Unexpected enhancement of molten salt corrosion by fission products: Superior performance of Fe-based 316L SS over Ni-based Inconel 600

Molten salts are widely used in high-temperature nuclear systems, yet their interactions with structural alloys, particularly under the influence of fission product species, are still not fully understood. In this study, the corrosion behaviors of Fe-based 316L stainless steel (316L SS) and Ni-based Inconel 600 alloy were investigated in LiCl-KCl eutectic molten salt at 500 °C, under the influences of thermodynamically active lanthanide and less-active lanthanide/non-lanthanide fission product species. The results reveal that both active and less-active lanthanide species enhance the corrosion of alloys in molten salt, whereas less-active non-lanthanide barely affect the alloy’s corrosion as thermodynamically expected. The unexpected corrosion enhancement caused by less-active lanthanide species (Ce 3 + , La 3+ , Nd 3+ , Sm 3+ , Pr 3+ , Gd 3+ , and Y 3+ ) is attributed to the formation of lanthanide oxychlorides (LnOCl, Ln represents less-active lanthanide species), driven by trace oxygen present in Ar atmosphere. Furthermore, the 316L SS was found to exhibit better corrosion resistance than Inconel 600 alloy in LiCl-KCl molten salt containing fission products, despite Ni-based alloys being widely regarded as more corrosion-resistant than Fe-based alloys in molten salt environments. This study systematically investigates, for the first time, the effects of fission products on both Fe-based and Ni-based alloys in molten salt, providing a comprehensive understanding of the behavior of structural alloys for molten salt applications in the nuclear industry.