Finland’s Onkalo begins path to bury spent nuclear fuel deep underground

With the push of a button, the elevator descends hundreds of meters in seconds into the dark depths of Onkalo, Finland’s underground facility meant to permanently dispose of spent nuclear fuel. During a tour of the tunnels, geologist Tuomas Pere said workers were driving through “1.9-billion year old bedrock” and that the site’s remoteness was a key part of its design: “It’s the isolation from civilization and mankind on the surface that’s important,” he said as the disposal area neared the point where it would be sealed from future human access.

Onkalo, which means “cave” in Finnish, is on the island of Olkiluoto on Finland’s west coast, in a wooded area near three of the country’s five nuclear reactors. The closest town is Eurajoki, about 15 kilometers (9.3 miles) inland, with a population of about 9,000, and many residents work at the nuclear power plant or related storage facilities. After decades of construction, the project—an estimated 1 billion euros ($1.2 billion)—is expected to move toward operations after authorities grant a license within months, a step that could make it the world’s first permanent disposal site for commercial spent nuclear fuel.

Officials describe the project as a multi-layer effort to isolate waste. Using unmanned machinery at a nearby encapsulation plant, radioactive rods are sealed in copper canisters before being buried deep in tunnels over 400 meters underground. Posiva then describes additional engineered protection in the form of “buffer” layers of water-absorbing bentonite clay around the canisters, while the surrounding bedrock remains part of the long-term containment concept.

Posiva says Onkalo can store 6,500 tons of spent nuclear fuel, and it describes the repository’s purpose as keeping canisters sealed “long enough for the radioactivity of spent fuel to decrease to a level not harmful to the environment.” The company’s communications manager, Pasi Tuohimaa, said in a tour of the facility that “The solution that we have, it’s the missing point for sustainable use of nuclear energy.” Posiva also estimates the repository will be in place for hundreds of thousands of years before radioactivity falls to background levels.

The long timelines are part of why some outside experts urge caution about the uncertainties of geologic disposal. Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, said the question remains difficult because even geologic disposal is still “fraught with ‘uncertainties.’” Lyman said that copper canisters eventually will corrode and that scientific opinions differ on how fast that corrosion could occur, adding, “The hope is that is such a slow process that most of the radioactive material will have decayed away by then. But again, there are uncertainties.”

Lyman said keeping spent fuel above ground is also risky because highly radioactive material makes handling and transport difficult, but he also pointed to security concerns about what could happen far into the future. He argued that leaving material “on the surface of the Earth forever” is worse because it would be vulnerable to sabotage. Lyman said that over time, radioactive components decay and become less risky to handle, though he said the risk question ultimately can shift as plutonium becomes more accessible. He said a theoretical path to nuclear weapon use would require an “off-site reprocessing capability,” describing reprocessing as the step in which spent fuel is separated to recover uranium and plutonium for reuse.

Finland’s approach to the waste program also reflects its own regulatory decisions. Finnish officials say a 1994 act required radioactive waste generated in Finland to be handled, stored and permanently disposed of within the country’s borders. Environment Minister Sari Multala said, “Back then… some of the waste was still exported, but we wanted to take care of it ourselves,” and she added, “We also stick to the decisions, unlike many other countries.” Multala said she did not rule out eventually accepting limited amounts of nuclear waste from other countries, “as long as it is allowed by the international regulators.”

The question of what future societies should know about repositories is also drawing attention. An Austrian artist and inventor, Martin Kunze, led an expert effort on long-term information preservation at an international nuclear agency connected to the Organization for Economic Cooperation and Development. Kunze described a “nuclear message” system intended to survive for very long periods, in which information is printed on a solid ceramic plate under a hard glazed surface. He said the ceramic plates are “inexpensive and very robust” and that they should ideally be buried “in large numbers” around a repository and also “inside the foundations” of houses in the community.

For now, the work at Onkalo continues below ground, even as the facility’s access for humans is expected to end as disposal tunnels close. The underground repository is designed to operate until the 2120s, when it would be permanently sealed, and Posiva has described it as part of a final strategy for spent fuel that is intended to keep the surrounding environment protected over time. Globally, there is currently no permanent underground disposal facility for commercial nuclear waste operational anywhere in the world, according to the facility description in the report, though Sweden and France have ongoing projects, including Sweden’s repository in Forsmark under construction with expected opening in the late 2030s and France’s Cigéo project still in its early stages.