The evolution of the nearfield in a deep geological repository after closure defines the corrosion evolutionary path which describes the time-dependant corrosion behaviour of disposal canisters. As the conditions in the vicinity of the canister evolve, so will the corrosion reaction mechanisms and rates change. The stresses from tunnel convergence and swelling of bentonite, which is used as buffer, will in combination with the corrosion, determine the canister’s lifetime. The evolution of the repository is determined by repository-induced effects which are divided in four main categories:
- Thermal effects arising from the decay heat generated by the waste.
- Rock-mechanical effects arising from the mechanical disturbance to the host rock caused by the excavation of the emplacement drifts and other underground structures.
- Hydraulic and gas-related effects related to repository resaturation and to gas generation due to the corrosion of metals within the repository.
- Chemical effects arising from the interactions between the engineered barrier materials as well as the waste and the host rock.
With this paper we present the evolution of the environmental conditions in the vicinity of a carbon steel canister for the disposal of spent fuel and high-level waste based on the latest scientific understanding of relevant repository-induced effects with the focus on canister integrity. The purpose of this storyboard is to identify and describe the expected conditions in the repository, including the uncertainties, and provide input to research related to both improved site-specific coupled processes modelling of the environmental conditions and corrosion-related investigations. We also aim to demonstrate the improved scientific understanding of safety-relevant processes achieved during the last decade [Johnson and King 2008].
Among others, the following processes will be evaluated:
- Evolution of the temperature on the canister surface and the nearfield.
- Evolution of mechanical stresses applied on the canister resulting from host rock creep and bentonite swelling.
- Evolution of the relative humidity at the canister surface during the progressive resaturation of the repository resulting from the interplay between porewater ingress and gas generation and pressure build-up.
- Evolution of the gas phase composition at early phase.
- Evolution of the porewater composition at later phases due to e.g. interactions between iron corrosion products and bentonite or microbial activity in the EDZ and diffusion of sulphide towards the canister.
References
Johnson, L. and King F. (2008): The effect of the evolution of environmental conditions on the corrosion evolutionary path in a repository for spent fuel and high-level waste in Opalinus Clay. Journal of Nuclear Materials, 379, p. 9-15.
corrosion, canister lifetime, repository-induced effects, steel-bentonite interacitons