First five disposal tunnels excavated at Finnish repository

01 July 2022

The excavation of the first five actual disposal tunnels has been completed at the Onkalo underground used nuclear fuel repository near Olkiluoto, Finnish radioactive waste management company Posiva Oy announced.

One of the first five disposal tunnels at Onkalo (Image: Posiva)

Posiva said the final rock-blasting detonation was carried out on 18 June and the end of the fifth tunnel was completed on 21 June. The total length of the tunnels, whose excavation began in May 2021, is about 1700 metres. The excavation contractor was YIT Suomi Oy, which has been excavating tunnels for Posiva for several years.

"Now the construction of the disposal tunnels will continue with the reinforcement of the tunnels and the levelling of the tunnel floor," noted programme manager Kimmo Kemppainen.

Posiva said holes will be drilled in the first five disposal tunnels to hold about 180 disposal canisters.

Used nuclear fuel will be placed in the bedrock, at a depth of about 450 metres. The disposal system consists of a tightly sealed iron-copper canister, a bentonite buffer enclosing the canister, a tunnel backfilling material made of swellable clay, the seal structures of the tunnels and premises, and the enclosing rock.

It is estimated that 100 deposition tunnels will be excavated during the 100-year operational period of the final disposal facility, and will have a total length of about 35 kilometres. The maximum length of each tunnel will be 350 metres. The tunnels will be about 4.5 metres high and about 3.5 metres wide.

The excavation of the first five tunnels is part of Posiva's approximately EUR500 million (USD520 million) EKA project that covers all the final disposal facilities needed, including both their construction and equipment, as well as the start of the final disposal operation in the first deposition tunnel.

The repository - the first in the world for used fuel - is expected to begin operations in the mid-2020s. A similar repository is planned at Forsmark in Sweden.

Researched and written by World Nuclear News