There are deer, wolves and even lynx living among the pine forests on Olkiluoto Island and soon this quiet corner of Finland will be home, too, to a facility that its creators hope one day will be as inconspicuous as some of the local wildlife.

Finland has become the first country in the world to build a storage facility deep underground for spent fuel from its nuclear power plants. It is a feat being pursued by many nations that see geological disposal as the best solution to the unresolved issue of how to deal with decades of highly radioactive waste.

The Onkalo repository, about 170 miles west of Helsinki in the municipality of Eurajoki, is being developed by Posiva Oy, a company founded 30 years ago by Teollisuuden Voima Oyj and Fortum, the operators of Finland’s nuclear reactors, for researching and creating a method of final disposal of spent nuclear fuel from their plants.

Construction of the facility and its labyrinth of tunnels, excavated more than a quarter of a mile below sea level, started in 2004. The first enriched uranium fuel pellets are due to be received in the mid-2020s. A trial run with mock fuel will start in August. The tunnels, which eventually will span 30 miles, will be capable of taking the 6,500 tonnes of waste generated during the entire planned lifespan of each of Finland’s five nuclear reactors.

Remote it may be, but the site is attracting attention from far beyond the Gulf of Bothnia. Scientists in Britain, for example, are looking to Finland for inspiration. The concept will form the template for a final solution to the disposal of the 5 per cent to 10 per cent of nuclear waste that is the most radioactive and cannot be stored at the UK’s low-level waste repository in Cumbria. That includes spent nuclear fuel pellets and the byproducts of fuel reprocessing.

The process of finding and developing a site in Britain is being led by the state-backed Nuclear Waste Services, a division of the Nuclear Decommissioning Authority. This is the third significant attempt, the first of which was in 1987. However, according to Amy Shelton, principal site evaluation manager for NWS, “we’ve never before got to the stage of the conversations that we’re having right now”. Three locations have been identified as potential sites, in mid and south Copeland in Cumbria and at Theddlethorpe in Lincolnshire. Finding “a willing community” is key.

In Finland, 101 sites were identified initially. These were whittled down to four. Olkiluoto won. The resulting disposal facility is located about a kilometre from three of the country’s nuclear reactors, which generate a third of Finland’s electricity. It is also where the spent fuel is being stored in temporary casks.

Once it is up and running, the casks will be transported to the arrival hall of the disposal facility and will be brought by a transfer trolley to the encapsulation chamber. The fuel rods, in bundles of 12, will be placed inside a cast-iron insert that sits inside a copper canister. An inner lid will be fitted before a copper lid is welded on with a specialised machine. Then the canisters will be stored, ready to be taken underground.

Once underground, the copper canisters will sit in deposition holes that are about 8m deep, dug into each side tunnel. Every cavernous tunnel is about 350m long and capable of holding 35 canisters. All the processes are fully automated.

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After they reach capacity, each will be filled with concrete and bentonite, a clay-like material that expands when it comes into contact with moisture, and will be sealed with a giant concrete plug. Posiva estimates that it will take 100 years for the facility to be filled, which will be done gradually while construction to expand the site takes place.

The failure of one containment barrier will not compromise the security of the waste, according to Posiva. About 58 boreholes have been drilled over the past four decades to identify suitable rock that is not prone to flooding and is capable of withstanding seismic movements. The tunnels have been designed with a 100,000-year lifespan in mind, about double the time that modern humans have been in Europe and far exceeding the time it will take the radioactivity to reduce to safe levels.

The task facing the UK is far greater, though. Britain has about 80,000 canisters of waste suitable for an underground facility, compared with Finland’s 3,250. While the Finnish site occupies two square kilometres, a British facility would need to measure 36 square kilometres. The budget for the project has been set at a wide range of £20 billion to £53 billion, compared with £2.3 billion for Onkalo.

The thinking is that a site would have adequate capacity to take waste that would be derived from plants generating 24 gigawatts, in line with the government’s 2050 target for stepping up nuclear power. A site would not be expected to start receiving intermediate-level waste until the 2050s and spent fuel by 2075. Final site selection is not expected until ten to fifteen years from now.

Geology is key, but different types of rock — clays, but also halite-type rocks — may be suitable, according to Shelton. “Each of them provide different opportunities for how they would provide isolation and containment and it’s the selection of materials that we use for the engineered barriers that would work together overall to provide safety.”

In Finland, the foundations for Onkalo were laid in 1983 and the project was running on schedule, Mika Pohjonen, managing director of Posiva Solutions, the group’s consulting unit, said. “The thinking first, in the beginning of the 1980s, was that, of course, the big nuclear countries like the UK, US, France, Germany and Japan, they [would] solve this and we [would] just copy paste here. But it went the other way around.”

The development has been funded by Posiva, which is majority-owned by Teollisuuden Voima Oyj. Private oversight has helped to expedite the project. “We are arm’s-length from politics, so our decision-makers don’t change,” Pohjonen said. “In state organisations, they change and governments change and policies change.”

In Britain, geological disposal will be taxpayer-funded, but Shelton said it had cross-party support. “I think the uniqueness of our project is that radioactive waste exists — we have it in the UK now — and we have to find a viable and permanent solution for disposing of the waste and that is recognised by both [political] parties.”

A consent-led approach is a key difference to how the latest attempt at finding a site is being led compared with past efforts. “One of the other things that was learnt is being able to articulate the benefits and what’s in it for the community,” Shelton said.

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About 4,000 jobs should be created in the first 25 years of the project, NWS estimates, with as much as 2,000 more each year over the 175-year span of constructing and filling the facility. There is also community funding for local projects, including £1 million for those that put themselves forward as a potential location.

NWS is also seeking to understand more about the geology of potential sites to discount those that are unsuitable, such as Allerdale in west Cumbria, which was eliminated from the running last year. Other factors, such as areas where there has been mining, are also discounted.

Transparent and open communication about the safety of storing nuclear waste was crucial in winning over any nervous residents in Eurajoki, according to Vesa Lakaniemi, its mayor. So, too, was the municipal government’s absolute right to veto any disposal facility.

The property taxes paid to the municipality by Olkiluoto Nuclear Power Plant and Posiva were a benefit to the area’s public services, Lakaniemi said. “It’s a steady income for us.” Eurajoki, which has a population of about 9,000, has the highest property tax revenue per capita in Finland, but one of the lowest municipal tax rates.

Some familiarity with nuclear power has helped. In Britain, the two Cumbrian sites are not far from Sellafield, where the majority of the country’s radioactive waste is being stored. That might inform how to solve the logistical challenge of bringing waste from sites that are geographically scattered to a single area. Marine, rail and road are all being considered.

“We’re the generation that’s had the benefits of the activities that have led to the radioactive waste, so we have a responsibility to find a permanent solution to managing those wastes,” Shelton said. But while the need is clear, the practicalities will take much more time to iron out.