58
.
As i n t h e previous set of c o r e specimens, t h e s t r a p s of h e a t 5055 showed more cracks i n t h e nominally u n s t r a i n e d c o n d i t i o n t h a n d i d t h e
w
A s e c t i o n of a s t r a p from
tensile specimens on t h e same s t r i n g e r .
s t r i n g e r RL2 t h a t had been exposed, along w i t h t h e specimens shown i n Figures 33 and 34, is shown i n Fig. 37.
The cracks i n t h i s as-polished
view are v i s i b l e t o a depth of about 3 mils, about twice as deep as i n t h e s t r a p exposed 12,000 hr during 235U o p e r a t i o n (Fig. 22).
Heat 5055
straps were a l s o used on the s t r i n g e r s exposed only during t h e 233U operation (7200 h r ) . Fig. 38.
A specimen of one of t h e s e s t r a p s i s shown i n
I n t h e as-polished condition, cracks w e r e v i s i b l e t o a depth
of about 1 m i l ; e t c h i n g made them v i s i b l e t o a depth of about 3 mils. The cracking w a s q u i t e uniform along a l l s u r f a c e s of t h e s t r a p s , i n d i c a t i n g t h a t t h e deformation of t h e 20-mil s t r a p s during removal w a s not
a f a c t o r i n t h e appearance of t h e cracks.
Examination of u n i r r a d i a t e d
c o n t r o l s t r a p s f a i l e d t o r e v e a l a s i m i l a r type of cracking. One o t h e r i n t e r e s t i n g specimen t h a t showed e x t e n s i v e cracking w a s
.
a p i e c e of t h i n INOR-8 s h e e t (heat 5075) that had been a t t a c h e d t o t h e
s t r a p shown i n Fig. 38.
0.5 h r a t 1180OC.
The s h e e t had been r o l l e d t o 4 mils and annealed
The edges of t h e f o i l were wrapped around t h e s t r a p
-L
t o hold t h e material i n place.
Thus t h e o u t s i d e s u r f a c e of t h e f o i l
would have been exposed t o flowing s a l t and t h e underside and t h e folded ends t o s a l t t h a t flowed less r a p i d l y .
The f o i l w a s extremely b r i t t l e
and broke while i t was being removed from t h e s t r a p .
The photomicrographs
i n Fig. 39 show t h a t t h e f o i l had e x t e n s i v e g r a i n boundary cracks, with many appearing t o extend throughout t h e 4 m i l thickness.
I n some areas
t h e cracks were more numerous on t h e o u t s i d e where the material was curved and w a s i n c o n t a c t w i t h r a p i d l y flowing s a l t .
Photomicrographs of a
s t r a p and f o i l t h a t were exposed t o s t a t i c s a l t i n t h e c o n t r o l f a c i l i t y
are shown i n Figs. 40 and 41.
The samples showed no evidence of i n t e r -
granular cracking. A f r a c t u r e s u r f a c e of t h e f o i l from t h e PlSRE was examined by t h e
scanning e l e c t r o n microscope (SEM) and Auger spectroscopy.
is shown i n Fig. 42 and i s i n t e r g r a n u l a r .
The f r a c t u r e
The SEM w i t h a d i s p e r s i v e x-ray
a n a l y t i c a l system i n d i c a t e d t h e presence only of t h e elements normally
.