450 metres beneath the Juchlistock
The Grimsel Test Site is located at an altitude of 1730 metres above sea-level in the granitic formations of the Aar Massif. It is reached via the access tunnel of the Oberhasli AG (KWO) hydropower plant. The total length of the laboratory tunnels is around one kilometre; the tunnel network was excavated in 1983 mainly using a full-face boring machine and was extended in 1995 and 1997.
Some 300 million years ago, magmas formed granitic rocks in the Grimsel area. New molten masses flowed into fissures in the cooling rock and formed dyke rocks (lamprophyres). During the alpine orogeny, which affected the Grimsel area around 40 million years ago, the rocks of the Aar Massif were passed over by the northward-moving alpine nappes and subsided by around 12 kilometres. The rocks were then overprinted under high temperature and pressure conditions and shear zones and fracture systems were formed. Uplift (0.5 to 0.8 mm/a) and erosion processes, which are still continuing today, brought the rocks once more to the surface. The fracture minerals encountered in the Grimsel area formed around 16 million years ago.
Not a laboratory in the conventional sense
Deep in the rock, the range of geological conditions found in the laboratory (fractured/water-bearing and homogeneous/tight areas of rock) present ideal conditions for investigating the functioning of both the geological and the engineered barriers of deep repositories. Projects that study disposal concepts on a large scale are also carried out. A controlled zone permits the use of radionuclides under monitored conditions and allows the transport of radioactive substances in the rock to be examined directly.
Internationally recognised research centre
Today, around twenty partner organisations, as well as universities, research institutes and consulting companies from various countries, are involved in the projects at the Test Site. The European Union and the Swiss State Secretariat for Education and Research provide financial support to several projects. The work at the Test Site makes an important contribution to long-term maintenance and transfer of know-how to future generations.
Meeting of the Grimsel Test Site's «International Steering Committee» (ISCO) in 2012. (Image: Comet)