Crack Mitigation for Dry Storage Canisters

Welded stainless steel canisters that contain spent nuclear fuel (SNF) at near-marine sites have been found with salts on their outer surface that can produce an aggressive chemical environment that could lead to pitting, stress corrosion cracking (SCC), and potential release of radioactive materials. Welds that are most susceptible to SCC are difficult to reach because they are located inside the canister’s concrete overpack with only a small air gap available for access.We propose to develop a process and device for mitigating potential SCC in dry storage canisters for SNF. The process will eliminate high residual tensile stresses in the heat-affected zones of the welds using a safe and benign process that will not affect the mechanical strength of the canister. The process will be administered by a small robotic device that can be inserted into the natural convection flow space between the canister and the overpack. In Phase I, we will optimize the mitigation process, use finite element analysis (FEA) for detailed evaluation of stresses near the weld, produce a conceptual design of the robotic mitigation device, and demonstrate the process using prototypical weld samples. We will optimize the process using phenomenological models of the weld treatment process combined with FEA. We will validate our models through proof-of-concept experiments on prototypical weld samples and post-treatment metallurgical analysis. Finally, we will produce a detailed concept design of the robotic device along with concepts of operation describing how the device will function in the field.Commercial Applications and Other Benefits: Creare’s system will enable spent fuel storage facility operators to mitigate the effects of potential SCC. The benign process can be widely adopted and the compact, robotic device will be sized to enable treatment of canisters in all major commercial storage systems. Creare will sell mitigation systems to existing vendors of spent fuel canister maintenance systems as well as vendors of systems for strengthening welds in other large non-DSC structures.