Challenges and approach to a geological 3-D modeling workflow to identify potential areas for a repository for high-level radioactive waste

In 2020, the Bundesgesellschaft für Endlagerung mbH (BGE) published the Sub-areas Interim Report, identifying areas with favorable geological conditions for a deep repository site for storage of high-level radioactive waste in Germany. One key step was the identification of geological settings, where potential host rock formations (claystone, rock salt and crystalline rock) fulfil legally defined minimum requirements, e.g. depth (> 300 m), areal extension (varying between host rocks), and vertical thickness (> 100 m). Therefore, we examined 21 existing regional 3-D models generated by various German federal and state authorities with a different focus, detail and coverage (e.g. Rhine Graben, North German Basin). Hence, we had to deal with a large amount of data, different model scales, inhomogeneity and possible inconsistencies at the state boundaries. In order to identify the potential host rock formations within the geological 3-D models and to ensure an equal processing, we generated a semi-automated workflow in SKUA-GOCADTM that extracted areas that fulfil the minimum requirements. However, the heterogeneous input data produced inconsistencies in the results of the workflow that required extensive quality control and correction. Another challenge was related to thickness calculations in the presence of fault surfaces. We quantified potential inaccuracies and showed that their impact is negligible with respect to the model scale. Considering our approach, we provided a transparent and reproducible workflow within the search for a repository site for storage of high-level radioactive waste.