Explosion rocks another Japanese nuclear reactor building
By the CNN Wire Staff
March 13, 2011 11:25 p.m. EDT

...The incident is the latest affecting the Daiichi, the hardest hit of several nuclear plants affected since Friday's 8.9-magnitude earthquake and subsequent tsunami.

Officials said that the explosion was likely caused by a buildup of hydrogen gas, similar to what had happened Saturday at the same nuclear plant's No. 1 reactor.

The 600 residents remaining within 20 kilometers (12 miles) of the plant, despite an earlier evacuation order, have been ordered to stay indoors, according to Edano.

Officials earlier said that they were operating on the presumption that there may be a partial meltdown in the No. 3 and No. 1 nuclear reactors at the Daiichi plant. Authorities have not yet been able to confirm a meltdown, because it is too hot inside the affected reactors to check.

The Tokyo Electric Power Company, which runs the plant, said in a press release late Sunday that radiation levels outside that plant remain high.

Japan's Kyodo newsagency, citing the same company, said that there were measurements of 751 microsieverts and 650 microsieverts of radiation early Monday. Both are above the legal limit, albeit less than one reading recorded Sunday. A microsievert is an internationally recognized unit measuring radiation dosage, with people typically exposed during an entire year to a total of about 1,000 microsieverts.

On Sunday, Chief Cabinet Secretary Yukio Edano said accumulating hydrogen gas "may potentially cause an explosion" in the building housing the No. 3 reactor at the Daiichi plant
...
Edano has said there have been no leaks of radioactive material at any plants. Radioactive steam has been released intentionally to lessen growing pressure in the two Daiichi reactors -- in an amount authorities have described as minimal.

Still, on Sunday, Edano said nine people who were evacuated from near the Daiichi plant tested positive for high radiation on skin and clothing. This is in addition to at least three electric company workers who fell ill due to possible exposure, the Tokyo Electric Power Co. said in a statement.

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