The more than sufficient extent of the Opalinus Clay at the site is one of the central arguments contributing to the post-closure safety of the deep geological repository (Explanatory Report on the General Licence Applications, NTB 24-12, Chapter 5).

At the selected site, the more than sufficient spatial extent of the Opalinus Clay ensures the retention of radionuclides and a high degree of flexibility for arranging the layout of the repository elements. The Opalinus Clay at the site has a large, constant thickness and a continuous lateral extent (Sicherheitsbericht (“Safety Report” (in German)), NTB 24-01, Section 4.5.2).

Thanks to the more than sufficient spatial extent of the Opalinus Clay at the site, the layout of the deep geological repository can be flexibly arranged (Post-Closure Safety Report, NTB 24-10, Chapter 10.2). This allows the engineered barriers to be optimally adapted to the natural conditions, ensuring that the host rock will remain largely protected from repository-induced effects and that the retention of the radionuclides can be ensured. The performance assessment of the barriers shows that their function is particularly well predictable under these conditions (Post-Closure Safety Report, NTB 24-10, Section 6.2).

In the Nördlich Lägern siting region, there is a large, tectonically stable zone between the Weiach-Glattfelden-Eglisau Lineament and the Baden-Irchel-Herdern Lineament, in which the Opalinus Clay exhibits very small variations in thickness (Geosynthesis of Northern Switzerland, NTB 24-17, Section 4.3.4 and Section 4.2.6).

The subsurface conditions in the potential disposal zone are very easy to explore and the spatial extent of the Opalinus Clay has been reliably characterised (Geosynthesis of Northern Switzerland, NTB 24-17, Section 4.2.6). In addition, the large area that shows no seismically mappable faults and the straightforward geometry of the host rock allow a high degree of flexibility with regard to the layout of the deep geological repository (Geosynthesis of Northern Switzerland, NTB 24-17, Section 4.3).