Four decades after the Chernobyl (known today as 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," Weissenborn adds.
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. Scientists Examine Chornobyl's Radioactive Dust in Unprecedented Detail Despite decades of research, scientists still do not fully understand why radioactive particles from Chornobyl break down at different speeds.
As these materials weather, they can produce several forms of uranium oxide, making their long term behavior difficult to predict. Investigating these changes requires exceptionally precise equipment, including synchrotron X-ray diffraction, a technique that reveals the arrangement of atoms inside crystalline materials. 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.
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