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  • 2020-2024  (22)
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  • 11
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    Simulation of diffusive uranium transport and sorption processes in the Opalinus Clay (2020)
    In:  Applied Geochemistry
    Details
    Publication Date: 2023-01-19
    Description: Diffusive transport and sorption processes of uranium in the Swiss Opalinus Clay were investigated as a function of partial pressure of carbon dioxide , varying mineralogy in the facies and associated changes in porewater composition. Simulations were conducted in one-dimensional diffusion models on the 100 m-scale for a time of one million years using a bottom-up approach based on mechanistic surface complexation models as well as cation exchange to quantify sorption. Speciation calculations have shown, uranium is mainly present as U(VI) and must therefore be considered as mobile for in-situ conditions. Uranium migrated up to 26 m in both, the sandy and the carbonate-rich facies, whereas in the shaly facies 16 m was the maximum. The main species was the anionic complex . Hence, anion exclusion was taken into account and further reduced the migration distances by 30 %. The concentrations of calcium and carbonates reflected by the set determine speciation and activity of uranium and consequently the sorption behaviour. Our simulation results allow for the first time to prioritize on the far-field scale the governing parameters for diffusion and sorption of uranium and hence outline the sensitivity of the system. Sorption processes are controlled in descending priority by the carbonate and calcium concentrations, pH, pe and the clay mineral content. Therefore, the variation in porewater composition resulting from the heterogeneity of the facies in the Opalinus Clay formation needs to be considered in the assessment of uranium migration in the far field of a potential repository.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 12
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    Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri (2021)
    In:  Minerals
    Details
    Publication Date: 2023-01-19
    Description: Transport properties of potential host rocks for nuclear waste disposal are typically determined in laboratory or in-situ experiments under geochemically controlled and constant conditions. Such a homogeneous assumption is no longer applicable on the host rock scale as can be seen from the pore water profiles of the potential host rock Opalinus Clay at Mont Terri (Switzerland). The embedding aquifers are the hydro-geological boundaries, that established gradients in the 210 m thick low permeable section through diffusive exchange over millions of years. Present-day pore water profiles were confirmed by a data-driven as well as by a conceptual scenario. Based on the modelled profiles, the influence of the geochemical gradient on uranium migration was quantified by comparing the distances after one million years with results of common homogeneous models. Considering the heterogeneous system, uranium migrated up to 24 m farther through the formation depending on the source term position within the gradient and on the partial pressure of carbon dioxide pCO2 of the system. Migration lengths were almost equal for single- and multicomponent diffusion. Differences can predominantly be attributed to changes in the sorption capacity, whereby pCO2 governs how strong uranium migration is affected by the geochemical gradient. Thus, the governing parameters for uranium migration in the Opalinus Clay can be ordered in descending priority: pCO2, geochemical gradients, mineralogical heterogeneity.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 13
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    Preface to the special issue of the Division Energy, Resources and the Environment at the EGU General Assembly EGU22 (2022)
    In:  Advances in Geosciences
    Details
    Publication Date: 2023-02-01
    Description: The European Geosciences Union (EGU) is one of the leading global bottom-up societies that promotes earth, planetary and space sciences. In its annual general assemblies, EGU brings together experts from all over the world to discuss cutting-edge research and implementation of findings in their respective disciplines and beyond via its inter-and transdisciplinary sessions, and thus offers a unique forum for scientific exchange, science-policy interaction, and joint development of strategies for future research endeavours. Within that framework the Energy, Resources and the Environment (ERE) Programme Group provides the platform for discussion about adequate and reliable supplies of affordable energy and other georesources in environmentally sustainable ways. This special issue in Advances in Geosciences comprises a collection of contributions from the ERE Programme Group, which were presented at the General Assembly 2022. It was held in hybrid mode for the first time from 23–27 May 2022, after two virtual assemblies in 2020 and 2021.
    Language: English
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  • 14
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    Characterizing offshore freshened groundwater along the Maltese Islands through geophysical and geochemical data integration (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-12
    Description: The rising demand for potable water in densely populated coastal regions has recently promoted growing research interest in detecting offshore freshened groundwater (OFG) worldwide. Recent geophysical studies along the continental margins offshore Israel, New Zealand, Malta, and the United States of America provide some examples of integrating geophysical and borehole data to constrain the spatial extent of OFGs and estimate their pore-water salinity. However, occurrences of OFGs and the interaction between terrestrial, carbonate-hosted groundwater systems with seawater are understudied in many coastal regions by complicated seafloor morphology. In this study, we investigate whether OFG can exist offshore a semi-arid carbonate coastline along the Maltese Islands and explore the possibility of sustainably exploiting these reservoirs as an unconventional source of potable water to relieve freshwater scarcity. We present an integration of 2-D resistivity models derived from marine controlled source electromagnetic (CSEM) measurements with 2-D and 3-D seismic data, core samples, borehole data, and geochemical measurements. Electrical resistivity models identify localized resistive anomalies (〉 10 ohm-m) offshore the northeastern coast of Gozo (the second-largest island in the Maltese archipelago). Furthermore, a resistive body is observed at ~ 300 m below sea level close to the coast of Gozo which extends northeastwards and disappears at ~ 8 km offshore. If the anomalous resistive body is associated with pore-water salinity variations or, alternatively, caused by lithological changes, will be discussed through an integrative geological model developed along each profile.
    Language: English
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  • 15
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    Hydrogeochemical impact of Opalinus Clay system shown in migration lengths of uranium (2023)
    In:  Safety of Nuclear Waste Disposal - SaND
    Details
    Publication Date: 2023-09-08
    Description: Models and simulations allow a prognosis of how processes in the geosphere might occur in the future by considering physical and chemical processes. They are the only way to test future scenarios and hypotheses and to evaluate how a repository site will develop over a period of a million years, e.g. by quantifying potential radionuclide migration in the hydrogeological system of the containment providing rock unit. An example is used to demonstrate the extent to which simulated migration lengths can vary for a million years, depending on the model concept and on the underlying data and parameters. In the case of uranium in the potential host rock Opalinus Clay (Switzerland), the range extends from 5 m, by applying experimentally determined transport parameters, over 50 m, using process-based approaches and taking hydrogeology into account, and up to 80 m, depending on the thermodynamic data set used. The degree of reliability of the models is derived from comparison with laboratory tests, data from boreholes and underground laboratories or natural analogues. This is the only way to assess the simulation results. In addition, indications can be provided regarding where new data need to be collected. So our task is to find an answer to the following question: how accurate do the models for the repository site search have to be in order to produce resilient and robust forecasts? To reduce the uncertainty related to the migration length of uranium in the Opalinus Clay, the calcite carbonate ion and the hydrogeological system at a potential disposal site need to be known, whereas the quantity of clay minerals plays a subordinate role, as long as it is enough, which is the case in argillaceous formations.
    Language: English
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  • 16
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    Time to change the geoscientific perspective!? (2023)
    In:  Safety of Nuclear Waste Disposal - SaND
    Details
    Publication Date: 2023-09-08
    Description: The Repository Site Selection Act (StandAG) explicitly emphasises that targeting the disposal of high-level radioactive waste is a so-called learning process. For example, progress in scientific knowledge, in the methodological approach or in new data should be accounted for. We believe that now is a good time to reflect on what we have learned so far and to put the methodological approach to the test. Therefore, we need to question the perspective of the problem: is the bottom-up strategy (data-based), which reduces the remaining search area more and more, objectively feasible enough, or is there a complementary methodological approach? We are of the opinion that the procedure and the available data should be combined with geoscientific knowledge in a top-down (knowledge-based) manner to support the identification of siting regions. The current bottom-up strategy of continually narrowing down the areas can be purposeful, but it postpones a fundamental problem to a later point in time: how do we compare host rock types? So far, this question has only been addressed qualitatively (BGR, 2007). If this approach were to be developed intellectually and quantitatively, then the following fundamental question could be addressed: does one type of host rock in Germany generally always perform better or worse than another?
    Language: English
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  • 17
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    Numerical simulation of spatial temperature and salinity distribution in the Waiwera geothermal reservoir, New Zealand (2023)
    In:  Grundwasser
    Details
    Publication Date: 2023-09-20
    Description: The geothermal reservoir in Waiwera was not sustainably managed for many decades. Hence, the responsible authority introduced a water management concept, whereby various independent models were developed and calibrated using observations. As these models were not yet able to reproduce all observations, constant model revisions are critical for efficient reservoir management. Results of a recent field campaign were used for the current model revision, considering two new main structural geological findings to reconstruct the natural reservoir state. Our simulation results demonstrate that a recently proven north-south trending fault in the study area plays a key role in improving the model. Further analysis suggests the presence of a not yet confirmed additional west-east aligned geologic fault in the north, since thermal convection is observed inland. Additional field campaigns are needed to acquire more information on the main geological fault zones as well as additional data on temperature and salinity distributions.
    Language: English
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  • 18
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    Stable Isotopes and Water Level Monitoring Integrated to Characterize Groundwater Recharge in the Pra Basin, Ghana (2023)
    In:  Water
    Details
    Publication Date: 2024-01-16
    Description: The yield and composition of tar depending on coal rank and pressure during underground coal gasification (UCG) were studied. Two coals were used in a series of ex-situ UCG experiments: a Welsh semi-anthracite (Six Feet) and a Polish bituminous coal (Wesoła). Four high-pressure gasification trials under two distinct pressure regimes (20 and 40 bar) were conducted. The tar samples were collected directly from the reactor outlet. The following groups of compounds were analysed by use of gas chromatography (GC-MS): light monoaromatic hydrocarbons (BTEX – benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and phenols. A series of gasification experiments revealed significant differences in tar yields and composition depending on the coal rank and gasification pressure. Significant decreases in tar contents were observed with the increase in gasification pressure from 20 to 40 bar for both coals. The total yields of the analysed tar components per kg of gasified coal were 2.58 g and 0.41 g for the experiments conducted on the Six Feet samples at 20 bar and 40 bar, respectively. The corresponding values for the Wesoła coal amounted to 5.48 g and 0.95 g. In all experiments, BTEX was a dominant group of tar components, constituting 69–86 % of the total tar yield within the tested range of compounds. The present study further proves that gasification pressure has a significant effect on the chemical composition of the produced UCG tars for both coal samples under study.
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  • 19
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    Uranium migration lengths in Opalinus Clay depend on geochemical gradients, radionuclide source term concentration and pore water composition (2023)
    In:  Advances in Geosciences
    Details
    Publication Date: 2024-01-15
    Description: 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.
    Language: English
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  • 20
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    Preface to the special issue of the Division Energy, Resources and the Environment at the EGU General Assembly 2023 (2024)
    In:  Advances in Geosciences
    Details
    Publication Date: 2024-01-22
    Description: The European Geosciences Union (EGU) brings together geoscientists from all over Europe and the rest of the world, covering all disciplines of Earth, planetary and space sciences. The Division on Energy, Resources and the Environment (ERE), as part of the EGU, follows an interdisciplinary approach to serve society and provide solutions to challenges of our time and in the future. One task for humankind, for example, is to provide adequate and reliable supplies of affordable energy and other resources, obtained in environmentally sustainable ways, which will be essential for economic prosperity, environmental quality and political stability around the world. This volume of Advances in Geosciences spans the range of topics of the division and continues a series of ten ERE special issues over the course of the last ten years. We incorporate emerging topics into the division ERE along the line and we advocate that every idea and opportunity should be studied and tested.
    Description: The European Geosciences Union (EGU) brings together geoscientists from all over Europe and the rest of the world, covering all disciplines of Earth, planetary and space sciences. The Division on Energy, Resources and the Environment (ERE), as part of the EGU, follows an interdisciplinary approach to serve society and provide solutions to challenges of our time and in the future. One task for humankind, for example, is to provide adequate and reliable supplies of affordable energy and other resources, obtained in environmentally sustainable ways, which will be essential for economic prosperity, environmental quality and political stability around the world. This volume of Advances in Geosciences spans the range of topics of the division and continues a series of ten ERE special issues over the course of the last ten years. We incorporate emerging topics into the division ERE along the line and we advocate that every idea and opportunity should be studied and tested.
    Language: English
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