Ab Initio Thermodynamics of Copper Immunity in Deep Geological Repositories

Copper barrier immunity to corrosion in groundwater conditions is a significant concern for nuclear waste isolation in deep geological repositories (DGR). Ongoing discussion surrounding the use of copper as a corrosion-resistant barrier highlights the need for further investigation, particularly through computational thermodynamic modeling, to refine our understanding of its immunity behavior. Here we re-examine the thermodynamic feasibility of copper oxidation in oxygen-free aqueous environments using updated thermodynamic data derived from density functional theory (DFT). Thermodynamic immunity is revisited in the context of possible deep geological repository (DGR) conditions, contrasting it with the potential for spontaneous copper oxidation. To this end, we map aqueous electrochemical conditions encountered by the copper surface of nuclear waste disposal containers, including O2 free anoxic environments, surface effects, and chloride- and sulfide-containing electrolyte solutions. We utilize predominance diagrams, generated using state-of-the-art DFT and the revised Helgeson–Kirkham–Flowers method, to probe the sensitivity of copper’s immunity to these various environmental parameters. We show that copper oxidation is thermodynamically favored over certain elevated temperatures and pressures─conditions that copper-lined nuclear waste disposal containers might be subjected to. Moreover, copper immunity is not assumed under all possible DGR conditions, strongly suggesting the use of multibarrier systems for long-term repositories that utilize copper as one corrosion resistance layer.