<human>:  When did the Chernobyl disaster happen?
<bot>: The Chernobyl disaster happened on 26 April 1986. It was a nuclear accident that occurred at the Chernobyl Nuclear Power Plant in Ukraine. It was the worst nuclear accident in history, and resulted in the deaths of thousands of people and the forced evacuation of hundreds of thousands of people. The disaster was caused by a series of human errors, including the failure of safety systems and the actions of the plant operators.