| Abstract Scope |
Molten fluoride salts are promising coolants, fuels, and breeding media for advanced fission and fusion systems, but material compatibility remains a challenge. Trace impurities can dominate corrosion by oxidizing reactive alloying elements, driving localized intergranular attack. While most studies emphasize anodic alloy dissolution, our earlier work showed that Fe impurities can unexpectedly mitigate corrosion by depositing near grain boundaries. Building on this observation, this talk examines the coupled cathodic process: where electrochemically reduced impurity products form, whether they deposit on alloy surfaces, and how deposition sites alter corrosion pathways. Using Ni-20Cr exposed to FLiNaK with selected metal fluoride additions, we compare protective grain-boundary-localized deposition, ineffective off-site deposition, and cases where suppressed penetration coincides with surface damage. These comparisons show that the corrosion response cannot be predicted from impurity identity alone. Overall, impurity effects depend on redox potential, concentration, and site selectivity, suggesting controlled impurity management rather than complete removal. |