Chernobyl nuclear waste is treated with X-rays
It has been three and a half decades since Chernobyl Reactor 4 failed catastrophically and spewed out fallout across Europe. But while authorities have done their best to keep the reactor contained, it is still covered in what amounts to hardened radioactive lava.
This hardened glassy substance not only withstood all cleaning efforts – it made it difficult to study at all. But researchers have now successfully tested a technique that could help glean more detail from this nearly impenetrable shell.
First, the scientists had to create their own materials to mimic what you’ll find in Chernobyl. Now, by placing tiny samples of this material under some of the world’s most powerful x-rays, researchers have found a way to reconstruct the history of this substance.
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Their work, published in the Journal of Materials Chemistry A, shows that this technique could be used to unravel the mysteries of nuclear disaster waste in the real world.
It’s “like a forensic analysis of a crime scene,” says Claire Corkhill, one of the aforementioned scientists and nuclear researcher at the University of Sheffield in the UK, in a report. “The chemical analysis carried out on our simulating materials allowed us to reconstruct the last moments of Chernobyl nuclear fuel.”
The Chernobyl nuclear power plant, about 60 miles north of the Ukrainian capital, Kiev, housed four reactors in operation at the time of the accident. Three of those reactors have since been safely decommissioned, but not Reactor 4, which is buried in a shed shaped shell– like the pathogenic corpse of a plague victim.
In 1986, the uranium fuel from Reactor No.4 melted and reacted chemically with components of its structure and environment – including materials like zirconium, graphite, steel, and concrete – and cooked together into a lava-like curry that scientists call “corium”. This dangerous sludge flowed from the reactor core, eventually cooling and hardening into a kind of highly radioactive vitreous ceramic, including formations like the “Elephant’s foot.”
To ultimately determine the best way to remove corium and completely detoxify Chernobyl, scientists must first understand corium, how the mixture varies in the old reactor, and exactly how it formed. But the corium is too radioactive to approach. Combined with its hardness, this means that samples of Chernobyl corium are rare. In fact, Russian scientists would have used a literal weapon to get anything loose at all.
Far on the other side of Europe, at the University of Sheffield, researchers like Corkhill are building what scientists call “simulants”. They together melt imitation waste from many of the same building blocks you find in a nuclear power plant. But there is one key difference: Sheffield simulants are much less radioactive than the real thing and much easier to handle.
For this research, the Sheffield researchers took their simulants to synchrotrons, extremely bright x-ray sources, particularly at the Paul Scherrer Institute in northern Switzerland and the Brookhaven National Laboratory in Long Island, New York.
The researchers sliced and polished their thin simulants – very thin, up to the width of a human hair – before making them glow with x-rays. By observing how the x-rays were absorbed differently through the simulant, the researchers were able to identify the finer details. For example, they could identify crystal structures of uranium-containing compounds that are smaller than fog droplets.
This gave the researchers further confirmation that their simulants indeed resemble reality quite closely. “Our analyzes are consistent with the limited data available on real samples, which is extremely exciting,” says Corkhill.
Additionally, the x-ray data allowed the researchers to piece together the order in which the components of their sample melted together under extreme conditions. In other words, they could replay the moments right after the collapse.
Reid peterson, a nuclear waste researcher at the Pacific Northwest National Laboratory in Richland, Wash., says it’s a good use of new technology to examine old waste.
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He also says it highlights the need for high quality simulants. “One of the things we’ve found is that nuclear waste can have some very interesting properties that you can’t predict,” he says.
The researchers say that being able to use such small samples, even though they are highly radioactive, significantly reduces the risk of exposure. But Peterson points out that this is just one technique among many, and using very small samples could be misleading.
“These complex mixtures require a number of techniques to get a complete picture of what the specific phases are in radioactive waste,” he says.
Nevertheless, the researchers believe their technique is ripe for the real world. The study, says Corkhill, “paves the way for the analysis of real nuclear fuels from Chernobyl and Fukushima.”
Indeed, the site of the 2011 Fukushima Daiichi nuclear disaster in Japan is also coated with its own unique blend of corium. And there, the researchers have not yet penetrated the heart of the reactor for samples.