“Onkalo,” which means cavity, or cavern, in Finnish, is an apt name for Finland’s repository for radioactive waste. Touted as a “100,000-year tomb,” the Onkalo facility on Olkiluoto—a small island in western Finland—is currently being built at a depth of 450 metres, inside bedrock. It will be the world’s first permanent disposal site for spent nuclear fuel.
Other countries, including the United States, the United Kingdom, Sweden, France, Germany, Canada and Japan have attempted, for years, to set up nuclear-waste disposal sites, but their plans have stalled because of political, environmental and social roadblocks. Finnish leaders, on the other hand, have managed to drum up popular support for the repository by convincing locals that it will be a financial asset to their community. The Finnish government granted Posiva—a nuclear-waste management company—the construction licence for Onkalo in 2015 and the firm expects to begin depositing waste in the facility in the early 2020s. Tunnels will first be drilled into granite bedrock. Copper canisters, 5.2 metres long, will be filled with spent nuclear fuel, and buried in tunnels whose openings will be sealed with bentonite clay, a material that expands when it comes into contact with water. On its website, Posiva states that copper is known to last hundreds of thousands of years without corroding, and that bentonite clay will prevent groundwater from reaching the canisters. Over the next century, if all goes as planned, Onkalo will be home to roughly 70 kilometres of tunnels, which will store 3,250 copper canisters containing about 6,500 tonnes of spent nuclear fuel. This makes it an especially immense project for a small country.
Spent nuclear fuel, which contains uranium and plutonium, is highly radioactive, and its disposal is regulated by international safeguards. At the moment, countries with nuclear-power plants store their waste in interim storage facilities located above the ground or near the surface. Although such “high-level waste” comprises only 3 percent of the total volume of waste produced by nuclear generation, it produces 95 percent of the radioactivity arising from nuclear power, making it the industry’s most lethal by-product. There is a growing consensus among several countries for the geological disposal of this fuel—a solution that seeks to isolate it, blocking its interaction with the biosphere for centuries, until the radioactivity falls to safe levels.