ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site

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and there was never any evidence sf a soEuble telluride species, However,
considerable evidence existed that tellurium "moved" through salt from one
point to another in a salt system.
The hypothesis was that the tellurium
actually moved as a low-pressure pure metall vapor and not as a reacted
species. 'Ehe most representative experimental system dle~el~iped for ex-
posing metal specimens eo tel%urim invo%~ed suspendling the spe~imen~ in
a skirred vessel of salt: with granu%@S 0% Cr3Te4 and CPgT@6 lying at the
bottom of the salt. A very low partial pressure of tePEurim was in equi-
librim with the Ck3T@4 and C~gTe6~ which resulted in BaStePEOy-M speci-
mens w ith crack severities similar to those noted in samples from the
MSRE, NUEIBRH.LS samples were exposed to salt that contained tellurium, and
the most important finding was that modified Hastelloy-N c~ntai~~ing 1 to 2% niobiW had good reSistaXlC@ to eTRb8-i&e%ement by tt?llUgf-UlR (Fig. 16).
h e Sekfe.5 Qf experiments Was Tun to inVeStfgatf2 the effects O f the
oxidation state of tellurium-containing salt on the temdency for cracks
to be f o ~ ~ ~ me d , supposition being examined was that the salt might be
made reducing enough to tie up the tellurium in some fnnocuo~~ metal com-
plex.
The salt was made more oxidizing by adding WiF2 and more reducing
by adding elemental beryblim. The experiment had electrochemical probes
for determining the ratio of urarnim in the +4 state (UPq) to that im the
4-3 state (UF3) as an indicator of the sxfdation state of the salt,
sile spe~imens of standard ~asteiloy-~ were suspended in the salt for
about 260 k at 700°C.
the specimens were inserted so that each set of specimens was exposed to
one condition. After exposurep the specimens were strained to failure and
were examined metallographically to determine the extent of cracking e '%he
results of measurements at several oxidation states are shown in Fig. 17.
~t ~4+/~3+ ratios sf QO or less, very little cracking occurred, and at
ratios above 80, the cracking was extensive. These observations offer
encouragement. that 8 reactor could be operated in a chemical regime where
the tellurium would not be embrittling even to standard Hastelloy-N.
least le6% of the uranium would need to be in the +3 oxidation state
(UF3js amd this eonditi~n seems quite reasonable from chemical and prac-
tical considerations.
Ten-
The oxidation state of the salt was stabilized, and
At