Describe the disaster at Chernobyl.

On April 26, 1986, the world's worst nuclear accident happened at the Chernobyl plant near Pripyat, Ukraine, in the Soviet Union. An explosion and fire in the No. 4 reactor sent radioactivity into the atmosphere. Plant operators made several mistakes, creating a poisonous and unstable environment in the reactor core. A peculiarity of the design of the control rods caused a dramatic power surge as they were inserted into the reactor.