Finland is moving closer to putting into operation what is expected to become the world’s first facility designed for the permanent disposal of spent nuclear fuel, after decades of research, planning and construction. The facility, known as Onkalo, is being developed deep beneath the bedrock near the Olkiluoto nuclear power plant in southwestern Finland and is intended to isolate radioactive waste from the environment for extremely long periods.
The project represents Finland’s long-running effort to address one of the most difficult challenges associated with nuclear energy: what to do with spent fuel after it has been removed from reactors. While nuclear power produces relatively small quantities of waste compared with the amount of electricity generated, the material remains highly radioactive and requires careful management for thousands of years.
Onkalo, which means “cave” in Finnish, has been under development for more than two decades, following several decades of research into geological disposal. Construction began in 2004, with the facility eventually extending hundreds of metres beneath the surface. The repository is being built at a depth of around 400 to 430 metres, within extremely old and stable Finnish bedrock. Posiva, the company responsible for Finland’s nuclear waste management, has developed the facility after more than 40 years of scientific and technical work.
The disposal process is based on several layers of protection rather than relying on a single barrier. Spent nuclear fuel will first be enclosed in corrosion-resistant iron-copper canisters. These containers will then be surrounded by bentonite clay, which can absorb water and help protect the canisters. The sealed packages will finally be placed deep inside specially drilled holes in the surrounding rock. The combination of engineered barriers and the natural properties of the bedrock is intended to prevent radioactive material from reaching the surface.
In August, Finland’s Radiation and Nuclear Safety Authority, STUK, issued a favourable safety assessment for the facility. The assessment considered both the facility’s operational safety and its ability to protect people and the environment over extremely long timescales. The positive assessment cleared an important regulatory hurdle and allowed the government to move ahead with preparations for a decision on Posiva’s operating licence.
The project has now entered another important phase. In August, Posiva began drilling the first actual deposition hole intended for a spent-fuel canister. The drilling machine took about 10 hours to create a hole measuring 8.4 metres deep and 1.75 metres across in rock estimated to be about 1.9 billion years old. Test drilling had already been carried out at the site, but the new work marks the beginning of preparations for actual final disposal.
The repository is expected to accommodate about 6,500 tonnes of spent nuclear fuel. Finland currently stores used nuclear fuel in temporary facilities, including water-filled cooling pools and dry storage systems. The move towards a permanent underground repository is intended to eliminate the need for indefinite above-ground storage.
The significance of the Finnish project extends beyond the country itself. Nuclear power is attracting renewed attention globally as governments seek low-carbon sources of electricity and greater energy security. At the same time, many countries that operate nuclear reactors have yet to establish permanent repositories for their high-level radioactive waste. The International Atomic Energy Agency has noted that geological disposal in deep, stable formations is the long-term approach being pursued for spent fuel and other high-level radioactive waste.
Finland’s experience could therefore become an important reference for other countries dealing with the same problem. However, geological repositories remain complex and expensive projects, requiring suitable geology, extensive scientific assessment, regulatory oversight and long-term political commitment.
With the Finnish authorities having completed a major safety review and Posiva advancing work underground, Onkalo is now considerably closer to becoming operational. If the remaining regulatory process proceeds as planned, Finland could soon demonstrate how spent nuclear fuel can be moved from temporary storage to a purpose-built underground repository designed to isolate it from the environment for generations to come.
