Chornobyl Radioactive Particles Retain Original Structure After 40 Years
Scientists find that radioactive particles from Chornobyl have preserved much of their internal structure despite decades in the environment.
Four decades after the Chornobyl nuclear disaster, microscopic radioactive particles remain scattered throughout the surrounding soil. The explosions that devastated the reactor released enormous quantities of debris, leaving behind contamination that continues to pose serious health risks. Even after 40 years, particles measuring just 8 to 50 micrometers remain highly radioactive, and entering affected areas still requires protective clothing.
Scientists have now taken a closer look at these tiny remnants and uncovered a surprising finding: some have preserved much of their original internal structure despite decades of 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 category originated during the extreme temperatures reached 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. Under normal operating conditions, the graphite moderator slows fast neutrons, helping sustain the nuclear chain reaction. During the disaster, however, the graphite ignited and continued burning 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 readily break apart into microscopic fragments. Wind can then carry these radioactive particles through the environment, where inhaling them presents serious health hazards.
Despite decades of research, scientists still do not fully understand why radioactive particles from Chornobyl break down at different speeds. Investigating these changes requires exceptionally precise equipment, including synchrotron X-ray diffraction, a technique that reveals the arrangement of atoms 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 kind at the Rossendorf Beamline in Grenoble. Working with Weissenborn, Hennig analyzed six particles recovered from the Chornobyl region. By identifying the different crystalline phases within them, the researchers gained information that could help determine how quickly radioactive substances escape into the surrounding environment.
The results revealed something unexpected. Despite spending 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 produced by the Chornobyl disaster is more chemically stable than researchers previously believed. However, the researchers emphasize that their findings should not be interpreted as evidence that Chornobyl's radioactive contamination is becoming harmless.
