Chemical analysis of salt samples that were periodically withdrawn from the loop showed a slight increase in chromium concentration, while concentrations of other metals remained unchanged. During a typical run, the chromium concentration reached an asymptotic limit after about 5000 hr of operation, as shown in Fig. 6. This limit was between 300 and 500 ppm at 1300째F and between 600 and 800 ppm at 1400 and 1500째F.
The corrosion data for INOR-8, exposed in the p p loops, indicate that corrosion reactions with fluoride salts at MSRE temperatures are essentially complete within the first 5000 hr of operation, do not generally exceed 1 mil even after 20,000 hr, and are probably associated only with impurity reactions. No significant increase in corrosion occurs due to temperature increase until about 1500째F. At this temperature, noticeable depletion of chromium occurs, as indicated by subsurface voids, and the corrosion mechanism associated with components of the salt is probably effective. The safety factor of the corrosion resistance of INOR-8 appears to be ample, even for the temperature excursions or hot spots that could occur during the MSRE reactor operation.
Compatibility of Graphite and INOR-8 in Molten Salt
Since the MSRE uses a graphite moderator in direct contact with molten-salt f'uel, the compatibility of graphite and INOR-8 in a fluoride fuel was investigated. The tendency for INOR-8 to be carburized was investigated in static pots containing LiF-BeF2-UF4 (67-32-1mole $) and graphite at 1300째F for times ranging from 2000 to 12,000 hr.
Fig. 6. Concentration of Corrosion Products in Fluoride Salt Circulated in an INOR-8 Forced-Convection Loop.