- Fuel rods appear to be melting inside three over-heating reactors
- Experts class development as 'partial meltdown'
- Molten fuel could burn through reactor safety shields
- Earlier blast at Fukushima nuclear plant felt 25 miles away
- Eleven workers injured after hydrogen ignited
- 180,000 people have been evacuated from the area
- Engineers desperately trying to cool reactors with sea water
- Up to 160 people so far exposed to radiation
That means there is a risk that molten nuclear fuel can melt through the reactor's safety barriers and cause a serious radiation leak.
There have already been explosions inside two over-heating reactors at the Fukushima Dai-ichi nuclear plant, and the fuel rods inside a third were partially exposed as engineers desperately fight to keep them under control after the tsunami knocked out emergency cooling systems.
Japanese chief cabinet secretary Yukio Edano said it was 'highly likely' that the fuel rods inside all three stricken reactors are melting.
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