Preliminary Test and Analysis of TWIN-Tandem Wire Arc Additive Manufacturing for Producing High-Purity Copper Overpacks in Spent Nuclear Fuel Disposal Canisters: Focus on Microstructure and Dilution Behavior

• CMT TWIN-tandem WAAM is feasible for fabricating pure Cu wire directly onto CI substrate. • Narrower D IP or optimized temperature control is recommended for sufficient wettability and coverage. • CMT TWIN-tandem with weaving strategy reduces the number and size of internal porosity. • Reduction of α-Fe phases within deposited Cu matrix is found as a function of layer height increases. • Relation between α-Fe phases and grain refining of Cu matrix is observed, but further study is needed. The market for disposal canisters for spent nuclear fuel is growing significantly. Despite new manufacturing techniques, conventional methods for producing copper overpacks remain unchanged. As a novel alternative, this study investigates the application of cold metal transfer (CMT) TWIN-tandem wire arc additive manufacturing (WAAM) for depositing high-purity copper onto a nodular cast iron substrate, a critical fabrication step for the corrosion-resistant overpack of spent nuclear fuel (SNF) disposal canisters. Deposited copper matrices mostly consisted of equiaxed grains, although columnar structures appeared as the number of deposited layers increased. The size and fraction of α-Fe phases from the remelted cast iron decreased as the number of layers increased. The process displayed high sensitivity to minor temperature fluctuations, highlighting the need for precise thermal management. Results indicate that CMT TWIN-tandem WAAM is a promising method for manufacturing copper overpacks for spent nuclear fuel disposal. Further research should focus on optimizing process parameters, refining thermal control, and assessing the long-term performance of components fabricated by this innovative technique.