Four decades after the Chernobyl (or Chornobyl) nuclear disaster, microscopic radioactive particles still permeate the surrounding soil. The reactor explosions hurled enormous amounts of debris into the environment, creating a persistent contamination that requires protective clothing for anyone entering the affected zone. Even after 40 years, particles ranging from 8 µm to 50 µm remain highly radioactive.
A recent detailed investigation of these remnants has revealed a surprising discovery: several particles have retained much of their original crystal structure despite prolonged exposure to the environment.
“There are three classes of these particles,” explains Tobias Weissenborn, a physicist and doctoral candidate at 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 second class originated during the extreme temperatures inside the reactor. As the nuclear fuel melted, it combined with zirconium, a highly resistant metal used in the fuel’s protective outer layer.
“The third type of particle was created when the graphite‑moderator caught fire,” Weissenborn adds.
Under normal operation, the graphite moderator slows fast neutrons to sustain the chain reaction. During the disaster, however, the graphite ignited and burned for ten days.
“In the process, the fuel oxidized into various uranium oxides,” such as U₃O₈.
Unlike more stable materials, this uranium oxide is mechanically fragile and can break apart easily into microscopic fragments. Wind can then transport these radioactive particles, posing serious inhalation hazards.
Scientists Examine Chornobyl’s Radioactive Dust in Unprecedented Detail
Despite decades of research, scientists still do not fully understand why Chornobyl’s radioactive particles degrade at different rates. As they weather, these materials can produce several uranium‑oxide forms, making long‑term behavior difficult to predict.
Investigating such changes requires highly precise equipment, including synchrotron X‑ray diffraction, which reveals atomic arrangements inside crystalline materials.
Dr. Christoph Hennig, a crystallographer at the Helmholtz‑Zentrum Dresden‑Rossendorf (HZDR), has now completed the first successful structural analysis of radioactive fragments of this type at the Rossendorf Beamline in Grenoble.
Working with Weissenborn, Hennig analyzed six particles recovered from the Chornobyl region. By identifying the distinct crystalline phases within them, the researchers obtained data that could help determine how quickly radioactive substances escape into the environment.
“The colleagues from Hanover and I used various methods to isolate the particles from Ukrainian soil samples and attach them to tungsten electrodes,” Weissenborn explains.
Because the samples were highly radioactive, they were enclosed in multiple layers of containment before being shipped to Grenoble. There, Hennig’s team employed X‑ray diffraction to examine the internal structures, measuring how X‑rays scattered as they passed through the material.
“First, we had to figure out how to examine the particle structure,” Christoph Hennig explains. “Ultimately, we fully rotated the particles in an X‑ray beam focused down to 100 µm—about the thickness of a human hair. We measured each particle from 2 000 different angles to seamlessly capture all the reflections.”
The measurements enabled the scientists to distinguish different uranium‑oxide phases within the radioactive fragments, revealing details that were previously inaccessible.
A Surprising Discovery About 40‑Year‑Old Nuclear Fallout
The results revealed something unexpected. Even after four decades in the environment, the nuclear fuel inside the six examined particles had retained much of its original crystal structure.
This suggests that at least some of the radioactive debris from the Chornobyl disaster is more chemically stable than previously believed.
Such stability could have important environmental implications. Rather than rapidly releasing radioactive substances, the particles appear capable of retaining fission products within their structures. If this behavior is widespread, it could help limit the movement of contaminants into nearby soil and water.
However, the researchers caution that their findings should not be interpreted as evidence that Chornobyl’s contamination is becoming harmless.
“However, every single particle has a different structure,” warns Weissenborn, “and our experiment only studied six such particles from two different locations.”
The relatively small sample size means the findings cannot yet establish how radioactive particles behave across the entire contaminated region. To understand their stability more comprehensively, scientists would need to investigate many additional particles collected from a much broader range of locations.
Why Chornobyl’s Radioactive Legacy Remains Unpredictable
Even with substantially more data, predicting the long‑term dangers of Chornobyl’s radioactive debris would remain challenging. Individual particles can differ in composition, structure, and resistance to environmental weathering, potentially affecting when they release radioactive materials.
“And 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,” Weissenborn cautions. “Because 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.”
These persistent particles could continue emitting radioactive substances long after other remnants have broken down, complicating efforts to assess future contamination and health risks.
For this reason, the new findings do not suggest that restrictions on the Chornobyl Exclusion Zone can be lifted anytime soon.
Research into the disaster’s enduring consequences is ongoing. Weissenborn and Hennig are already conducting additional experiments focused on highly radioactive transuranic phases found in the remaining debris. Their work could provide a clearer picture of how Chornobyl’s nuclear materials evolve over time and how long their environmental effects may persist.