<human>:  When did the nuclear disaster at Chernobyl happen?
<bot>: The Chernobyl nuclear power plant accident happened on April 26, 1986. It was the worst nuclear accident in history. The explosion at Chernobyl released radiation into the atmosphere, and it contaminated large parts of the surrounding area. The accident was caused by a series of human errors, including a design flaw in the reactor core, and a flawed safety test. The explosion killed 31 people immediately, and it took decades for the radioactive contamination to die down.