Uranium migration lengths in Opalinus Clay depend on geochemical gradients, radionuclide source term concentration and pore water composition
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Published:2023-10-18
Issue:
Volume:62
Page:21-30
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ISSN:1680-7359
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Container-title:Advances in Geosciences
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language:en
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Short-container-title:Adv. Geosci.
Author:
Hennig Theresa, Kühn MichaelORCID
Abstract
Abstract. Safety assessments of highly radioactive waste disposal sites are done based on simulation of radionuclide migration lengths through the containment providing rock zone. For a close to real case situation, the present model concept established for uranium is derived from the hydrogeological evolution and geochemical and mineralogical data measured at the deep geothermal borehole Schlattingen including the effect of geo-engineered barriers on the source term. In the Schlattingen area, the Opalinus Clay is tectonically undeformed compared to the Mont Terri anticline and represents the geochemical and temperature conditions at the favoured disposal depth. The geochemical conditions are more or less constant with slightly decreasing concentrations of pore water components towards the footwall aquifer. Uranium migrates less compared to the Opalinus Clay system at Mont Terri, where gradients of pore water geochemistry towards the embedding aquifers are more pronounced. This means, stable geochemical conditions with no or low concentration gradients are to be favoured for a safe disposal since migration lengths strongly depend on spatial and temporal variation of the hydrogeological and geochemical conditions within the host formation. The engineered barriers reduce the source term concentration what, in turn, is associated with a decrease in uranium migration. Stable geochemical conditions further enable the application of the Kd approach to estimate the impact of the barriers. The hydrogeological system must always be considered when quantifying radionuclide migration.
Publisher
Copernicus GmbH
Subject
General Chemical Engineering
Reference38 articles.
1. Aubourg, C., Kars, M., Pozzi, J. P., Mazurek, M., and Grauby, O.: A magnetic geothermometer in moderately buried shales, Minerals, 11, 957, https://doi.org/10.3390/min11090957, 2021. a 2. Davies, C. W. and Shedlovsky, T.: Ion Association, J. Electrochem. Soc., 111, 85C, https://doi.org/10.1149/1.2426129, 1964. a 3. Ewing, R. C.: Long-term storage of spent nuclear fuel, Nat. Mater., 14, 252–257, https://doi.org/10.1038/nmat4226, 2015. a 4. Gimmi, T., Waber, H. N., Gautschi, A., and Rübel, A.: Stable water isotopes in pore water of Jurassic argillaceous rocks as tracers for solute transport over large spatial and temporal scales, Water Resour. Res., 43, W04410, https://doi.org/10.1029/2005WR004774, 2007. a, b, c, d, e, f, g 5. Grenthe, I., Gaona, X., Plyasunov, A. V., Rao, L., Runde, W., Grambow, B., Konings, R. J. M., Smith, A. L., and Moore, E. E.: Second update on the chemical thermodynamics of uranium, neptunium, plutonium, americium and technecium, Chemical Thermodynamics no. 14, OECD Nuclear Energy Agency, Boulogne-Billancourt, France, https://www.oecd-nea.org (last access: 19 September 2023), 2020. a
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