How the nuclear emergency unfolded

Saturday's explosion at the Fukushima Daiichi nuclear made leaking radiation, or even a meltdown, the primary threat facing a country just beginning to grasp the scale of devastation from the earthquake and tsunami.Normal operationIn operation since the early 1970s, Japan’s Fukushima Daiichi nuclear plant uses six boiling water reactors, which rely on uranium nuclear fission to generate heat.