By ERIC TALMADGE
The Associated Press
Wednesday, July 18, 2007; 2:36 AM

KASHIWAZAKI, Japan -- A top power company official defended safety standards at an earthquake-ravaged nuclear plant Wednesday, even as the company said a radioactive leak was bigger than first reported and the mayor ordered the plant be shut down until its safety could be confirmed.

Plant operator Tokyo Electric Power Co. announced that a leak of radioactive water into the Sea of Japan was actually 50 percent bigger than initially announced Monday night. But the levels were still well below danger levels, it said.

"We made a mistake in calculating the amount that leaked into the ocean. We apologize and make correction," the statement said. Spokesman Jun Oshima said the amount was still "one-billionth of Japan's legal limit."

Hiroshi Aida, mayor of Kashiwazaki, a city near the epicenter that is home to the plant and 93,500 people, ordered operations at the plant halted Wednesday for "safety reasons."

"I am worried," he said. "It would be difficult to restart operations at this time. ... The safety of the plant must be assured before it is reopened."

The International Atomic Energy Agency, meanwhile, pressed Japan to undertake a transparent and thorough investigation of the accidents to see if there are lessons that can be applied to nuclear plants elsewhere in the world.

Adding to the urgency was new data from aftershocks of Monday's deadly 6.8-magnitude quake suggesting a fault line may run underneath the mammoth power plant.

Kashiwazaki-Kariwa is the world's largest nuclear plant in power output capacity. Signs of problems after Monday's quake came first not from the officials, but in a plume of smoke that rose up when the quake triggered a small fire at an electrical transformer.

It was announced only 12 hours later that the quake also caused a leak of about 315 gallons of water containing radioactive material. Officials said the water leak was well within safety standards. The water was flushed into the sea.

Later Tuesday, it said 50 cases of "malfunctioning and trouble" had been found. Four of the plant's seven reactors were running at the time of the quake, and they were all shut down automatically by a safety mechanism.

Tsunehisa Katsumata, president of plant operator Tokyo Electric Power Co., toured the site Wednesday morning, declaring it "a mess" and apologizing for "all the worry and trouble we have caused."

"It is hard to make everything go perfectly," he said. "We will conduct an investigation from the ground up. But I think fundamentally we have confirmed that our safety measures worked."

Speaking in Malaysia, IAEA chief Mohamed ElBaradei said a thorough review was key and offered to have his Vienna-based agency pull together global experts.

"It doesn't mean that the reactor structure or system has been damaged," ElBaradei said. "I would hope and I trust that Japan would be fully transparent in its investigation of that accident. The agency would be ready to join Japan through an international team in reviewing that accident and drawing the necessary lessons."

Meanwhile, TEPCO spokesman Hiroshi Itagaki said that information accumulated by studying aftershocks shows that a fault line stretches under the ocean near the coast, which is not far away from the plant. He declined to say how close to the plant the fault might come, but the company is planning to further study the issue.

Osamu Kamigaichi, an official at Japan's Meteorological Agency, which monitors earthquakes, said it was possible the fault line stretched in the direction of the nuclear facility and may reach underneath its grounds.

Across town, more than 8,000 residents hunkered down for their second night in shelters. The death toll _ nine, with one person missing _ was not expected to rise significantly. Most of the newer parts of town escaped major damage.

For residents, thousands of whom work at the plant, the controversy over its safety compounded already severe problems, which included heavy rains and the threat of landslides, water and power outages, and spotty communications.

"Whenever there is an earthquake, the first thing we worry about is the nuclear plant. I worry about whether there will be a fire or something," said Kiyokazu Tsunajima, a tailor who sat outside on his porch with his family, afraid an aftershock might collapse his damaged house.

"It's frightening, but I guess we are used to it," said Ikuko Sato, a young mother who was spending the night in a crowded evacuation center near her home, which was without water or power.

"It's almost the summer swimming season," she said. "I wonder if it'll be safe to go in the water."

The area around Kashiwazaki was hit by an earthquake three years ago that killed 67 people, but the plant suffered no damage.

The malfunctions and a delay in reporting them fueled concerns about the safety of Japan's 55 nuclear reactors, which have suffered a string of accidents and cover-ups. Nuclear power plants around Japan were ordered to conduct inspections.

The plant in Kashiwazaki-Kariwa, 135 miles northwest of Tokyo, eclipsed a nuclear power station in Ontario as the world's largest power station when it added its seventh reactor in 1997.

The Japanese plant, which generates 8.2 million kilowatts of electricity, has been plagued with mishaps. In 2001, a radioactive leak was found in the turbine room of one reactor.

The plant's safety record and its proximity to a fault line prompted residents to file lawsuits claiming the government had failed to conduct sufficient safety reviews when it approved construction of the plant in the 1970s. But in 2005, a Tokyo court threw out a lawsuit filed by 33 residents, saying there was no error in the government safety reviews.

Environmentalists have criticized Japan's reliance on nuclear energy as irresponsible in a nation with such a vulnerability to powerful quakes.

"This fire and leakage underscores the threat of nuclear accidents in Japan, especially in earthquake zones," said Jan Beranek, a Greenpeace official in Amsterdam. "In principle, it's a bad idea to build nuclear plants in earthquake-prone areas."

Japan has a history of nuclear accidents, some of them deadly.

In 2004, five workers at the Mihama nuclear plant in western Japan were killed and six were injured after a corroded pipe ruptured and sprayed plant workers with boiling water and steam. The accident was the nation's worst at a nuclear facility.

The U.S. Nuclear Regulatory Commission requires that nuclear plants be built with the capacity to withstand the strongest earthquake to hit its site within 100 years. In a "safe shutdown earthquake," the chain reaction in the reactor stops, but the cooling system keeps running so excess heat is carried away from the core.

William Miller, a professor of nuclear engineering at the University of Missouri, said the Kashiwazaki-Kariwa plant "did what it was supposed to. It shut down."

Although its operator said there were leaks, Miller called the amounts he had heard were "so small as to be negligible."

However, David Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists, noted that fire and loss of power, both of which occurred at Kashiwazaki-Kariwa, are the two most likely causes of meltdowns at nuclear facilities.

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Associated Press writers Hiroko Tabuchi and Kozo Mizoguchi in Tokyo and Sarah DiLorenzo in New York contributed to this report.