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.
In the trial run - expected to take several months - the operation of the final disposal facility will be tested comprehensively, 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. It said the purpose of the trial run is to "verify safe final disposal before the start of the actual final disposal operation". The company added that the trial run can be described as "a joint functional test of all the systems and equipment".
"Posiva has come a long way to reach this point," the company's Production Director Karri Osara said. "The trial run of final disposal is not only an excellent opportunity for learning and development, but also an extremely demanding showcase of the capabilities of our organisation."
Posiva President and CEO Ilkka Poikolainen added: "Posiva's operation now takes a significant step toward the start of the actual final disposal operation. This is a momentous occasion also to our employees and cooperation partners."
The site for Posiva's repository at Eurajoki, near the Olkiluoto nuclear power plant, was selected in 2000. The Finnish parliament approved the decision-in-principle on the repository project the following year. Posiva - jointly owned by Finnish nuclear utilities Fortum and TVO - submitted its construction licence application to the Ministry of Employment and the Economy in December 2013. Posiva studied the rock at Olkiluoto and prepared its licence application using results from the Onkalo underground laboratory, which will be expanded to form the basis of the repository. The government granted a construction licence for the project in November 2015 and construction work on the repository started a year later.
Posiva submitted its application, together with related information, to the Ministry of Economic Affairs and Employment on 30 December 2021 for an operating licence for the used fuel encapsulation plant and final disposal facility. The repository is expected to begin operations in the mid-2020s. Posiva has applied for an operating licence for a period from March 2024 to the end of 2070.
The government will make the final decision on Posiva's 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.
