The dual role of chromium in molten salt corrosion: Active dissolution vs. oxide formation

Pyrochemical reprocessing of spent fuel via molten chloride electrolysis is a fundamental approach to achieving a closed nuclear fuel cycle. However, the rapid corrosion of apparatus materials poses significant challenges to the safe implementation of this technology. A key unresolved question is whether the Cr-alloying approach is viable for enhancing high-temperature corrosion resistance under molten chloride conditions. Herein, we conduct a systematic examination of the impact of Cr content on the corrosion behavior of structure steels in molten LiCl-KCl eutectic. Our results reveal that Cr exerts a dual role in corrosion resistance by modulating both chemical oxidation and active dissolution processes. Specifically, when the Cr level is insufficient to form a continuous Cr-rich oxide layer via chemical oxidation, increasing Cr concentration markedly accelerates electrochemical corrosion in molten chloride. Our research elucidates the fundamental mechanism by which Cr functions in molten salt corrosion and furnishes essential direction for the compositional design of corrosion-resistant alloys in pyrochemical reprocessing settings.