Geoscientific Characterisation of Sub-areas as Part of the German ‘Repository Site Selection Act‘

According to the ‘Repository Site Selection Act’ (Standortauswahlgesetz – StandAG), the German site selection procedure is an iterative process and consists of three phases with increasing levels of detail in which the assessed area is continuously reduced during the process. Starting with an empty, so-called ‘white map of Germany’, BGE (implementer of the German site selection procedure) completed Step 1 of Phase I in September 2020 with the submission of the Sub-areas Interim Report (BGE 2020). In the report, BGE identified 90 individual sub-areas (in claystone, rock salt and crystalline rock), where favourable geological conditions for the safe disposal of high-level radioactive waste can be expected.

In Step 2 of Phase I, BGE aims to localise siting regions within the 90 sub-areas by applying preliminary safety assessments and other scientific criteria. Within the preliminary safety assessments, subsurface data are interpreted and the results documented. The workflow comprises the detailed characterisation and interpretation with focus on the host rock formation that acts as the main geological barrier, but also considers the surrounding rock formations.

This contribution describes some of the compulsory geoscientific interpretation steps (e.g. well log interpretation, subsurface modelling) that are required during the preliminary safety assessments, focusing on sub-areas with flat bedded rock salt. The assessment of the spatial geometry of potential barrier rocks as well as the interpretation of their internal configuration (e.g. facies) and the understanding of relevant geological processes affecting the safety of a potential repository site are important characteristics.