We’re now 40 years on from the worst nuclear disaster in history, and scientists have been analyzing radioactive particles blown out by Chornobyl to see what’s left of the fuel that got scattered – and what state those particles are in.
Knowing how these chemical pellets have held up to decades of weathering and decay is valuable for understanding the safety of nuclear plants in the future – and for working out when it might be safe to return to the Chornobyl site without a protective suit.
What stood out most from the analysis was the “remarkably persistent” structure of the radioactive dust particles, which showed much more stability than expected.
That means most of the radioactive material remains locked inside.
The researchers behind the work, from Leibniz University Hannover and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, have published their findings in the Journal of Hazardous Materials.
Six fuel particles were analyzed in total, split into three categories depending on what happened to them during the original reactor explosion. Some, for example, had melted and bonded with their coating of zirconium.
“There are three classes of these particles,” says physicist Tobias Weissenborn, from Leibniz University Hannover.
“First, there are particles that are chemically and physically still very similar to the nuclear fuel uranium dioxide.
“Then, there are particles that are partially or fully encased in, or completely fused with, their zirconium layer. The third type of particle was created when the graphite moderator caught fire.”
Each of these particle classes has ended up with a different chemical composition, which can affect how they degrade. The sampled particles measured a mere 8–50 micrometers in size (so at least 20 would fit inside a single millimeter), and were all collected from inside the Chornobyl Exclusion Zone.
A technique known as diffraction analysis was used to look inside these microscopic specks, with the atomic crystal structure being determined through the way X-rays reflected away from it.
“Ultimately, we fully rotated the particles in an X-ray beam focused down to 100 micrometers – about the thickness of a human hair,” says crystallographer Christoph Hennig from HZDR.
“We measured each particle from 2,000 different angles to seamlessly capture all the reflections.”
Across all three particle types, the researchers found the structure holding the nuclear fuel had largely remained intact. That suggests a greater chemical stability in these fuel specks than previously assumed.
The study also gives scientists a better idea of how these particle groups are put together – exactly how the disaster and its subsequent chemical chain reaction shifted the composition of the fuel crystals.
“Our findings demonstrate that Chornobyl fuel particles act as remarkably persistent reservoirs,” write the researchers in their published paper.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>The researchers frame this as potentially good news: It means the particles may be releasing radioactive material into the environment more slowly than previously assumed.
While it’s not safe to go back, the findings could help scientists better assess the long-term environmental risks.
However, there’s a flip side.
The radioactive material hasn’t gone anywhere, which means these particles will remain dangerous for decades. Breathing these particles in is still going to be extremely hazardous to health, and they could get kicked up from the ground by wind, erosion, or passing animals.
The researchers also acknowledge that six particles – all sourced from two locations – are a small sample. Weighing up the current risks in Chornobyl will require more comprehensive sets of data collected over longer periods.
“Even if we obtained some averages at some point, we still wouldn’t be able to make universal statements about health risks in the region,” says Weissenborn.
“Even if the particles decay in a largely uniform pattern, there will always be outliers, more persistent particles, that will release radionuclides at a later point in time.”
The research has been published in Journal of Hazardous Materials.
This article was fact-checked by Peter Dockrill and edited by Peter Dockrill. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
