Final disposal

The Construction of ONKALO

The method used for excavating ONKALO is drilling and blasting. The shafts are constructed by raise boring.

The access tunnel is excavated by drilling and blasting: at the beginning of excavation, a number of holes are drilled and then filled with explosives. Once the rock material has been blasted, the rock waste is moved away. The rock walls are then washed and any broken stones are dropped down.

The rock is sealed, where necessary, by grouting before and after excavation, as well as by using structural water insulation. Cemented anchor bolts made of ribbed steel bars as well as shotcrete are used to strengthen the rock.

Shafts Constructed by Raise Boring

There will be three shafts in ONKALO: a personnel shaft, a supply air shaft and an exhaust air shaft. The diameter of the passenger shaft is 4.5 m and the diameters of the supply air shaft and exhaust air shaft are 3.5 m.

While ONKALO is being constructed, the personnel shaft is used as a combined exhaust air and smoke outlet shaft. This shaft will be used for its nominal purpose once the ONKALO construction project is finished and the permanent personnel lift to the research tunnel is installed in the shaft.

The exhaust air shaft is used as supply air shaft while ONKALO is being constructed. The exhaust air shaft is also equipped with a maintenance and hoisting lift that can be used when

  • performing installations and controls
  • in emergency situations, for lifting people up from lower levels
  • as a connection path for the fire brigade.


The shafts are constructed with the raise boring method. In the raise boring method, a pilothole is first drilled down. Once the drill is down, a reamer bit is installed to the drill, which is then pulled up while the bit is rotating. The reamer bit moves upward at about half a meter per hour. Approximately 100 m of shaft is drilled at one time.


ONKALO – ten-year construction project

ONKALO is an underground bedrock research facility excavated as part of the location studies performed in Olkiluoto in Eurajoki. Research conducted at ONKALO has verified the suitability of the Olkiluoto bedrock for final disposal. In addition, it has identified the areas where the construction of the final deposition tunnels would be most cost-effective.

With this research, Posiva has compiled further information on the bedrock and groundwater conditions at the final disposal site, as well as concerning the impact of construction on these conditions. In addition to bedrock research, ONKALO has provided an opportunity to innovate in the area of rock construction and to further develop final disposal techniques in realistic conditions.

Posiva began constructing ONKALO in 2004. Research has been conducted at the site since construction began.

The underground research facility vehicle access tunnel reaches to a depth of 455 m. The gradient of the tunnel is 1:10. It is 5.5 m wide and 6.3 m high. In addition to the access tunnel, ONKALO comprises a personnel shaft and two ventilation shafts.

The excavation methods during ONKALO’s construction were boring and blasting. The shafts were constructed by raise boring.

Later, the ONKALO bedrock facilities can be put into use when building and using the repository.

Air photo 2004
The ONKALO area in August 2004. The first blast of the construction had been implemented a few months before...

Air Photo summer 2014
...and this is how the area looked in summer 2014, ten years later.


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