The tunnels where nuclear waste will be stored for 100,000 years

Nuclear waste is a problem that humanity will have to solve one way or another. Compared to other types of waste, its volume is not that large, but its extreme risk demands storage parameters that are not easy to achieve. One of the most advanced projects for long-term nuclear waste disposal is Onkalo, near the Olkiluoto nuclear plants in Finland. The idea is for the spent material from the plants to remain there for 100,000 years, taking advantage of the region's geological stability.

Lessons from Chernobyl and Fukushima

Last month we were able to closely observe the consequences of the largest nuclear accidents in history. On one hand, we have the Chernobyl Sarcophagus, an impressive structure 110 meters high that, in addition to isolating radioactive material, must also contain the old protective structure. An impressive project by any standard, which will need to last for many, many years. On the other hand, we have the abandonment of regions near the Fukushima plants. The official exclusion zone has a radius of 20 kilometers, and everything was left there, frozen in time. Authorities continue to struggle to clean up the disaster and limit its effects.

The current state of nuclear waste storage

But those were accidents. What about the nuclear plants that operate today? Where does all the waste they generate end up? For now, they are limited to local storage. No geological repository for nuclear waste exists in the world. One of the most publicized examples is Yucca Mountain in the United States, but it is mired in a political war from which it will likely never emerge. On the other side, we have the case of Finland.

Onkalo: Finland's underground solution

The Onkalo nuclear repository is being built by the company Posiva near the Olkiluoto nuclear plants, on the western coast of the country. The access tunnels descend and extend to a depth of 450 meters, drilling into a region that has remained geologically stable for the last two billion years. The waste will be placed in giant iron and copper containers, which will ultimately be located in the disposal tunnels and surrounded by bentonite clay with low hydraulic conductivity. In other words, water cannot pass through the clay.

Initially, the containers need a 500-year lead so that a person can stand next to them safely, but there are other radioactive elements with a much slower decay process that must not enter natural water deposits or the biosphere. Therefore, the goal is to isolate the waste for approximately 100,000 years. Onkalo is stable, suffers no earthquakes, and there are no records of natural disasters. So, what's the problem?

Keeping people away, of course. How can we warn future archaeologists about the risk of the material buried there? How can we universally communicate that this place is dangerous and must remain intact? Once completed and filled to capacity, Onkalo will hold 6,500 tons of spent uranium. Now, there is a curious proposal: Do not mark the site. Seal it completely, remove all traces on the surface, and let time itself erase it.

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