What happened?
The day before the nuclear disaster, operators were preparing for a one-time shutdown to perform routine maintenance on one of the reactors. The operators ended up disabling plant equipment including the automatic shutdown mechanisms, which was later discovered to be a violation of safety regulations.
A photo is displayed at the Ukrainian National Chernobyl Museum on April 20, 2007, in Kiev, Ukraine. (Photo by Francois LOCHON/Gamma-Rapho via Getty Images)
At 1:23 a.m. on April 26, an immense amount of steam was created, which caused more reactivity in the nuclear core of reactor number 4. There was a power surge that caused a massive explosion, detaching the 1,000-ton plate covering the reactor and releasing radiation into the atmosphere.