Thin-layer mixed-potential model for the corrosion of high-level nuclear waste canisters

A thin-layer mixed-potential model (TLMPM) is described for calculating redox and corrosion potentials for high-level nuclear waste (HLNV) canisters in a tuff repository. The model assumes that the canister surface is covered by a thin liquid (water) layer which is irradiated by γ-photons from the decay of radionuclides in the waste. The dose rate and temperature at the surface are assumed to decay exponentially with time. Redox and corrosion potentials are calculated by equating the sum of partial currents for charge-transfer reactions involving various electroactive radiolysis products and the metal substrate to zero. Estimated polarization data for type 304L (UNS S30403) and type 316L (UNS S31603) stainless steels, alloy 825 (UNS N08825), and copper alloys CDA 102 (UNS C10200), CDA 613 (UNS C61300), and CDA 715 (UNS C71500) in high-temperature aqueous solutions were combined with the TLMPM to calculate redox and corrosion potentials over a 1000-year time period. The model predicts that the corrosion potential will increase with time due to the dominant effect of decreasing temperature.