TOKYO (Reuters) - The operator of the nuclear power plant at the centre of a radiation scare after being disabled by Japan's earthquake and tsunami confirmed on Tuesday that there had been meltdowns of fuel rods at three of its reactors.
Tokyo Electric Power Co said meltdowns of fuel rods at three reactors at the Fukushima Daiichi plant occurred early in the crisis triggered by the March 11 disaster.
The government and outside experts had said previously that fuel rods at three of the plant's six reactors had likely melted early in the crisis, but the utility, also known as Tepco, had only confirmed a meltdown at the No.1 reactor.
Tepco officials said a review since early May of data from the plant concluded the same happened to reactors No.2 and 3.
The preliminary finding, which was reported to Japan's nuclear safety agency, represents part of an initial effort to explain how events at Fukushima spiralled out of control early in the crisis.
Also on Tuesday, the government appointed Yotaro Hatamura, a Tokyo University professor of engineering who has studied how complex systems and designs fail, to head a committee that will investigate the cause and handling of the nuclear crisis.
The moves came as a team of investigators from the International Atomic Energy Agency began a two-week visit to Japan to prepare a report on the accident to be submitted to the United Nations agency in June.
Some analysts said the delay in confirming the meltdowns at Fukushima suggested the utility feared touching off a panic by disclosing the severity of the accident earlier.
"Now people are used to the situation. Nothing is resolved, but normal business has resumed in places like Tokyo," said Koichi Nakano, a political science professor at Tokyo's Sophia University.
Nakano said that by confirming the meltdowns now, Tepco may be hoping the news will have less impact. The word "meltdown" has such a strong connotation that when the situation was more uncertain more people would likely have fled Tokyo, he said.
Engineers are battling to plug radiation leaks and bring the plant 240 km (150 miles) northeast of Tokyo under control more than two months after the 9.0 magnitude earthquake and deadly tsunami that devastated a vast swathe of Japan's northeast coastline and tipped the economy into recession.
The disaster has triggered a drop of more than 80 percent in Tepco's share price and forced the company to seek government aid as it faces compensation liabilities that some analysts say could top $100 billion.
Japanese trade minister Banri Kaieda said the government would approve the formation of a committee later on Tuesday that will make sure Tepco follows through with restructuring plans.
Tepco officials said damage to the No.2 reactor fuel rods had begun three days after the quake, with much of the fuel rods eventually melting and collecting at the bottom of the pressure vessel containing them.
Fuel rods in the No.3 reactor were damaged by the afternoon of March 13, they said.
The Tepco officials repeated that the tsunami had disabled power to the reactors and knocked out their cooling capability.
Hidehiko Nishiyama, a spokesman for the government's Nuclear and Industrial Safety Agency, expressed a similar view.
"We don't think the quake affected the important parts of the plant, such as its cooling capacity," Nishiyama told reporters on Tuesday, although he added there were still some aspects that needed to be clarified by inspecting the site directly.
That process is likely to make months because of the high radiation readings in areas of the plant, experts have said.
"It could very well be that Tepco is rushing to conclude that the tsunami is to blame to prevent further questions and give more momentum to the nuclear camp. It's not just Tepco, it's the whole nuclear industry, maybe business circles as a whole. It's highly political," said Sophia University's Nakano.
Others said that from a very early stage the tsunami, not the quake, was the likely cause of the overheating and subsequent damage of the reactors at Daiichi.
"As with the other nuclear reactors, such as Onagawa (in northeastern Japan), those at Daiichi deactivated after the quake. It is our belief that it was the tsunami that knocked out power and took out the systems and pumps that cool the reactors, resulting in their damage and radiation leakage," said Kazuhiko Kudo, a Kyushu University professor who specialises in nuclear engineering.
Despite a steady flow of information on how the clean-up is proceeding -- Tepco and the government's nuclear watchdog hold news conferences twice a day on most weekdays -- the authorities have faced criticism for what some have said is a lack of timely disclosure.
"I am very sorry that the public is mistrustful of the various disclosures made by the government on the accident," Prime Minister Naoto Kan said in parliament on Monday.
(Additional reporting by Linda Sieg and Yoko Nishikawa; Editing by Chris Gallagher and Michael Watson)