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，加拿大的核反应堆生产了近260万束用过的燃料束。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**来处理乏核燃料的长期遏制问题，核废料管理**组织负责设计和执行加拿大的计划。对长期**安全和有保障的管理选择的评估导致了**加拿大使用过的燃料在深层地质储存库(DGR)中的集中围堵和隔离。加拿大的设计与其他设计的不同之处**是所提议的耐腐蚀的外层铜涂层。与现有的双外壳外包装**设计(钢壳上厚厚的铜套)不同，耐腐蚀的铜涂层更薄(3毫米厚)，**与钢壳整体结合。这种设计极大地降低了每个UFC所需的铜量**和钢壳上的机械应力。NWMO已经选择了电沉积来在钢制容器上产生铜**涂层，然后将用过的核燃料束装载到钢容器上，并用**覆铜的帽端关闭它们。冷气体动态喷涂(CGDS或冷喷涂)被选为在安全壳和帽端接头(闭合焊接区)完成铜涂层的首选**技术。**NWMO仍在寻找一种新的创新方法，以减少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**撞击之前控制衬底温度。这项建议旨在建立在少数几项有限研究的基础上，这些研究突出了衬底预热作为CGDS之前的一种表面准备方法的潜力。可以预见，在通过CGDS在钢上涂覆铜涂层之前**适当的衬底加热可以提高涂层的结合强度(通过**增加机械和冶金结合)，并且允许仅使用氮气作为工艺气体。这将是一种安全、高效、经济的闭合焊接区CGDS涂层解决方案。

Canadas nuclear reactors have produced almost 2.6 million used fuel bundles over the last decades. 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.