Monitoring of helium gas leakage from canister storing spent nuclear fuel: Radiological consequences and management

•Consequence of He gas leakage due to CISCC and managements by monitoring temperature-difference on canister were proposed.•The monitoring method can detect leakage to avoid air ingress into the canister and oxidation of spent fuel.•The monitoring method can detect leakage to avoid violating regulatory limits on offsite dose under normal condition. Chloride-induced stress corrosion cracking (CISCC) of canisters has been identified as a potential degradation mechanism requiring ageing management — especially in a marine air environment. Methods for monitoring helium gas leakage from canisters have been developed on the basis of a phenomenon that the bottom temperature of the canister increases as the top temperature of the canister decreases when helium gas leaks during storage. In this paper, we consider the radiological consequences of CISCC based on two scenarios of helium gas leakage and propose effective management that includes a timeline for monitoring and mitigation. Monitoring helium gas leakage by measuring the difference in temperature between canister surfaces in the dry cask storage of spent fuel (SF) can detect leakage before SF undergoes oxidation as a result of air ingress and before country-specific regulatory limits of off-site doses are exceeded, thereby enabling mitigatory action.