The island of Olkiluoto off the west coast of Finland is to be the site of the world’s first attempt to find a permanent solution for radioactive waste.
The government plans to build a $4bn tunnel network that is capable of containing the material for 100,000 years – or long enough for the radioactivity of plutonium to fall by about 94%.
The project, to be called the Onkalo Spent Nuclear Fuel Repository, will involve constructing a network of tunnels 420m below ground. Once this is complete, by 2020, they will be filled with about 5,500 tonnes of nuclear waste.
At present, Onkalo consists of a one 5km-long tunnel with three shafts for access and ventilation. Eventually the repository will stretch for 42km underground.
The project will continue into the 2100s, according to Stuk, Finland’s nuclear regulator.
The repository was designed by Posiva, a Finnish company formed to carry out permanent disposal projects for nuclear waste. Its plan was approved by Stuk in February 2015, after a two-year assessment process.
At the time, Stuk inspector Jussi Heinonen commented that the "operational and long-term safety of the nuclear waste facility are on a sufficiently high level for granting the construction licence".
The expected state of the site after all tunnelling work is completed
He added: "This is a new type of facility, which is why the appropriate approach is to progress in phases and, at the same time, assess and elaborate the designing of the facility on the basis of accumulated knowledge."
As well as being entombed, the spent nuclear rods will be placed in iron sarcophaguses, then sealed into copper canisters. These will be "encapsulated" by bentonite, a type of clay that will protect them from water and seismic activity. More clay blocks will fill the tunnels before they are sealed up.
The method was developed in Sweden where a similar project is under way.
Opponents of nuclear power, such as Greenpeace, have raised concern about potential radioactive leaks. The group’s Finnish spokesperson told the phys.org website: "Nuclear waste has already been created and therefore something has to be done about it, but certain unsolved risk factors need to be investigated further.
Posiva is jointly owned by Finnish nuclear utilities Fortum and TVO. It submitted its application to build Onkalo in December 2012 with the aim of permanently storing spent fuel from its owners’ plants. The repository was agreed in principle by the Finish parliament in 2001.
Olkiluoto is already home to a nuclear plant, which has two functioning reactors and a third-generation EPR pressurised water reactor that is expected to be completed nine years after its original deadline.
Videos presenting the project can be viewed here.
Images courtesy of Posiva