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Th e e f f e c t s of m e t a l l u r g i c a l v a r i a b l e s such as d i s l o cation d e n s i t y , g r a i n s i z e , and the e x i s t e n c e of a s e c ond p h ase a r e a l s o c o n s i d e r e d in this t r e a t m e n t . In addition, f u r t h e r e x p e r i m e n t a l r e s u l t s a r e p r e s e n t e d that tend to support p r e v i o u s observations.~'6-8 E X P E R I M E N T A L TECHNIQUES A l l of the w o r k in this study w a s p e r f o r m e d on Type 304 s t a i n l e s s s t e e l i r r a d i a t e d in the E B R - I I r e a c t o r (Argonne National L a b o r a t o r y ) , a s o d i u m - c o o l e d , f a s t b r e e d e r r e a c t o r that o p e r a t e s at a t y p i c a l flux l e v e l of 2 • 10 z5 n p e r sq c m p e r sec > 0.1 m e v . Most of the r e p o r t e d i r r a d i a t i o n t e m p e r a t u r e s and e x p o s u r e l e v e l s a r e c a l c u l a t e d r a t h e r than m e a s u r e d v a l u e s , due to the n a t u r e of the r e a c t o r . This m e a n s that n e u t r o n fluxes a r e only known within • pct and i r r a d i a t i o n t e m p e r a t u r e s within •176 The p r i n c i p a l i n f o r m a t i o n r e q u i r e d for this study w as how the void s i z e , n u m b e r d e n s i t y , and v o l u m e v a r i e d with i r r a d i a t i o n t e m p e r a t u r e and n e u t r o n e x p o s u r e . The p r i n c i p a l t o o l s u s e d to gain this i n f o r m a tion w e r e t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) and i m m e r s i o n d e n s i t y , although s o m e X - r a y s m a l l a n g l e s c a t t e r i n g was a l s o p e r f o r m e d . T E M s a m p l e s w e r e p r e p a r e d , by c o n v e n t i o n a l t e c h niques within a shielded hood, f r o m a-1m." s e c t i o n s of the i r r a d i a t e d m a t e r i a l that had been p r e v i o u s l y cut and e l e c t r o p o l i s h e d within a r e m o t e handling c a v e f a c i l i t y . F r o m TEM it is p o s s i b l e to obtain an e s t i m a t e of the a v e r a g e void s i z e and s p a t i a l a r r a n g e m e n t . All void s i z e m e a s u r e m e n t s w e r e m a d e u n d er k i n e m a t i c a l s c a t t o t i n g conditions. One of the p r i n c i p a l c o n t r a s t m e c h a n i s m s u n d e r t h e s e conditions w a s the f o r m a t i o n of a d a r k F r e s n e i f r i n g e at the edge of the void. S a m p l e s VOLUME 2.MAY 1971-1457

(a)

(b)

Fig. 1--Transmission electron micrographs focussed (a) above and (b) below exact focus to demonstrate the existence of Fresnel fringes around voids. w e r e f o c u s s e d to f o r m such a f r i n g e to m i n i m i z e m e a s u r e m e n t d i f f i c u l t i e s . E v i d e n c e that the dark r i n g obs e r v e d to f o r m around voids is, in f a c t , a F r e s n e l f r i n g e is p r e s e n t e d in F i g s . l(a) and (b). T h e s e a r e m i c r o g r a p h s of the s a m e a r e a in which the m i c r o s c o p e was f o c u s s e d above and below the e x a c t focus.