by g r a p h i t e . While i t w i l l n o t

demonstra te b reed ing , t h i s r e a c t o r experiment i s in tended t o

show t h a t a mol ten-sa l t f u e l e d r e a c t o r is a p o s s i b l e , indeed a n I

I

a t t r a c t i v e , means by which t o ach ieve thermal breeding. A I

I r e c e n t c o l l e c t i o n of pape r s has d e s c r i b e d t h i s r e a c t o r and t h e I

e x t e n s i v e development work which l e d t o its c o n s t r u c t i o n and I

o p e r a t i o n [ l ] . i 1

I n cons ide r ing p o s s i b l e m a t e r i a l s which could s e r v e as

c o n s t i t u e n t s i n such a thermal b reede r r e a c t o r , G r i m e s [ 2 ]

reached t h e conc lus ion t h a t t h e cho ice of major s a l t components

is l a r g e l y l i m i t e d t o mix tu re s of L i 7 F and BeF, by t h e need f o r

neu t ron economy, low v o l a t i l i t y , and chemical s t a b i l i t y . While

i n t h e LiF-BeF, system (F ig . 1 ) mix tu re s w i t h m e l t i n g p o i n t s

below 5 0 0 ~ ~ occur i n t h e range 0.33 - 0.73 mole f r a c t i o n BeF, [ 3 ] ,

composi t ions nea r 0.33 BeF, appear t h e most s u i t a b l e . (Here, and

e lsewhere , numbers p reced ing a s a l t component deno te mole f r a c t i o n ) .

( l )Resea rch sponsored by t h e U. S .- Atomic Energy commission under c o n t r a c t w i th t h e Union Carbide Corporat ion.

The composition of the MSRE fuel salt is 0.65 LiF, 0.291 BeF,,

0.05 ZrF4, 0.009 UF4. That of the coolant and flush salt is

LiF - 0.34 BeF, . As part of the development of the MSRE, a considerable I

amount of chemical and thermodynamic information has been gathered

about LiF-BeF, melts near this composition. Most such information

has been gained by the use of heterogeneous equilibria involving

reactions of gases or solids, or both, with the liquid phase. In

general, these studies gave fairly direct information about impor-

tant chemical questions related to the MSRE.

It is the present purpose to review this information, much

of which is not yet generally available, and to indicate its

application to the chemistry of the MSRE. It will then be sum-

marized by thermodynamic methods as a means of extending its

usefulness. This seems fitting and proper at this stage in the

development of the molten salt reactor concept. Future such

reactors evidently will employ salt mixtures similar to those ,

of the MSRE considered here; hence, a knowledge of the thermo-

dynamics of these solutions should prove generally useful.

2. Reactions in LiF - 0.33 BeF, Table I lists the reactions studied, the form of the equili-

brium constants, and values of a and b in the following expression

which gives the numerical:.value of the equilibrium constants in

LiF - 0.33 BeF, log K = a + b(lo3/T) - (1)

This expression, implying a constant heat (AH = -2.3Rb) and

entropy (AS = 2.3Ra) of reaction, adequately approximates the

measured values in the temperature range studied (usually 500 - 700~~). The concentration scale is the mole fraction; e.g.,

+ n. .' LIF + "B~F, 1 Gas pressures are expressed in atmospheres, and at the low pres-

sures and high temperatures involved, gases are assumed ideal.

The standard states for reactants and products generally

can be seen from the form of K. ' Here and elsewhere for most solutes the standard state is the hypothetical one mole fraction

. . . . Table I

Reactions in LiF-0.33BeF2 .P

[log K = a + b (10~1~) ]

Reduction Reactions Involving riydrogen8

1 ' H2(g) + ~iF2(d) * ~i(s) + 2HF(g) .

2 II~(~) + FeFa(d) * Fe(s) + ~HF(~)

3 ~2(g) + ~rFz(d) * ~r(s) + ~RF(~)

4 &2(g) + UF4(d) * UF3(d) +. ,(g)

5 Hn(g) + ~eF,(d) * Be(s) + ~BF(~)

Metathesis Reactions Involving Gases

6 ~z~(g) + ~e~z(d) * BO(S) + 2~~(g)

7 2~20(g) + ZrF4(d) * Zrop(s) + 4~(g)

8 H20(g) + 2~-(d) + 02-(d) + ~HF(~)

9 ~20(g) + F-(d) * OH-(d) +

10 H~s(~) + 2~-(d) * s2-(d) + ~HF(~)

Metathesis Reactions Involving Solid Oxides

-

Kb Est . 2 Error

a b in log K C Source

1 2/(pH2) (%iF2 8.37 -3.60 0.04 Ref- 4

(P,) 2/(pI11 5.20 -5.31 0.02 Ref; 4

(P,) (xrrF2) 5.12 . -9.06 0.06 Ref. 4 1 -

(P,) (%J)/(pH22)(XUF4) 4*07 -9.33 0.02 Ref. 5 i

7.U -21.56 0.1. Refs. 6,7

2/(pH20) 4.23 -5.67 0.02 Ref. 9 /

(P,)~/(~,,~)~(X~) 11.21 -10.66 0 04 Ref. 10 ;

( P ~ ) 2((Xo2-)/(~H20) 4.20 -8.64 . . 0.08 , Ref. 9

(P,) (x~~-)/(P~~~) ,

-1.03 -2.08 0.04 . Ref. 9

( P ~ ) 2(Xs~-)/(pH2s) log K(~&'K) < -4 ---- Ref. 12

(P,) (%-)/(prn) log ~(763'~) I -3 ---- Ref. 13

r

X &3'4 . .

-2.75 , -0.69 ' 0.05 6,7; Ref. 15

%4 . -2.07 -1.74 0 07- 12,14; Ref. 15

(xZ~F~)/(XUF~) ' -0.67 1.05 . 0 05 Ref. 15

(%'@F~)/(XUF~) log ~(1023'~) Z 1.2 . ---- ' Ref. 18

Table I (continued)

E s t . 2 Error K~

C Solubility Reactions - a - b i n log K Source

. .

16 B ~ O ( S ) * Be2+(d) + 02-(d) X02- -0. 04 -2.96 ' 0.08 6,8 .

20 N ~ O ( S ) + Ni2+(d) + 02-(d) ( x ~ ~ 2 + ) ( ~ ~ 2 - 1 -2.58 -4.39 --- EQs. 25, 26, Ref. 32

1 2 l F e ~ ( s ) ' Fe2+(d) + 02-(6) (52+)(x02-) -0.52. -4 12 --- EQs. 25, 26, Ref. 32

0.30 -2.07 0.01 Ref. 4

! 23 FeFz(s) * FeFa(d) ' 2.45 -3 05 0.01 Ref. 4 3 3 9 2 I

I . I 24 IaF3(s) = I a ~ 3 ( d ) k l ? ~ 1 58 -3.38 0.02 Ref. 20 I /

25 ceF3(s) * ceF3(d) x CeFs 1.64 -3.38 0.02 Ref. 20

26 SrnFs(s) = %E'3(d) . . . x 1.97 -3.38 0.02 Ref. 20 m3

27 ~ @ 3 ( s ) * ~ u ~ 3 ( d ) k 3 1.30 -3.15 Ref 19 .

a The notations ( s ) , (d), and (g) indicate respectively the solid, dissolved, and gaseous states.

Pi i s expressed i n atmospheres; xi i s the mole fraction and, for UF-0=33BeF2, i s equal t o moles of i/kg of salt/30.03.

C Numbers other than reference numbers and numbers .of equations in text refer t o reactions in t h i s table.

r \. '

. '

solution. Exceptions are LiF, BeF, , ~e", Li+, and F-, for

. which the solvent composition LiF - 0.33 BeF, is taken as the I

standard State. The notation (s) , (d) , and (g) denote, .respectively, solid, dissolved, and gaseous states. In the majority of reactions

listed, F- is the only anion involved, and for simplicity the

dissolved components are written in the molecular form, though

this is not.intended to imply the actual species present in

solution. When anions other than F- appear in the reaction,

ionic species are written. 'In some cases. this is done to avoid

the choice of a neutral component'in the liquid phase and in

others to indicate that complete dissociation 'of an anion (e.g.,

02') and a cation (e.g., zr4+) is assumed.

Estimates of activity coefficients as a function of solvent

. composition and solute concentration are discussed in Section 3.

On the basis of these estimates, the values of K indicated in . Table I include, where necessary, a correction of the original

measurements .to a melt composition of LiF - 0.33 BeF,. 2.1 Hydrogen Reduction Reactions

The reduction of the bivalent f1uoride.s of nickel, iron and

chromium by hydrogen in BeF2-0.38LiF was investigated by Blood [4]

in a series of careful transpiration experiments. The equilibrium

quotients which were measured for the reaction

were found to be independent of x MF2

at the low concentrations

. studied. These concentrations were limited by the solubilities

of the fluorides. The reduction of UF4 dissolved in LiF-BeF,-UF4

melts by hydrogen as well as the reduction of UF4 solid to UF,

solid has recently been investigated by Long [5]. He summarized'

his results by the.following expressions: For the reduction of

U F ~ to UF, in solution

<

a For the reduction of UF4 solid to UF, solid

5 - 10g(PH+/PH12) = 3.57' - 6 . 87(103 /T) . (5)

While t h e r e d u c t i o n of BeF, i n LiF-0. 33BeFz by hydrogen is

' . i n a c c e s s i b l e t o d i r e c t measurement, r e c e n t l y D i r i a n [ 6 ] and

Rornberger [ 7 ] have made measurements on t h e fo l lowing ce l l

Pd,Hz,HF ( LiF-0.33BeFzI Be

The ce l l r e a c t i o n w a s taken t o be

Hz (g) + BeF, (d) + ~ e ( s ) + 2HF(g) ( 6 )

With PHF and PH c o r r e c t e d t o 1 a t m , t h e p o t e n t i a l w a s found t o . 2

be . .

1

F r o m ' t h i s t h e e q u i l i b r i u m c o n s t a n t expansion i n Table I has been

c a l c u l a t e d . The two e l e c t r o d e s - ~ e ' + I Be and F-,H, , ~ d 1 HF - ,were judged t o be r e v e r s i b l e from p o l a r i z a t i o n measurements.

I These r e s u l t s show t h a t n i c k e l is t h e most noble of t h e

1 t h r e e s t r u c t u r a l metals s t u d i e d , ~ i ~ + being r e a d i l y reduced by

~ hydrogen (Fig . 2 ) . chromium was t h e l e a s t nob le , crZ+ be ing

reduced by hydrogen wi th d i f f i c u l t y . The s p a r g i n g of molten

f l u o r i d e s wi th hydrogen t o reduce s t r u c t u r a l m e t a l i m p u r i t i e s

is r o u t i n e l y used a s a p u r i f i c a t i o n . s t e p . The c o n c e n t r a t i o n s of

~ i " , ~ e ~ + and cr2,+ and t h e r a t i o u4+/u3+ i n LiF-0.33BeFz expec ted

. . under two sets of condi t i ,ons i s . i n d i c a t e d i n F ig . 2 . On t h e l e f t of t h e f ' i gu re , wherein t h e e q u i l i b r i u m c o n s t a n t s , a r e p l o t t e d , i t

appea r s t h a t only ~ i ' + is e x t e n s i v e l y reduced by a mix tu re of Hz

and HF, both a t u n i t a c t i v i t y ( 1 a tm). Nickel is a r e l a t i v e l y

i n e r t c o n t a i n e r material f o r LiF-BeF2 m e l t s i n t h e presence of

exces s hydrogen. On t h e r i g h t of F ig . 2 are much more r educ ing

c o n d i t i o n s which approximate t h o s e i n t h e MSRE. The c o n c e n t r a t i o n

of cr2+ is set a t 100 ppm i n e q u i l i b r i u m wi th t h e pure metal.

I t is seen t h a t ~ e ' + and N i Z + should be reduced e s s e n t i a l l y com-

p l e t e l y t o t h e metals and some u4+ should be reduced t o u3+. The

r e a c t i o n of u4+ i n t h e MSRE f u e l w i th t h e c o n t a i n e r m e t a l (INOR-8, .. a n icke l -base a l l o y c o n t a i n i n g about 770 C r , 570 Fe and 16% Mo)

Cu(in INOR-8) + ZUF4 (d) + 2UF3 (d) + CrF, ( a ) , l o g K (873°)m-.9 .0

(8)

., is, t h e on ly c o r r o s i o n r e a c t i o n expec ted , and t h e e x t e n t l o f t h i s

reaction should be small [8]. In the absence of UF4 (i.e., the i / flush salt) no reaction between the salt and the container metal 1

. . . is expected. I

' 2.2 Metathesis Reactions Involving HF and H,O

Extensive equilibrium measurements'of ,reactions between

water in hydrogen carrier gas with LiF-BeF, melts .were made by

Mathews and Baes [9]. Equilibrium quotients for the reaction

H,O(g) + BeF, (d) = BeO(s) . + 2HF(g) (9

(wherein'beryllium oxide was present as a saturating solid' phase) 0 were measured from 500 - 700 C over the composition range . .

X BeF2 = 0.3 - 0.8, limited at one extreme by the LiF liquidus .

(Fig. 1) and at the other by rapidly increasing viscosity. The

results were summarized by the expression

log ('HF' "H, 0 X ~ e ~ , ) = a + b xii; + c xiiF (10)

wherein a, b and c all were, linear functions of ~/TOK

a = 3.90.0 - 4.418(103/T),

From this expression the' activities of BeF, and, by a Gibbs-

Duhem integration, the activities of LiF were estimated (Fig. 5).

In the same investigation, measurements were made upon melts not

saturated with BeO. In addition to the reaction

for the formation of oxide ion, it became evid,ent, both from . these measurements and from those upon.Be0 saturated melts, that

hydroxide ion also was formed .

H,O(g) + F-(d) s' OHW(d) + HF(~) (12)

While the equilibrium quotients for these two 'reactions were less

accurately determined than was the previous one for Be0 saturated

melts (ca. f 207'0 and 2 107'0 respectively compared to 5 57'0) because '.of limitations inherent in the transpiration method used, they

were sufficient to show that both oxide and hydroxide increase in

s t a b i l i t y wi th i n c r e a s i n g tempera ture . The s t a b i l i t y of hydroxide

wi th r e s p e c t t o ox ide , however, dec reases w i t h i n c r e a s i n g t e m -

p e r a t u r e and i t is low enough t h a t hydroxide can be r e a d i l y

decomposed i n t h e s e f l u o r i d e m e l t s by spa rg ing wi th an i n e r t

g a s (e . g . , hydrogen) . OH- + F- + HF(g) + 02', l o g K = 5 .2 .3 - 6.56(103/T) (13)

S i m i l a r measurements have a l s o been made by Baes and . .

H i t c h [ i ~ ] i n whi'ch. t h e LiF-0. 33BeF2 conta ined added ZrF4 . With

X ZrF4 > -- 3 x ZrO, is t h e s t a b l e s a t u r a t i n g ox ide s o l i d ,

hence t h e fo l lowing e q u i l i b r i u m may be w r i t t e n

2H20(g) + ZrF4 (d) = ZrO, ( s ) + 4HF(g) (14)

.From t h e s e measurements t h e a c t i v i t y c o e f f i c i e n t of ZrF4 could be

e s t ima ted (Fig . 5) a s w e l l as t h e s o l u b i l i t y of ZrO, (Sec t .. 2.5) . I t w a s a l s o found t h a t t h e e q u i l i b r i a (11 and 1 2 ) ' f o r t h e format ion

of ox ide and hydroxide i o n s were s h i f t e d . t o t h e r i g h t ~ w i t h ' . i n c r e a s -

i n g x i . e . , i n t h e d i r e c t i o n of g r e a t e r s t a b i l i t y of t h e s e ZrF4 ' i o n s .

Thes.e r e s u l t s a r e ' g e n e r a l l y c o n s i s t e n t wi th .p rev ious

obse rva t ions ' t h a t LiF-BeF, m e l t s a r e r e a d i l y f r e e d of ox ide con-

t amina t ion by t r ea tmen t wi th gaseous mix tures of H, and HF,

ano the r r o u t i n e l y used p u r i f i c a t i o n s t e p . The measured e q u i l i -

brium q u o t i e n t s i n LiF-0.33BeF2 were used t o c a l c u l a t e t h e

e f f i c i e n c y of HF u t i l i z a t i o n i n such a t r e a t m e n t a s a f u n c t i o n of

t empera ture and HF p a r t i a l p r e s s u r e wi th t h e assumption t h a t

equ i l i b r ium is mainta ined between t h e gas stream, t h e molten s a l t , .

and any Be0 s o l i d p r e s e n t . Th i s c a l c u l a t i . o n (F ig . 3 ) shows t h a t

t h e e f f i c i e n c y i n t h e removal of ox ide t o a f i n a l v a l u e of 16 ppm

(x02 - = 3.3 x l o -= ) is q u i t e h igh over a wide range of c o n d i t i o n s . '

The removal of ox ides from LiF-0.33BeF2 m e l t s by Hz-HF s p a r g i n g

d u r i n g t h e p r e p a r a t i o n of f l u s h s a l t s and c o o l a n t s a l t s f o r t h e

, MSRE [ll] was performed on 100 kg ba t ches i n c y l i n d r i c a l v e s s e l s

wi th a s i n g l e gas d e l i v e r y l i n e . I t a p p e a r e d - t h a t about 2/3 of

t h e c a l c u l a t e d e f f i c i e n c y w a s ob t a ined even i n t h i s r e l a t i v e l y

• s imple equipment.

. I n t h e presence of ZrF, and ZrO , t h e i n c r e a s e d s t a b i l i t y

of oxide and hydroxide r ende r more d i f f i c u l t t h e removal of

ox ide from such me,l ts t han is t h e c a s e wi th t h e s o l v e n t s a l t .

Because of t h i s , i n t h e p u r i f i c a t i o n of LiF-BeF,-ZrF, m e l t s i t

was found expedien t t o decant t h e molten s a l t away from t h e

p r e c i p i t a t e d Z r O , a s a s imple means of removing most of t h e

ox ide be fo re HF-H, t r e a t m e n t .

2 .3 M e t a t k ~ s l s Reac t ions Involv ing HF-H,S and HF-HI

An a t tempt has been made t o s tudy t h e removal of s u l f i d e ,. .... . ....

from LiF-0.33BeF2 m e l t s by HF-H, spa rg ing [1'2]

b u t , u n f o r t u n a t e l y , t h e e f f l u e n t H,S/H, .mix ture r e a c t e d wi th

t h e r e l a t i v e l y c o o l e r s u r f a c e s of t h e n i c k e l e x i t ' t u b i n g used.

The s u l f i d e was e v i d e n t l y p r e c i p i t a t e d from t h e m e l t , presumably

a s B ~ S , though no d i r e c t ev idence of t h i s w a s ob t a ined . I n tests

on t h e removal of i o d i d e by HF-H, spa rg ing [13]

H F ( ~ ) + I-(d) =+ ~ - ( d ) + HI(^), log K > ( l o 4 (16)

t h e r e . w a s a l s o i n t e r f e r e n c e caused by. r e a c t i o n of t h e e f f l u e n t . .

gases w i th t h e metal s u r f a c e s i n t h e gas ex i t " : l i ne s . Because .of

t h e s e d i f f i c u l t i e s i t i s p o s s i b l e , a t p r e s e n t , only t o a s s i g n

lower l i m i t s t o t h e e q u i l i b r i u m c o n s t a n t s of r e a c t i o n s (15) and

(16) . These p re l imina ry r e s u l t s do s e r v e t o conf i rm, however,

obse rva t ions t h a t t h e HF-H, t r ea tmen t used i n p u r i f y i n g molten

s a l t s seems t o remove any s u l f i d e , a s w e l l a s ox ide , which may

be p r e s e n t a s an impur i ty . The u s e of HF s p a r g i n g a l s o may prove

a v a l u a b l e means of removing t h e i o d i n e p recu r so r of t h e impor-

t a n t f i s s i o n p roduc t , ~ e ~ ~ ~ , i n an o p e r a t i n g r e a c t o r .

2.4 Me ta thes i s Reac.tions Invo lv ing S o l i d Oxides

By combina t ion .of r e a c t i o n s 9 and 14 , i t is p o s s i b l e t o

c a l c u l a t e t h a t both Be0 and ZrO, w i l l co -ex i s t a t e q u i l i b r i u m

wi th LiF-0. 33BeF2 c o n t a i n i n g ox ide . i o n

ZrO, ( s ) + 2 ~ e , + ( d ) + Zr4+(d) + 2BeO(s). (17) \

when ZrF4 is present at concentration of approximately 3 x

mole fraction. With larger amounts of added ZrF4 , ZrO, becomes the less soluble (stable) oxide.

It was decided to include ZrF4 in the MSRE fuel composition

to prevent the precipitation of UO, which otherwise would result

from inadvertent oxide contamination of the fuel. Measurements

of the metathesis reaction

ZrO, (s) + UF4 (d) + ZrF4 (d) + UO, (s) (18)

have shown that the mole ratio of ZrF4 to UF4 at equilibrium with

both UO, and ZrO,, while varying somewhat with temperature and

melt composition, remains well below that chosen for the fuel

salt [14,15]. As a consequence, a considerable amount of zr4+ - an amount easily detected by chemical analysis of the fuel

salt - would be precipitated by oxide contamination before any U02 should precipitate.

In connection with these studies, it was ascertained that,

contrary to published UO,~Z~O, phase diagrams [16], (U-Zr) 0,

solid solutions are not formed in the temperature range 500 - 7 0 0 ~ ~ . Because of the obvious importance of this to the MSRE,'

experiments have been carried'out in which both U0,-ZrO, mixtures

and (U-Zr)02 solid solutions prepared by fusion were equilibrated

with LiF-BeF, melts. At the present writing, no solid solution

formation has been detected below 1 1 0 0 ~ ~ [17].

The metathesis equilibrium in Table I involving UO, and

Tho2 is an estimate from results of Shaffer et al, in LiF-0.4

NaF [18].

2.5 Oxide Solubilities

,The oxide concentration in LiF-0.33BeF2 saturated with Be0

may be estimated by combining the equilibrium results for reactions. " , ,. . (9) and (11). 'The solubility increased rapidly with temperature,

but no strong dependence on XBeF, was found. In these measure-

. ments [9], the mole fraction of oxide at Be0 saturation probably

was less than 0.002. Hence, the activities of BeF, and LiF which

were derived from them are probably not appreciably different

from the corresponding.activiti.es in oxide-free mixtures.

,- From t h e s i m i l a r measurements i n ZrF,-containing m e l t s [ l o ]

t k e s o l u b i l i t y product of ZrO, could be e s t ima ted . With i n c r e a s -

i n g x ZrF4 ' t h e concen t r a t i on of ox ide a t ZrO, s a t u r a t i o n a t f i r s t

f a l l s a s would be expected from t h e e q u i l i b r i u m

Z r O z (s) + z r 4 + ( d ) + 2 0 ~ - ( d ) .(19>

However, it then l e v e l s o f f and subsequent ly rises wi th f u r t h e r

i n c r e a s e s i n x Z r F4 (F ig . 4 ) . Th i s could be caused, a t l e a s t i n

p a r t , by t h e format ion of a complex i o n , zro2+

z r4+(d ) + OZ'(d) s z r o 2 + ( d ) (20)

o r i t could be caused e n t i r e l y by t h e i n f l u e n c e of t h e changing

mel t composit ion on t h e a c t i v i t y c o e f f i c i e n t s of t h e s p e c i e s

zr4+ and 0'-. The p l o t i n F ig . 4 i n d i c a t e s approximately t h e

"oxide t o l e r a n c e " of .MSRE f u e l s a l t - f l u s h . s a l t mix tu re s ; i , e . ,

t h e amount of d i s s o l v e d ox ide t h e s e mixtures ' can c o n t a i n with- '

~ u t ox ide p re . c ip i t a t5on . . I t is seen t h a t the ox$de. t o l e r a n c e

i n c r e a s e s r a p i d l y w i th tempera ture , e s p e c i a l l y nea r t h e f u e l

composit ion (x r 0.05) , i n d i c a t i n g t h a t any e x c e s s ox ide Z r F, p r e s e n t might be removed by c o l l e c t i n g ZrO, on a r e l a t i v e l y coo l

s u r f a c e i n t h e MSRE system.

The s o l u b i l i t y p roduc t s o f N i O and F e 0 , i n d i c a t e d i n Table I , . were e s t ima ted from t h e p rev ious ly c i t e d e q u i l i b r i u m r e s u l t s

(Sec t . 4.3) . 2.6 F l u o r i d e S o l u b i l i t i e s

Table I a lso .summarizes t h e s o l u b i l i t y measurements by

Blood [ 4 ] of FeF, and NiF, , t h o s e by , Barton [19 ] ' of PuF,, and

t h o s e by Ward,et a1 [ 2 0 ] of r a r e e a r t h t r i f l u o r i d e s . ~ h e s e l a s t

i n v e s t i g a t o r s found f l u o r i d e s o l i d s o l u t i o n format ion and po in ted

o u t t h a t t h i s could prov ide a u s e a b l e method f o r removing' r a r e -

e a r t h f i s s i o n produc ts from a r e a c t o r f u e l s t ream by exchange

3. E f f e c t of Melt Composition Upon A c t i v i t y C o e f f i c i e n t s

I n s e v e r a l of t h e i n v e s t i g a t i o n s c i t e d above t h e e f f e c t of

mel t composit ion on e q u i l i b r i u m was s t u d i e d and fr'om t h e s e r e s u l t s

t h e corresponding v a r i a t i o n of a number of a c t i v i t y c o e f f i c i e n t s

can be determined. The curves shown i n F ig . 5 r e p r e s e n t t h e s e

v a r i a t i o n s a s a f u n c t i o n of t h e s o l v e n t composit ion ( l e f t -hand

f i g u r e ) . a n d ' a s a f u n c t i o n of t h e mole f r a c t i o n of s o l u t e added

t o LiF-0.33BeF2 ( r igh t -hand f i g u r e ) . The s t a n d a r d s t a t e s

remain t h e same; i . e . , f o r t h e s o l v e n t components i t is

LiF-0.33BeF2 and f o r t h e s o l u t e s i t i s t h e h y p o t h e t i c a l mole

f r a c t i o n s o l u t i o n i n LiF-0.33BeF2.

The curves (F ig . 5 , on t h e l e f t ) f o r LiF and f o r BeF, a r e

d e r i v e d from Eqn. 1 0 , yBeF, being ob ta ined d i r e c t l y and yLiF

be ing ob ta ined by a Gibbs-DUhem i n t e g r a t i o n . The c u r i e s f o r

PuF, and CeF, a r e based on t h e s o l u b i l i t y measurements of Barton

[19] and of Ward,et a 1 [ 2 0 ] . The curves f o r UF4 a r e based on Long's

r e s u l t s (Eqn. 4) wi th t h e assumption t h a t yUF3 is s i m i l a r t o

Y ~ e ~ 3 and y The curve f o r ZrF4 is from t h e p re l imina ry PuF, ' measurements of Baes and Hi t ch (Eqn. 14) . The curve f o r NiF, is

an e s t i m a t e based on t h e obse rva t ion t h a t yNiF2 i n NaF-ZrF4, ( a s

i n d i c a t e d by r e a c t i o n 3 [ 4 ] ) v a r i e s l e s s wi th ZrF4 i n t h i s s o l v e n t

t han does yCeF3 ( a s i n d i c a t e d by i ts ' s o l u b i l i t y [20] ' ) .

I These a c t i v i t y c o e f f i c i e n t curves w e r e used , where neces sa ry ,

t o c o r r e c t e q u i l i b r i u m measurements t o t h e r e f e r e n c e composit ion

LiF-0.33 PuF,. I t is seen t h a t t h e v a r i a t i o n of a c t i v i t y coef-

f i c i e n t s wi th composit ion is not l a r g e and t h a t , i n g e n e r a l , t h e

v a r i o u s curves a r e o rdered accord ing t o t h e r a t i o of charge t o

i o n r a d i u s ( z / r ) f o r t h e c a t i o n . A s more d a t a become a v a i l a b l e ,

i t w i l l be of cons ide rab le i n t e r e s t t o t e s t t h e c o r r e l a t i o n of

YMF, w i th z / r , s i n c e i t could prov ide a s imple b a s i s f o r e s t i m a t e s

of a c t i v i t y c o e f f i c i e n t s where d a t a on t h e e f f e c t of m e l t compo-

I s i t i o n a r e l ack ing .

4 . Thermodymamfc C o r r e l a t i o n s f 4 . 1 Hea ts and F ree Energ ies of Formation (AHf and a G ) .

I From t h e e q u i l i b r i u m measurements (Table I ) and publ i shed

v a l u e s of &If and a~~ f o r HF(g) and H,O(g) [ 2 l ] , fo rmat ion h e a t s @ and f r e e e n e r g i e s may be c a l c u l a t e d f o r 8 e 0 ( s ) , B ~ F , ( s ) , NiF, ( s ) , ..

and FeF2(s) i n t h e tempera ture range of i n t e r e s t he re (Table 1 1 ) .

I n a d d i t i o n , Long has c a l c u l a t e d AHf and A G ~ f o r UF, from h i s

measurements (Eqn. 5 ) , adopt ing t h e cor responding v a l u e s g iven

by Rand and Kubaschewski [22 ] f o r UF4 ( s ) . I n g e n e r a l , t h e

agreement of t h e s e c a l c u l a t i o n s w i th prev ious e s t i m a t e s is

s a t i s f a c t o r y , except i n t h e c a s e of NiF , ( s ) . G r i m e s ha s p rev ious ly

i n d i c a t e d [23 ] t h a t t h e p r e s e n t v a l u e s f o r NiF, ( s ) , based on

Blood ' s measurements, d i f f e r cons ide rab ly from - and a r e probably

more nea r ly c o r r e c t t h a n - prev ious e s t i m a t e s f o r NiF,(s) based

on measurements of J e l l i n e k and Rudat [ 2 4 ] . Long's v a l u e s f o r

UF,(s) ag ree wi th a p rev ious estimate by B r e w e r [ 2 5 ] bu t d i f f e r

cons ide rab ly from e s t i m a t e s by Glassner 1261 and Rand and

Kubaschewski [ 2 2 ] .

Included i n Table I1 a r e o t h e r h e a t s and f r e e e n e r g i e s of

fo rmat ion from t h e l i t e r a t u r e [ 2 7 , 2 8 ] . These were used i n t h e

c a l c u l a t i o n of nfif and acf v a l u e s f o r d i s s o l v e d components a able 111) ; i . e . , t h e p a r t i a l molal h e a t s and f r e e e n e r g i e s of fo rmat ion

f o r t h e components i n t h e s o l u t i o n s t a n d a r d s t a t e s de f ined pre-

v i o u s l y .

The flf a n d acf v a l u e s i n Table I11 f o r LiF(d) , BeF, (d) , NiF, (d) , FeF, (d) and CrF, (d) come most d i r e c t l y from t h e e q u i l i -

brium measurements, wi th AHf and a G f f o r H F ( ~ ) , H , o ( ~ ) , and L ~ F ( S )

only being r e q u i r e d from t h e l i t e r a t u r e . I n t h e ca se of t h e f t e t r a v a l e n t f l u o r i d e s , l i t e r a t u r e v a l u e s of AH and a G f f o r t h e

corresponding oxide; were u t i l i z e d , bu t t h e s e i n g e n e r a l , a r e more

a c c u r a t e l y known than a r e t h o s e f o r t h e f l u o r i d e s . The v a l u e s of

&If and A G ~ f o r t h e r a r e e a r t h s a r e based on t h e s o l u b i l i t y measure-

ments [20] and on Brewer 's e s t i m a t e s f o r t h e s o l i d s [ 2 8 ] .

The p a r t i a l molal f r e e e n e r g i e s of fo rmat ion (Table 111).

i n d i c a t e t h e r e l a t i v e s t a b i l . i t i e s of t h e d i s s o l v e d f l u o r i d e s . f I n terms of a G p e r g atom of f l u o r i d e LiF i s t h e most s t a b l e ,

fo l lowed by t h e rare e a r t h s . BeF, and ThF4 nex t f a l l t o g e t h e r ,

t h e n UF4 and ZrF4. Leas t s t a b l e a r e t h e s t r u c t u r a l meta l f l u o r i d e s . a

Table I1

Formation Heats and Free Energies of Fluorides and Oxides

(700-1000~~) '

-uf ( ~ o o o ~ K ) , st . f Error, compounda -d, kcal kcal kc a 1 Source

b

1 HF(g) . 65.19 66 20 0.3 Ref. 21

46.04 Ref. 21 2 ~ 2 0 ( g ) 59 07 0.1

3 Ii.F(s) 146.50 123.39 0.7 Ref. 21

4 B ~ O ( S ) 145 47 . . 118.84 0 6 5,6, (2)

5 B e ~ z ( 1 ) ' 237.00 207.57 0.6 5,6, (1) 9 ~ ~ 0 10

6 ~ r 0 2 ( s ) 260.4 . 216.0 1 Ref. 21

7 U F ~ ( S ) L f%8. 5 381.1 Ref. 22

8 U O ~ ( S ) 258.0 218.0 1 Ref. 22

9 U!?3(s) 351.9 299.8 . (71, (1) 5

10 Th02(s) 293 250 4 Ref. 27

7 11 IaFs(s) 421 360 Ref. 28

12 ceF3(s) 416 355 7 Ref. 28

a The notations ( s ) , (l), and (g) indicate respectively the solid,

'

l iquid, and.gaseous s ta tes .

Nmbers not i n parentheses r e fe r t o CO values f o r reactions i n Table I. Numbers i n parentheses r e fe r t o CO values i n t h i s tab le .

Table 111

Formation Heats and Free Energies f o r Solutes in LiF-0.33BeFz

-& f , ( ~ o o o ~ K ) , st . + Error, b solutea -& f, kcal kcal kcal Source

1 Ii+ + F- 142.70 124.79 (3), Eq. 10

a The standard s t a t e of the ions i s the hy-pothetical mole *action .

solution i n UF-0.33BeF2, with the exception of Id+, ~ e ~ + , and F-, f o r which the standard s t a t e i s LiF-0.333eF2

Numbers not i n parentheses, numbers i n parentheses, and numbers in brackets r e fe r respectively t o items l i s t e d in Tables I, 11, and in t h i s tab le .

4.2 E lec t rode P o t e n t i a l s

The r e s u l t s i n Table I I I . a r e expressed perhaps i n a more

f a m i l i a r way i n Table I V a s e l e c t r o d e p o t e n t i a l s f o r v a r i o u s

h a l f ce l l r e a c t i o n s wi th

H F ( ~ ) + e = ~ - ( d ) + l / 2 ~ , ( g ) , EO = o (21)

The s t anda rd s t a t e s remain t h e same. The manner i n which t h e s e

are c a l c u l a t e d is most e a s i l y shown by p o i n t i n g ou t t h a t any

combination of h a l f c e l l r e a c t i o n s which g i v e s a complete r e a c t i o n

of t h e form

w i l l y i e l d t h e Acf v a l u e given i n Table 111. (i - is t h e number of

e q u i v a l e n t s of charge and - F i s t h e Faraday) .

The p o s i t i o n s of t h e v a r i o u s c a t i o n s i n t h e e l ec t rochemica l

s e r i e s i n LiF-0.33BeF2 is seen t o be q u i t e s i m i l a r t o t h a t i n

aqueous s o l u t i o n s . This is i l l u s t r a t e d on t h e l e f t s i d e i n F ig . 6 ,

wherein t h e E0 v a l u e s i n LiF-0.33BeF2 a t 1 0 0 0 ~ ~ a r e p l o t t e d - v s

t h e . E0 v a l u e s f o r t h e same h a l f - c e l l r e a c t i o n i n aqueous s o l u t i o n s I ~ a t 2 5 O ~ [ 2 9 ] . I t i s n o t a b l e from t h i s comparison t h a t t h e s t r u c -

t u r a l me ta l s a r e r e l a t i v e l y more noble i n t h e molten f l u o r i d e t han

they a r e i n water . Also u4+ is more s t a b l e w i th . r e s p e c t t o u3+ i n t h e molten f l u o r i d e . When t h e E0 v a l u e s i n t h e f l u o r i d e s o l v e n t

' a r e compared t o v a l u e s i n LiC1-KC1 e u t e c t i c given by Liu [ 3 0 ] ' (on t h e r i g h t i n F ig . 6) t h e s a m e d i f f e r e n c e s p e r s i s t . .To t h i s

I e x t e n t i t might be s a i d t h a t t h e molten c h l o r i d e s o l v e n t i s rr:ore

l i k e water t h a n l i k e LiF-0.33BeF2. These d i f f e r e n c e s - t h e

r e l a t i v e n o b i l i t y of t h e s t r u c t u r a l me ta l s Fe, N i , and C r and

t h e r e l a t i v e s t a b i l i t y of u4+ with r e s p e c t t o u3+ - t end t o . .

f avo r LiF-0.33BeF;as a r e a c t o r f u e l s o l v e n t . .The c o r r e l a t i o n

i n F ig . 6 could prove a u s e f u l means of e s t i m a t i n g t h e E0 v a l u e s

(Ac va lues ) of r e a c t i o n s f o r which d a t a a r e l a c k i n g .

1 A number of o t h e r o b s e r v a t i o n s , i n p a r t ev iden t from t h e ~ equ i l i b r ium measuremehts, a r e more c l e a r l y apparen t from t h e E0

v a l u e s i n Table I V . The s t a b i l i t y of t h e t r i v a l e n t r a r e e a r t h

c a t i o n s is such t h a t d i r e c t r e d u c t i o n t o t h e metals a s a means of

Table IV a Calculated Electrode Potentials in LiF-0.33BeF2

(773-i000~~) . .

Temperature b

Half Cell Reactions EO. (lOOoO~), V Coefficient mVl0c

a Calculated from values in Table 111. .

Standard states for ions are defined in footnote (a) of Table. 111.

removing r a r e - e a r t h f i s s i o n p roduc t s would be accompanied by

r e d u c t i o n of ~ e , + a s w e l l a s u4+. T r i v a l e n t uranium should

d i s p r o p o r t i o n a t e .

4UF3 (d) + 3UF4 (d) + U(s) , E 0 ( 8 7 3 0 ~ ) = -0.08'6 v . (23)

However, t h e d i f f e r e n c e i n EO va lues f o r t h e u4+/u3+ and t h e

cr2+/cr couples i s s o l a r g e t h a t t h e amount of U3+ produced by .

r e a c t i o n wi th t h e c o n t a i n e r meta l should be sma l l (Eqn. 8) and,

i n f a c t , t h e r e d u c t i o n of u4+ t o UO by chromium

should no t be s i g n i f i c a n t [8 . ] . The s t r o n g e s t reduc ing agent

,which can be used i n LiF-0.33BeF2 without r educ ing t h e s o l v e n t

components is bery l l ium me ta l , which indeed has been used as a

r educ ing agent du r ing p u r i f i c a t i o n of such m e l t s [ l l ] . With

ZrF4 p r e s e n t , a weaker reduc ing agent ( e . g . , zirconium metal )

must be used.

4 .3 Est imated S o l u b i l i t i e s of Other Oxides

From t h e equ i l i b r ium d a t a , t h e f r e e energy change a s s o c i a t e d

wi th t h e fo l lowing r e a d t i o n ' i s known

F- + 1/4 0, (g) = 1 / 2 0'- + 1/2 F2 (g) , ~ ~ ( 1 0 0 0 ~ ~ ) = 53.34

Kcal (25)

By combining t h i s w i th *Gf v a l u e s f o r t h e f l u o r i d e s i n Table 111,

AGf v a l u e s f o r t h e corresponding d i s s o l v e d ox ides are ob ta ined .

These v a l u e s i n t u r n may be compared t o publ i shed v a l u e s f o r AG f

of t h e s o l i d ox ides t o y i e l d an e s t i m a t e of t h e cor responding

s o l u b i l i t y p roduc ts

l o g K = -(&f f - AG ) /2 .3 RT SP (26)

Such c a l c u l a t i o n s show t h a t , a s i d e from t h e ox ides a l r e a d y con-

s i d e r e d (BeO, ZrO, , UO, , Tho,) t h e ox ides of NiZ+ and Fe2+ a r e

t h e only o t h e r s of t h e c a t i o n s l i s t e d i n Table I11 which a r e

p r e d i c t e d t o have low ' s o l u b i l i t y (Table I ) , . ,The l e s s s o l u b l e

a of t h e s e two is N i O . The p r e d i c t e d v a l u e of xNiFi i n LiF-0.33BeFz

\

s a t u r a t e d wi th Be0 and N i O i s fir a t 1 0 0 0 ~ ~ . T h i s i s h i g h e r

t han is expected f b r a t y p i c a l r e a c t o r system, i . e . , n e i t h e r

N i O (nor FeO) is expected a s a s t a b l e s o l i d ' p h a s e under normally

reduc ing cond i t i ons .

Less exac t but u s e f u l e s t i m a t e s of t h e s o l u b i l i t i e s of

o t h e r ox ides can be,,made from t h e fo l lowing r e a c t i o n

l / z . M F ~ ( S ) + 1/2 02-(d) +. F-(d) + l / z MO~/ , (S) ( 27 )

wherein t h e l a s t AG t e r m corresponds t o r e a c t i o n (25) ' above. A

s u r v e y of a v a i l a b l e A G ~ d a t a f o r ox ides and f l u o r i d e s of Group I ,

11, 111, and I V c a t i o n s , and of t h e b i v a l e n t f i r s t t r a n s i t i o n

meta l c a t i o n s i n d i c a t e s t h a t a s i d e from t h e ox ides a l r e a d y con-

s i d e r e d only ~ 1 ~ + and perhaps s c 3 + should be s i g n i f i c a n t l y insolu-.

b l e . This s c a r c i t y of i n s o l u b l e ox ides i s caused by t h e r e l a t i v e

g r e a t e r s t a b i l i t y of f l u o r i d e s . I t o f f e r s l i t t l e h e l p i n t h e

s e a r c h f o r r e f r a c t o r y m a t e r i a l s which might prove u s e f u l a g e n t s .

f o r 1on exchange o r p r e c i p i t a t i o n r e a c t i o n s which could be made

t h e b a s i s f o r f u e l r ep roces s ing schemes. For example, an a t t r a c t i v e

p o s s i b i l i t y would be t h e removal of r a r e e a r t h f i s s i o n p roduc t s

by i o n exchange r e a c t i o n s involv5sg r a r e - e a r t h ox ides of s u i t a b l e

low neut ron c a p t u r e c r o s s s e c t i o n , bu t t h e s e ox ides a r e expected

t o be t o o s o l u b l e i n a LiF-0.33BeF2 and s,hould cause t h e p r e c i p i -

t a t i o n of B e 0 ( o r UO,, i f UF, is p r e s e n t ) .

4 .4 Formation of Carbides

D i r e c t r e a c t i o n s between c o n s t i t u e n t s of t h e MSRE f u e l and

g r a p h i t e t o form c a r b i d e s may be r ep re sen ted by t h e fo l lowing ,

g e n e r a l r e a c t i o n f o r which chromium meta l was chosen a s t h e

r educ ing agen t . .

Values f o r t h e f r e e energy change a s s o c i a t e d wi th t h i s . r e a c t i o n

a t 1 0 0 0 ~ ~ a r e l i s t e d i n Table V. They i n d i c a t e t h a t Z r , U , and

Th c a r b i d e s should not be formed.

5 . Conclusions

The mutual ly r e - en fo rc ing r e l a t i o n s h i p between chemist ry

and thermodynamics i n a r e a c t o r development program is , I t h i n k ,

w e l l i l l u s t r a t e d i n t h e ca se of t h e molten s a l t r e a c t o r program.

The chemical i n fo rma t ion most u r g e n t l y needed i n o r d e r t h a t

development of t h e MSRE might proceed was ob ta ined by d i r e c t

experiment. . B u t , by conduct ing t h e s e exper iments i n a s u f f i c i e n t l y

c o n t r o l l e d manner t h a t t h e chemical e q u i l i b r i a involved could be

' i d e n t i f i e d and t h e a s s o c i a t e d equ i l i b r ium c o n s t a n t s measured,

each experiment could c o n t r i b u t e t o a growing knowledge of t h e

thermodynamics of t h e p e r t i n e n t molten s a l t systems. Th i s

knowledge, i n t u r n , has been u s e f u l i n s e v e r a l ways. I t has

extended t h e s i g n i f i c a n c e of t h e chemical i n fo rma t ion upon which

i t i s based, i t has i n d i c a t e d where new chemical problems may

arise and how t o d e a l wi th them, and .it provides a growing s t r u c t u r e

which w i l l con t inue t o grow i n e x t e n t as more d a t a a r e . a c q u i r e d ,

and i n u s e f u l n e s s a s .more problems appear which r e q u i r e s o l u t i o n s .

Table V

Carbide Formation

2 2 - ~ ( d ) + C(S) + Cr(s) ' Cr~;(d) + ; MC z Y

Carbide LGf ( 1 0 0 0 ~ ~ ) ,a ' LG (~eac t ion , 1 0 0 0 ~ ~ ) ,

kcal kcal

a Ref. 27, page 587.

Figure Capt ions

F ig . 1.

Fig. 2 .

F ig . 3.

.._ . . . Fig . 4.

F ig . 5.

F ig . 6.

The System LiF-BeF,. ORNL-Dwg. 65-2526

Oxidation-Reduction Reac t ions i n LiF-0.33BeF2.

L e f t ; r e a c t i o n of C r , Fe, and .Ni w i th HF ( 1 atm)

and Hz ( 1 atm) : r i g h t ; mole f r a c t i o n s of FeF, , NiF, and t h e xUF3 /xUF3 r a t i o i n e q u i l i b r i u m wi th

mole f r a c t i o n CrF, and chromium meta l .

ORNL-Dwg. 65-4608 Rev.

HF-H, Sparging. Ca lcu l a t ed e f f i c i e n c y of ox ide

removal from LiF-0.33BeF2 by spa rg ing wi th HF-H,

mixtures . The o v e r a l l u t i l i z a t i o n o f , HF r e q u i r e d .

t o lower t h e r e s i d u a l ox ide c o n t e n t t o mole/kg

i s p l o t t e d - v s t h e i n i t i a l ox ide c o n t e n t . The t o t a l

p r e s s u r e is 1 a t m . ORNL-Dwg. 65-4187 , .

Oxide Concent ra t ion a t S a t u r a t i o n i n LiF-0.33BeF2

a s a Funct ion of t h e Concent ra t ion of ZrF4 Added.

ORNL-Dw~. 65 -2542~ . .

V a r i a t i o n of A c t i v i t y C o e f f i c i e n t s i n LiF-BeF, , 6 0 0 ~ ~ .

L e f t , a s a f u n c t i o n of xBeF; a t low s o l u t e c o n c e n t r a t i o n ;

r i g h t , YZrF4 a s a f u n c t i o n of xZrF4 f u n c t i o n of x

and " U F ~ as a

up4 added t o LiF-0.33BeF2., z / r is t h e c a t i o n

charge t o r a d i u s r a t i o .

E l e c t r o d e P o t e n t i a l s i n LiF-0.33BeF2 ( v s - HF/H2,Fm

e l e c t r o d e ) a t 1 0 0 0 ~ ~ Compared ( l e f t ) t o Aqueous E l e c t r o d e . .

P o t e n t i a l s a t 2 5 O ~ and Compared ( r i g h t ) t o E l e c t r o d e

P o t e n t i a l s i n LiC1-KC1 E u t e c t i c ( v s - A ~ + / A ~ ) a t 450°c.'.

ORNL-Dw~. 65-4607R. . .

FIGURE 1.

The System LiF-BeF2 .

O R N L - D w ~ . 65-2526

TEMPERATURE (OC) 800 700 600

4 o8

ORNL- DWG 65-4608

TEMPERATURE (OC) 500 800 700 600 500

4

'OoO/~ (OK) 100o/~ (OK)

ORNL-DWG 65-4187

INITIAL OXIDE CONTENT ( mole/ kg )

ORNL-DWG 65- 2542 l0-1. .

z 0 - 'I- 6 w, I- 7 W

/Be0 SATURATION

1 0 - ~ 0.004 . 0.01 0.02 0.05 .0.1 0 . 2 0.5 1

Z ~ F ~ CONCENTRATION (mole/kg )

ORNL-DWG 65-4607

-3 -2 - 1 0 1

E0 IN H20 ( volts )

References

Br iggs , R. B . , e d . , Molten-Salt Reactor Program Semi-

annua l P rog res s Report , USAEC' Report ORNL-3708, Nov. 1964.

G r i m e s , W . R.', Nuclear News - ANS, May (1964) 3/18.

Thoma, R. E. e t a l , i n Oak Ridge Nat iona l Laboratory Repor t ,

ORNL-3789, A p r i l (1965) 3/7.

Blood, C. M . , Oak Ridge Na t iona l Laboratory Repor t ,

ORNL-CF-61~5-4, sept . (1961) . Long, G . , i n r e f . 3 , 65/72. Papers i n p r e p a r a t i o n .

D i r i a n , G . , , i n r e f . 3 , 76/79. Paper i n p r e p a r a t i o n .

Romberger, K. A . , p r i v a t e communication.

Grimes, W . R . ; t n r e f . 1, 235/2.44.

Mathews, A. L . , and Baes, C. F . , Oak Ridge Na t iona l . Laboratory Report , ORNL-TM-1129, May (1965). Paper i n

p r e p a r a t i o n .

1 0 . Baes, C. F . , and Hi t ch , B. F . , i n r e f .. 3 , 61/65.

11. S h a f f e r , J. H . , i n r e f . l.,, 288/303; S h a f f e r , J . H . , e t a l ,

i n r e f . 3 , 99/109.

1 2 . S tone , H. H . , and Baes, C. F . , i n r e f . 3 , 72/76.

13. F r e a s i e r , B. F . , S tone , H. H . , ' a n d Baes, C. F . , Work i n

p rog res s .

14. ~ h a f f e r , J. H . , i n Oak Ridge Nat iona l Laboratory Repor t ,

ORNL-3122, Feb. (1961) 120/122.

15. Eorgan, J. E . , e t a l , i n Oak Ridge Na t iona l Laboratory Report ,

ORNL-3591, May (1964), 45/46.

1 6 . Cohen, I . , and Schaner , B. E.., J. Nuclear M a t e r i a l s , - 9 ,

(1963) 18/52.

17. Romberger, K. A . , ' e t a l , i n r e f . 3 , 243/245. " .

18.' S h a f f e r , J . H . , and Watson, G. M . , i n Oak Ridge Na t iona l

.Labora to ry Report , ORNL-2931, A p r i l (1960) 90. .

1 9 . . Bar ton , C. J . , J. Phys.ica1 Chem., .- 64 (1960) 306/309.

. , 2 0 . , Ward, W . T . , e t al . ; Oak Ridge Na t iona l Laboratory Report , .

ORNL-2749, (Oct. 1959). See a l s o , G r i m e s , W . R . , -- e t a l ,

Chem. Eng. Prog . , 55, No. 27 (1959) 65/70. -

References - Contd.

21. JANAF (Joint Army-Navy-Air Force) Interim Thermochemical

Tables, Thermal Research Laboratory, Dow Chemical Co.,

Midland, Mich.

22. Rand, M. H., and Kubaschewski, O., The Thermal Properties

of Uranium Compounds, Interscience Publishers, New ~ o r k

(1963) 7.1,.

23. . Blood,. C. M., lank ens hi^, I?. F., Grimes, W. R., and

Watson, G. M., ~ctivities of Some Transition Metal Fluorides

in Molten Fluoride Mixtures, Paper 208 (presented by Grimes),

7th ~nternational ~ o n f . on Coordination Chemistry, Stockholm, June, 1962.

/

24. ~ellinek, K., and Rudat, A., Z. Anorg. u. Allgem. Chem.,

175 (1928) 281. - 25. . Brewer, L., et al, MDDC-1543 (Sept. 1945).

26. Glassner, A., The Thermochemical Properties of the Oxides, 0 . Fluorides and Chlorides to 2500 K, Argonne National

Laboratory Report ANL-5750 (1958).

27. Smithells, C.. J., Metals Reference Book, Interscience

Publishers, New York (1955) 591. 28. Brewer, L., in The Chemistry and Metallurgy of Miscellaneous

Materials; Thermodynamics (Quill, L. L., ed.), McGraw-Hill,

New York (1950) -- 76/192.

29. Latimer, W. M., The Oxidation States of the Elements and

Their Potentials In Solution, Prentice-Hall, .New'York,

2nd Ed. (1952). . . . .

30. .Liu, C; H. in Handbook of Analytical Chemistry (Meites, L.,

N ed.) , McGraw-Hill, New York (1963) 5-218 -- 5-221. 31., ' Grimes, W. R., in ref., 1, 237. 32. Elliott, J. F., and Gleiser, M., Thermochemistry for

Steelmaking, Addison-Wesley, Reading, Mass. (1960) 177, 190.'

ORNL-DWG 65-2526

300 LiF

LIQUID 548

LiF + LIQUID

457.6

BeF2 + LIQUID

LiF + 2LiF BeF2 360.3 I

I I I

2LiF BeF2 + BeF2

BeF2 (mole O/O)