v c o n c e n t r a t e d s o l u t i o n s ,, o r t o p r e c i p i t a t e f o l l o w i n g mixing o f c o o l a n t
salt i n t o fuel salt.
( i i i )Apparently a n oxide s p e c i e s forms i n t h e
c o o l a n t s a l t phase which i s more s t a b l e t h a n U02, s i n c e no UO
2
precipi-
t a t i o n was observed even when molten c o o l a n t - f u e l s a l t mixtures were a g i t a t e d w h i l e exposed t o a i r f o r several hours.
Thus, l a r g e amounts
of oltygenated compounds could b e added t o t h e f l u o r o b o r a t e c o o l a n t s a l t for t h e purpose of s e q u e s t e r i n g tritium, s i n c e l e a k a g e o f such a c o o l a n t
s a l t i n t o t h e f u e l salt,would not l e a d t o p r e c i p i t a t i o n o f uranium or thorium. Investigation
o f NaBF4 melts by x-ray powder d i f f r a c t i o n , i n f r a r e d
s p e c t r o s c o p y and Raman spectroscopy have i d e n t i f i e d t h e s t a b l e r i n g compound N a B F 0
3 3 6 3
melts.
as t h e probable oxygen-containing s p e c i e s i n c o o l a n t
Measurements of condensates t r a p p e d from t h e CSTF l o o p show a
tritium c o n c e n t r a t i o n o f 1 05 r e l a t i v e t o t h e s a l t , s u g g e s t i n g t h a t a v o l a t i v e s p e c i e s may be s e l e c t i v e l y t r a n s p o r t i n g tritium from t h e l o o p through t h e vapor.
may e x i s t as a
Recent r e s u l t s i n d i c a t e t h a t BF;2H,O J
L
molecular compound i n t h e vapor and could be r e s p o n s i b l e f o r t h e tritium trapping. A l l the above resuLts are f a v o r a b l e for t h e u s e o f NaBF4-NaF (92-8
mole % ) melts as an MSBI3 secondary c o o l a n t .
S a t i s f a c t o r y tritium t r a p p i n g ,
an important c o o l a n t c r i t e r i o n , appears h i g h l y p r o b a b l e , vigorous chemical r e a c t i o n s or p r e s s u r e s u r g e s were n o t encountered on mixing c o o l a n t and f u e l s a l t , and p r e c i p i t a t i o n or s e g r e g a t i o n o f f i s s i l e components w a s not encountered. A t e r n a r y s a l t NaF-LiF-BeF
2
as an a l t e r n a t e coolant ( S e c t i o n
(45-22-33 mole % ) , has been c o n s i d e r e d
6 ) . Two p u b l i s h e d r e f e r e n c e s gave