Radiochemical measurement of diffusion in the cesium chloride-tin and barium-sodium systems
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A N D S. H. C H I A N G
Diffusion coefficients for c e s i u m c h l o r i d e in molten t i n f r o m 308 to 396~ and for b a r i u m in liquid sodium f r o m 290 to 396~ w e r e m e a s u r e d r a d i o c h e m i c a l l y . C e s i u m c h l o r i d e coefficients were d e t e r m i n e d by m e a s u r e m e n t of nonsteady state s u r f a c e c o n c e n t r a t i o n s of c e s i u m chloride deposited on the s u r f a c e of c y l i n d r i c a l s p e c i m e n s . C e s i u m c h l o r i d e t r a c e d with c e s i u m - 1 3 7 was deposited on the s p e c i m e n s f r o m a s u p e r s a t u r a t e d s o l u t i o n d i s p e r s e d in the m o l t e n tin and m e a s u r e d by g a m m a s p e c t r o s c o p y after r e m o v a l of the s p e c i m e n f r o m the solution. Diffusion coefficients for b a r i u m in sodium were m e a s u r e d by a unique method in which r a d i o a c t i v e c e s i u m - 1 3 7 (half-life of 33 y r s ) d i s s o l v e d in the sodium s e r v e d as a v o l u m e t r i c s o u r c e for its s h o r t - l i v e d b a r i u m - 1 3 7 daughter (half-life of 2.6 min). Since b a r i u m deposited on the s u r f a c e of the s p e c i m e n , m e a s u r e m e n t of the e q u i l i b r i u m b a r i u m 137m g a m m a activity on the s p e c i m e n s u r f a c e s after r e m o v a l f r o m the solution yielded b a r i u m diffusion coefficients. The equations for these diffusion coefficients with 95 pct confidence l i m i t s a r e : C e s i u m chloride in t i n (308 to 396~ B a r i u m in sodium (290 to 496~
D = [(4.84 9 0.14) • 10 .4] exp [ - 6720 :~ 6400)/RT]
D = [(4.27 9 0.05) • 10.4] exp [ - 4600 + 990)/RT]
1" L I Q U I D m e t a l s , n o t a b l y sodium, s o d i u m - p o t a s s i u m alloy (NaK), p o t a s s i u m , l i t h i u m , and m e r c u r y , have b e e n used as coolants in high p e r f o r m a n c e s y s t e m s . In p a r t i c u l a r , s o d i u m has b e e n s e l e c t e d as the coolant for the fast b r e e d e r r e a c t o r , now b e i n g i n d e p e n d e n t l y developed by the United Kingdom, F r a n c e , G e r m a n y , USSR, Japan, and the United States. S e v e r a l i m p o r t a n t p r o c e s s e s in liquid m e t a l s y s t e m s a r e dependent upon m a s s t r a n s f e r m e c h a n i s m s . D i s solved oxygen, which e n h a n c e s c o r r o s i o n , is r e m o v e d by " c o l d t r a p p i n g " , a s y s t e m which m a i n t a i n s oxygen at low c o n c e n t r a t i o n s by p r e c i p i t a t i n g oxygen c o m pounds f r o m a low t e m p e r a t u r e b y p a s s s t r e a m . C a r bon is t r a n s f e r r e d f r o m r e g i o n s of high c a r b o n a c t i v ity to r e g i o n s of low c a r b o n activity. Local c a r b o n a c t i v i t i e s a r e functions of both l o c a l t e m p e r a t u r e and m a t e r i a l c o m p o s i t i o n . The c o r r o s i o n p r o c e s s involves d i s s o l u t i o n of s t r u c t u r a l m e t a l s at the high t e m p e r a t u r e s u r f a c e s of the
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