Technischer Bericht NTB 08-03

Vorschlag geologischer Standortgebiete für das SMA- und das HAA-Lager.Darlegung der Anforderungen, des Vorgehens und der Ergebnisse

Important steps in the process of managing radioactive waste have already been implemented in Switzerland. These include the handling and packaging of the waste, waste characterisation and documentation of waste inventories and interim storage along with associated transport. In terms of preparing for deep geological disposal, the necessary scientific and technical work is well advanced and the feasibility of constructing geological repositories that provide the required long-term safety has been successfully demonstrated for all waste types arising in Switzerland; these feasibility demonstrations have been approved by the Federal Council. Sufficient knowledge is available to allow the next steps in the selection of repository sites to be defined. The legal framework is also in place and organisational measures have been provided that will allow the tasks to be performed in the coming years to be implemented efficiently. The conceptual part of the Sectoral Plan for Deep Geological Repositories that was approved by the Federal Council on 2nd April 2008 plays a major role, as it regulates the details of the site selection process to be conducted over the next years. The Sectoral Plan specifies that selection of geological siting regions and sites for repositories in Switzerland will be conducted in three stages. Stage 1 ends with the definition of geological siting regions within which the repository projects will be elaborated in more detail in the later stages of the Sectoral Plan (stages 2 and 3). The final step will be the identification of sites for construction of the repositories and granting of the required general licences.

As a first step, the Sectoral Plan calls for the waste producers to submit proposals for geological siting regions for the repositories for low- and intermediate-level waste (L/ILW) and high-level waste (HLW). This report documents and justifies the siting proposals prepared by Nagra on behalf of the waste producers for stage 1 of the Sectoral Plan process. 

Formulation of these proposals in accordance with the Sectoral Plan is conducted in five steps: 

  • In a first step, the waste inventory, which includes reserves for future developments, is allocated to the L/ILW and HLW repositories.
  • Based on this waste allocation, the second step involves defining the barrier and safety concepts for the two repositories. With a view to evaluating the geological siting possibilities, quantitative and qualitative guidelines and requirements on the geology are derived on the basis of these concepts. These relate to the time period to be considered, the space requirements for the repository, the properties of the host rock (depth, thickness, lateral extent, hydraulic conductivity), long-term stability, reliability of geological findings and engineering suitability.

Steps 3 to 5 cover the evaluation of the geological siting possibilities:

  • In the third step, the large-scale geological-tectonic situation is assessed and large-scale areas that remain under consideration are defined. From the viewpoint of long-term stability and explorability of spatial conditions, all large-scale geological-tectonic areas in Switzerland come into consideration for the L/ILW repository. For the HLW repository, the Alps, the Folded Jura, the western Tabular Jura and a small part of the Molasse Basin (western sub-Jurassic zone) are excluded.
  • The fourth step involves selecting the preferred host rock formations within the large-scale areas still under consideration. This is done in several sub-steps and leads to the following results: Proposed for the L/ILW repository are the Opalinus Clay with its confining units, the claystone sequence 'Brauner Dogger' with its confining units, the Effingen Beds and the marl formations of the Helveticum. For the HLW repository, the Opalinus Clay with its confining units is proposed as the preferred host formation.
  • The configurations of the preferred host rocks within the large-scale areas under consideration are evaluated in the fifth step. Taking into account the presence of regional geological features (regional fault zones, over-deepened valleys resulting from glacial erosion, zones with indications of small-scale tectonic dissection, other zones to be avoided for reasons of neotectonics), preferred areas are identified within which the preferred host rocks can be found at a suitable depth and with sufficient thickness and lateral extent. The preferred areas are used as the basis for delimiting the geological siting regions. Some siting regions contain several preferred areas and sometimes more than one host rock type.

The stepwise procedure adopted for narrowing down the geological siting possibilities and identifying geological siting regions is shown in simplified form in Figure I of the German version of this abstract. The procedure leads to the following geological siting regions:

For the L/ILW repository:

  • Südranden (Canton Schaffhausen) with the host rock Opalinus Clay and its confining units
  • Zürcher Weinland (Cantons Zürich, Thurgau) with the host rocks Opalinus Clay and the claystone sequence 'Brauner Dogger' with their confining units
  • North of Lägeren (Cantons Zürich, Aargau) with the host rocks Opalinus Clay and the claystone sequence 'Brauner Dogger' with their confining units
  • Bözberg (Canton Aargau) with the host rock Opalinus Clay and its confining units
  • Jura-Südfuss (southern foot of the Jura, Cantons Solothurn, Aargau) with the host rocks Opalinus Clay and its confining units and the Effingen Beds
  • Wellenberg (Cantons Nidwalden, Obwalden) with the host rock marl formations of the Helveticum

For the HLW repository:

  • Zürcher Weinland (Cantons Zürich, Thurgau) with the host rock Opalinus Clay and its confining units
  • North of Lägeren (Cantons Zürich, Aargau) with the host rock Opalinus Clay and its confining units
  • Bözberg (Canton Aargau) with the host rock Opalinus Clay and its confining units

In three of the geological siting regions (Zürcher Weinland (Cantons Zürich, Thurgau), North of Lägeren (Cantons Zürich, Aargau) and Bözberg (Canton Aargau)), the possibility exists in principle of siting the L/ILW and HLW repositories together as a so-called "combined repository".

The evaluation conducted in accordance with the conceptual part of the Sectoral Plan gives the following results: For the L/ILW repository, the geological siting regions Südranden, Zürcher Weinland and Bözberg are considered very suitable and North of Lägeren, Jura-Südfuss and Wellenberg are considered suitable. For the HLW repository, the siting regions Zürcher Weinland and Bözberg are considered very suitable and North of Lägeren is considered suitable.

The work done by Nagra to narrow down and evaluate the siting options from the point of view of geology and safety will be supplemented by a survey of land use planning performed by the authorities. The authorities and the Federal Council may choose to include additional non technical-scientific criteria in the decision-making process.

The evaluation and assessment of the geological siting possibilities discussed in this report use all available geological information that is relevant in the context of deep geological disposal. The most recent scientific literature has been used and the geological database has been expanded (e.g. through participating in investigations being carried out by third parties or by acquiring third-party data). Where meaningful, data have also been re-analysed (e.g. seismic measurements, hydraulic tests). The technical-scientific knowledge base varies from region to region, but still allows priorities for the next steps to be set with confidence and well founded proposals to be made for geological siting regions to be carried through to the next stages of the Sectoral Plan.

The siting proposals will be evaluated by the federal authorities and, following a public hearing phase, the decision of the Federal Council on the geological siting regions is expected in around 2½ years. This will be followed by stage 2 (identification of at least 2 sites each for L/ILW and HLW within the geological siting regions defined in stage 1) and stage 3 with the general licence procedure. The siting decision for the geological repositories for L/ILW and HLW as part of the general licence is expected in around 10 years. The general licence is to be granted by the Federal Council but must be approved by Parliament and is subject to an optional national referendum.