Challenges and best practices for modelling fractures in geological repositories

Abstract. Crystalline rock formations, which are considered potential host formations for geological repositories in Germany, often exhibit fractures that complicate the generation of safety assessment models. To quantify criteria outlined Ordinance on Repository Safety Requirements accurately, it is necessary to take these into account and consider both intact mass properties numerical The consideration models a challenge due complex three-dimensional nature fractures. In literature, various methods approach this documented, but combination assumptions simplifications associated with can lead significant uncertainties calculations. address challenge, we evaluated suitability modelling approaches fractured media, based such as accuracy, computational efficiency, ease implementation, specific types problems. Comparative calculations (benchmarks) used develop corresponding previously defined generic contain way, possible clarify influence different results, thus providing basis assessing required case. We would like give an overview two R&D projects, SUSE (Safety analyses repository systems crystalline rocks) PRECODE (Investigating impacts mining activities at great depths integrity context high-level radioactive waste disposal). addresses hydraulic problems, specifically groundwater flow rock. Analysing direction rate crucial assess transport radionuclides geosphere, they most likely be transported by groundwater. Different were tested, explicit manner try upscale heterogeneous fracture properties, compared each other via benchmark cases. cases specified differ mainly number (single network) physical processes simulated (fluid solute transport). PRECODE, hand, focuses mechanical barrier. must shown demonstrating dilatant strength expected fluid pressure do not exceed explicitly represent using discontinuum continuum well upscaling only integral mass, assumed respective scale considered, borehole, tunnel, scales. Overall, research provides insight challenges best practices improving disposal.