Corrosion of Copper-coated Steel Containers for Long-Term Used Nuclear Fuel Storage

Abstract

Copper-coated steel containers are currently considered by the Nuclear Waste Management Organization (NWMO) for the long-term storage of used nuclear fuel. NWMO has conducted extensive investigation of various techniques for coating copper on steel and the feasibility of coating very large cylindrical steel containers (> 2 m long and ~ 0.5 m in diameter). The results from their investigation have allowed NWMO to identify two preferred coating methodologies, namely electrodeposition for the container prior to being loaded with used nuclear fuel, and cold spray for covering the closure weld of a filled container at a packaging facility. Considering that these containers will be housed in deep geological repositories (DGRs) for thousands of years, their long-term corrosion performance is one of the life limiting factors. Of particular interest is the comparison of the corrosion behaviour of the copper coating to that of the wrought copper for which extensive data is available in the literature.Differences in the properties of two coatings were determined in the as-received condition (top down) and after preparing polished cross-sections. Long-term electrochemical experiments were performed on annealed cold spray (CSA), electrodeposited (ED) and SKB wrought copper (SKB) samples under different redox conditions for a period of 150 days or greater. Additional samples placed in the bottom of the cell were used to determine the evolution of the surface oxide composition as a function of the immersion time. The results from these measurements indicate that there is no significant difference in the corrosion behavior of the CSA and ED samples and that their corrosion behaviourwas similar to that of the SKB copper. In addition, the oxide composition is also similar for the samples examined in this study and is consistent with the expected composition under different exposure conditions.