To address the considerable interest in molten salt compatibility for nuclear reactor applications, thermal convection loops (TCLs) are an important initial method in assessing molten salt compatibility and especially mass transfer. Two similar monometallic type 316H stainless steel TCL experiments were conducted for comparison with purified FLiNaK and FLiBe salts both with a peak temperature of 650°C. Initial capsule experiments with 316H specimens in a 316H capsule showed small mass losses for both salts. Post-test FLiBe characterization showed increases in the Fe, Cr and Mn contents of the salt with the values affected when Be was added to the FLiBe. In the FLiNaK TCL, 316H specimen mass losses were observed in the hot leg and mass gains in the cold leg were due to Fe deposition. In the FLiBe TCL, the mass changes were small but mass gains were not observed in the cold leg, perhaps due to post-test oxidation during the salt removal. GDOES characterization of the FLiBe-exposed 316H specimens suggested Cr surface depletion in the hot and cold legs and Fe deposition in the cold leg. To further understand and model mass transport in these salts, the relative solubilities of Cr and Fe are being measured at 550°-750°C using unalloyed Fe and Cr specimens in Mo capsules. Similar experiments
conducted in chloride salts showed similar Cr and Fe solubilities at 700°C.