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11.08.2016

Constructing a repository at great depth in the Opalinus Clay is very challenging

As part of the process for selecting sites for deep geological repositories, Nagra has submitted the additional information called for by ENSI.

As part of the process for selecting sites for deep geological repositories, Nagra has submitted the additional information called for by ENSI in September 2015; ENSI's requirements were then specified in more detail in November. «Our analyses have shown that constructing a repository at great depth in the Opalinus Clay is highly challenging», explains Piet Zuidema, a member of Nagra's Executive Board. The additional information will now be included by ENSI in its ongoing review of the safety-based comparison of the six potential siting regions. ENSI's final evaluation of Stage 2 of the Sectoral Plan process is expected for spring 2017.

The additional information required by ENSI (Swiss Federal Nuclear Safety Inspectorate) is particularly relevant with respect to the Nördlich Lägern siting region. In January 2015, Nagra (National Cooperative for the Disposal of Radioactive Waste) proposed that the two siting regions Jura Ost and Zürich Nordost be investigated in more depth in Stage 3 of the Sectoral Plan process and that the regions Südranden, Nördlich Lägern, Jura-Südfuss and Wellenberg be placed in reserve. According to ENSI, Nagra has to show whether construction at greater depth involves disadvantages in terms of safety and whether modifying the repository concept would be advantageous for such depths. In this connection, Nagra has considered a range of concepts for disposal chambers and sealing sections at different depths. Variants of potential repository and barrier concepts were also described and compared from the viewpoint of depth of construction.

In Nagra's view, the evaluation of the siting regions submitted in January 2015 can be confirmed: unless it is necessary, a repository for high-level waste in the Opalinus Clay should be constructed no deeper than 700 metres and a repository for low- and intermediate-level waste no deeper than 600 metres. The repository concept considered up till now continues to be preferable to other concepts. «It is important for safety that we should give priority to conditions that are straightforward in terms of construction», says Zuidema. This allows extreme conditions during construction, operation and possible waste retrieval to be avoided and prevents the geological barrier from being unnecessarily compromised. Nagra is of the opinion that a depth greater than 600 metres for the low- and intermediate-level waste repository and 700 metres for the high-level waste repository would bring disadvantages with respect to safety.

It is impossible to predict today whether ENSI will share this view in its overall final assessment. In order to avoid further delays in the site selection process, Nagra will therefore carry out 3D seismic measurements in the Nördlich Lägern region from autumn 2016 and prepare applications for exploratory boreholes in the region.

Contact

Media Relations
Marisa Brauchli
076 582 12 26
marisa.brauchli@nagra.ch

Picture: © Comet Photoshopping, Dieter Enz


According to Swiss nuclear energy legislation, the producers of radioactive waste are responsible for its safe management and disposal. In 1972, the nuclear power plant operators and the Federal Government set up the National Cooperative for the Disposal of Radioactive Waste (Nagra) to perform this task. Nagra, which has its headquarters in Wettingen (AG), is the national technical competence centre in the field of deep geological disposal of radioactive waste.

Out of a strong sense of responsibility for the long-term protection of man and the environment, 110 employees are involved daily in performing this important work. The high level of competence is secured by targeted research programmes in two Swiss underground rock laboratories and intensive international collaboration.

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