ONKALO ventilation is one step closer to being ready – inlet air shaft raise-bored
The inlet air shaft of the underground ONKALO research facility is now complete. The last stretch of the shaft from 455 m to 290 m was raise-bored in early February. The work, which lasted for about 1.5 months, was performed by the Swedish-based Bergteamet AB.
The shaft was raise-bored in four segments and will provide ONKALO with fresh air in the future. " The shaft was built through the technical facilities located at the depth of 437 metres. The raise-boring accuracy was as planned," says Kimmo Lehtola, construction superviser at Posiva.
In addition to the inlet air shaft, ONKALO includes two other shafts. The exhaust air shaft was completed at its final length (depth of 437 m) in early 2012. The personnel shaft has been raise-bored from the depth of 290 m to the ground. The boring of the last segment from 455 m to 290 m will commence in ONKALO in February. "The sealing of all shafts with cement and silica mass has been a great success. After the last segment of the personnel shaft has been raise-bored, we can arrange ONKALO's ventilation to its final form," says Lehtola.
"We will go through the shafts in the spring to find out whether reinforcement is needed. In the spring, additional reinforcement will be performed in ONKALO in any case. In addition, a steel concrete plug will be cast there later. Eventually, final disposal tunnels will be sealed with such plugs."