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 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 canisters are installed in concrete over-pack structures with limited access.Mitigation approaches must meet stringent requirements for safety and avoid processes that can affect the mechanical strength of the canister.We propose to develop a process and system 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 can be administered using relatively inexpensive equipment and conventional methods for handling loaded canisters.We proved the feasibility of our SCC mitigation process through structural analysis, proof-of-concept demonstrations, measurements of residual stress fields near treated and untreated welds, and conceptual design of a full-scale device for treating canister welds.Thermal and structural analysis helped guide a series of proof-of-concept tests in which we used our process to modify residual stress fields around sample welds.We measured the residual stress fields and showed that our process performs as expected and can be used to convert residual tensile stresses to compressive stresses in the weld fusion and heat affected zones.We then used design information for SNF canisters to show how the process can be applied to loaded canisters in the field using simple and inexpensive hardware.We will design and build a facility for process development and optimization using fully-prototypical process equipment and weld samples.We will apply the process, measure the resulting residual stresses, feedback results, and specify the process for all weld types used in fielded canisters.We will produce a detailed conceptual design of a system that applies our process to welds on loaded canisters.Creare’s system will ensure safe long-term storage of SNF and is uniquely able to treat canisters that are already loaded and deployed in the field.The process can also be used during manufacture of new canisters before loading.Creare will sell systems to managers of spent fuel storage facilities, manufacturers of SNF storage canisters and systems, and vendors of other large welded structures to mitigate crack growth.