Trial operation underway at Posiva’s used fuel repository in Finland is expected to last several months. Finnish waste management company Posiva said the first stage of the trial run has been completed. This involved placing disposal cannisters in the Onkalo used nuclear fuel repository.
The aim is to test the final disposal facility in its entirety, albeit without the used fuel. The plant has many unique devices and systems that were developed as a result of decades of research and are now being operated together for the first time. Therefore, the test run is being called a co-operation test.
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.
During the trial, four cannisters will be deposited in holes which are eight metres deep and located in a 70-metres long final disposal tunnel. The tunnel will then be filled with bentonite clay and sealed with a concrete plug. The trial run also includes retrieval of a damaged cannister.
The trial involves 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 NPP, to Posiva’s nearby encapsulation plant along a prespecified route.
According to Posiva, the transfer to a large extent, follows the same procedures as those used in TVO’s own fuel transfers at the power plant, but the cask used in the trial run is Posiva’s test transport cask. “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,” Posiva noted.
When the repository is in full operation, transfers of used fuel from the interim storage to Posiva’s facility will take place every few weeks following similar procedures. The trial will now continue with the filling and closure of the capsule, which is done completely by remote control in radiation-protected premises.
Posiva has been preparing for the disposal of used nuclear fuel for more than 40 years. Its encapsulation plant is located above ground, and the fuel repository of underground disposal facility is located in the bedrock at a depth of approximately 400-430 metres. Posiva has applied for an operating licence to the Ministry of Economic Affairs & Employment and expects to dispose of their used fuel in the facility between 2024 and 2070.
The government will make the final decision on Posiva’s application, after the Radiation and Nuclear Safety Authority (STUK – Säteilyturvakeskus) has given its approval. STUK began its review in May 2022 and the ministry had requested STUK’s opinion by the end of 2023. Earlier this year, STUK asked for the deadline to be extended until the end of 2024 noting that the project was progressing without major problems, but at a slightly slower pace than was previously anticipated.
