Technischer Bericht NTB 08-04

On 2nd April 2008, the Federal Council approved the conceptual part of the Sectoral Plan for Deep Geological Repositories. The Plan, which was prepared by the Federal Office of Energy (SFOE), sets out the details of the site selection procedure for geological repositories for low- and intermediate-level waste (L/ILW) and high-level waste (HLW).

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 based on criteria and requirements set out in the Sectoral Plan.

The proposals for geological siting regions are documented in a report (Nagra 2008a) prepared by Nagra on behalf of the waste producers for stage 1 of the Sectoral Plan process. The report sets out the procedures and arguments used in identifying the geological siting regions for the L/ILW and HLW repositories proposed in stage 1 and follows the criteria and requirements set out in the Sectoral Plan. It is supplemented inter alia by the current report, which presents and illustrates the geoscientific background leading to the results of the site selection process in greater detail than in Nagra (2008a).

The geoscientific background is based on the one hand on an evaluation of the geological investigations previously carried out by Nagra on deep geological disposal of HLW and L/ILW in Switzerland (investigation programmes in the crystalline basement and Opalinus Clay in Northern Switzerland, investigations of L/ILW sites in the Alps, research in rock laboratories in crystalline rock and clay); on the other hand, new geoscientific studies have also been carried out in connection with the site selection process. These include:

• Presentation of the geological conditions in Switzerland based on the most recent scientific publications.
• Preparing an inventory of sedimentary formations in Switzerland based on 27 stratigraphic composite profiles.
• An in-depth re-interpretation of data from various seismic campaigns carried out by Nagra and third parties on a digital basis with a standardised depth conversion. The results are used to prepare digital elevation models of the marker horizons Base Tertiary, Base Malm and Base Opalinus Clay taking into account additional surface data and an extended comprehensive borehole databank.
• Preparation of a digital elevation model of the rock surface (Base Quaternary) in the central and eastern midlands (plateau) based on information from several thousand boreholes and other sources.
• Compilation of all available data on hydraulic conductivity and porewater composition of potential host rocks.
• Conducting and evaluating the results of additional investigations (mineralogical studies, hydraulic tests, porewater investigations) in boreholes of third parties in potential host rocks.
• Continuing ongoing experiments in the Nagra rock laboratories and initiating new ones as required.
• International collaboration and monitoring scientific and technological developments in foreign repository programmes.

The results of the geological studies that are relevant for stage 1 of the Sectoral Plan are documented in around 50 Nagra reference reports, several publications in technical journals and in numerous reports on rock laboratory projects (particularly Mont Terri).
Formulation of the siting 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.

The first two steps are documented in detail in a separate report (Nagra 2008b). Steps 3 to 5 cover the evaluation of the geological siting possibilities, for which the geological knowledge base and key geoscientific aspects are discussed in the present report:

• In the third step, the large-scale geological-tectonic situation is assessed and large-scale areas that remain under consideration are defined. For the L/ILW repository - for which the time period considered for long-term safety is 100,000 years - there are no large-scale geotectonic units that, as a whole, would be unsuitable from the viewpoint of long-term geological stability and would have to be excluded. Regionally and locally, however, critical zones will have to be avoided when locating the disposal chambers in order to ensure long-term stability. The space required for the L/ILW repository is comparatively small and there is considerable flexibility in arranging the individual disposal chambers. This means that none of the large-scale units need to be deferred because of spatial conditions, although there are significant differences among the units with respect to tectonic dissection and the resulting spatial situation. For the HLW repository - with a time period of 1 million years being considered for long-term safety - the Alps have to be excluded if long-term stability (including uplift and erosion during the period being considered) is to be assured. There are also reservations regarding the long-term geological stability of the Folded Jura, the western Tabular Jura and the western sub-Jurassic zone. Because of strong tectonic dissection and the resulting insufficient spatial conditions, these three units are excluded for a HLW repository.
• The fourth step involves selecting the preferred host rock formations within the large-scale geotectonic units 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. Although the crystalline bedrock and the clay-rich formations of the Lower and Upper Freshwater Molasse fulfil the minimum requirements for a host rock, these options have been deferred because of the large variability of rock properties and the resulting difficulties with exploration. In the case of the Molasse formations, the relatively high horizontal hydraulic conductivity caused by sandstone layers and channels is a further reason for putting these possibilities on hold.
• The configurations of the preferred host rocks within the large-scale geotectonic units 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 procedure leads to the following geological siting regions:

For the L/ILW repository:

• Southern Schaffhausen (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 Southern Schaffhausen, 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 included 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 granted by the Federal Council but must be approved by Parliament and is subject to an optional national referendum.

Beilagen:

Titelblatt und Inhaltsverzeichnis des Beilagenbandes (84 KB)

Beil. 2.1-1: Informationsquellen geologischer Daten in der Schweiz (1.1 MB)
Beil. 2.2-1: Geologischer Profilschnitt Mitte (496 KB)
Beil. 2.2-2: Geologischer Profilschnitt Ost (507 KB)
Beil. 2.2-3: Geologischer Profilschnitt West (494 KB)
Beil. 2.4-1: Orogener Fahrplan der Schweizer Alpen (Eozän - Gegenwart) (726 KB)
Beil. 2.5-1: Tektonische Übersicht 1:500'000 (2.6 MB)
Beil. 2.7-1: Herdmechanismen in der Schweiz und Umgebung, 1976 - 2006 (3.1 MB)
Beil. 4-2-1: 27 Stratigraphische Sammelprofile (Beil. 4.2-1/1 bis 4.2-1/27) (1.5 MB)
Beil. 5.2-1: Fazies-Korrelation Süd (Faltenjura - Jura-Südfuss) (1.7 MB)
Beil. 5.2-2: Fazies-Korrelation Nord (Tafeljura) (1.2 MB)
Beil. 5.2-3: Isohypsenkarte Basis Opalinuston (4.5 MB)
Beil. 5.2-4: Isohypsenkarte Basis Malm (4.5 MB)
Beil. 5.2-5: Isohypsenkarte Basis Tertiär (4.5 MB)
Beil. 5.2-6: Tektonische Übersicht Nordschweiz 1:250'000 (1.2 MB)
Beil. 5.2-7: Geologisches Profil 22 (Seismiklinien 83-NS-22 & 85-SE-07 (4.6 MB)
Beil. 5.2-8: Geologisches Profil 01 (Seismiklinie 83-BN-01) (2 MB)
Beil. 5.2-9: Geologisches Profil 02 (Seismiklinie 83-NF-02) (2.5 MB)
Beil. 5.2-10: Geologisches Profil 08 (Seismiklinie 83-SE-08) (1.8 MB)
Beil. 5.2-11: Geologisches Profil 06 (Seismiklinie 83-NF-06) (1.8 MB)
Beil. 5.2-12: Geologisches Profil 12 (Seismiklinie 83-SE-12) (1.9 MB)
Beil. 5.2-13: Geologisches Profil 10 (Seismiklinie 82-NF-10) (3.6 MB)
Beil. 5.2-14: Geologisches Profil 30 (Seismiklinien 82-NF-30, 83-NF-31ST &  

      83-NF-31HR) (3.8 MB)
Beil. 5.2-15: Geologisches Profil 55 (Seismiklinien 83-NF-55 & 83-SE-06) (3.3 MB)
Beil. 5.2-16: Geologisches Profil 15 (Seismiklinien 83-NF-15 ST & 83-NF-15 HR)  

      (2.5 MB)
Beil. 5.2-17: Geologisches Profil 70 (Seismiklinie 82-NS-70) (4 MB)

Beil. 5.2-18: Geologisches Profil 58 (Seismiklinie 91-NO-58) (2.1 MB)
Beil. 5.2-19: Geologisches Profil 62 (Seismiklinie 91-NO-62) (2.5 MB)
Beil. 5.2-20: Geologisches Profil 61 (Seismiklinie 91-NO-61) (2.4 MB)
Beil. 5.2-21: Geologisches Profil 65 (Seismiklinie 84-NF-65) (3.6 MB)
Beil. 5.2-22: Geologisches Profil 75 (Seismiklinie 91-NO-75) (3.4 MB)
Beil. 5.2-23: Geologisches Profil 77 (Seismiklinie 91-NO-77) (2.3 MB)
Beil. 5.2-24: Geologisches Profil 68 (Seismiklinie 91-NO-68) (3.7 MB)
Beil. 5.2-25: Geologisches Profil 79 (Seismiklinie 91-NO-79) (2.9 MB)
Beil. 5.2-26: Geologisches Profil 74 (Seismiklinie 91-NO-74) (2.5 MB)
Beil. 5.2-27: Tektonische Charakterisierung Nordschweiz (2.1 MB)
Beil. 5.2-28: Quartärmächtigkeiten Nordschweiz (2.1 MB)

Alle Beilagen als .zip-Ordner (89 MB)