Nuclear waste: Insights into the Finnish repository Onkalo

Finland relies on nuclear power: The Finnish reactor Olkiluoto 3 has gone into regular operation and is now supplying electricity from the European Pressurized Water Reactor (EPR). Meanwhile, the Onkalo repository, which has been under construction on the island of Olkiluoto for the past two decades, is awaiting commissioning. Permission to store nuclear waste underground on the island is expected in 2024.


The English author Robert Macfarlane visited the Onkalo deposit during construction for his book “Im Unterland” (2019). At this point we publish an excerpt from it again. The text first appeared under the title “The Hiding Place” in issue 9/2019 of MIT Technology Review.


A tomb is being built deep in the bedrock of the island of Olkiluoto in south-west Finland. It should not only survive the people who dreamed it up, but the entire species. Without further care, it should survive the next 100,000 years unscathed and even survive a coming ice age. 10,000 years ago, three major river systems flowed through the Sahara. Anatomically modern humans began their migration from Africa 100,000 years ago. The oldest pyramid is about 4,600 years old, the oldest still standing church less than 2,000 years.

This Finnish tomb is encased in security enclosures of unparalleled standards: safer than the tombs of the pharaohs, safer than any maximum security prison. What lies buried here, it is hoped, will never leave its grave except by the movement of the earth itself.

The tomb is an experiment in post-human architecture, it’s called Onkalo, the Finnish term for “cave” or “hiding place”. Highly radioactive waste is to be hidden in Onkalo, perhaps the darkest matter man has ever produced.

Since man has been producing nuclear waste, he has been trying to figure out how to dispose of it. Formed in supernova explosions 6.6 billion years ago, uranium is part of the space dust that makes up our planet. It is as common in the earth’s crust as tin or tungsten and is stored in the rocks on which we live. In lengthy, costly, miraculous, dangerous experiments, man has discovered how to turn uranium into energy. We know how to use uranium to generate electricity and bring death, but we still don’t know how to dispose of it once it’s done its work. It is estimated that more than a quarter of a million tons of highly radioactive waste are currently waiting for disposal worldwide, with around 12,000 tons being added every year.

Uranium is mined in Canada, Russia, Australia, Kazakhstan and maybe soon in southern Greenland. The ore is crushed and ground, then the uranium is extracted with acid, gasified, enriched and finally resolidified and formed into pellets. A single enriched uranium pellet, one centimeter in diameter, one centimeter long, releases about the same amount of energy as a ton of coal. The pellets are packed in shiny fuel rods, which are usually made of a zirconium alloy and are bundled thousands of times and inserted into the reactor core, where nuclear fission is finally triggered. Nuclear fission produces heat that forces steam into a turbine, whose shaft drives an electrical generator.

When nuclear fission reaches the point where it has become slow and therefore inefficient, the fuel rods need to be replaced. But they are still extremely hot and deadly radioactive. The volatile uranium oxide continues to emit alpha and beta particles and gamma waves. If you stood next to an uncovered bundle of fuel rods just emerging from the reactor core, the radioactivity would enter the body, destroying cells and damaging DNA. You would probably die within a few hours from bleeding and vomiting.

Therefore, the spent fuel rods, shielded from water or another liquid, are taken out of the reactor by machine and initially stored in deep underground basins for a few years before they are transported on to Castoren for reprocessing or final storage. In the pools, the water patiently sucks up the particle rain from the fuel rods. Because this rain warms the water, it must be constantly circulated and cooled to prevent it from vaporizing and exposing the fuel rods, which would result in disaster.

But even after decades, the fuel rods are still hot, toxic and radioactive. There is only one way they can stop harming the biosphere: long-term natural decay. In the case of high-level radioactive waste, this can take tens of thousands of years during which the spent fuel must be safely stored away from contact with the air, the sun, drinking water, life.

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