Oxidation-Driven Lithium Uptake in Nickel-Base Alloys – Smoking-Gun Evidence for an Inner Cathode under LWR Conditions

Journal article, 2026

Lithium hydroxide is widely used for pH control in pressurized water reactors, yet lithium incorporation in chromia-forming Ni-base alloys has been linked to degraded corrosion resistance. Using lithium as a tracer for protons, we show that Li⁺ uptake is consistent with an inner-cathode mechanism for oxidation by water, in which hydroxylated oxide grain boundaries transport molecular water equivalents toward a cathodic region near the alloy/oxide interface. First-principles calculations demonstrate that both H⁺ and Li⁺ promote chromium oxidation by NiO and catalyse metallic nickel precipitation within the oxide scale, compromising scale integrity. Unlike hydrogen, lithium cannot be removed by molecular evolution and therefore accumulates at the inner cathode. This work provides a mechanistic elucidation of experimentally observed lithium enrichment, which has been suggested to promote stress corrosion cracking in LiOH-containing reactor water.