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Zürich Nordost Luftaufnahme

Zürich Nordost – a potential siting region for a deep geological repository

The “Zürich Nordost” region is situated in the Zürcher Weinland – mainly in Canton Zürich and a very small section in Canton Thurgau. Investigations show that the underground in this region can safely contain radioactive waste. Zürich Nordost is therefore a potential siting region for a deep geological repository.

Interactive map of Zürich Nordost, one of three potential siting regions

In the future, Switzerland will dispose of its radioactive waste in a deep geological repository. This will comprise both underground and surface facilities. The decision on where to construct the repository depends on geology. The radioactive waste will be safely enclosed in rock formations at a depth of several hundreds of metres for a very long time period. The most important of these rock formations are the Opalinus Clay and those lying directly above and below it. They can also be found in the Zürich Nordost region where they have favourable properties.

Zürich Nordost is one of three potential siting regions that we have been investigating in detail since 2008 within the framework of the Sectoral Plan for Deep Geological Repositories of the Federal Government. We now know which properties the rocks have and how much space is available for a repository. We work with the region in deciding where to locate the surface facilities. Aside from Zürich Nordost, Nördlich Lägern and Jura Ost are also potential siting regions. As part of the Sectoral Plan process, we compare these regions to identify which one is most suitable for a repository. In a few years, the Federal Council will decide where the repository will be constructed.

Overview: What would a repository in Zürich Nordost look like?

For the Zürich Nordost siting region located in the Zürcher Weinland, we developed a repository project adapted to the region. This incorporates the insights from our geological investigations and the results of our collaboration with the region.

Das mögliche Lagerprojekt der Nagra im Standortgebiet Zürich Nordost.
Overview over the repository project in the Zürich Nordost geological siting region

The geological siting region delineates the underground rock area suitable for the disposal of radioactive waste. Areas with geological fault zones are avoided for repository construction. By investigating the underground (particularly with 3D seismics), we were able to identify such fault zones. Priority is given to the investigation perimeter that includes the most suitable part of the rock area and is designated to host the emplacement rooms for the waste. For this reason, it was investigated in depth. The main underground connection area comprises the endpoint for accesses from the surface and the starting point for accesses to the emplacement rooms.

The auxiliary access facilities are located at surface level. The auxiliary access facility for ventilation lies within the blue perimeter and supplies the underground section of the repository with fresh air. The auxiliary access facility for operations serves to transport building materials and people as well as to supply power and water. Just like the surface facility (e.g. the ZNO-6b site), the auxiliary access facilities form part of the surface infrastructure of a deep geological repository. In the surface facility, the waste is prepared for emplacement and then transported below ground. The site for the surface facility in Zürich Nordost is still being discussed at present. If the surface facility were to be constructed at the ZNO-6b site, the fresh air supply and the auxiliary access facility for operations could be merged into one auxiliary access facility, ZNO-BL1.

Detailed information on the Zürich Nordost siting region (in German)

State-of-the-art investigation methods used to complete overall picture

The geological underground in Zürich Nordost was explored and characterised using numerous investigation methods, including seismics, Quaternary boreholes and deep boreholes.

Nagra and other companies have investigated the geological underground of Northern Switzerland using various methods. Points indicate borehole investigations whose data are included in the siting decision. Areas and lines indicate seismic surveys. The three potential siting regions for a deep geological repository are: Jura Ost (left), Nördlich Lägern (centre) and Zürich Nordost (right).

In winter 2015/16, we carried out large-scale 3D seismic measurements to obtain an image of the underground in Zürich Nordost. This method can be compared to medical ultrasound images or an echo sounder used on ships. The seismic images we obtained provided important information on the structure of the rock formations. We were also able to identify the presence of geological fault zones and assess the space available for a repository.

Bei den seismischen Messungen werden Vibrationsfahrzeuge eingesetzt. Die Fahrzeuge auf dem Bild waren in Benken unterwegs.
Vibration vehicles are used for seismic measurements. The vehicles shown in this picture were driving through Benken.

We drilled four deep boreholes in Zürich Nordost: Rheinau (2021, additional borehole), Marthalen (2020), Trüllikon (2019/20) and Benken (1998/99). These reached a depth of several hundred metres and went far below the Opalinus Clay that will host the waste. By drilling these boreholes, we were able to obtain samples from various rock layers and determine their properties. Investigations showed that the Opalinus Clay, but also the rock formations lying directly above and below it, are very tight. The deep boreholes also revealed the depth at which the individual layers are located.

In earlier investigations, we identified deeper underground faults with a vertical trend in the eastern part of the Rheinau community. We are now drilling a borehole in Rheinau to investigate the fault zone in the Opalinus Clay. This will provide important insight into the properties of the Opalinus Clay in all three potential siting regions.

Drohnenfoto der Tiefbohrung der Nagra in Trüllikon
Nagra was able to recover many rock samples from the Trüllikon deep borehole.

To provide long-term safety, the emplacement rooms of a deep geological repository that hold the waste must lie sufficiently deep below ground. Only then is the repository safe from erosion caused by rivers and glaciers. Traces of past erosion processes are also visible in the Zürich Nordost siting region. Glaciers cut deep troughs into the landscape, and glacial advances will also occur in the future. To learn more about the impact of glaciers and rivers and to develop future scenarios, we conducted Quaternary investigations. With these, we were able to investigate the topmost – and our planet’s most recent – rock layer located just beneath the surface. Quaternary investigations primarily include boreholes that are drilled to a depth ranging from a few dozen metres to around three hundred metres. In 2018, we drilled in Marthalen-Oobist, and in 2019 Quaternary boreholes were drilled in Neuhausen, Trüllikon-Rudolfingen and Kleinandelfingen-Laubhau. In 2020, we completed the Andelfingen-Niederfeld and Adlikon-Dätwil boreholes.

Die Quartärbohrung der Nagra in Andelfingen-Niederfeld
Nagra’s Quaternary borehole in Andelfingen-Niederfeld

With the most recent investigations, we were able to complement and complete the already existing knowledge of the geological underground in Zürich Nordost. We are now in possession of a comprehensive image of the geological underground. Based on this, we have been able to develop the Zürich Nordost repository project. We have also thoroughly investigated the other two potential siting regions, Jura Ost and Nördlich Lägern, and can now objectively compare the three regions with one another.

Collaboration on the site for the surface infrastructure

Where will the buildings at the surface and accesses for a deep geological repository eventually be constructed? These are the questions Nagra is addressing together with the siting regions. Our dialogue partners are the Zürich Nordost Regional Conference, Cantons Zürich and Thurgau as well as representatives from neighbouring Germany. These can express their views on the proposals that we publish as a basis for collaboration and discussion. By collaborating from this early stage, the responsible Swiss Federal Office of Energy ensures that the needs of the Zürich Nordost siting region are considered to the greatest extent possible.

Websites of the region’s representatives (in German)

In 2019, we published specific proposals for the Zürich Nordost region on what the surface infrastructure might look like in this region. The proposals are the result of previous collaboration with the region. Together with the other siting regions, the issue of where to place the encapsulation plant for spent fuel assemblies was also discussed. The Zürich Nordost Regional Conference, Cantons Zürich and Thurgau as well as representatives from Germany have worked intensively on the placement of the surface infrastructure and have submitted their position statements. These form the basis for the further concretisation of the surface infrastructure with a view to the general licence application.

Position statements of the Zürich Nordost Regional Conference (still outstanding) and Cantons Zürich and Thurgau (in German)

Next steps

In 2022, we will announce which siting region we consider most suitable for a deep geological repository. We will then submit a general licence application for this region. Our work is conducted in line with federal authority stipulations as set out in the Sectoral Plan for Deep Geological Repositories. This forms the basis for the decision of the Federal Council, which will decide on the site around 2029 and submit its decision to the Federal Assembly for approval around 2030. Once the definite site has been confirmed, we will plan and construct the deep geological repository there.

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