A promising sequence stratigraphic approach to identify potential siting regions in claystone formations

The selection procedure to identify the site “best possible” to host Germany’s repository for the final disposal of its high activity nuclear waste considers claystone, rock salt and crystalline rock as potential host rocks. Preliminary considerations estimate the area required for a claystone-hosted repository to be 10 km². There are nine “sub-areas” (i. e. areas with conditions expected to be favourable for the safe final disposal of high activity nuclear waste) having claystone formations as potential host rock. Their sizes range between 943 and 62,885 km², which is roughly 90 to 6000 times the size considered necessary for a claystone-hosted repository. Consequently, reducing sub-area size sophisticatedly constitutes a major challenge to the site selection procedure.

The project SEPIA aims to apply a sequence stratigraphic approach to characterize and correlate barrier properties of Aalenian rock formations, namely the Opalinus Clay (OPA), in Southern Germany. Therefore, four drillcores constituting an approx. 330 km long transect have been acquired to derive the spatial distribution of clay-rich and -poor horizons across the sedimentary basin, eventually leading to a paleofacies map. In addition, correlation with results from similar investigations in Switzerland adds another 100 km to the transect. This will allow assessing to which degree results from the OPA characterization carried out in the Swiss site selection procedure can be transferred to Southern Germany. Overall, the approach used in SEPIA appears to be a promising one to identify potential siting regions of reasonable size out of the large sub-areas for detailed exploration.