Plutonium Partitioning Methods in Power Reactor Fuel Reprocessing

20 Plutonium Partitioning Methods in Power Reactor

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on February 20, 2016 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch020

Fuel Reprocessing ALFRED

S C H N E I D E R and B A R R Y G . W A H L I G

School of Nuclear Engineering, Georgia Institute of Technology, Atlanta, G A 30332

The bismuth phosphate process, developed and used during World War II for the isolation and purification of plutonium, did not provide for the recovery of uranium. Furthermore, this was inherently a batch process and thus not amenable to improvements in chemical processing which can be obtained with continuous operation. In the immediate postwar period, attention was devoted to solvent extraction methods which promised to overcome the shortcomings of the bismuth phosphate process. The Redox process, employing methyl isobutyl ketone (hexone) as the organic solvent and aluminum nitrate as the "salting agent" to promote the extraction of uranium and plutonium, was developed at the Argonne National Laboratory. Pilot-plant testing of the Redox process was done at the Oak Ridge National Laboratory (ORNL) in 1948 and 1949 and its large-scale use started at Hanford in 1952. In the Purex process, tributyl phosphate (TBP) in a hydrocarbon diluent is the organic solvent, while nitric acid is used as the "salting agent." T h i s p r o c e s s , d e v e l o p e d a t a b o u t t h e same t i m e a s t h e Redox p r o c e s s by t h e K n o l l s A t o m i c Power L a b o r a t o r y and ORNL, was p u t i n t o l a r g e - s c a l e o p e r a t i o n a t t h e S a v a n n a h R i v e r P l a n t i n 1954 and a t H a n f o r d i n 1956. O v e r two d e c a d e s l a t e r and a f t e r numerous s t u d i e s o f a l t e r n a t e r e p r o c e s s i n g methods a n d i n t e n s i v e s e a r c h e s f o r b e t t e r s o l v e n t s , the Purex p r o c e s s remains the prime r e p r o c e s s i n g method f o r s p e n t n u c l e a r f u e l s t h r o u g h o u t t h e w o r l d . Uranium-Plutonium P a r t i t i o n i n g i n the

Purex

Process

Tljie U - P u s e p a r a t i o n i s b a s ^ d o n t h e much l o w e r e x t r a c t a b i l i t y of Pu i o n s by TBP t h a n o f Pu i o n s and t h e r e l a t i v e e a s e o f o x i d a t i o n and r e d u c t i o n o f p l u t o n i u m i n s o l u t i o n s . The o r i g i n a l Purex p r o c e s s u t i l i z e d F e to a c h i e v e the r e d u c t i o n of Pu* to Pu . Since n i t r i t e i o n s , which are g e n e r a l l y present i n n i t r i c acid solutions, reoxidize Pu and t h u s a f f e c t t h e n e t r e d u c t i o n r a t e , a " h o l d i n g r e d u c t a n t " i s added t o s c a v e n g e n i t r i t e i o n s . S u l f a m a t e i o n , N H S 0 i s a n e f f e c t i v e h o l d i n g r e d u c t a n t and t h i s l e d to the s e l e c t i o n of f e r r o u s s u l f a m a t e , F e ( N H S 0 ) a s the 3

+

2

3

2

3

2

3

2

0-8412-0527-2/80/47-117-279$05.00/0 © 1980 American C h e m i c a l Society In Actinide Separations; Navratil, James D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


280

ACTINIDE SEPARATIONS

r e d u c i n g a g e n t i n t h e o r i g i n a l P u r e x p r o c e s s (_1>_2)· The U - P u p a r t i t i o n i n g i s done i n c o u n t e r c u r r e n t s o l v e n t e x t r a c t i o n c o n t a c t o r s ( F i g , 1). S e v e r a l i n c e n t i v e s arose f o r m o d i f y i n g the o r i g i n a l p a r t i t i o n i n g method w i t h f e r r o u s s u l f a m a t e : t h e c o r r o s i v e a c t i o n o f b o t h i r o n and s u l f a t e ( t h e e v e n t u a l d e g r a d a t i o n p r o d u c t o f s u l f a m a t e i o n s ) on p r o c e s s e q u i p m e n t , p a r t i c u l a r l y the h i g h l e v e l l i q u i d waste t a n k s ; the d e s i r e to a v o i d the i n t r o d u c t i o n of a d d i t i o n a l s a l t s i n t h e w a s t e ; t h e much h i g h e r p l u t o n i u m c o n t e n t o f power r e a c t o r f u e l s , e s p e c i a l l y Pu b r e e d e r f u e l , compared w i t h t h a t i n t h e i r r a d i a t e d u r a n i u m f r o m Pu p r o d u c t i o n r e a c t o r s ; a n d t h e much g r e a t e r b u r n u p and c o n s e q u e n t l y f i s s i o n p r o d u c t c o n t e n t o f power r e a c t o r f u e l s . The m o d i f i c a t i o n s were g e n e r a l l y a i m e d at replacement of F e and N H S 0 ~ w i t h o t h e r r e a g e n t s b u t , more r e c e n t l y , t h e r e have b e e n more r a d i c a l d e v e l o p m e n t s i n v o l v i n g n o v e l e q u i p m e n t c o n c e p t s and f l o w s h e e t m o d i f i c a t i o n s . 2

Alternate

2

R e d u c i n g A g e n t s and H o l d i n g

Reductants

H y d r a z i n e ( N H ^ ) was f o u n d t o be a n e f f e c t i v e s c a v e n g e r of N 0 i o n s and t h u s a p r o m i s i n g h o l d i n g r e d u c t a n t . Production s c a l e t e s t s a t H a n f o r d i n 1968 w i t h h y d r a z i n e - s t a b i l i z e d f e r r o u s n i t r a t e were p l a g u e d by p r o b l e m s a s s o c i a t e d w i t h t h e c a r r y o v e r o f n i t r i t e , t h o u g h t h e s o u n d n e s s o f t h i s method was d e m o n s t r a t e d 2

2

(3).

^

+

U* r e d u c e s Pu* to P u and was shown t o be a n e f f e c t i v e reductant f o r U-Pu p a r t i t i o n i n g (4). The n e t r e a c t i o n i s : 1

1

2Pu*

+

3

+ υ" — * +

2Pu

3 +

+ U

6

+

.

W h i l e t h e u s e o f υ*"" a v o i d s t h e i n t r o d u c t i o n o f e x t r a n e o u s m e t a l i o n s , t h e h o l d i n g r e d u c t a n t must be r e t a i n e d t o p r e v e n t n o t o n l y t h e r e o x i d a t i o n o f Pu , but a l s o the a u t o c a t a l y t i c oxida t i o n o f U* to U . H y d r a z i n e has b e e n t h e p r e f e r r e d h o l d i n g reductant. S e v e r a l methods a r e a v a i l a b l e f o r t h e p r o d u c t i o n o f U ( N 0 ) : c a t a l y t i c or e l e c t r o l y t i c r e d u c t i o n of U 0 ( N 0 ) ; d i s s o l u t i o n o f t h e h y d r a t e d o x i d e o f U* i n n i t r i c a c i d ; aluminum powder r e d u c t i o n of U 0 ( N 0 ) ; e t c . The p a r t i t i o n i n g method u s i n g U ( N 0 ) - h y d r a z i n e was t r i e d a t H a n f o r d i n 1970 and h a s b e e n e m p l o y e d i n r e p r o c e s s i n g p l a n t s i n W e s t e r n E u r o p e , J a p a n , and the Soviet Union. While p a r t i t i o n i n g with U * i s generally satisfac t o r y , the need to i n t r o d u c e a d d i t i o n a l uranium i n t o the p r o c e s s s t r e a m s h a s two d r a w b a c k s : f u e l s with high plutonium content ( e . g . b r e e d e r f u e l ) may r e q u i r e a s u b s t a n t i a l i n c r e a s e i n t h r o u g h p u t c a p a c i t y to accomodate the l a r g e e x c e s s of u r a n i u m ; and, u n l e s s the U e n r i c h m e n t of t h e u r a n i u m r e d u c t a n t matches t h a t of the uranium i n the f u e l , t h e r e i s a l o s s i n the v a l u e of the recovered uranium. T h i s l e d to the development of i n s i t u U * p r o d u c t i o n , such as the e l e c t r o c h e m i c a l m e t h o d s ^ d e s c r i b e d below. The i n s i t u p h o t o c h e m i c a l p r o d u c t i o n o f U c o n t a i n e d i n the o r g a n i c phase has a l s o been s t u d i e d ( 3 4 , 3 5 ) . 1

6

S

%

2

3

2

1

2

3

3

2

k

+

2

3

5

1

In Actinide Separations; Navratil, James D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

SCHNEIDER

A N D WAHLIG

Pu Partitioning

H90

R.A. &

HNo

281

Methods to SR.

3

4

HNOo


-1

U,Pu,F.R

TBP

I

TBP

1

F. P.

Pu

Figure la. Chssical Purex partitioning schemes—early partitioning; ( ) aque ous streams, ( ) organic streams; R. Α., reducing agent; TBP, n-tributyl phos phate in an aliphatic diluent; S. R., solvent recovery.

HNO3 (DIL.)

to

R.A. &

S.R

HNO3

A

HNOo

J

H 0 2

A

HNOn

U,Pu,F.P.

TBP

TBP

6>L

F.P.

Figure lb.

U,Pu

to S.R.

TBP

Pu

Chssical Purex partitioning schemes—late partitioning



282


H y d r o x y l a m i n e s a l t s were f o u n d t o be good r e d u c t a n t s o f p l u tonium, under c e r t a i n c o n d i t i o n s ( 5 ) . I n t e r e s t i n these reducing a g e n t s stemmed f r o m t h e d e s i r e t o a v o i d t h e i n t r o d u c t i o n o f m e t a l l i c c a t i o n s i n the separated plutonium product. Hydro x y l a m i n e s u l f a t e was u s e d o n a l a r g e s c a l e a t t h e S a v a n n a h R i v e r P l a n t (6)· W h i l e p a r t i t i o n i n g was s a t i s f a c t o r y , t h e o b j e c t i o n a b l e presence o f s u l f a t e i o n s l e d t o the a d o p t i o n of hydroxylamine n i t r a t e (HAN). The r e a c t i o n mechanism a n d k i n e t i c s o f t h e HAN r e d u c t i o n o f p l u t o n i u m h a v e b e e n s t u d i e d e x t e n s i v e l y (_7>j8)« The m a j o r p r o b l e m w i t h HAN h a s b e e n t h e s l o w r e d u c t i o n r a t e w i t h i n c r e a s i n g HN0 c o n c e n t r a t i o n s . Barney d e r i v e d the f o l l o w i n g e q u a t i o n w h i c h r e l a t e s t h e Pu r e d u c t i o n r a t e w i t h t h e r e c i p r o c a l 3

°f[HV:

,

-d[p»(IV)] d t

,

.

tPu(IV)]'[NH OH]'

r

3

- k -

W

:

[Pu(III)]

2

[H J* ( K + { Ν θ 7 ] ) +

2

d

W h i l e a l o w HNO3 c o n c e n t r a t i o n i s p o s s i b l e i n p l u t o n i u m p u r i f i c a t i o n c y c l e s , a h i g h e r HN0 c o n c e n t r a t i o n i s n e c e s s a r y t o r e t a i n the uranium i n t h e o r g a n i c phase d u r i n g t h e p r i m a r y U - P u p a r t i tioning. P l a n t - s c a l e e x p e r i e n c e was o b t a i n e d a t H a n f o r d w i t h HAN i n t h e s e c o n d Pu a n d U c y c l e s (_3 ) , a n d a t S a v a n n a h R i v e r i n t h e p r i m a r y p a r t i t i o n i n g c y c l e , where HAN was p a r t i c u l a r l y effective when u s e d w i t h F e ( N 0 ) , a s w e l l a s i n t h e s e c o n d p l u t o n i u m c y c l e (6,_9). Two a p p r o a c h e s were p r o p o s e d t o a l l e v i a t e t h e a f o r e m e n t i o n e d p r o b l e m w i t h u n f a v o r a b l e k i n e t i c s when HAN i s u s e d i n t h e primary U-Pu p a r t i t i o n i n g : A l o w a c i d s c r u b c o n t a i n i n g HAN a n d NjH^ i s i n t r o d u c e d a t t h e t o p o f t h e p a r t i t i o n i n g c o l u m n w h i c h r e d u c e s a l l o f t h e Pu and caus_es i t t o s t r i p i n t o t h e aqueous phase a l o n g w i t h some o f t h e U , w h i l e a h i g h a c i d s t r e a m i s i n t r o d u c e d i n t h e l o w e r p a r t o f t h e column which c a u s e s t h e uranium t o t r a n s f e r back i n t o the o r g a n i c phase. The i n t e r n a l r e f l u x i n g of uranium e v e n t u a l l y l e a d s t o near s a t u r a t i o n of the s o l v e n t , which f u r t h e r enhances the s t r i p p i n g of the p l u t o n i u m . 3

3

2

6

The s e c o n d a p p r o a c h , w h i c h r e p r e s e n t s a d e p a r t u r e f r o m p r e v i o u s J^urex p a r t i t i o n i n g , p r o v i d e s f o r the q u a n t i t a t i v e reduction o f Pu t o Pu w i t h HAN a n d Ν Η^ ( a s t h e h o l d i n g r e d u c t a n t ) p r i o r to the i n t r o d u c t i o n of t h e U - and P u - c o n t a i n i n g f e e d i n t o a second c y c l e e x t r a c t i o n column ( F i g . 2 ) . T h i s method was p r o p o s e d f o r b o t h t h e EXXON r e p r o c e s s i n g p l a n t i n T e n n e s s e e ( 1 0 ) a n d t h e ORNL R e p r o c e s s i n g F a c i l i t y f o r LMFBR f u e l (_1_1). HAN w i l l c o n t i n u e t o be a n a t t r a c t i v e r e d u c t a n t b e c a u s e , n o t o n l y i s t h e i n t r o d u c t i o n o f m e t a l l i c c a t i o n s a v o i d e d , b u t HAN i s decomposed s a f e l y b y h e a t i n g a t t e m p e r a t u r e s above 6 0 ° C , w h i c h s i m p l i f i e s t h e r e o x i d a t i o n o f Pu t o Pu** p r i o r to subsequent e x t r a c t i o n cycles. 2

H y d r o g e n i n tljie p r e s e n c e o f a r e d u c t i o n c a t a l y s t w i l l a l s o r e d u c e Pu t o Pu and c a n t h u s be u s e d a s a r e d u c t a n t f o r U - P u partitioning. The f e a s i b i l i t y o f t h i s c o n c e p t was d e m o n s t r a t e d i n 1965 ( 3 8 , 3 9 ) .


20.

Electrochemical


Pu Partitioning

SCHNEIDER AND W A H L i G

283

Methods

Partitioning

The s e a r c h f o r a n i n s i t u r e d u c t i o n o f U and P u to avoid t h e need f o r t h e i n t r o d u c t i o n o f e x t r a n e o u s U into a partitioni n g c o l u m n , l e d S c h n e i d e r and c o w o r k e r s t o i n v e s t i g a t e , i n 1967, the e l e c t r o l y t i c r e d u c t i o n of uranium i n a heterogeneous dispers i o n o f t h e T B P - c o n t a i n i n g s o l v e n t i n the c o n t i n u o u s aqueous phase ( 1 2 ) . These s t u d i e s p r o g r e s s e d r a p i d l y from s m a l l - s c a l e c e l l experiments w i t h uranium and p l u t o n i u m t o the s u c c e s s f u l development of s e v e r a l types of l a r g e - s c a l e "electropulse columns" (13) ( F i g . 3 ) . A f u l l - s c a l e u n i t with a nominal p l u t o nium p a r t i t i o n i n g c a p a c i t y i n e x c e s s o f 75 k i l o g r a m s p e r d a y was i n s t a l l e d at the Barnwell Nuclear F u e l P l a n t i n South C a r o l i n a . P l a n t c h e c k o u t s o f t h i s u n i t , u s i n g o n l y u r a n i u m , have b^en i n p r o g r e s s s i n c e 1977. In these t e s t s , the f r a c t i o n of U reduced t o U * was d e t e r m i n e d f o r a w i d e r a n g e o f o p e r a t i n g c o n d i t i o n s . 6

+

%

+

%

+

6

B a u m g a r t n e r a n d c o w o r k e r s a t K a r l s r u h e h a v e , s i n c e 1968, done numerous s t u d i e s o n t h e a p p l i c a t i o n o f e l e c t r o l y t i c reduct i o n - o x i d a t i o n methods t o P u r e x r e p r o c e s s i n g schemes ( 1 5 , 1 6 ) (Fig. 4). The u t i l i t y o f t h e i n s i t u e l e c t r o l y t i c reduction method was d e m o n s t r a t e d w i t h good r e s u l t s o n a s m a l l s c a l e f o r a b r e e d e r r e a c t o r f u e l c o n t a i n i n g 15% Pu ( 1 7 ) . E l e c t r o l y t i c reduct i o n s t u d i e s were r e p o r t e d i n F r a n c e ( 1 8 ) , t h e S o v i e t U n i o n (_19,_20), t h e U n i t e d Kingdom (27), a n d C h i n a (_37). N o n - R e d u c t i v e P a r t i t i o n i n g Methods S e v e r a l methods were p r o p o s e d f o r P u - U p a r t i t i o n i n g w h i c h a r e n o t based on a r e d u c t i o n o f p l u t o n i u m t o t h e l e s s e x t r a c t a b l e trivalent state. The s e p a r a t i o n i s a c h i e v e d by e i t h e r f o r m i n g a q u e o u s Pu* c o m p l e x e s w h i c h have a l o w s o l u b i l i t y i n t h e T B P h y d r o c a r b o n s o l v e n t o r by s a t u r a t i n g t h e o r g a n i c s o l v e n t w i t h uranium, which depresses the e x t r a c t a b i l i t y of p l u t o n i u m . 1

C o m p l e x i n g w i t h H S 0 h a s been u s e d f o r some t i m e t o promote t h e s t r i p p i n g o f p l u t o n i u m f r o m TBP s o l u t i o n s . The U - P u p a r t i t i o n i n g i n s m a l l - s c a l e reprocessing t r i a l s of h i g h l y i r r a d i a t e d f a s t r e a c t o r f u e l was done a t W i n d s c a l e by s c r u b b i n g w i t h d i l u t e HjSO^ ( 2 1 ) . T h o u g h t h e P u - U p a r t i t i o n i n g a c h i e v e d was s a t i s f a c t o r y , c o n t i n u e d use of H S 0 i s not f o r e s e e n because of i t s c o r r o s i v e n e s s and i n c o m p a t i b i l i t y w i t h e v e n t u a l waste s o l i d i f i c a tion processes. 2

k

2

%

T h e u t i l i t y of c a r b o x y l i c a c i d s ( f o r m i c , a c e t i c ) , which a l s o f o r m Pu** c o m p l e x e s s p a r s e l y s o l u b l e i n TBP s o l u t i o n s , was i n v e s t i g a t e d by G e r m a i n (_22) a n d McKay ^ 2 3 ) . The r e s u l t s were n o t encouraging. +

A p a r t i t i o n i n g method w h i c h d o e s n o t r e q u i r e any a d d i t i v e s was p r o p o s e d by Weech ( 2 4 ) . The p l u t o n i u m s e p a r a t i o n i s a c c o m p l i s h e d by r e c y c l i n g p a r t o f t h e s e p a r a t e d u r a n i u m t o a r e f l u x column i n which a h i g h s a t u r a t i o n of uranium i s m a i n t a i n e d i n the organic phase. The p l u t o n i u m e x t r a c t i o n i s t h u s g r e a t l y


284

ACTINIDE

H A N , N H„

to

&HN0 (dil.)

SR.

2

3

HN0

HAN,N H 2

4 /

&HNO3

3

* l

*

SEPARATIONS

HNO, (d il.)

π -Ε*—

J

to S.R.

. .1

HAN & N H


2

4

Feed

U,Pu,F.R

Adjustment HNO3

(cone.)

TBP

TBP^

F.P.

U,Pu

Pu

Figure 2. Prereduction partitioning scheme; HAN, hydroxyhmine nitrate; hydrazine.

Figure 3. AGNS laboratory-scale elec tropulse column: 1, diaphragm; 2, cath ode; 3, anode; 4, spacers; 5, cathode bus bar; 6, anode bus bar; 7, cathode cham ber; 8, anode chamber; 9, organic feed; 10, organic effluent; 11, aqueous feed; 12, aqueous effluent; 13, anolyte effluent; 15, air purge; 16, air purge; 17, vent; 18, vent; 19, thermocouple; 20, pulse leg.

Allied-General Nuclear Services


NH 2

h

SCHNEIDER AND W A H L i G

Pu Partitioning Methods


20.

Figure 4.

KFK electrolytic contactors; a. mixer settler, b. pulsed column.


286

ACTINIDE

SEPARATIONS

depressed. I t i s c l a i m e d t h a t by s u i t a b l e c o n t r o l o f t h e HN0 c o n t e n t i n the lower p a r t of the r e f l u x column, t h a t a c c e p t a b l e d e c o n t a m i n a t i o n s were o b t a i n e d f r o m P u i n t h e o r g a n i c s t r e a m c o n t a i n i n g U a n d f r o m U i n t h e a q u e o u s s t r e a m c o n t a i n i n g Pu a n d N p .


3

A more r a d i c a l m o d i f i c a t i o n o f t h e P u r e x p r o c e s s , the A q u a f l u o r p r o c e s s , d e v e l o p e d by G e n e r a l E l e c t r i c f o r i t s M i d w e s t F u e l R e c o v e r y P l a n t , r e t a i n e d o n l y a s i n g l e TBP c o - d e c o n t a m i n a t i o n c y c l e f o l l o w e d by a c o n t i n u o u s a n i o n exchange c o n t a c t o r i n w h i c h p l u t o n i u m was t o be removed f r o m t h e U - P u n i t r a t e s o l u t i o n . The p e r f o r m a n c e o f t h i s p l a n t was n e v e r t e s t e d w i t h p l u t o n i u m , s i n c e G e n e r a l E l e c t r i c d e c i d e d to f o r e g o o p e r a t i o n of the p l a n t after t e c h n i c a l d i f f i c u l t i e s developed d u r i n g the " c o l d " c h e c k out t r i a l s . Equipment Conventional solvent extraction contactors, mixer-settlers o r p u l s e d c o l u m n s , have b e e n u s e d e x c l u s i v e l y u n t i l now f o r t h e Pu-U p a r t i t i o n i n g s t e p . C e n t r i f u g a l c o n t a c t o r s have been c o n s i d e r e d , b u t t h e r e has b e e n some c o n c e r n a b o u t t h e c o m p a t i b i l i t y o f s h o r t r e s i d e n c e time w i t h the k i n e t i c s of p l u t o n i u m r e d u c t i o n . The d e v e l o p m e n t o f i n s i t u e l e c t r o l y t i c methods by A l l i e d Chemical r e s u l t e d i n a n o v e l u n i t , the e l e c t r o p u l s e column, i n w h i c h mass t r a n s f e r and e l e c t r o l y t i c r e d u c t i o n a r e c a r r i e d o u t simultaneously (25). The b a s i c f e a t u r e o f t h e e l e c t r o p u l s e column, ( F i g . 3 ) , i s the d u a l f u n c t i o n of the h o r i z o n t a l p e r f o r a t e d p l a t e s , a c t i n g a s c a t h o d e s a s w e l l as p u l s e p l a t e s , and t h e i n t r o d u c t i o n o f v e r t i c a l anode s c r e e n s c o n t a i n e d i n p o r o u s ceramic sleeves. T h i s d e s i g n was f o u n d p a r t i c u l a r l y s u i t a b l e f o r Pu-U p a r t i t i o n i n g , s i n c e i t p e r m i t s o p e r a t i o n w i t h an a q u e o u s c o n t i n u o u s p h a s e , w h i c h i s needed to m a i n t a i n adequate e l e c t r i c a l c o n d u c t i v i t y , w h i l e t h e o r g a n i c t o aqueous f l o w r a t i o i s k e p t q u i t e l a r g e to o b t a i n a h i g h p l u t o n i u m c o n c e n t r a t i o n i n the e x i t i n g aqueous s t r e a m . The p a r a l l e l e l e c t r o l y t i c r e d u c t i o n d e v e l o p m e n t s a t K a r l s r u h e a p p e a r t o h a v e c o n c e n t r a t e d i n i t i a l l y more on t h e r e d u c t i o n o f Pu and U i n e l e c t r o d e - e q u i p p e d m i x e r - s e t t l e r s i n w h i c h t h e r e d u c t i o n o c c u r r e d l a r g e l y i n t h e s e t t l e d aqueous phase r a t h e r than i n a heterogeneous m i x t u r e . I t was d e t e r m i n e d t h a t a s e p a r a t i n g membrane^may n o t be n e c e s s a r y b e c a u s e o f t h e r e d o x p o t e n t i a l s i n the U * - U - U s y s t e m and t h e a b s e n c e o f g a s e o u s p r o d u c t s at the e l e c t r o d e s which c o u l d l e a d to e x p l o s i v e m i x tures. A p u l s e d column, w i t h i n t e r n a l s q u i t e d i f f e r e n t from t h o s e o f A l l i e d C h e m i c a l ' s e l e c t r o p u l s e c o l u m n , was e v e n t u a l l y d e v e l o p e d and s u c c e s s f u l l y t e s t e d ( 1 5 , 2 6 ) ( F i g . 4). +

5

8

+

A c o m b i n e d e l e c t r o c h e m i c a l c e l l and p u l s e d s o l v e n t e x t r a c t i o n c o l u m n i n w h i c h one o f t h e e l e c t r o d e s c o n s i s t s o f a bed o f e l e c t r i c a l l y c o n d u c t i n g p a r t i c l e s was d e v e l o p e d a t t h e U . K . Atomic Energy A u t h o r i t y (27).


20.

Pu Partitioning

SCHNEIDER AND w A H L i G

Methods

287


Flowsheet M o d i f i c a t i o n s The l o c a t i o n o f t h e P u - U p a r t i t i o n i n g s t e p i n P u r e x f l o w s h e e t s and t h e s e l e c t i o n of s p e c i f i c o p e r a t i n g v a r i a b l e s ( f l o w rates, concentrations, t e m p e r a t u r e ) were g e n e r a l l y d e t e r m i n e d by t h e t y p e o f f u e l t o be r e p r o c e s s e d , t h e s u b s e q u e n t w a s t e management s c h e m e s , a n d t h e d e s i r e d c h a r a c t e r i s t i c s o f t h e p r o d u c t s . The P u r e x P r o c e s s h a s b e e n u s e d e i t h e r w i t h " e a r l y " o r w i t h " l a t e " Pu-U p a r t i t i o n i n g ( F i g . 1). The e a r l y s p l i t i n t h e f i r s t c y c l e a v o i d s t h e c o - s t r i p p i n g o f u r a n i u m a n d p l u t o n i u m w h i c h may r e s u l t i n higher plutonium l o s s e s . In other f l o w s h e e t s , the p a r t i t i o n i n g i s d e l a y e d u n t i l the second c y c l e . W h i l e no p a r t i c u l a r t r e n d h a s b e e n o b v i o u s , some o f t h e r e c e n t f l o w s h e e t s i n which the plutonium i s reduced p r i o r to r e - e x t r a c t i o n (10,11) w i l l n e c e s s a r i l y r e q u i r e a second c y c l e p a r t i t i o n i n g . C o n s i d e r a b l e e f f o r t has been d e v o t e d i n r e c e n t y e a r s t o f l o w s h e e t s w h i c h a r e more " p r o l i f e r a t i o n r e s i s t a n t . " This genera l l y c o n s i s t s o f a v o i d i n g t h e s e p a r a t i o n o f p u r e p l u t o n i u m , by e i t h e r p r o v i d i n g f o r c o - p r o c e s s i n g ( i . e . a p a r t i a l Pu-U p a r t i t i o n i n g ) or incomplete removal of f i s s i o n products ( " s p i k i n g " ) , to c o m p l i c a t e the subsequent m a n i p u l a t i o n s w i t h p l u t o n i u m . There a r e no f u n d a m e n t a l r e a s o n s why a n y o f t h e p a r t i t i o n i n g methods d e s c r i b e d c o u l d n o t be a d a p t e d t o c o - p r o c e s s i n g a n d p a r t i a l d e c o n t a m i n a t i o n a n d t h e r e s u l t s o f s e v e r a l s t u d i e s were p u b l i s h e d (28, 2 9 , 3 0 , 3 1 , 3 2 ) . A . M o c c i a and c o w o r k e r s r e p o r t e d good r e s u l t s w i t h the use of l o n g - c h a i n a l i p h a t i c amides f o r the s e l e c t i v e e x t r a c t i o n of U f r o m HN0 s o l u t i o n s o f U and Pu" ( 3 6 ) . This i s b e l i e v e d t o be u s e f u l i n c o - p r o c e s s i n g f l o w s h e e t s where t h e Pu-U p a r t i t i o n i n g i s l i m i t e d t o the removal of a s m a l l f r a c t i o n of excess uranium. I n t e r e s t has a l s o developed i n s o - c a l l e d "denatured f u e l c y c l e s , " u s u a l l y based on U-Th r e a c t o r s , i n which the U produced i s d i l u t e d w i t h n a t u r a l uranium to a f i s s i l e c o n t e n t b e l o w 12%. S i n c e a p p r e c i a b l e amounts o f p l u t o n i u m w i l l be p r o d u c e d i n s u c h f u e l , t h e r e p r o c e s s i n g f l o w s h e e t s must p r o v i d e f o r some P u - T h - U s e p a r a t i o n s . C o n c e p t u a l f l o w s h e e t s have b e e n developed f o r s e v e r a l cases (33) ( F i g . 5 ) . T y p i c a l l y , U , P u , and Th a r e c o - e x t r a c t e d i n t o a TBP s o l u t i o n a n d Pu i s p a r t i t i o n e d by r e d u c t i v e s t r i p p i n g i n the f i r s t c y c l e . P a r t i a l or complete p a r t i t i o n i n g o f U a n d Th i s o b t a i n e d by a T h - l i m i t i n g extraction i n a second c y c l e . Additional p u r i f i c a t i o n cycles are foreseen f o r the P u , T h , and U ( o r T h - U ) p r o d u c t s . 6

2

3

3

6

3

Conclusions The P u r e x p r o c e s s w i l l c o n t i n u e t o be t h e m a i n method f o r the r e p r o c e s s i n g o f n u c l e a r r e a c t o r f u e l s . The i n h e r e n t f l e x i b i l i t y o f t h i s p r o c e s s a l l o w s f o r m o d i f i c a t i o n s needed to accomod a t e a l a r g e range of f u e l c o m p o s i t i o n s and p r o d u c t s p e c i f i c a tions. Among t h e s e v e r a l p l u t o n i u m p a r t i t i o n i n g methods d e v e l oped, those a v o i d i n g the i n t r o d u c t i o n of extraneous metal ions



288 R.A.

HoO

&HNO3

4

HNOo


~

H 0

to

to

2

S.R. HNO-3

S.R.

'

Ί

JULPu, Th,F.P.

TBP

TBP

F.P.

Pu

Figure 5.

UJh

Th(part)

Partitioning scheme for U-Pu-Th

Th(part),U

fuel

( e . g . U , H A N , e l e c t r o l y t i c ) a r e l i k e l y t o be f a v o r e d . In s i t u r e d u c t i o n methods h a v e i n t r o d u c e d new e q u i p m e n t c o n c e p t s w h i c h may be p a r t i c u l a r l y w e l l s u i t e d f o r t h e p r o c e s s i n g o f b r e e d e r f u e l with high plutonium content.

Literature Cited 1. 2.

3. 4.

5. 6.

Irish, E. R., and Reas, W. Η., "Symposium on the Reprocessing of Irradiated Fuels, Held at Brussels," USAEC Report TID-7534 (Bk. 1), 1976; pp. 83-106. Cooper, V. R., and Walling, Jr., M. T., "Proceedings of the Second International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958," United Nations, N.Y., 1959; pp. 291-323. Walser, R. L . , "The Hanford Purex Plant Experience with Reductants," USAEC Report ARH-SA-69, Atlantic Richfield Hanford Co., Richland, WA, 1970. Schlea, C. S., Caverly, M. R., Henry, Η. Ε., and Jenkins, W. J., "Uranium (IV) Nitrate as a Reducing Agent for Pluto nium (IV) in the Purex Process," USAEC Report DP-808, Ε. I. du Pont de Nemours & Co., Aiken, S.C. 1963. Seaborg, G. T., Ed., "The Actinide Elements," McGraw-Hill Book Co., Inc., New York, 1954; pp. 274-276. Orth, D. Α., McKibben, J. Μ., and Scotten, W. C., "Proceed ings of the International Solvent Extraction Conference I.S.E.C. 71," Soc. of Chemical Industry, London, 1971; pp. 514-533.


20. SCHNEIDER AND WAHLIG 7.

8.


9. 10. 11. 12.

13.

14.

15. 16. 17. 18. 19. 20. 21.

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289

Richardson, G. L . , and Swanson, J. L . , "Plutonium Partition ing in the Purex Process with Hydrazine-Stabilized Hydroxyl amine Nitrate," Report HEDL-TME-75-31, Hanford Engineering Development Lab., Richland, WA, 1975. Barney, G. S., "Kinetic Study of the Reaction of Pu(IV) with Hydroxylamine," Report ARH-SA-207, Atlantic Richfield Hanford Co., Richland, WA, 1975. Thompson M. C., Burney, G. Α., and McKibben, J. Μ., "Recent Savannah River Experience with Actinide Separations," Paper presented at this Conf. (INDE #142). Exxon Nuclear Co., "PSAR Nuclear Fuel Recovery and Recycling Center," Vol. 4, US NRC, Docket-50564-7; 1976. Irvine, A. R., and Jones, F. J., "LMFBR Spent Fuel Repro cessing: A Study of an Industrial-Scale Facility," Report ORNL/TM-5723, Oak Ridge National Lab., 1977. Schneider, Α., and Ayers, A. L . , (to Allied Chemical Corp.), "Electrochemical Concentration of Metallic Solutions," and "Electrochemical Oxidation or Reduction," U.S. Patents 3,616,275 and 3,616,276; 1971. Cermak, A. F., Gray, J. Η., Murbach, E. W., Neace, J. C., and Spaunburgh, R. G., "Development of the Electropulse Column for the BNFP," in Back End of the LWR Fuel Cycle Conf. held in Savannah, GA, 1978 (CONF-780304), p. V-11. Cermak, A. F., and Spaunburgh, R. G., "Development of the Electropulse Column for Uranium-Plutonium Partitioning in the AGNS Reprocessing Plant," Paper presented at this Conf. (INDE #162). Schmieder, H., Baumgärtner, F., Goldacker, Η., and Hausberger, Η., "Electrolytic Methods in the Purex Process," Report KFK2082 (in German) Kernforschungszentrum Karlsruhe, 1974. Baumgärtner, F., Goldacker, Η., and Schmieder, Η., "Electro redox Procedures for Plutonium in Power Reactor Fuel Repro cessing," Paper presented at this Conf. (INDE #163). Ochsenfeld, W., "Versuche zur Aufarbeitung von Schnell -Brüter Brennstoffen in der Anlage MILLI," Report KFK-2396 (in German), Kernforschungszentrum Karlsruhe, 1977. Miquel, P., and Boudry, J. C., "First Experiments on the Reprocessing of Fast Reactor Fuels in France," Paper presented at 82nd AIChE Mtg., Atlantic City, N.J., 1976. Fomin, V. V., Atomnaya Energia, 1977, 43, 481. Dem'ianovich, Μ. Α., Atomnaya Energia, 1977, 43, 486. Warner, B. F., Naylor, Α., Duncan, Α., and Wilson, P. D., "Proceedings of the International Solvent Extraction Conf. I.S.E.C. 74," Soc. of Chem. Industry, London, 1974, pp. 1481-1497. Germain, Μ., Bathellier, Α., and Berard, P., "Proceedings of the International Solvent Extraction Conf. I.S.E.C. 74," Soc. of Chem. Industry, London, 1974, pp. 2075-2092. McKay, H. A. C., Miles, J. Η., and Park, H. S., "Possible Use of Carboxylic Acids for U/Pu Separation in Nuclear Fuel Reprocessing," Report AERE-R-8509, Harwell, U.K., 1976.


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RECEIVED May 14, 1979.


Plutonium Partitioning Methods in Power Reactor Fuel Reprocessing

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