NOVA: Building Chernobyl's Mega Tomb In 1986, in the heart of the Ukraine, the Chernobyl nuclear reactor exploded, releasing 400 times more radiation than the Hiroshima Bomb. It was the world's worst nuclear disaster. Thirty workers died. 50,000 people fled the nearest city. And radioactive fallout made an area larger than Long Island a no-go zone. Hastily, a so-called "sarcophagus" was built to contain the radioactive materials that lingered at the site after the explosion. But thirty years later, the sarcophagus is crumbling, and another disaster at Chernobyl looms.