For decades, countries that rely on nuclear power have faced one major challenge: what to do with highly radioactive waste that remains dangerous for thousands of years.
Finland now believes it has found an answer.
Deep beneath a forest in southwestern Finland, engineers have built a vast underground repository designed to safely isolate spent nuclear fuel from people and the environment for up to 100,000 years. The facility, known as Onkalo, is expected to become the world’s first permanent disposal site for high-level nuclear waste once it receives final regulatory approval.
Why Nuclear Waste Remains a Global Challenge?
Nuclear power plants generate electricity without producing large amounts of greenhouse gases, but they also create radioactive waste.
Spent nuclear fuel remains hazardous long after it leaves a reactor. Since the 1950s, many countries have stored this waste in temporary cooling pools or dry storage facilities while searching for a permanent solution.
Scientists and policymakers have debated for decades how to safely manage these materials over extremely long periods of time.
Finland’s Onkalo project is the first large-scale attempt to permanently solve that problem.
What is Onkalo, and where is it located?
The Onkalo repository is located near the Olkiluoto nuclear power plant in Eurajoki, on Finland’s west coast.
Engineers carved the facility into stable bedrock that formed approximately 1.9 billion years ago. The underground tunnels extend more than 400 meters below the surface, where radioactive waste will remain isolated from human activity and environmental changes.
The project has been under development for more than two decades and is now approaching the final phase before operations begin.
How Finland Plans to Store Radioactive Waste for 100,000 Years?
The storage system relies on several protective barriers.
First, workers will place spent nuclear fuel inside specially designed canisters made with highly corrosion-resistant copper.
The canisters will then be lowered into individual disposal holes drilled into the bedrock. Engineers will surround them with bentonite clay, a material that expands when exposed to moisture and helps create a protective seal.
Over time, the repository will hold approximately 6,500 tonnes of spent uranium fuel generated by Finland’s nuclear reactors. Deposits are expected to continue for around a century before the facility is permanently sealed.
Scientists Aim for a Facility That Can Last Beyond Human Civilisations
The central challenge of the project is ensuring safety over timescales that far exceed recorded human history.
“Basically, it needs to be safe forever,” said Lauri Parviainen, a chemist at Posiva, the company responsible for the project.
Unlike conventional infrastructure, the repository must remain secure without maintenance or human intervention long after current societies, governments, and technologies disappear.
The design focuses on passive safety, meaning the facility should continue functioning even if future generations never return to monitor it.
What Risks Do Experts Still See?
Although scientists generally consider the repository one of the safest long-term solutions available, experts continue to study potential risks.
Researchers have identified copper canister corrosion and geological changes linked to future ice ages as key challenges that could affect the repository over thousands of years. However, extensive safety assessments have repeatedly concluded that the facility can safely contain radioactive material under expected conditions.
Finnish authorities are expected to make a final regulatory decision soon, paving the way for operations to begin later this year or early next year.
Why the World Is Watching Finland’s Nuclear Experiment
Countries including Sweden, France, the United States, and others continue to explore long-term solutions for nuclear waste disposal.
If Onkalo performs as planned, it could become a blueprint for future repositories around the world and help address one of the biggest criticisms of nuclear energy.
As Finland moves closer to opening the facility, the project represents a historic moment in nuclear waste management—one that could influence how future generations handle radioactive materials long after today’s reactors stop operating.
