Abstract
Radioactive waste is planned to be disposed in a deep geological repository in the Opalinus Clay (OPA) rock formation in Switzerland. Cu coating of the steel disposal canister is considered as potential a measure to ensure complete waste containment of spent nuclear fuel (SF) and vitrified high-level waste (HLW) or a period of 100,000 years. Sulphide is a potential corroding agent to Cu under reducing redox conditions. Background dissolved sulphide concentrations in pristine OPA are low, likely controlled by equilibrium with pyrite. At such concentrations, sulphide-assisted corrosion of Cu would be negligible. However, the possibility exists that sulphate reducing bacteria (SRB) might thrive at discrete locations of the repository’s near-field. The activity of SRB might then lead to significantly higher dissolved sulphide concentrations. The objective of this work is to employ reactive transport calculations to evaluate sulphide fluxes in the near-field of the SF/HLW repository in the OPA. Cu canister corrosion due to sulphide fluxes is also simplistically evaluated.
Highlights
Background and objectivesIn Switzerland, spent nuclear fuel (SF) and vitrified high-level waste (HLW) are planned to be disposed in a repository constructed in the Opalinus Clay (OPA) at a depth of about 600-900 m
Pessimistic estimates of sulphide concentrations and sulphide fluxes towards the canister can be derived from simplified models
We set out to develop a model with the aim to evaluate upper limits of sulphide fluxes towards the canister by considering geochemical constraints on sulphide generation and transport
Summary
In Switzerland, SF and vitrified HLW are planned to be disposed in a repository constructed in the Opalinus Clay (OPA) at a depth of about 600-900 m. Nagra (the Swiss National Cooperative for the Disposal of Radioactive Waste) is considering candidate designs for Cu-coated steel canisters [1]. Sulphide has been recognised as a potential Cu corroding agent under anaerobic conditions, and its effect has been evaluated by various nuclear waste disposal organisations that have considered Cu for canister material [2-5]. Sulphide cycling under repository conditions would be affected by a complex system of biogeochemical reactions and transport processes. SRB to generate elevated sulphide concentrations in the repository’s near-field by considering specific geochemical constraints, (2) quantify main model uncertainties, and (3) to evaluate maximum sulphide fluxes towards the canister as well as, in a simplified manner, assess their potential to corrode the Cu canister coating
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