abstract will be provided later

Long-term safety assessments for a deep geological repository for highly radioactive waste require evaluating potential future geological and climatic developments over the next one million years. Therefore, the impact of potential future cold stages and glaciations on the geological barrier needs to be considered. The glaciation of a repository site is likely to have the largest effect; however, repository sites located outside the maximum ice-sheet extent may also be affected. Relevant processes with potentially large impacts that can reach repository-relevant depths include glacigenic erosion, ice-load induced deformation, and permafrost formation. A sound understanding of the processes during past glaciations is key to assessing the potential impact of future glaciations, which may serve as analogues. We present examples from current case studies that use reconstructions and numerical modelling of Pleistocene processes to support long-term safety assessments. The first case study focuses on the incision of Pleistocene tunnel valleys in northern Germany. Based on zones of similar depth, the potential for future subglacial erosion is assessed (Breuer et al. 2023). The distribution and orientation of tunnel valleys are compared to the regional structural framework to understand the geological control on subglacial incision (Lang et al. 2025). The second case study presents a numerical model of the response of salt structures to ice-sheet loading (Lang & Hampel 2023), offering new insights into the controlling factors of ice-salt interactions.

References:

Breuer et al. (2023) DOI: https://doi.org/10.5194/egqsj-72-113-2023

Lang & Hampel (2023) DOI: https://doi.org/10.1007/s00531-023-02295-5

Lang et al. (2025) DOI: https://doi.org/10.1111/bor.12694

The Opalinuston-Formation in Southern Germany comprises a thick sequence of Middle Jurassic silty claystones. In parts of Bavaria and Baden-Württemberg, the formation has been designated as a sub-area by the Federal company for radioactive waste disposal (BGE), indicating that favorable geological conditions for the final disposal of high-level radioactive waste can be expected there. However, state-of-the-art sedimentological and stratigraphic data for the complete formation is typically lacking. This contribution provides new and coherent data on the geological variability of the Opalinuston-Formation in Southern Germany based on four drill cores that penetrated through the entire formation. Cores were examined in high resolution using a combination of classic core description techniques, non-destructive analytical tools such as XRF core scanner and high-frequency sampling for a precise stratigraphic classification and geochemical-mineralogical characterization. Particularly with respect to changes in grain size, clay mineralogy and sedimentary facies, results exhibit both, notable variability but also similarities between sites, and in comparison to observations from Switzerland. Such sedimentological and stratigraphic patterns can be explained by the interplay of a complex, bottom-current dominated depositional environment, and differential subsidence, leading to relative-sea-level changes on a sub-basin scale. In summary, this contribution highlights the geological variability of the Opalinuston-Formation in Southern Germany and beyond, and discusses the possibilities of a sequence stratigraphic approach to accelerate exploration efforts of siting regions in claystone formations in order to rapidly identify the most suitable parts for the final disposal of high-level radioactive waste.

The predictability of transport pathways in potential host rock formations for deep geological disposal of nuclear waste is crucial, as it helps to understand contaminant mobility and importantly, retention processes and the mechanistical understanding causing these reactions. This is currently being investigated at the BUKOV Underground Research Facility in the Czech Republic. In the recent study by Kuva et al. 2025, transport pathways were intensively analyzed using a drill core sample, with extraction approved by SÚRAO (Radioactive Waste Repository Authority).

Their analysis revealed that the core was overprinted by a complex network of fractures and veins, and the surrounding rock exhibited noticable variations in porosity. Revisiting those samples, this study focuses on the trace element enrichment within multiple carbonate infills to better understand the genesis and retention capacity of these migration paths. Trace element analysis was conducted using µXRF and LA-ICP-MS. Cluster analysis enabled the identification of several precipitation events. Comparisons of selected areas using SEM-CL and SEM-EBSD demonstrated that, in these samples, carbonate trace element incorporation is primarily influenced by fluctuations in the initial solution composition.

By comparing our findings with the characteristics of the fracture network, we traced some of the investigated transport paths, allowing us to connect geochemical observations with the structure of migration pathways.

References:

Kuva, Jukka; Jooshaki, Mohammad; Jolis, Ester; Sammaljärvi, Juuso; Siitari-Kauppi, Marja; Jankovský, Filip et al. (2025): Characterizing heterogeneous rocks in 3D with a multimodal deep learning approach – Implications for transport simulations. In: Tomography of Materials and Structures 7, S. 100055. DOI:10.1016/j.tmater.2025.100055.

The study of the long-term evolution of permeability of crystalline rocks under different high-pressure/temperature conditions is important for various geological underground projects, including the safety disposal of nuclear waste. As one of the specific objectives of the AMPEDEK project, this work focuses not only on studying the thermo-hydro-mechanical response of a representative granitic rock sample from the German crystalline basement under different high-pressure/temperature conditions, but also on analyzing the dynamics of permeability through long-term flow-through experiments.

The experiments were conducted using the Thermo-Triaxial device, which was designed to perform triaxial tests under high pressure/temperature. Cylindrical plugs were tested under different combinations of vertical and lateral stresses at three temperatures (30, 60, and 90 °C). Matrix permeability and the resulting deformation of the plugs were continuously monitored throughout the entire experiment (12 days).

At 30 °C and 60 °C, permeability exhibited minor and reversible changes during one or two load–unload cycles, indicating limited alteration of the rock structure under these conditions. In contrast, at 90 °C, a pronounced and irreversible decrease in permeability—by more than two orders of magnitude—was observed during the first load cycle, suggesting permanent structural changes or clogging effects within the pore network. During the second cycle at 90 °C, the permeability behavior resembled the reversible trends observed at the lower temperatures.

Permeability changes can be categorized into two types based on the prevailing stress conditions: (1) instantaneous changes resulting from the modification of the mean stress, and (2) gradual changes attributed to time-dependent deformation (creep-effect).

In accordance with § 57b of the German Atomgesetz, the Asse II potash and salt mine has to be closed down immediately after the retrieval of the stored radioactive waste. Due to the current technological and geological status of the mine, a new retrieval mine is indispensable for achieving this goal. Thus, an extensive exploration of the currently undisturbed part of the Asse salt dome in the southeast of the current mine is required.

Given the internal complexity of steep salt formations and the resulting challenges with exploring those, a cross-discipline approach was and still is irreplaceable for creating the required geological model of the Asse salt dome. This presentation discusses the used multi-method workflow starting with detailed drill core analysis utilising a combination of traditional geological core description and a variety of non-destructive and destructive geochemical analyses. The resulting lithology log is subsequently extrapolated into the 3D-space using mainly borehole ground-penetrating radar with different frequency ranges. In the last step a detailed model of the subsurface is constructed using the results of the afore mentioned methods in combination with modern surface based geophysical measurements like 3D seismic and rechecked or partially revised historical data like mine plans and drill logs. The approach contributes to best practices in geological modelling of salt structures (e.g., for deep geological repositories), and can serve as a template for similar projects in comparable geological settings.