08.07.2011 13:31

ONKALO access tunnel excavation completed

The excavation of the underground ONKALO research facility is ready at the technical level at a depth of 438 metres. The excavation included in tunnel contract 5 was finished on 6 June. Bolting and concrete spraying included in the contract will be performed in ONKALO in the summer.

Kimmo Lehtola, Posiva's Building Supervisor, says that tunnel contract 5 was completed in the original schedule. Destia was the excavation contractor.

The excavation of the central tunnel of the demonstration facilities, very important for Posiva, has also been completed in ONKALO. The approximately 70 metres long, 8.5 metres wide and slightly over 6 metres high tunnel leads excavation workers and researchers to Demonstration Tunnel 1 and 2.

The plan is to complete the almost 50-metre-long Demonstration Tunnel 1 as a research facility by Midsummer. The excavation of Demonstration Tunnel 2 is scheduled to begin by mid-July. It is estimated that the 120-metre-long tunnel will be finished in late December 2011.

Final disposal canister testing holes (approx. 8 m deep, approx. diameter 1.8 m) will be made in both demonstration tunnels.

Posiva will use the demonstration facilities to show the skills of excavating the final disposal tunnels and of carrying out the necessary research in them. At the same time, Posiva will prove that a safe final disposal can be implemented with the intended vertical placement option.


Shafts to be raise-bored


The raise-boring of the exhaust air duct in ONKALO will begin in late June. All three ONKALO shafts (exhaust air, intake air and personnel) will be raise-bored in the summer and early autumn from the depth of 438 metres upwards to a depth of 290 metres. The raise-boring will be performed by the Sweden-based Bergteamet AB. Once the raise-boring is ready, all shafts of the underground research facility will have been bored from the bottom up to the surface.

”The ventilation of ONKALO will be redirected to operate as intended during next winter. This means that the air will soon pass through the ventilation plant that will soon be completed," says Lehtola.

Although the excavation of ONKALO has now reached the research level at the depth of 438 metres, the underground research facility still requires a lot of work. Considerable excavation will be carried out in the next few years. Lehtola says that the schedule of the upcoming excavation tasks will be further specified during the summer.

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