Deep underground on a lush green island, Finland is preparing to bury its highly-radioactive nuclear waste for 100,000 years—sealing it up and maybe even throwing away the key.
Tiny Olkiluoto, off Finland’s west coast, will become home to the world’s costliest and longest-lasting burial ground, a network of tunnels called Onkalo—Finnish for “The Hollow”.
Countries have been wrestling with what to do with nuclear power’s dangerous by-products since the first plants were built in the 1950s.
Most nations keep the waste above ground in temporary storage facilities but Onkalo is the first attempt to bury it for good.
Starting in 2020, Finland plans to stow around 5,500 tons of nuclear waste in the tunnels, more than 420 metres (1,380 feet) below the Earth’s surface.
Already home to one of Finland’s two nuclear power plants, Olkiluoto is now the site of a tunnelling project set to cost up to 3.5 billion euros ($4 billion) until the 2120s, when the vaults will be sealed for good.
“This has required all sorts of new know-how,” said Ismo Aaltonen, chief geologist at nuclear waste manager Posiva, which got the green light to develop the site last year.
The project began in 2004 with the establishment of a research facility to study the suitability of the bedrock.
At the end of last year, the government issued a construction license for the encapsulation plant, effectively giving its final approval for the burial project to go ahead.
At present, Onkalo consists of a twisting five-kilometre (three-mile) tunnel with three shafts for staff and ventilation. Eventually the nuclear warren will stretch 42 kilometres (26 miles).
The temperature is cool and the bedrock is extremely dry—crucial if the spent nuclear rods are to be protected from the corrosive effects of water.
The waste is expected to have lost most of its radioactivity after a few hundred years, but engineers are planning for 100,000, just to be on the safe side.
Spent nuclear rods will be placed in iron casts, then sealed into thick copper canisters and lowered into the tunnels.
Each capsule will be surrounded with a buffer made of bentonite, a type of clay that will protect them from any shuddering in the surrounding rock and help stop water from seeping in.