The Chernobyl nuclear power plant in Ukraine was the site of history's worst nuclear disaster. Reactor number four exploded during a safety test on April 26th 1986, exposing its core to the air. Out streamed more than 100 radioactive elements, from iodine (which loses half its volume to decay every eight days) to technetium (which needs 200,000 years). The last of the plant's four reactors shut down for good in 2000. A concrete sarcophagus was erected over the ruined reactor after the disaster. A new protective dome, known as the new safe confinement (NSC), was slid into place in 2016 atop the sarcophagus. The project, orchestrated by the European Bank for Reconstruction and Development (EBRD), took 22 years and cost $1.6bn. The NSC was designed to contain radiation for a century. It is the largest moveable land-based structure in the world.
Russian troops briefly occupied the plant on the first day of the invasion in 2022.
Research by Gennady Laptev and Oleg Voitsekhovych of the Ukrainian Hydrometeorology Institute showed that drinking water provided no more than 10% of people's total long-term internal radiation dose after the accident, and probably closer to 1%. The rest came from food and, in particular, milk.
Chernobyl's cooling ponds, which had been topped up with water from the Pripyat River until 2014, have been slowly draining. The relatively clean groundwater beneath the ponds had acted as a barrier, hemming in more contaminated groundwater closer to the ruined reactor. As the ponds drain, strontium levels in local waterways have risen above WHO drinking-water guidelines.
Valery Kashparov of the Ukrainian Institute of Agricultural Radiology has found that soil type is the most important factor in how radioactive particles affect farmland: peaty and sandy earth gives up its contaminants to growing plants far more readily than black, humus-rich soils. Different crops also absorb radionuclides differently: oats disproportionately draw in strontium; peas, caesium. Wheat and potatoes leave more radionuclides in the earth.
Countermeasures include feeding livestock a chemical called Prussian Blue, which binds to caesium and helps it to be excreted; converting contaminated milk into forms (such as butter or cheese) that can outlive dangerous radioactivity; and adding lime or mineral fertilisers to soil to impede uptake.
Olena Pareniuk of the Institute for Safety Problems of Nuclear Power Plants has studied bacteria living inside the ruined reactor. They survive in an inhospitably alkaline environment with virtually no nutrients—and are breaking down the wildly radioactive mixture of melted uranium fuel, concrete and metal known as corium. Different bacteria can impede or enhance the transfer of radionuclides from soil to food: inoculating soil with the impeding kind produces cleaner crops, while introducing the enhancing kind turns plants into disposable contaminant sponges that help clean up soil.
The evacuation of the exclusion zone has become a well-documented experiment in rewilding. Wolf and deer populations bounced back; long-gone species such as the lynx returned. Jim Smith of Portsmouth University, who has studied the zone since 1990, reports that apart from an early spike in mostly non-lethal thyroid cancer, an exact count of human deaths caused by the ensuing radiation exposure is all but impossible. The disaster left little legacy in animal populations or their DNA, though the zone has no three-eyed fish—perch in the most contaminated areas seem slower to develop sexually.
On Valentine's Day 2025 a Russian drone pierced the NSC and started a fire—the first flames over the plant since 1986. The blaze consumed more than half of an inner protective layer. Some 300 openings had to be cut into the structure to fight the fire. The blaze destroyed parts of the dome's airtight seal, making it vulnerable to corrosion within a few years. Balthasar Lindauer, the EBRD's head of nuclear safety, warned that such corrosion could lead parts of the post-1986 sarcophagus to collapse and stir up radioactive dust. The IAEA initially called the damage superficial; its director, Rafael Grossi, later said that without repairs it would become "a far more costly" threat. No radioactive leak occurred.
In October 2025 Ukrainian workers covered the gaping hole with a metal sheet. To fully restore the NSC's integrity the dome must be resealed, possibly by removing it, fixing it offsite and replacing it—without exposing workers to high radiation. The EBRD is trying to raise the funds, but soliciting money for Ukraine is a hard sell.
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