Subsurface uncertainties and the screening of areas for a deep geological repository for high-level radioactive waste in Germany

In the current phase of the German Site Selection Procedure for a deep geological repository, large areas of Germany’s subsurface are being screened in order to identify the most-suited regions. The portfolio of host rocks includes claystone, rock salt, and crystalline rocks. These geological formations can exhibit significantly different properties and key subsurface uncertainties relevant to a geological repository.

Additionally, in alignment with the regulations, only existing subsurface data are used during this screening phase, i.e., data acquired for other purposes, such as hydrocarbon, potash exploration, etc. Hence, the available dataset is heterogeneous, both in terms of data types and in terms of geographical distribution.

The estimation of the subsurface uncertainties is relevant for the robustness evaluation during the safety assessment. Consequently, the uncertainty estimation concept includes methods tailored for the specific requirements.

For large areas with heterogeneous data, a semi-quantitative method for a consistent and efficient assessment of the subsurface uncertainties was developed. This method estimates a “degree of confidence”, which represents the reliability of given statements concerning the interpretation of the subsurface. The “degree of confidence” will be assessed for all investigated sub-areas in claystone, rock salt (stratiform), and crystalline host rock. It comprises the combination of data quality and quantity, on the one hand, and the geological complexity, on the other. This contribution gives an insight into the method and the preliminary results.