Reactive-transport model for the production, transport, and consumption of sulfide in a spent nuclear fuel deep geological repository in crystalline rock

A 1-D reactive-transport model has been developed to describe the production and transport of sulfide in a deep geological repository in crystalline rock and the subsequent corrosion of the copper canister. The model accounts for various processes, including: (i) the microbial reduction of sulfate by organotrophic and lithotrophic sulfate-reducing bacteria, (ii) the supply of sulfate from both the ground water and from the dissolution of gypsum present as an accessory mineral in the bentonite buffer, (iii) diffusive transport of reactants and products, and (iv) sequestration of a fraction of the microbially produced sulfide by precipitation as mackinawite. The results of a base case simulation and of sensitivity analyses indicate that the extent of uniform corrosion is approximately 0.2 mm after 1 million years and that the maximum flux of sulfide to the canister surface is below the threshold for localized corrosion or stress corrosion cracking.