b'Characterizing corrosionExpanding the fundamental knowledge of corrosion mechanisms in chloride mechanisms of structuralmolten salts maximizes the integrity and safety of molten chloride fast reactors.alloys in actinide-basedC hloride molten salt reactors can reach criticality with molten chloride spent fuel containing high concentrations of impurities, such as actinide molten chloride salt products like uranium (III) chloride (UCl), a promising capability to consume spent fuels that will enhance the environmental sustainability of the uranium fuel cycle. However, the redox potential of chloride molten salt fuels may change in the presence of these impurities, dictating their corrosivity and in turn the corrosion performance of structural components, such as those constructed from nickel-based alloys. This investigation characterized nickel-based super alloysPROJECT NUMBER:Alloy 617, Hastelloy N, and Hastelloy C-276to molten chloride salt mixtures with 21P1056-012FP and without the presence of UCl using a multiscale, multi-modal characterization approach that elucidated the interfacial corrosion mechanism with and without TOTAL APPROVED AMOUNT:the presence of the actinide product. The characterization involved x-ray computed $391,000 over 3 years tomography, scanning electron/focused ion beam microscopy, and transmission PRINCIPAL INVESTIGATOR:electron microscopy. Alloy 617 was exposed to potassium chloride (KCl)-magnesium Trishelle Copeland-Johnson,chloride (MgCl) and lithium chloride (LiCl)-KCl-UCl salt mixtures up to 1000 h Glenn T. Seaborg Distinguished Postdoctoral Fellow at 700C. Hastelloy N and C-276 were corroded in KCl-MgCl and sodium chloride (NaCl)-UCl salt mixtures up to 1000 h at 700C. KCl-MgCl is commonly studied CO-INVESTIGATOR: as a heat transfer fluid for chloride molten salt reactors, LiCl-KCl-UCl is common in Lingfeng He, INL nuclear electrorefining applications, and NaCl-UCl is a fuel salt mixture of interest for industrial partners in the Advanced Reactor Development Program sponsored by the Office of Nuclear Energy. The corrosion mechanism of Alloy 617 was the most sensitive to the different salt mixtures, exhibiting an interfacial corrosion mechanism in KCl-MgCl that selectively diffused chromium, molybdenum, iron, and nickel from the alloy along specific grain boundaries but a non-preferential corrosion mechanism in LiCl-KCl-UCl. Uranium permeated into the material and the distribution of alloying elements chromium, molybdenum, and nickel, and the microstructure in the affected region underwent significant changes from the alloys original state. Hastelloy N and C-276 behavior was more consistent despite the different salt mixtures. The corrosion attack was limited to grains intersecting with the surface of the chromium depleted alloy, and selective chromium diffusion was observed along specific grain boundaries leading to that depletion layer. Results from this investigation expand our fundamental knowledge of the corrosion performance of reactor structural materials in molten chloride fast reactors, enhancing structural integrity and safety basis. 52'