In 1986 a catastrophic blast, 400 times more potent than the Hiroshima bomb, blew the lid off Chernobyl's Reactor No. Four, igniting fires that burned for days and sending a radioactive cloud across Europe. Ill-equipped workers heroically sealed the smoldering reactor in a concrete sarcophagus, but the hastily constructed shelter was only built to last 30 years. Now, 30 countries have come together to pay for a 25,000-ton steel shelter which will...