One element of the site investigations conducted at Olkiluoto is the excavation of the underground rock characterisation facility (ONKALO) that will be extended to the final disposal depth (approximately -400m).
ONKALO aids in collecting the further data needed for the application for the construction licence that will be 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.
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.