The story of how a massive arched shelter was slid into place over the Chernobyl nuclear disaster site in Ukraine. The inside story of a unique engineering feat at the site of the world's worst nuclear disaster, as technicians move an enormous roof over the still irradiated remains of the plant's No 4 reactor. The superstructure is intended to contain radiation from the nuclear waste within the exploded reactor. Chernobyl's reactor No 4 exploded on April 26, 1986, and over the ensuing 10 days, its nuclear fuel continued to burn, issuing clouds of poisonous radiation and contaminating as much as three quarters of the European continent, hitting northern Ukraine, Russia and Belarus, especially hard.