MOSCOW (Reuters) - The concrete shield thrown up to block radiation escaping the Chernobyl nuclear power station after it exploded in 1986 is collapsing and needs urgent reinforcement, Russia's atomic energy minister said Tuesday. Alexander Rumyantsev was speaking at a news conference almost exactly 17 years after one of Chernobyl's four reactors exploded and spewed clouds of radioactivity over much of Europe in the world's worst civilian nuclear disaster. "We can see a situation where the roof could fall in, or rather the supports that hold up the roof could fall down," he said, adding that the concrete itself was...