Development of a sustainable solution for the elimination of helium in copper cold spray process for used nuclear fuel containers

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Canadas nuclear reactors have produced almost 2.6 million used fuel bundles over the last decades. Thisnumber is expected to double over the next 40 years. Only very recently has Canada adopted a course of actionto deal with the long-term containment of the spent nuclear fuel, with the Nuclear Waste ManagementOrganization (NWMO) responsible for designing and implementing Canada's plan. Assessment of long-termsafe and secure management options has led to the development of a centralized containment and isolation ofCanada's used fuel in a deep geological repository (DGR). What differentiates the Canadian design from othersis the corrosion-resistant outer copper coating that is proposed. As opposed to existing dual-shell overpackdesigns (thick copper sleeve on steel shell), the corrosion resistant copper coating is thinner (3 mm thick) andintegrally bonded to the steel shell. This design reduces drastically the amount of copper required for each UFCand mechanical stresses on the steel shell. NWMO has selected electrodeposition to produce the coppercoatings on the steel vessels prior to loading them with used nuclear fuel bundles and closing them with acopper coated cap end. Cold Gas Dynamic Spraying (CGDS or cold spray) was selected as the preferredtechnique to complete the copper coating at the containment vessel and cap end junction (closure weld zone).NWMO is still seeking a new innovative way to alleviate the use of helium in the CGDS process. Analternative approach to enhance CGDS coating adhesion is the control of substrate temperature prior to particleimpact. This proposal aims to build on few limited studies that have highlighted the potential of substratepreheating as a surface preparation method prior to CGDS. It is envisioned that proper substrate heating priorto applying copper coating on steel by CGDS could result in enhanced coating adhesion strength (fromincreased mechanical and metallurgical bonds) and allow the use of nitrogen only as the process gas. Thiswould represent a safe, highly efficient and cost-effective solution for the CGDS coating of the closure weld zone.