Corrosion of Inconel 800HT Alloy in Molten Fluoride Salts

Molten salt reactors are one of the technologies developed under GEN IV nuclear research. The mol-ten mix of LiF and BeF2, LiF, NaF nad KF, or NaBF4 and NaF act both as a reactor coolant both in primary and secondary loop. The combination of molten fluorides and high temperature creates high-ly corrosive environment. The aim of this work was to test corrosion resistance of Inconel 800HT alloy in molten FLiNaK, FliBe and NaBF4-NaF mix. The testing tube was filled with salt mixture and heated to 600-725 °C for a total of 1800 hours. The material exposed to NaBF4-NaF mix shoved mild corrosion attack on grain boundaries. Samples exposed to FLiNaK salt were more damaged, largely the part above the salt surface. The intergranular corrosion was also observed, more severe than in the case of NaBF4-NaF environment. Corrosion in the FLiBe salt caused depletion of alloying metals from the material’s surface. In all cases was dissolving of Cr into the melt identified as the main mechanism. The corrosion was accelerated by impurities in the salt mix, mostly water forming hydrogen fluoride gas in combination with insufficient seal of the testing tube.