Finland Prepares for the Launch of Onkalo, the World’s First Deep Geological Nuclear Waste Repository

Finland is nearing the operational debut of Onkalo, the first facility in the world dedicated to the deep geological disposal of spent nuclear fuel. Located on the island of Olkiluoto in the Eurajoki municipality, this project represents a pioneering global answer to the challenge of long-term radioactive waste management. Managed by Posiva—a company established in 1995 by shareholders Teollisuuden Voima (60%) and Fortum (40%)—the facility is scheduled to begin the final disposal of fuel by the end of 2026, following the successful completion of integrated system trials.

The decision to site the repository at Olkiluoto was made in 2000, in compliance with the 1994 Finnish Nuclear Energy Act, which mandates that all domestic nuclear waste must be handled within the country. Onkalo, which means "small cave," penetrates 1.9-billion-year-old granite bedrock at depths exceeding 400 meters. Radioactive rods will be hermetically sealed within copper canisters at a specialized nearby encapsulation plant using automated technology. These canisters will then be lowered into tunnels and encased in a buffer of bentonite clay.

With a total project cost estimated at 1 billion euros, Onkalo is designed to accommodate 6,500 tons of spent nuclear fuel and is expected to remain operational until the 2120s, after which the entrance will be permanently sealed. Extensive system testing began on August 30, 2024, to ensure the seamless coordination of all equipment, including the handling of a dummy test canister. Karri Osara, the production director at Posiva, stated that the team is ready to transition to the trial operation phase of the underground facilities using non-radioactive fuel mock-ups.

Finland stands alone as the only nation currently building a comprehensive complex for deep geological disposal, an achievement the International Atomic Energy Agency (IAEA) described as a "game changer" in 2020. Despite these technological milestones, some scientific concerns remain regarding the long-term durability of the containment barriers. For instance, Edwin Lyman from the Union of Concerned Scientists has raised questions regarding the potential rate of copper corrosion over several thousand years, even though geological burial is generally preferred over surface-level storage. Similar studies in Sweden regarding the KBS-3 method have highlighted potential corrosion risks, suggesting that certain canisters could fail within 100 to 1,000 years.

Alongside Sweden, Finland is demonstrating international leadership in finding a permanent resolution for nuclear waste. Sweden commenced the construction of its own disposal site at Forsmark in 2025, with plans to open by the late 2030s. The Onkalo repository, which will serve the nation until the 2120s, fulfills Finland's commitment to avoiding the transfer of waste responsibilities to future generations, while still allowing for the potential retrieval of fuel during its first 100 years of operation. The entire infrastructure is designed to isolate radioactive materials from the biosphere for hundreds of thousands of years.