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Ukraine marks the 40th anniversary of the Chernobyl nuclear disaster on April 26—a date that remains a reference point in the global debate on nuclear energy and one that carries renewed weight as the plant at the center of that 1986 catastrophe continues to face risks from the ongoing war.
At 1:23 a.m. on April 26, 1986, a human error during a safety test triggered an explosion in reactor No. 4 at the Chernobyl nuclear plant in northern Ukraine, then part of the Soviet Union.
The blast tore the interior of the building apart, sending a plume of radioactive smoke into the atmosphere. Nuclear fuel burned for more than 10 days.
Thousands of tonnes of sand, clay and lead ingots were dropped by helicopter in an effort to contain the radioactive leak.
The International Atomic Energy Agency (IAEA) later determined the main cause of the disaster was "severe deficiencies in the design of the reactor and the shutdown system," combined with "violation" of operation procedures.
In the days that followed, the radioactive plume heavily contaminated Ukraine, Belarus and Russia before spreading across Europe.
The first public alert came two days after the explosion, on April 28, when Sweden detected a spike in radiation levels on its territory.
The IAEA was officially notified on April 30. Soviet leader Mikhail Gorbachev did not publicly acknowledge the disaster until May 14, more than two weeks after the explosion.
Estimates of the death toll vary considerably. A 2005 U.N. report put the number of confirmed and projected deaths at 4,000 across the three worst-affected countries.
Greenpeace estimated in 2006 that the disaster caused close to 100,000 deaths. According to the United Nations, some 600,000 people involved in the clean-up operation—known as "liquidators"—were exposed to high levels of radiation.
The disaster fueled a surge in anti-nuclear movements across Europe.
Russian forces occupied the Chernobyl power plant on the first day of Moscow's 2022 military operation in Ukraine.
They captured the facility without fighting after sending tens of thousands of troops and hundreds of tanks into Ukraine from Belarus.
Russian soldiers dug trenches and set up camps in areas including the so-called Red Forest—named after the color its trees turned following the 1986 explosion.
Russia's army withdrew around a month into the conflict, as part of a broader pullback after failing to encircle and capture the capital Kyiv amid Ukrainian resistance.
The remains of the plant are covered by an inner steel-and-concrete structure known as the sarcophagus, hastily built after the 1986 disaster.
A newer, hi-tech outer shell—the New Safe Confinement—was installed in 2016 and 2017, designed to eventually replace the sarcophagus, which was not intended as a permanent solution.
That outer structure was punctured by a Russian drone in February 2025, losing its ability to contain radiation.
In a report published in April, Greenpeace said the outer shell "cannot be repaired at the moment" and "cannot function as it was designed," adding there is "a possibility of radioactive releases."
Repairs are expected to take three to four years. The plant's director told Agence France-Presse (AFP) in December 2025 that another Russian strike could cause the radiation shelter to collapse.
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