Inside Onkalo: World’s first nuclear waste repository, isolated for 100,000 years World News

Deep in the pine forests of southwestern Finland, the rocks arrive first. Its antiquity makes human architecture feel temporary, shaped by geological time rather than anything built on the surface. The underground facility known as the Onkalo Nuclear Power Plant, located near Eurajoki, has nothing above ground to really hint at what’s going on hundreds of meters below, PBS reports. Deep down, the tunnel feels reduced to the essentials: humid air, rock walls, cables running along uneven surfaces, and the slow echo of movement. It is not a place designed for comfort or spectacle. It is built around the more ultimate goal of long-term disposal of nuclear waste that cannot simply be forgotten or moved elsewhere.

How Finland plans to lock nuclear waste inside ancient bedrock

According to reports, the idea behind the site is not storage in the usual sense, but rather moving away from human contact. The spent fuel is first sealed in corrosion-resistant copper canisters and then surrounded by bentonite, which expands when exposed to moisture. The purpose of this arrangement is to reduce movement, seal gaps, and limit slow interaction with groundwater.Each jar is lowered into a drilled hole in the tunnel floor. Once filled, the sections are permanently sealed layer by layer with reinforced plugs. The tunnels themselves will eventually be closed one by one until nothing can be accessed from the surface infrastructure. The planned production capacity is approximately 6,500 tons of uranium fuel, covering the output of Finland’s existing reactors.According to PBS, “We are now at about minus 430 meters (1,411 feet),” geologist Tuomas Pere said as he drove through a maze of man-made tunnels. “We’re traveling through bedrock that’s 1.9 billion years old.”

Finland’s nuclear waste disposal project enters final regulatory stage

The project has taken decades to reach its current stage, undergoing design changes, political shifts and repeated safety reviews. The final regulatory assessment is currently being carried out by the Finnish Radiation and Nuclear Safety Authority (STUK), which is expected to complete the final assessment before granting an operating license.The companies behind the site, including Posiva and utility operator Teollisuuden Voima Oyj, said operations would begin cautiously once approval is given. Initial fuel transfers are expected to begin gradually, with materials already stored at nearby facilities awaiting underground transportation. Even at this stage, there is little sense of completion. The system has been built but is not yet fully operational and appears to be waiting for work to shift to regular burial work.

Nuclear safety design spanning tens of thousands of years

As stated in a research report published in ScienceDirect titled “Waiting for Waste: The Nuclear Imagination and the Politics of Finland’s Distant Future‘, what sets Onkalo apart is the time frame in which it was built. Security models can stretch 100,000 years into the future, even as current infrastructure, language, and political systems have changed beyond recognition.Engineers focus on slow processes rather than sudden failures. Copper corrosion, clay stability, groundwater flow and the potential for future ice age seismic changes are all part of the long-term assessment. No single factor is expected to cause failure on its own, but their interactions over long time spans need to be treated with caution.According to a U.S. Department of Energy YouTube video, the fuel will be safely stored in corrosion-resistant tanks more than 1,300 feet below the Earth’s surface.

Finnish public trust and silent acceptance

In Finland, attitudes towards repositories have shifted over time to a form of actual acceptance. Early objections did exist, especially when the concept was first discussed decades ago, but they have softened as the project moved from theory to visible construction.The researchers noted that trust in national regulators and long-term scientific assessments played a role in this shift. The law also requires that nuclear waste generated in Finland must stay within the country, which rules out the possibility of exporting the problem elsewhere. Still, concerns aren’t entirely gone. Environmental groups continue to argue that no engineered system can be guaranteed to be safe over such long periods of time, and that natural processes and human oversight will inevitably diverge.