HR: 11:50h
AN: B31F-07    [PDF]
TI: Modeling Biogeochemical Reactive Transport in Fractured Granites: Implications for the Performance of a Deep Geological Repository
AU: * Molinero, J
EM: molinero@iccp.udc.es
AF: Civil Engineering School. University of A Coruna, Campus de Elvina s/n, A Coruna, 15192 Spain
AU: Samper, J
EM: jsc@iccp.udc.es
AF: Civil Engineering School. University of A Coruna, Campus de Elvina s/n, A Coruna, 15192 Spain
AU: Pedersen, K
EM: karsten.pedersen@gmm.gu.se
AF: Deep Biosphere Laboratory, Department of Cell and Molecular Biology. Goteborg University, Goteborg, SE-4050 30 Sweden
AU: Puigdomenech, I
EM: ignasi.puigdomenech@skb.se
AF: Swedish Nuclear Fuel and Waste Management Co., SKB, Stockholm, SE-102 40 Sweden
AB: Several countries around the world are considering deep repositories in fractured granitic formations for the final disposal of high-level radioactive waste. Evaluating the long term safety of such repositories requires sound conceptual and numerical models which are being developed from data and knowledge gained from in situ experiments carried out at deep underground laboratories such as that of Žsp” in Sweden. One of the key aspects for performance assessment concerns to groundwater redox conditions because: (a) the presence of oxygen will affect to the corrosion of canisters, (b) possible production of hydrogen sulphide from sulphate reduction will also have a negative effect on these metallic containers, and (c) several long-lived radionuclides are much more soluble and mobile under oxidizing conditions. Several projects have been performed at Žsp” to investigate different aspects of the groundwater redox evolution. The vast amount of in situ-generated information has been used in this work to set up coupled hydrobiogeochemical models. Numerical models account for saturated groundwater flow, solute transport by advection, dispersion and molecular diffusion, geochemical reactions involving both the liquid and solid phases, and microbially-catallyzed processes. For the Žsp” site, modelling results provide quantitative support for the following conclusions. (A) At the operational phase of the repository, shallow fresh groundwater could reach the depth of the underground facility. Shallow groundwaters loose dissolved oxygen during the infiltration through soil layers and then, respiration of dissolved organic matter is induced along the flow paths through the reduction of Fe(III)-bearing minerals of the fracture zones. Microbial anaerobic respiration of DOC provides additional reducing capacity at the depth of the tunnel. (B) After repository closure, atmospheric oxygen will remain trapped within the tunnel. Abiotic consumption of this oxygen has been computed to occur in a period of about 1,000 years as a result of diffusion-reaction processes. Coupled biogeochemical mechanisms, such as respiration of dissolved organic matter and aerobic methane oxidation, accelerate the oxygen uptake to less than a month.
DE: 1055 Organic geochemistry
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 3210 Modeling
DE: 3230 Numerical solutions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting