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TL;DR: It is a material whose atoms we have destabilised. Certain types will far outlive our species, and we currently have nowhere it put it. Putting it in a place where it will not endanger future humans or ecosystems is an engineering problem for the ages.

Hundreds of thousands of years in the future, when even the pyramids have been ground to dust by wind, one human structure on Earth will remain. At least that’s the plan for Onkalo, a building under construction right now in Finland. If successful, it may be one of the final artifacts of human civilisation.

If we look back at history, any attempt at creating something so long-lived, like the Pyramids, Stonehenge, or Easter Island’s statues, usually had some religious purpose.Β But Onkalo is much more mundane.

It’s the world’s first permanent nuclear waste storage site.

This is surprising for a couple of reasons. First, why is it so important to build a storage site that will outlive our civilisation? Second,Β how can it be theΒ firstΒ permanent nuclear waste storage site? Haven’t we been using nuclear power for decades?

Let’s jump in and find out.

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The entrance to Onkalo, which will be cemented over in 2120 and disguised.

The amount of effort that’s going into Onkalo could be seen as symbolic of the unique times we live in.

Specifically, about our waste.

We make 2.6 trillion pounds of it each year, weighing more than 7,000 Empire State Buildings. We’re on track for there to be more pounds of plastic in the oceans than pounds of fish by 2050.

The trash skyscrapers in Wall-E are not far from reality.

It follows that waste is one of our most enduring effects on the planet, and as our technology and standard of living improve, the more we seem to produce.

But of all our waste, the nuclear variety is by far the longest-lived.Β One type is called ‘plutonium-239’, and it’s a product of most nuclear plants. One thousand tons of it is currently in storage, with twenty additional tons being added each year as the plants operate.

Nuclear power has some advantages as an energy source, but its creation of plutonium-239 is not one of them.Β Its toxicity is similar to that of nerve gas, and the accidental inhalation of just one-millionth of a gram of its dust would give you cancer. A single pound of it is enough to kill 2 million people.

Once it’s been made, it takes over one hundred thousand years to degrade.

A ring of plutonium.

I want to spend a moment to explainΒ why nuclear waste like plutonium is like it is, and why it’s dangerous.

Fundamentally it’s an atom that’s unstable.

Either it’s too big, or has an unbalanced ratio of protons to neutrons. The atoms ‘decay’ which means they shed protons, neutrons, and other forms of radiation until their atoms are small enough to be stable again.

This can take anywhere from seconds to millions of years.

Radon 220 being pumped into a special liquid solution, allowing us to see the radiation it emits.

It’s possible for radioactive substances to occur naturally, but most of it on Earth is man-made.

We make it as a byproduct of nuclear fission, where we break apart atoms to access the energy inside and use it for electricity and bombs.

A nuclear bomb test.

One of the first researchers into radioactivity was Marie Curie, the first woman to receive a Nobel Prize.

Unfortunately, she didn’t realise that her radioactive materials were killing her while she worked.

Radiation strikes and kills our cells, or alters their internal molecules like DNA.

In Marie’s case, it killed the irreplaceable cells inside her bone marrow, which stopped her body’s ability to make blood. She slowly died of aplastic anemia.

Nowadays we have a much better understanding of what radiation can do and are much more careful. Marie Curie’s notebooks for instance, which are over 100 years old and still radioactive, are stored within a dense, lead-lined box in a museum.


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We now know that if radiation strikes the wrong spot in our DNA, it can change the fundamental instructions in our cells, such as when a cell should start and stop replicating.

As a consequence, the cell may start replicating out of control, with every new cell inheriting the same faulty instructions.

Before long, it makes a dense clump called a tumour, which (in some cases) can break apart and form new tumours around the body. If you hadn’t guessed, this disease is cancer.

We also know that not all types of radiation are bad. It’s often used in medicine to diagnose internal problems. But these are different types of radiation that areΒ much lower energy, break down within a few hours,Β and do not damage the body.

A doctor is unlikely to use plutonium to diagnose our broken bones.

This brings us around to the Onkalo storage facility.

What do we do with a substance that is so toxic, yet lives for so long? It takes over 100,000 years for a lump of plutonium-239 to sufficiently decay, and that is a really long time.

For some perspective, the pyramids are ‘just’ 5,000 years old.

100,000 years ago, our distant Homo Sapiens ancestors had not yet left Africa, and the area around theΒ Onkalo facility was inhabited by an entirely separate species of human, Homo Neanderthalensis.

The world 100,000 years ago contained woolly mammoths, woolly rhinoceroses, and cave lions.

No one truly knows what it will look like in another 100,000 years.

What do we do with a substance (that we already have a thousand tons of) that remains toxic on timescales so far into the future, that by then that it’s possible that humans might have split into different species?

For the most part, the answer isΒ we don’t know.

All of the nuclear waste that we have ever produced, including plutonium, is currently in “temporary storage until a permanent solution is found“.

Many of these temporary storage facilities are not designed to last more than thirty years, and are nearing or have past their expiration date.

The one exception is the nuclear waste that’s created by Finland, who is building the world’s first permanent nuclear waste storage facility. Onkalo.

The plan is to bury it deep within the Earth, in a place where there is very little geologic activity, and whereΒ not even theΒ glaciers of an Ice Age in the distant future can disturb it.

Onkalo’s blueprint.

The wildcard, and the biggest risk of the site being disturbed, is future human beings.

No matter how well disguised Onkalo is, a clever person will still be able to tell that it’s different from the surrounding landscape, even far into the future.

So the Finnish government has determined that a message has to be left for these people.

We have to find a way to warn them to stay away, but without making them even more curious.

Not an easy task when our language is almost certain to be unrecognisable to them.

A few ideas have been proposed.

One was to build a forbidding landscape of concrete spikes to create the impression that the area is unwelcoming and dangerous.

Anyone who has seen the Lion King will know that won’t work.

An unusual idea was to genetically engineer a species of cats to glow when radiation is present,Β and release them in the area. Hopefully, people would be frightened of the descendants of the strange animals and stay away.

But even this may end up creating a curiosity that invites further explanation.

Unfortunately there is no definitive answer on what form a message should take.

But for when we do work it out, Academics at Sandia National Laboratories have concluded what the message should convey.

They composed this chilling passage for the people of the distant future. It reads:

This place is not a place of honor… no highly esteemed deed is commemorated here… nothing valued is here.

What is here is dangerous and repulsive to us. This message is a warning about danger.

The danger is still present, in your time, as it was in ours.

The danger is to the body, and it can kill.

The form of the danger is an emanation of energy.

The danger is unleashed only if you substantially disturb this place physically.

This place is best shunned, and left uninhabited.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.