Effects of Oxide Inclusions on Cold Sprayed Copper Corrosion in Bisulfide-Containing Environment

In Canada, the current design of the containers for used nuclear fuel includes a cold spray copper coating as part of a multi-barrier system for long-term disposal in a deep geological repository. The oxygen trapped during emplacement will potentially cause initial copper coating oxidation, while bisulfide ions produced by sulfate-reducing bacteria will act as a long-term oxidant by forming copper sulfides. Bisulfide ions will first meet oxide-covered used fuel containers, and conversion of oxide to sulfide will take place. Unlike wrought copper, cold spray copper contains microstructural features such as entrapped cuprous oxide inclusions at particle-particle interfaces. This study examined the impact of these entrapped oxide inclusions on the surface oxide formation and corrosion behaviour of cold spray copper in an anoxic bisulfide-containing environment. Electrochemical tests and surface characterization showed that oxide inclusions significantly influence the initial oxidation process and accelerate copper corrosion and oxide-to-sulfide conversion. These findings provided insight into the role of copper’s microstructure in the long-term performance of used fuel containers.