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    Hydrogeochemical characterisation and modelling of groundwaters in a potential geological repository for spent nuclear fuel in crystalline rocks (Laxemar, Sweden)

    Gimeno, M.J. and Auque, L.F. and Acero, Patricia and Gomez, J.B. (2014) Hydrogeochemical characterisation and modelling of groundwaters in a potential geological repository for spent nuclear fuel in crystalline rocks (Laxemar, Sweden). Applied Geochemistry 45 , pp. 50-71. ISSN 0883-2927.

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    Abstract

    Two sites in the eastern coast of Sweden have been investigated by the Swedish Nuclear Fuel and Waste Management Company (SKB), within the framework of the site characterisation programme, as possible candidates for hosting the proposed repository for the long-term storage of spent nuclear fuel: Forsmark and Laxemar. This study presents the main results concerning the hydrogeochemical characterisation of the groundwaters in the second site, Laxemar. The distribution of the main chemical variables in groundwaters are shown and interpreted in combination with the results from speciation-solubility and reaction-path simulations, together with the available mineralogical information. The results indicate that the main processes determining the overall geochemical evolution of the Laxemar groundwaters are advective/diffusive mixing and water-rock interactions driven by past and present climatic changes inducing the input of different recharge waters over time (glacial meltwater, old marine water and modern meteoric water) and affecting the preexisting very old saline groundwaters in the bedrock. The superimposed effects of these mixing events, deduced from the behaviour of the conservative elements (Cl and δ18O), have generated a rather steep salinity gradient in the groundwater system, with diluted waters in the upper part, brackish waters in the middle, and saline waters in the lower part of the bedrock. The resultant successive disequilibrium states imposed by mixing have conditioned the water-rock interaction processes that have affected the non-conservative elements to different degrees. The main chemical reactions found to be important in controlling some of the variability of these elements and some important parameters like pH and alkalinity, are: aluminosilicate and carbonate dissolution/precipitation, quartz and fluorite equilibrium, cation exchange, and gypsum dissolution. These reactions and their importance in the system are presented in this paper. Once the main hydrogeochemical features of the Laxemar groundwaters and the potentially controlling water-rock interactions in the system have been identified and justified with the help of thermodynamic simulations, a general geochemical conceptual model has been proposed. This model will be used as the basis for predicting the future evolution of the groundwater chemistry as an essential part of the safety assessment of the future repository.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): Water-rock interaction, Geochemical modelling, Crystalline systems, Radioactive waste disposal
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Administrator
    Date Deposited: 14 Mar 2014 15:17
    Last Modified: 11 Oct 2016 15:27
    URI: http://eprints.bbk.ac.uk/id/eprint/9344

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