Finland is about to open the world’s first permanent repository for high-level nuclear waste. How did it succeed when other countries failed?
It is located on an island off the west coast of Finland. Onkalo, “cavity” or “pit” in Finnish, will be the world’s first permanent landfill for high-level nuclear waste, a major achievement for Finland.
In a few years, spent reactor fuel rods, locked in gigantic copper drums as tall as giraffes, will arrive there by elevator before robotic vehicles take them into one of dozens of dead-end storage tunnels that will form an anthill in the basement.
After burying 30 to 40 copper drums in the tunnel floor, the holes will be plugged with bentonite, a clay that absorbs water. Each tunnel will be filled with bentonite and sealed with concrete. The barrels will then begin their long vigil. They should remain unchanged for 100,000 years, even if the global warming of the next centuries ushers in the next ice age.
According to them, this is the final disposal, in the stable bedrock of Finland, 430 meters underground, 420 meters below sea level.
Two of Finland’s four reactors are at Olkiluoto. Once the new Olkiluoto reactor is connected to the grid later this year, nuclear energy will account for more than 40% of the country’s electricity.
This electricity has a downside: irradiated, hot and highly radioactive uranium fuel rods. In Finland, bars are cooled for decades in water basins; in other countries they are stored in concrete and steel drums. Either way, surface storage is vulnerable to accidents, leaks, or neglect for the thousands of years that the waste remains hazardous.
Without a long-term solution, the waste accumulates. Finland had some 2,300 tons of waste in 2019 and some 263,000 tons of spent fuel are in interim storage facilities around the world, according to a report released this year by the International Atomic Energy Agency.
Many experts consider permanent deep repositories like Onkalo to be the best solution, but getting community buy-in is often a hurdle.
However, Finland has had very few problems with Onkalo, which the government approved as a site in 2000. It helped that the people of Eurajoki, the nearest town to Onkalo and neighboring reactors, were comfortable with nuclear energy, everyone has a relative or acquaintance who works in the sector.
But experts say Onkalo’s success also reflects Finland’s unique cultural and political conditions: high trust in institutions, community engagement, the absence of state-level centers of power, and the balance power between industry and stakeholders. .
Geologists say Onkalo’s bedrock has remained stable for the most part over the past billion years, although there is evidence that earthquakes have occurred in the past 10,000 years when glaciers massifs retreated at the end of the last ice age and bedrock recovered.
Scientists don’t expect major earthquakes to hit the region until the next ice age.
One of the main problems is water leaks. But they say that if the water could seep into the tank, it would have to overcome the bentonite and copper to reach the spent fuel.
Upon arrival in Onkalo, the spent fuel will be unpacked in an encapsulation plant. In a stainless steel room surrounded by 1.3 meter thick concrete walls, robots will suck the remaining water on the fuel rods during their stay in the storage pools and seal them inside a cast iron container nested inside another copper. Argon will be injected between the two containers to create an inert atmosphere and the copper container will be brazed.
In addition to the containers themselves, the bentonite that surrounds them will also prevent the escape of radionuclides, regulators say. The mineral not only prevents water from entering, but also prevents microbes from reaching the surface of the container.
Copper corrodes slowly, and by the time groundwater reaches Onkalo’s depths, chemical or microbial reactions will have depleted all of its dissolved oxygen, making it less reactive. But there are counter-opinions that it’s only a matter of time, between decades and centuries, before the unalloyed copper chests start to crack on Onkalo.
If all of these barriers failed, the escaping debris would face one final hurdle: the decades it would take for them to migrate to the surface, with ever-decreasing levels of radioactivity.
More information: www.science.org (English text) – www.posiva.fi