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

在过去的几十年里，加拿大的核反应堆已经生产了近260万个使用过的燃料棒。这个数字预计将在未来40年翻一番。加拿大只是在最近才采取行动，处理长期封闭乏核燃料的问题，由核废料管理组织负责设计和执行加拿大的计划。对长期安全和可靠管理备选方案的评估导致开发了一个将加拿大用过的燃料集中封闭和隔离在一个深层地质处置库中的办法。加拿大设计与其他设计的区别在于所提出的耐腐蚀外部铜涂层。与现有的双壳外包装设计（钢壳上的厚铜套）相反，耐腐蚀铜涂层更薄（3 mm厚），并与钢壳一体结合。这种设计大大减少了每个UFC所需的铜量和钢壳上的机械应力。西北气象组织选择了电沉积，在钢容器上产生铜涂层，然后将其装载用过的核燃料棒束，并用铜涂层盖端封闭。选择冷气体动力喷涂（CGDS或冷喷涂）作为完成安全壳和盖端接头（闭合焊接区）铜涂层的首选技术。NWMO仍在寻求一种新的创新方法，以减少CGDS工艺中氦气的使用。提高CGDS涂层附着力的另一种方法是在颗粒撞击之前控制基体温度。该建议旨在建立在少数有限的研究，强调了作为CGDS之前的表面制备方法的衬底预热的潜力。可以预见的是，在通过CGDS在钢上涂覆铜涂层之前，适当的基底加热可以导致增强的涂层附着强度（从增加的机械和冶金结合），并且允许仅使用氮气作为工艺气体。这将是一种安全、高效和经济的封闭焊接区CGDS涂层解决方案。

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.