Encapsulation plant on ground level
Posiva's other project in the process towards final disposal is the construction of the encapsulation plant. The spent nuclear fuel assemblies are transported to the encapsulation plant where they are dried and packed in a gas-tight manner in the final disposal canisters. Work is progressing on schedule and the structures of the plant will reach ground level height already this autumn.
–So far the construction of the encapsulation plant has taken place underground. We started at a depth of 12–13 metres and have now reached the ground level. It is estimated that roughly half of all concrete to be used in the construction of the plant will go to underground structures, explains Construction Manager Juha Riihimäki.
Once the final disposal operation starts, the spent nuclear fuel is transported to the reception and storage area of the encapsulation plant, located on the ground level. However, the deposition canister for nuclear fuel is moved in the underground spaces at the different work phases. Building services systems are also located on the lowermost levels of the encapsulation plant.
–The spent nuclear fuel is placed in the final disposal canister in the hot chamber which features concrete walls that are about 1.3 metres thick. The welding of the canister takes place in the welding chamber. It is located on the ground level, but only the end of the copper canister that is welded is raised into the chamber.
The encapsulation plant will be ready for operation in time for the joint functional test to be carried out in 2023. The plant features a lot of special technology not used anywhere else in the world.
–The design and production process of the equipment is ongoing at present. We utilise both Finnish and foreign equipment manufacturers. The first deliveries of special equipment for the encapsulation plant will take place later in 2021, Mr. Riihimäki says.
The lift for the canister shaft, for example, comes from a German supplier who specialises in mine technology. The canister lift is the first of its kind in the whole world. The equipment for the transfer and handling of spent nuclear fuel is also tailored for this project.
–The welding method selected for the copper canister is the friction stir welding method where the sealing joint is fused on the copper lid. Posiva has developed the method together with the Swedish regulatory body SKB that is responsible for the final disposal of spent fuel in Sweden, Mr. Riihimäki elaborates.
Demanding injection operation in central tunnel 6.
About half of the concrete needed for the encapsulation plant is used for underground structures.
Spent nuclear fuel is encapsulated into copper canisters in the encapsulation plant.
Main contractor: Skanska Talonrakennus Oy
Construction period: 2019–2022
Volume: 70000 m3
Area: 11500 floor-m2
External dimensions: 72 x 40 metres