The Test That Went Wrong

At 1:23 AM on April 26, 1986, engineers at Reactor No. 4 were running a safety test — ironically, one meant to verify the plant could handle an emergency. The test required disabling safety systems that were supposed to protect the reactor from exactly the scenario being simulated.

What followed was a chain of operator errors, design flaws, and bureaucratic pressure. When the emergency shutdown was triggered, the control rods began to enter the core, but their graphite tips initially increased reactivity. Within seconds, the reactor's power spiked to roughly 100 times its normal level; deformation then left rods stuck as two explosions blew the 2,000-ton reactor lid through the roof and released 400 times more radioactive material than the Hiroshima bomb.