<human>:  When did the nuclear disaster at Chernobyl happen?
<bot>: The Chernobyl nuclear power plant accident happened on April 26, 1986. It was a major nuclear accident that released large amounts of radioactive material into the environment. The accident resulted in the evacuation of over 100,000 people living within a 30 km radius of the plant, and the deaths of an estimated 4,000 people.