HR: 1340h
AN: H43F-0419    [Abstracts]
TI: Anaerobic Sulphate Reduction and Transport in a Rock Fracture Intersecting a Deposition Canister for Radioactive Waste
AU: * Sidborn, M
EM: masi@ket.kth.se
AF: Department of Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, SE-10044 Sweden
AU: Neretnieks, I
EM: niquel@ket.kth.se
AF: Department of Chemical Engineering and Technology, Royal Institute of Technology, Stockholm, SE-10044 Sweden
AB: A model was developed describing the concentration gradients of sulphate and sulphide in a fracture intersecting a deposition hole for radioactive waste material. Sulphate is present in groundwaters around the $\ddot{A}$sp$\ddot{o}$ area in Sweden in concentrations ranging from 50-700 mg/l. The reduction of sulphate produces sulphide that may diffuse into the backfill material and corrode the copper canisters. The rate of sulphate reduction may also be increased, mediated by microorganisms. Anaerobic sulphate reduction mediated by microbes at present receives extensive attention in the literature, for example in the formation of large carbonate crusts in sea sediments with methane as the reducing agent: $CH_{4} + SO_{4}^{2-} \rightarrow HCO_{3}^{-} + HS^{-} + H_{2}O$ Methane exists in the $\ddot{A}$sp$\ddot{o}$ groundwaters in concentrations up to 1 mM. Hence, this or similar processes could be possible also in the anaerobic environment surrounding the repository and, in the long term, be a threat to the canisters. The microbial activity is most likely close to the copper canisters since corrosion of those is the main sink of the produced sulphide. However, the small pores in the bentonite clay are not large enough to allow a microbe population within the backfill material. Therefore, the model includes microbially mediated reduction of sulphate at the fracture opening facing the deposition hole. Transport of substrates to the microbes occurs by diffusion perpendicular to the potential flow lines in the fracture. The model domain consists of part of the fracture surrounding the deposition hole. The three-dimensional transport of sulphide within the backfill material is included implicitly. The aims of the model are to explore the transport processes of sulphate and sulphide in a fracture intersecting a deposition hole, and to evaluate the amount of sulphide that may be transported into the backfill material at different conditions.
DE: 3210 Modeling
DE: 1832 Groundwater transport
DE: 1615 Biogeochemical processes (4805)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting