Corrosion of nickel-based structural materials for nuclear reactors by molten fluoride salt: From bulk content of corrosion products to elemental imaging of corrosion changes

This work is focused on the study of corrosion treatment of molten fluoride salt (MFS) on three candidate structural materials (Ni, ferritic steel with protective Ni coating, and Ni-based alloy). The samples were exposed to an MFS mixture (60 mol% LiF + 40 mol% NaF) at a temperature of 680 degrees C for 112, 350 and 1000 h. Their corrosion resistance was tested by the determination of the content of corrosion products in MFS by ICP-OES (Inductively Coupled Plasma with Optical Emission Spectrometry) analysis and comparison of elemental ratios. Distinctive differences in the ratios were found for ferritic steel with protective Ni coating. Morphological changes induced by MFS treatment were revealed and studied by EPMA (Electron Probe Micro Analysis) and LA-ICP-MS (Laser Ablation Inductively Coupled Plasma of Mass Spectrometry). Elemental maps of the corroded area were acquired by both methods. The analyses of corrosion products show that the best candidate material is nickel.