ORNL-TM-3258 by Jon Morrow

3 Y45b 0566293 2

N U C L E A R DIVISION

U.S. ATOMIC ENERGY COMMISSION

ORNL- TM- 3258 t-

-.-

^...>..

ENGINEERING DEVELOPMENT STUDIES FOR MOLTEN-SALT BREEDER REACTOR PROCESSING NO, 8 L. E. McNeese

NOTICE T h i s d o c u m e n t c o n t a i n s i n f o r m a t i o n o f a p r e l i m i n a r y nature and w a s prepared p r i m a r i l y for i n t e r n a l u s e a t t h e Oak R i d g e N a t i o n a l L a b o r a t o r y . I t i s s u b j e c t t o r e v i s i o n or c o r r e c t i o n a n d therefore does n o t represent a f i n a l report.

ORNL-TM-3258

Contract No

. W-7405-eng-26

CHEMICAL TECHNOLOGY DIVISION

ENGINEERING DEVELOPMENT STUDIES FOR MOLTEN-SALT BREEDER REACTOR PROCESSING NO. 8 L. E. McNeese

MAY 1 972

OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION f o r the U.S. ATOMIC ENERGY COMMISSION

Reports p r e v i o u s l y i s s u e d i n t h i s s e r i e s are as follows:

ORNL-4366

Period ending September

ORNL-TM-3053

Period ending

ORNL-TM-3137

Period ending

ORNL-TM-3138

P e r i o d ending

ORNL-TM-3139

Period ending

ORNL-TM-3140

Period ending

ORNL-TM-3141

P e r i o d ending

ORNL-TM-3257

Period ending

1968 December 1968 March 1969 June 1969 September 1969 December 1969 March 1970 June 1970

iii

CONTEIKCS Page SUMMARIES

1. INTRODUCTION.

2. ANALYSIS OF THE FLUORINATION--REDUCTIVE EXTRACTION AND METAL TRANSFER FLOWSHEET. m o

2.1 2.2

2.3 2.4

v:. 1.

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

Isolation of Protactinium in a Secondary Salt, Using Fluorination and Reductive Extraction

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

3 Mathematical Analysis of Flowsheet in Which Protactinium Is Isolated in a Secondary Salt, Using Fluorination and Reductive Extraction 6 Calculated Results on Operation of the Protactinium Isolation Syst,em 12 Combination of Discard Streams from the Fluorination--Reductive Extraction-Metal Transfer Flowsheet. 19

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

3. ANALYSIS OF URANIUM REMOVAL FROM FUEL SALT BY OXIDE PRECIPITATION

3.1

Mathematical Analysis of a Uranium Oxide Precipitator

3.2

Calculated Results

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

DEVELOPMENT OF A FROZEN-WALL FLUORINATOR: INSTALLATION OF A SIMULATED FLUORINATOR FOR STUDYING INDUCTION HEATING

. ..

.................. Status of Equipment Installation. . . . . . . . . . . . . .

26 29

4.1 4.2

Experimental Equipment.

5. MEASUREMENT OF AXIAL DISPERSION COEFFICIENTS AND GAS HOLDUP IN OPEN BUBBLE COLUMNS

5.1 5.2

5.3

5.4 5.5 5.6 5.7 5.8

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

........... Mathematical Analysis of Unsteady-State Axial Dispersion in aBubbleColumn. . . . . . . . . . . . . . . . . . . . . . Equipment . . . . . . . . . . . . . . . . . . . . . . . . . Experimental Procedure. . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion of Data on Axial Dispersion. . . . . . . . . . . Discussion of Data on Gas Holdup. . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . Previous Studies on Axial Dispersion.

31 33

44 45

45 54 56

CONTENTS (continued) Page

. Equipment for Experiment MTE-2 . . . Materials Used in Experiment MTE-2 . Status of Experiment MTE-2 . ..

6. DEVELOPMENT OF THE METAL TRANSFER PROCESS 6.1 6.2 6.3

. . .. ... ...

. . . . . . . 58 . . . . . . . 59

. . . . . . 63 . . . . . . 63 e

7. SEMICONTINUOUS REDUCTIVE EXTRACTION EXPERIMENTS IN A MILD-STEEL

. . . . . . . . . . . . . . . . . . . . .64 Preparation for Mass Transfer Run UTR-3 . . . . . . 65 Mass Transfer Run UTR-3 .. . . . . . . . . . . 67 Preparation for Mass Transfer Run UTR-4 . . . . . . . . . 70 Mass Transfer Run UTR-4 . . . . . . . . . . . . . . . 71 Mathematical Analysis of Mass Transfer with Primary Resistance to Transfer in the Salt Phase. . . . . . . . . . . . 75

FACILITY

7.1 7.2 7.3

7.4 7.5

. .

7.6 7.7

Discussion of Mass Transfer Data from Runs UTR-3 and UTR-4.

Preparation for Zirconium Mass Transfer Experiments; Run UTR-5 . . . . . . . . . . . . . . . . ~ . . . . . . . ~ . . . 8 0

. . . 84 Salt-Metal Treatment Vessel . . . . . . . . . . . 87 . . . . . . . . . . 87 7.10 Maintenance of Equipment. PREVENTION OF AXIAL DISPERSION IN PACKED COLUMNS. . . . . . . . . 9 0

. 7-8 Summary of Hydrodynamic Data with Present Column. . 7.9 Examination of 304 Stainless Steel Corrosion Specimens from e

9. ELECTROLYTIC REDUCTION OF LiCl USING A BISMUTH CATHODE AND A GRAPHITE ANODE

. 94 . . . . . . . . . . . 94 . 96 Postoperational Examination of Equipment . . . . . . STUDY OF THE PURIFICATION OF SALT BY CONTINUOUS METHODS . . . . . . 97 10.1 Iron Fluoride Reduction Runs R-1 and R-2. . . . . . . . . 97

9.1 9.2 9.3 10.

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

. . Operating Conditions and Results. .

Equipment and Materials Used.

10.2 Mathematical Analysis ofthe Rate of Iron Fluoride Reduction; Calculated Mass Transfer Coefficients for Runs R-1 and R-2. 99

10.3 Equipment Modifications and Maintenance

..... . ..

.lo1

CONTENTS (continued) Page 11. ELECTROLYTIC OXIDATION OF Pa4e to pa5+ IN MSBR FUEL SALT

.. .

11.1 Estimated Anode Current Density f o r the Case of No Inter* action Between Protactinium and Uranium. 11.2

11.3

106

. . . . . . . . 107 Estimated Anode Current Density f o r the Case of Equilibrium Between Protactinium and Uranium . . . . . . . . . 110 Calculated Results and Discussion. . . . . . . . . . . 113

12. REFERENCES.

116

. .

vii

SUMMARIES ANALYSIS OF THE FLUORINATION--REDUCTIVE EXTRACTION AND METAL TRANSFER FLOWSHEET

An improved flowsheet was developed i n which p r o t a c t i n i u m i s i s o l a t e d from t h e f u e l s a l t of an MSBR and h e l d for decay i n a secondary s a l t stream t h a t i s p h y s i c a l l y and chemically i s o l a t e d from t h e r e a c t o r .

A processing

p l a n t based on t h i s flowsheet should be much e a s i e r t o c o n t r o l t h a n one based on t h e e a r l i e r flowsheet i n which t h e p r o t a c t i n i u m w a s i s o l a t e d i n bismuth a t a p o i n t i n t e r m e d i a t e i n t h e p r o t a c t i n i u m e x t r a c t i o n column.

Use

of t h e new flowsheet should r e s u l t i n a c o n s i d e r a b l e saving i n c a p i t a l equipment c o s t .

A mathematical a n a l y s i s showed t h a t e s s e n t i a l l y complete ex-

t r a c t i o n of t h e p r o t a c t i n i u m on a 10-day c y c l e could be obtained w i t h f i v e e q u i l i b r i u m s t a g e s and a r e d u c t a n t a d d i t i o n r a t e of about 200 equivlday

f o r a uranium removal e f f i c i e n c y of 99% i n t h e primary f l u o r i n a t o r , or an a d d i t i o n r a t e of about 300 equivlday f o r a uranium removal e f f i c i e n c y of

95%. The number of e q u i l i b r i u m s t a g e s could be reduced t o as f e w as t h r e e without i n c r e a s i n g t h e p r o t a c t i n i u m removal time a p p r e c i a b l y i f t h e r e d u c t a n t a d d i t i o n yate were i n c r e a s e d t o 371 equivlday f o r a primary f l u o r i n a t o r eff i c i e n c y of 95%, or t o 257 equiv/day f o r a f l u o r i n a t o r e f f i c i e n c y of 99%. A method was developed for combining and f l u o r i n a t i n g t h e v a r i o u s waste

streams produced by t h e flowsheet.

Use of t h i s method w i l l e l i m i n a t e

s e v e r a l p o t e n t i a l r o u t e s f o r l o s s of f i s s i l e material from t h e system. ANALYSIS OF URANIUM REMOVAL FROM FUEL SALT BY OXIDE PRECIPITATION C a l c u l a t i o n s were made t o i n v e s t i g a t e t h e o p e r a t i o n of' an oxide prec i p i t a t o r f o r removing uranium from f u e l s a l t t h a t c o n t a i n s no p r o t a c t i n i u m . The r e s u l t s i n d i c a t e t h a t g r e a t e r t h a n 99% of t h e uranium can be removed with about t h r e e e q u i l i b r i u m s t a g e s i n a c o u n t e r c u r r e n t system and t h a t t h e UO

Tho

stream produced w i l l have a U02 c o n c e n t r a t i o n of g r e a t e r t h a n 90%.

o f t h e thorium f e d t o t h e system would be p r e c i p i t a t e d w i t h Less t h a n 1% t h e uranium.

No s i g n i f i c a n t e f f e c t on p r e c i p i t a t o r performance was ob-

served when t h e amount of s a l t remaining w i t h t h e oxide d u r i n g t h e t r a n s f e r of s a l t between s t a g e s w a s v a r i e d from 2 t o 1 0 moles p e r mole of o x i d e ,

viii

DEVELOPMENT OF A FROZEN-WALL FLUORINATOR: INSTALLATION OF A SIMULATED FLUORINATOR FOR STUDYING INDUCTION HEATING An experiment t o demonstrate p r o t e c t i o n a g a i n s t c o r r o s i o n by t h e use of l a y e r s of f r o z e n s a l t i n a continuous f l u o r i n a t o r r e q u i r e s a corrosionr e s i s t a n t h e a t source t o be p r e s e n t i n t h e molten s a l t .

High-frequency

i n d u c t i o n h e a t i n g has been proposed as t h e source of h e a t .

There a r e un-

c e r t a i n t i e s i n determining t h e e f f e c t of bubbles i n t h e molten s a l t w i t h t h i s h e a t i n g method and i n e s t i m a t i n g t h e amount of h e a t t h a t w i l l be g e n e r a t e d i n t h e m e t a l walls of t h e f l u o r i n a t o r .

Equipment i s b e i n g in-

s t a l l e d f o r studying h e a t g e n e r a t i o n i n a simulated frozen-wall f l u o r i n a t o r containing provisions f o r induction heating.

be used t o s i m u l a t e molten s a l t i n t h e system. c o n s i s t s of a 5-in.-OD sched 40 p i p e .

by 5-ft-long

31 w t % HN03 s o l u t i o n w i l l The simulated f l u o r i n a t o r

s e c t i o n of 8-in.

304 s t a i n l e s s s t e e l

The system a l s o c o n t a i n s a pump f o r c i r c u l a t i n g t h e a c i d

through t h e column and a h e a t exchanger f o r removing h e a t t h a t i s g e n e r a t e d i n the acid.

MEASUREMENT OF AXIAL DISPERSION COEFFICIENTS AND GAS HOLDUP I N OPEN BUBBLE COLUMNS An improved experimental technique was developed f o r measuring a x i a l d i s p e r s i o n c o e f f i c i e n t s i n open bubble columns.

T h i s t e c h n i q u e c o n s i s t s of

i n j e c t i n g a s m a l l amount of K C 1 t r a c e r s o l u t i o n a t t h e t o p of a column and u s i n g a c o n d u c t i v i t y probe t o measure t h e r a t e a t which t h e t r a c e r i s d i s persed throughout t h e colurnn.

Twenty-nine r u n s were made i n order t o

measure t h e a x i a l d i s p e r s i o n c o e f f i c i e n t i n open bubble columns having diameters of 1 . 5 , 2 , and 3 i n . ; 59 runs were made t o determine gas holdup. The new t e c h n i q u e appears t o b e s u p e r i o r t o t h e e a r l i e r s t e a d y - s t a t e technique i n t h a t (1)l e s s s c a t t e r i s observed i n t h e d i s p e r s i o n c o e f f i c i e n t d a t a , and ( 2 ) d a t a can u s u a l l y be obtained i n l e s s t h a n 10% of t h e time r e q u i r e d f o r t h e s t e a d y - s t a t e technique.

The axial d i s p e r s i o n c o e f f i c i e n t s

obtained w i t h t h e new t e c h n i q u e a r e i n agreement w i t h t h o s e measured prev i o u s l y ; however, d a t a were obtained over a wider range of s u p e r f i c i a l gas v e l o c i t i e s i n t h e p r e s e n t study.

A t low gas flow r a t e s (where bubble flow

o c c u r s ) , gas holdup was found t o b e p r o p o r t i o n a l t o t h e s u p e r f i c i a l gas v e l o c i t y and independent of t h e column diameter.

A t h i g h e r g a s flow r a t e s ,

t h e gas holdup w a s found t o b e i n v e r s e l y p r o p o r t i o n a l t o t h e column diameter and t o i n c r e a s e , i n a g r a d u a l manner, as t h e gas f l o w r a t e i n c r e a s e d . DEVELOPMENT OF THE METAL TRANSFER PROCESS

A second engineering experiment (MTE-2) i s p r e s e n t l y i n p r o g r e s s .

The

experiment was designed t o demonstrate a l l phases of an improved r a r e - e a r t h removal method known as t h e metal t r a n s f e r p r o c e s s o t h e experiment a r e :

The main o b j e c t i v e s of

( I ) t o demonstrate t h e s e l e c t i v e removal of r a r e e a r t h s

from f l u o r i d e s a l t c o n t a i n i n g thorium f l u o r i d e , ( 2 ) t o c o l l e c t t h e r a r e e a r t h s i n a lithium-bismuth s o l u t i o n , and ( 3 ) t o v e r i f y previous d i s t r i b u t i o n Experiment MTE-2 i s being performed a t 660째c i n a 6-in.-

coefficient data.

d i m carbon s t e e l v e s s e l t h a t i s d i v i d e d i n t o two compartments i n t e r c o n n e c t e d a t t h e bottom by a pool of thorium-saturated molten bismuth.

One compartment

% LiF-BeF2-ThF4) t o which 7 m C i Oi 147Nd and s u f f i c i e n t LaF t o produce a c o n c e n t r a t i o n of 0 . 3 mole % has been added. 3 The second compartment c o n t a i n s L i C 1 , a 35 a t % L i - B i s o l u t i o n ( i n a cup) , c o n t a i n s f l u o r i d e s a l t (72-16-12 mole

and a pump f o r c i r c u l a t i n g t h e L i C l through t h e cup a t a flow r a t e of about 25 cm3 /min.

The pump i s c o n s t r u c t e d of carbon s t e e l and u s e s molten bismuth

as check v a l v e s .

Thus f a r , t h e experiment appears t o be proceeding satis-

f a c t o r i l y ; however, no d a t a a r e a v a i l a b l e a t t h i s t i m e . SEMICONTINUOUS REDUCTIVE EXTRACTION EXPERIMENTS I N A MILD-STEEL FACILITY

We continued t o o p e r a t e a m i l d - s t e e l system which can be used t o c a r r y o u t semicontinuous r e d u c t i v e e x t r a c t i o n experiments, i n g t h e mass t r a n s f e r performance of an 0 82-in. - I D e

packed w i t h 1/4-in.

We a r e p r e s e n t l y study-

, 2b-in.

-long column

molybdenum Raschig r i n g s .

Following t h e second uranium mass t r a n s f e r r u n (UTR-2), t h e s a l t and bismuth were r e t u r n e d t o t h e t r e a t m e n t v e s s e l and 122.5 g of thorium metal

was added t o t h e g r a p h i t e c r u c i b l e through a 3/4-ine-diam t u b e .

The thorium

d i s s o l v e d slowly i n t h e bismuth, a t about t h e same r a t e observed a f t e r thorium w a s added t o t h e bismuth feed t a n k p r i o r t o run UTR-2. A second charge of thorium m e t a l (119 g ) w a s lowered i n t o t h e bismuth phase i n a p e r f o r a t e d s t e e l b a s k e t t o a c c e l e r a t e t h e r e a c t i o n between t h e thorium and t h e bismuth.

After t h i s a d d i t i o n , t h e thorium d i s s o l u t i o n r a t e i n -

creased t o about t e n times t h e r a t e observed e a r l i e r .

Subsequent samples

of t h e bismuth revealed a nonuniform thorium c o n c e n t r a t i o n i n t h e bismuth p o o l , a p p a r e n t l y t h e r e s u l t of poor mixing during t h e p e r i o d i n which t h e bismuth and s a l t approached chemical e q u i l i b r i u m f o l l o w i n g t h e r e d u c t a n t addition.

It was a l s o found t h a t thorium c o n c e n t r a t e s i n t h e lower p a r t

of a sample during t h e slow f r e e z i n g of t h e bismuth because of t h e tendency of t h e more dense thorium bismuthide t o s e t t l e t o t h e bottom.

The previous sample p r e p a r a t i o n method, which involves d i s c a r d i n g t h e lower 15% of t h e

sample, w a s r e v i s e d i n order t o avoid s u b s t a n t i a l e r r o r s i n t h e r e p o r t e d c o n c e n t r a t i o n of thorium i n t h e bismuth. Run UTR-3 w a s c a r r i e d out w i t h m e t a l - t o - s a l t 1 . 2 2 , and 0.91.

flow r a t e r a t i o s of 2.05,

Seven p a i r s of bismuth and s a l t samples were removed from

t h e s a l t and bismuth streams l e a v i n g t h e column, showed t h a t , as t h e bismuth-to-salt

Analyses of t h e s e samples

flow r a t e r a t i o was decreased from 2.05

t o 0.91, t h e f r a c t i o n of t h e uranium removed from t h e s a l t decreased from O . g l t o 0.73. Following run UTR-3 t h e s a l t and bismuth phases were r e t u r n e d t o t h e

treatment v e s s e l .

S u f f i c i e n t thorium m e t a l was t h e n charged t o t h e v e s s e l

t o produce a thorium c o n c e n t r a t i o n of about 1000 ppm, which i s about 10%

g r e a t e r t h a n t h e s o l u b i l i t y of thorium and bismuth a t t h e bismuth f e e d t a n k o p e r a t i n g temperature (540OC). Observed v a r i a t i o n s i n thorium c o n c e n t r a t i o n i n t h e bismuth appeared t o b e due t o i n s u f f i c i e n t mixing of t h e bismuth phase.

I n run UTR-4, t h e f r a c t i o n of uranium e x t r a c t e d from t h e s a l t in-

creased from 0.63 t o 0.74 a s t h e flow r a t e r a t i o w a s i n c r e a s e d from 0.75 t o 1.0. I n c o r r e l a t i n g t h e uranium e x t r a c t i o n d a t a from runs UTR-3 and -4, it was assumed t h a t t h e r a t e a t which uranium t r a n s f e r s t o t h e bismuth i s cont r o l l e d by t h e d i f f u s i v e r e s i s t a n c e i n t h e s a l t f i l m when t h e e x t r a c t i o n

f a c t o r i s high and when t h e s a l t f i l m i s composed l a r g e l y of nontransf e r r i n g ions.

It was found t h a t t h e data could b e c o r r e l a t e d i n terms

of t h e h e i g h t of an o v e r a l l t r a n s f e r u n i t based on t h e s a l t phase. HTU v a l u e i n c r e a s e d from 0.77 f t t o 2 . 1 f t as t h e bismuth-to-salt

The flow

r a t e r a t i o decreased from 2.05 t o 0.75. I n o r d e r t o measure mass t r a n s f e r rates i n t h e column under more c l o s e l y c o n t r o l l e d c o n d i t i o n s and under c o n d i t i o n s where the c o n t r o l l i n g r e s i s t a n c e i s not n e c e s s a r i l y i n t h e s a l t phase, p r e p a r a t i o n s were begun f o r experiments i n which t h e r a t e of exchange of zirconium i s o t o p e s w i l l be measured between s a l t and bismuth phases otherwise a t chemical e q u i l i b -

rium.

The s a l t and bismuth were t r a n s f e r r e d t o t h e t r e a t m e n t v e s s e l and

were c o n t a c t e d w i t h a 70-30 mole % H2-HF mixture f o r 20 h r i n o r d e r t o remove r e d u c t a n t Prom t h e bismuth phase.

After b e i n g sparged s u c c e s s i v e l y

w i t h hydrogen and argon, t h e s a l t and bismuth were t h e n t r a n s f e r r e d t o t h e i r respective feed tanks.

The r e p o r t e d uranium c o n c e n t r a t i o n s i n s a l t samples

removed from t h e column e f f l u e n t v a r i e d by

2 35%, which

was s u r p r i s i n g

s i n c e no e x t r a c t i o n of uranium from t h e s a l t occurred during t h e run.

The

hydrodynamic d a t a obtained during c o u n t e r c u r r e n t flow of s a l t and bismuth i n t h e p r e s e n t column were found t o be i n good agreement w i t h t h e p r e d i c t e d column throughput a t f l o o d i n g , which i s based on s t u d i e s with mercury and aqueous s o l u t i o n s . PREVENTION OF AXIAL DISPERSION I N PACKED COLUMNS Packed columns a r e being considered f o r u s e i n c o u n t e r c u r r e n t l y c o n t a c t i n g molten s a l t and bismuth i n MSBR f u e l p r o c e s s i n g systems,

have p r e v i o u s l y made a x i a l d i s p e r s i o n measurements i n packed columns during t h e c o u n t e r c u r r e n t flow of mercury and aqueous s o l u t i o n s and have shown t h a t a x i a l d i s p e r s i o n can s i g n i f i c a n t l y reduce column performance under some o p e r a t i n g c o n d i t i o n s of i n t e r e s t .

A s p a r t of our c o n t a c t o r

development program, w e are e v a l u a t i n g column m o d i f i c a t i o n s t h a t w i l l reduce t h e e f f e c t of a x i a l d i s p e r s i o n t o an a c c e p t a b l e l e v e l .

We have

devised and t e s t e d an improved a x i a l d i s p e r s i o n p r e v e n t e r , which c o n s i s t s of an i n v e r t e d bubble cap having a s i n g l e 3/8-in.-OD

t u b e a t t h e upper

xii

s u r f a c e of t h e bubble cap.

During o p e r a t i o n , t h e metal phase accumulates

around t h e bottom of t h e bubble cap and t h e r e s u l t i n g seal f o r c e s t h e continuous phase t o flow through t h e tube i n t h e upper s u r f a c e of t h e cap.

This design allows t h e depth of t h e m e t a l phase t o i n c r e a s e t o t h e

p o i n t where a s u f f i c i e n t l y high head of l i q u i d m e t a l i s produced t o f o r c e t h e m e t a l through t h e d i s p e r s i o n preventer a t a h i g h throughput.

The ex-

t e n t of a x i a l d i s p e r s i o n observed with t h i s d e s i g n i s probably s u f f i c i e n t l y low f o r most a p p l i c a t i o n s of i n t e r e s t .

However, it i s b e l i e v e d t h a t

t h e p r e s e n t design allows f o r s a l t and bismuth throughputs t h a t can be as high a s t h e column throughputs a t flooding. ELECTROLYTIC REDUCTION OF L i C l USING A BISMUTH CATHODE AND A GRAPHITE ANODE

One method f o r p r o v i d i n g t h e L i - B i

s o l u t i o n s r e q u i r e d by t h e m e t a l

t r a n s f e r process f o r r a r e - e a r t h removal would c o n s i s t of e l e c t r o l y t i c a l l y reducing L i C l produced i n t h e p r o c e s s i n g system.

We have performed an

experiment i n o r d e r t o determine t h e g e n e r a l o p e r a t i n g c h a r a c t e r i s t i c s of an e l e c t r o l y t i c c e l l having a bismuth cathode and a g r a p h i t e anode. experiment w a s c a r r i e d out i n a h - i n . - d i m

a 3.5-in.-dim

q u a r t z c e l l v e s s e l i n which

molybdenum cup c o n t a i n i n g t h e bismuth cathode w a s placed.

The anode c o n s i s t e d of a 1 - i n . - d i m at

This

graphite rod.

The c e l l was operated

6 7 0 a~t ~a maximum anode c u r r e n t d e n s i t y of 8.6 A/cm 2 . Apparently,

t h e r e w a s no l i m i t i n g anode c u r r e n t d e n s i t y under t h e c o n d i t i o n s used i n t h i s experiment, and disengagement of t h e c h l o r i n e gas produced a t t h e anode proceeded smoothly and without d i f f i c u l t y .

During o p e r a t i o n , t h e L i C l be-

came r e d i n c o l o r , probably because t h e cathode s u r f a c e became s a t u r a t e d w i t h L i B i (which p a r t i a l l y d i s s o l v e d i n t h e L i C 1 ) .

Measurement of t h e

c e l l c u r r e n t e f f i c i e n c y was not p o s s i b l e because of t h e r e a c t i o n of t h e c h l o r i n e gas produced i n t h e c e l l w i t h i r o n components i n t h e upper p a r t

of t h e c e l l v e s s e l .

The experiment confirms o u r e x p e c t a t i o n t h a t e l e c -

t r o l y t i c r e d u c t i o n of L i C l u s i n g a bismuth cathode and a g r a p h i t e anode should proceed r e a d i l y and t h a t t h e a t t a c k on t h e g r a p h i t e anode should b e minimal, i f it occurs a t a l l .

xiii

STUDY OF THE PURIFICATION OF SALT BY CONTINUOUS METHODS

We have continued sJdu,21cs of t h e p u r i f i c a t i o n of s a l t by counterc u r r e n t c o n t a c t w i t h hydrogen i n a 1.25-in.-diam, w i t h 1/4-in.

n i c k e l Raschig r i n g s .

'(-ft-long

During t h i s r e p o r t p e r i o d , a s u f f i c i e n t

q u a n t i t y of FeF2 was added t o t h e s a l t (66-34 mole t h e i r o n c o n c e n t r a t i o n from 20 ppm t o 425 ppm. runs ( R - 1 and R-2)

were c a r r i e d o u t s

% LiF-BeF2) t o i n c r e a s e

Two i r o n f l u o r i d e r e d u c t i o n

A s a l t flow r a t e of 100 cm3/min was

used i n each; t h e hydrogen flow rates were literslmin respectively.

column packed

about 20 l i t e r s / m i n and 13.5

Accurate c o n t r o l of t h e flow rates of s a l t and

gas t o t h e column proved t o be d i f f i c u l t , and e r r a t i c r e s u l t s were o b t a i n e d . The c a l c u l a t e d mass t r a n s f e r c o e f f i c i e n t s f o r t h e two runs were 2.4 and 5.4

moles/sec~cm3. S e v e r a l equipment m o d i f i c a t i o n s were made i n o r d e r t o

c o r r e c t t h e d i f f i c u l t i e s noted d u r i n g t h e s e r u n s .

A p r o t a c t i n i u m i s o l a t i o n method based on t h e s e l e c t i v e p r e c i p i t a t i o n

of Pa 0 from MSBR f u e l s a l t has r e c e n t l y been proposed. The process r e 2 5 4+ i n t h e s a l t t o Pa5+ (and most of t h e U3+ t o q u i r e s o x i d a t i o n of t h e Pa U

4+) p r i o r t o p r e c i p i t a t i o n of t h e Pa 0

of t h e Pa''

It w a s suggested t h a t o x i d a t i o n 2 5' be c a r r i e d o u t e l e c t r o l y t i c a l l y . Estimates of t h e c u r r e n t

d e n s i t i e s , t h e s i z e of t h e proposed e l e c t r o l y t i c o x i d a t i o n system, and t h e f e a s i b i l i t y of such a r e d u c t i o n s t e p were made.

It w a s concluded t h a t a

low c u r r e n t d e n s i t y would be observed a t t h e anode because of t h e low conc e n t r a t i o n of Pa4+ i n t h e s a l t , and t h a t a c u r r e n t d e n s i t y l i m i t a t i o n w a s not l i k e l y a t t h e cathode s i n c e t h e c o n c e n t r a t i o n of t h e m a t e r i a l t o be reduced i s h i g h e r , by about two o r d e r s of magnitude, t h a n t h e t o t a l conc e n t r a t i o n of m a t e r i a l s t o be oxidized a t t h e anode. t i o n of

E l e c t r o l y t i c oxida-

4+ p r i o r Pa

t o p r e c i p i t a t i o n of Pa 0 i s not considered a t t r a c t i v e 2 5 because of t h e l a r g e anode s u r f a c e a r e a r e q u i r e d . It i s b e l i e v e d t h a t o x i d a t i o n of t h e Pa w

b+ t o Pa5+ by t h e u s e of HF-H 0-H mixtures i s more 2 2

promising and t h a t a d d i t i o n a l d a t a should be obtained t o allow e v a l u a t i o n of t h i s s t e p .

1. INTRODUCTION

A molten-salt breeder reactor (MSBR) will be fueled with a molten fluoride mixture that will circulate through the blanket and core regions of the reactor and through the primary heat exchangers. We are developing processing methods for use in a close-coupled facility for removing fission products, corrosion products, and fissile materials from the molten fluoride mixture. Several operations associated with MSBR processing are under study. The remaining parts of this report discuss: (1) an improved flowsheet for processing MSBR fuel salt by fluorination--reductive extraction and the metal transfer process, (2) analysis of methods for removing uranium from fuel salt by

precipitation as U02-Th02 solid solutions,

( 3 ) installation of a simulated continuous fluorinator for studying induction heating in molten salt,

(4) measurement of gas holdup and axial dispersion coefficients in open bubble columns, using a recently devised transient technique,

( 5 ) installation of experiment MTE-2 for demonstration of the metal transfer process for removing rare earths from MSBR fuel carrier salt,

( 6 ) experiments conducted in a mild-steel reductive extraction facility, to increase our understanding of the rate at which uranium is extracted from molten salt into bismuth in a packed column,

( 7 ) the design and testing of devices for preventing axial dispersion in packed columns during the countercurrent flow of molten salt and bismuth,

(8)

operation of a static electrolytic cell for reduction of LiCl using a bismuth cathode and a graphite anode,

(9)

s t u d i e s of t h e p u r i f i c a t i o n of s a l t by continuous methods, and

(10) a n a l y s i s of t h e f e a s i b i l i t y of t h e e l e c t r o l y t i c o x i d a t i o n of t e t r a v a l e n t p r o t a c t i n i u m t o p e n t a v a l e n t p r o t a c t i n i u m p r i o r t o t h e p r e c i p i t a t i o n of Pa 0 2

This work was c a r r i e d out i n t h e Chemical Technology D i v i s i o n during t h e p e r i o d J u l y through September

1970.

3 2. ANALYSIS OF THE FLUORINATION--REDUCTIVE EXTRACTION AND METAL TRANSFER FLOWSHEET

M. J. Bell

L. E. McNeese

A flowsheet in which fluorination is used for removing uranium and reductive extraction is used for isolating protactinium from MSBR fuel salt has been described.1 9 2

However, we have found that a considerable

simplification in the flowsheet and a significant reduction in partial fuel cycle cost can be achieved by holding the isolated protactinium in a secondary salt phase, rather than in bismuth, as previously considered.

A flowsheet that employs this improved mode of operation has been developed, and the partial fuel cycle costs corresponding to several sets of operating conditions have been calculated. We have also observed that the waste streams from the protactinium isolation and the rare-earth removal portions of the new flowsheet can be conveniently combined for uranium recovery prior to disposal, thus decreasing the probability of loss of fissile material and also eliminating the need for adding 7LiF to the protactinium decay tank in order to obtain an acceptably low liquidus temperature. A method for J

combining the waste streams is described.

2.1 Isolation of Protactinium in a Secondary Salt, Using Fluorination and Reductive Extraction Analysis of the fluorination--reductive extraction flowsheet for isolating protactinium from MSBR fuel salt has revealed several undesirable features and has suggested an improved method for removing fission product zirconium and for retaining 233Pa during its decay to 233U.

In the flow-

sheet described previously, zirconium was extracted into the bismuth stream exiting from the lower column of the protactinium isolation system; it was removed from this stream by hydrofluorinating a small fraction of the bismuth in the presence of salt that was withdrawn from the system. Since the bismuth stream also contained protactinium and uranium, the portion of the stream that was hydrofluorinated represented a compromise between (1)maintaining an acceptably low zirconium concentration in the bismuth in the

4 lower p a r t of t h e column and ( 2 ) t r a n s f e r r i n g a c c e p t a b l y small amounts of p r o t a c t i n i u m and uranium t o t h e waste s a l t from which t h e s e m a t e r i a l s must be recovered.

The remaining bismuth w a s h y d r o f l u o r i n a t e d i n t h e p r e s e n c e

of s a l t t h a t was then r e c y c l e d t o a p o i n t ahead of t h e f l u o r i n a t o r i n order t o remove uranium as UF

This o p e r a t i o n a l s o r e s u l t e d i n t h e r e -

c y c l e of zirconium, which, under o p e r a t i n g c o n d i t i o n s of i n t e r e s t , w a s o x i d i z e d and reduced s e v e r a l times b e f o r e i t s removal.

Such r e c y c l i n g

caused t h e q u a n t i t y of r e d u c t a n t r e q u i r e d f o r i s o l a t i n g t h e p r o t a c t i n i u m t o be i n c r e a s e d s i g n i f i c a n t l y . We have observed t h a t t h e flowsheet can be s i m p l i f i e d by h y d r o f l u o r i n a t i n g t h e e n t i r e bismuth stream i n t h e presence of a secondary s a l t stream,

as shown i n F i g . 1. S a l t i s withdrawn f r o m t h e r e a c t o r on a 10-day c y c l e and i s f e d t o a f l u o r i n a t o r , where 95 t o 99% of t h e uranium i s removed. The s a l t f r o m t h e f l u o r i n a t o r i s t h e n s e n t t o an e x t r a c t i o n column where p r o t a c t i n i u m , zirconium, and t h e remaining uranium are e x t r a c t e d i n t o a bismuth stream c o n t a i n i n g r e d u c t a n t .

F i n a l l y , t h e bismuth stream i s

h y d r o f l u o r i n a t e d i n t h e presence of t h e secondary s a l t stream, which res u l t s i n t r a n s f e r of t h e e x t r a c t e d m a t e r i a l s t o t h e s a l t .

Reductant i s

added t o t h e recovered bismuth, and t h e m e t a l stream t h u s produced i s recycled t o t h e e x t r a c t i o n column as i n t h e previous flowsheet.

The sec-

ondary s a l t stream i s c i r c u l a t e d s u c c e s s i v e l y through a h y d r o f l u o r i n a t o r , a f l u o r i n a t o r , and a p r o t a c t i n i u m decay t a n k .

The f l u o r i n a t o r i s used t o

maintain an a c c e p t a b l y low uranium c o n c e n t r a t i o n i n t h e p r o t a c t i n i u m decay P e r i o d i c a l l y , s a l t i s withdrawn from t h e decay t a n k t o remove z i r -

tank.

conium and o t h e r f i s s i o n products t h a t have accumulated.

The s a l t i s h e l d

f o r a s u f f i c i e n t period b e f o r e f i n a l d i s c a r d t o a l l o w 233Pa t o decay t o

233U, which i s recovered from t h e s a l t by b a t c h f l u o r i n a t i o n . These flowsheet m o d i f i c a t i o n s o f f e r t h e f o l l o w i n g advantages over t h e e a r l i e r flowsheet:

1. The bismuth i n v e n t o r y i n t h e system i s g r e a t l y reduced, t h e r e b y avoiding a s i g n i f i c a n t inventory charge. 2.

The p r o t a c t i n i u m decay t a n k can be f a b r i c a t e d from a n i c k e l - b a s e a l l o y r a t h e r t h a n molybdenum, which w i l l r e s u l t i n a c o n s i d e r a b l e saving i n t h e i n s t a l l e d equipment c o s t .

BeF2 Thb

SALT PUR IF I CAT 101J

SALT DISCARD

ORNL- DWG 70 - 28 4 !RCR

PROCESSED SALT

STDUCTIOPJ

I I I

IB'

SALT CONTAINING RARE EARTHS

uF6

)

H i ACTOR

I I I I I

EXTRA(

(0 5 MOLE FRACTION L I )

I I I

-'4

I I

'-I

FLUOPINATOR

EARTHS

Po CECAY

FLUOR INATOR

B l l

t LI

-c URANIUM REMOVAL

PROTACTI NlUM REMOVAL

i T

RARE E A R T H REMOVAL.

Fig. 1. Flowsheet for Processing a Single-Fluid MSBR by Fluorination-Reductive Extraction and the Metal Transfer Process.

Control of the protactinium isolation system is greatly simplified.

Zirconium will not be recycled in the lower part of the protactinium isolation system, thus reducing the consumption of reductant.

The isolated protactinium is retained in such a manner that maloperation of the extraction column cannot return l a r g e quantities of protactinium to the reactor.

6. The flowsheet is simplified; recycle of fuel salt containing uranium, zirconium, and protactinium to the primary fluorinator is avoided.

Operation of the secondary salt circuit is restricted

only by heat removal and uranium inventory considerations.

Very efficient hydrofluorination of the bismuth stream would permit the initial salt inventory in the protactinium decay tank to contain natural lithium rather than 7Li.

2.2 Mathematical Analysis of Flowsheet in Which Protactinium Is Isolated in a Secondary Salt, Using Fluorination and Reductive Extraction

A mathematical analysis was carried out for the protactinium isolation system described in the previous section. Of main interest were (1)the effects of the primary fluorinator uranium removal efficiency and the reductant addition rate on the performance of the protactinium extraction column, and (2) the rate at which LiF must be added to the secondary salt in the prot-

actinium decay system in order to maintain an acceptably low liquidus temperature. Also of interest was the uranium inventory in the protactinium decay tank for various values of the secondary fluorinator efficiency and the flow rate of the secondary salt through the fluorinator. In making the analysis, we assumed that salt of a designated composition was withdrawn from the reactor at a known flow rate and fed to the primary fluorinator, where a specified fraction of the uranium was removed as UF

The extraction column was assumed to consist of a specified number

of theoretical stages. With this approach, calculations proceed from one

7 end of t h e column, where flow r a t e s and c o n c e n t r a t i o n s a r e known o r assumed, t o t h e opposite end of t h e column, where an a p p r o p r i a t e check i s made on t h e c a l c u l a t e d v a l u e s ( i f t h e s t a r t i n g c o n c e n t r a t i o n s and flow r a t e s were assumed v a l u e s ) .

The c a l c u l a t i o n s involve t h e successive

a p p l i c a t i o n of e q u i l i b r i u m and m a t e r i a l b a l a n c e r e l a t i o n s f o r each of t h e theoretical stages.

Data r e l a t i v e t o t h e e q u i l i b r i u m d i s t r i b u t i o n

of m a t e r i a l s of i n t e r e s t have been obtained by F e r r i s and co-workers. 3 The d i s t r i b u t i o n c o e f f i c i e n t f o r m a t e r i a l A, between s a l t and bismuth c o n t a i n i n g a r e d u c t a n t , i s given by t h e expression: t

l o g DA = nA l o g DLi + l o g KA, where

DA = d i s t r i b u t i o n c o e f f i c i e n t f o r A, = %/'SA = c o n c e n t r a t i o n of element A i n m e t a l phase, mole f r a c t i o n ,

XSA = c o n c e n t r a t i o n of f l u o r i d e of element A i n s a l t phase, mole

fraction,

A = v a l e n c e of element A i n s a l t phase,

= d i s t r i b u t i o n c o e f f i c i e n t of l i t h i u m , DL; KA = modified e q u i l i b r i u m c o n s t a n t . t

The v a r i a t i o n of t h e modified e q u i l i b r i u m c o n s t a n t , KA' w i t h temperature i s given by t h e r e l a t i o n : t

l o g KA = A + B/T, where

A, B = c o n s t a n t s , T = temperature, OK.

I n s e t t i n g up t h e e q u i l i b r i u m r e l a t i o n s f o r a system containing N

+ 1

components t h a t d i s t r i b u t e between t h e molten s a l t and bismuth phases, one component i s c o n v e n i e n t l y chosen as t h e r e f e r e n c e component.

The r e l a t i v e

c o n c e n t r a t i o n s of m a t e r i a l s i n t h e two phases a r e t h e n r e l a t e d by t h e f o l lowing s e t of expressions t h a t can be derived from Eq. (1):

. where Xsi,si 'Sr X ' Mr

= mole f r a c t i o n of component i i n s a l t and metal, r e s p e c t i v e l y ,

= mole f r a c t i o n of r e f e r e n c e component i n s a l t and m e t a l , respectively,

ni,n r = valence of component i and r e f e r e n c e component, r e s p e c t i v e l y , i n salt. The f i n a l e x p r e s s i o n r e q u i r e d f o r c a l c u l a t i n g e q u i l i b r i u m c o n c e n t r a t i o n s i n t h e two phases i s given by t h e following r e l a t i o n :

nixMi

(4)

N+1

1 -

'Mi i=l

where X M R = e q u i v a l e n t s of t r a n s f e r r a b l e components p e r mole of bismuth.

This r e l a t i o n r e q u i r e s t h a t t h e number of e q u i v a l e n t s of t r a n s f e r r a b l e metals p e r mole o f bismuth remain

constant.

A m a t e r i a l balance around s t a g e j of a column i n which t h e s t a g e s a r e numbered from t h e t o p

yields the relation:

where

= flow r a t e of s a l t l e a v i n g s t a g e j, moles/day,

= flow r a t e o f metal l e a v i n g s t a g e j , moles/day,

'si,

XMi,j

= mole f r a c t i o n of component i i n s a l t l e a v i n g s t a g e j , = mole f r a c t i o n of component i i n m e t a l l e a v i n g s t a g e j .

The notation used in analyzing the remaining parts of the protactinium isolation system (see Fig. 2) is as follows:

FDS = flow rate of discarded salt, moles/day, FH = flow rate of salt entering hydrofluorinator, moles/day,

FM = flow rate of metal entering hydrofluorinator, moles/day, FLIF = rate of addition of LiF to Pa decay tank, moles/day, FSP = flow rate of salt leaving hydrofluorinator, moles/day, H = uranium removal efficiency in fluorinator, XM = mole fraction of a component in metal phase,

XS = mole fraction of a component in salt phase, VDK = volume of protactinium decay tank, moles, -1 X = radioactive decay constant for 233Pa, day In addition, various suffixes were added to the flow rates and concentrations to indicate the location of a stream in the flow diagram, and the following suffixes were appended to the concentrations to denote the element being considered: L = lithium,

P = protactinium, T = thorium, U = uranium, Z = zirconium. Thus, the symbol XS2P refers to the mole fraction of protactinium in salt at point 2 in the flowsheet. In the model, the protactinium decay tank was treated as a completely mixed vessel and the hydrofluorinator was assumed to remove all transferrable metals from the bismuth. For these conditions, one can write the material balance relations given below. For 233Pa : FMeXMP + FShaXS4P = F S ~ V X S ~ P , FS20XS2P = FS3*XS3P, (FS3

FDS)*XS3P = (XaVDK + FSh)*XShP.

-J

uu LLX

I L

LLX

0 Ia 2 -

0 3

A LL

a n >

FM.XMU + FS4*XSbU = FS2*XS2U, (FS3 - FDS)*XS3U + X*VDK*XS4P= FSbmXS4U, FS3*XS3U = FS2*XS2U*(1- H). For

7Li: FMeXML + FS4.XSbL = FS2*XS2L, FS2oXS2L = F S ~ O X S ~ L , (FS3

FDS) *XS3L + FLIF = FS4*XS4L.

For 232Th :

F M o X M T + FSh*XS4T = FS2*XS2T, FS2 oXS2T = FS3 *XS3T, (FS3 - FDS)*XS3T = FS40XS4T.

. For Zr:

FMoXMZ + FSh*XSkZ = FS2*XS2Z, FS2 *XS2Z = FS3 *XS3Z, (FS3 - FDS)*XS3Z = FS4.XS4Z. From an overall material balance:

FM.(XM~ +

xMu + XML +

XMT + XMZ) + FS4 = FS2,

FS2 = FS3 + FS2*XS2U.H, FS3 + FLIF = FDS + FS4. The system is also under the constraint that LiF must be added to the protactinium decay tank at a sufficient rate (FLIF) to obtain a suitable salt liquidus temperature. An LiF-ThF4 mixture containing

71 mole % LiF

has a liquidus temperature of 568'~, which is acceptably low.

It was

assumed that the presence of zirconium, protactinium, and uranium fluorides

a t low c o n c e n t r a t i o n s would n o t i n c r e a s e t h e s a l t l i q u i d u s temperature t o an unacceptable l e v e l ; and, i n t h e c a l c u l a t i o n s , t h e v a l u e of FLIF w a s determined

t h a t XS4L was e q u a l t o 0.71.

Each of t h e sets of e q u a t i o n s

( 6 ) - (10)1 c o n s i s t s of t h r e e e q u a t i o n s r e l a t i n g t h r e e concen-

[ i . e . , Eqs

However, t h e e q u a t i o n s are n o t l i n e a r because of t h e dependence

trations.

of t h e flow r a t e s on t h e uranium c o n c e n t r a t i o n , as i n d i c a t e d by Eq. ( l l b ) . The q u a n t i t i e s FM, XMP, X M U , XMT, XML, XMZ, VDK, H , XShL, and FS4 a r e known; t h e remaining v a r i a b l e s a r e t o be determined.

I n t h e a l g o r i t h m adopted f o r

s o l v i n g t h e above system of e q u a t i o n s , t h e equations were l i n e a r i z e d by assuming a v a l u e for t h e s a l t d i s c a r d r a t e , which, w i t h Eqs. (8a) and ( l l a )

( l l c ) f i x e s a l l of t h e s a l t flow r a t e s .

(8c)

The remaining e q u a t i o n s

can be solved f o r t h e unknown c o n c e n t r a t i o n s , and Eqs. (llb) and ( l l c ) can be used t o o b t a i n an improved e s t i m a t e of t h e s a l t d i s c a r d r a t e .

This

algorithm converges i n only a few i t e r a t i o n s s i n c e t h e e q u a t i o n s are n o t strongly nonlinear.

2.3

C a l c u l a t e d R e s u l t s on Operation of t h e P r o t a c t i n i u m I s o l a t i o n System

The mathematical model d e s c r i b e d i n t h e previous s e c t i o n w a s used t o

compute c o n c e n t r a t i o n s and flow r a t e s throughout t h e secondary s a l t system and t o e v a l u a t e t h e performance of t h e p r o t a c t i n i u m i s o l a t i o n system f o r an assumed 10-day p r o c e s s i n g c y c l e .

T h e v a r i a t i o n of t h e p r o t a c t i n i u m re-

moval t i m e w i t h t h e primary f l u o r i n a t o r uranium removal e f f i c i e n c y and w i t h t h e r a t e a t which r e d u c t a n t i s added t o t h e e x t r a c t i o n column i s shown i n F i g . 3.

A s can be observed, e s s e n t i a l l y complete e x t r a c t i o n of t h e p r o t -

actinium i s o b t a i n e d i f t h e r e d u c t a n t a d d i t i o n r a t e i s adequate.

A re-

d u c t a n t a d d i t i o n r a t e of about 200 equiv/day i s r e q u i r e d f o r a uranium removal e f f i c i e n c y of

99%, and an a d d i t i o n r a t e of about

300 equivlday i s

r e q u i r e d f o r a uranium removal e f f i c i e n c y of 95%. The r a t e a t which LiF must be added t o t h e secondary s a l t i n o r d e r t o maintain a LiF concentrat i o n o f 0 . 7 1 mole f r a c t i o n depends on b o t h t h e uranium removal e f f i c i e n c y i n t h e primary f l u o r i n a t o r and on t h e r e d u c t a n t a d d i t i o n r a t e . i n Fig. 4,

A s shown

a LiF a d d i t i o n r a t e of about 40 moles/day i s r e q u i r e d i n o r d e r

ORNL DWG. 71-13586 REDUCTANT

(EQUIVALENTS

FEED PER

RATE

DAY 1

50 c5

n Y

c -I

a >

0 =E W

a E

3 z

I-

n IO PROCESSING CYCLE TIME TEMPERATURE STAGES IN Pa EXTRACTOR 0 IO0

IO DAYS 640째 C

PR I MA R Y

FLUOR I N A T 0 R

E F F IC1 ENCY (Yo)

Fig. 3. Effects of Primary Fluorinator Efficiency and Reductant Feed Rate to Protactinium Extraction Column on Protactinium Removal Time.

O R N L DWG. 71-13587 I

REDUCTANT

FEED

(EQUIVALENTS

PER

RATE

DAY 1

TEMPERATURE STAGES I N Pa EXTRACTOR

64OOC

100

PR I M A R Y

F L UO R I N AT 0 R

E F F I CI E NCY

(%I

Fig. 4. Effects of Primary Fluorinator Efficiency and Reductant Feed Rate to Protactinium Extraction Column on LiF Addition Rate.

t o achieve a uranium removal e f f i c i e n c y of 99% when t h e r e d u c t a n t add i t i o n r a t e i s 200 equiv/day.

The same LiF a d d i t i o n r a t e i s a l s o r e -

quired t o achieve a uranium removal e f f i c i e n c y of 95% when t h e r e d u c t a n t a d d i t i o n r a t e i s 371 equiv/day.

The v a r i a t i o n of p r o t a c t i n i u m removal

time w i t h number of s t a g e s i n t h e p r o t a c t i n i u m e x t r a c t i o n column i s shown i n Fig. 5.

A s can be observed, l i t t l e b e n e f i t i s obtained from

use of more t h a n f i v e s t a g e s , and as few as t h r e e s t a g e s could be used

a t t h e higher r e d u c t a n t feed r a t e without i n c r e a s i n g t h e p r o t a c t i n i u m removal time a p p r e c i a b l y .

The v a r i a t i o n of t h e uranium inventory i n

t h e p r o t a c t i n i u m decay tank w i t h t h e uranium removal time from t h e tank and w i t h t h e uranium removal e f f i c i e n c y i n t h e primary f l u o r i n a t o r i s shown i n F i g . 6.

A s can be observed, a uranium inventory t h a t i s 0.1%

or l e s s of t h e r e a c t o r uranium inventory can be obtained over a wide range of o p e r a t i n g c o n d i t i o n s . Both t h e q u a n t i t y of r e d u c t a n t r e q u i r e d and t h e r a t e a t which f u e l c a r r i e r s a l t must be removed from t h e r e a c t o r t o compensate f o r t h e LiF added by t h e p r o t a c t i n i u m i s o l a t i o n system depend on t h e f r a c t i o n of t h e uranium t h a t i s removed from t h e f u e l s a l t by t h e primary f l u o r i n a t o r .

For a uranium removal e f f i c i e n c y of 95% and a r e d u c t a n t a d d i t i o n r a t e of 371 equiv/day, f u e l c a r r i e r s a l t must be withdrawn a t t h e r a t e of 0 . 3 3 f t /day; f o r a removal e f f i c i e n c y of 99% and a r e d u c t a n t a d d i t i o n r a t e 3 of 200 equiv/day, f u e l s a l t must be removed a t t h e r a t e of 0.16 f t /day. Table 1 g i v e s a comparison of t h e components of t h e p a r t i a l f u e l c y c l e c o s t f o r t h e p r e s e n t p r o t a c t i n i u m i s o l a t i o n system i n which t h e p r o t a c t i n i u m i s i s o l a t e d i n s a l t and t h o s e f o r t h e previous p r o t a c t i n i u m i s o l a t i o n system

i n which t h e p r o t a c t i n i u m was i s o l a t e d i n bismuth.

For t h e p r e s e n t system,

t h e chemical and inventory charges amount to 0.047 mill/kWhr f o r a uranium removal e f f i c i e n c y of 95% and a r e d u c t a n t a d d i t i o n r a t e of 371 moles/day. These charges a r e reduced t o 0.034 mill/kWhr f o r a uranium removal e f f i -

ciency of 99% and a r e d u c t a n t a d d i t i o n r a t e of 200 equiv/day. The s a l t 3 inventory i n t h e p r o t a c t i n i u m decay t a n k i s 150 f t i n each case. The uranium inventory i n t h e t a n k i s about 0.1% of t h e r e a c t o r uranium inventory

ORNL DWG 71-13588Rl I

T E M P E R A T U R E 6 4 0 *'c I Pa CYCLE T I M E IO DAYS FLUORINATOR EFFICIENCY 95 O h 99 %-

----

REDUCTANT F E E D RATE (EQUIVALENTS / DAY 1

Fig. 5. Effect of Number of Stages in Protactinium Extraction Column on Protactinium Removal Time for Primary Fluorinator Efficiencies of 95% and 99%.

O R N L DWG. 71-13589 2.3

TEMPERATURE PROCESSING CYCLE T I M E S T A G E S IN Pa E X T R A C T O R

z a

64OOC I O DAYS

1.6

PRIMARY FLUORINATOR EFFICIENCY =95O/o REDUCTANT F E E D R A T E = 3 7 1 EQUIVALENTSIDA

w, Q a

1.2

-z W

a0 C

zJ w>:z

0.8

-I&

3 - $

0.4

za a

0 0

URANIUM

REMOVAL

TI ME

(DAYS 1

F i g . 6 . E f f e c t of Uranium Removal T i m e i n Secondary S a l t C i r c u i t on Uranium Inventory i n P r o t a c t i n i u m Decay Tank for Primary F l u o r i n a t o r E f f i c i e n c i e s o f 95% and 99%.

Table 1. Partial Fuel Cycle Costs for Present and Past Protactinium Isolation Systems Pa Isolation in Salt

Pa Isolation in Bi

Reductant addition rate, moles/day

371

200

429

Fluorinator efficiency, %

Resulting components of cost, mill/ kWhr

Reductant

0 0131

0 0071

0 0151

Fluorine

0.0115

0 0115

Salt replacement

0 0206

0.0134

0 0163

Uranium inventory

0.0004

0 0004

0.0030

Loss in breeding ratio

o.oooo

0.0006

0 0013

HF and H2

0 0010

0 0007

0* 0010

0 0097

B i inventory

Total

0.0467

0.0336

0 0579

2.4

Combination of Discard Streams from t h e F l u o r i n a t i o n - Reductive E x t r a c t i o n - M e t a l T r a n s f e r Flowsheet

The flowsheet shown i r t l F i g . 1 r e q u i r e s t h a t about 40 moles of LiF be added d a i l y t o t h e p r o t a c t i n i u m decay t a n k i n order t o o b t a i n a s u i t a b l e l i q u i d u s temperature.

Lithium f l u o r i d e purchased for t h i s a d d i t i o n would

i n c r e a s e t h e f u e l c y c l e c o s t by o n l y 0.0014 mill/kWhr; however, we have observed t h a t an a c c e p t a b l e l i q u i d u s temperature can a l s o b e obtained by hydrofluorinating t h e Li-Bi

stream from t h e d i v a l e n t r a r e - e a r t h s t r i p p e r

i n t h e presence of t h e s a l t from t h e decay t a n k ,

This o p e r a t i o n adds 50 moles of LiF and about 1.1 moles of r a r e - e a r t h f l u o r i d e s t o t h e decay

t a n k per day.

With t h i s a d d i t i o n , t h e composition of t h e s a l t i n t h e

decay tank i s 72-24-3

mole % LiF-ThF4-ZrF4,

1 mole

% divalent rare-earth

f l u o r i d e s , and 360 ppm of t r i v a l e n t r a r e - e a r t h f l u o r i d e s . f l u o r i n a t o r e f f i c i e n c y of per day a r e assumed.)

( A primary

99% and a r e d u c t a n t feed r a t e of

200 e q u i v a l e n t s

The s a l t has a l i q u i d u s t e m p e r a t u r e of 57OoC; a t

t h i s temperature, t h e r a r e - e a r t h f l u o r i d e c o n c e n t r a t i o n i s w e l l w i t h i n c

the rare-earth solubility. We have a l s o observed t h a t it i s p o s s i b l e t o combine a l l waste streams from t h e m e t a l t r a n s f e r system and t h e p r o t a c t i n i u m i s o l a t i o n system f o r uranium r e c o v e r y p r i o r t o d i s p o s a l , as shown i n F i g . 7 .

In t h i s operation,

waste s a l t from t h e p r o t a c t i n i u m decay t a n k would be combined w i t h t h e The L i - B i stream from t h e t r i v a l e n t

f u e l c a r r i e r s a l t d i s c a r d stream.

r a r e - e a r t h s t r i p p e r would be h y d r o f l u o r i n a t e d i n t h e presence of t h e r e s u l t i n g s a l t , and t h e combined stream would be h e l d f o r p r o t a c t i n i u m decay. The p r o t a c t i n i u m c o n c e n t r a t i o n i n t h e combined streams would b e only 500 ppm i n i t i a l l y , and it would decrease t h e r e a f t e r . e r a t i o n r a t e would be a c c e p t a b l y l o w .

The s p e c i f i c h e a t gen-

The s a l t i n t h e waste holdup t a n k

would be f l u o r i n a t e d b e f o r e d i s c a r d t o remove uranium.

The composition

% LiF-ThF4-BeF2mole % t r i v a l e n t r a r e - e a r t h f l u o r i d e s , and 0.3 mole % d i v a l e n t

of t h e d i s c a r d e d s a l t would be 74 7-13 5-9 5-0 8 mole ZrF4, 1 . 2

rare-earth fluorides.

Although t h e l i q u i d u s temperature of t h e s a l t i s

near 500째C, t h e s a l t t e m p e r a t u r e would have t o be maintained a t about 600째c t o prevent p r e c i p i t a t i o n of t h e t r i v a l e n t r a r e - e a r t h f l u o r i d e s .

ORNL DWG 71-2858

Li-Bi t DIVALENT RARE EARTHS 50 MOLES Li/DAY

HYDROPO,U, LI, Th, Zr -C FROM Pa ISOLATION FLUORINATOR -c FLUORINATOR -c

Pa DECAY TANK , Li-Bi +TRIVALENT

FUEL CARRIER SALT DISCARD 240 MOLESIDAY 0.16 F T s / W Y

WASTE SALT HOLDUP TANK

HYDROFLUORINATOR

UF6

BATCH FLUORINATOR

Bi TO RECYCLE

SALT TO WASTE -0.27 FTs/WY

Fig. 7. Method for Combining Waste Streams from Protactinium Isolation and Rare-Earth Removal Processes. Flow rates are shown for a uranium removal efficiency in the primary fluorinator of 99% and a reductant addition rate of 200 equivalents/day.

This p r o c e s s i n g scheme would r e q u i r e t h a t s a l t be d i s c a r d e d a t t h e r a t e of 60 f t 3 every 220 days.

ANALYSIS OF URANIUM REMOVAL FROM FUEL SALT BY OXIDE PRECIPITATION M. J . B e l l

L . E . McNeese

Oxide p r e c i p i t a t i o n i s b e i n g considered as an a l t e r n a t i v e method f o r s e l e c t i v e l y removing p r o t a c t i n i u m from MSBR f u e l s a l t and f o r subsequently removing uranium from t h e f u e l s a l t p r i o r t o t h e removal o f r a r e e a r t h s . We have made c a l c u l a t i o n s t h a t d e s c r i b e t h e performance of a m u l t i s t a g e c o u n t e r c u r r e n t p r e c i p i t a t o r f o r removing uranium from f u e l s a l t which i s f r e e of protactinium.

The r e s u l t s i n d i c a t e t h a t

99% of t h e uranium can

Se -removed from t h e s a l t by u s i n g about t h r e e e q u i l i b r i u m s t a g e s and t h a t t h e UO -Tho s o l i d s o l u t i o n which i s p r e c i p i t a t e d w i l l c o n t a i n g r e a t e r 2 2 t h a n 90% U O ~ .

3.1 Mathematical A n a l y s i s of a Uranixn Oxide P r e c i p i t a t o r e

A mathematical a n a l y s i s of a m u l t i s t a g e c o u n t e r c u r r e n t e q u i l i b r i u m

p r e r i p i t a t o r was c a r r i e d o u t t o determine t h e f e a s i b i l i t y of p r e c i p i t a t i n g most of t h e uranium from MSBR f u e l s a l t without t h e a t t e n d a n t p r e c i p i t a t i o n of l a r g e q u a n t i t i e s of Tho2.

The d a t a o f Bamberger and Baes

for the

e q u i l i b r i u m c o n c e n t r a t i o n of UO -Tho s o l i d s o l u t i o n s i n c o n t a c t w i t h 2 2 molten LiF-BeF2-ThF UF salts were employed in t h e analysis. T h e equi4- 4 l i b r i u m q u o t i e n t , Q, d e f i n e d as

= %02 'ThF4/"Th02

'UF4)'

for the reaction UF4 + Tho2 = U02 + ThF4

i s given by t h e e x p r e s s i o n

(14) where T i s t h e a b s o l u t e temperature (OK). I n t h e a n a l y s i s , each s t a g e was t r e a t e d a s an e q u i l i b r i u m c o n t a c t o r and it was assumed t h a t t h e s o l i d l e a v i n g a s t a g e would have a s p e c i f i e d q u a n t i t y of s a l t a s s o c i a t e d w i t h i t .

The s a l t / s o l i d mole r a t i o i n t h i s

stream was assumed t o be c o n s t a n t f o r each of t h e s t a g e s .

Material

balances around s t a g e N ( s e e F i g . 8 ) y i e l d t h e following r e l a t i o n s .

For

uranium and thorium i n s a l t : (FS + FR) [XSU(N) + XST(N)] = FR [XSU(N

+ 1) + XST(N + l ) ] + FS [XSU(N

- 1) + XST(N - l)];

(15)

and f o r uranium: (FS + FR)*XSU(N) + FO*XOU(N) = FR.XSU(N

+ 1) + FS*XSU(N- 1) + FO*XOU(N + l),

where

FO = flow r a t e o f oxide, moles/day, FR = flow r a t e of s a l t accompanying oxide, moles/day,

FS = flow r a t e of s a l t flowing c o u n t e r c u r r e n t t o oxide, moles/day, XOU = mole f r a c t i o n UO

i n oxide,

XST = mole f r a c t i o n ThFL i n s a l t , XSU = mole f r a c t i o n UF4 i n s a l t . Equation ( 1 5 ) s t a t e s t h a t t h e r a t e a t which UF4 and ThF4 l e a v e s t a g e N must

equal t h e r a t e a t which t h e s e m a t e r i a l s e n t e r i n s a l t from s t a g e ( N 1) and i n s a l t a s s o c i a t e d w i t h s o l i d s from s t a g e ( N + l), s i n c e it i s assumed t h a t t h e flow r a t e of oxide from s t a g e t o s t a g e i s f i x e d .

Equation

(16)

s t a t e s t h a t t h e amount of uranium l e a v i n g s t a g e N i n t h e s a l t and t h e oxide must be equal t o t h e amount of uranium e n t e r i n g i n t h e s a l t from s t a g e

ORNL DWG. 71-1359ORl

FS;XSU(N) ,XST(N)

FO;XOU(N+I) FR; X S U ( N + I ) , X S T ( N + I )

STAGE N

FS; XSU ( N - I ) , X S T ( N - I )

FO; X O U ( N ) FR;XSU (N),XST(N)

F i g . 8. Nomenclature Used i n Mathematical Analysis of a M u l t i s t a g e Countercurrent Uranium Oxide P r e c i p i t a t o r .

. .

1) p l u s t h a t e n t e r i n g i n t h e s o l i d s and a s s o c i a t e d s a l t from s t a g e

+ 1). I n s o l v i n g t h e s e t of equations r e p r e s e n t e d by E q s . ( 1 5 ) and (16),one t a k e s account of two f a c t s : t h e s a l t flow r a t e and t h e com(N

p o s i t i o n of t h e s a l t a r e known a t t h e p o i n t where s a l t i s f e d t o t h e p r e c i p i t a t o r , and no s a l t accompanies t h e oxide f e d t o t h e o p p o s i t e end of t h e p r e c i p i t a t o r .

Other d a t a r e q u i r e d f o r e v a l u a t i n g p r e c i p i t a t o r

performance i n c l u d e t h e number of s t a g e s i n t h e p r e c i p i t a t o r , t h e tempe r a t u r e , t h e moles of s a l t p e r mole of oxide i n t h e oxide stream l e a v i n g a s t a g e , and t h e composition of t h e UO -Tho 2

s o l i d s o l u t i o n produced i n a

given s t a g e , which i s given by Eq. ( 1 2 ) .

3.2

Calculated Results

Typical r e s u l t s showing t h e e f f e c t s of temperature and number of s t a g e s on p r e c i p i t a t o r performance a r e shown i n F i g . 9 .

These r e s u l t s

i n d i c a t e t h a t g r e a t e r t h a n 99% of t h e uranium can be removed from MSBR f u e l s a l t w i t h t h r e e or more s t a g e s and t h a t t h e oxide stream produced w i l l have a U02 c o n c e n t r a t i o n of g r e a t e r t h a n 90%. Over a wide range of c o n d i t i o n s , less t h a n 1% of t h e thorium f e d t o t h e system would be p r e c i p i t a t e d w i t h t h e uranium.

as t h e temperature i n c r e a s e s .

A decrease i n performance i s observed

No s i g n i f i c a n t e f f e c t on g r e c i p i t a t o r

performance w a s observed when t h e amount o f s a l t remaining w i t h t h e oxide during t h e t r a n s f e r of s a l t between s t a g e s was v a r i e d from 2 t o 1 0 moles per mole of oxide.

DEVELOPMENT OF A FROZEN-WALL FLUORINATOR: INSTALLATION OF A SIMULATED FLUORINATOR FOR STUDYING INDUCTION HEATING

J. R . Hightower, Jr.

C . P. Tung L. E. McNeese

An experiment t o demonstrate p r o t e c t i o n a g a i n s t c o r r o s i o n by t h e u s e of l a y e r s o f f r o z e n s a l t i n a continuous f l u o r i n a t o r r e q u i r e s a corrosionr e s i s t a n t h e a t source t o be p r e s e n t i n t h e molten s a l t .

High-frequency

i n d u c t i o n h e a t i n g has been proposed as t h e source of h e a t , and t h e e s t i m a t e d

ORNL DWG 70-8995

100.0

---

/--------,

9 9.0

98.0 0

0 W

97.0

9 6.0

a W

95.0

/ 94.0

- / /

580' C 62OOC

93.0 -

MOLES SALT RECYCLED/ M O L E OXIDE = 2

92 .O I .o

1. I

1.2

1.3

MOLES O F OXIDE REMOVED PER MOLE OF UF4 F E D F i g . 9. E f f e c t s o f Temperature, Number of S t a g e s , and Oxide Removal Rate on Percentage Uranium Recovered i n a n Oxide P r e c i p i t a t i o n .

26 performance5 o f a frozen-wall f l u o r i n a t o r having an i n d u c t i o n c o i l embedded i n t h e f r o z e n s a l t near t h e f l u o r i n a t o r w a l l has i n d i c a t e d t h a t t h i s may be an a c c e p t a b l e h e a t i n g method.

There a r e u n c e r t a i n t i e s as-

s o c i a t e d w i t h determining t h e e f f e c t of bubbles i n t h e molten s a l t and i n e s t i m a t i n g t h e amount o f h e a t t h a t w i l l be generated i n t h e metal w a l l s of t h e f l u o r i n a t o r .

Equipment i s Geing assembled for studying

h e a t g e n e r a t i o n i n a simulated frozen-wall f l u o r i n a t o r c o n t a i n i n g a n embedded i n d u c t i o n c o i l .

I n t h i s experiment, a 31 w t

HNO

solution,

which has e l e c t r i c a l p r o p e r t i e s similar t o t h o s e of molten s a l t s , w i l l be used t o s i m u l a t e molten s a l t i n t h e f l u o r i n a t o r v e s s e l .

The equip-

ment f o r t h e experiment i s d e s c r i b e d i n t h e remainder of t h i s s e c t i o n .

4 . 1 Experimental Equipment The induction-heated

simulated f l u o r i n a t o r c o n s i s t s of a 5-in.-OD,

5-ft-long

g l a s s t u b e i n s e r t e d i n an i n d u c t i o n c o i l and placed i n s i d e a

5-ft-long

s e c t i o n o f 8-in.

304 s t a i n l e s s s t e e l sched

40 p i p e .

The n i t r i c

a c i d i n s i d e t h e g l a s s t u b e r e p r e s e n t s t h e molten s a l t i n t h e f l u o r i n a t o r , t h e space between t h e g l a s s t u b e and t h e p i p e w a l l (which c o n t a i n s t h e

i n d u c t i o n c o i l ) r e p r e s e n t s t h e f r o z e n s a l t l a y e r , and t h e p i p e r e p r e s e n t s the fluorinator vessel w a l l .

A s shown by t h e flow diagram i n F i g . 1 0 ,

t h e a c i d i s pumped, f i r s t , through t h e g l a s s column (where it i s heated

by t h e i n d u c t i o n c o i l ) and, t h e n , through a h e a t exchanger (where t h e h e a t i s removed).

The r a t e a t which heat i s generated i n t h e a c i d w i l l

be determined from a heat balance on t h e a c i d p a s s i n g through t h e column.

The p i p e r e p r e s e n t i n g t h e f l u o r i n a t o r w a l l i s equipped w i t h a j a c k e t through which c o o l i n g water p a s s e s .

The heat generated i n t h e p i p e w i l l

b e c a l c u l a t e d from t h e change i n t e m p e r a t u r e of t h e water flowing through the jacket.

A d r a i n t a n k i s provided f o r holding t h e n i t r i c a c i d d u r i n g

system maintenance.

A i r , a t r a t e s up t o 2 cfm, can be c o u n t e r c u r r e n t l y

c o n t a c t e d w i t h t h e downflowing a c i d stream

i n t h e column.

The g l a s s column and i n d u c t i o n c o i l are shown i n Fig. 11. The c o i l

17 s e c t i o n s of smaller c o i l s , each of which i s 5.6 i n . i n i n s i d e diameter and 3 i n . l o n g . The c o i l s e c t i o n s are made of 6.5 t u r n s i s made up of

ORNL DWG 70-8964 a

COOL1 NG 7 ' WATER

JACK ETED PIPE

COOLING WATER

AIR

1-1

DRAlN TANK

F i g . 1 0 . Flow Diagram of F l u o r i n a t o r Simulation and N i t r i c Acid Recirc u l a t i o n System.

03 03 01

0 0

0 6 r

rl rl cd

s E

u (I) (I)

cd rl

rl .ti

of 0.25-in.-OD directions.

Monel t u b i n g , and a d j a c e n t c o i l s a r e wound i n o p p o s i t e The t o t a l l e n g t h of t h e c o i l assembly i s 5 f t .

The c o i l s

a r e connected e l e c t r i c a l l y i n p a r a l l e l between headers made from 5/8i n . - d i m Monel t u b i n g ; a l l c o i l s wound i n t h e same d i r e c t i o n a r e connected t o one p a i r of headers, and t h e two p a i r s o f headers a r e , i n

t u r n , connected e l e c t r i c a l l y , i n p a r a l l e l .

The inductance of t h e work

c o i l (when i n s t a l l e d i n s i d e t h e 8-in.-diam

p i p e ) w a s found t o b e 5.8

uH. The e f f e c t i v e r e s i s t a n c e a t a frequency of 1000 Hz w a s found t o b e 0.135 R. Figure 12 shows t h e a c i d r e c i r c u l a t i o n system b e f o r e thermal i n s u l a t i o n w a s added t o t h e j a c k e t e d p i p e t h a t s i m u l a t e s t h e f l u o r i n a t o r v e s s e l (shown a t t h e r i g h t o f t h e photograph).

The a c i d r e c i r c u l a t i o n system i s

c o n s t r u c t e d of s t a i n l e s s s t e e l t u b i n g ; t h e p a r t s of t h e pump t h a t c o n t a c t t h e a c i d a r e made of s t a i n l e s s s t e e l and Teflon; and t h e g a s k e t s i n t h e glass-to-metal Viton-A.

j o i n t s a t each end of t h e g l a s s column a r e f a b r i c a t e d from

The r e c i r c u l a t i o n system i s l o c a t e d behind a s p l a s h s h i e l d ( n o t

shown i n F i g . 1 2 ) and can be operated e n t i r e l y from i n f r o n t of t h e s p l a s h shield. The h e a t exchanger i s an American Standard s t a i n l e s s s t e e l s h e l l and t u b e exchanger which has one s h e l l s i d e and one t u b e s i d e p a s s . The 2 heat-transfer area i s 9 f t The pump i s a Crane Company Chempwnp made

o f 316 s t a i n l e s s s t e e l w i t h Teflon g a s k e t s and i s designed t o o p e r a t e a t a temperature of 150째F.

A t a f l o w r a t e of 1 gpm (approximately t h e max-

i m u m a c i d f l o w ) , the pump develops a t o t a l head of 74 ft of f l u i d .

The rf g e n e r a t o r i s a 25-kWTher-monicmodel a t a frequency of 400 kHz.

1400 o s c i l l a t o r o p e r a t i n g

The rf t r a n s m i s s i o n l i n e s a r e f l e x i b l e water-

cooled c o a x i a l c a b l e s made by t h e L. C . M i l l e r Company. 4.2

S t a t u s of Equipment I n s t a l l a t i o n

The n i t r i c a c i d r e c i r c u l a t i o n system and t h e rf g e n e r a t o r have been installed.

We a r e p r e s e n t l y matching t h e impedances of t h e g e n e r a t o r and

work c o i l i n o r d e r t o d e l i v e r s u f f i c i e n t power t o t h e work c o i l .

Fig. 12. Installed Fluorinator Simulation and Nitric Acid Recirculation System.

MEASUREMENT OF AXIAL DISPERSION COEFFICIENTS AND GAS HOLDUP I N OPEN BUBBLE COLUMNS M . S. B a u t i s t a J . S. Watson L. E. McNeese

Axial d i s p e r s i o n i s an important c o n s i d e r a t i o n i n t h e d e s i g n and performance of continuous f l u o r i n a t o r s .

Since molten s a l t s a t u r a t e d w i t h

f l u o r i n e i s c o r r o s i v e , f l u o r i n a t o r s w i l l be simple open v e s s e l s having a p r o t e c t i v e l a y e r of f r o z e n s a l t on a l l exposed m e t a l s u r f a c e s .

I n such

systems, t h e r i s i n g gas bubbles may cause a p p r e c i a b l e a x i a l d i s p e r s i o n i n the salt.

For t h e p a s t two y e a r s , w e have been involved i n a program f o r

measuring a x i a l d i s p e r s i o n d u r i n g t h e c o u n t e r c u r r e n t flow of a i r and water i n open bubble columns.

The o b j e c t i v e s of t h i s program a r e t o e v a l u a t e

t h e e f f e c t of axial d i s p e r s i o n on f l u o r i n a t o r performance and t o account f o r t h i s e f f e c t i n t h e d e s i g n of f l u o r i n a t o r s .

5.1

Previous S t u d i e s on A x i a l D i s p e r s i o n

I n i t i a l i n v e s t i g a t i o n s o n a x i a l d i s p e r s i o n i n open bubble columns were made by B a u t i s t a and McNeese, and water i n a 2-in.-ID,

observed.

6 who s t u d i e d t h e c o u n t e r c u r r e n t flow of a i r

72-in.-long

column.

Two r e g i o n s of o p e r a t i o n were

The f i r s t of t h e s e c o n s i s t e d of a "bubbly" r e g i o n ( a t low g a s

flow r a t e s ) i n which t h e a i r moved up t h e column as i n d i v i d u a l bubbles and coalescence was minimal.

The second r e g i o n c o n s i s t e d of a "slugging" r e g i o n

( a t h i g h e r gas flow r a t e s ) i n which t h e a i r coalesced r a p i d l y i n t o bubbles having diameters equal t o t h e column diameter.

A p l o t of t h e l o g a r i t h m of

t h e d i s p e r s i o n c o e f f i c i e n t v s t h e l o g a r i t h m of t h e g a s flow r a t e w a s l i n e a r i n both regions.

However, t h e s l o p e of t h e l i n e r e p r e s e n t i n g data i n t h e

slugging r e g i o n w a s h i g h e r t h a n t h a t f o r data i n t h e bubbly r e g i o n .

The

t r a n s i t i o n between t h e two r e g i o n s was w e l l d e f i n e d . The same column and a s s o c i a t e d equipment were used by A. M. Sheikh and 3. D. Dearth 7 of t h e MIT P r a c t i c e School f o r i n v e s t i g a t i n g t h e e f f e c t s of

t h e v i s c o s i t y and s u r f a c e t e n s i o n of t h e l i q u i d .

The d i s p e r s i o n c o e f f i c i e n t

was found t o d e c r e a s e i n t h e bubbly r e g i o n as t h e v i s c o s i t y of t h e l i q u i d was i n c r e a s e d from 1 t o 15 CP by t h e a d d i t i o n of g l y c e r o l t o t h e water;

l i t t l e e f f e c t w a s noted i n t h e slugging r e g i o n .

An i n c r e a s e i n t h e d i s -

p e r s i o n c o e f f i c i e n t was observed as t h e s u r f a c e t e n s i o n of t h e l i q u i d was decreased by a d d i t i o n of 2-butanol t o t h e water, The equipment was a l s o used by A. A. J e j e and C. R . Bozzuto,8 of t h e MIT P r a c t i c e School, who i n v e s t i g a t e d t h e e f f e c t s of g a s i n l e t diameter

and column diameter on a x i a l d i s p e r s i o n and obtained d a t a on g a s holdup i n bubble columns.

I n t h e slugging r e g i o n , t h e d i s p e r s i o n c o e f f i c i e n t

appeared t o b e p r o p o r t i o n a l t o t h e square r o o t of t h e volumetric g a s flow and was independent of column diameter.

I n t h e bubbly r e g i o n , t h e d i s p e r -

s i o n c o e f f i c i e n t was dependent only on t h e volumetric gas flow r a t e f o r columns having diameters of 2 i n . or l a r g e r . obtained w i t h a 1.5-in.-diam

Dispersion c o e f f i c i e n t d a t a

column d e v i a t e d from t h i s c o n d i t i o n .

A t low

gas flow r a t e s , g a s holdup was l i n e a r l y dependent on t h e s u p e r f i c i a l g a s v e l o c i t y and w a s independent of column diameter.

A t superficial velocities

above t h e t r a n s i t i o n from bubbly t o s l u g flow, t h e gas holdup d a t a for t h e v a r i o u s column diameters diverged; t h e holdup was g r e a t e s t f o r t h e s m a l l e s t column diameter. A l l of t h e d i s p e r s i o n c o e f f i c i e n t d a t a o b t a i n e d t h u s f a r r e s u l t from

measurements of t h e s t e a d y - s t a t e a x i a l d i s t r i b u t i o n of a c u p r i c n i t r a t e t r a c e r t h a t i s c o n t i n u o u s l y i n j e c t e d i n t o t h e bottom of t h e column near t h e water e x i t .

The t r a c e r c o n c e n t r a t i o n w a s measured a t 20 p o s i t i o n s ,

l o c a t e d 3.5 i n . a p a r t , along t h e column. Water w a s withdrawn a t a low r a t e (about 1 cm3 /min) by a s m a l l m a g n e t i c a l l y d r i v e n c e n t r i f u g a l pump a t each of t h e p o s i t i o n s , and t h e water stream was c i r c u l a t e d through a p h o t o c e l l and t h e n r e t u r n e d t o t h e o p p o s i t e s i d e of t h e column a t t h e same e l e v a t i o n .

This experimental technique o p e r a t e d s a t i s f a c t o r i l y f o r

a range of water and a i r flow r a t e s .

It w a s found t h a t t h e a x i a l d i s p e r -

s i o n c o e f f i c i e n t was independent of both axial p o s i t i o n i n t h e column and

water s u p e r f i c i a l v e l o c i t y i n t h e range of i n t e r e s t .

This experimental

technique had t h e following two p r i n c i p a l disadvantages:

(1)t h e measure-

ments were time consuming s i n c e about 2 h r was r e q u i r e d f o r t h e column t o

33 r e a c h s t e a d y s t a t e , and ( 2 ) a t s u f f i c i e n t l y high gas r a t e s , a i r t h a t w a s e n t r a i n e d w i t h t h e water c i r c u l a t i n g through t h e p h o t o c e l l s accumulated i n t h e c e n t r i f u g a l pumps and prevented s a t i s f a c t o r y o p e r a t i o n .

For t h e s e

r e a s o n s , a n attempt was made t o develop an a l t e r n a t i v e experimental technique t h a t would circumvent t h e s e problems.

The remainder of t h i s s e c t i o n

d e s c r i b e s a t r a n s i e n t technique t h a t has a number of advantages over t h e s t e a d y - s t a t e technique.

5.2

Mathematical Analysis of Unsteady-State Axial Dispersion i n a Bubble Column

A t r a n s i e n t t e c h n i q u e , which has been used p r e v i o u s l y by Ohki and

Inoue,â&#x20AC;&#x2122;

was examined t o determine i t s a p p l i c a b i l i t y under c o n d i t i o n s of

interest.

I n t h i s t e c h n i q u e , t h e r e i s no n e t flow of water through t h e

column; however, d a t a o b t a i n e d by u s e of t h e s t e a d y - s t a t e technique ind i c a t e d t h a t t h e water flow r a t e does not a f f e c t t h e a x i a l d i s p e r s i o n c o e f f i c i e n t i n t h e range of flow r a t e s of i n t e r e s t .

A small amount of

e l e c t r o l y t e t r a c e r i s r a p i d l y i n j e c t e d i n t o t h e t o p of t h e column, and t h e c o n c e n t r a t i o n of t h e t r a c e r i s measured continuously a t a p o i n t near t h e bottom of t h e column by u s e of a c o n d u c t i v i t y probe.

It w a s assumed

t h a t t h e r a t e of movement of t r a c e r down t h e column would be d e s c r i b e d by t h e one-dimensional d i f f u s i o n equation:

a *c -ac- - D at e az2â&#x20AC;&#x2122; where C = t r a c e r c o n c e n t r a t i o n i n column a t p o i n t Z and time t ,

t = time, Z = a x i a l p o s i t i o n i n column measured from t h e t o p of t h e column, De = a x i a l d i s p e r s i o n c o e f f i c i e n t .

Since t h e t r a c e r cannot d i f f u s e a c r o s s t h e upper and lower boundaries of t h e column, one r e q u i r e s t h a t t h e following boundary c o n d i t i o n be met a t Z = 0

and Z = L:

ac = az

The i n s t a n t a n e o u s i n j e c t i o n a t t h e t o p of t h e column of a s p e c i f i e d quant i t y of s o l u t i o n c o n t a i n i n g a s p e c i f i e d t r a c e r c o n c e n t r a t i o n i s r e p r e s e n t e d by t h e following r e l a t i o n s a t t = 0:

c = c0 , O Z Z L A c = o ,

A < Z < L ,

where co

- c o n c e n t r a t i o n of t r a c e r i n s o l u t i o n i n a t h i n l a y e r a t t o p of column a t t = 0 ,

A = depth of s o l u t i o n having c o n c e n t r a t i o n C

at t = 0,

L = column l e n g t h , of Eq. (1'7) w i t h t h e boundary c o n d i t i o n s s p e c i f i e d by E q s . (18) y i e l d s t h e following r e l a t i o n for t h e r e l a t i v e t r a c e r concentrat i o n a t p o s i t i o n Z and time t :

C -

2L +ITA

n=l

sin

nrA cos L

where C M = f i n a l t r a c e r c o n c e n t r a t i o n i n column a f t e r t r a c e r i s uniformly

dispersed.

For t h e c o n d i t i o n where A < < L , t h i s s o l u t i o n reduces t o t h e following r e l a t i o n f o r t h e r e l a t i v e t r a c e r c o n c e n t r a t i o n i n t h e column a t p o s i t i o n Z and time t :

35 The r e l a t i v e t r a c e r c o n c e n t r a t i o n i s t h u s a f u n c t i o n of t h e normalized p o s i t i o n i n t h e column, Z/L, and of t h e dimensionless time, B , which i s 2

equal t o t h e q u a n t i t y ( T / L ) D t . I n t h e p r e s e n t c a s e , t h e r e l a t i v e t r a c e r e c o n c e n t r a t i o n i s dependent only on t h e dimensionless time @ and was measured a t only one p o i n t i n t h e column.

In principle, a value f o r t h e a x i a l

d i s p e r s i o n c o e f f i c i e n t could be obtained by f i t t i n g Eq. ( 2 0 ) t o t h e exp e r i m e n t a l l y determined relathe-tracer-concentration-vs-time o n l y one p o i n t (C/Cco = 0.5, f o r example).

curve a t

O h k i and Inoue p o i n t o u t ,

however, t h a t g r e a t e r accuracy i s u s u a l l y achieved i f t h i s curve i s f i t t o Eq. ( 2 0 ) a t two p o i n t s ( o t h e r t h a n t = 0 ) s i n c e t h e r e s u l t i s l e s s s e n s i t i v e t o e r r o r s i n t h e i n j e c t i o n time and i n t h e d u r a t i o n of t h e inj e c t i o n period.

I n t h e p r e s e n t c a s e , t h e curves were f i t t o Eq. ( 2 0 ) a t

r e l a t i v e t r a c e r c o n c e n t r a t i o n v a l u e s of 0 . 3 and 0 . 7 .

Here, t h e a x i a l

d i s p e r s i o n c o e f f i c i e n t i s given by t h e r e l a t i o n :

where '0.3"0.7

= dimensionless t i m e a t which C/Cm has v a l u e s of 0 . 3 and

0.7, respectively,

.7 = time a t which

C/C,

has v a l u e s of 0 . 3 and 0.7, r e s p e c t i v e l y .

The e r r o r i n t h e measured a x i a l d i s p e r s i o n c o e f f i c i e n t r e s u l t i n g from an e r r o r i n t h e r e l a t i v e p o s i t i o n of t h e c o n d u c t i v i t y probe i n t h e column can be estimated from Eq. ( 2 0 ) by c a l c u l a t i n g t h e v a r i a t i o n of t h e q u a n t i t y w i t h r e l a t i v e probe p o s i t i o n , as shown i n F i g . 1 3 . The r a t e of '0.3 w i t h a change i n r e l a t i v e probe p o s i t i o n change of t h e q u a n t i t y 60.7 '0.3

'0.7

a t a Z / L v a l u e of 0.7 i s 1.8, which i n d i c a t e s t h a t an e r r o r i n probe posit i o n of 2 cm would produce an e r r o r i n t h e measured a x i a l d i s p e r s i o n coe f f i c i e n t of 2 . 3 % .

The r e l a t i v e probe p o s i t i o n was measured t o w i t h i n 1

cm i n t h e p r e s e n t work.

37’

I n t h e previous a n a l y s i s , it was assumed t h a t t h e t r a c e r s o l u t i o n i s Since t h i s i s not

i n j e c t e d i n t o t h e t o p of t h e column i n s t a n t a n e o u s l y .

a c t u a l l y t h e c a s e , a new a n a l y s i s w a s made i n o r d e r t o estimate t h e e r r o r i n t h e measured a x i a l d i s p e r s i o n c o e f f i c i e n t caused by a nonzero i n j e c t i o n I n t h e l a t t e r a n a l y s i s , it w a s assumed t h a t t r a c e r was added a t t h e

time.

t o p of t h e column a t a c o n s t a n t r a t e f o r a s p e c i f i e d t i m e p e r i o d , and t h a t t h i s r e s u l t e d i n a nonuniform t r a c e r c o n c e n t r a t i o n p r o f i l e i n t h e column a t t h e end of t h e i n j e c t i o n p e r i o d .

After t h i s t i m e , t h e t r a c e r was as-

sumed t o d i f f u s e throughout t h e column w i t h t h e boundary c o n d i t i o n s repr e s e n t e d by Eq. ( 1 8 ) .

The c o n c e n t r a t i o n of t r a c e r i n t h e column d u r i n g

t h e p e r i o d i n which t r a c e r i s added t o t h e t o p of t h e column a t a c o n s t a n t

r a t e i s r e p r e s e n t e d by Eq. ( 1 7 ) and t h e following i n i t i a l and boundary conditions:

C = O

f o r a l l Z a t t = O

-a -c - o~ ,

e aZ

-ac = aZ

, , a t Z = L

, ~

where F

= f l u x of t r a c e r a t t o p of column.

The c o n c e n t r a t i o n of t r a c e r a t t h e end of t h e t r a c e r i n j e c t i o n p e r i o d i s given by t h e following r e l a t i o n :

c = - FoL [ $ + Det D

where

’

3 ( -~ z

) -~

6~~

22 7T

cos n=l

exp

2 2 ’

D n r t eL2

= l e n g t h of i n j e c t i o n p e r i o d .

The c o n c e n t r a t i o n of t r a c e r i n t h e column d u r i n g t h e p e r i o d following t r a c e r i n j e c t i o n i s given by s o l u t i o n of Eq. ( 1 7 ) w i t h t h e boundary c o n d i t i o n s rep-

r e s e n t e d by Eq. (18) and t h e i n i t i a l c o n d i t i o n r e p r e s e n t e d by Eq. ( 2 2 ) .

38 The r e l a t i v e t r a c e r c o n c e n t r a t i o n i n t h e column a t t i m e t and p o s i t i o n Z i s given by t h e following r e l a t i o n :

where

= -FOt -

t r a c e r c o n c e n t r a t i o n i n column a f t e r a uniform concentrat i o n i s reached,

6’ =

D n2tf e 3

L“

For t h e column l e n g t h used i n t h i s work and t h e range of d i s p e r s i o n coeff i c i e n t s observed, an i n j e c t i o n time of 2 sec ( t ’ )would r e s u l t i n a n e r r o r i n t h e measured a x i a l d i s p e r s i o n c o e f f i c i e n t of l e s s t h a n 5%. The a c t u a l i n j e c t i o n t i m e was always l e s s t h a n 2 sec and u s u a l l y l e s s t h a n 1 s e c .

5.3

Equipment

The equipment used i n t h e s t u d y (shown s c h e m a t i c a l l y i n F i g .

14) con-

s i s t e d of a n open bubble column, a means f o r i n j e c t i n g K C 1 t r a c e r s o l u t i o n a t t h e t o p o f t h e column, a c o n d u c t i v i t y probe l o c a t e d a t an i n t e r m e d i a t e

a x i a l p o i n t along t h e column f o r determining t h e K C l c o n c e n t r a t i o n i n t h e aqueous s o l u t i o n a t t h a t p o i n t , an e l e c t r o n i c s system and a r e c o r d e r for r e c o r d i n g t h e o u t p u t from t h e c o n d u c t i v i t y probe, an a i r supply and meteri n g system t h a t allowed a i r t o be f e d a t a known flow r a t e t o a g a s d i s p e r s e r l o c a t e d i n t h e b a s e of t h e column, and a manometer f o r o b t a i n i n g d a t a on g a s holdup i n t h e column.

These p a r t s of t h e system a r e d i s c u s s e d

i n d e t a i l i n t h e remainder of t h i s s e c t i o n .

5.3.1

Column The open bubble columns used i n t h i s s t u d y c o n s i s t e d of L u c i t e t u b e s ,

8 f t long and 1 . 5 , 2 , and 3 i n . i n i n s i d e diameter, t h a t were mounted i n a

O R N L D W G 71-13966

KCI

W E T TEST METER .__

BUBBLECOLUMN

MANOMETER

0 0 0 0

0 c

0 0 0 0 0 0

CONDUCTIVITY PROBE

1 RECORDER I

V ROTAMETER A I R SUPPLY Fig. 14. Schematic Flow Diagram of Equipment Used f o r Study of Axial Dispersion in an Open Bubble Column by a Transient Technique.

v e r t i c a l position.

P r o v i s i o n w a s made f o r i n s t a l l i n g a c o n d u c t i v i t y probe

a t a p o i n t 70.5 cm from t h e bottom of t h e column.

P r o v i s i o n was a l s o made

f o r a t t a c h i n g a manometer f o r o b t a i n i n g g a s holdup d a t a a t any of 20 p o i n t s l o c a t e d 3.5 i n . a p a r t along t h e axis of a column.

A gas d i s p e r s e r w a s

l o c a t e d i n t h e bottom of t h e column. 5.3.2

Gas D i s p e r s e r

The gas d i s p e r s e r c o n s i s t e d of a O.Oh-in.-ID t h e column. as l a r g e as

opening i n t h e bottom of

P r o v i s i o n was made for u s e of g a s d i s p e r s e r s having a diameter

1/4 in.

However, i n t h e p r e s e n t s t u d y , only one d i s p e r s e r s i z e

was used. 5.3.3

A i r Supply and Metering System

Compressed a i r ( 9 0 p s i g ) from t h e b u i l d i n g supply was passed through a demister t r a p and was reduced i n p r e s s u r e t o

15 p i g .

The a i r w a s t h e n

metered through e i t h e r of two r o t a m e t e r s having m a x i m u m flow c a p a c i t i e s

of 0.216 l i t e r / m i n and 0.840 l i t e r / m i n and subsequently passed i n t o t h e

gas d i s p e r s e r i n t h e bubble column.

The r a t e a t which a i r flowed through

t h e column w a s monitored w i t h a wet-test meter as t h e a i r e x i t e d from t h e column 5.3.4

. K C l Tracer S o l u t i o n I n j e c t i o n System

A 5-ml

s y r i n g e w a s connected t o a sparger through which a known quan-

t i t y of c o n c e n t r a t e d K C 1 t r a c e r s o l u t i o n could be i n j e c t e d . r e q u i r e d for i n j e c t i n g t h e t r a c e r w a s l e s s t h a n 2 s e c .

The t o t a l t i m e

The t r a c e r s o l u t i o n

was d i s t r i b u t e d throughout t h e column by u s e of f o u r s e c t i o n s o f 1/16-in.diam t u b i n g . 5.3.5

Conductivity Probe The c o n d u c t i v i t y probes were prepared by u s e of l/h-in.-diam

as shown i n F i g . 15. A O.Ogb-in.-diam

bolts,

h o l e was d r i l l e d along t h e axis of

O R N L D W G 71-13967RI

RUBBER

EPOXY RESIN\

. WIRES SILVER' S O L D E R E D TO Pt E L E C T R O D E S Fig. 1 5 .

kY ""ITE - ILUb

CO LUMN WALL

Method for Installing Conductivity Probe in Column.

42 t h e b o l t , and two i n s u l a t e d wires were s i l v e r - s o l d e r e d t o s e p a r a t e square platinum e l e c t r o d e s t h a t measured about 0.5 cm on a s i d e .

The e l e c t r o d e s

were p o s i t i o n e d 1 t o 2 mm a p a r t and were a t t a c h e d t o t h e head of t h e b o l t by u s e of epoxy r e s i n .

The h o l e i n t h e b o l t through which t h e wires ex-

tended was a l s o s e a l e d w i t h epoxy, and a l l s u r f a c e s o t h e r t h a n t h o s e of t h e platinum e l e c t r o d e s were coated w i t h epoxy.

The s e p a r a t i o n d i s t a n c e

between t h e e l e c t r o d e s was a d j u s t e d i n o r d e r t h a t water would be h e l d between t h e e l e c t r o d e s by s u r f a c e t e n s i o n .

The s u r f a c e s of t h e e l e c t r o d e s

were p l a t i n i z e d t o reduce p o l a r i z a t i o n by i n s e r t i n g t h e probe i n a platinum c h l o r i d e s o l u t i o n and imposing a dc potential. of about 3 V a c r o s s t h e probe f o r a p e r i o d of about 1 min. versed f o r 1 min.

The d i r e c t i o n of c u r r e n t flow w a s t h e n re-

The output from t h e c o n d u c t i v i t y probe and e l e c t r o n i c s

system was shown t o be l i n e a r l y dependent on t h e c o n c e n t r a t i o n of K C 1 i n a n aqueous s o l u t i o n i n which t h e probe w a s placed (see F i g . 1 6 ) .

When t h e

probe i s used i n a column, r e l a t i v e l y l a r g e f l u c t u a t i o n s i n o u t p u t s i g n a l a r e observed d u r i n g t h e f i r s t p a r t of an experiment.

I n i t i a l l y , these

f l u c t u a t i o n s were b e l i e v e d t o be t h e r e s u l t of a i r p a s s i n g between t h e electrodes.

L a t e r , it was observed t h a t t h e y become minimal a f t e r t h e

K C 1 t r a c e r has been d i s p e r s e d uniformly throughout t h e column. Apparently,

t h e n , t h e f l u c t u a t i o n s a r e produced by v e l o c i t y g r a d i e n t s i n t h e column i n t h e presence of a s i g n i f i c a n t K C 1 c o n c e n t r a t i o n g r a d i e n t . A probe w a s i n s t a l l e d ( s e e F i g .

15) s o t h a t t h e

head of t h e b o l t w a s

l o c a t e d i n s i d e t h e column; t h e threaded s e c t i o n of t h e b o l t extended through a rubber g a s k e t and a h o l e i n t h e column.

A nut w a s t i g h t e n e d on t h e b o l t

from o u t s i d e t h e column t o compress t h e g a s k e t and t h e r e b y s e c u r e t h e probe and s e a l t h e h o l e through which t h e b o l t w a s passed. 5.3.6

E l e c t r o n i c s System and Recorder The c o n d u c t i v i t y probe was connected t o a Leeds and Northrup Model

4988 c o n d u c t i v i t y monitor, which imposed a 60-HZ s i g n a l a c r o s s t h e e l e c t r o d e s of t h e probe and produced a n o u t p u t v o l t a g e p r o p o r t i o n a l t o t h e c u r r e n t p a s s i n g through t h e probe.

It was not p o s s i b l e t o v a r y t h e f r e -

quency of t h e s i g n a l impressed a c r o s s t h e probe; however, t h e r e was no

O R N L D W G 71-13969

I m m GAP SPACE

K C I CONCENTRATION ( m e q / I i t e r ) Fig. 16. Variation of Output from Conductivity Probe and Electronics System with Concentration of K C 1 in an Aqueous Solution. c

evidence of p o l a r i z a t i o n .

The s i g n a l from t h e c o n d u c t i v i t y monitor passed

through a high-impedance a m p l i f i e r , having a g a i n of u n i t y , i n o r d e r not t o overload t h e c o n d u c t i v i t y monitor.

The output s i g n a l from t h e am-

p l i f i e r was damped s l i g h t l y t o reduce t h e e f f e c t of high-frequency f l u c tuations.

S e v e r a l d u p i n g p e r i o d s i n t h e range 0.1 t o 0 . 5 sec were t e s t e d ;

3 be d e t e c t e d . no e f f e c t on t h e q u a n t i t y t o e 7- t o Ocould of 0.5 sec was used i n succeeding r u n s .

A damping p e r i o d

The output from t h e e l e c t r o n i c s

system was recorded on a Hewlett-Packard Model 7lOOB r e c o r d e r having a c h a r t speed of 0 . 1 i n . / s e c , or 2 in./min,

5.3.7

and a c h a r t width of 1 2 i n .

Manometer f o r Gas Holdup Measurements The r e l a t i v e p r e s s u r e and t h e r e l a t i v e h e i g h t of t h e a i r - w a t e r m i x t u r e

were measured a t s e v e r a l p o i n t s along t h e a x i s of t h e column i n o r d e r t o determine t h e average gas holdup i n t h e p o r t i o n of t h e column above t h e measuring p o i n t .

g l a s s t u b i n g w a s used

A manometer made from 0.25-in.-diam

for t h e pressuredeterminations.

The lower end of t h e manometer w a s con-

nected t o a p o i n t on t h e column, and t h e upper end was connected t o a p o i n t on t h e column off-gas l i n e near t h e t o p of t h e column.

The v a r i a t i o n of

gas holdup w i t h a x i a l p o s i t i o n along t h e column c o u l d be determined by obt a i n i n g r e a d i n g s a t s e v e r a l p o s i t i o n s along t h e column.

5.4

Experimental Procedure

P r i o r t o a r u n , t h e column w a s f i l l e d w i t h d i s t i l l e d water t o a l e v e l t h a t would produce an a i r - w a t e r mixture h e i g h t of approximately 230 cm a t t h e gas flow r a t e t o be used i n t h e subsequent r u n .

The gas holdup i n each

column had p r e v i o u s l y been determined as a f u n c t i o n of g a s f l o w r a t e .

The

a i r flow r a t e was t h e n s e t a t t h e approximate value by use of a r o t a m e t e r , and a i r e x i t i n g from t h e column w a s r o u t e d through a wet-test meter t o acc u r a t e l y measure t h e a i r f l o w r a t e .

The a i r was allowed t o flow through

t h e meter f o r a s u f f i c i e n t l e n g t h of time t o o b t a i n an a c c u r a t e measurement; a t low gas f l o w r a t e s , t h i s p e r i o d w a s c o n s i d e r a b l y l o n g e r t h a n t h e time r e q u i r e d f o r a d i s p e r s i o n c o e f f i c i e n t measurement. The t r a c e r i n j e c t i o n s y r i n g e w a s t h e n f i l l e d w i t h t h e d e s i r e d volume of t r a c e r s o l u t i o n , and t h e c o n d u c t i v i t y monitor and r e c o r d e r were t u r n e d on.

The t r a c e r w a s i n j e c t e d as quickly as p o s s i b l e , and t h e i n j e c t i o n

45 t i m e was marked on t h e r e c o r d e r c h a r t .

A s t h e t r a c e r was d i s p e r s e d

throughout t h e column, t h e r e c o r d e r i n d i c a t e d t h e i n c r e a s e i n c o n d u c t i v i t y of t h e s o l u t i o n a t t h e probe p o s i t i o n .

The r u n w a s continued u n t i l no

f u r t h e r i n c r e a s e i n r e c o r d e r o u t p u t w a s observed, and t h e times r e q u i r e d f o r t h e r e c o r d e r r e a d i n g t o i n c r e a s e t o 30% and 70% of i t s t o t a l d e f l e c t i o n d u r i n g t h e run were determined and recorded.

The s e n s i t i v i t y of t h e re-

corder and t h e volume of t r a c e r i n j e c t e d were s e l e c t e d s o t h a t t h e t o t a l r e c o r d e r d e f l e c t i o n observed d u r i n g a r u n was 70 t o 90% of t h e c h a r t width. During t h e r u n , t h e h e i g h t of t h e air-water mixture i n t h e column was determined t o w i t h i n 1 cm.

A more a c c u r a t e d e t e r m i n a t i o n would have been

d i f f i c u l t because of v a r i a t i o n i n t h e p o s i t i o n of t h e air-water mixture a t t h e t o p of t h e column.

5.5

Results

Twenty-nine r u n s were made i n o r d e r t o measure a x i a l d i s p e r s i o n coeff i c i e n t v a l u e s i n open bubble columns having diameters of 1 . 5 , 2 , and 3 i n . These d a t a are summarized i n Tables 2-4. F i f t y n i n e r u n s were made t o

determine g a s holdup i n t h e same columns.

I n each r u n , v a l u e s f o r t h e pres-

sure a t a p a r t i c u l a r l o c a t i o n and t h e h e i g h t of t h e air-water mixture above

t h i s l o c a t i o n were determined a t t h r e e t o seven p o i n t s along t h e column a x i s . The r e s u l t i n g d a t a were f i t by t h e method of l e a s t squares t o a s t r a i g h t l i n e on a p l o t of p r e s s u r e v s d i s t a n c e down t h e column.

The r e s u l t i n g data showed

t h a t gas holdup does not depend on a x i a l p o s i t i o n along t h e column, s i n c e t h e s t a n d a r d d e v i a t i o n v a l u e s were l e s s t h a n 2.5% of t h e holdup v a l u e s i n most c a s e s .

For t h i s r e a s o n , experimentally determined v a l u e s f o r t h e pres-

s u r e and h e i g h t of t h e air-water mixture a t t h e v a r i o u s p o i n t s along t h e

column a x i s a r e not given.

Values f o r t h e gas holdup (and t h e a s s o c i a t e d

s t a n d a r d d e v i a t i o n ) f o r each of t h e runs a r e summarized i n Tables 5-7.

5.6

Discussion of Data on Axial Dispersion

The v a r i a t i o n of t h e a x i a l d i s p e r s i o n c o e f f i c i e n t with g a s s u p e r f i c i a l v e l o c i t y i s shown i n Fig.

17 f o r columns having diameters of 1.5, 2 , and 3 in..

Table 2.

Summary of Data on Axial D i s p e r s i o n i n a 1.5-in.-ID $2 cm3

Tracer i n j e c t i o n volume:

Run NO.

Gas Flow Rate" (cm3/sec )

7el9

Superficial Gas Velocity (cm/sec )

Relative Probe Positionb

Open Bubble Column

0.3

t 0.7

(sec)

Dispersion Coefficient (cm2/sec)

0.631

0.697

181.8

411.0

18.3

89.8

7.88

0.700

51.0

108.6

74.2

35.4

3.11

0.701

87.6

196.2

39.4

288.9

25.3

0.700

18.5

39.5

194

236

20.7

0.691

23.5

49.5

154

152.1

13.3

0.696

31.8

73.2

100.3

128.1

11.2 0.683 ?Measured under c o n d i t i o n s a t t o p of' column.

34.2

75.6

97.6

-h

u R a t i o o f d i s t a n c e of probe from s u r f a c e of gas-water m i x t u r e t o t o t a l h e i g h t of gaswater m i x t u r e .

47 Table 3.

Summary of Data on Axial Dispersion i n a 2-in.-ID Tracer i n j e c t i o n volume:

-~ ~- - -

Run NO.

2 cm3

Gas Flow R a t ea (cm3/sec)

Superficial Gas Velocity (cm/sec )

Relative Probe Positionb

t0.3 (sec )

t 0.7 (sec )

Dispersion Coefficient (cm2/sec )

206

10.2

0.TOO

30.6

69.0

113.2

304

15 .O

0.687

27.6

54.0

148

375

18.5

0.683

17.4

37.5

139

473

23.3

0.680

16.7

38.0

176

425

21.0

0 0679

15.7

34.8

145

495

24.4

0.680

13.8

27.1

282

515

25.4

0.680

16.0

35.7

192

764

37 -7

0.705

11.7

23.0

265

604

29.8

0.674

12.3

26.3

258

7.79

0.384

0.682

102

326

21.4

57.3

2.83

0.690

71.1

158.1

46.0

32.3

1.59

0.703

100.8

219.6

33.1

0.380

0.794

103 5

234 9

31.0

Open Bubble Column

7071

a Measured under c o n d i t i o n s a t t o p of column.

bRatio of d i s t a n c e of probe from s u r f a c e of gas-water mixture t o t o t a l h e i g h t of gas-water mixture.

Table 4 .

Summary o f Data on Axial D i s p e r s i o n i n a 3-in.-ID Tracer i n j e c t i o n volume:

Run NO.

Gas Flow Rat ea (crn3ysec

Superficial Gas Velocity (cm/sec )

Relative Probe Positionâ&#x20AC;&#x2122;

Open Bubble Column

2 crn3

(sec )

(sec

Dispersion Coefficient (crn2/sec )

0.3

0.7

488. o

10.7

o .701

27.0

61.8

123.6

832.8

18.3

0.696

19.6

45 .O

164

882.1

19.3

0.692

18.0

37.6

207.1

168.6

3.70

0.700

45.0

99.0

74.0

334.0

7.32

0.709

39.0

87.0

94.2

31.9

0.700

0.684

67.2

218.0

4.78

o .700

44.1

99.0

78.9

153

43.0

528 3

11.6

0.692

25 99

56.5

131.8

505.6

11.1

0.695

25.5

60.0

119.4

a Measured under c o n d i t i o n s a t t o p of column.

R a t i o of d i s t a n c e of probe from s u r f a c e of gas-water mixture t o t o t a l h e i g h t of gas-water m i x t u r e .

49 Table 5.

Summary of Data on Gas Holdup in a 1.5-in.-ID Open Bubble Column

Run No.

Superficial Gas Velocity" (cm/sec)

Number of Points

Gas Holdup

Standard Deviation

Relative Deviation

5.26

0.140

0.00387

2.76

9.74

0.228

0 00537

2.36

(%I

15.2

0.320

0.00838

2.62

21.6

0 397

0.00852

2.15

26.4

0.460

0.00892

1.94

31.1

0.469

0.01017

2.17

3.03

0.0905

0.00291

3.22

4.28

0.119

0.00247

2.08

7.65

0.191

0.00406

2.13

12.5

0.278

0.00743

2.67

24.8

0 433

0.01269

2.93

18.4

0 371

0.01146

3-09

32.6

0.485

0.01500

3.09

27.2

0.445

0.01265

2.84

28.4

0.467

0.01326

2.84

. a Measured under conditions at top of column.

Table

6. Summary

of Data on Gas Holdup i n a 2-in.-ID Open Bubble Column

~~~

Run No.

Superficial Gas Velocity" (cm/sec )

Number o f Points

0.260

1.90

Holdup

Standard Deviation

Relative Deviation (%>

0.0094

0.000446

0.47

0.0638

0.00268

4.20

3.88

0.109

0.00124

1.14

7.80

0.191

0.00336

1.76

Gas

13.4

0 *277

0.00592

2.14

16.3

0.320

0.00857

2.68

19.5

0 356

0.00873

2.45

26.9

0.412

0.00996

2.42

14.3

0.294

0.00717

2.44

9.13

0.197

0.00450

2.28

9.32

0.197

0.00239

1.21

0.341

0.00851

2.50

~~~

20.7

6.02

0.151

0.00261

1.73

6.37

0.152

0.00222

1.46

5.92

0.145

0.00144

0.99

Measured under c o n d i t i o n s at top o f column.

T a b l e 7. Summary of Data on Gas Holdup i n a 3-in.-ID Open Bubble Column Superficial

Run

Gas V e l o c i t y

No.

(cm/sec j

Number of Points

Gas Holdup

Standard Deviation

Relative Deviation (%)

12.6

0.249

0.00312

1.25

11.9

0.230

0.00455

1.98

11.0

0.217

0.00482

2.22

10.2

0.204

0.00360

1.76

9.32

0.189

0.00345

1 .a3

8.40

0.177

0.00290

1.64

7.61

0.165

0.00288

1.75

5.94

0.137

0.00259

1.89

9.03

0.154

0.00259

1.68

1-75

0.0481

0.00101

2.10

0.234

0.00299

1.28

13.1

41 42

7.57

0.146

0.000562

0.38

8.93

0.182

0.00108

0.59

0.209

0.00207

0.99

11.0

5.71

0.134

0.00203

1.51

5.08

0.134

0.00133

0 -99

3.55

0.102

0.00125

1.23

2.65

0.0813

0.00161

1.98

1.86

0.0598

0.000613

1.03

0.988

0.0360

0.00112

3.11

14.0

0.237

0.00509

2.15

24 .O

0.319

0.00508

1.59

15.2

0.248

0.00485

1.96

20.2

0.268

0.00476

1.78

0.152

0.00266

1.75

7.50

24.8

0.320

0.00662

2.07

33.0

0.378

0.00884

2.34

29.6

0.342

0.00554

1.62

21.6

0.291

0.00457

1.57

"Measured under c o n d i t i o n s a t t o p of column.

53 The l i n e shown f o r a column diameter of 2 i n . i s t h e same as t h a t rep o r t e d e a r l i e r , based on d a t a obtained by u s e of t h e s t e a d y - s t a t e technique.

I n t h e p r e s e n t s t u d y , however, d a t a have been obtained a t h i g h e r

gas flow r a t e s t h a n were p r e v i o u s l y used; t h e s e d a t a show minimal s c a t t e r , and t h u s t h e curves f o r t h e v a r i o u s column diameters are more c l e a r l y defined.

On t h e b a s i s of t h e s e d a t a , t h e t r a n s i e n t technique appears t o

be f a r s u p e r i o r t o t h e e a r l i e r s t e a d y - s t a t e technique i n t h a t (1)l e s s s c a t t e r i s observed i n t h e d i s p e r s i o n c o e f f i c i e n t d a t a , and ( 2 ) d a t a can be o b t a i n e d much more r a p i d l y w i t h t h e t r a n s i e n t technique.

A typical

r u n u s i n g t h e t r a n s i e n t technique r e q u i r e s l e s s t h a n 1 0 min, whereas more t h a n 2 hr i s r e q u i r e d f o r a r u n u s i n g t h e s t e a d y - s t a t e technique. The d a t a on a x i a l d i s p e r s i o n obtained w i t h t h e l.5-ine-diam a r e q u i t e similar t o t h o s e r e p o r t e d e a r l i e r .

column

However, t h e h i g h q u a l i t y

of t h e p r e s e n t d a t a shows t h a t , a t high gas flow r a t e s , t h e d i s p e r s i o n c o e f f i c i e n t v a l u e s obtained w i t h t h e 1.5-in. t h a n v a l u e s obtained w i t h a 2-in.-diam gas ve l oc i t y.

column a r e s l i g h t l y lower

column a t t h e same s u p e r f i c i a l

When t h e gas flow r a t e i s i n c r e a s e d s u f f i c i e n t l y t o produce

a slugging c o n d i t i o n , t h e d i s p e r s i o n c o e f f i c i e n t d a t a f o r t h e two column

diameters r e s u l t i n p a r a l l e l l i n e s t h a t are s e p a r a t e d by about 15%. A t lower gas flow r a t e s where bubbly flow o c c u r s , t h e curves f o r t h e two column diameters have widely d i f f e r e n t s l o p e s (as had been r e p o r t e d earlier).

The s l o p e of t h e curve f o r t h e 1.5-in.-diam

column appears

t o change only s l i g h t l y i n moving from bubbly t o s l u g flow, Thus f a r , t h e p r i n c i p a l advantage of u s i n g t h e t r a n s i e n t technique h a s been improved a x i a l d i s p t r s i o n c o e f f i c i e n t d a t a for t h e 3-in.-diam column.

Although t h e s c a t t e r i n t h e p r e s e n t data i n c r e a s e s as t h e column

diameter i s i n c r e a s e d , t h e d a t a f o r t h e 3 - i n . - d i m

column appear t o ad-

e q u a t e l y d e f i n e t h e dependence of a x i a l d i s p e r s i o n c o e f f i c i e n t on superf i c i a l gas v e l o c i t y .

There appear t o be t h r e e d i s t i n c t r e g i o n s of opera-

t i o n , and t h e d a t a from each r e g i o n can be f i t by a s t r a i g h t l i n e as ind i c a t e d i n F i g . 17.

I n t h e f i r s t r e g i o n , bubbly flow i s observed f o r

s u p e r f i c i a l gas v e l o c i t i e s up t o about 3 cm/sec.

The second mode of

o p e r a t i o n c o n s i s t s of a t r a n s i t i o n r e g i o n covering s u p e r f i c i a l gas veloc-

i t i e s from about 3 t o about 25 cm/sec.

The t h i r d mode of o p e r a t i o n con-

s i s t s of s l u g flow, which occurs a t s u p e r f i c i a l gas v e l o c i t i e s g r e a t e r

t h a n 25 cm/sec.

The a x i a l d i s p e r s i o n c o e f f i c i e n t v a l u e s measured w i t h columns i n t h e s l u g flow r e g i o n show l i t t l e d i f -

t h e 2- and 3-in.-diam ference.

5.7

Discussion of Data on Gas Holdup

The v a r i a t i o n of gas holdup w i t h s u p e r f i c i a l gas v e l o c i t y aiid column

diameter i s shown i n F i g . 18. A t low g a s flow r a t e s ( i n which bubbly flow o c c u r s ) , gas holdup i s p r o p o r t i o n a l t o t h e s u p e r f i c i a l g a s v e l o c i t y and i s independent of t h e column d i a m e t e r .

A t h i g h e r gas flow r a t e s , g a s hold-

up d a t a from t h e d i f f e r e n t column diameters begin t o d i v e r g e and holdup i n c r e a s e s , b u t i n a more g r a d u a l manner, as t h e g a s s u p e r f i c i a l v e l o c i t y i n c r e a s e s ; f o r a g i v e n gas s u p e r f i c i a l v e l o c i t y , holdup i n c r e a s e s a s t h e column diameter i s decreased. Davies and Taylor''

r e p o r t t h a t t h e r a t e of r i s e of a s i n g l e g a s "slug"

i n a column f i l l e d with s t a t i o n a r y l i q u i d i s g i v e n by t h e r e l a t i o n :

where

V1 = r a t e of r i s e of gas s l u g , g = gravitational acceleration, d = column d i a m e t e r .

I n an open bubble column o p e r a t i n g a t s t e a d y s t a t e , a number o f gas s l u g s w i l l b e e s s e n t i a l l y evenly spaced throughout t h e column.

In t h i s case, t h e

r e l a t i v e v e l o c i t y of t h e l i q u i d between t h e g a s s l u g s w i l . 1 be e q u a l t o t h e s u p e r f i c i a l gas velocity.

If t h e s l u g v e l o c i t y as d e f i n e d by Davies and

Taylor i s assumed t o b e t h e r e l a t i v e v e l o c i t y between l i q u i d and gas i n an open bubble column, t h e gas holdup would be given by t h e r e l a t i o n :

s 0

r! 0

dn010H SV9

c.- c.-

c u . .

$=A

v +v

â&#x201A;Ź 5 1

where Cp = gas holdup,

= s u p e r f i c i a l gas v e l o c i t y .

A p l o t of t h e gas holdup d a t a i n t h e form suggested by Eq. ( 2 5 ) i s shown

i n Fie;. 19. It should be noted t h a t t h e holdup d a t a from t h e l . 5 - , and 3-in.-diam

2-,

columns a r e brought t o g e t h e r on a s i n g l e l i n e which p a s s e s

through t h e o r i g i n .

However, t h e slope of t h e l i n e i s approximately 0.78,

r a t h e r t h a n t h e expected v a l u e o f

loo.

Thus, while Eq. ( 2 5 ) does not

produce an exact f i t of t h e gas holdup d a t a , it appears t o be u s e f u l i n suggesting a form for c o r r e l a t i n g t h e d a t a .

B e c a u s e t h e slope of t h e

r e s u l t i n g l i n e i s not u n i t y , t h e t h e o r e t i c a l b a s i s for t h e c o r r e l a t i o n s t i l l must be e s t a b l i s h e d .

5.8

Conclusions

An improved experimental method f o r measuring a x i a l d i s p e r s i o n coeff i c i e n t s i n open bubble columns has been developed.

T h i s method, an un-

s t e a d y - s t a t e technique, has been shown t o be more a c c u r a t e and t o be app l i c a b l e over a wider range of s u p e r f i c i a l gas v e l o c i t i e s t h a n t h e steadys t a t e t e c h n i q u e employed p r e v i o u s l y .

I n a d d i t i o n , u s e of t h e t r a n s i e n t

t e c h n i q u e allows completion of an experiment i n l e s s t h a n 10% of t h e time r e q u i r e d f o r t h e s t e a d y - s t a t e technique.

Axial d i s p e r s i o n c o e f f i c i e n t

d a t a o b t a i n e d i n columns having diameters of 1 . 5 , 2 , and 3 i n . a r e i n agreement w i t h p r e v i o u s l y obtained d a t a .

A t h e o r e t i c a l b a s i s for cor-

r e l a t i n g t h e s e d a t a , as w e l l as t h o s e on gas holdup i n bubble columns, must be developed b e f o r e such r e s u l t s can be used t o p r e d i c t gas holdup and t h e e f f e c t of a x i a l d i s p e r s i o n i n continuous f l u o r i n a t o r s .

- 3 in. D i a m . COLUMN

A - 2 i n . Diam. COLUMN 0 -1.5 in. Diam. C O L U M N

.I2

,116

,210 .24

,218

d .d

.d2 . 6 0 .4 4 :. 8 V,/(V, + 0.35 -1

.5Z

Fig. 19. V a r i a t i o n of Gas Holdup i n 1.5-, 2-, Bubble Columns w i t h t h e Quantity Vg/ (Vg + 0.35

.56

.614

and 3-in.-diam

.$8

.7;

Open

.7 6

58 The unsteady-state technique for measuring axial dispersion coefficients does not require water to be fed through the open bubble column, and it may prove especially useful in studying effects on axial dispersion resulting from changes in the physical properties of the continuous (water) phase.

Since at least one measurement (and possibly several measurements)

of the axial dispersion coefficient can be made with one column volume of the liquid phase, it should be possible to work with materials that would have been considered too expensive with the steady-state technique.

6. DEVELOPMENT OF THE METAL TRANSFER PROCESS E. L. Youngblood

L. E. McNeese

It has been found that rare earths distribute selectively into molten lithium chloride from bismuth solutions containing r a r e earths and thorium, and an improved rare-earth removal process based on this observation has been devised.

We are currently engaged in a demonstration of all phases

of the improved rare-earth removal method, which is known as the metal 11 transfer process. In a previous engineering experiment (MTE-i), we studied the removal of rare earths from single-fluid MSBR fuel salt During this experiment, approximately 50% of the

by this process.

lanthanum and 25% of the neodymium originally present in the fluoride salt were removed at approximately the predicted rate. However, the lanthanum and neodymium that were removed from the fluoride salt did not accumulate in the lithium-bismuth solution used for removing these materials from lithium chloride as expected. Reaction of impurities in the system with the rare earths is believed to have caused this unexpected behavior under way.

A second engineering experiment (MTE-2) is currently

The main objectives of this experiment are:

(1)to demonstrate

the selective removal of rare earths from fluoride salt containing thorium fluoride, (2) to collect the rare earths in a Li-Bi solution, and (3) to verify previous distribution coefficient data.

6 . 1 Equipment f o r Experiment MTE-2 Experiment MTE-2 i s b e i n g c a r r i e d o u t i n a v e s s e l made of 6-in.-diam carbon-steel p i p e ( s e e F i g . 2 0 ) .

The v e s s e l i s d i v i d e d i n t o two compart-

ments by a p a r t i t i o n t h a t extends t o w i t h i n 1 / 2 i n . of t h e bottom of t h e vessel.

The compartments a r e i n t e r c o n n e c t e d by a 2-in.-deep

pool of

thorium-saturated molten bismuth, which forms a s e a l between t h e two comOne compartment c o n t a i n s MSBR f u e l c a r r i e r s a l t (72-16-12 mole

partments.

% LiF-BeF2-ThF4) t o which t r a c e r q u a n t i t i e s of l47Hd and s u f f i c i e n t LaF t o produce a lanthanum c o n c e n t r a t i o n of" 0.3 mole

were added.

The o t h e r

compartment c o n t a i n s LfCl, L i - B i s o l u t i o n ( i n a c u p ) , and a pump f o r c i r c u l a t i n g t h e L i C l through t h e cup a t a flow r a t e of about 25 cm3/min. c o n c e n t r a t i o n of r e d u c t a n t (35 a t ,

The

% L i ) i n t h e L i - B i s o l u t i o n i s suf-

f i c i e n t l y high t o permit e s s e n t i a l l y a l l of t h e lanthanum and neodymium t o be e x t r a c t e d from L i C l i n e q u i l i b r i u m w i t h t h e L i - B i s o l u t i o n . I n o r d e r t o o b t a i n mixing i n t h e main bismuth p o o l , about 10% of t h e

metal volume i s forced t o flow back and f o r t h every 7 min through t h e 1/2i n . s l o t l o c a t e d below t h e p a r t i t i o n between t h e f l u o r i d e and c h l o r i d e compartments.

This flow i s e f f e c t e d by reducing t h e p r e s s u r e of t h e argon

cover gas i n t h e f l u o r i d e compartment r e l a t i v e t o t h a t i n t h e c h l o r i d e compartment.

Gas-lift sparge t u b e s a r e used t o d i s p e r s e d r o p l e t s of b i s -

muth i n t h e s a l t phase t o improve c o n t a c t between t h e s a l t and bismuth phases i n each compartment.

Lumps of thorium metal ( a t o t a l of

149 g ) ,

measuring approximately 0.5 i n . on a s i d e , were placed i n t h e bottom of t h e v e s s e l i n o r d e r t o ensure t h a t t h e bismuth phase i s s a t u r a t e d w i t h thorium.

The amount of thorium added i n t h i s manner i s about f i v e t i m e s

t h e amount t h a t could d i s s o l v e i n t h e bismuth.

The lower s e c t i o n of t h e

v e s s e l i s heated t o t h e o p e r a t i n g temperature (650 t o 660Oc) by a n 8-kW furnace.

The f l a n g e and upper 6 i n . of t h e v e s s e l are wrapped w i t h

cooling c o i l s through which water flows i n o r d e r t o m a i n t a i n t h e f l a n g e

a t approximately 100째C.

This p r o v i s i o n p r e v e n t s damage t o t h e neoprene

gasket used f o r s e a l i n g t h e f l a n g e t o t h e v e s s e l .

The e x t e r i o r of t h e

v e s s e l was s p r a y coated w i t h 20 m i l s of n i c k e l aluminide t o p r o t e c t a g a i n s t a i r o x i d a t i o n of t h e carbon s t e e l .

. O R N L D W G 70-12503

LEVEL E L E C T R O D ~ ARGON INLET AND VENT

3 1

I -CARBON STEEL PUMP WITH MOLTEN B i CHECK VALVES

CARBON STEEL PART IT IO N

~ 6 - i CARBON n STEEL PIPE

2 4 in

7 2 - 16- I2 MOLE F l EL CARRIER SA1

Th-Bi

Fig. 20.

TLiCI

Carbon S t e e l Vessel Used f o r Metal T r a n s f e r Experiment MTE-2.

61 The pump used f o r c i r c u l a t i n g t h e L i C l through t h e cup c o n t a i n i n g t h e L i - B i s o l u t i o n i s constructed of carbon s t e e l and uses molten bismuth as check v a l v e s ( s e e Fig. 2 1 ) .

The q u a n t i t y of L i C l pumped during one

c y c l e of o p e r a t i o n i s c o n t r o l l e d by l e v e l e l e c t r o d e s ( i n t h e pump chamber) t h a t a c t u a t e a solenoid v a l v e i n a gas supply l i n e t o t h e pump chamber. A p r e s s u r e of about 18 i n . H20 i s maintained i n t h e L i C l compartment of

t h e main v e s s e l by t h e u s e of a mercury bubbler i n t h e v e s s e l off-gas. When t h e p r e s s u r e i n t h e pump chamber i s decreased t o near atmospheric p r e s s u r e , L i C l flows i n t o t h e pump chamber u n t i l t h e upper e l e c t r o d e i s contacted by s a l t .

A t t h i s p o i n t , t h e solenoid v a l v e opens and argon i s

admitted i n t o t h e pump chamber t o discharge t h e L i C 1 .

When t h e s a l t

l e v e l f a l l s below t h e lower e l e c t r o d e , t h e solenoid v a l v e i s closed and t h e pump chamber i s again vented.

The pumping r a t e i s determined by t h e

d i s t a n c e between t h e two e l e c t r o d e s and t h e frequency of t h e pumping c y c l e . An e l e c t r i c a l l y operated counter i s a t t a c h e d t o t h e solenoid valve i n order t o record t h e number of pumping c y c l e s t h a t have occurred. Provisions were made f o r o b t a i n i n g f i l t e r e d samples of t h e s a l t and bismuth phases i n t h e experiment.

The samplers, which a r e c o n s t r u c t e d of

s t a i n l e s s s t e e l , c o n s i s t of i/h-in.-OD, t h a t have a l e n g t h of 1/16-in.-OD

1-in.-long

s t a i n l e s s s t e e l capsules

c a p i l l a r y t u b i n g a t t a c h e d t o one end and

a porous m e t a l f i l t e r (mean pore s i z e , 20 p ) a t t a c h e d t o t h e o t h e r .

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

a h o l e i n a T e f l o n plug l o c a t e d i n a chamber above a b a l l v a l v e l e a d i n g i n t o t h e system.

The chamber i s purged w i t h argon b e f o r e t h e b a l l v a l v e

i s opened i n o r d e r t o prevent a i r f r o m e n t e r i n g t h e system.

The c a p i l l a r y

t u b e i s used t o push t h e sample t o t h e proper l o c a t i o n w i t h i n t h e v e s s e l . An argon purge i s maintained through t h e c a p i l l a r y t u b i n g t o prevent mat e r i a l from e n t e r i n g t h e sampler b e f o r e t h e sampler reaches t h e l e v e l a t which a sample i s t o b e taken.

When t h e sampler i s i n p o s i t i o n , a sample

i s o b t a i n e d by a p p l y i n g vacuum t o t h e c a p i l l a r y t u b i n g .

The sample i s

t h e n removed and prepared f o r a n a l y s i s by removing t h e f i l t e r and c a p i l l a r y t u b i n g and c l e a n i n g t h e o u t s i d e s u r f a c e of t h e sampler w i t h emery c l o t h . The sample i s analyzed for neodymium and radium by d i r e c t gamma counting; t h e lanthanum c o n c e n t r a t i o n i s determined by a neutron a c t i v a t i o n t e c h n i q u e a f t e r t h e sample has been d i s s o l v e d .

ORNL DWG 70-8981

ELECT R 0 DE S FOR LIQUID LEVEL MESUREMENT

I1/2" CARBON STEEL TUBING 28" LONG

DISCHARGE

1/4"CARBON STEEL

TUBING

MOLTEN BISMUTH

INTAKE

F i g . 21. Carbon S t e e l Pump Having Molten Bismuth Check Valves Used t o C i r c u l a t e L i C l i n Metal T r a n s f e r Experiment MTE-2.

63 6.2

M a t e r i a l s Used i n Experiment MTE-2

The q u a n t i t i e s of m a t e r i a l s used i n experiment MTE-2 a r e given i n

Table 8.

The L i C l was p u r i f i e d p r i o r t o u s e by c o n t a c t w i t h thorium-

s a t u r a t e d bismuth a t 6 5 0 " ~ . Both t h e c a r b o n - s t e e l v e s s e l and t h e bismuth were t r e a t e d w i t h hydrogen a t 6 5 0 " ~t o remove o x i d e s .

The f l u o r i d e s a l t

used i n t h e experiment was p u r i f i e d by t h e Reactor Chemistry D i v i s i o n . The argon used as cover g a s for t h e experiment was p u r i f i e d by passage through a bed of uranium t u r n i n g s h e l d a t 600Oc and a bed of molecular sieves

Table 8.

M a t e r i a l s Used i n Metal T r a n s f e r Experiment MTE-2 Quantity cm3 g-moles

Material Fluoride salt (LiF-BeFz-ThFb-LaF3, 72-15.7-12-0.3 mole 7 m C i 147NdF3)

Bismuth s a t u r a t e d w i t h thorium

LiCl (35 a t .

6.3

40.7

799

36.9

1042

36.6

164

9.5

Li-Bi

789

% lithium)

S t a t u s of Experiment MTE-2

To d a t e , experiment MTE-2 appears t o be o p e r a t i n g s a t i s f a c t o r i l y ; however, no d a t a a r e a v a i l a b l e a t t h i s t i m e .

SENICONTINUOUS REDUCTIVE EXTRACTION EXPERIMENTS I N A MILD-STEEL FACILITY

B. A . Hannaford C . W. Kee L. E. McNeese We have continued o p e r a t i o n of a f a c i l i t y i n which a system c o n s t r u c t e d of mild s t e e l can b e used t o c a r r y o u t semicontinuous r e d u c t i v e e x t r a c t i o n experiments .I2 I n i t i a l work w i t h t h e f a c i l i t y w a s d i r e c t e d toward o b t a i n i n g d a t a on t h e hydrodynamics o f c o u n t e r c u r r e n t flow o f molten s a l t and bismuth i n a n 0.82-in.-ID, Raschig r i n g s .

24-in.-long

column packed w i t h 1 / 4 - i n . molybdenum

We have been a b l e t o show t h a t f l o o d i n g d a t a o b t a i n e d w i t h

t h i s column a r e i n agreement w i t h p r e d i c t i o n s from a c o r r e l a t i o n based on s t u d i e s o f t h e c o u n t e r c u r r e n t flow of mercury and aqueous s o l u t i o n s i n packed columns .13 We have r e c e n t l y undertaken experiments f o r d e t e r m i n i n g t h e mass t r a n s f e r performance of t h e packed column.

I n t h e i n i t i a l experi-

ments, a s a l t stream c o n t a i n i n g UF4 was c o u n t e r c u r r e n t l y c o n t a c t e d , over a wide r a n g e of o p e r a t i n g c o n d i t i o n s , w i t h bismuth c o n t a i n i n g r e d u c t a n t .

The

f i r s t uranium mass t r a n s f e r experiment (UTR-1) was v e r y s u c c e s s f u l hydro-

dynamically and demonstrated t h a t simultaneous samples of t h e bismuth and

s a l t streams l e a v i n g t h e e x t r a c t i o n column can be t a k e n e a s i l y .

However,

t h e r u n f a i l e d t o p r o v i d e mass t r a n s f e r d a t a because of d i f f i c u l t i e s t h a t prevented t h e a d d i t i o n o f r e d u c t a n t t o t h e bismuth p r i o r to t h e experiment. 1 4

During t h e second uranium mass t r a n s f e r r u n (UTR-2), bismuth c o n t a i n i n g r e d u c t a n t w a s f e d t o t h e column a t t h e r a t e o f 247 cm3 /min, and s a l t (7216-12 mole

% LiF-BeF2-ThF4) c o n t a i n i n g

3000 ppm of uranium as UF4 was f e d

t o t h e column a t t h e r a t e of 52 cm3 /min.

The f l o w r a t e s of bismuth and

s a l t were b o t h s t e a d y o v e r a p e r i o d of about 40 min, and 95% of t h e uranium

was e x t r a c t e d from t h e s a l t .

The experiment r e p r e s e n t e d t h e f i r s t known

demonstration of t h e continuous e x t r a c t i o n of uranium from molten s a l t i n t o bismuth c o n t a i n i n g r e d u c t a n t and was encouraging i n t h a t it suggested t h a t h i g h uranium removal e f f i c i e n c i e s can be o b t a i n e d i n a packed column having

a reasonable length.

7 . 1 P r e p a r a t i o n f o r Mass T r a n s f e r Run UTR-3

Following r u n UTR-2, t h e s a l t and bismuth were r e t u r n e d t o t h e t r e a t ment v e s s e l and 122.5 g of thorium metal w a s added t o t h e g r a p h i t e c r u c i b l e P e r i o d i c a l l y , bismuth samples were t a k e n

through a 3/4-in.-diam

tube.

with graphite l a d l e s .

Analyses of t h e s e samples showed t h a t t h e thorium

c o n c e n t r a t i o n i n t h e bismuth i n c r e a s e d a t t h e r a t e of about 2 ppm/hr, which i s t h e same r a t e of i n c r e a s e observed following t h e e a r l i e r a d d i t i o n of thorium t o t h e bismuth f e e d t a n k p r i o r t o r u n UTR-2.

The thorium con-

c e n t r a t i o n i n t h e bismuth was only 800 ppm a f t e r 250 h r , which i s f a r below

i t s s o l u b i l i t y a t 660째c ( L e . , 3500 ppm)

The r a t e of d i s s o l u t i o n appeared

t o b e l i m i t e d by poor c o n t a c t of t h e bismuth w i t h t h e 0.5-in. thorium.

cubes of

I n o r d e r t o improve t h e e x t e n t of c o n t a c t between thorium and

bismuth, a second charge of thorium metal (119 g ) was loaded i n t o a 1-in.d i m , 6-in.-long phase.

p e r f o r a t e d s t e e l basket and w a s lowered i n t o t h e bismuth

After t h i s a d d i t i o n , t h e observed thorium d i s s o l u t i o n r a t e i n c r e a s e d

t o about t e n times t h e e a r l i e r r a t e (20 ppm/hr based on g r a p h i t e l a d l e samples, and 25 ppm/hr based on change i n weight of t h e a d d i t i o n b a s k e t ) . About 85% of t h e thorium d i s s o l v e d d u r i n g a 22-hr p e r i o d .

After approxi-

mately 24 a d d i t i o n a l hours, t h e thorium c o n c e n t r a t i o n i n a l a d l e d bismuth sample was 1665 ppm, which i s 95% of t h e v a l u e expected from complete dissolution. S u r p r i s i n g l y , bismuth samples t a k e n 50, 1 0 0 , and 350 h r a f t e r comp l e t i o n of t h e thorium a d d i t i o n showed a s h a r p decrease i n thorium conc e n t r a t i o n ( t o 1000 ppm), which w a s followed by a slow i n c r e a s e i n thorium c o n c e n t r a t i o n ( t o 1200 ppm).

I n o r d e r t o check f o r a c o n c e n t r a t i o n g r a d i e n t

w i t h i n t h e pool o f bismuth, samples were t a k e n w i t h a l a d l e a t a p o i n t about 1 i n . from t h e bottom of t h e v e s s e l and a t a p o i n t c l o s e t o t h e bismuth-

s a l t i n t e r f a c e (about 6 i n . from t h e bottom o f t h e v e s s e l ) .

Two p a i r s of

samples showed t h a t t h e thorium c o n c e n t r a t i o n was higher near t h e bottom of t h e v e s s e l (17% higher i n one c a s e and 88% i n t h e o t h e r ) . T h i s behavior can be explained as f o l l o w s .

After thorium had been added to t h e bismuth,

t h e composition of t h e bismuth phase changed slowly as t h e bismuth and s a l t

66 approached a s t a t e of chemical e q u i l i b r i u m .

During t h i s p e r i o d , p a r t

of t h e thorium was oxidized from t h e bismuth phase by r e a c t i o n w i t h LiF from t h e s a l t and w a s r e p l a c e d w i t h t h e same number of e q u i v a l e n t s of lithium.

I n t h e absence of mixing i n t h e bismuth phase, a s h a r p d e n s i t y

g r a d i e n t would have been produced i n which t h e least-dense m a t e r i a l would occur a t t h e t o p of t h e bismuth pool and t h e most-dense m a t e r i a l would occur a t t h e bottom of t h e bismuth pool.

It w a s concluded t h a t t h e mixing

w i t h i n t h e bismuth phase was inadequate t o m a i n t a i n a uniform composition. F i l t e r e d samples of t h e bismuth phase were u s u a l l y t a k e n , u s i n g t h e s t a i n l e s s s t e e l samplers, a t t h e same time t h a t samples were obtained w i t h a graphite ladle.

The thorium content of samples obtained i n t h e s t a i n l e s s

s t e e l samplers w a s c o n s i s t e n t l y lower t h a n t h a t of samples o b t a i n e d w i t h t h e g r a p h i t e samplers.

I n order t o check t h e p o s s i b i l i t y t h a t t h e method

f o r p r e p a r i n g t h e f i l t e r e d samples for a n a l y s i s might be a t f a u l t , two s t a i n l e s s s t e e l samplers were c u t i n t o two or t h r e e segments and analyzed separately.

The r e s u l t s showed t h a t t h e thorium c o n c e n t r a t i o n i n t h e b o t -

tom t h i r d of t h e sample capsule was much higher (about 1900 ppm) t h a n i n t h e upper t h i r d (about 300 ppm).

T h i s c l e a r l y confirmed our s u s p i c i o n

t h a t thorium w a s c o n c e n t r a t i n g i n t h e bottom of t h e sample c a p s u l e during

t h e slow f r e e z i n g of t h e sample.

Presumably, t h e observed c o n c e n t r a t i o n

of thorium r e s u l t e d from t h e f a c t t h a t t h e d e n s i t y of thorium bismuthide ( 1 1 . 4 g/cm 3 ) i s greater t h a n t h e d e n s i t y o f bismuth ( 9 . 6 6 g/cm3). Thus, t h e method f o r p r e p a r i n g samples t a k e n i n a s t a i n l e s s s t e e l sampler, which involved d i s c a r d i n g t h e bottom of t h e c a p s u l e ( c o n t a i n i n g t h e porous m e t a l f i l t e r and about

15% of t h e bismuth), r e s u l t e d i n s u b s t a n t i a l e r r o r s

i n t h e measured thorium c o n c e n t r a t i o n .

The sample p r e p a r a t i o n method w a s

r e v i s e d s o t h a t t h e o u t s i d e s u r f a c e of t h e porous m e t a l f r i t was mechanicall y cleaned; however, t h e f r i t w a s l e f t a t t a c h e d t o t h e c a p s u l e .

We have

continued t o r e l y p r i m a r i l y on samples obtained w i t h a g r a p h i t e l a d l e f o r a n a l y z i n g f o r thorium i n bismuth because t h e m e t a l sample can e a s i l y be removed from t h e l a d l e and i s not s u b j e c t t o d i f f i c u l t i e s p e c u l i a r t o t h e l e a c h i n g o p e r a t i o n r e q u i r e d for t h e f i l t e r e d samples,

7.2

Mass T r a n s f e r Run UTR-3

Immediately p r i o r t o r u n UTR-3, about 5 l i t e r s of s a l t was t r a n s f e r r e d from t h e treatment v e s s e l t o t h e s a l t f e e d t a n k .

On completion of t h i s

o p e r a t i o n , a t o t a l of 1 5 l i t e r s of s a l t , i n which t h e uranium c o n c e n t r a t i o n w a s about 2000 ppm, w a s p r e s e n t i n t h e f e e d t a n k .

About 1 5 l i t e r s of b i s -

muth was t h e n t r a n s f e r r e d from t h e t r e a t m e n t v e s s e l t o t h e bismuth f e e d tank. The experiment was i n i t i a t e d by s e t t i n g t h e s a l t flow r a t e through t h e column a t approximately t h e d e s i r e d v a l u e ; subsequently, t h e flow of bismuth through t h e column w a s i n i t i a t e d as shown i n F i g o 22,

During t h e i n i t i a l p a r t of

t h e r u n , bismuth and s a l t were c o u n t e r c u r r e n t l y c o n t a c t e d i n t h e packed col3 umn a t flow r a t e s of 205 and 100 cm /min, r e s p e c t i v e l y . Five sets of samples were obtained from t h e s a l t and bismuth streams l e a v i n g t h e column a t t h e

times i n d i c a t e d i n F i g . 22. The s a l t flow r a t e was t h e n i n c r e a s e d t o 160 cm3/min, and a s i n g l e s e t of s a l t and bismuth samples was t a k e n a f t e r a s a l t volume e q u i v a l e n t t o t h r e e column volumes had passed through t h e column,

The s a l t flow r a t e was t h e n increased t o 220 cm /min, and a f i n a l s e t of s a l t and bismuth samples was t a k e n a f t e r t h r e e a d d i t i o n a l column volumes

of s a l t had passed through t h e column.

The temperature along t h e e x t r a c -

t i o n column d u r i n g t h e r u n v a r i e d from 627Oc a t t h e bottom of t h e column t o 640째C a t t h e t o p . Data o b t a i n e d d u r i n g r u n UTR-3 a r e summarized i n Table g e The h i g h

uranium c o n c e n t r a t i o n i n t h e f i r s t s a l t sample i s probably t h e r e s u l t of d i l u t i o n i n t h e s a l t e f f l u e n t p i p i n g which i n i t i a l l y contained s a l t w i t h a uranium c o n c e n t r a t i o n equal t o t h a t i n t h e f e e d t a n k , For t h i s r e a s o n , t h e p o i n t corresponding t o t h i s sample w a s excluded from c o n s i d e r a t i o n i n c a l c u l a t i n g t h e f r a c t i o n of uranium t h a t w a s t r a n s f e r r e d .

A s t h e bismuth-

t o - s a l t flow r a t e r a t i o w a s decreased, t h e f r a c t i o n of t h e uranium removed from t h e s a l t decreased, as expected, from an average v a l u e of 0,gl d u r i n g t h e f i r s t p e r i o d of o p e r a t i o n t o 0.73 d u r i n g t h e f i n a l p e r i o d of o p e r a t i o n .

A s i n t h e previous r u n , t h e uranium c o n c e n t r a t i o n i n t h e bismuth i n t h e r e c e i v e r t a n k (528 ppm) was s i g n i f i c a n t l y higher t h a n t h a t which would be c a l c u l a t e d (about 440 ppm) by i n t e g r a t i n g t h e product of t h e uranium con-

-m w m 3

z I

W -J

U v)

rc +

rr)

+ +

I I

0 0

0 0,

0 a0

0 (0

.-c

O W

OZ t0

Table 9.

Sample

Uranium Conc. in Salt Phase ( PPm 1

Feed tanks

Fraction of Uranium Remaining in Salt

Summary of Mass Transfer Data Obtained During Run UTR-3

Volumetric Flow Ratio, Bismuth/Salt

210c

U Coric.

Zr Conc. ppm meq/liter

Bismuth Phase Th Conc. ppm meq/iiter

ppm

meq/liter

200

32.4

6.6

1200

199

ppm

Li Coiic. meq/liter

s,lJJE meqjliter

30a

41.4

260

Flowing strean 0.220

2.05

475

77.1

9.4

254

)+2.3

17.3

176

103

0.049

2.05

405

65.8

6.1

420

73.0

51.5

193

160

0.076

3.05

404

65.6

7.7

300

50.0

55.7

i79

158

0.075

2.05

362

58.8

7 -1

208

34.6

50.1

151

326

0.155

2.05

420

68.2

8.9

282

47.0

h8.7

17 3

4L 5

0.217

1.22

458

74.4

9.0

192

32.0

37 .o

151

561

0.267

0.91

502

81.5

8.7

226

37.6

37 . 6

165

461

170

Ave.

Receiver tanks

272

U balance, flowing stream samples =

528

85.7

- 129 millimoles U - o.78 leaving salt - 160 millimoles U -

U entering Bi

&Equilibrium lithium concentration calculated from thorium analysis. bEissume zirconium concentration = 8 . 1 meqjliter.

407

67.8

47.3

209

70 c e n t r a t i o n i n t h e flowing bismuth samples and t h e bismuth flow r a t e .

similar d i f f e r e n c e i s a l s o noted i n t h e measured and c a l c u l a t e d v a l u e s f o r t h e t o t a l number of e q u i v a l e n t s of t r a n s f e r r a b l e materials ( U , Th, Zr, and

L i ) p e r l i t e r of bismuth.

T h i s q u a n t i t y should be i n v a r i a n t during an

experiment, except f o r changes r e s u l t i n g from t h e f a c t t h a t t h e uranium i n t h e e x i t s a l t has a v a l e n c e of 3+ r a t h e r t h a n However, t h i s e f f e c t accounts f o r only about

4+ as i n

the entering salt.

5 meq of r e d u c t a n t p e r l i t e r ,

o r l e s s t h a n 2% of t h e t o t a l m i l l i e q u i v a l e n t s of t r a n s f e r r a b l e m a t e r i a l s per l i t e r of bismuth.

Therefore, t h e observed v a r i a t i o n i n t h e number of

m i l l i e q u i v a l e n t s of t r a n s f e r r a b l e m a t e r i a l s p e r l i t e r of bismuth must be a s c r i b e d t o e r r o r s i n t h e sampling procedure or i n t h e method of a n a l y s i s ,

or t o t h e presence of oxidants i n t h e system. during t h e run was

7.3

The uranium material b a l a n c e

78%, based on a n a l y s i s of t h e flowing stream samples. P r e p a r a t i o n for Mass T r a n s f e r Run UTR-4

Following mass t r a n s f e r r u n UTR-3,

b o t h t h e s a l t phase and t h e bismuth

phase were t r a n s f e r r e d t o t h e t r e a t m e n t v e s s e l f o r a 16-hr e q u i l i b r a t i o n period.

A f t e r b o t h phases were sampled, most of t h e s a l t was t r a n s f e r r e d

t o t h e s a l t feed t a n k .

A t t h i s p o i n t , t h e treatment v e s s e l c o n t a i n e d about

15 l i t e r s of bismuth and about 2 l i t e r s o f s a l t .

S u f f i c i e n t thorium m e t a l

was charged t o t h e treatment v e s s e l t o produce a thorium c o n c e n t r a t i o n of about 1000 ppm, which i s about 10% g r e a t e r t h a n t h e s o l u b i l i t y of thorium i n bismuth a t t h e bismuth f e e d tank o p e r a t i n g temperature ( 9 0 0 ppm a t 5 4 0 O C ) . A f i l t e r e d sample of t h e bismuth t a k e n

44 h r

a f t e r a d d i t i o n of t h e thorium

i n d i c a t e d a thorium c o n c e n t r a t i o n o f 980 ppm, which i s near t h e expected value.

The r a t e of d i s s o l u t i o n of t h e thorium, based on t h e observed thorium

c o n c e n t r a t i o n , w a s about t h a t observed p r i o r t o run UTR-3* However, v i s u a l i n s p e c t i o n of t h e thorium a d d i t i o n basket showed t h a t l e s s t h a n h a l f of t h e thorium had d i s s o l v e d i n t h e bismuth.

The b a s k e t was r e t u r n e d t o t h e b i s -

muth phase, and t h e t e m p e r a t u r e of t h e t r e a t m e n t v e s s e l was i n c r e a s e d from 600Oc t o

6 6 0 " ~ . A f t e r a t o t a l p e r i o d of 115 h r , t h e a d d i t i o n b a s k e t was

removed and weighed. solved.

It was found t h a t about 90% of t h e thorium had d i s -

The bismuth was t h e n sampled and t r a n s f e r r e d t o t h e bismuth f e e d

tank.

The r e p o r t e d thorium c o n t e n t s of two samples removed from t h e

treatment v e s s e l were 828 ppm and 710 ppm.

Because of t h e d i s c r e p a n c i e s

i n t h e s e c o n c e n t r a t i o n s , t h r e e a d d i t i o n a l samples of t h e bismuth were t a k e n from t h e bismuth f e e d t a n k and were analyzed by 'both t h e c o l o r i m e t r i c method and a s p e c t r o s c o p i c technique. a r e shown i n Table 1 0 .

R e s u l t s of t h e s e analyses

Although t h e v a l u e s r e p o r t e d f o r t h e two d i f f e r e n t

a n a l y t i c a l techniques showed a p p r e c i a b l e s c a t t e r , t h e bismuth i n t h e feed tank appeared t o have a nonuniform composition.

The lower c o n c e n t r a t i o n

of thorium near t h e bottom of t h e tank might have been due t o a lower temperature a t t h e bottom o f t h e t a n k and a correspondingly lower thorium solubility.

Table 1 0 .

Thorium C o n c e n t r a t i o n s Reported for Bismuth Samples Removed from t h e Bismuth Feed Tank Prior t o Run UTR-4

Location a t Which Sample Was Taken Bottom of tank

Type of Sampler

iThorium Concentration ( ppm ) Colorimetric Spectroscopic Analysis Analysis

Graphit e l a d l e

714

830

15 i n . from bottom

Graphit e l a d l e

1080

1200

Middle of bismuth pool

Stainless steel, filtered

1189

920

7.4

Mass T r a n s f e r Run UTR-4

Immediately p r i o r t o r u n UTR-4,

about 15 l i t e r s of bismuth and about

15 l i t e r s of salt were t r a n s f e r r e d from t h e t r e a t m e n t v e s s e l t o t h e s a l t and bismuth f e e d t a n k s . The uranium c o n c e n t r a t i o n i n t h e s a l t was 1681 ppm. A s shown i n F i g . 23, t h e run w a s i n i t i a t e d by s t a r t i n g a s a l t flow a t a low r a t e through t h e column.

A f t e r t h e s a l t metering system was determined t o

+ + + + +

+ 7

O R N L D W G 71-1398 I

+++

I I 12 13

6 9 IO

14 S A MP L E NUMBERS

BISMUTH ----- SALT

BISMUTH 140 cms/min

--I

BISMUTH I57 cmVmin

\ '\

4 118 cmVmin

TIME ( m i n )

Fig. 23. Volumesof Bismuth and Salt Remaining in Feed Tanks vs Run Time, Run UTR-4.

b e f u n c t i o n i n g s a t i s f a c t o r i l y , a bismuth flow w a s s t a r t e d through t h e c o l umn, and t h e s a l t and bismuth flow r a t e s were a d j u s t e d to 149 and 140 cm3/ min, r e s p e c t i v e l y .

Seven p a i r s of s a l t and bismuth samples were o b t a i n e d

from t h e s a l t and bismuth streams l e a v i n g t h e column.

The s a l t and bismuth

flow r a t e s were t h e n decreased t o 118 and 117 cm3 /min, r e s p e c t i v e l y , and t h r e e p a i r s of s a l t and bismuth samples were withdrawn. The s a l t and bismuth flow r a t e s were t h e n a d j u s t e d t o 210 and

157

cm 3 /min, r e s p e c t i v e l y .

t h e s e flow r a t e s were maintained during only about one-half of t h e r u n .

However,

of t h e remainder

During t h i s p e r i o d , f o u r a d d i t i o n a l p a i r s of s a l t and bismuth

samples were t a k e n from t h e s a l t and bismuth streams l e a v i n g t h e column. The temperature along t h e e x t r a c t i o n column during t h e r u n v a r i e d from

615Oc a t t h e bottom of t h e column t o 6 3 0 ' ~ a t t h e t o p . Data o b t a i n e d during r u n UTR-4 a r e summarized i n Table 11. A n o t i c e -

a b l e change i n t h e f r a c t i o n of uranium e x t r a c t e d from t h e s a l t i s observed as t h e bismuth-to-salt

1.0.

f l o w r a t e r a t i o v a r i e s throughout t h e range 0.75 t o

The t o t a l number of m i l l i e q u i v a l e n t s of t r a n s f e r r a b l e m a t e r i a l s p e r

l i t e r of bismuth i n t h e bismuth stream l e a v i n g t h e column was e s s e n t i a l l y c o n s t a n t throughout t h e r u n , and i s i n agreement w i t h t h e v a l u e o b t a i n e d by a n a l y z i n g a sample from t h e bismuth r e c e i v e r t a n k .

The t o t a l number

of m i l l i e q u i v a l e n t s of t r a n s f e r r a b l e m a t e r i a l s p e r liter of bismuth, as i n d i c a t e d by a n a l y s i s of bismuth from t h e f e e d t a n k , i s about 30% higher t h a n v a l u e s observed during t h e run and v a l u e s obtained by analyzing t h e m a t e r i a l p r e s e n t i n t h e bismuth r e c e i v e r t a n k .

The i n d i c a t e d l i t h i u m

c o n c e n t r a t i o n i n t h e bismuth i n t h e feed t a n k i s higher t h a n expected and could s i g n i f y t h a t t h e bismuth sample w a s contaminated w i t h s a l t .

s l i g h t change i n t h e t o t a l number of m i l l i e q u i v a l e n t s of t r a n s f e r r a b l e mat e r i a l s p e r l i t e r of bismuth i s expected s i n c e t h e uranium remaining i n t h e s a l t has a v a l e n c e of 3+ r a t h e r t h a n

4+ as

i n the i n l e t salt.

However,

t h i s e f f e c t would r e s u l t i n a change of only about LO meq of t r a n s f e r r a b l e m a t e r i a l s per l i t e r of bismuth.

. w.

r-m

d1Q

t - M

. 0. 0.

L n L n L A

p7r7r7

75 7.5

Mathematical Analysis of Mass T r a n s f e r with Primary R e s i s t a n c e t o Transfer i n t h e S a l t Phase

It has been noted15 t h a t t h e uranium e x t r a c t i o n d a t a from r u n s UTR-3 and

-4 can b e c o r r e l a t e d i n terms of t h e h e i g h t of an o v e r a l l t r a n s f e r u n i t

based on t h e s a l t phase (HTU) i f s e v e r a l assumptions are made.

The c h i e f

assumption i s t h a t t h e r a t e a t which uranium t r a n s f e r s t o t h e bismuth phase

w i l l be c o n t r o l l e d by t h e d i f f u s i v e r e s i s t a n c e i n t h e s a l t f i l m when t h e e x t r a c t i o n f a c t o r i s h i g h and when t h e s a l t f i l m i s composed l a r g e l y of nontransferring ions.

I n r u n s UTR-3 and

-4, a small amount of uranium was

added t o t h e s a l t a f t e r it had been e q u i l i b r a t e d w i t h t h e bismuth phase, which c o n t a i n e d r e d u c t a n t .

Thus, no s i g n i f i c a n t t r a n s f e r of l i t h i u m and

thorium between t h e s a l t and bismuth occurred i n t h e column.

In t h i s case,

t h e o v e r a l l t r a n s f e r c o e f f i c i e n t based on t h e s a l t phase i s equal t o t h e individual salt film transfer coefficient.

By d e f i n i t i o n , t h e ?dTU and t h e

number of o v e r a l l t r a n s f e r u n i t s based on t h e s a l t phase developed i n t h e column a r e r e l a t e d as:

. H = HTU-NTU,

where H = column l e n g t h , HTU = h e i g h t of an o v e r a l l t r a n s f e r u n i t based on t h e s a l t phase,

NTU = number o f o v e r a l l t r a n s f e r u n i t s based on t h e s a l t phase. I f it i s assumed t h a t uranium i s t h e major component t r a n s f e r r i n g from t h e

s a l t and t h a t t h e c o n t r o l l i n g r e s i s t a n c e t o t r a n s f e r i s i n t h e s a l t phase, t h e HTU can be d e f i n e d as f o l l o w s : V

HTU =

S ka â&#x20AC;&#x2122;

where

Vs = s u p e r f i c i a l v e l o c i t y o f s a l t i n t h e column, cm/sec, k = o v e r a l l mass t r a n s f e r c o e f f i c i e n t based on t h e s a l t phase, cm/sec,

a = i n t e r f a c i a l a r e a between s a l t and bismuth phases p e r u n i t column 2 3 volume, cm /cm

76 It has been observed p r e v i o u s l y 1 6 t h a t t h e dispersed-phase holdup i s approximately p r o p o r t i o n a l t o t h e flow r a t e of t h e d i s p e r s e d phase i n a packed column, except a t c o n d i t i o n s near f l o o d i n g ,

We would, t h e r e f o r e ,

expect t h e i n t e r f a c i a l a r e a between t h e s a l t and bismuth phases t o be p r o p o r t i o n a l t o t h e bismuth flow r a t e ; t h u s , one can w r i t e t h e f o l l o w i n g relation: I

ka = k VBi,

where

-1 kl = a c o n s t a n t , cm , 'Bi

= s u p e r f i c i a l v e l o c i t y of t h e bismuth i n t h e column, cm/sec.

The number of o v e r a l l t r a n s f e r u n i t s (based on t h e s a l t phase) developed i n t h e column i s d e f i n e d a s : iX0 I

mu= p

x*-x,

1'-

where

X = uranium c o n c e n t r a t i o n i n t h e b u l k s a l t , ppm, %

= uranium c o n c e n t r a t i o n i n s a l t i n e q u i l i b r i u m w i t h t h e b u l k bismuth

phase, PPm,

= uranium c o n c e n t r a t i o n i n t h e s a l t f e d t o t h e column, ppm, 'i Xo = uranium c o n c e n t r a t i o n i n t h e s a l t l e a v i n g t h e column, ppm. A s shown i n Table 1 2 , t h e value of X

a t t h e bottom of t h e column i s much

smaller t h a n t h e value of Xo; t h u s , one would expect t h a t t h e v a l u e of X would be much l e s s t h a n t h e v a l u e of X throughout t h e column.

In t h i s

c a s e , Eq. ( 2 9 ) can be i n t e g r a t e d t o y i e l d t h e following expression:

NTU = -In

0 -

Table 1 2 .

Run UTR-3

UTR-4

Summary o f Mass T r a n s f e r Data Obtained During Uranium Mass T r a n s f e r Runs UTR-3 and UTR-4

Uranium Concentration i n S a l t (ppm) Salt Salt Maximum Feed, Effluent Equilibrium X Value , a X* x, 2100

1680

Metal-to-Salt Flow Rate R a tio

Fraction of Flooding

F r a c t i o n of Uranium Remaining i n Salt

159

3.6

2.05

0.87

0.076

445

9.4

1.22

1.04

0.212

561

10.3

0.91

1.23

0.267

524

9.7

0.94

0.85

0.312

439

7.2

1.0

0.69

0.261

646

11.5

0.75

1.07

0.384

a C a l c u l a t e d as t h e c o n c e n t r a t i o n t h a t would b e i n e q u i l i b r i u m w i t h t h e observed c o n c e n t r a t i o n s of r e d u c t a n t ( l i t h i u m ) and uranium i n t h e bismuth e f f l u e n t .

Combining Eqs

( 2 6 ) , ( 2 7 ) , ( 2 8 ) , and ( 3 0 ) , and r e a r r a n g i n g , y i e l d s t h e

relation:

which states t h a t a semilogarithmic p l o t o f t h e f r a c t i o n of uranium remaining i n t h e s a l t v s t h e bismuth-to-salt

a s t r a i g h t l i n e having a s l o p e of -k'H.

flow r a t e r a t i o should y i e l d This l i n e should p a s s through

an o r d i n a l v a l u e of 1 . 0 a t a bismuth-to-salt

7.6

flow r a t e r a t i o of z e r o .

Discussion of Mass T r a n s f e r Data from Runs UTR-3 and UTR-4

The mass t r a n s f e r d a t a o b t a i n e d d u r i n g r u n s UTR-3 and i n Table 1 2 .

-4 are summarized

A s shown i n Fig. 24, t h e d a t a a r e w e l l r e p r e s e n t e d by Eq. ( 3 1 ) .

For t h e s e d a t a , t h e c o n s t a n t k' h a s t h e v a l u e of 0.0208 c ~ I - ~ .The product of t h e o v e r a l l mass t r a n s f e r c o e f f i c i e n t , based on the s a l t phase and t h e i n t e r f a c i a l area, i s given by t h e r e l a t i o n :

ka = 0.0208 VBi,

where ka = o v e r a l l r a t e c o n s t a n t based on t h e s a l t phase, s e c 'Bi

-1

= s u p e r f i c i a l v e l o c i t y of bismuth i n t h e column, cm/sec.

Values f o r t h e o v e r a l l r a t e c o n s t a n t f o r t h e p r e s e n t d a t a range from 0.012 -1 and compare f a v o r a b l y w i t h a p r e l i m i n a r y v a l u e of 0.0076 t o 0.021 sec -1 measured17 f o r t h e t r a n s f e r of uranium from a 96.2-3.6-0.2 w t % Cdsec Mg-U s o l u t i o n t o a molten s a l t (50-30-20 mole e r a t u r e s r a n g i n g from 560 t o

% MgC12-NaC1-KC1) a t temp-

610~~.

The h e i g h t of an o v e r a l l t r a n s f e r u n i t based on t h e s a l t phase, as c a l c u l a t e d from t h e d a t a from r u n s UTR-3 and

7.44 'Bi"s

-4, i s

given by t h e e x p r e s s i o n

(33)

79 ORNL DWG 71-2865 R 2 I .o

O U T R - 3 Data 0 U T R - 4 Data

E W

0.1

z a

0.01

0.5

I .o

i.5

2 .o

2.5

3.0

F i g . 24. V a r i a t i o n of F r a c t i o n of Uranium Remaining i n S a l t w i t h Bismuth-to-Salt Flow Rate R a t i o During t h e Countercurrent Contact of S a l t and Bismuth i n a 0.82-in.-long Packed Column.

where HTU = h e i g h t of t h e o v e r a l l t r a n s f e r u n i t based on t h e s a l t phase,

cm, = bismuth-to-salt

volumetric flow r a t e r a t i o .

The lower and upper l i m i t s of t h e HTU v a l u e s were 0.77 f t and 2 . 1 f t , which corresponded t o flow r a t e r a t i o s of 2.05 and 0.75, r e s p e c t i v e l y .

The amount

o f r e d u c t a n t p r e s e n t i n t h e bismuth a p p a r e n t l y had no measurable e f f e c t on

t h e r a t e of uranium t r a n s f e r .

Uranium mass t r a n s f e r d a t a from a n e a r l i e r

experiment (UTR-2) a r e n o t i n agreement w i t h t h e d a t a shown i n F i g . 24. However, i n experiment UTR-2, t h e thorium r e d u c t a n t was added t o t h e b i s muth i n t h e f e e d t a n k and t h e bismuth and s a l t phases were n o t i n chemical e q u i l i b r i u m w i t h r e s p e c t t o thorium and l i t h i u m as t h e y e n t e r e d t h e column. Thus, both uranium and l i t h i u m were b e i n g e x t r a c t e d from t h e s a l t phase by r e a c t i o n w i t h thorium from t h e bismuth phase, and it i s not s u r p r i s i n g t h a t t h e r e s u l t i n g uranium mass t r a n s f e r r a t e i s not i n agreement w i t h d a t a obt a i n e d d u r i n g r u n s UTR-3 and -4.

7.7 P r e p a r a t i o n f o r Zirconium Mass T r a n s f e r Experiments; Run UTR-5 I n o r d e r t o measure mass t r a n s f e r rates i n t h e column under more c l o s e l y c o n t r o l l e d c o n d i t i o n s and under c o n d i t i o n s where t h e c o n t r o l l i n g resis-

t a n c e i s not n e c e s s a r i l y i n t h e s a l t phase, p r e p a r a t i o n s were begun f o r experiments i n which t h e r a t e of exchange of zirconium i s o t o p e s w i l l be measured between s a l t and bismuth phases o t h e r w i s e a t chemical e q u i l i b r i u m . I n t h e p r e s e n t system, t h e r e i s no means f o r e f f e c t i n g a s e p a r a t i o n of z i r conium i s o t o p e s ; t h u s , by d e f i n i t i o n , t h e s e p a r a t i o n f a c t o r between 9 7 Z r

(16.8-hr h a l f - l i f e ) and n a t u r a l zirconium w i l l be u n i t y , as shown i n Eq. (34): D a = - =9 7 ~ r 1,

DZr

(34)

where a =

'"~r-~r separation factor,

= 97Zr distribution coefficient , Zr = Zr distribution coefficient. DZr

This relation also shows that the distribution coefficient for 97Zr will be equal to the distribution coefficient for natural zirconium and hence can be varied at will by adjusting the concentration of reductant in the bismuth phase.

In the experiments to be carried out, a small amount of

natural zirconium will be added to the system, and prior to each experiment the reductant concentration in the bismuth will be adjusted to obtain the desired zirconium distribution coefficient.

Immediately prior

to an experiment, 97Zr tracer will be added to the salt o r bismuth phase in its respective feed. tank, and the phases will be countercurrently contacted in the packed column under the desired operating conditions. During an experiment, the 97Zr tracer will exchange for natural zirconium and the mass transfer performance of the column can be evaluated by determining the 97Zr activity in the salt and bismuth streams leaving the column. This ex-

perimental technique has several advantages over the technique used thus far in runs UTR-2, -3, and

-4.

can be adjusted as desired.

First, the zirconium distribution coefficient

However, even for high values of the zirconium

distribution coefficient, no chemical changes other than the exchange of zirconium isotopes will occur in the salt or bismuth.

In this case, the

driving force for the transfer of 97Zr between the salt and bismuth phases will be accurately known at all points throughout the column. Since the

g7Zr tracer can be added either to the salt or bismuth feed tank, experiments can be carried out in which the primary resistance to mass transfer is in either the salt or bismuth phase, or in which the resistance to transfer in both phases is of importance. Before the zirconium mass transfer runs could be carried out, it was necessary that (1)most of the reductant be removed from the bismuth, (2) that undissolved thorium added to the bismuth feed tank prior to run UTR-2 be removed, and ( 3 ) that the salt and bismuth phases be brought to chemical

82 equilibrium.

It w a s decided t h a t t h e best way f o r e f f e c t i n g t h e s e changes

c o n s i s t e d of completely removing r e d u c t a n t from t h e bismuth i n t h e t r e a t ment v e s s e l , a f t e r which t h e s a l t and bismuth would be t r a n s f e r r e d t o t h e i r respective feed tanks.

An adequate p e r i o d f o r d i s s o l u t i o n of thorium from

t h e bismuth f e e d t a n k would be allowed; t h e n t h e s a l t and bismuth would be c o u n t e r c u r r e n t l y c o n t a c t e d i n t h e packed column.

This o p e r a t i o n would pro-

v i d e a d d i t i o n a l i n f o r m a t i o n on t h e hydrodynamics of c o u n t e r c u r r e n t f l o w i n t h e packed column, and would provide a n o p p o r t u n i t y t o o b t a i n flowing stream s a l t and bismuth samples under c o n d i t i o n s where e s s e n t i a l l y no u r a n i -

um mass t r a n s f e r should occur (and hence e s s e n t i a l l y no v a r i a t i o n should be observed i n t h e uranium c o n c e n t r a t i o n i n t h e s a l t and bismuth streams l e a v i n g t h e column). The s a l t and bismuth were t r a n s f e r r e d t o t h e t r e a t m e n t v e s s e l and were contacted w i t h a nominal 70-30 mole

% H2-HF mixture f o r

20 h r .

A t t h e end

of t h i s p e r i o d , t h e s a l t was sparged, f i r s t , w i t h hydrogen f o r 6 h r i n o r d e r t o reduce FeF2 t o m e t a l l i c i r o n and, t h e n , w i t h argon a t t h e r a t e of about 0.13 f t 3 /hr f o r 1 5 hr t o ensure complete removal of HI?.

The s a l t and b i s -

muth were subsequently sampled and were t r a n s f e r r e d t o t h e i r r e s p e c t i v e A f t e r a d e l a y of about 20 h r , t h e next experiment (UTR-5) was

feed tanks. begun

I n t h e i n i t i a l p a r t of t h e experiment, bismuth and s a l t were f e d t o t h e column a t t h e rates of 115 and 1 2 3 cm3 /min, r e s p e c t i v e l y , and seven p a i r s of samples were taken o f s a l t and bismuth l e a v i n g t h e column ( s e e Fig. 2 5 ) .

Throughout t h e remainder of t h e experiment, t h e s a l t and b i s -

muth flow r a t e s were v a r i e d i n o r d e r t o o p e r a t e near expected f l o o d i n g conditions.

During t h i s p e r i o d , s i x s a l t samples were o b t a i n e d from t h e

s a l t stream l e a v i n g t h e column i n order t o check f o r evidence of bismuth entrainment.

A f t e r about

116 min of o p e r a t i o n , t h e column flooded and

an alarm i n d i c a t i n g a high s a l t l e v e l i n t h e colwan was noted.

At this

p o i n t , t h e bismuth entrainment s e p a r a t o r became f i l l e d w i t h bismuth.

r e s t r i c t i o n i n t h e d r a i n l i n e from t h e entrainment s e p a r a t o r prevented t h e accumulated bismuth from d r a i n i n g out of t h e s a l t e x i t l i n e , and, i n

. I

I I

-.-c -E E

F2 - 0

E 0

b 0

e! 0

5 0

z 0

cue E

.-c

E -

0 yc

s1 0

84 order t o overcome t h e r e s u l t i n g back p r e s s u r e , an argon o v e r p r e s s u r e of 2 1 i n . H20 w a s imposed on t h e t o p of t h e column f o r t h e remainder of t h e

experiment.

The s a l t samples taken d u r i n g t h e l a t t e r h a l f of t h e experi-

ment c o n t a i n e d l a r g e q u a n t i t i e s of bismuth (>SO vol % ) . It i s l i k e l y t h a t t h i s w a s caused by t h e r e s t r i c t i o n i n t h e entrainment s e p a r a t o r d r a i n l i n e and t h e subsequent accumulation of bismuth i n t h e s a l t stream sampler. from

The temperature along t h e e x t r a c t i o n column during t h e r u n v a r i e d

615'~ a t t h e bottom of t h e column t o

622Oc a t t h e t o p .

Data o b t a i n e d during t h e f i r s t h a l f of t h e run by a n a l y z i n g s a l t and bismuth samples from t h e treatment v e s s e l , t h e f e e d t a n k s , t h e s a l t and bismuth streams l e a v i n g t h e column, and t h e s a l t and bismuth r e c e i v e r t a n k s a r e shown i n Table 13.

The c o n c e n t r a t i o n of thorium i n t h e bismuth

samples i n c r e a s e d , as expected, from about 0 . 3 ppm for samples from t h e treatment v e s s e l t o

66 ppm f o r samples from t h e bismuth r e c e i v e r tank.

Al-

though t h e i n c r e a s e was l e s s t h a n expected, it does i n d i c a t e t h a t t h e holdup of thorium i n t h e bismuth f e e d and r e c e i v e r t a n k s was decreased s i g n i f i c a n t ly.

The uranium c o n c e n t r a t i o n i n each of t h e bismuth samples was below t h e

l i m i t of d e t e c t i o n (<1ppm) except i n t h e c a s e of t h e r e c e i v e r t a n k sample, f o r which a uranium c o n c e n t r a t i o n of 1.1 ppm was i n d i c a t e d .

Thus, no

t r a n s f e r of uranium t o t h e bismuth phase occurred d u r i n g t h e experiment. S u r p r i s i n g l y , t h e r e p o r t e d uranium c o n c e n t r a t i o n s i n t h e s a l t samples r e moved from t h e column e f f l u e n t v a r i e d by 235% from t h e average v a l u e , which w a s i n e x c e l l e n t agreement w i t h t h e i n d i c a t e d uranium c o n c e n t r a t i o n s of t h e s a l t feed and c a t c h t a n k s .

Under almost t h e same c o n d i t i o n s of flow d u r i n g

run UTR-1, t h e v a r i a t i o n i n t h e i n d i c a t e d uranium c o n c e n t r a t i o n i n samples of t h e s a l t l e a v i n g t h e column was only about 210%.

These r e s u l t s confirmed

t h a t , i n any f u t u r e uranium t r a n s f e r experiments, we must c o n t i n u e t o r e l y upon s e v e r a l p a i r s of samples a t a g i v e n s e t of c o n d i t i o n s i n o r d e r t o obt a i n a r e l i a b l e e s t i m a t e of t h e f r a c t i o n of t h e uranium t h a t i s t r a n s f e r r e d .

7.8

Summary of Hydrodynamic Data w i t h P r e s e n t Column

Hydrodynamic d a t a obtained d u r i n g c o u n t e r c u r r e n t flow of s a l t and b i s muth i n t h e p r e s e n t column a r e summarized i n Table

14.

The v a l u e s f o r t h e

Table 13.

Concentrations of Uranium and Thorium i n S a l t and Bismuth Samples from Run UTR-5

Bismuth Samples Thorium Uranium Conc. Conc ( PPm ) (PPm)

Sample Source Treatment v e s s e l

0.32, 1 0

Feed t a n k s

9, 1.2

Uranium Conc. i n S a l t Samples ( PPm 1

3030, 3400

3005

Flowing stream

2500

3.4

3000

Ave

Receiver t a n k s

8.3

2650

5 01

3240

0.83

3340

26.

4310

2040

14.

3010

1.1

3030

. Table 14. S m a r y of Hydrodynamic Data Obtained During Countercurrent Flow of Salt and Bismut.h in a 0.82-in.-ID, 24-in.-long Column Packed with 1/4-in. Molybdenum Raschig Rings

Volumetric Flow Rate (ml/min) Salt Bismuth

Bismutht0- Salt Flow R a t i o

Fraction of Floodinga

Run

Interval (min)

HR-9

115

121

0.94 0.95

0.48 0.69

Apparent Bismuth Holdup

(S)

HR-9

175

177

0.99

1.03

HR-9

221

133

1.66

1.02

14 14 14 17

HR-9

221

107

2.07

0.93

HR-9

15 12

150

1.00

0.88

45 175

68 68

0.66

0.33

274

HR-10 HR-10 HR-10

6 7.5

2.57

0.68

3.81

0.92

21.7

HE-10

440

72 20.3

HR-11

210

4.12

0.95 0.69

330

0.93

406

6.60 8.64

17 17

HR-11

8 7 6

1.07

18-27

HR-11

3.5

228

100

2.28

0.92

HR-11

UTR-1

100

1.0

0.59

130

1.0

UTR-2

247

0.76 0.77

UTR-3

23.5

205

100

2.05

0.87

UTR-3

195

100

1.95

0.84

UTR-3

9 5

17 17 17 6 6

200

160

1.25

1.05

UTR-3

5.2

220

0.89

1.22

0.94 0 -99

0.85 0.69

16 16

UTR-4

19 5 140

UTR-4

117

149 118

157

UTR-4

Holdup increasing; flooding

UTR-1

4.75

Comments

210

0.75

1.07

115

123

0.93

0.70

16 17

146 276

161

0.91

0.90

Holdup increasing; flooding

UTR-5

42 8 5

1.00

UTR- 5

219

3-07 4.38

29 44

Holdup increasing; flooding

UTR- 5 UTR- 5

7.5

0.70

The value of V aFraction of flooding = [(Vsalt1I2 + VBi1/2)/V 'I2l2. which corresponds to 676 ml/min in the presen? column.

Holdup increasing; flooding

(superficial slip velocity) used was 392 ft/hr,

apparent bismuth holdup were c a l c u l a t e d from measurements of t h e p r e s s u r e a t t h e base of t h e column ( s a l t i n l e t ) , and t h e column overpressure.

During

most of t h e p e r i o d s of steady--state o p e r a t i o n , t h e values f o r t h e apparent bismuth holdup were e s s e n t i a l l y c o n s t a n t ( l e s s t h a n

5% v a r i a t i o n during t h e

p e r i o d ) ; however, i n a few p e r i o d s t h e v a r i a t i o n was c o n s i d e r a b l y l a r g e r (about 33%). A comparison w i l l be made i n a l a t e r r e p o r t i n t h i s s e r i e s of t h e apparent bismuth holdup w i t h previous measurements of t h e apparent holdup of mercury during c o u n t e r c u r r e n t flow of mercury and aqueous solut i o n s i n packed columns.

I n r u n UTR-5,

the calculated flooding condition.

f l o o d i n g was observed a t 90% o f

This low f l o o d i n g v a l u e could be ex-

p l a i n e d by t h e nonwetting c o n d i t i o n of t h e s a l t following t h e hydrogen-HF treatment.

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

work with mercury and aqueous s o l u t i o n s 1 6 w i t h t h e hydrodynamic d a t a summarized i n Table

i s shown i n F i g . 26.

A s can be observed, t h e agreement

between t h e p r e d i c t e d and measured v a l u e s i s q u i t e s a t i s f a c t o r y .

7.9

Examination of 304 S t a i n l e s s S t e e l Corrosion Specimens from Salt-Metal Treatment Vessel

The 304 s t a i n l e s s s t e e l v e s s e l , which c o n t a i n s t h e g r a p h i t e c r u c i b l e t h a t c o n s t i t u t e s t h e s a l t - m e t a l treatment v e s s e l , i s exposed t o an H2 -HF mixture during t h e i n f r e q u e n t treatment of bismuth and s a l t t o remove oxides and t o t r a n s f e r d i s s o l v e d metals from t h e bismuth t o t h e s a l t .

Cor-

r o s i o n specimens of 304 s t a i n l e s s s t e e l were removed from t h e t r e a t m e n t vess e l a f t e r a p e r i o d o f 1 0 months, which included a t o t a l o f about 60 hr of exposure t o a 30 mole % HF-H2

mixture.

A f t e r t h e specimens were c l e a n e d

w i t h a w i r e brush, a change of only 20.002 i n . i n t h i c k n e s s w a s observed. The temperature of t h e specimens w a s about 55OoC a s compared w i t h a nominal v e s s e l t e m p e r a t u r e of 600Oc.

On t h e b a s i s of t h e s e d a t a , c o r r o s i o n of t h e

s t a i n l e s s s t e e l treatment v e s s e l t o t h e p r e s e n t time i s judged t o be v e r y slight.

7.10

Maintenance of Equipment

Three t r a n s f e r l i n e f a i l u r e s occurred during t h i s r e p o r t p e r i o d ; a11 were due t o s t r e s s e s produced by f r o z e n bismuth.

Failures i n transfer lines

O R N L DWG 7 1 - 2 8 4 0 R 4

S A L T F L O W , ml/ min

100

200

300

400 500 600700 1

PREDICTED FLOODING C U R V E ~ 1 9 . 8(, f t / h r ) " 2

700 600

Vgi'/2 +Vs'/2

500 FLOODED NON FLOODED

.*\ 00

400

300

200

.-t E '.

s 0

5 IO 15 ( S A L T S U P E R F I C I A L VELOCITY ,VI , f t / h r ) 1 / 2

Fig. 26. Summary of Flooding Data with S a l t and Bismuth in a 0.82i n . - d i m , 24-in.-long Column Packed w i t h 1/4-in. Raschig Rings.

were noted a t two p o i n t s during heatup of t h e flow system p r i o r t o experiment UTR-3.

The f i r s t f a i l u r e occurred on t h e o u t s i d e of a bend i n t h e

s a l t l i n e connecting t h e s a l t j a c k l e g t o t h e bottom of t h e column; t h e second f a i l u r e was l o c a t e d i n t h e bismuth e x i t l i n e from t h e column.

About

125 ml o f bismuth and 500 m l of s a l t drained from t h e system as a r e s u l t of these failures.

The s a l t l e a k occurred i n a bend t h a t had expanded 5 t o 10%

i n diameter a t a l o c a t i o n which i s normally f i l l e d w i t h bismuth during cooldown p e r i o d s .

The w a l l t h i c k n e s s of t u b i n g a d j o i n i n g t h e s i t e o f f a i l u r e

i n t h e bismuth e x i t l i n e w a s unchanged (0.080 i n . ) , i n d i c a t i n g t h a t mass t r a n s f e r of i r o n was not a c o n t r i b u t i n g f a c t o r as was t h e case i n some of the earlier failures.

The e x t e r n a l s u r f a c e s of t h e t u b i n g examined were

only s l i g h t l y a i r o x i d i z e d ; t h e e x t e n t of o x i d a t i o n appears t o have been decreased by t h e o x i d a t i o n r e t a r d a n t p a i n t used on t h e l i n e s and by t h e p r a c t i c e of h e a t i n g t h e t r a n s f e r l i n e s t o o p e r a t i n g temperature only when an experiment i s planned.

Approximately 1 5 freeze-thaw c y c l e s had been ac-

cumulated i n t h e f a i l e d a r e a s .

The i m p l i c a t i o n of t h e s e observations w a s

t h a t f u t u r e o p e r a t i o n should attempt t o minimize t h e number of t h e r m a l c y c l e s a t t h e expense of i n c r e a s i n g t h e l e n g t h of time during which t h e l i n e s a r e held a t e l e v a t e d temperature.

Subsequently, attempts were made

t o m a i n t a i n t h e l i n e s a t temperatures of about 350 t o 400째C,which a r e cons i d e r a b l y higher t h a n t h e m e l t i n g p o i n t of bismuth ( 2 7 l o C ) .

In practice,

t h i s procedure had a s e r i o u s shortcoming i n t h a t f r e e z e v a l v e s c o n t a i n i n g bismuth would not seal; t h i s , i n t u r n , made t h e r o u t i n e t r a n s f e r of bismuth and s a l t between v e s s e l s more d i f f i c u l t .

We u l t i m a t e l y r e t u r n e d t o t h e

o r i g i n a l procedure of cooling t h e t r a n s f e r l i n e s tQroom temperature between experiments. During a r o u t i n e cooldown of t h e flow system following experiment UTR-5, a l e a k occurred i n t h e bismuth d r a i n l i n e from t h e entrainment s e p a r a t o r .

About 50 m l of bismuth was r e l e a s e d through a l o n g i t u d i n a l crack i n t h e 1/2-in.-diam

mild-steel tubing.

t h e f a i l u r e s discussed e a r l i e r .

The f a i l u r e was s i m i l a r i n appearance t o

8. PREVENTION OF AXIAL DISPERSION I N PACKED COLUMNS J . S. Watson

L . E . McNeese

Packed columns are b e i n g c o n s i d e r e d for u s e i n c o u n t e r c u r r e n t l y cont a c t i n g molten s a l t and bismuth streams i n MSBR f u e l p r o c e s s i n g systems. P r e v i o u s l y , we made measurements of a x i a l d i s p e r s i o n f o r v a r i o u s packing m a t e r i a l s i n columns d u r i n g t h e c o u n t e r c u r r e n t flow of mercury and aqueous solutions.

We showed t h a t a x i a l d i s p e r s i o n can s i g n i f i c a n t l y reduce t h e

performance of t h i s type of c o n t a c t o r under some o p e r a t i n g c o n d i t i o n s of interest.â&#x20AC;?

A s p a r t of our c o n t a c t o r development program, we a r e cur-

r e n t l y e v a l u a t i n g column m o d i f i c a t i o n s t h a t w i l l reduce t h e e f f e c t of a x i a l d i s p e r s i o n t o an a c c e p t a b l e l e v e l .

The proposed m o d i f i c a t i o n s con-

s i s t of devices t o be i n s e r t e d a t p o i n t s along t h e column t o reduce d i s -

persion a t these points.

If t h e devices a r e s e p a r a t e d by a column l e n g t h

e q u i v a l e n t t o one t h e o r e t i c a l s t a g e ( a n e x t e n t of s e p a r a t i o n t h a t can be achieved even i f t h e l i q u i d s between t h e devices a r e completely mixed), t h e s t a g e e f f i c i e n c y of t h e column segment w i l l b e g r e a t e r t h a n 75% i f 15%

or l e s s of t h e s a l t flowing through t h e segment i s r e c y c l e d t o t h e previous segment.

We have p r e v i o u s l y t e s t e d d e v i c e s c o n s i s t i n g of i n v e r t e d bubble

caps c o n t a i n i n g a number of small-diameter h o l e s through which t h e s a l t flows a t an increased velocity.*â&#x20AC;&#x2122;

It was found t h a t t h e e x t e n t of a x i a l d i s p e r s i o n

could be reduced c o n s i d e r a b l y and, i n p r i n c i p l e , t o v e r y low v a l u e s by t h e u s e of s u f f i c i e n t l y small h o l e s .

However, t h e column c a p a c i t y , or through-

put a t f l o o d i n g , was reduced by about a f a c t o r of 6.

During t h e c u r r e n t

r e p o r t p e r i o d , we d e v i s e d and t e s t e d an improved design of a x i a l d i s p e r s i o n preventer.

I n t h i s d e s i g n , shown s c h e m a t i c a l l y i n Fig. 2 7 , t h e s m a l l -

diameter h o l e s i n t h e upper p o r t i o n of t h e i n v e r t e d bubble cap have been r e p l a c e d w i t h a s i n g l e 3/8-in.-OD has f o u r 1/4-in.-diam

t u b e t h a t i s s e a l e d a t t h e t o p b u t which

h o l e s near t h e t o p of t h e t u b e .

This d e s i g n al.lows

t h e m e t a l phase t o r i s e t o t h e bottom of t h e s a l t e x i t h o l e s i n t h e v e r t i c a l t u b e , t h e r e b y p r o v i d i n g a s u f f i c i e n t l y h i g h l i q u i d metal head for f o r c i n g t h e d i s p e r s e d phase through t h e a x i a l d i s p e r s i o n p r e v e n t e r a t a h i g h throughput.

Two a x i a l d i s p e r s i o n preventer designs were t e s t e d during t h e counter-

O R N L D W G 71-13973

PACKED COLUMN

Fig.

27.

Schematic Diagram of a n Improved A x i a l Dispersion P r e v e n t e r .

c u r r e n t flow of mercury and water i n a 2-in.-diam

I n t h e f i r s t d e s i g n , t h e water flowed upward through

i n . Raschig r i n g s .

a l/h-in.-diam,

column packed w i t h 3 / 8 -

1/4-in.-long

was i n c r e a s e d t o 1 / 2 i n .

tube.

I n t h e second d e s i g n , t h e t u b e l e n g t h

Data o b t a i n e d w i t h t h e second a x i a l d i s p e r s i o n

preventer d e s i g n i s summarized i n Fig. 28. v e l o c i t y w a s v a r i e d from about

40 t o

v e l o c i t y w a s v a r i e d from about 2.7 t o

The mercury s u p e r f i c i a l

1 5 0 f t / h r , and t h e water s u p e r f i c i a l

ft/hr.

A marked e f f e c t of t h e

m e t a l flow r a t e on t h e e x t e n t of a x i a l d i s p e r s i o n w a s noted; t h a t i s , h i g h e r m e t a l s u p e r f i c i a l v e l o c i t i e s l e d t o a g r e a t e r e x t e n t of a x i a l d i s p e r s i o n . A s expected, no d i f f e r e n c e between t h e t w o devices was noted w i t h r e g a r d

t o axial dispersion.

The major e f f e c t of u s i n g a longer t u b e i s t h a t of

o b t a i n i n g an i n c r e a s e i n t h e m e t a l throughput.

It i s b e l i e v e d t h a t t h i s

d e s i g n would a l l o w f o r s a l t and bismuth throughputs t h a t can be a s h i g h as t h e column throughputs a t flooding.

Although t h e e x t e n t of a x i a l d i s p e r -

s i o n i s s t i l l s i g n i f i c a n t w i t h e i t h e r of t h e d e v i c e s , it i s probably suff i c i e n t l y low f o r most a p p l i c a t i o n s of i n t e r e s t .

The e x t e n t of a x i a l d i s -

p e r s i o n provided w i t h t h e p r e s e n t device i s i n t e r m e d i a t e between t h a t provided by bubble caps having one l/b-in.-diam f o u r l/h-in.-diam

hole and bubble caps having

h o l e s through which t h e water i s allowed t o flow.

The

performance of t h e p r e s e n t a x i a l d i s p e r s i o n p r e v e n t e r could probably be increased by u s i n g o n l y a s i n g l e hole i n t h e s i d e of t h e v e r t i c a l t u b e i n s t e a d of t h e four holes as i n t h e c u r r e n t d e s i g n .

ELECTROLYTIC REDUCTION OF L i C l USING A BISMUTH CATHODE AND A GRAPHITE ANODE

J. R . Hightower, Jr.

C . P e Tung

L. E. McNeese

The m e t a l t r a n s f e r process f o r removing r a r e e a r t h s from an MSBR r e q u i r e s t h e use of L i - B i

s o l u t i o n s f o r e x t r a c t i n g t h e r a r e e a r t h s from L i C 1 .

One method f o r p r o v i d i n g t h e s e L i - B i

s o l u t i o n s would c o n s i s t of e l e c t r o -

l y t i c a l l y reducing L i C l t h a t i s produced i n t h e p r o c e s s i n g system.

We have

c a r r i e d out an experiment i n o r d e r t o determine t h e g e n e r a l o p e r a t i n g chara c t e r i s t i c s of an e l e c t r o l y t i c c e l l having a bismuth cathode and a g r a p h i t e anode.

The o b j e c t i v e s of t h e experiment were t o determine t h e maximum anode

ORNL DWG. 71-13591

0.9 655 ml/min

0.8

MERCURY FLOW R A T E = 3 8 0 ml/min 0.7 -

1518 ml/min

1020 ml/min (3

- 0,6 X I

* 0.5

a m

0.4

0 I-

o a

0.3

0.2

0.1

C 0

WATER

R A T E ,

IO0

I20

140

ml/min

F i g . 28. V a r i a t i o n of F r a c t i o n of Backmixing w i t h Water and Mercury Flow Rate for a n Axial D i s p e r s i o n P r e v e n t e r Having a S i n g l e 1/4-in.-ID, 1/2-in.-long Tube Through Which t h e Water Flowed.

c u r r e n t d e n s i t y a c h i e v a b l e , t h e c u r r e n t e f f i c i e n c y , t h e e x t e n t of a t t a c k on t h e g r a p h i t e anode, and o p e r a t i o n a l d i f f i c u l t i e s a s s o c i a t e d w i t h format i o n of L i - B i

s o l u t i o n s a t t h e cathode.

9.1 Equipment and Materials Used The experimental equipment c o n s i s t e d of a b-in.-diam, q u a r t z c e l l v e s s e l ; a 3.5-in.-diam,

3.5-in.-high

i n g t h e bismuth cathode; a 1 - i n . - d i m , d i m , 10-in.-high

18-in.-long

molybdenum cup contain-

7-in.-long

g r a p h i t e anode; a 4-in.-

bismuth p u r i f i c a t i o n v e s s e l ; and a 4-in.-diam,

high L i C l p u r i f i c a t i o n v e s s e l .

15-in.-

The assembled e l e c t r o l y t i c c e l l i s shown

i n F i g . 29. P r o v i s i o n w a s made f o r measuring t h e volume of c h l o r i n e produced a t t h e anode by allowing t h e c h l o r i n e t o d i s p l a c e argon from a 25-ft-long s e c t i o n of 3/4-in.-diam

copper t u b i n g .

A w e t - t e s t meter was provided f o r

measuring t h e volume of t h e d i s p l a c e d argon. Seven kilograms of bismuth was charged t o t h e bismuth t r e a t m e n t v e s s e l , where it w a s sparged w i t h hydrogen a t 6 5 0 " ~u n t i l t h e water c o n c e n t r a t i o n i n t h e off-gas was l e s s t h a n 1 ppm.

The bismuth w a s t h e n t r a n s f e r r e d through

a porous molybdenum f i l t e r i n t o t h e e l e c t r o l y t i c c e l l .

Eleven hundred grams

of oven-dried L i C l was charged t o t h e s a l t t r e a t m e n t v e s s e l .

The s a l t w a s

p u r i f i e d by c o n t a c t w i t h 2 kg of p u r i f i e d bismuth t o which 93 g of thorium

metal had been added.

The L i C l w a s c o n t a c t e d w i t h t h e thorium-bismuth

s o l u t i o n f o r a p e r i o d of about 100 h r a t 6 5 0 ' ~ ; t h e n it was t r a n s f e r r e d through a porous molybdenum f i l t e r i n t o t h e c e l l v e s s e l .

The porous molyb-

denum f i l t e r s were made from 0.63-in.-diam,

porous molybdenum

d i s k s having a mean

1/8-in.-thick

p o r e s i z e of 30 t o 40 p.

The f i l t r a t i o n r a t e a t 6 5 0 " ~

f o r t h e L i C l w a s 0.8 cm3/sec w i t h a p r e s s u r e drop of 6.2 p s i , and t h e f i l t r a t i o n r a t e f o r t h e bismuth w a s 0.4 cm3/sec w i t h a p r e s s u r e drop of 2 p s i .

9.2

Operating Conditions and Results

The c e l l w a s o p e r a t e d a t 670째C w i t h t h e following anode c u r r e n t d e n s i t i e s (based on t h e p r o j e c t e d area of t h e bottom of t h e anode, 5.06 cm2 ) :

Fig. 2 9 .

Assembled Electrolytic Cell Vessel Used for LiCl Reduction.

4.37 A/cm2 f o r 7 min, 6.7 A/cm2 f o r 6 min, and 8.6 A/cm 2 f o r 6 min.

There

appeared t o b e no l i m i t i n g anode c u r r e n t d e n s i t y i n t h i s o p e r a t i n g range. Disengagement of t h e c h l o r i n e g a s produced a t t h e anode (which had been rounded s l i g h t l y t o promote g a s disengagement) proceeded smoothly and withWith t h e i n i t i a t i o n of c u r r e n t flow through t h e c e l l , t h e

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

L i C l became r e d i n c o l o r ; t h e c o l o r of t h e s a l t grew d a r k e r as t h e opera-

t i o n continued u n t i l , f i n a l l y , t h e s a l t became opaque. Measurement of t h e c h l o r i n e e v o l u t i o n r a t e (and hence t h e c u r r e n t eff i c i e n c y ) was not p o s s i b l e because of r e a c t i o n of t h e c h l o r i n e w i t h i r o n components i n t h e upper p a r t of t h e c e l l v e s s e l .

9.3

P o s t o p e r a t i o n a l Examination of Equipment

After t h e c e l l had cooled t o room t e m p e r a t u r e , examination showed t h a t

t h e t o p f l a n g e and t h e anode s u p p o r t , b o t h of which were made of mild s t e e l , A m i x t u r e of yellow and w h i t e powders (FeC12 and

were s e v e r e l y corroded. L i C l containing 1.3 w t

3-ft-long

bismuth) covered t h e f l a n g e and n e a r l y f i l l e d a

s e c t i o n of t h e l/h-in.-diam

copper o f f - g a s l i n e .

A thin metallic

film, which had covered t h e L i C l s u r f a c e , w a s removed i n t a c t when t h e anode

w a s r a i s e d a t t h e end of t h e experiment. c o n s i s t e d of i r o n and about 3 w t

The m e t a l l i c p o r t i o n of t h e f i l m

% bismuth.

The L i C l appeared t o c o n t a i n a

l a r g e amount o f suspended b l a c k m a t e r i a l , which w a s found t o be i r o n .

The

bismuth c o n c e n t r a t i o n i n t h e L i C l w a s r e l a t i v e l y h i g h (about 0.63 w t % ) . The molybdenum cup, which c o n t a i n e d t h e bismuth c a t h o d e , appeared t o b e u n a t t ac ked. It i s b e l i e v e d t h a t t h e a t t a c k of i r o n components i n t h e c e l l by gas-

eous c h l o r i n e w a s t h e o n l y d e t r i m e n t a l a c t i o n which o c c u r r e d d u r i n g operat i o n of t h e c e l l .

The FeCl

c o r r o s i o n product was p a r t i a l l y t r a n s f e r r e d t o

t h e L i C 1 , where it w a s reduced t o m e t a l l i c i r o n . The material t h a t caused t h e s a l t t o t u r n r e d d u r i n g t h e experiment w a s probably L i Siâ&#x20AC;&#x2122;, which d i s s o l v e d i n t h e L i C 1 .

It i s known t h a t L i B i

d i s s o l v e s t o a n a p p r e c i a b l e e x t e n t i n an LiC1-LiF e u t e c t i c which i s i n c o n t a c t w i t h s o l i d L i B i or a bismuth s o l u t i o n t h a t i s s a t u r a t e d w i t h

97 L i Bi,21 and t h a t a dark r e d s o l u t i o n i s formed. The cathode probably 3 p o l a r i z e d r a p i d l y a t t h e cathode c u r r e n t d e n s i t i e s used i n t h i s experi-

ment, r e s u l t i n g i n bismuth s a t u r a t e d w i t h L i B i a t t h e LiC1-bismuth i n t e r -

face.

P o l a r i z a t i o n of t h e cathode could be prevented by any of s e v e r a l

methods, i n c l u d i n g l i m i t i n g t h e cathode c u r r e n t d e n s i t y or i n c r e a s i n g t h e e x t e n t of mixing of t h e bismuth phase near t h e LiC1-bismuth i n t e r f a c e . The e q u i l i b r i u m c o n c e n t r a t i o n s of l i t h i u m and bismuth i n L i C l are r e p o r t e d t o be s i g n i f i c a n t l y reduced when t h e bismuth i s not s a t u r a t e d w i t h L i B i . 22

3 Although t h i s experiment pointed o u t an unexpected complication, it

confirms our e x p e c t a t i o n t h a t e l e c t r o l y t i c r e d u c t i o n of L i C l u s i n g a b i s muth cathode and a g r a p h i t e anode should p r o c e e d r e a d i l y a n d t h a t l i t t l e , i f any, a t t a c k should occur on t h e g r a p h i t e anode.

10.

STUDY OF THE PURIFICATION OF SALT BY CONTINUOUS METHODS R . B. Lindauer

L. E. McNeese

W e have p r e v i o u s l y d e s c r i b e d equipment for s t u d y of t h e p u r i f i c a t i o n

of s a l t by continuous methods.23

I n i t i a l work w i t h t h i s system was d i r e c t e d

a t measurement of t h e f l o o d i n g r a t e s i n a 1.25-ine-diam, packed w i t h 1/4-in.

n i c k e l Raschig r i n g s .

column

Flooding d a t a were o b t a i n e d dur-

i n g t h e c o u n t e r c u r r e n t flow of molten s a l t (66-34 mole drogen or argon.24

7-ft-long

% LiF-BeF 2 ) and hy-

The o b j e c t i v e of t h e p r e s e n t work is t o study t h e con-

t i n u o u s r e d u c t i o n of i r o n f l u o r i d e i n molten s a l t by c o u n t e r c u r r e n t c o n t a c t of t h e s a l t with hydrogen i n a packed column.

During t h i s r e p o r t p e r i o d , a

s u f f i c i e n t q u a n t i t y of FeF 2 (34.5 g ) w a s added t o t h e s a l t (66-34 mole $ LiF-BeF2) t o i n c r e a s e t h e i r o n c o n c e n t r a t i o n from 20 ppm t o 425 ppm. Two i r o n f l u o r i d e r e d u c t i o n r u n s ( R - 1 and -2) were c a r r i e d o u t , and s e v e r a l equipment m o d i f i c a t i o n s were made.

10.1

I r o n F l u o r i d e Reduction Runs R-1 and R-2

After FeF2 had been added t o t h e 1 4 - l i t e r s a l t charge, two i r o n f l u o r i d e r e d u c t i o n runs were c a r r i e d o u t a t a column temperature of 700째C.

During t h e

f i r s t r u n , a s a l t flow r a t e of 100 cm3/min and a hydrogen flow r a t e of about 20 l i t e r s / m i n were used.

A low hydrogen supply p r e s s u r e r e s u l t e d

i n a f l u c t u a t i n g hydrogen flow r a t e throughout most of t h e r u n .

The

v a r i a t i o n s i n t h e g a s flow r a t e caused t h e p r e s s u r e a t t h e t o p of t h e c o l umn t o f l u c t u a t e ; i n t u r n , t h i s f l u c t u a t i o n r e s u l t e d i n an i r r e g u l a r s a l t f e e d r a t e t o t h e column.

During t h e r u n , t h e i r o n f l u o r i d e c o n c e n t r a t i o n

i n t h e salt w a s reduced from an i n l e t v a l u e of 425 ppm t o 307 ppm. I n t h e second r u n (R-2), a s a l t flow r a t e of 100 cm3/min and a hydrogen flow r a t e

of 13.5 l i t e r s / m i n were used.

Operation of t h e column a t t h e d e s i r e d con-

d i t i o n s was d i f f i c u l t i n t h i s r u n , although performance of t h e system had been s a t i s f a c t o r y d u r i n g previous f l o o d i n g r u n s i n which t h e g a s flow rates were as high as about 25 l i t e r s / m i n .

A f t e r only 4.0 l i t e r s of t h e 1 4 - l i t e r

s a l t b a t c h had been f e d through t h e column, t h e p r e s s u r e a t t h e b a s e of t h e column r e s u l t i n g from t h e p r e s s u r e drop a c r o s s t h e column and column o f f gas l i n e was s u f f i c i e n t l y high t o f o r c e t h e g a s - s a l t s a l t l o o p below t h e column,

i n t e r f a c e o u t of t h e

A t t h i s p o i n t , t h e flow of hydrogen w a s t e r -

minated and t h e remaining s a l t was t r a n s f e r r e d t o t h e s a l t r e c e i v e r v e s s e l through t h e s t a t i c column of s a l t . i n Table

15.

Table 15.

Run No.

Data for t h e two r u n s are summarized

Summary of Data from I r o n F l u o r i d e Reduction Runs R-1 and R-2

Hydrogen Flow Rate (std liters/min)

Salt Flow Rate (cm3/min)

Length of Run (min)

Analysis of F i l t e r e d Samples" (ppm of i r o n ) Feed Product

F r a c t i o n of Salt Contacted w i t h H2

R-P

20 .o

100

425

307

0.685

R- 2

13.5

100

307

228

0 276 e

Samples were t a k e n from t h e combined s a l t volumes i n t h e s a l t r e c e i v e r vessel.

99 10.2

Mathematical Analysis of t h e Rate of I r o n F l u o r i d e Reduction; Calculated Mass T r a n s f e r C o e f f i c i e n t s f o r Runs R-1 and R-2

The c o u n t e r c u r r e n t c o n t a c t , i n a packed column, of hydrogen w i t h s a l t c o n t a i n i n g FeF

results i n the reaction: FeF

2(d)

H2(g)

= Fe

+ 2HF

(35)

(g)

A material balance on FeF2 i n t h e s a l t contained i n a d i f f e r e n t i a l l e n g t h

of t h e column y i e l d s t h e r e l a t i o n :

-L dx = r A dh,

(36)

where

L = s a l t flow r a t e , moles/sec, x = c o n c e n t r a t i o n of FeF2 i n b u l k s a l t , mole f r a c t i o n , r = r a t e of FeF,L r e d u c t i o n per u n i t column volume, moles FeF,/sec*cm 2 A = c r o s s - s e c t i o n a l area of column, cm ,

h = column h e i g h t , cm. The r e d u c t i o n of FeF2 by r e a c t i o n w i t h hydrogen can be a f f e c t e d by a number of f a c t o r s t h a t may c o n t r i b u t e t o s e t t i n g t h e o v e r a l l r a t e of r e a c t i o n . one of t h e o b j e c t i v e s of t h i s work i s t o determine t h e r a t e - c o n t r o l l i n g s t e p s involved i n t h e r e d u c t i o n of FeF2 and e v a l u a t i o n of t h e a s s o c i a t e d r a t e constants.

Two l i m i t i n g c a s e s f o r t h e r a t e of r e d u c t i o n of FeF2 a r e of in-

terest:

(1)t h e c a s e i n which t h e r a t e of r e d u c t i o n i s l i m i t e d by t h e r a t e

of t r a n s f e r of FeF2 t o t h e g a s - s a l t i n t e r f a c e f r o m t h e b u l k s a l t , and ( 2 ) t h e c a s e i n which t h e r a t e of r e d u c t i o n i s l i m i t e d by t h e r a t e of r e a c t i o n between FeF2 and H2 a t t h e g a s - s a l t i n t e r f a c e . 10.2.1

Case f o r Which t h e Rate of FeF? Reduction Is Limited by t h e Rate of T r a n s f e r of FeF2 t o t h e Gas-Salt I n t e r f a c e

For t h e c a s e i n which t h e r a t e of t r a n s f e r of FeF 2 t o t h e g a s - s a l t *

i n t e r f a c e i s r a t e l i m i t i n g , t h e r a t e of r e d u c t i o n w i l l be given by t h e expression:

LOO

r = k R a ( x - x % ),

(37)

where

- mass t r a n s f e r c o e f f i c i e n t f o r t r a n s f e r o f FeF2 from t h e b u l k s a l t kt t o t h e s a l t - g a s i n t e r f a c e , moles/sec*cm2 , 2 3 i n t e r f a c i a l area p e r u n i t column volume, cm /cm ,

a = gas-salt

= c o n c e n t r a t i o n of FeF

i n s a l t t h a t would be i n e q u i l i b r i u m w i t h

t h e H -HF mixture a d j a c e n t t o t h e s a l t being c o n s i d e r e d , mole 2 fraction. Combining Eqs.

( 36) and ( 37) y i e l d s t h e r e l a t i o n :

L dx = -k ~ A ( x- x ) dh.

If t h e v a l u e of x

i s small i n comparison w i t h t h e v a l u e of x, Eq.

( 3 8 ) can

be i n t e g r a t e d over t h e column l e n g t h t o y i e l d t h e following r e l a t i o n : kRa =

L AH

i , X

(39)

where

H = column h e i g h t , cm, x i = c o n c e n t r a t i o n of FeF2 i n s a l t f e d t o column, mole f r a c t i o n , x0 = c o n c e n t r a t i o n of FeF2 i n s a l t l e a v i n g column, mole f r a c t i o n . 10.2.2

Case f o r Which t h e Rate of FeFp Reduction Is Limited by t h e Rate of Reaction of FeF? w i t h H p a t t h e Gas-Salt I n t e r f a c e

and H a t t h e 2 2 g a s - s a l t i n t e r f a c e i s r a t e l i m i t i n g , t h e r a t e of r e d u c t i o n w i l l be g i v e n by For t h e c a s e i n which t h e r a t e of r e a c t i o n between FeF

t h e expression:

101

where

ks = r e a c t i o n r a t e c o n s t a n t , cm3 / s e e ,

KH = Henry's l a w c o n s t a n t f o r hydrogen i n s a l t , moles/cm3~atm, = p a r t i a l p r e s s u r e of hydrogen i n g a s , a t m . pH:!

Combination of Eqs. ( 3 6 ) and ( 4 0 ) y i e l d s t h e r e l a t i o n :

L dx = -kS v

(41)

x dh. H2

If t h e v a r i a t i o n i n t h e v a l u e of pu throughout t h e column i s small, t h i s "2 r e l a t i o n can b e i n t e g r a t e d over t h e column l e n g t h t o y i e l d t h e e x p r e s s i o n :

in X

10.2.3 c

(42)

out

Calculated Reaction Rate Constants f o r Runs R-1 and R-2

Values f o r t h e mass t r a n s f e r c o e f f i c i e n t and t h e r e a c t i o n r a t e c o n s t a n t , as defined by Eqs. (39) and ( 4 2 ) f o r t h e two l i m i t i n g c a s e s of i n t e r e s t , were calculated.

These v a l u e s and a s s o c i a t e d information are summarized i n Table

16. For t h e c a s e i n which t h e r e d u c t i o n r a t e i s c o n t r o l l e d by mass t r a n s f e r , it i s seen t h a t t h e FeF

c o n c e n t r a t i o n i n s a l t i n e q u i l i b r i u m w i t h g a s Laving

a composition e q u a l t o t h a t of g a s l e a v i n g t h e column i s n e g l i g i b l e i n comp a r i s o n w i t h t h e i n l e t or o u t l e t FeF2 c o n c e n t r a t i o n s i n t h e s a l t .

The re-

sLclking v a l u e s f o r t h e o v e r a l l r a t e c o n s t a n t ( k a ) a r e 0.028 and 0.064

R moles/sec *em3 and a r e i n s a t i s f a c t o r y agreement with each o t h e r

Since

t h e p a r t i a l p r e s s u r e of hydrogen w a s t h e same f o r both r u n s , t h e r e a c t i o n r a t e c o n s t a n t , ks, i s p r o p o r t i o n a l t o k a .

In future runs, the controlling

mechanism w i l l b e determined by varying t h e i n l e t hydrogen p a r t i a l p r e s s u r e . 10.3

Equipment Modifications and Maintenance

S e v e r a l d i f f i c u l t i e s were encountered d u r i n g o p e r a t i o n of t h e system throughout t h e c u r r e n t r e p o r t p e r i o d .

These d i f f i c u l t i e s were as f o l l o w s :

4-i

fll

4 H

0;r

cdo X

Lri

x(H aJ

102

(1) an u n d e s i r a b l y h i g h p r e s s u r e drop i n t h e column off-gas system, which caused t h e s a l t - g a s i n t e r f a c e i n t h e column t o be f o r c e d out of t h e s e a l loop below t h e column; ( 2 ) r e s t r i c t i o n s i n t h e s a l t f i l t e r i n l e t and o u t l e t vent l i n e s , which probably c o n t r i b u t e d t o t h e e r r a t i c o p e r a t i o n of t h e system during t h e two i r o n f l u o r i d e r e d u c t i o n r u n s ; (3)

f a i l u r e of a weld i n c o n t a c t w i t h s a l t i n t h e sampler i n t h e s a l t e f f l u e n t l i n e from t h e column;

(4)

f a i l u r e of t h e l i q u i d l e v e l d i p l i n e above t h e s a l t r e c e i v e r t a n k ; and

( 5 ) d e p o s i t i o n of Be0 ( i n t h e column), which reduced t h e column throughput. 10.3.1

R e s t r i c t i o n i n t h e Off-Gas Line from t h e Column

I n t h e i n i t i a l system d e s i g n , s a l t l e a v i n g t h e bottom of t h e column flowed through a 30-in.-deep

loop t h a t formed a gas seal and prevented gas

from flowing out w i t h t h e s a l t .

The s a l t used i n i t i a l l y i n t h e system had

a s p e c i f i c g r a v i t y of 2, and a p r e s s u r e of 60 i n . H20 a t t h e bottom of t h e column was s u f f i c i e n t t o f o r c e s a l t out of t h e s e a l loop.

The t o t a l pres-

s u r e a t t h e bottom of t h e column i s t h e sum of (1)t h e p r e s s u r e a t t h e t o p of t h e column, and ( 2 ) t h e p r e s s u r e drop a c r o s s t h e column.

The p r e s s u r e

a t t h e t o p of t h e column i s u s u a l l y c o n t r o l l e d by a t h r o t t l i n g v a l v e ; howe v e r , an abnormally high v a l u e w i l l r e s u l t i f t h e r e i s a r e s t r i c t i o n i n t h e off-gas l i n e l e a v i n g t h e column.

The p r e s s u r e drop a c r o s s t h e column in-

c r e a s e s as t h e s a l t and gas flow r a t e s a r e i n c r e a s e d , r i s i n g s h a r p l y as t h e f l o o d i n g p o i n t i s approached.

During r u n R-1, t h e p r e s s u r e a t t h e b a s e

of t h e column remained s u f f i c i e n t l y low t h a t s a l t w a s not forced from t h e s e a l loop.

However, during r u n R-2, t h e p r e s s u r e a t t h e t o p of t h e column

w a s h i g h e r ; and, a f t e r about h a l f of t h e s a l t ( 6 l i t e r s ) had been f e d through t h e column, t h e column p r e s s u r e drop increased t o about 35 i n . H20.

A t t h i s p o i n t , t h e p r e s s u r e a t t h e base of t h e column w a s s u f f i c i e n t t o

104

f o r c e s a l t o u t of t h e s e a l and t h e run w a s terminated. 1/2-in.-OD

Examination of t h e

off-gas l i n e l e a v i n g t h e column showed t h a t t h e l i n e w a s almost

completely r e s t r i c t e d w i t h s a l t . packed w i t h a 6-in.-long

An 8-in.-long,

h-in.-diam

heated v e s s e l

s e c t i o n of n i c k e l wool ( s e e F i g . 3 0 ) w a s i n s t a l l e d

i n t h e off-gas l i n e i n order t o remove s a l t from t h e gas s t r e a m l e a v i n g t h e column.

The v e s s e l was p o s i t i o n e d i n such a manner t h a t s a l t would d r a i n

from t h e packirrg and r e t u r n t o t h e t o p of t h e column through a gas s e a l loop

10.3,2 R e s t r i c t i o n s i n Vent Lines on S a l t F i l t e r Following r e d u c t i o n runs R-1 and -2,

it w a s found t h a t t h e vent l i n e s

on t h e i n l e t and o u t l e t s i d e s of t h e s a l t f i l t e r had become plugged w i t h The r e s t r i c t i o n i n t h e i n l e t vent l i n e probably r e s u l t e d from-en-

salt.

trainment of s a l t w i t h t h e gas t h a t was forced out of t h e s e a l l o o p below t h e column d u r i n g r u n R-2.

The s a l t i n t h e o u t l e t v e n t l i n e on t h e f i l t e r

w a s t h e r e s u l t of a cold s e c t i o n i n t h e l i n e (between t h e f i l t e r and t h e

s a l t r e c e i v e r t a n k ) t h a t caused s a l t t o f i l l t h e f i l t e r v e s s e l .

The

r e s t r i c t e d p o r t i o n s of t h e vent l i n e s were removed and r e p l a c e d .

10.3.3

F a i l u r e of a Weld on t h e Flowing-Stream S a l t Sampler

During f l o o d i n g test 11 (which followed r e d u c t i o n runs R - 1 and - 2 ) , t h e p r e s s u r e drop a c r o s s t h e column suddenly i n c r e a s e d .

It w a s found

t h a t f a i l u r e o f a submerged weld i n t h e flowing stream s a l t sampler had allowed s a l t t o c o n t a c t a Calrod h e a t e r on t h e s a l t e x i t l i n e between t h e sampler and t h e r e c e i v e r , t h e r e b y causing t h e h e a t e r t o f a i l .

Failure

of t h e h e a t e r and, i n t u r n , a decrease i n t h e temperature of t h e e x i t l i n e

( t o below t h e s a l t l i q u i d u s temperature) caused an accumulation of s a l t i n t h e column and r e s u l t e d i n t h e observed i n c r e a s e i n t h e column p r e s s u r e drop.

To circumvent t h e s e d i f f i c u l t i e s , t h e lower s e c t i o n of t h e sampler

w a s r e d e s i g n e d t o e l i m i n a t e welds below t h e normal s a l t l e v e l .

ORNL D W G 72-1384 D I F F E R E N T I A L PRESSURE INSTRUMENT LINES

OUTLET COLUMN

I/-

GAS TO VENT

F i g . 30.

S a l t Entrainment S e p a r a t o r .

106

10.3.4 F a i l u r e of a Liquid Level Dip Line on t h e S a l t Receiver Tank One of t h e d i p l i n e s i n t h e s a l t r e c e i v e r t a n k w a s found t o be r e s t r i c t e d by s a l t i n t h e v i c i n i t y of t h e t o p of t h e v e s s e l .

A d r i l l was

used t o remove t h e s a l t from t h e l i n e ; however, we found t h a t a t t e m p t s t o t r a n s f e r s a l t from t h e r e c e i v e r t o t h e feed tank l e d t o a f a i l u r e i n t h e l i q u i d l e v e l d i p l i n e a t t h e p o i n t where t h e s a l t plug had been r e moved.

We b e l i e v e t h a t t h e r e a s o n f o r t h e f a i l u r e was improper c e n t e r i n g

of t h e d r i l l and a decrease i n t h e w a l l t h i c k n e s s of t h e t u b i n g . 10.3.5

D e p o s i t i o n of Be0 i n Column

A f t e r t h e f i r s t two r e d u c t i o n runs ( R - 1 and -2) had been completed, we found t h a t t h e p r e s s u r e drop a c r o s s t h e column w i t h argon flow o n l y (flow r a t e , 5 l i t e r s / m i n ) had increased from 5.7 i n . H2 0 t o 1 2 . 0 i n . H20. Since only 7 g of i r o n had been reduced i n t h e system, it was b e l i e v e d t h a t t h e r e s t r i c t i o n w a s caused by an accumulation of r e l a t i v e l y i n s o l u b l e BeO, which may have been formed i n t h e system as t h e r e s u l t of low concentrat i o n s of i m p u r i t i e s i n t h e argon or hydrogen or because of inleakage of a i r i n t o t h e system.

Up t o t h i s t i m e , our u s u a l procedure has been t o

m a i n t a i n a low argon flow r a t e through t h e system, which i s h e l d a t atmos p h e r i c p r e s s u r e d u r i n g p e r i o d s of nonoperation.

We have now adopted t h e

procedure o f m a i n t a i n i n g a p o s i t i v e p r e s s u r e of a t l e a s t 1 p s i g i n t h e system during such p e r i o d s i n order t o minimize t h e p o s s i b i l i t y of a i r i n l e a k age.

J . S. Watson

L. E. McNeese

Baes, Bamberger, and Ross25 have r e c e n t l y proposed a p r o t a c t i n i u m i s o The p r o c e s s l a t i o n method based on t h e s e l e c t i v e p r e c i p i t a t i o n of Pa,O,. r e q u i r e s o x i d a t i o n of t h e Pa 4+ i n MSBR f u e l s a l t t o Pa5+L(&d most of t h e

U3+ t o U

4+)

p r i o r t o t h e subsequent oxide p r e c i p i t a t i o n s t e p .

A process

s t e p was proposed i n which o x i d a t i o n of t h e p r o t a c t i n i u m and uranium, as w e l l as subsequent r e d u c t i o n of about 1% of t h e U4+ t o U3+, would be carr i e d out e l e c t r o l y t i c a l l y .

The estimated c u r r e n t d e n s i t i e s , t h e s i z e of

t h e proposed e l e c t r o l y t i c o x i d a t i o n r e d u c t i o n system, and t h e f e a s i b i l i t y of such a r e d u c t i o n s t e p w i l l be considered i n t h e remainder of t h i s section. The proposed system c o n t a i n s t h r e e e l e c t r o d e s :

a cathode, an anode,

and a t h i r d low-current e l e c t r o d e t h a t f u n c t i o n s sometimes as a cathode and a t o t h e r times as an anode.

The c u r r e n t between t h e f i r s t two e l e c -

t r o d e s i s expected t o be l i m i t e d by t h e r a t e of d i f f u s i o n of U3+ and Pa

t o t h e anode s u r f a c e , where a low c u r r e n t d e n s i t y i s estimated because of t h e low c o n c e n t r a t i o n s of t h e s e m a t e r i a l s i n t h e s a l t .

The t o t a l concen-

t r a t i o n of m a t e r i a l s t o be reduced a t t h e cathode ( p r i m a r i l y U4+) i s h i g h e r by about two o r d e r s of magnitude t h a n t h e t o t a l c o n c e n t r a t i o n of m a t e r i a l s t o be oxidized a t t h e anode, and a c u r r e n t d e n s i t y l i m i t a t i o n i s not expected a t t h e cathode.

11.1 Estimated Anode Current Density f o r t h e Case of No

I n t e r a c t i o n Between P r o t a c t i n i u m and Uranium The maximum r a t e a t which Pa4+ can t r a n s f e r t o t h e anode s u r f a c e i s t h e r a t e which would be obtained by assuming t h e c o n c e n t r a t i o n of Pa be

n e g l i g i b l e a t t h e anode s u r f a c e .

In t h i s case, the

4+ t r a n s f e r Pa

rate

can b e estimated by t h e f o l l o w i n g expression: DCeA

Rpa4+

6 â&#x20AC;&#x2122;

(43)

where

R ~ a 4 =+ r a t e a t which Pa

4+ t r a n s f e r s t o t h e anode s u r f a c e and i s

oxidized t o Pa5+, moles/sec

4+ i n MSBR f u e l s a l t under c o n d i t i o n s p r e s e n t D = d i f f u s i v i t y of Pa n

i n t h e boundary l a y e r a t t h e anode s u r f a c e , cm / s e e , = e f f e c t i v e c o n c e n t r a t i o n of Pa4+ i n t h e b u l k s a l t a d j a c e n t t o

â&#x20AC;&#x2DC;e

t h e anode s u r f a c e , moles/cm

108 A = anode s u r f a c e area, cm2,

6 = t h i c k n e s s of boundary l a y e r a d j a c e n t t o anode s u r f a c e , cm. The e f f e c t of t h e e l e c t r i c a l p o t e n t i a l g r a d i e n t w i t h i n t h e boundary l a y e r has been neglected s i n c e t h e p o t e n t i a l g r a d i e n t w i l l be d i s s i p a t e d by t h e high c o n c e n t r a t i o n of nonreacting i o n s i n t h e l a y e r t h a t w i l l a c t as a supporting e l e c t r o l y t e .

The r e q u i r e d anode s u r f a c e area i s g i v e n , t h e n ,

by r e a r r a n g i n g Eq. ( 4 3 ) t o o b t a i n t h e following e x p r e s s i o n : 6

Rpa4+

A =

(44)

DCe It should b e noted t h a t t h e r a t e a t which Pa 4+ t r a n s f e r s t o t h e anode surf a c e i s approximately equal t o t h e r a t e a t which p r o t a c t i n i u m i s produced It w i l l be u s e f u l , subsequently, t o under d e s i r a b l e o p e r a t i n g c o n d i t i o n s . a l s o n o t e t h e following r e l a t i o n s f o r t h e f r a c t i o n of Pa 4+ t h a t i s o x i d i z e d

t o Pa5+ and f o r t h e r a t e a t which Pa 4+ i s o x i d i z e d t o Pa*+ i n a system ope r a t i n g a t steady state: f = l - Cpa4+out

‘pab+in

’

(45)

where f = f r a c t i o n of Pa4+ t h a t i s oxidized t o Pa 5+ ,

= c o n c e n t r a t i o n of Pa4+ i n b u l k s a l t l e a v i n g anode s u r f a c e , C~a4+out 3 moles/cm , = c o n c e n t r a t i o n of Pa 4+ i n s a l t e n t e r i n g o x i d i z e r from r e a c t o r , Cpa4+in moles/cm3;

and

Rpa4+ = fFC Pa4+ i n ’

(46)

where F = r a t e a t which s a l t i s processed f o r p r o t a c t i n i u m removal, cm3/ s e c .

11.1.1 Case f o r No A x i a l Mixing Along Anode Surface

If t h e r e i s no a x i a l mixing along t h e anode s u r f a c e , t h e e f f e c t i v e Pa

c o n c e n t r a t i o n w i l l b e t h e logarithmic mean average of t h e i n l e t and o u t l e t Pa

4+ c o n c e n t r a t i o n s , which i s given by t h e r e l a t i o n :

ce =

‘pah+in

‘~ab+out

(47)

‘pa4+in

‘pa4+out S u b s t i t u t i o n of Eq. ( 4 7 ) i n t o Eq. ( 4 4 ) y i e l d s t h e following r e l a t i o n f o r t h e r e q u i r e d anode s u r f a c e a r e a : 1 .

In 1 - f

11.1.2 Case f o r Complete Mixing of S a l t Along Anode Surface If t h e s a l t along t h e anode s u r f a c e i s assumed t o be p e r f e c t l y mixed,

t h e e f f e c t i v e Pa

c o n c e n t r a t i o n w i l l be equal t o t h e o u t l e t Pa

4+ concen-

t r a t i o n , which can be expressed by u s e of Eq. ( 4 5 ) i n t h e following manner:

ce S u b s t i t u t i o n of Eq.

= (1 - f ) Cpa4+in’

(49)

( 4 1 ) i n t o Eq. ( 4 4 ) y i e l d s t h e following r e l a t i o n f o r

t h e anode s u r f a c e a r e a i n t h i s c a s e :

A =

‘*pa4+

1 1 - f

DC~a4+in

The p r o c e s s i n g c y c l e time i s d e f i n e d by t h e following r e l a t i o n :

‘I

= V/F,

(51)

110

where T

= p r o c e s s i n g c y c l e time, s e c , P V = volume of f u e l s a l t i n r e a c t o r , cm 3

The p r o t a c t i n i u m removal time i s t h e n r e l a t e d t o t h e p r o c e s s i n g c y c l e time by t h e f o l l o w i n g expression:

where T

R = Pa removal t i m e , s e c .

S u b s t i t u t i o n of Eqs.

(46), ( 5 1 ) ,

and ( 5 2 ) i n t o Eq. ( 5 0 ) y i e l d s t h e f o l l o w i n g

e x p r e s s i o n f o r t h e r e q u i r e d anode s u r f a c e a r e a f o r t h e case i n which p e r f e c t mixing along t h e anode s u r f a c e i s assumed:

11.2 Estimated Anode Current D e n s i t y f o r t h e Case of Equilibrium Between P r o t a c t i n i u m and Uranium I n t h e c a s e s d i s c u s s e d t h u s f a r , no c o n s i d e r a t i o n has been g i v e n t o t h e simultaneous o x i d a t i o n of U3+ t o U 4+ d u r i n g t h e o x i d a t i o n of Pa 4+ or 4+ t o t h e e f f e c t of t h e o x i d a t i o n of uranium on t h e r a t e a t which Pa i s oxidized.

If we assume t h a t p e r f e c t

mixing occurs a l o n g t h e anode s u r f a c e

and t h a t t h e uranium and p r o t a c t i n i u m s p e c i e s a r e a t chemical e q u i l i b r i u m , t h e c o n c e n t r a t i o n s of t h e l a t t e r s p e c i e s a r e r e l a t e d by t h e f o l l o w i n g exp r e s si o n :

where

Cp,5+

= c o n c e n t r a t i o n of Pa5+ i n bulk s a l t , moles/cm 3

111

4+ i n b u l k s a l t , moles/cm 3 , ' ~ a 4 += c o n c e n t r a t i o n of Pa Cu3+ = c o n c e n t r a t i o n of U3+ i n b u l k s a l t , moles/cm 3 ,

Cu4+ = c o n c e n t r a t i o n of U 4+ i n bulk s a l t , moles/cm 3 , Q = equilibrium constant.

The f o l l o w i n g equation shows t h e r e l a t i o n s h i p of t h e Pa5+ and Pa

concen-

4+ t h a t i s oxidized: t r a t i o n s t o t h e f r a c t i o n of t h e Pa

1 1 - f The c o n c e n t r a t i o n of U of b o t h Pa4+ and U3+.

4+ w i l l

remain approximately c o n s t a n t during o x i d a t i o n

Thus, t h e c o n c e n t r a t i o n of U3+ w i l l be g i v e n by t h e

following r e l a t i o n , which i s o b t a i n e d by s u b s t i t u t i n g Eq. ( 5 5 ) i n t o Eq.

(54):

The t o t a l r a t e a t which Pa

4+ and U3+ a r e o x i d i z e d i s given by t h e following

expression:

R = FC Pa 4+i n where R = t o t a l r a t e a t which Pa

f +

F(CU3+in

(57)

cu3+),

and U3+ a r e o x i d i z e d , moles/sec.

If it i s assumed t h a t t h e c o n c e n t r a t i o n s of Pa4+ and U3+ a r e n e g l i g i b l e at

t h e anode s u r f a c e i n comparison w i t h t h e i r c o n c e n t r a t i o n s i n t h e b u l k s a l t , t h e t o t a l r a t e a t which t h e s e m a t e r i a l s a r e o x i d i z e d w i l l a l s o be g i v e n by t h e following expression:

R = -At 6

(Dpa4+ cpa4+

Du3+ cu3+) 3

where At = t o t a l anode s u r f a c e a r e a r e q u i r e d f o r o x i d a t i o n of Pa 2 cm

4+ and U 3+,

112 If Eqs.

( 5 7 ) and (58) a r e equated and i f it i s assumed t h a t t h e d i f f u 4+

and U3+ i n molten s a l t a r e e q u a l , one o b t a i n s t h e f o l -

s i v i t i e s of Pa

lowing r e l a t i o n f o r t h e r e q u i r e d anode s u r f a c e a r e a : ”

= - ti D

‘pa‘+in

‘ ~ 3 + i n- ‘~3+out 9

(59)

‘~ak+in+ ‘~3+out

where D = d i f f u s i v i t y of Pa

4+ or U3+ i n s a l t ,

S u b s t i t u t i o n of Eqs. ( 5 7 ) and (58) y i e l d s t h e following e x p r e s s i o n f o r t h e r e q u i r e d anode s u r f a c e area:

D C ~ a 4n+ fi

‘u4+

l - f + Q 4+ C

An e x p r e s s i o n showing t h e r e l a t i v e anode s u r f a c e a r e a r e q u i r e d f o r t h e c a s e i n which e q u i l i b r i u m i s assumed between t h e p r o t a c t i n i u m and uranium s p e c i e s and t h e c a s e i n which no i n t e r a c t i o n between uranium and p r o t a c t i n i u m i s assumed i s g i v e n by d i v i d i n g E q .

-*t = A

( 6 0 ) by Eq. (SO), which y i e l d s :

f + ‘~a‘+in ‘~3+in

cu4+ cpa4+in

(Y).

‘ T T ~ +

f + Q C

+ ;

The r a t e a t which p r o t a c t i n i u m i s produced i n a 1000-MW(e) MSBR i s about 11.1 moles/day, and t h e c o n c e n t r a t i o n of U4+ i n t h e s a l t i s about 0.0033 mole fraction.

If removal of p r o t a c t i n i u m i n t h e r e a c t o r by neutron c a p t u r e and

r a d i o a c t i v e decay of 233Pa i s n e g l e c t e d , t h e r e l a t i v e c o n c e n t r a t i o n s of U and Pa

i n s a l t e n t e r i n g t h e p r o t a c t i n i u m i s o l a t i o n system w i l l be given by

t h e following r e l a t i o n :

where 'I:

= Pa removal t i m e , days.

Since t h e r a t i o of t h e U3+ c o n c e n t r a t i o n t o t h e U4+ c o n c e n t r a t i o n i n MSBR f u e l s a l t i s about 0 . 0 1 , t h e r a t i o of t h e U3+ and Pa

4+ c o n c e n t r a t i o n s " i n

s a l t e n t e r i n g t h e p r o t a c t i n i u m i s o l a t i o n system i s given by t h e following relation: =

7 .43/rR.

(63)

'~ah+in

S u b s t i t u t i o n of Eqs. ( 6 2 ) and ( 6 3 ) i n t o Eq. ( 6 1 ) y i e l d s t h e following exp r e s s i o n f o r t h e r e l a t i v e anode s u r f a c e a r e a :

-At -A

11.3

'I:

b.43

743Q (1 -

1 + 743Q Tc

C a l c u l a t e d R e s u l t s and Discussion

Processing c y c l e t i m e s of i n t e r e s t ( 3 t o 1 0 days) correspond t o s a l t flow r a t e s of about 1 t o 3 gpm f o r a 1000-MW(e) MSBR. ficients for

4+ and Pa

The d i f f u s i o n coef-

U3+ i n molten s a l t a r e estimated t o be

cm / s e c .

Since t h e s a l t flow r a t e i s r e l a t i v e l y low, r e c i r c u l a t i o n of s a l t through t h e anode compartment w i l l be r e q u i r e d t o achieve Reynolds numbers s u f f i c i e n t l y h i g h t o o b t a i n f i l m t h i c k n e s s e s i n t h e d e s i r e d range of 0 . 0 1 t o 0.05 cm.

For example, a s a l t flow r a t e of 1 gpm through an anode compart-

ment t h a t i s 2 i n . wide and 78.7 i n . ( 2 m ) l o n g corresponds t o a Reynolds number of

1 6 , A film t h i c k n e s s of about 0.03 cm would r e s u l t from a

Reynolds number of 4000 f o r t h e same anode c o n f i g u r a t i o n .

It i s t h u s ap-

p a r e n t t h a t s u f f i c i e n t r e c i r c u l a t i o n of s a l t w i l l be r e q u i r e d i n t h e anode compartment t o g i v e s a l t which w i l l be e s s e n t i a l l y p e r f e c t l y mixed.

t h i s c a s e , Eq. ( 5 0 ) must be used f o r e s t i m a t i n g t h e anode s u r f a c e a r e a r a t h e r t h a n Eq. (48), which a p p l i e s t o t h e c a s e i n which no mixing along t h e anode s u r f a c e i s assumed. Values f o r t h e r e q u i r e d anode s u r f a c e a r e a for s e v e r a l combinations of p r o t a c t i n i u m removal time and p r o c e s s i n g c y c l e time a r e shown i n Table

17.

The minimum r e q u i r e d anode s u r f a c e a r e a ranges from 1 6 . 7 t o 167 m 2 as t h e p r o t a c t i n i u m removal time i s decreased from 1 0 days t o 1 day. An anode a r e a of about 83.5 m 2 i s r e q u i r e d t o o b t a i n a 3-day p r o t a c t i n i u m removal time w i t h a p r o c e s s i n g c y c l e time of 1 day, and an a r e a of 23.9 m 2 i s r e quired t o o b t a i n a p r o t a c t i n i u m removal time of 1 0 days w i t h a p r o c e s s i n g c y c l e time of 3 d a y s o Table 1 7 .

Estimated Values for t h e Required Anode Surface Area f o r t h e Case of No I n t e r a c t i o n Between P r o t a c t i n i u m and Uranium Species Reactor s a l t volume = 1700 f t 3 S a l t film t h i c k n e s s e s = 0.03 cm

Pa Removal Time (days 1

P r o c e s s i n g Cycle Time (days 1

Required Anode Area (m2)

167

55 07

16.7

3 10

1 3

83.5 23.9

Values f o r t h e r e l a t i v e anode s u r f a c e a r e a r e q u i r e d f o r t h e c a s e i n which e q u i l i b r i u m between t h e p r o t a c t i n i u m and uranium s p e c i e s i s assumed a r e shown i n Table 18 for two p r o c e s s i n g c y c l e t i m e s , f o u r p r o t a c t i n i u m removal t i m e s , and two e q u i l i b r i u m c o n s t a n t s t h a t r e p r e s e n t extremes of t h e estimated v a l u e s f o r t h i s c o n s t a n t . 2 6

It i s seen t h a t t h e r e q u i r e d

a r e a depends s t r o n g l y on t h e v a l u e of t h e e q u i l i b r i u m c o n s t a n t and r a n g e s

from about 20% of t h e area r e q u i r e d for t h e c a s e i n which no i n t e r a c t i o n m

of p r o t a c t i n i u m and uranium s p e c i e s i s assumed t o about 11 times t h e area

r e q u i r e d for t h a t c a s e . Table 18. R e l a t i v e Anode Surface Areas Required f o r t h e Case of Equilibrium Between Protactinium and Uranium Species I

Protactinium Removal T i m e (days)

Processing Cycle T i m e (days)

R e l a t i v e Anode Area, A t /A Q = 0.0005 Q = 0.01 ~~

5 097

0.412

5.92

0.266

5-90

0 207

4 6

10.9

0.761

10.8

0.521

10.6

0 330

It i s concluded t h a t e l e c t r o l y t i c o x i d a t i o n of Pa 4+ p r i o r t o p r e c i p i t a t i o n of Pa 0 i s n o t a t t r a c t i v e because of t h e l a r g e anode s u r f a c e a r e a s 25 4+ t o Pa5+ by t h e use o f HFr e q u i r e d . We b e l i e v e t h a t o x i d a t i o n of t h e Pa H,O-H -

mixtures (as suggested by B a e ~ i~s ~more ) promising and recommend

t h a t a d d i t i o n a l d a t a be obtained f o r e v a l u a t i o n of t h i s s t e p .

116

1 2. REFERENCES

1. L. E. McNeese, MSR Program Semiann. Progr. Rept. Feb. 4548, pp. 282-88.

28, 1970, ORNL-

2. M. J. Bell and L. E. McNeese, MSR Program Semiann. Progr. Rept. Aug. 31, ORNL-4622, pp. 199-202. 1970 '

3. MSR Program Semiann. Progr. Rept. Feb. 28, 1970, ORNL-4548, pp. 289-92.

E., Bamberger and C. F. Baes, J r . , J. Nucl. Mater.

35, 177 (1970)

5. L e E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No 7, ORML-TM-3257 , pp. 16-29

6. M. S. Bautista and L e E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No

4 , ORNL-TM-3139 , pp .

38-83.

7. L. E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No. 5, ORNL-TM-3140, pp. 22-30. 8. L. E. McNeese, Engineering Development Studies Reactor Processing NO

f o r Molten-Salt Breeder

6, ORNL-TM-3141 , pp 13-23. e

9. Y. Ohki and H. Inoue, Chem. Eng. Sci, 25, 1 (1970). 10. R. M. Davies and G. I. Taylor, Proc. Roy. SOC. (London), Ser. A 200,

375 (1950). 11. L. E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No. 7, ORNL-TM-3257, pp. 29-46. 12. L. E. McNeese, Engineering Development Studies for Molten-Salt Breeder Reactor Processing No. 1, ORNL-TM-3053, pp. 1-14.

L. E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No. 6, ORNL-TM-3141, pp. 73-79.

14. L. E. McNeese, Engineering Development Studies f o r Molten-Salt Breeder Reactor Processing No. 7, ORNL-TM-3257, pp. 52-56. 15

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26. C. F. Baes, Jr., personal communication to J. S. Watson, May 1970. 27

C. F a Baes, Jr., personal communication to L. E. McNeese. June 8 -

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