Four decades after the Chornobyl Nuclear Power Plant disaster, which occurred on April 26, 1986, scientists continue to uncover new details about the behavior of radioactive materials. An international research team uniting specialists from Leibniz University Hannover and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany has conducted a detailed analysis of microparticles from Ukrainian soil. The findings shed light on the chemical composition and structure of hazardous fragments that remain the focus of intense scientific scrutiny.

Classification and Origin of Radioactive Fragments

The researchers focused on six so-called "hot particles" ranging from 8 to 50 micrometers in size. As explained by Tobias Weissenborn, a physicist and PhD student at Leibniz University Hannover, these micro-objects can be divided into three distinct classes. The first class still resembles the primary nuclear fuel of the reactor in the form of uranium dioxide in terms of its chemical and physical properties. The second class likely formed as a result of an extreme temperature spike where molten fuel fused firmly with the zirconium protective layer of the metal framework.

Fire Hazards and Structural Features

Of particular concern to specialists is the third class of particles, formed during large-scale ten-day fires in the reactor's graphite moderator. Under intensive burning conditions, the fuel oxidized, forming unstable compounds such as triuranium octoxide. Such mechanically unstable compounds easily break down into microscopic fragments that can be carried by the wind over considerable distances and pose a serious inhalation hazard. To study the internal structure of such small objects, scientists had to use a complex scanning technique at a research facility in Grenoble, France, rotating the samples within an X-ray beam.

Unexpected Conclusions and Long-Term Risks

The phase analysis results surprised scientists: the crystal structure of the nuclear fuel in the examined particles remains largely unchanged. This indicates that the consequences of the Chornobyl accident are "chemically more stable" than previously assumed, and fission products are contained within the matrices, which may be good news for soils and water bodies around Chornobyl. Nevertheless, researchers urge caution. Because each particle has a different structure and anomalous, more resistant fragments will always release radionuclides later, making universal statements about regional health risks premature.