Query: When did the Chernobyl disaster happen?
Context: On September 30, 1989, thousands of Belorussians, denouncing local leaders, marched through Minsk to demand additional cleanup of the 1986 Chernobyl disaster site in Ukraine. Up to 15,000 protesters wearing armbands bearing radioactivity symbols and carrying the banned red-and-white Belorussian national flag filed through torrential rain in defiance of a ban by local authorities.