// Site Investigation and Assessment

WIBASTA

Investigations on the effectiveness of the geological and geotechnical barrier system with regard to site selection in magmatic rocks

In the disposal of waste in magmatic or highly metamorphic rocks, it should be noted that compared to disposal concepts in salt or clay, the technical and geotechnical barriers have a greater significance for safety demonstration due to the limited isolation potential of the host rock. Therefore, a goal of this research project was to gain a clearer understanding of the role of individual components of the geological, geotechnical, and technical barrier systems regarding the demonstration of repository safety, respectively, site suitability, and thus, the requirements placed on them regarding isolation potential. A concept was developed on how to assess the role of each part of the barrier system, as well as the relevant properties, parameters, uncertainties, etc., through the designation of protective functions for each part of the barrier system and their significance in the model-based demonstration of long-term safety. Each barrier contributes to the isolation effect of the overall system, thus having its own "protective functions." Using available data for the rock types basalt and gneiss, an analysis was conducted for a selected modeling area to determine the extent to which each barrier and its protective functions contribute to ensuring repository safety. Due to significant data deficits, the calculations are merely indicative. However, the work, which also considers typical impacts on the technical barriers, demonstrates a methodology for conducting safety assessments. Through stochastic parameter variations and sensitivity analysis, the influence of parameters relevant to the safety function of the various barriers on the safety of the entire repository system was examined. It was found that with a limited isolation potential of the typically fractured geological barrier, the lifespan of waste containers and the effectiveness of bentonite embedding become important. If compromises are made in the effectiveness of the technical and geotechnical barriers, the requirements for the geological barrier and thus for site selection increase significantly. As part of concept optimization, it is therefore necessary to establish appropriate requirements for the technical and geotechnical barriers based on reliable site data and considering feasibility to limit remaining uncertainties.