Methodology for Assessing Stainless Steel Compatibility in Fluoride Salts at 550°-850°C

Abstract

Molten halide salts are of interest for several applications including next generation nuclear reactors. However, salt compatibility is a concern especially for higher temperature applications (750°-850°C) or off-normal conditions for lower temperature (≤650°C) designs. Recent physics-based lifetime modeling work has used Cr dissolution data (i.e. mass loss and concentration) in Cl salts to predict the Cr depletion in Ni-Cr and Fe-Cr alloys. A similar modeling strategy is being pursued for fluoride salts including FLiNaK and FLiBe but initial results revealed both Fe and Cr dissolved in the salt after exposure of type 316H stainless steel in both static and flowing salt. Thus, initial results are presented for dissolution of Cr and Fe in FLiNaK at 550°-850°C with additional FLiBe results in progress. The Cr and Fe dissolution in FLiNaK at 550°-750°C for up to 2000 h was not strongly affected by time or temperature, which is consistent with the compatibility results in flowing FLiNaK. The most recent results at 850°C showed less Cr dissolution than at lower temperatures. In contrast, increased Cr dissolution was observed for similar experiments in Cl salts at 700°-1000°C.