The Development of Cold Spray Surface Preparation and Coatings for Crack Sealing of Postulated Chloride-Induced Stress Corrosion Cracking (CISCC) of Dry Cask Storage System (DCSS) Canisters

Abstract The lifetime of stainless steel dry cask storage systems (DCSS) for intermediate storage of spent nuclear fuel (SNF) is being extended due to the absence of a permanent repository. To ensure integrity over the course of the extended canister lifetime, solutions to postulated degradation mechanisms must be developed and established. Chloride-induced stress corrosion cracking (CISCC) has been identified as the bounding degradation mechanism given the potentially corrosive environment in which DCSS are installed in conjunction with the tensile stress and susceptible material present in the heat affected zone (HAZ) of the spent nuclear fuel (SNF) canister closure fusion welds. Cold spray has been identified as one of the most promising mitigation and repair solutions for CISCC with ASME draft code case N-927 currently being developed to implement the technology for Section XI mitigation activities for DCSS canisters. With the viability and benefits of cold spray for the CISCC DCSS application already established, this present work looks to develop cold spray surface preparation and coating process parameters to increase the largest sealable crack width to 75 μm. Key parameters, including powder blend composition, particle size for surface preparation and coating, and spray angle, were evaluated for crack sealing efficacy using helium leak rate testing. Optimized parameters were then applied to simulated CISCC samples within a canister-overpack mockup, advancing the technology toward field implementation.