The Chernobyl disaster was nuclear disaster(reactor core) that occurred on April 26, 1986 in now Ukraine. A nuclear disaster is an event that has led to a significant amount of damage to the environment and to the people. Some examples are:large radioactivity release or a reactor core melt which also releases a large damaging amount of radioactivity.
Chernobyl after nuclear disaster.
The video contains details of what exactly happened on April 26,1986.
Children born after 1986 have a higher chance of having heart defects, there was an increase in cancers, 99 percent of the environment is contaminated.