Drilling

The bedrock in Olkiluoto is investigated by drilling holes of up to one kilometre deep, from ground surface.  So far, a total of 52 holes have been drilled.

This drilling has continued since the late 1980s. A few holes are still drilled every year. Hole number 50 was drilled in the end of 2008. In the summer of 2009 two more holes were drilled and a third one will be drilled later on the year. During recent years, the drilling has concentrated on the previously scarcely-investigated eastern and north-eastern part of the island.

The drilling and investigations carried out in the drillholes will also continue in future years in order to allow the flexible planning of repository by utilising the entire area available.

Drilling produces a drill core sample of some five centimetres in diameter. It is carefully studied to establish the degree of fracturing and types of rock present in the bedrock. The in hole measurements and samples taken from the drillhole allow studying of the flow and qualities of groundwater. Geophysical measurements and imaging also take place in the holes.

The drilling investigations can be utilised for establishing the location and properties of particular bedrock structures. Geophysical methods also allow verifying the properties of modelled structures. The results of the investigations are, among others, utilised for planning the excavation and sealing of the ONKALO facility and for designing the repository.

In addition to holes drilled from surface, drilling also takes place underground, in ONKALO. They serve, among other things, to help predict the future excavation conditions and provide guidelines for planning and design. Long characterisation holes will also be drilled from ONKALO to the location of the repository.