The explosion at Chernobyl, Ukraine, in 1986 set the standard as the worst accident in the history of nuclear power. Today, the government of Japan officially upgraded the Fukushima-Daiichi disaster to equal Chernobyl, giving it 7 on a scale of 7. But comparison of the two accidents involves not just the amount of radiation released but the way the disasters have developed over time. Geoff Brumfiel, senior reporter with Nature magazine, has been covering the nuclear accident in Japan.