Computational Insights into the Corrosion Behavior of NbTaMoW and NbTaMoWV High-Entropy Alloys in Molten Fluoride Salts

Abstract

Molten salt reactors (MSRs), one of the six next-generation nuclear reactor designs, employ molten fluoride salts as the coolant and/or fuel solvent when operated in a thermal-neutron spectrum, and offer higher thermal efficiency compared to today’s water-cooled reactors. Nonetheless, the elevated temperatures, corrosive nature of salts, and high neutron irradiation in MSRs create a harsh environment for structural materials. The influx of impurities, namely moisture, into the molten salt medium has long been shown to exacerbate the corrosivity of fluorides. Owing to their superior thermal and mechanical robustness, refractory high-entropy alloys with a body-centered cubic (BCC) structure have been proposed as candidate containment materials for MSRs. Nonetheless, the degradation of these advanced materials in molten fluorides is an intricate process whose underlying mechanisms remain poorly understood. This study explores the corrosion behavior of BCC (100)-NbTaMoW and (100)-NbTaMoWV surfaces in pure and hydrated FLiBe salt via density functional theory and ab initio molecular dynamics simulations. Electronic structure analyses, including density of states and crystal orbital Hamilton population, provide insight into the interfacial bonding and charge transfer. Irrespective of salt purity, NbTaMoW exhibits minimal d-band shifts which highlight its electronic stability, and weak interactions with fluorine and oxygen. The addition of vanadium to form NbTaMoWV further diminishes susceptibility to oxidation and enhances stability at the salt interface, suggesting superior corrosion resistance in both pure and hydrated salt.