28 Flowsheet Development Work at the Idaho Chemical Processing Plant for the Partitioning of Actinides from Acidic Nuclear Waste L. D. McISAAC, J. D. BAKER, J. F. KRUPA, D. H. MEIKRANTZ, and N. C. SCHROEDER Allied Chemical Corporation-Idaho Chemical Programs, Idaho National Engineering Laboratory, Idaho Falls, ID 83401 The Idaho Chemical Processing Plant (ICPP) located at the Idaho National Engineering Laboratory near Idaho F a l l s , Idaho is a multipurpose reprocessing f a c i l i t y for DOE fuels containing highly enriched uranium. Fuels routinely processed at ICPP include stainless-steel-clad fast-reactor fuels, aluminum-clad test-reactor fuels, and zirconium-clad fuels for which the U enrichments before burnup vary from 50 to 93%. The stainless-steel-clad fuel is e l e c t r o l y t i c a l l y dissolved in HNO , the aluminum-clad fuels are dissolved in HNO -Hg(NO ) , and zirconium-clad fuels are dissolved in HF and HNO . These multi-headend dissolver solutions provide the feed for a single solvent extraction system which is comprised of a first cycle of TBP extraction followed by two cycles of methyl-isobutyl ketone extraction. The uranyl nitrate product from the extraction system is denitrated in a fluidized bed denitrator toUO for shipment. The aqueous fission product wastes resulting from the ICPP solvent extraction operations contain small amounts of uranium and transuranium elements; primarily neptunium, plutonium, and americium with traces of curium and transcurium isotopes. The safe and effective management of these nuclear wastes has been a primary goal of the ICPP operation for the past 27 years. The major technique for management of this waste has been to store the liquid waste safely for a period not to exceed 5 years, followed by solid i f i c a t i o n of the waste into a granular oxide and storage in stainless steel bins inside a concrete vault. Prior to calcination, the high- and intermediate-level liquid wastes (HLLW and ILLW) are stored in doubly-contained, cooled, stainless steel tanks. To date, there is no evidence of corrosion from the acidic wastes stored in these tanks. The HLLW have been s o l i d i f i e d on a routine basis in the Waste Calcining F a c i l i t y (WCF) since December 1963, with a resultant eight- to ten-fold volume reduction factor. To date, this pioneering effort has resulted in approximately 55% of the liquid wastes being converted to solids, with approximately 50,000 cubic feet in storage. Although the projected life of the solids storage bins is at least 500 years, the bins are designed 235
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0-8412-0527-2/80/47-117-395$05.00/0 © 1980 American Chemical Society
ACTINIDE SEPARATIONS
396
such that r e t r i e v a l of the wastes f o r f u r t h e r treatment or t r a n s port to a F e d e r a l r e p o s i t o r y might be accomplished whenever desired. The waste generated at ICPP is d i f f e r e n t w i t h r e s p e c t to a n t i c i p a t e d commercial p r o c e s s i n g p l a n t waste f o r two reasons. F i r s t , all of the multi-headend processes r e s u l t in complete d i s s o l u t i o n of the c l a d d i n g and m a t r i x as w e l l as the f i s s i o n products and a c t i n i d e elements; second, the p r o d u c t i o n of transuranium elements in h i g h l y enriched f u e l s is l e s s than in low enrichment/ h i g h burnup power f u e l s . A d d i t i o n a l l y , the t o t a l f i s s i o n product i n v e n t o r y in the f u e l is s u b s t a n t i a l l y lower at ICPP as compared to power r e a c t o r f u e l s and consequently, the r a d i o a c t i v i t y of the r e s u l t i n g waste s o l u t i o n s are very d i f f e r e n t f o r these two cases. Thus, the r a t i o of a c t i n i d e s to t o t a l s o l i d s in the ICPP waste is s i g n i f i c a n t l y l e s s than in c u r r e n t l y a n t i c i p a t e d commercial wastes. The b u l k of the r a f f i n a t e s t o r e d a t ICPP has been generated from the p r o c e s s i n g of z i r c a l o y - and aluminum-clad f u e l elements. The uranium recovery process f o r z i r c a l o y - c l a d elements r e q u i r e s the a d d i t i o n of aluminum n i t r a t e as both a s a l t i n g agent and a complexant f o r the f r e e f l u o r i d e present in the d i s s o l u t i o n process. When a v a i l a b l e , the d i s s o l v e r s o l u t i o n from aluminum-clad elements is coprocessed w i t h z i r c a l o y - c l a d elements, thus s e r v i n g the same purpose. Raffinâtes generated from these campaigns a r e , t h e r e f o r e , s i m i l a r . The chemical analyses of a major first-cycle r a f f i n a t e storage tank at ICPP are shown in Table I . A c t i n i d e analyses are a l s o given in Table I . TABLE I TYPICAL COMPOSITION OF ICPP Z r - A l FIRST-CYCLE WASTE Bulk Chemical (M) A c i d i t y (H+) 1.5
A c t i n i d e s (g/L) 2 37 1.2x10" 5
N p
Nitrate
2.36
2 38
Fluoride
3.12
2 39p
Aluminum
O.68
P u
240p
Zirconium
O.44
Iron
O.005
242p
Boron
O.22
Mercury
^O.002
2
u
u
^Pu
1
% 5Χ10" * 1.4xl0-
3
3.4xl0-
4
1.5Χ10"
4
4.8x10"
5
^Am
4.4x10"
5
243
1.2x10"
5
u
Am
A l i t r e of waste shown in Table I, when c a l c i n e d , r e s u l t s in the p r o d u c t i o n of ^250 g of t o t a l s o l i d s . The p l o t shown in F i g u r e 1 d e s c r i b e s s i g n i f i c a n t a c t i n i d e c o n c e n t r a t i o n s in ICPP c a l c i n e from a t y p i c a l r a f f i n a t e as a f u n c t i o n of time. Though uranium and neptunium are present in the c a l c i n e , t h e i r c o n t r i b u t i o n to alpha a c t i v i t y is not s i g n i f i c a n t . I t is apparent t h a t s e p a r a t i o n f a c t o r s of M.00 must be a t t a i n e d f o r the Pu and Am to
28. McisAAC E T AL.
Flowsheet Development Work
397
Years
Figure 1.
Significant actinidesinICPP calcine as a function of storage time
ACTINIDE SEPARATIONS
398
reach the d e s i r e d a l p h a - f r e e g u i d e l i n e of
