The work explores modelling challenges in fractured crystalline rock formations. Addressing safety criteria requires integrating intact rock and fracture properties accurately. The intricate 3D nature of fractures complicates numerical models. Various methods exist, but assumptions lead to uncertainties. The study evaluates modelling approaches with a special focus on their accuracy and efficiency. Comparative calculations aid in understanding their impact.

For the deep geological disposal of high-level nuclear waste in rock salt formations, the safety concept includes the backfilling of open cavities with crushed salt. For the prognosis of the sealing function of the backfill for the safe containment of the nuclear waste, it is crucial to have a comprehensive process understanding of the crushed-salt compaction behavior. The KOMPASS projects were initiated to improve the scientific knowledge of using crushed salt as backfill material.

In the AREHS project, the effect of the alternation of cold and warm periods over 1 million years on the hydrogeological system in the vicinity of a repository was simulated. This was done with thermal–hydraulic–mechanical (–chemical) simulations. The simulations were implemented for generic 3D models for all three host rock formations: clay rock, salt rock and crystalline rock. In addition to the results for the generic sites, a workflow was developed that can be applied to concrete sites.

This contribution gives an overview of how the BARIK constitutive model was developed and tested. BARIK is an extended Hoek–Brown model for fractured crystalline rock that takes up to three fracture systems into account. It gives a numerical value to qualitative integrity criteria to show that the containment-providing rock zone in crystalline host rock is still intact. The BARIK model is a step forward in understanding and modeling the complex behavior of fractured crystalline hard rock.

In the framework of the Site Selection Act – StandAG, the geoscientific and planning requirements and criteria for the site selection for a repository for high-active nuclear waste are specified. This includes, among others, the modelling of hydrogeological scenarios such as how future cold and warm periods and associated glaciation events can change the (petro-)physical properties as well as the natural hydrogeological properties of the overall system which is the focus of the AREHS project.