Tokyo: Japanese authorities Sunday fought to avert a nuclear disaster after problems at two earthquake-damaged nuclear power plants, but the government rejected reports of a meltdown at the Fukushima I plant.
There had been no meltdown in reactor number 3, said government spokesman Yukio Edano, who had earlier said that a "partial meltdown" could not be ruled out.
After Friday`s massive earthquake, which triggered a tsunami, there were fears of a meltdown in two of the plant`s reactors as cooling systems broke down.
A meltdown is a severe nuclear incident in which the reactor core is damaged by overheating.
But radiation levels had surpassed the legal limits at Fukushima I in the north-eastern prefecture of Fukushima, 240 km north of Tokyo, Edano said.
Radiation was at 882 microsievert per hour and briefly topped 1,204. Japan allows an hourly exposure of 500 microsievert, which measures the biological effects of radiation.
Hisanori Nei, an official at the Nuclear and Industrial Safety Agency, was quoted by Jiji Press agency as saying there was a high possibility of a partial meltdown ahead of a vapour explosion at reactor number 1 Saturday. It would have been the first partial meltdown in Japan`s history, he said.
Nuclear reactors at the Fukushima I and II plants lost their cooling functions after power and backup generators were cut off Friday, operator Tokyo Electric Power Co (TEPCO) said.
Engineers were in the process Sunday of releasing another dose of radioactive steam from a second reactor into the atmosphere, Edano said.
According to Japanese news reports, the cooling water in the reactor has decreased so much that up to 3 metres of the fuel rods were exposed.
Fresh water was injected into the cooling system of the number 3 reactor, Edano said. Radiation levels at that reactor were "very small and under control", he said.
However, a senior official in the Economy, Trade and Industry Ministry told a news conference, "I don`t think the fuel rods themselves have been spared damage," Kyodo news agency reported.
On Saturday, an explosion destroyed part of the containment structure around reactor number 1 at the plant. TEPCO said it was caused by water vapour.
Technicians had begun to use seawater and boron to reduce pressure, releasing a cloud of steam containing radioactive elements, such as caesium-137.
The International Atomic Energy Agency (IAEA) said it had been informed by Japanese authorities that the explosion occurred outside the primary containment vessel, not inside. TEPCO confirmed that the primary containment remained intact.
About 200,000 people have been evacuated from a 20-km safety zone around the two plants. At least 19 people had been exposed to radiation, Kyodo reported.
Meanwhile the IAEA said Sunday that Japan had informed it that it had declared the first, or lowest, state of emergency at Onagawa nuclear power plant in Miyagi prefecture, the hardest hit by the earthquake and tsunami.
"The alert was declared as a consequence of radioactivity readings exceeding allowed levels in the area surrounding the plant," the IAEA said. The reactors at the plant were however "under control".
Prime Minister Naoto Kan said he had approved conducting planned power outages starting Monday to prevent any massive supply disruptions. TEPCO said the outages would be done by region, for periods of three hours at a time.
In response to a request for help with energy supplies, Russia Sunday sent a tanker holding 19,500 cubic metres of liquefied natural gas (LNG) to Japan, the Interfax news agency reported. A second delivery of 100,000 cubic metres was scheduled for Monday.
"Japan has already asked for an increase in energy deliveries," Russian Deputy Prime Minister Igor Sechin said.
South Korea Sunday also redirected some of its incoming shipments of LNG to send them to Japan to help address potential energy shortages, the Economy Ministry in Seoul said.
Japan is the largest and South Korea the second-largest importer of LNG in the world.