The elevator takes 90 seconds to descend half a kilometre underground. The cage door opens onto a dark, damp tunnel deep in the Swedish rock, where groundwater trickles down the granite walls as trucks rumble by.

Here, at the Äspö Hard Rock Laboratory in the southeastern Swedish town of Oskarshamn, researchers are using an underground maze of four kilometres (2.5 miles) of tunnels to test methods to enable Sweden to become the first country in the world to bury spent nuclear fuel for hundreds of thousands of years.

The Swedish Nuclear Fuel and Waste Management Company (SKB), an independent company owned by nuclear power plant operators, is due to select a site sometime in June for its final repository for high-level spent nuclear fuel from Sweden’s 10 reactors.

“If all goes as planned, construction could begin in 2016 and the first canister could be deposited in the repository in 2022 or 2024,” SKB spokesman Jimmy Larsson-Hagberg told AFP.

Nuclear power has been around for decades and currently accounts for 14 percent of the world’s electricity production. But while there are interim storage facilities for high-level nuclear waste, no permanent storage solution exists yet.

And as climate concerns and opposition to fossil fuels prompt numerous countries to re-think their aversion to nuclear power, the need for final repositories is growing, experts say.

In Sweden, where 45 percent of electricity production comes from nuclear power, the government in February reversed a decision to phase out the country’s 10 nuclear reactors.

Instead, they can now be replaced at the end of their life spans as part of an ambitious new climate programme.

While many countries have to cope with angry shouts of “not in my backyard” when searching for a location to store radioactive waste, the two eastern Swedish towns of Oskarshamn and Östhammar, both already home to nuclear power plants, are competing to welcome the spent fuel.

Around 80 percent of people in the two municipalities are in favour of hosting the site.

Both towns have open facilities where residents, school classes, and foreign visitors can tour the premises to see how nuclear waste is currently being handled.

Experts say the open sites and frequent dialogue with locals have led to broad acceptance for the project, which will attract billions of dollars of investments and create new jobs.

“Local acceptance is a must for SKB in its decision-making process,” SKB guide Kajsa Engholm said.

High-level nuclear waste from Sweden’s reactors has since 1985 been stored at a central interim storage facility (CLAB) in Oskarshamn. Waste from across the country is transported by a specially-equipped ship to CLAB.

CLAB currently has 4,993 tonnes of high-level spent fuel stored, and can take in a maximum of 10,000 tonnes, guide Britta Freudenthal told AFP, stressing the need for a permanent storage site within 30 to 40 years.

After several decades of interim storage, about one percent of the radioactivity remains. But only after 100,000 years will the radioactivity decline to the level the uranium ore had when it was mined — another reason a permanent storage facility is needed.

In Oskarshamn, where the country’s first nuclear reactor opened in 1972 and which is home to three reactors, local officials have lobbied hard for the final repository.

“We have had interim storage of spent fuel in Oskarshamn since 1985. People here want a final solution,” Lars Blomberg, a member of Oskarhamn’s city council, explained.

SKB completed construction on the Äspö Hard Rock Laboratory in 1995, and has since then tested various methods of storing canisters in the 1.8 billion-year-old granite bedrock.

“We think of things from a geological perspective, where 100,000 years is nothing compared to 1.8 billion years,” Engholm says as she leads a group of visitors in hard hats through one of the dimly-lit tunnels.

The massive laboratory was built solely for test purposes and will not be used for the final repository. But it will continue as a test site in the future.

Sweden, Finland and France all aim to have final repositories in place by 2030.

“The generations that created the waste have a responsibility to take care of it,” Engholm said.

The Swedish technique consists of storing two tonnes of spent fuel in copper-coated canisters that weigh 25 tonnes each.

Each canister is welded shut using a special technique and then mechanically deposited in a tunnel in the repository.

A buffer of bentonite clay, a volcanic ash that when mixed with water swells to provide a watertight barrier and protect against earthquakes, is then injected to fill the hole in the rock.

“The canisters are buried several metres apart so the rock can absorb the heat generated by the radioactive materials in each copper canister,” Engholm explains.

Once a tunnel in the repository is full, the tunnel is filled in with a mixture of bentonite and rock.

Six empty test canisters have already been buried at Äspö, with electric heaters simulating the heat generated by radioactive materials.

Regular tests are conducted to see how the materials react to temperature, water pressure, humidity and microbes.

Each copper canister of spent fuel can hold the equivalent of one year’s electricity consumption for Sweden’s third-biggest city of Malmö with 286,000 inhabitants.

The chosen site will be protected against terrorist attacks, SKB said, refusing to disclose details of the security measures.

Opposition to the project has so far been limited.

But Johan Swahn, director of the Swedish NGO Office for Nuclear Waste Review, is one of the most vehement critics.

He cited a Swedish scientific study from 2007 that suggested the copper canisters could corrode after a few hundred or a thousand years, and thereby pose a major safety hazard.

“There is increasing awareness that the chosen method lacks information about how copper corrosion and bentonite clay work in that kind of heat over thousands of years,” Swahn told AFP.

“If the canisters begin to rust right away, the radioactive waste could reach the surface in 50 to 100 years at the Oskarshamn site,” he said.

SKB has rejected the argument, saying no other studies have been able to confirm the hypothesis that copper can corrode without oxygen.

“And even if the copper were to corrode, the containers will not leak according to our safety assessment,” Larsson-Hagberg stressed.

The cost of the project is estimated at 20 to 25 billion kronor ($2.5 to 3.2

billion, $1.9 to 2.4 billion), funded entirely by the nuclear industry.

Once SKB has chosen its site it will submit two applications to Swedish environmental and nuclear authorities. If both give the thumbs up, the government will then take a decision, probably around 2014.