Key Points
- Finland is preparing to open the world’s first permanent deep‑geological repository for commercial spent nuclear fuel at Onkalo, on the island of Olkiluoto.
- The Onkalo facility, costing about 1 billion euros, is designed to store around 6,500 tonnes of spent fuel at depths of over 400 metres within migmatite‑gneiss bedrock.
- Radioactive rods will be sealed in copper canisters and surrounded by bentonite clay “buffer” layers, with the repository expected to operate until the 2120s before being sealed.
- Posiva, the Finnish waste‑management company, says the system is engineered so that radioactivity falls to non‑harmful levels over hundreds of thousands of years.
- Critics, including Edwin Lyman of the Union of Concerned Scientists, warn that geological disposal carries long‑term uncertainties and that the risks will mainly fall on future generations.
- The International Atomic Energy Agency estimates that nearly 400,000 tonnes of spent fuel have been produced globally since the 1950s, with two‑thirds still in temporary surface storage.
Bury(Manchester Mirror)April 10, 2026-Olkiluoto, a small island on Finland’s west coast, is at the centre of a global experiment in nuclear waste disposal that could shape how other countries, including the UK, handle radioactive by‑products for centuries to come. Onkalo the world’s first deep‑geological repository for permanent storage of spent nuclear fuel is nearing operational readiness after two decades of tunnelling through 1.9‑billion‑year‑old bedrock, yet safety experts warn that the long‑term risks may fall on future generations who had no say in the decision.
What is Onkalo and why is Finland using it?
As reported by the Associated Press, Onkalo means “cave” in Finnish and refers to a maze of tunnels bored more than 430 metres beneath Olkiluoto’s surface. The facility is located near three of Finland’s five nuclear reactors, close to the coastal town of Eurajoki, which has a population of about 9,000 and where many residents work at the nearby power plant or storage operations.
Posiva, the Finnish state‑owned company responsible for long‑term management of the country’s spent nuclear fuel, says Onkalo is designed to hold up to 6,500 tonnes of spent fuel. The project, costing roughly 1 billion euros (about 1.2 billion dollars), has been financed by Finland’s nuclear power companies, which have set aside funds for decades to cover construction and eventual closure.
How the waste will be stored
The process begins at a nearby encapsulation plant, where used fuel rods are sealed in corrosion‑resistant copper canisters using unmanned machinery. These canisters are then transported underground and placed in disposal tunnels more than 400 metres deep, where they are surrounded by bentonite clay “buffer” layers that absorb water and help limit movement of any leaked material.
As described by Posiva, the canisters are designed to remain sealed for long enough that radioactivity decreases to levels no longer harmful to the environment. The company estimates that it will take hundreds of thousands of years for radioactivity to fall to normal background levels, meaning the facility must function effectively far beyond the timescale of recorded human history.
Why geologists chose this site
Geologist Tuomas Pere, who guided the Associated Press through part of the tunnel system, explained that Onkalo sits within migmatite‑gneiss bedrock described as highly stable and with low earthquake risk. Pere told reporters that the key factor was the isolation from surface civilisation.
The site’s remoteness and the surrounding dense forest also contribute to the decision, as they reduce the likelihood of human intrusion once the repository is sealed. Posiva and Finnish authorities argue that burying the waste deep underground offers a safer long‑term solution than continued storage in surface facilities such as spent‑fuel pools or dry‑cask installations.
Global context of nuclear waste storage
According to a 2022 report by the International Atomic Energy Agency (IAEA), about 400,000 tonnes of spent fuel have been generated worldwide since the 1950s, with two‑thirds remaining in temporary storage at reactor sites and the rest undergoing reprocessing. The world currently has no other permanent underground facility for commercial nuclear waste in operation, making Onkalo a precedent for other nuclear‑reliant countries such as Sweden, France and the UK.
Sweden has begun work on a similar repository in Forsmark, north of Stockholm, but it is not expected to open until the late 2030s. France’s Cigéo project has also faced delays and local opposition, underscoring the political and technical challenges of deep‑geological disposal.
Experts’ concerns and uncertainties
Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, told the Associated Press that geological disposal of nuclear waste carries “uncertainties” and warned that the risks “will mainly affect future generations.” He added that while there is no ideal solution, geological disposal is likely the “least bad” option among a range of undesirable choices.
Lyman pointed out that the copper canisters used to contain the spent fuel will eventually corrode, and there is no scientific consensus on how quickly that process will occur. He said the hope is that corrosion will be so slow that most radioactive material decays before significant leakage can take place, but that cannot be guaranteed over the hundreds of thousands of years for which the waste remains hazardous.
How Finland plans to manage the long‑term timeline
Posiva officials state that Onkalo is expected to operate until the 2120s, after which it will be permanently sealed. The design calls for the repository to be filled gradually with waste, with each disposal tunnel backfilled and monitored before final closure.
Finnish law, introduced in 1994, requires that radioactive waste produced in Finland must be managed, stored and permanently disposed of within the country’s borders, which has driven the move towards a national geological repository rather than exporting waste. Officials argue that Onkalo is a core part of Finland’s long‑term nuclear‑energy strategy and that it allows the country to continue using nuclear power while meeting its domestic obligations.
The push to build Onkalo stems from decades of debate over how to handle spent nuclear fuel, which remains highly radioactive for tens of thousands of years. In the absence of a widely accepted permanent solution, utilities have traditionally stored fuel in pools at reactor sites or in dry‑cask facilities above ground, both of which expose the waste to human and environmental risks over time.
Finland’s decision to develop a deep‑geological repository followed extensive research into stable crystalline bedrock formations and lessons from research projects in other countries. The project was also shaped by a national licensing process that required rigorous safety assessments, public consultation and a commitment to financial responsibility by the nuclear operators.
For audiences in the United Kingdom, Finland’s experience with Onkalo offers a potential model for how to manage the country’s own growing stock of nuclear waste, but it also raises questions about risk transfer across generations. The UK already operates several nuclear power stations and has long‑term plans that include new reactors, which will produce more spent fuel unless alternative disposal or recycling strategies are adopted.
If the UK government and regulators decide to pursue a similar deep‑geological repository, the Finnish case could shape technical standards, safety‑case design and public‑engagement approaches. However, given that the risks of corrosion, groundwater movement and human intrusion would extend far beyond the lifetimes of current policymakers and nuclear‑industry workers, the Onkalo precedent may also prompt intensified debate about intergenerational equity and the ethics of locking future citizens into long‑term nuclear‑waste legacies.
