Chernobyl's hot particles held their reactor-fuel structure for 40 years
A Leibniz University Hannover and HZDR team found six Chernobyl hot particles kept their reactor-fuel structure 40 years on, more stable than assumed. It eases worries about soil and water, but the team says six grains cannot speak for the region's health risks.
The Scientist · Science desk
What happened
- The fragments measure only 8 to 50 micrometers across and remain highly radioactive four decades after the explosions spread reactor debris through the surrounding soil.
- Crystallographer Christoph Hennig ran the first successful structural analysis of fragments this radioactive, at the Rossendorf Beamline in Grenoble.
- People may still enter the affected areas only while wearing protective suits.
Why it matters
- constraint A stability claim for the region would need samples from far more sites and far more than six particles; until then the result describes grains, not places.
- capability The same analysis measures how fast each grain releases its radionuclides, the per-particle release rate an exposure estimate needs.
- decision Exposure estimates that assumed these fragments weather and disperse now have a measured counterexample, and the authors say the method could make such assessments more precise.
A grain that holds its crystal lattice holds its fission products inside, rather than oxidizing and crumbling, and that is what these six fragments have done after 40 years [2][14]. The study, by a Leibniz University Hannover and HZDR team, appears in the Journal of Hazardous Materials [1][3]. The researchers say the radionuclides staying put is better news for the surrounding soil and water than for anything else [14].
The finding is narrow. Weissenborn, the Leibniz physicist who prepared the samples, said that "every single particle has a different structure," and that the team "only studied six such particles from two different locations" [15][6]. Even averages, he said, would not get to the point: "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" [17].
Getting a particle onto a beamline is laborious. The fragments were isolated from Ukrainian soil, fixed to tungsten electrodes, sealed behind several confinement layers and shipped to Grenoble [11]. There the beam was narrowed to about 100 micrometers, roughly the width of a human hair [13]. "We measured each particle from 2,000 different angles to seamlessly capture all the reflections," Hennig said [12].
Only some of the fragments are the stable, fuel-like kind [7]. The debris that drifts and is dangerous to breathe formed differently: when the graphite moderator burned for 10 days, the fuel oxidized into uranium oxides such as U3O8, a mechanically unstable compound that crumbles into microscopic dust and blows on the wind, and inhaling it poses severe health risks [9]. A separate kind formed when reactor temperatures spiked and melted the fuel into its zirconium cladding [8]. Why the kinds weather at such different rates is still unknown, and six grains from two sites do not settle it [18].
What to watch
- Whether a larger, multi-site sampling campaign confirms the stability finding beyond these six grains.
- Whether follow-up work pins down why the three particle types weather at such different rates.
- Whether the measured per-particle release rates feed into revised exposure models for the area around Chernobyl.
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Claim ledger
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- [1]
Researchers at Leibniz University Hannover and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) examined six tiny, highly radioactive fragments, or 'hot particles,' released from the destroyed Chernobyl reactor after the 1986 disaster.
- [2]
Analyses show the examined hot particles are far more stable than had previously been assumed, and the crystal structure of the reactor fuel inside them has remained largely intact after 40 years.
- [3]
The study is published in the Journal of Hazardous Materials.
- [4]
The particles measure only 8 to 50 micrometers and remain highly radioactive even 40 years after the explosions scattered reactor debris across the soil around Chernobyl.
- [5]
Even today, people may enter the affected areas only while wearing protective suits.
- [6]
Tobias Weissenborn is a physicist and doctoral candidate at Leibniz University Hannover.
- [7]
The researchers identify three classes of particle: ones still chemically and physically similar to uranium dioxide fuel; ones partially or fully encased in or fused with their zirconium layer; and ones created when the graphite moderator caught fire.
- [8]
The zirconium-fused particles formed when temperatures in the reactor spiked dramatically, melting the fuel and bonding it to its surrounding layer of zirconium.
- [9]
During the accident the graphite moderator burned for 10 days, and the fuel oxidized into uranium oxides such as U3O8, a mechanically unstable compound that rapidly forms microscopic particles easily borne away by wind; inhaling such dust poses severe health risks.
- [10]
HZDR crystallographer Christoph Hennig carried out the first successful structural phase analysis of highly radioactive fragments of this kind, on six Chernobyl particles, at the Rossendorf Beamline in Grenoble.
- [11]
The particles were isolated from Ukrainian soil samples, attached to tungsten electrodes, secured behind several confinement layers and shipped to Grenoble.
- [12]
We measured each particle from 2,000 different angles to seamlessly capture all the reflections.
- [13]
The X-ray beam was focused down to about 100 micrometers, roughly the thickness of a human hair.
- [14]
The examined particles retain their fission products within themselves, which the researchers say might be good news for the soil and water around Chernobyl.
- [15]
every single particle has a different structure, and our experiment only studied six such particles from two different locations.
- [16]
Drawing more general conclusions about the stability of Chernobyl particles would require gathering samples from far more locations and examining many more particles.
- [17]
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.
- [18]
It remains largely unclear why these particles weather at different rates in their environment.
- [19]
The phase analysis lets researchers estimate the rate at which the particles release radioactive substances.
- [20]
The findings could allow for more precise assessments of the health risks posed by such radioactive particles.
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Sources
3 independent publishers whose own reporting we read for this story.
- interestingengineering.comMicroscopic nuclear fuel particles from Chernobyl still intact after 40 years
1 article · October 7, 2026
- phys.orgChernobyl particles reveal unexpectedly stable nuclear fuel after 40 years
1 article · October 6, 2026
- popsci.comChernobyl particles look remarkably similar to explosion day in 1986
1 article · October 8, 2026
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