The explosion and fire at Reactor No. 4 of the Chernobyl Nuclear Power Plant in Soviet Ukraine on April 26, 1986 — the worst nuclear-power accident in history — which killed dozens in the immediate aftermath and released radioactive contamination across Europe, forcing the permanent evacuation of Pripyat, exposing the Soviet system's institutional pathologies, and accelerating the political dynamics that would end the USSR by 1991.
At 1:23 in the morning on April 26, 1986, a safety test at a Soviet nuclear plant went wrong in a way its operators did not know was possible. The reactor design contained a flaw — confirmed and classified by Soviet engineers years earlier — that made it briefly more reactive as it began to shut down, rather than less. When the test hit that window, the reactor surged to roughly thirty times its maximum rated power in a fraction of a second. Two explosions followed. The graphite core burned for ten days. For the first forty-eight hours, the Soviet government told its own citizens almost nothing.