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行动方针**，处理长期封存乏核燃料的问题，由核废料管理组织**负责设计和执行加拿大的计划。对长期**安全和可靠的管理方案的评估导致开发了一种集中遏制和隔离**加拿大用过的燃料的深层地质储存库（DGR）。加拿大设计与其他国家设计的不同之处在于，它采用了耐腐蚀的外层铜涂层。与现有的双壳包覆设计（钢壳上的厚铜套）相反，耐腐蚀的铜涂层更薄（3毫米厚），并且与钢壳完整地结合在一起。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，然后将它们装载用过的核燃料束，并用涂有铜的帽端关闭它们。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（封闭焊接区）铜涂层的首选技术。**NWMO仍在寻求一种新的创新方法来减轻在CGDS过程中氦气的使用。增强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。本提案旨在建立在少数有限的研究基础上，这些研究强调了在CGDS之前，衬底预热作为表面制备方法的潜力。可以设想，在用CGDS对钢进行铜涂层之前**适当的基材加热可以提高涂层的附着力（来自**增加的机械和冶金结合），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. This**number is expected to double over the next 40 years. Only very recently has Canada adopted a course of action**to deal with the long-term containment of the spent nuclear fuel, with the Nuclear Waste Management**Organization (NWMO) responsible for designing and implementing Canada's plan. Assessment of long-term**safe and secure management options has led to the development of a centralized containment and isolation of**Canada's used fuel in a deep geological repository (DGR). What differentiates the Canadian design from others**is the corrosion-resistant outer copper coating that is proposed. As opposed to existing dual-shell overpack**designs (thick copper sleeve on steel shell), the corrosion resistant copper coating is thinner (3 mm thick) and**integrally bonded to the steel shell. This design reduces drastically the amount of copper required for each UFC**and mechanical stresses on the steel shell. NWMO has selected electrodeposition to produce the copper**coatings on the steel vessels prior to loading them with used nuclear fuel bundles and closing them with a**copper coated cap end. Cold Gas Dynamic Spraying (CGDS or cold spray) was selected as the preferred**technique 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. An**alternative approach to enhance CGDS coating adhesion is the control of substrate temperature prior to particle**impact. This proposal aims to build on few limited studies that have highlighted the potential of substrate**preheating as a surface preparation method prior to CGDS. It is envisioned that proper substrate heating prior**to applying copper coating on steel by CGDS could result in enhanced coating adhesion strength (from**increased mechanical and metallurgical bonds) and allow the use of nitrogen only as the process gas. This**would represent a safe, highly efficient and cost-effective solution for the CGDS coating of the closure weld zone.