RADWASTE MANAGEMENT | FINLAND
Designing for disposal
Finland’s Posiva is collaborating to utilise modern technologies in the world’s first final disposal facility
Above: Posiva’s final disposal facility for spent nuclear fuel and its underground tunnels where KSAA will operate Photo credit: Posiva
FINLAND HAS FOUR NUCLEAR POWER units in operation. A fifth, Olkiluoto 3, will soon begin energy production. This form of electricity production generates radioactive waste, which must be handled in a manner that will not harm the environment now or in the future. This is an issue of assuring long-term safety of final disposal. “Nuclear waste has not been disposed of in any country
yet; instead, it is being kept in interim storage facilities or containers. Finland is the first country in the world to ensure safe final disposal of nuclear waste,” says Jarkko Stenfors, manager of Posiva’s Final Disposal Equipment Unit. Final disposal is an underground process that requires equipment and logistical operations to be developed in parallel. The process starts by boring disposal holes in tunnels
that have already been excavated, using a purpose- built boring machine. The machine is currently under manufacturing and will be tested in 2022 before the actual production starts. Underground disposal cannot begin until bentonite clay blocks are installed in the bottom of the disposal hole. Bentonite prevents water from moving around the canister and protects the canister from small rock movements. The canister is transferred from the loading station to the disposal tunnel using a dedicated canister transfer and installation vehicle (KSAA, see below), and the same
32 | May 2021 |
www.neimagazine.com
machine is used to install it in the disposal hole, which it does with an accuracy of a few millimetres. Once the canister is lowered into the hole, the upper
part of the hole is also filled with bentonite blocks and the tunnel is filled with granular bentonite clay. This tunnel backfill prevents water from flowing in the tunnels and holds the buffer material in place. When the entire disposal tunnel is filled with granular bentonite clay material, a thick concrete plug is casted at its end. Disposal will continue until all the spent nuclear fuel
in Posiva’s possession has been safely disposed of in the Olkiluoto bedrock. After this, all the tunnels and shafts leading to it will be closed, and the buildings on the ground will be demolished.
The equipment KSAA is the world’s first spent nuclear fuel canister transfer and installation vehicle and it was designed by consultant company Comatec. Cooperation between Posiva and Comatec started more than a decade ago. Stenfors describes Comatec as a ‘royal supplier,’ which has already designed several prototype devices to test the disposal concept. Now, the final production devices are being designed. “We do not have the required expertise to design vehicles in-house. We are a project organisation and the plant
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