ONKALO personnel shaft to be extended down to 290 metres
The personnel shaft of ONKALO is being extended from 180 metres down to 290 metres. The exhaust air shaft of ONKALO was earlier in the autumn raise-bored to this depth, and according to plans, the inlet air shaft will also be drilled down to 290 metres next year.
The extension of the personnel shaft was started by controlled drilling of a 30-cm pilot hole from the -180 m level in order to produce an as vertical hole as possible down to -290. According to Supervisor Kimmo Lehtola, the orientation accuracy achieved with the pilot hole was excellent, with a maximum deviation of 15 cm.
The backreaming of the shaft with a 4,5-metre reamer bit from the –290 level to the –180 level started toward the end of November at an average rate of 0.5 metres per hour and is expected to be completed in mid-December.
During the construction of ONKALO the personnel shaft is used as an exhaust air and smoke vent shaft. The use of the shaft as an actual personnel shaft starts at the end of the construction project, when it will be equipped with a personnel lift.
The raise-boring of the inlet air shaft will be carried out next year in three campaigns. The drilling contractor is the Swedish Bergteamet company.