Apr 26, 2026 - 08:58 am April 26, marks the 40th anniversary of the Chernobyl nuclear disaster in Ukraine. At 01:23 that morning, while concluding a safety test, reactor No. 4 went into meltdown, triggering a massive steam explosion that sent radioactive fallout across Europe. It remains the largest nuclear disaster in history, with an environmental, social and healthcare cost estimated to have exceeded $700 billion.