Technischer Bericht NTB 14-01

A number of important steps have been taken in Switzerland towards ensuring the safe management and disposal of radioactive waste. These include the conditioning and packaging of the waste already available, waste characterisation, the development of inventories as well as interim storage and the associated transport campaigns. The preparations for deep geological disposal make use of a sound scientific and technical basis; the feasibility of safe long-term disposal of all wastes arising in Switzerland in deep geological repositories has been demonstrated in so-called 'Entsorgungsnachweis' projects and was confirmed by the Federal Government. The site selection process is set out in the conceptual part of the "Sectoral Plan for Deep Geological Repositories" that was launched by the Federal Government in 2008. The lead authority in the process is the Swiss Federal Office of Energy (SFOE). The conceptual part of the Sectoral Plan specifies that the selection of sites for geological repositories in Switzerland is to be conducted in three stages. Stage 1 ended in 2011 with the identification of six potential geological siting regions. The repository projects will be concretised within these siting regions in Stages 2 and 3 of the process and safety will be evaluated in more detail. This will ultimately lead to the identification of the sites for repository implementation and granting of the general licences.

For Stage 1 of the process, Nagra proposed six geological siting regions for the repository for low- and intermediate-level waste (L/ILW) and three for the repository for high-level waste (HLW) in November 2008. These siting proposals were prepared on the basis of criteria relating to safety and technical feasibility, as well as other requirements set out in the Sectoral Plan. It was noted for the three siting regions that were proposed for both the HLW and the L/ILWrepositories that the two repository types could be co-located at the same site; the term used for such a facility is a 'combined repository'. The siting regions proposed by Nagra were entered in the Sectoral Plan with a decision by the Federal Council in November 2011.

In Stage 2, proposals for siting the repository surface facility within the so-called planning perimeters of the regions had to be prepared together with the siting regions and the affected Cantons for potential areas. Nagra put forward siting proposals for the surface facility at the beginning of Stage 2 and these then formed the basis for a discussion and cooperation with the regional participation bodies. The proposals were evaluated and reviewed by the regions and the Cantons during the course of Stage 2 and were also, upon their request, modified and supplemented with additional proposals. As a result, Nagra was able to propose at least one siting area for the surface facility in each of the siting regions and to complete the associated planning studies. These planning studies serve as the basis for the socio-economic-ecological impact studies for each region that are prepared under the lead of the SFOE and for the preliminary investigations for the environmental impact assessment to be conducted at a later stage.

Stage 2 also includes a narrowing-down of the potential geological siting regions to at least two for each repository type for further investigation for Stage 3. This is done by conducting a safety-based comparison of the siting regions, with the highest priority being assigned to the long-term safety of the repository. A geological siting region can only be placed in reserve in Stage 2 if it shows clear disadvantages in terms of safety compared with the other regions. Aspects of spatial planning, ecology, economy and society are of secondary importance as selection criteria and the socio-economic studies have no impact on the selection of the geological siting regions.

According to the Sectoral Plan and the requirements specified by the Swiss Federal Nuclear Safety Inspectorate (ENSI), Nagra has to carry out a provisional safety analysis and a safetybased comparison for each siting region; an overall comparative assessment is then carried out based on the results. Based on this comparative assessment, geological siting regions are to be proposed for further investigation for Stage 3.

The purpose of the present report is to propose the geological siting regions for the HLW and L/ILW repositories for further investigation for Stage 3 and to explain and justify these proposals. The requirements behind the selection procedure are explained and an overview is provided of the information used for evaluating and narrowing down the sites and the stepwise narrowing-down process is explained. The proposals were prepared in five steps:

• In the first step, the methodology used in Stage 1 is modified to address the changes in boundary conditions. Besides the requirements set out in the conceptual part of the Sectoral Plan and the specifications provided by ENSI, the comments and reviews made by the authorities on Stage 1 and the specific properties of the host rocks and geological siting regions proposed in Stage 1 are also taken into consideration. Optimisation is considered a key element in Stage 2 of the process: in order to make best possible use of the proposals from Stage 1, a three-stage optimisation is undertaken (identifying the priority host rocks in the siting regions with more than one potential host rock, defining optimised disposal perimeters within the geological siting regions and placing siting regions with clear disadvantages into reserve; cf. steps 2, 3 and 5).

• In the second step, a safety-based comparison of the host rocks leading to identification of the priority host rock that will be used for the next steps is carried out in the siting regions for the L/ILW repository with more than one host rock. This step is not required for the HLW repository as only the Opalinus Clay was identified as a host rock in Stage 1.

• In the third step, an optimised spatial configuration of the priority host rock is selected within the siting regions identified in Stage 1 (identification of optimised disposal perimeters).

• In the fourth step, the suitability of the geological siting regions and the associated disposal perimeters in terms of safety is reviewed, on the one hand using dose calculations (characteristic dose intervals) and, on the other hand, through a qualitative assessment using the criteria relating to safety and technical feasibility set out in the Sectoral Plan.

• The fifth step involves a safety-based comparison and overall comparative assessment of the geological siting regions and the associated disposal perimeters based on the relevant features specified by ENSI (identification of siting regions with clear disadvantages).

To implement the methodology, the information from Stage 1 is used as well as new data acquired in the meantime, particularly from participation in drilling projects by third parties, new 2D seismic investigations and reprocessing of existing seismic results. Where necessary, alternative situations and parameter values are evaluated in each assessment step in order to investigate the sensitivity of the siting proposals to existing uncertainties.

The procedure has led to the identification of two geological siting regions each for the L/ILW and HLW repositories. These are proposed by Nagra, on behalf of the waste producers, for further investigation for Stage 3 of the Sectoral Plan process.

The siting regions proposed for the L/ILW repository are

• Zürich Nordost (Cantons ZH, TG) with the siting area ZNO-6b for the surface facility and

• Jura Ost (Canton AG) with the siting area JO-3+ for the surface facility

and the siting regions proposed for the HLW repository are

• Zürich Nordost (Cantons ZH, TG) with the siting area ZNO-6b for the surface facility and

• Jura Ost (Canton AG) with the siting area JO-3+ for the surface facility.

The potential exists in both regions for constructing the L/ILW and HLW repositories at the same site, i.e. a so-called combined repository.

The proposals submitted will be reviewed by the authorities. Following an open consultation phase, the decision of the Federal Council on the proposed geological siting regions is expected in around two and a half years. In Stage 3, the siting regions for HLW and L/ILW remaining in the process will undergo more detailed investigations with a view to selecting the sites for the preparation of the general licence applications. According to the SFOE, the general licence applications will be submitted around 5 years after the end of Stage 2 and the siting decision for the repositories for HLW and L/ILW will be made by the Federal Council around 2027. The general licence has to be approved by Parliament and is subject to an optional national referendum. This will be followed by the construction of a site-specific rock laboratory and an underground investigation programme, leading to the nuclear construction licencing procedure. According to current planning, the start of the operational phase for the L/ILW repository is scheduled for 2050 and that for the HLW repository for 2060.