Workers at the Fukushima 1 nuclear power plant in the north-east of the country pumped seawater into three reactors in a last-ditch attempt to make them safe after emergency cooling systems failed to stabilise the radioactive cores.
More than 200,000 people were evacuated as officials imposed a 20km exclusion zone around the power station and a 10km zone surrounding the Fukushima 2 power plant nearby. Japanese officials told the International Atomic Energy Agency they would distribute potassium iodide pills as a precaution against an increased risk of thyroid cancer from radiation.
The most urgent crisis centred on Fukushima 1, where officials were braced for an explosion similar to one that blew the roof off the building that housed reactor 1 yesterday morning, after hydrogen escaped from the reactor as engineers vented steam from the pressurised vessel.
The failure of the cooling system caused uranium fuel rods to overheat and split the cooling water into hydrogen and oxygen. The hydrogen exploded, devastating the building, but the containment vessel around the reactor was undamaged, Japan's chief cabinet secretary, Yukio Edano, said.
Desperate engineers were forced to vent steam from two other reactors at the power station before pumping in seawater, despite the risk of triggering further explosions.
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