The safety of a deep geological repository relies on the tightness of the rock. Allowing human actions that could impact the planned site, such as drilling, would not be advisable. For this reason, a so-called provisional protection zone has been set aside to ensure the safety of the repository. In its general licence application, Nagra will propose the size of this provisional protection zone. Two areas will be protected: the area of the rock at depth that will one day host the repository and the area through which the underground access routes will be constructed.
Design flexibility thanks to generous spatial reserve
Switzerland’s deep geological repository will be constructed in a layer of Opalinus Clay that is over 100 metres thick. However, the provisional protection zone will not only protect the Opalinus Clay, but also some of the over- and underlying rock formations. Overall, a 300-metre-thick rock layer will be protected.
The disposal areas of the deep geological repository are expected to cover an area of around two square kilometres. A generously dimensioned area will be set aside to allow for the flexible positioning of the underground repository installations: this protected area will cover around 30 square kilometres.
It will be delimited above and below by rock formations that play a less important role in the containment of radioactive waste. The perimeters of this zone will be demarcated by fault zones in the rock or by the boundaries of the meticulously investigated area of the siting region.
Repository access routes
There are two solutions to gaining access to the underground level of the repository: either by means of vertical shafts, or by a combination of shafts and a downward-spiralling ramp. When applying for the general licence, Nagra will also request protection of a sufficiently large area of rock to allow for both access options. In practice, this means protecting a rock column with a diameter of 3 kilometres.
Are there any restrictions on use?
The provisional protection zone for the deep geological repository does not restrict conventional underground activities such as drilling or gravel extraction. These require the usual cantonal authorisations, which means that, for example, only a cantonal permit is needed when drilling to a depth of 0 metres above sea level (around 400 metres below the surface) for geothermal probes. A borehole that would go below 0 metres above sea level (i.e. deeper than 400 metres from the surface) would require an additional permit from the federal government, as it would penetrate the provisional protection zone. It will thus remain possible to install geothermal probes above the provisional protection zone.
Outlook
In the general licence application, Nagra will propose to the federal authorities that the provisional protection zone be dimensioned as described above. The Federal Council can modify Nagra’s proposal when granting the general licence. With the operating licence (expected for 2050), the provisional protection zone will become the definitive protection zone. This zone will be smaller.
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