Predicting the uptake of Cs,Co, Ni,Eu, Th and U on argillaceous rocks using sorption models for illite |
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| Institution: | 1. Laboratory for Waste Management, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland;2. Belgian Nuclear Research Centre (SCK?CEN), Expert Group Waste & Disposal, 2400 Mol, Belgium;1. Laboratoire SUBATECH, UMR 6457 CNRS-IN2P3/Ecole des Mines de Nantes/PRES UNAM, 4 rue A. Kastler, 44307 Nantes Cedex, France;2. Radiochemistry Lab, School of Nuclear Science & Technology, Lanzhou University, Lanzhou 730000, China;3. Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei, Anhui 230031 PR China;4. ANDRA, Research and Development Division, 1/7 rue Jean Monnet, 92298 Châtenay-Malabry cedex, France;1. Univ. Orléans, CNRS, BRGM, ISTO, UMR 7327, F-45071 Orléans, France;2. BRGM, 3 avenue Claude Guillemin, Orléans 45060, France;3. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;4. Andra, 1 – 7 rue Jean Monnet, Châtenay-Malabry 92298, France |
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| Abstract: | Reliable predictions of radiocontaminant migration are a requirement for the establishment of radioactive waste repositories. Parametrization of the necessary sorption models seems to be, however, extremely challenging given the multi-mineralic composition of the lithosphere. In this study it is shown for two argillaceous rocks – Boda and Opalinus Clay relevant for the Hungarian and Swiss repository concepts, respectively – that this task can be substantially simplified by taking into account only the most sorptive mineral fraction, namely the 2:1 clay minerals illite and illite/smectite mixed layers. Two different models were required to blind predict the sorption isotherms of Cs, Co, Ni, Eu, Th and UO2 measured on the two clay rock samples in a synthetic porewater. Cs sorption was modelled with the generalised Cs (GCs) sorption model and the sorption of the other cations with the 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) model. The 2SPNE SC/CE model for illite was extended with surface complexation reactions on weak sites for Co, Ni, Eu, UO2 and on strong sites for Eu-carbonato complexes. Complementary to the sorption measurements and modelling, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to probe the retention mechanism of Ni on illite, Boda and Opalinus Clay at higher loadings. The reliable blind predictions of the selected metal cations, which are representative for monovalent alkaline metals, divalent transition metals, lanthanides, and trivalent, tetravalent and hexavalent actinides, confirms the applicability of this simplified bottom up approach, and, renders the underlying sorption models particularly useful to predict sorption for the wide range of cations to be considered in the safety analysis of radioactive waste repositories in clay-rich environments. |
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