Boreholes provide a direct insight into the underground geological environment and its structure.
Two drilling techniques are widely used:
In destructive drilling, the rock is crushed in the borehole. A fluid is pumped through the drill-pipe, which flushes the rock fragments (cuttings) to the surface. The drilling fluid is circulated in a closed circuit.
In cored boreholes, which are more costly to drill, hollow drill-bits grind only the rock at the edge of the borehole and the core in the centre remains intact. The core is loosened and pulled to the surface where the rock can be investigated in more detail.
The investigations are also supplemented by a range of borehole measurements - so-called logs - as well as hydrogeological and rock mechanical tests.
According to the Nuclear Energy Act, Nagra’s exploratory boreholes require a permit from the Federal Department of the Environment, Transport, Energy and Communications (DETEC). Nagra intends to submit the necessary in 2016. The federal authorities will review the applications together with the affected Cantons and communities. The decision of the Federal Council on Stage 2 of the Sectoral Plan is expected for 2018. The first drillsites will be set up after this.
To date, Nagra has drilled around 1000 to 2500 metres of borehole in Northern Switzerland as part of the investigation programme for the demonstration of disposal feasibility (Entsorgungsnachweis). The boreholes are:
|Böttstein||1501 meters (1982 to 1983)|
|Weiach||2482 meters (1983)|
|Riniken||1801 meters (1983 to 1984)|
|Schafisheim||2006 meters (1983 bis 1984)|
|Kaisten||1306 meters (1984)|
|Leuggern||1689 meters (1984 to 1985)|
|Siblingen||1522 meters (1988 to 1989)|
|Benken||1007 meters (1998 to 1999)|