Modeling microbial sulfate reduction and the consequences for corrosion of copper canisters

The copper sulfide model (CSM) is a one‐dimensional reactive transport code for predicting the evolution of the corrosion behavior of a copper canister in a deep geological repository. Here, the CSM has been extended to simulate the microbial reduction of sulfate in the repository and the consequences for corrosion of the canister. Organotrophic and chemotrophic sulfate reduction are represented by Monod kinetics, along with the dissolution of solid organic matter and gypsum as sources of nutrient and an electron acceptor, respectively. Siderite dissolution in the buffer and tunnel backfill materials acts as a source of Fe(II), which can then precipitate the microbially produced sulfide as mackinawite. Results are presented for a simulation representing the expected evolution of the corrosion behavior and repository environment and for a series of sensitivity analyses designed to identify the most important processes in the overall reaction scheme. Microbial activity in the excavation‐damaged zone around the deposition hole and disposal tunnel, as well as in the backfill, can lead to the generation of sulfide by sulfate‐reducing bacteria. Diffusion of that sulfide to the canister surface can cause corrosion unless the sulfide is precipitated as mackinawite or other iron sulfides in the buffer and backfill.