Uniformed guards with holstered guns stand at the entrance and watch you lumber past. Ahead lies a wasteland of barren metal gantries, dormant chimney stacks and abandoned equipment.
You trudge towards the ruins of a large, derelict red-brick building. Your white hazmat suit and heavy steel-toe-capped boots make it difficult to walk. Your hands are encased in a double layer of gloves, your face protected by a particulate-filtering breathing mask. Not an inch of flesh is left exposed.
Peering into the building’s gloomy interior, the beam from your head torch picks out machinery and vats turned orange with rust. On a wall nearby, a yellow warning sign featuring a black circle flanked by three black blades reminds you of the danger lurking inside.
Apart from the sound of your own breathing behind your mask, the only thing you can hear is the crackling popcorn of your Geiger counter.
This is what entering the Prydniprovsky Chemical Plant is like for nuclear researchers, including Tom Scott, professor of materials at the University of Bristol and head of the UK Government’s Nuclear Threat Reduction Network.
Prydniprovsky was once a large Soviet materials and chemicals processing site on the outskirts of Kamianske in central Ukraine. Between 1948 and 1991, it processed uranium and thorium ore into concentrate, generating tens of millions of tonnes of low-level radioactive waste.
When the Soviet Union dissolved, Prydniprovsky was abandoned and fell into disrepair.
“The buildings are impressively awful and not for the faint-hearted,” says Scott. “As well as physical hazards, such as gaping holes in the floor, there’s no light or power. And obviously there are radiological hazards. Until very recently, the Ukrainian Government didn’t have a clue what had gone on at the site, so there were concerns about the high radiation levels and ground contamination.”
When radiation levels are deemed too high for humans, Scott sends in the robots. At Prydniprovsky, it was a robotic dog, nicknamed ‘Spot’, that had been developed by Boston Dynamics.
Spot, customised with radiation sensors, was wearing rubber socks – the sort you use to prevent your verruca spreading when you go swimming, but on this occasion, worn to prevent any radioactive material getting stuck on its feet.
Once activated, Spot trotted off into the building to explore further, using a light detection and ranging (LIDAR) system to create a 3D image of the environment and pinpoint any radioactivity in the area.
Scott and his team are known as industrial nuclear archaeologists, and they’re working to find, characterise and quantify the ‘legacy’ radioactive waste at sites around the world.
“High-level radioactive waste gives off a significant amount of radioactivity, sufficient to make humans sick if they get too close,” he says. “Some of this waste will be dangerously radioactive for very long periods of time, meaning that it needs to be physically kept away from people and the environment to ensure that no harm is caused.”
But finding legacy waste like this, which has been amassing since the 1940s, is only part of the challenge. Once it’s been found, it has to be isolated and stored long enough for it to no longer pose a threat. And that’s not easy.
“Currently we’re storing our high-level wastes above ground in secure, shielded facilities,” Scott says. “Such facilities need to be replaced every so often because buildings and concrete structures can’t last indefinitely.”
Safely storing the nuclear waste that already exists is only the start of the problem, however. With the world moving away from fossil fuels towards low-carbon alternatives, nuclear energy production is set to increase, which means more waste is going to be produced – a lot more.
Currently, nuclear energy provides roughly nine per cent of global electricity from about 440 power reactors. By 2125, however, the UK alone is predicted to have 4.77 million m3 (168 million ft3) of packaged radioactive waste. That’s enough to fill 1,900 Olympic swimming pools.
Hence, the world needs more safe storage sites for both legacy and new nuclear waste. And it needs them fast.
Safe spaces
In the UK, most nuclear waste is currently sent to Sellafield, a sprawling site in Cumbria, in the north-west of England, with about 11,000 employees, its own road and railway network, a special laundry service for contaminated clothes and a dedicated, armed police force (the Civil Nuclear Constabulary).
Sellafield processes and stores more radioactive waste than anywhere in the world.
But more hazardous material is on the way, much of which will come from the new nuclear power station being built at Hinckley Point in Somerset. To keep pace, experts have been hunting for other, much stranger, disposal solutions.
It’s a challenge for nuclear agencies all around the world. All sorts of proposals have been put forward, including some bizarre ideas like firing nuclear waste into space. (The potential risk of a launch failure showering the planet with nuclear debris has silenced that proposal’s supporters.)
So far, the most plausible solution is putting the waste in special containers and storing them 200–1,000m (660–3,280ft) underground in geological disposal facilities (GDFs). Eventually, these GDFs would be closed and sealed shut to avoid any human intrusion.
These ‘nuclear tombs’ are the safest, most secure option for the long-term and minimise the burden on future generations.
“In the UK, around 90 per cent of the volume of our legacy waste can be disposed of at surface facilities, but there’s about 10 per cent that we don’t currently have a disposal facility for. The solution is internationally accepted as being GDFs,” says Dr Robert Winsley, design authority lead at the UK’s Nuclear Waste Services.
“We estimate that about 90 per cent of the radioactive material in our inventory will decay in the first 1,000 years or so. But a portion of that inventory will remain hazardous for much longer – tens of thousands, even hundreds of thousands of years.
"GDFs use engineered barriers to work alongside the natural barrier of stable rock. This multi-barrier approach isolates and contains waste, ensuring no radioactivity ever comes back to the surface in levels that could do harm.”
But how do you keep that radioactivity in the ground? Radioactive waste is typically classified as either low-, intermediate- or high-level waste.
Before being disposed of deep underground, high-level waste is converted into glass (a process known as vitrification) and then packed in metal containers made of copper or carbon steel. Intermediate-level waste is typically packaged in stainless-steel or concrete containers, which are then placed in stable rock and surrounded by clay, cement or crushed rock.
The process isn’t set in stone yet, though. Other materials, such as titanium- and nickel-based alloys, are being considered for the containers due to their resistance to corrosion.
Meanwhile, scientists in Canada have developed ultra-thin copper cladding that would allow them to produce containers that take up less space, while providing the same level of protection.
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Rock solid
The hunt is also on to find facilities with bedrock that can withstand events such as wars and natural disasters (‘short-term challenges’, geologically speaking). Sites that won’t change dramatically over the millennia needed for nuclear waste to no longer pose a risk.
“A misconception is that we’re looking for an environment that doesn’t change, but the reality is the planet does change, very slowly,” says Stuart Haszeldine, professor of carbon capture and storage at the University of Edinburgh.
“Our generation must find a way to bury the waste very deep to avoid radioactive pollution or exposure to people and animals up to one million years into the future.”
To achieve this, the site ideally needs to be below sea level. If it’s above sea level, rainwater seeping down through fractures in the rock around the site might become radioactive and eventually find its way to the sea.
When this radioactive freshwater meets the denser saltwater, it’ll float upwards, posing a risk to anything in the water above.
Another challenge is predicting future glaciations, which happen roughly once every 100,000 years. During such a period, the sort of glaciers that cut the valleys in today’s landscape could form again, gouging new troughs in the bedrock that might breach an underground disposal facility.
“Accurate and reliable future predictions depend on how well you understand the past,” says Haszeldine.
“Typically, repository safety assessments cover a one-million-year timeframe, and regulations require a GDF site to cause fewer than one human death in a million for the next million years. Exploration doesn’t search for a single best site to retain radioactive waste, but one that’s good enough to fulfil these regulations.”
Hiding places
In 2002, the US approved the construction of a nuclear tomb in an extinct supervolcano in Yucca Mountain, Nevada, about 160km (100 miles) north-west of Las Vegas.
Research estimated the chances of a future volcanic eruption disrupting the proposed repository were one in 63 million per year. So, it wasn’t the potential of a radioactive volcanic eruption that prevented the construction of the site going ahead.
Instead, opponents cited concerns that it was too close to a fault line and, in 2011, US Congress ended funding for the project. Since then, waste from all US nuclear power plants has been building up in steel and concrete casks on the surface at 93 sites across the country.
Other sites have fared better, however. Already this year, construction has begun on a nuclear tomb in Sweden, expected to be ready in the 2030s, but it’s also the year the world’s first tomb – at a site in Finland, called Onkalo (Finnish for ‘cave’ or ‘hollow’) – could open its doors for waste.
“While there’s a lot of fractured rock at Onkalo, geologists carefully surveyed the area to work out the water flow,” says Haszeldine. “With little landscape topography, there’s no drive pushing water deep underground and so layers of water haven’t moved for hundreds of thousands of years.”
In January 2025, the UK Government announced plans to permanently dispose of its 140 tonnes of radioactive plutonium, currently stored at Sellafield. In a statement, energy minister Michael Shanks cited plans to put it “beyond reach”, deep underground.
Three potential sites in England and Wales are being explored by Nuclear Waste Services, and one of Haszeldine’s PhD students is independently investigating a fourth off the Cumbrian coast. The offshore site appears to be hydro-geologically stable (even over glacial timescales), but it would be expensive and difficult to engineer.
“Currently, about 75 per cent of the UK’s nuclear waste is already stored across 20 sites,” says Winsley. “People are surprised to hear you’re never far away from the most hazardous radioactive waste, wherever you are in the UK. Our mission is to make this radioactive waste permanently safe, sooner.”
Although the construction of excavated tunnels for nuclear tombs is expensive, the volume of waste needing to be buried is actually quite small. As such, a new ‘deep isolation’ approach is also being considered, which adapts the directional-drilling technology used to reach oil and gas reserves.
Essentially, it involves drilling horizontal boreholes into a layer of claystone rock, which can absorb some radioactive leakage and self-seal if fractures form. Disposal canisters containing spent fuel rods from nuclear reactors would go into these boreholes.
It’s potentially a simpler solution and doesn’t require anyone to excavate an entire network of large tunnels and chambers through different layers of rock deep underground.
The deep isolation approach costs less than a third of what it costs to construct a nuclear tomb and uses smaller sites, but the canisters are harder to recover if anything goes wrong.
Nevertheless, it’s a viable option for smaller nuclear countries and a second prototype is expected to undergo field testing at a deep borehole demonstration site in the UK in early 2025.
Locked in
When you think of radioactive waste, you probably imagine glowing rods or oil drums filled with green ooze and covered in warning symbols.
In fact, plutonium oxide (a byproduct of nuclear reactors) is stored as a powder that changes colour depending on the chemical composition. But researchers are investigating ways to change its chemical and physical form to make it ready for long-term disposal.
At the University of Sheffield, Dr Lewis Blackburn and his team are developing special ceramic materials in which to trap plutonium. Replacing atoms in the tightly ordered structure of ceramic with atoms of plutonium ‘locks in’ the radioactive particles.
Think of it like a chain-link fence made of strong, tightly woven metal wires: the researchers are trying to swap out some of those wires with the dangerous radioactive particles to trap them inside the still-strong structure.
The scientists are trying to engineer synthetic versions of ancient natural minerals to use as the ‘wires’ in these ceramic prisons – minerals like zirconolite and pyrochlore, left over from Earth’s formation.
For billions of years, these minerals have been exposed to the environment, subjected to natural weathering and exposed to water, microbial activity and temperature changes – so the researchers know they’re made of strong stuff.
To test whether their synthetic versions are equally durable and resistant to corrosion, the scientists fire high-energy ion beams at them for hours (to simulate radiation damage) while simultaneously exposing them to low-strength acid.
“These tests build a picture of how we think these materials will behave over a very long timescale,” says Blackburn.
“The half-life of plutonium 239 is about 24,100 years, but the requirement is to keep a ceramic in that state for up to a million years. Essentially, we’re trying to design materials that’ll last forever. I don’t think humans will be around in a million years’ time, so the work we do needs to outlast humanity.”
Hide and seek
But even after you’ve found a suitable site and buried the radioactive material safely inside it, you still need to warn future generations about what’s hidden inside.
The trouble is, even if humans are still around in a million years’ time, there’s no guarantee the languages our ancestors speak, or the symbols they use, will be anything like those of today.
In Japan, 1,000-year-old ‘tsunami stones’, which warned future generations to find high ground after earthquakes, have failed to prevent construction on vulnerable sites.
Even the radiation symbol we use today (that black circle flanked by black blades on a yellow background) isn’t universally recognised. Research by the International Atomic Energy Agency found that only six per cent of the global population know what it signifies.
That’s why scientists have been working with everyone from artists to anthropologists, librarians to linguists, and sculptors to science-fiction writers – to come up with other ways of warning future generations about nuclear tombs.
Before the plans for the site at Yucca Mountain were abandoned, suggestions included libraries, time capsules and physical markers, including spikes in the ground.
At Onkalo, as well as spikes, the panel has suggested a huge slab of black granite that would be heated to impassably hot temperatures by the Sun.
More outlandish ideas have included linguist Thomas Sebeok’s proposal of an ‘atomic priesthood’ that would pass on nuclear folklore (in much the same way that generations of clergy have been relaying the tenets of their respective faiths for thousands of years).
But why rely on people? The idea of so-called ‘ray cats’ has also been put forward – that is, genetically engineered creatures that would somehow change colour (or glow if bioluminescence could be harnessed) when exposed to radiation.
Perhaps not as fear inducing as, say, a fire-breathing dragon – but if a glowing cat crossed your descendants’ path, it would probably make them think twice about progressing any further.
“Some experts think the safest thing we can do is forget about the existence of the repositories altogether and not leave any markers that might entice intrigued ‘treasure hunters’,” says postdoctoral researcher Thomas Keating, from Linköping University, in Sweden.
“So far, every attempt to warn people against entering a crypt has failed. Ancient Egyptian tombs are one example of where messages of danger have been wilfully or accidentally ignored by subsequent generations. Communicating the memory of nuclear repositories is a unique problem – no one has pulled off anything like this before.”
While some back this active forgetting of future nuclear tombs, researchers like Scott are still trying to get everyone to remember the nuclear sites we’ve already forgotten. It’s like a game of nuclear ‘hide and seek’ – but the stakes are high, and there’s no room for error.
Thinking back to his time at the Prydniprovsky Chemical Plant in Kamianske, Scott remembers the hunt for radioactive waste coming to an end.
The robotic dog Spot returned from its foray in the darkness, and its rubber socks needed to be peeled off – carefully – and disposed of safely. Like the world’s increasing stockpiles of nuclear waste, they needed a home, fast.
Currently, nuclear tombs are our best bet, but it’s a burden humanity must shoulder for thousands of years, long after the benefits gained from nuclear technology will have faded.
“My personal opinion is, I don’t think we should allow future generations to forget about a geological disposal facility,” says Scott. “The material is both dangerous and, in longer timescales, potentially valuable. People need to be reminded of its presence.”
About our experts
Prof Tom Scott is a professor of materials at the University of Bristol and is head of the UK Government's Nuclear Threat Reduction Network. He has been published in various journals including Sensors, Journal of Radiological Protection and Frontiers in Robotics and AI.
Dr Robert Winsley is the design authority lead at the UK's Nuclear Waste Services. You'll find his work published in the likes of Mineralogical Magazine, The Nuclear Decommissioning Authority and Materials World.
Prof Stuart Haszeldine is a professor of carbon capture and storage at the University of Edinburgh. His work is published in the likes of Joule, International Journal of Greenhouse Gas Control and Chemical Society Reviews.
Dr Lewis Blackburn is a lecturer in nuclear materials at the University of Sheffield and a Royal Academy of Engineering Research Fellow. He has been published in Journal of Nuclear Materials, Materials Advances and Results in Physics to name a few journals.
Thomas Keating is a postdoctoral researcher in nuclear memory communication and assistant professor at Linköping University, in Sweden. His work has been published in journals such as Geografier, Progress in Human Geography and Progress in Environmental Geography.
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