Corrosion effect by preferential formation of Cr and Fe-based ceramic compounds under NaCl-KCl-MgCl2 molten salts

Abstract

The molten salt reactor (MSR) is a promising next-generation nuclear reactor; the structural materials for MSR must exhibit high corrosion resistance as chemical corrosion can cause structural problems in MSR systems at high temperatures. In this study, the corrosion behaviors of Fe-based stainless steel 316L, Ni-based Hastelloy C-276, and Hastelloy N10003 were observed in NaCl–KCl–MgCl2 molten salt at 800 °C for 48 h. For MgCl2, the strong hygroscopicity affects the corrosion of the alloy. Notable amounts of Cr and Fe depletion were observed in the corrosion-affected layer on the alloy surface for the three alloys that were loaded in the high-temperature molten salt. The cause of corrosion appears to be dominated by the quantities of Ni, Cr, and Fe, which are the main elements constituting the alloys, and the ceramic compounds generated by moisture and impurities. The Fe-based alloy mainly exhibited intergranular corrosion, and the corrosion depth was approximately five times greater than that of the Ni-based alloys. Hastelloy N10003, with a Cr content of 7%, exhibited the best corrosion resistance among the three alloys. However, if Hastelloy N10003 is also used as a long-term MSR structural material, surface modification is required to prevent corrosion.