Evaluation of vanadium and vanadium-base alloys in hot-trapped sodium
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C o r r o s i o n t e s t s w e r e c o n d u c te d with v a n a d i u m - b a s e a l l o y s in z i r c o n i u m - p u r i f i e d s o d i u m f r o m 450 ~ to 750~ f o r 500 to 4000 h r . The m a t e r i a l s t e s t e d w e r e v a n a d i u m , b i n a r y v a n a d i u m a l l o y s containing f r o m 10 to 40 wt pct T i , and two t e r n a r y a l l o y s : V - 5 T i - 1 5 C r and V - 1 5 T i - 7 . 5 C r . The s o d i u m was a n a l y z e d to contain f r o m 1.7 to 8.7 ppm O by the v a c u u m - d i s t i l l a t i o n technique. The b e h a v i o r of t h e s e m a t e r i a l s was d e t e r m i n e d f r o m weight change data, and f r o m c h e m i c a l , m e t a l l o g r a p h i c , and e l e c t r o n - m i c r o p r o b e a n a l y s e s of the t e s t s p e c i m e n s . At t e m p e r a t u r e s up to 650~ the m a x i m u m w e i g h t - c h a n g e v a r i e d f r o m a weight l o s s of 0.45 f o r vanadium to a weight gain of 0.46 mg p e r sq d m - d a y f o r the V - 4 0 T i alloy. C h e m i c a l a n a l y s e s of the c o r r o s i o n t e s t s p e c i m e n s i n d i c a t e d that v a n a d i u m - b a s e m a t e r i a l s w e r e s e n s i t i v e to the a c t i v i t y of oxygen, c a r b o n , a n d / o r n i t r o g e n in s o d i u m . Alloys containing >10 wt pct T i i n c r e a s e d in oxygen, c a r bon, and in s o m e t e s t s , n i t r o g e n content, indicating that a l l o y s of this t i t a n i u m content a r e not c o m p a t i b l e with sodium of the p r e s e n t p ur i t y . C o m p l e x t i t a n i u m c a r b i d e p r e c i p i t a t e s w e r e obs e r v e d n e a r the s u r f a c e . V - 5 T i - 1 5 C r a ll o y was m o r e r e s i s t a n t to liquid s o d i u m than the o t h e r vanadium m a t e r i a l s investigated. V A N A D I U M h as b e e n p r o p o s e d a s a backup cladding m a t e r i a l to s t a i n l e s s s t e e l f o r the l i q u i d - m e t a l fast b r e e d e r r e a c t o r . ~ Vanadium a l l o y s have the p o t en t i al of c o n t r i b u t i n g low n e u t r o n a b s o r p t i o n , little s u s c e p t i b i l i t y to f a s t - n e u t r o n d a m a g e , good s t r e n g t h at r e l a t i v e l y high t e m p e r a t u r e s , and s u i t a b l e c o m p a t i b i l i t y with s o d i u m and p o te n t ia l fuel m a t e r i a l s . H o w e v e r , t h e r e i s a need for a c q u i r i n g a c o m p r e h e n s i v e b a c k ground on the c o r r o s i o n of v a n a d i u m a l l o y s in sodium of known i m p u r i t y content. T h i s work was u n d e r t a k e n with that o b j e c t i v e in mind. V - T i a l l o y s have b e e n studied f o r r e a c t o r a p p l i c a tion since 1955. 2 Although t h e i r s t r e n g t h a p p e a r s to be s u p e r i o r to s t a i n l e s s s t e e l at 650~ inconsistenc i e s e x i s t in data r e l a t i v e to t h e i r c o r r o s i o n in liquid s o d i u m . 3 T h e i r b e h a v i o r is s e n s i t i v e to oxygen conc e n t r a t i o n , and V - 2 0 T i was s e l e
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