Technischer Bericht NTB 88-20

Untersuchungen zur Standorteignung im Hinblick auf die Endlagerung schwach- und mittelaktiver Abfälle:Übersicht über die Untersuchungen der Phase I an den potentiellen Standorten Bois de la Glaive, Oberbauenstock und Piz Pian Grand

In 1983, Nagra submitted to the Federal Government the necessary applications for investigation permits for the sites Bois de la Glaive (VD), Oberbauenstock (UR) and Piz Pian Grand (GR); these sites were to be investigated with a view to disposal of low- and intermediate-level radioactive waste. The applications also covered the construction of an exploratory tunnel at all three sites. On 30th September 1985, the Government granted the permits to a limited extent – investigations were licensed only in so far as they could be carried out without construction of the exploratory tunnels (Phase I). The decision on construction of the tunnels and related experiments (Phase II) was suspended until such time as Nagra had completed and evaluated the licensed investigations at all three sites, an application had been drawn up for preparatory investigations at an additional site and provisional site-related repository construction projects were available. The licensed investigations were carried out as far as possible in 1986/87 and evaluated in 1988.

The restricted Phase I investigations were insufficient to allow a final assessment of site suitability. Nagra's research during this Phase therefore concentrated on identifying possible grounds on which a particular site would have to be ruled out, i.e. investigations were directed towards assessing the most important geological and hydrogeological aspects of site selection which are relevant from a safety point of view. The results of this work led to the following conclusions:

  • At none of the three sites were there indications of any geological, hydrogeological or rock mechanical conditions which might prove prohibitive to the safe disposal of low- and intermediate-level radioactive waste.
  • The absence of such adverse conditions was confirmed at Oberbauenstock and Piz Pian Grand by way of field studies which exhausted the Phase I investigation possibilities. The present state of knowledge on these two sites can not be improved without construction of an exploratory tunnel.
  • At Bois de la Glaive, actual field investigations were thwarted by politically motivated opposition in the community. However, the picture of geological, hydrogeological and rock mechanical conditions provided by the detailed surface mapping programme gave no indication that the site would fail to meet the disposal safety criteria. There are therefore no reasons for ruling out this site.

Nagra is therefore requesting that the Federal Government should license construction of exploratory tunnels and related investigation programmes to assess the host rock at all three sites. Before a tunnel is constructed at Bois de la Glaive, the Phase I investigations will have to be completed in so far as necessary. Nagra is also requesting that the condition that work at all three sites should proceed in parallel be dropped and that the application for an additional site be restricted to the disposal of long-lived intermediate-level waste. This report summarises the results of the Phase I investigations and explains and substantiates Nagra's requests to the Federal Government.