On April 26, 1986, the world's worst nuclear accident happened<span> at the </span>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. <span>A peculiarity of the design of the control rods </span>caused<span> a dramatic power surge as they were inserted into the reactor.</span>
