At the repository, used fuel will be placed in the bedrock, at a depth of about 430 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.
Posiva announced in late August the start of a trial run - expected to take several months - of the operation of the final disposal facility, albeit still without the used fuel. Four cannisters will be deposited in holes which are eight metres deep and located in a 70-metres long final disposal tunnel. The final disposal tunnel will then be filled with bentonite clay and sealed with a concrete plug. The trial run also covers the retrieval of a damaged cannister back above ground. Posiva noted that the equipment and systems of the final disposal facility will be tested together for the first time in accordance with planned processes during the trial run stage.
The company has announced the completion of the initial stage of the trial run - the transfer of a test transport cask for used nuclear fuel from Teollisuuden Voima Oyj's (TVO's) interim storage for used fuel at the Olkiluoto nuclear power plant, to Posiva's nearby encapsulation plant along a prespecified route.
The transfer cask is lowered onto the transport cask transfer trolley (Image: Posiva)
"The transfer carried out by Posiva follows, to a large extent, the same procedures as those used in TVO's own fuel transfers in the power plant, but the cask used in the trial run is Posiva's test transport cask," Posiva said. "The transfer vehicle proceeds at a maximum speed of five kilometres per hour and is accompanied by security staff. The security staff also blocks other traffic from accessing the route to ensure an uninterrupted and safe transfer operation."
Once Posiva starts full operation of the repository, transfers of actual used fuel from the interim storage to Posiva's facility will take place every few weeks following similar procedures, it noted.
The test run will now continue with the filling and closure of the capsule, which is done completely by remote control in radiation-protected premises.
Posiva has applied for an operating licence for the repository for a period from March 2024 to the end of 2070. The government will make the final decision on its application, but a positive opinion by Finland's Radiation and Nuclear Safety Authority (STUK) is required beforehand. The regulator began its review in May 2022 after concluding Posiva had provided sufficient material. The ministry had requested STUK's opinion on the application by the end of 2023. However, in January this year, STUK requested the deadline for its opinion on Posiva's operating licence application be extended until the end of 2024.
