Chernobyl's 40-Year-Old Fallout Particles Are More Stable Than Expected

How do you X-ray a radioactive dust grain?

Scientists still don't fully understand why these particles break down at different speeds, because weathering produces several forms of uranium oxide that are hard to predict. Answering that question required synchrotron X-ray diffraction — a technique that reveals how atoms are arranged inside crystalline materials.

The team isolated six particles from Ukrainian soil samples and attached them to tungsten electrodes. Because the material was so radioactive, the samples had to be sealed within several layers of containment before shipping to the Rossendorf Beamline in Grenoble, France.

"First, we had to figure out how to examine the particle structure," Hennig said. "Ultimately, we fully rotated the particles in an X-ray beam focused down to 100 micrometers — about the thickness of a human hair. We measured each particle from 2,000 different angles to seamlessly capture all the reflections."

That let the researchers distinguish different uranium oxide phases inside each fragment, details that had been inaccessible before.

Why is stability good news — and limited news?

The surprise: despite 40 years in the environment, the fuel inside all six particles had retained much of its crystal structure. That suggests at least some of the debris is more chemically stable than researchers assumed.

If that holds more broadly, the particles could trap fission products inside their structures rather than releasing them, limiting the spread of radioactive contaminants into nearby soil and water.

But the authors are careful about what six particles can prove. "Every single particle has a different structure," Weissenborn said, "and our experiment only studied six such particles from two different locations."

That sample is far too small to describe behavior across the whole contaminated region. Scientists would need to analyze many more particles from many more sites.

Can the Exclusion Zone reopen?

No — and even much larger datasets wouldn't settle the question. Individual particles differ in composition, structure and resistance to weathering, so they release radioactive materials at different times.

"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 said. "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."

Those stubborn outliers could keep releasing radioactive substances long after other remnants have broken down, complicating any long-term risk assessment. The new findings offer no basis for lifting restrictions on the Chornobyl Exclusion Zone.

The research continues. Weissenborn and Hennig are already running follow-up experiments on highly radioactive transuranic phases in the remaining debris, work that could clarify how the site's nuclear materials change over time — and how long their environmental effects will persist.