One element of the site investigations conducted at Olkiluoto is the excavation of the underground rock characterisation facility (ONKALO) that will be extended approximately to the depth of 450 meters.
ONKALO has aided in collecting the data needed for the application for the construction licence that was submitted in 2012. The bedrock is studied with methods from geology, hydrology and geochemistry.
In addition to facilitating bedrock research, ONKALO also provides an opportunity to develop excavation techniques and final disposal techniques in realistic conditions. Later, the ONKALO facilities can be put into use when building and using the repository.
Posiva started to construct ONKALO in 2004. Research has been conducted there since the beginning of its construction. The access tunnel of ONKALO reaches the depth of 455 meters.
ONKALO consists of one access tunnel and three shafts: a personnel shaft and two ventilation shafts. The slope of the tunnel is 1:10. It is 5.5 m wide and 6.3 m high.