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Finland is expected to be the first country to open an underground storage facility for nuclear waste, utilizing deep bedrock tunnels located 430 meters (roughly 1,400 feet) below ground.
Blasted into 1.9 billion-year-old stable bedrock in Eurajoki, southwest Finland, the geological repository for spent nuclear waste, dubbed Onkalo, which means cave in Finnish, is nearly ready to start operations.
The Finnish Radiation and Nuclear Safety Authority (STUK) is scheduled to issue its final assessment approval in June, clearing the path for an operating license.
"We hope we can start operations either at the end of this year or, most probably, at the beginning of next year," said Philippe Bordarier, chief executive of nuclear operator Teollisuuden Voima Oyj (TVO).
His voice echoed through the damp tunnel where spent nuclear fuel will be buried in holes drilled directly into bedrock, remaining hazardously radioactive for thousands of years.
Waste currently cooling in water pools at an interim facility—located at the nearby Olkiluoto Power Plant along the Baltic Sea—will be the first to be deposited, Bordarier noted.
With space for 6,500 tons of uranium, Onkalo is aimed at providing permanent storage for spent fuel from Finland's five nuclear reactors, three of them located in Olkiluoto.
Nuclear waste management company Posiva began building the site in 2004, with the cost now estimated at €1 billion ($1.16 billion).
Spent fuel is planned to be deposited in Onkalo's massive network of tunnels for 100 years, but operations may be extended if new nuclear reactors are built.
Subsequently, the vault will be sealed to provide safe storage for at least 100,000 years.
"Basically, it needs to be safe forever," noted Lauri Parviainen, a Posiva chemist. The fuel will be highly radioactive for "tens of thousands of years," he added.
After 100,000 years, the waste will be about the same level as the uranium ore from which the fuel is made.
Above ground, the spent nuclear fuel will be encapsulated in highly corrosion-resistant copper canisters.
The canisters will be lowered into holes drilled in the tunnels, before the holes are filled with bentonite clay to seal them, Parviainen explained.
"So if the bentonite stays in place, we are safe," he said.
Once each 300-meter-long disposal tunnel is filled, it will be sealed with a steel-reinforced concrete plug.
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Jarkko Kyllonen, an expert on nuclear safety at Finland's nuclear regulator STUK, has assessed risk scenarios for the Onkalo project stretching up to a million years into the future.
"Considering the hazard potential of the waste, the first 10,000 years are very important for keeping the capsules intact," he told AFP.
The main long-term risks are corrosion of the copper canisters or earthquakes during future ice ages, which could potentially damage the capsules and cause radioactive fuel to leak, Kyllonen said.
But the results of various risk assessments conducted over the years have been "positive."
While France's plans for a similar underground nuclear tomb have met with strong opposition, Onkalo has received broader backing in Finland.
There was some opposition locally when the plans were first introduced in the 1970s, but "people have gotten used to it and they trust the assessments made by STUK," Matti Kojo, a social sciences professor at Lut University, told AFP.
"At the moment, support for nuclear power is at a historically high level in Finland," he noted.
The Finnish Association for Nature Conservation, however, remains critical of the project, insisting that nuclear waste poses a serious, long-term risk.
"No one can guarantee the safety of Onkalo for thousands of years," director Tapani Veistola told AFP in an e-mail.
Under Finnish law, nuclear waste produced in Finland has to be deposited in the country, Climate and Environment Minister Sari Multala told AFP.
"Before the legal change in 1994, the spent nuclear fuel was exported to, for example, Russia," she said.
Increasing nuclear power in Finland has been a priority for the right-wing government, and the country is considering building small modular reactors (SMRs).
How the spent nuclear fuel from future SMRs would be managed "has not been decided yet," Multala said. An assessment should be completed by March next year, she added.
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