Nagra investigated the whole of Switzerland in its search for suitable sites for a deep geological repository. The potential siting regions were narrowed down step by step. In the final stage of the site selection process, the three remaining siting regions were investigated in great detail. All three regions are located in Northern Switzerland. The reason behind this is that the rock formation known as the Opalinus Clay is present at the right depth, quality and extent for the construction of a safe deep geological repository.
Geology is the decisive factor
Nagra proposes to construct Switzerland’s deep geological repository in Nördlich Lägern. This is where the nation’s radioactive waste is to be disposed of. The surface facility is planned at the Haberstal site in the community of Stadel, Canton Zürich.
The two other potential siting regions that Nagra investigated in depth in recent years are also located in Northern Switzerland. Why is this region best suited for the construction of a deep geological repository? The decisive factor is its geology.
Rock forms a geological barrier
Switzerland can be roughly divided into three regions: the Alps, the Molasse Basin and the Jura Mountains. During the alpine orogeny, rock formations fractured and were pushed on top of each other. The underground in the alpine region is so strongly deformed that it is not suitable for a repository – or at least not for a high-level waste repository for spent fuel assemblies from nuclear power plants.
The Folded Jura and the Tabular Jura, both located in northwestern Switzerland, are mostly strongly deformed and therefore not an option. In contrast, the Molasse Basin (the Swiss Plateau) located between the Alps and the Folded Jura shows considerably less deformation, particularly in the central and eastern sections. The Opalinus Clay is also found here.
This rock is of particular interest in connection with the disposal of radioactive waste. For one, the Opalinus Clay is largely impermeable to water. It can also self-seal fissures and has the capacity to bind radioactive substances. For all these reasons, this clay rock functions as a geological barrier that can safely enclose the deep geological repository.
Right place, right depth
In the Folded Jura and in the very north of Switzerland, the Opalinus Clay is located close to the surface. From there, it continuously dips towards the Alps where it reaches a depth of several kilometres.
The construction of a deep geological repository requires comparatively large areas and thick rock layers that show little deformation. To serve as an optimal geological barrier, a sufficiently thick layer of the Opalinus Clay has to surround the repository on all sides.
At the same time, the Opalinus Clay also has to be located at the right depth: between 400 and 1000 metres. The correct depth is crucial for the long-term protection of the repository from external impacts such as erosion by glaciers and rivers.
Undisturbed areas and the right depth: these two conditions are met only in the Molasse Basin of Northern Switzerland, both at its northern margin and in the adjacent, eastern part of the Tabular Jura. This is why Nagra has focused on this region in its search for a repository site. Here, the Opalinus Clay shields humans and the environment from radioactive waste – today and far into the future.
The siting proposal
In September 2022, Nagra proposed Nördlich Lägern as the site for Switzerland’s deep geological repository.
You can find more information about Nagra’s siting proposal in this report.
Download report
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