O2- affected corrosion of nickel-based alloy in LiCl-KCl molten salt for pyroprocessing of spent nuclear fuel

Abstract

Pyroprocessing of spent nuclear fuel is an important step in nuclear fuel cycle with the purpose of minimizing the radiation impact on environment and recycling useful elements. One major concern in the development of pyroprocessing is the structural material corrosion in LiCl-KCl molten salt electrolyte, which is the core component of the spent nuclear fuel reprocessing. To understand the influence of O^2- impurity on the structural material corrosion in LiCl-KCl molten salt, the study investigates the corrosion behavior of Inconel 600 alloy in LiCl-KCl molten salt containing different amounts of O^2- impurities at 500 °C by immersion corrosion experiments and electrochemical analyses.The results indicate that O^2- could accelerate the high-temperature corrosion behavior. The alloy surface developed a bilayer oxide structure following 500-hour exposure to molten salt with 3 mol % O^2-, identified as a 3.36-µm-thick outer Li₂NiO₂ layer and a 1.11-µm-thick inner LiCrO₂ layer. Based on the corrosion behaviors of Inconel 600 alloy in LiCl-KCl molten salt with different amounts of O^2- impurities, a new O^2- affected corrosion mechanism involving the formation of dual-layer oxide films and nickel-rich particles was proposed, which could provide new insights for the corrosion study in the applications of pyroprocessing of spent nuclear fuel.