Huge Blast At Japan Nuclear Power Plant

UPDATE: Container housing reactor not damaged.

Likely a steam explosion, when the hot core hits the cooling water, BUT —

It is not yet clear in exactly what part of the plant the explosion occurred or what caused it.

The government of Fukushima prefecture said radiation levels at the plant over one hour were equivalent to the annual allowable exposure.

Officials ordered the evacuation zone around the plant expanded from a 10km radius to 20km. BBC correspondent Nick Ravenscroft said police stopped him 60km from the Fukushima-Daiichi plant.

Japan’s nuclear agency said on Saturday that radioactive caesium and iodine had been detected near the number one reactor of the power station.

The agency said this may indicate that containers of uranium fuel inside the reactor may have begun melting.

Japanese broadcaster NHK screened a before and after image showing the damaged Fukushima plant

The container housing the reactor was not seriously damaged in the explosion, Kyodo news agency quoted the Nuclear and Industrial Safety Agency as saying.

Air and steam, with some level of radioactivity, has been released from several of the reactors at both plants in an effort to relieve the huge amount of pressure building up inside.

Mr Kan said the amount of radiation released was “tiny”.