Finnish waste management company Posiva has announced the start of construction of the used fuel encapsulation plant at Eurajoki, near the Olkiluoto in western Finland.

The Olkiluoto site was selected in 2000 and Finland’s parliament approved the decision-in-principle on the repository in 2001. Posiva, which is owned by Finnish nuclear utilities Fortum and Teollisuuden Voima Oyj (TVO), submitted its construction licence application to the Ministry of Employment and the Economy in 2013. Posiva began investigation of the rock at Olkiluoto in preparation for  its licence application using results from the Onkalo underground laboratory, which is to be expanded as the basis for the repository. The government granted a construction licence in 2015 and construction work on the repository began in 2016. Posiva is still required to obtain a separate operating licence for the facility. The estimated cost  totals about €500 million ($570 million).

Used fuel will be packed inside copper-steel canisters at an above-ground encapsulation plant and then transferred into the underground tunnels of the repository, at a depth of 400-450m, and further into deposition holes lined with a bentonite buffer. The repository is expected to begin operating in 2023. The used fuel will be delivered in transportation casks to the receiving area of the encapsulating plant  where the empty final disposal canisters will also be delivered. At the encapsulation plant, the transportation cask and the final disposal canister will be docked tightly inside the fuel handling cell, where the fuel will be transferred first to the drying station and then to the final disposal canister. Once all fuel assemblies have been transferred to the canister, it will be filled with argon gas and tightly closed with an inner steel cover.

Next, the filled canister will be transferred to a welding station where the lid will be sealed with electron beam welding. The tightness of the weld will then be examined at an inspection station using non-destructive testing methods, such as x-ray and ultrasonic testing. Canisters that pass the inspection will be transferred either by lift or by the access tunnel with a special-purpose vehicle to the final disposal facility.

In May, Posiva announced that the full-scale in situ system test at the Onkalo underground characterisation facility had proceeded to the concreting phase in the construction of the end plug for the deposition tunnel. This test ensures the functionality of storing nuclear fuel assemblies packed in the copper-steel canisters in tunnels drilled into rocks, as well as backfilling the tunnels with bentonite clay and sealing them with reinforced concrete plugs.  Posiva President Janne Mokka said: "The project's main focus requires experts who have worked for four decades on developing the safe final disposal concept, as well as professionals of project management and various partners. We expect to award contracts for the most significant works in the near future."

Sweden is planning a similar used fuel encapsulation and disposal facility using the same storage method. Under its current timetable, national radioactive waste management company Svensk Kärnbränslehantering AB plans to start construction of the used fuel repository and the encapsulation plant sometime early in the 2020s and they will take about 10 years to complete.
In Russia, used fuel is not considered as waste and is subject to reprocessing in order to extract useful components for re-use in a close the nuclear fuel cycle. However, the experience of Finland and other countries is being studied for its use in the construction of an underground research laboratory in the Nizhnekansky massif in the Krasnoyarsk Territory.

Date: Thursday, 27 June 2019
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