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Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters. After one and two years of incubation at 25 °C, respectively, supplemented SD80 microcosms con

Concerning the deep geological disposal of high-level radioactive waste (HLW), bentonite can be used because of its high swelling capacity and its low hydraulic conductivity as geo-technical barrier and buffering material in between the waste-containing canister (technical barrier) and the surrounding host rock (geological barrier). There are still many gaps in process understanding of bentonite transformations, especially in dependence of different temperatures and pore waters. Within the joint-project UMB (“Umwandlungsmechanismen in Bentonitbarrieren”), the co-operation partner Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Repository Safety Analysis), the University of Greifswald (Institute for Geography and Geology), the Federal Institute for Geosciences and Natural Resources (BGR, section of technical mineralogy), the Technical University of Munich (TUM; chair of theoretical chemistry, quantum chemistry) and the Helmholtz-Center Dresden-Rossendorf (HZDR, Institute of Resource Ecology) are supposed to define criteria which facilitate the selection of suitable bentonites in order to use them in the deep geological repository of high-level radioactive waste. HZDR analyzed two different bentonites (B36 and SD80) regarding their microbial diversity and potential microbial activity. In dependence of repository-relevant parameters (temperature, pore water, presence of substrates), microcosm experiments were set up at the GRS, containing the respective bentonites and Opalinus Clay pore water or cap rock solution, respectively. The long-term batches were incubated one year and two years at different temperatures (25 °C, 60 °C and 90 °C) in gastight bottles. Additionally, HZDR set up B36 short-term microcosms with Opalinus Clay pore water, which incubated for three month at 30 °C with six sampling points monitoring the microbial diversity and geochemical parameters. After one and two years of incubation at 25 °C, respectively, supplemented SD80 microcosms con