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产生了近260万束用过的燃料。这一数字预计将在未来40年翻一番。直到最近，加拿大才通过了一项处理长期封存乏核燃料的行动方针，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方案的评估导致了加拿大在深部地质储存库（DGR）中集中遏制和隔离用过燃料的发展。加拿大设计与其他国家设计的不同之处在于提出了耐腐蚀的外层铜涂层。与现有的双壳外包装设计（钢壳上的厚铜套）相反，耐腐蚀的铜涂层更薄（3毫米厚），并且与钢壳完整地粘合在一起。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。NWMO选择电沉积在钢容器上生产铜涂层，然后将其装载用过的核燃料束并用涂有铜的帽端关闭。选择冷气体动态喷涂（CGDS或冷喷涂）作为完成安全壳和帽端连接处（封闭焊缝区）铜涂层的首选技术。NWMO仍在寻求一种新的创新方法来减少在CGDS过程中氦的使用。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材温度。本提案的目的是建立在少数有限的研究基础上，这些研究强调了基板预热作为CGDS之前的表面制备方法的潜力。可以设想，在用CGDS对钢施加铜涂层之前，适当的基材加热可以提高涂层的粘附强度（来自增加的机械和冶金键），并且只允许使用氮气作为工艺气体。对于闭合焊缝区域的CGDS涂层来说，这将是一种安全、高效、经济的解决方案。

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.