Overview
- Reactor 4 exploded during a planned safety test in April 1986 that checked how long the turbines could keep coolant pumps running after a power loss.
- Operators led by deputy chief engineer Anatoly Dyatlov ran the reactor at very low power and bypassed safeguards, which left the core unstable and hard to control.
- When shift chief Alexander Akimov ordered the AZ-5 shutdown, graphite-tipped control rods displaced water in the core, spiked reactivity, and triggered steam explosions that exposed and ignited the graphite moderator.
- Evacuation of the nearby city of Pripyat came about 36 hours later, firefighters and plant staff suffered acute radiation sickness, and many later died at Moscow’s Hospital Number Six.
- Declassified East German Stasi files describe KGB–Stasi coordination to hide radiation data, script different press lines for audiences, and push contaminated food to West Germany or distribute it across the USSR outside Moscow to mute public outrage.