Chernobyl Dust Grains Still Hold Their Fuel Crystals After 40 Years

Forty years after the Chornobyl disaster, researchers have found that some of the tiny radioactive particles left in the soil are more chemically stable than expected, according to ScienceDaily. The fuel inside six particles studied with powerful X-rays had kept much of its original crystal structure, which suggests these grains may hold on to radioactive material instead of freeing it quickly.

The scientists stress that this does not mean the contamination is becoming harmless. The sample was small, and each particle turned out to have its own structure.

The numbers behind the study

• 40 years: the time since the disaster. Particles measuring 8 to 50 micrometers are still highly radioactive, and entering affected areas still requires protective clothing.
• Six particles: the number analyzed, all recovered from Ukrainian soil samples. The team notes that this is a very small sample.
• Two locations: where those six particles came from, so the results cannot yet speak for the whole contaminated region.
• 2,000 angles: the number of viewpoints from which each particle was measured, by rotating it fully in the X-ray beam.
• 100 micrometers: the width of the focused beam, about the thickness of a human hair.
• Ten days: how long the reactor's graphite moderator burned, a fire that produced one type of particle.

Three kinds of particles

Tobias Weissenborn, a physicist and doctoral candidate at Leibniz University Hannover, described three classes of particles. Some are still chemically and physically close to the original uranium dioxide fuel. Others are partly or fully wrapped in, or fused with, a layer of zirconium, a resistant metal used in the fuel's protective casing. That group formed when the melting fuel combined with the zirconium at extreme temperatures.

The third type formed when the graphite caught fire. In that process the fuel oxidized into various uranium oxides, such as U3O8. This material is mechanically fragile and can crumble into microscopic fragments, which wind can carry and which are hazardous if inhaled.

How the particles were examined

Scientists have long struggled to explain why Chornobyl particles break down at different speeds. As they weather, they can form several kinds of uranium oxide, which makes their long-term behavior hard to predict.

To look inside, Dr. Christoph Hennig, a crystallographer at the Helmholtz-Zentrum Dresden-Rossendorf, used synchrotron X-ray diffraction, a method that reveals how atoms are arranged in crystals. The work was done at the Rossendorf Beamline in Grenoble and is described as the first successful structural analysis of fragments of this kind. Weissenborn and colleagues in Hannover isolated the particles and attached them to tungsten electrodes. Because the samples were so radioactive, they were sealed in several layers of containment for transport.

What it means for the contaminated land

If the particles behave this way more widely, they could limit how much radioactive material seeps into nearby soil and water, since they appear able to keep fission products locked inside. That would be relevant for anyone assessing long-term risks in the affected region.

The researchers are cautious. Weissenborn warned that every single particle has a different structure and that the experiment covered only six of them from two places. Establishing how particles behave across the whole area would require many more samples from a much wider range of locations.

For now, the finding adds one piece to a puzzle that remains unsolved. Predicting how Chornobyl's debris will behave over the long term is still difficult, and the particles that crumble easily remain a hazard.

Around Prague, based on reporting by ScienceDaily