(Reuters) - A quake-hit nuclear plant where a reactor exploded has also lost the emergency cooling system at a second reactor, Japan's nuclear power safety agency said on Sunday.
The plant's operator, Tokyo Electric Power Co (TEPCO), said on Sunday morning it had started releasing air from a reactor container vessel at the No.3 reactor at its Fukushima Daiichi plant to lower pressure inside it and avoid any serious damage to the containment vessel.
"We are doing the two things at the same time - venting air out of the reactor and supplying water into the reactor," Chief Cabinet Secretary Yukio Edano told a news conference.
"Radiation released in the process is low enough not to affect people's health," he said.
Radiation levels have risen above the safety limit around TEPCO's nuclear plant and the company has informed the government of an "emergency situation", Kyodo agency reported on Sunday.
It did not pose an immediate threat to human health, the company said.
A similar rise in radiation levels occurred after the company released radioactive steam on Saturday from the plant's No.1 reactor to release pressure, also obliging it to notify authorities of an "emergency situation".
The attempt to release pressure from the No.1 reactor on Saturday blew off the roof and upper walls of the building housing it. But the safety agency said the explosion did not affect the containment vessel. No immediate risk was seen of similar further explosions, Edano said on Saturday.
To boost the cooling treatment, TEPCO began filling the damaged No.1 reactor with seawater and used boric acid to prevent it the reactor from reaching "criticality", or an uncontrolled nuclear reaction.
Seven boiling water reactors at the Fukushima Daiichi plant and the neighbouring Fukushima Daini plant, both operated by TEPCO, automatically shut down soon after the quake and subsequent tsunami on Friday that killed hundreds of residents along a lengthy stretch of Japan's northeast coastline.
The other three units had been under planned maintenance.
Following is a list of the manufacturers and the current status of reactors in the Fukushima Daiichi and Daini plants, excluding those under planned maintenance when the quake struck. Generation capacity is shown in megawatts.
Plant name Unit MW Mfr Status
Fukushima-Daiichi 1 460 GE Keeps filling with sea water
2 784 GE, Toshiba Preparing to release inner pressure
3 784 Toshiba Started on Sunday morning to release inner pressure
Fukushima-Daini 1 1,100 Toshiba Ready for releasing inner pressure
2 1,100 Hitachi Ready for releasing inner pressure
3 1,100 Toshiba Has been safely cooled
4 1,100 Hitachi Ready for releasing inner pressure
(Source: Tokyo Electric Power as of 0320 GMT on Sunday)
(Reporting by Risa Maeda, Kiyoshi Takenaka and Shinichi Saoshiro; Editing by Michael Watson)
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