Corrosion considerations in the design of a canister for the long term disposal of spent fuel and high level nuclear waste

摘要

Long term deep geological disposal of spent nuclear fuel and high level nuclear waste is aimed at shielding the biosphere from the harmful effects of radioactive materials until they decay. Thus, the design and construction of canisters which are able to survive for thousands of years in repository conditions without breach of containment is required. Apart from the very long time scales involved, the challenge of designing a nuclear waste disposal canister resides in understanding the evolution of the environmental conditions on the canister surface during its lifetime, as well as in identifying the relevant corrosion mechanisms and their interaction with structural performance. In this work we present the rationale guiding materials selection for a nuclear waste disposal canister in the context of the Swiss concept for deep geological disposal in Opalinus Clay. For one of the potential canister materials, carbon steel, Nagra has along with TWI performed a canister design study in which the material selection and corrosion considerations have been integrated. The evolution of critical parameters (temperature, humidity, availability of O_2, etc.) in the near field environment of the repository during the lifetime of the canister dictates the potential corrosion mechanisms (uniform corrosion, stress corrosion cracking, hydrogen induced cracking, microbial corrosion, etc.) that need to be considered, which are directly linked to the risk of the breach of containment. The study of the corrosion mechanisms prevailing for the different candidate materials is a critical step in the materials selection and overall design of the canister.