Fukushima No.1 nuclear power plant
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Japan nuclear power plant: A look inside

The cooling systems of two reactors at the Fukushima No.1 nuclear power plant failed after the 8.9-magnitude quake struck off the north-east coast.

On Saturday, a huge explosion blew apart the building housing reactor 1, where technicians had been venting steam to cool the reactor.

Sea water is being injected into the other reactor in an attempt to cool it.

So what is going on inside the plant, and how dangerous is the situation there?

The BBC's Science Correspondent David Shukman reports.

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