This conflicting evidence has delayed plans to build a repository in Sweden based on the same KBS-3 concept as Onkalo. But in January 2022, the Swedish government gave the green light to building a GDF in Forsmark, about 130km (81 miles) north of Stockholm – a development viewed by Hansen of Posiva as one that should put the copper controversy to bed.
“We have a robust, multi-barrier concept and we’re prepared for scenarios that might happen in the next million years,” says Hansen. “For example, we looked at what happens if a canister starts leaking early on, what if the clay is wrongly installed, what if there’s more water in the tunnels and the water chemistry is different from what we expected. The results of our risk assessments show that we’re on the safe side.”
For now, at least, Finland and Sweden are going ahead with the plans, though Szakalos says there will be more research on copper corrosion.
Both Onkalo and the proposed Swedish facility aim to keep radioactive waste safe for at least 100,000 years. “We’re trying to construct something that should work longer than the homo sapiens has been alive,” says Joutsen. “The time span is mind-boggling.”
When the facility is full, the tunnels will be sealed off, the buildings on the surface demolished and the land restored. “There will be animals, trees and plants, and houses,” says Joutsen. He says he would happily buy a plot of land in Onkalo if he were alive in 120 years.
What comes later is more uncertain. It’s entirely possible that all knowledge about Onkalo will be lost in a few thousand years.
Social scientists have been wrestling with the challenge of how to communicate with humans, or anyone else that might come after us in deep future, to warn them about the dangers we leave behind. (Read more about how to build a nuclear warning for 10,000 years’ time).
One discussion about marking Onkalo centred on trying to find a universally understood sign of danger, should language disappear in the future. The current thinking from Posiva, decision-makers and researchers, however, is not to mark Onkalo at all. “Future generations don’t need to know about this,” argues Joutsen. “It’s so deep and so isolated. There will be a lot of copper and plutonium down here and a sign may encourage people to start digging to retrieve it. A bit like the pyramids in Egypt that were looted by tomb robbers.”
No final decision has been made though. There’s no rush as the facility will remain open for 100 to 120 years.
Kauppi says it’s important to put the debate about marking the site in a perspective that people can relate to. She often reminds her students at the University of Helsinki that radioactivity was discovered only about 120 years ago. “We’re now talking about things that could be happening in the next hundreds of thousands of years. We don’t even know what could happen in the next hundred years.”
Kauppi says she is “very confident” Finland is doing a good job with Onkalo, but believes the door should still be kept open to other solutions.
“There might be wiser people after us who have new ideas about what to do with nuclear waste. They may invent something better. We just have to do our best now, with our current knowledge based on honest research.”
Extracted in full from: Finland’s plan to bury spent nuclear fuel for 100,000 years – BBC Future