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. 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.