Finnish radioactive waste management company Posiva Oy announced that the excavation of the first five tunnels for actual disposal of used nuclear fuel has been completed at the Onkalo underground nuclear fuel disposal depot near Olkiluoto.
The last rock blasting took place on June 18 and the end of the fifth tunnel was completed on June 21, Posiva said. Excavation of the tunnel, which has a total length of about 1,700 meters, will begin in May 2021. The digging contractor is YIT Suomi Oy, which has been digging tunnels for Posiva for several years.
"Construction of the disposal tunnel will now continue, along with reinforcement and leveling of the tunnel floor," said Project manager Kimmo Kemppainen.
Holes will be drilled in the first five disposal tunnels to accommodate about 180 disposal tanks, Posiva said.
Spent nuclear fuel will be placed in bedrock at a depth of about 450 meters. The disposal system consists of a tightly sealed iron-copper tank, a bentonite buffer surrounding the iron-copper tank, a tunnel backfill material made of expandable clay, a sealing structure for the tunnel and the house, and the surrounding rock.
It is estimated that 100 sedimentary tunnels will be excavated during the 100-year operation of the final disposal facility, with a total length of approximately 35 km. The maximum length of each tunnel will be 350 meters. The tunnel will be about 4.5 meters high and 3.5 meters wide.
The excavation of the first five tunnels is part of Posiva's approximately 500 million euro ($520 million) EKA project, which includes all required final disposal facilities, including its construction and equipment, as well as the commencement of final disposal operations at the first deposition tunnel.