Engineering-scale flow forming of high purity copper overpacks for spent nuclear fuel disposal canisters: A preliminary study for prototyping

Most countries have chosen the concept of deep geological disposal system for quasi-permanent isolation of spent nuclear fuels. Disposal canisters play a critical role in engineering barrier system. It is typically composed of an oxygen free copper overpack and a cast iron insert. The overpack conventionally made by the casting, forging, and extrusion, but the high material cost and low material efficiency present challenges. In this study, the engineering-scale flow forming was applied to fabricate a prototype copper overpack. The feasibility of the process to fabricate engineering-scale copper overpack was evaluated. A 1/3-scale long and 1/2-scale diameter prototype was well fabricated. The microstructure and mechanical properties were evaluated to validate the potential of flow forming for industrial application. The microstructural characteristics and mechanical properties were varied along the thickness direction and well aligned with process history. And it was found that the grain size effect was significantly influences material hardening in engineering-scale flow forming of copper. Based on the findings from this study, it was highlighted the effectiveness of flow forming process for fabricating copper overpacks. And it was suggested the recommendations for the future study and process optimization to achieve the real-scale fabrication.