Crack Growth and Tolerance of Stainless Steel Canisters in the Marine Environment

Abstract

Most of the dry storage cask systems that are used to contain nuclear fuel are austenitic stainless steel canisters. Past experience suggests that stainless steel is susceptible to stress corrosion cracking (SCC) in the presence of chloride salts. A crack growth rate (CGR) model has been developed and applied to evaluate the crack depth in stainless steel canisters over the timeframe of the storage at independent spent fuel storage installations. This study focuses on stainless steel canisters for dry storage systems in the two nuclear power plants in Taiwan. The crack depth was first evaluated using the CGR model, site climate data, and canister surface temperature. The critical crack size and depth were then determined from the structural tolerance assessment of the canister shells. It was found that the variations in the thermal and hydraulic properties of dry storage canisters produce large variations in the SCC initiation time but do not affect the surface temperature in the range of 55–60 °C. The CGR at the SCC initiation is high and the growth of flaws is significant. The surface temperature and CGR decrease with time. The total crack depth therefore may not vary greatly as a function of SCC initiation time. Overall, dry storage canisters show high structural tolerance to crack size and depth.