Solubility of magnesium oxide in calcium oxide-calcium chloride mixtures
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this p a p e r , we p r e s e n t an e x p e r i m e n t a l and t h e o r e t ical i n v e s t i g a t i o n of the s o l u b i l i t y of m a g n e s i u m oxide in the r e c i p r o c a l s a l t s y s t e m , Ca 2+, Mg 2ยง I CI-, O 2-, at 1133 K. Solubilities w e r e m e a s u r e d by f i l t e r i n g s a m p l e s of m o l t e n CaC12-CaO m i x t u r e s to which MgC12 had b e e n added. The m e a s u r e d s o l u b i l i t i e s a r e c o m p a r e d with s o l u b i l i t y p r o d u c t s c a l c u l a t e d f r o m a t h e r m o d y n a m i c cycle f i r s t p r o p o s e d by Flood, F d r l a n d and G r j o t h e i m (FFG) (Ref. 1). The t h e o r e t i c a l p r i n c i p l e s used h e r e can be b r o a d l y applied in the p r e d i c t i o n of s o l u b i l i t i e s in ionic m e l t s . 2 Thus, the p r e s e n t work s e r v e s as an i l l u s t r a t i o n of the p r a c t i c a l use of the F F G cycle in a p a r t i c u l a r case, i . e . , the c o m p a c t p y r o c h e m i c a l p r o c e s s developed for the s e p a r a t i o n , r e c o v e r y and p u r i f i c a t i o n of s p e n t f a s t b r e e d e r r e a c t o r fuels. 3'4 In o r d e r to achieve an a d e quate s e p a r a t i o n of the v a r i o u s e l e m e n t s in n u c l e a r m i x e d oxide fuels, a m o l t e n s a l t m i x t u r e is cycled b e tween two liquid m e t a l s o l u t i o n s d e s i g n a t e d as donor and a c c e p t o r a l l o y s . The t r a n s p o r t by the m o l t e n s a l t is b a s e d on the s e l e c t i v e t r a n s f e r of u r a n i u m o r pluton i u m f r o m one m e t a l l i c s o l u t i o n to the other, l e a v i n g the f i s s i o n - p r o d u c t e l e m e n t s in a waste salt. Some of the fuel c o m p o n e n t s a r e d i s s o l v e d in the s a l t p h a s e as t h e i r h a l i d e s , and the r e m a i n i n g in the m e t a l p h a s e as their elements. The r e d u c t i o n of the m i x e d p l u t o n i u m - u r a n i u m oxides is u n d e r t a k e n by v i g o r o u s l y fluxing the s o l i d fuel p e l l e t s with a m o l t e n CaF2-CaC12 m i x t u r e in the p r e s ence of a liquid C a - M g - C u alloy. The p r o d u c t s of t h e s e r e a c t i o n s a r e m e t a l l i c p l u t o n i u m and u r a n i u m and, u n d e r c e r t a i n c o n d i t i o n s , e i t h e r MgO a n d / o r CaO in the solid state. The m e t a l l i c U and Pu a r e s o l u b l e in the liquid alloy. The c a l c i u m oxide f o r m e d by the r e d u c t i o n of the oxide fuel with Ca is d i s s o l v e d by the m o l t e n c a l c i u m c h l o r i d e flux. 3'4 The m a g n e s i u m oxide, MgO(s), is o b t a i n e d as a p r o d u c t of the r e a c t i o n of the fuel oxides with m a g n e s i u m . However, if one r e f e r s to s i m p l e t h e r m o d y n a m i c c o n s i d e r a t i o n s 1'2 p r e s e n t e d in the d i s c u s s i o n , the solid MgO is then expected to be r a t h e r i n s o l u b l e in the CaC12 m i x t u r e . The s o l u b i l i t y of th
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