The inlet air shaft at ONKALO in Finland

The laboratory for Finland’s deep geological waste repository has bottomed out, Finnish nuclear waste management agency Posiva has reported.

All vertical shafts of the underground research facility ONKALO have now been drilled through. The last of the shafts to be drilled was the personnel shaft, with the final phase being completed in early April.

The inlet air shaft and personnel shaft reach a depth of 455 metres, while the exhaust air shaft reaches 437 metres.

The reinforcement of the personnel shaft and the partial reinforcement of both air shafts will begin in the latter half of this year.

The maintenance and hoisting cage will be removed from the exhaust air shaft and installed in its proper position in the inlet air shaft.

The exhaust air shaft will then be modified to fulfil its actual purpose, with exhaust air from ONKALO routed to flow via the designated route.

The ONKALO facility has aided in collecting the data needed for the final repository construction licence application that was submitted to Finland’s Ministry of Employment and the Economy in 2012. Construction work on the repository is expected to begin in 2015 after the permit has been granted. Final disposal of spent nuclear fuel is targeted for as early as 2022.

Canister welding method selected

In March, Posiva announced that it had chosen the friction stir welding method to close the copper and cast iron spent fuel container. Friction stir welding method is based on hot forming, where the required temperature is caused by friction of a tool rotating with high speed in the material to be welded. The waste encapsulation plant will be built at Olkiluoto.

The welding technique is the same as that chosen by Nordic neighbour Sweden’s spent fuel repository agency SKB. The companies have signed a specific technology agreement on friction strir welding to enhance current cooperation in a joint programme to develop the FSW equipment and methods further until they are qualified.

Photo: The inlet air shaft at ONKALO in Finland (Source: Posiva)