By Mayumi Negishi and Chisa Fujioka
TOKYO (Reuters) - Highly radioactive water has leaked from a reactor at Japan's crippled nuclear complex, the plant's operator said on Monday, while environmental group Greenpeace said it had detected high levels of radiation outside an exclusion zone.
Reflecting growing unease about efforts to control the six-reactor Fukushima Daiichi complex, plant operator Tokyo Electric Power Co (TEPCO) had appealed to French companies for help, the Kyodo news agency said.
The plant, 240 km (150 miles) north of Tokyo, was damaged in a March 11 earthquake and tsunami that left more than 28,000 people dead or missing across northeastern Japan.
Fires, explosions and radiation leaks have repeatedly forced engineers to suspend efforts to stabilize the plant, including on Sunday when radiation levels spiked to 100,000 times above normal in water inside reactor No. 2.
A partial meltdown of fuel rods inside the reactor vessel was responsible for the high levels, although Chief Cabinet Secretary Yukio Edano said the radiation had mainly been contained in the reactor building.
But TEPCO later said radiation above 1,000 millisieverts per hour had been found in water in underground concrete tunnels that extend beyond the reactor.
That is the same as the level discovered on Sunday. The U.S. Environmental Protection Agency says a single dose of 1,000 millisieverts is enough to cause hemorrhaging.
TEPCO officials said the tunnels did not flow into the sea but the possibility of radioactive water seeping into the ground could not be ruled out.
The nuclear crisis has compounded Japan's agony after the magnitude 9.0 quake and huge tsunami devastated its northeast coast, turning whole towns into apocalyptic landscapes of mud and debris.
About a quarter of a million people are living in shelters and damage could top $300 billion, making it the world's costliest natural disaster.
The suffering may not be over.
Greenpeace said its experts had confirmed radiation levels of up to 10 microsieverts per hour in the village of Iitate, 40 km (25 miles) northwest of the plant. It called for the extension of a 20-km (12-mile) evacuation zone.
"It is clearly not safe for people to remain in Iitate, especially children and pregnant women, when it could mean receiving the maximum allowed annual dose of radiation in only a few days," Greenpeace said in a statement.
More than 70,000 people have been evacuated from an area within 20 km (12 miles) of the plant and another 130,000 people within a zone extending a further 10 km are recommended to stay indoors. They have been encouraged to leave.
Beyond the evacuation zone, traces of radiation have turned up in tap water in Tokyo and as far away as Iceland.
Japanese officials and international experts have generally said the levels away from the plant were not dangerous for people, who anyway face higher radiation doses on a daily basis from natural substances, X-rays or flights.
But Greenpeace urged the government to acknowledge the danger and "stop choosing politics over science".
Nuclear safety agency deputy Hidehiko Nishiyama said the environmental group's measurement was not reliable and hardly any people were still living in that area. A Greenpeace nuclear expert later defended the reliability of their findings.
CALL FOR HELP
At the weekend, the spike in radiation forced a suspension of work at the reactor, with experts warning that Japan faced a long fight to contain the world's most dangerous atomic crisis in 25 years.
"This is far beyond what one nation can handle -- it needs to be bumped up to the U.N. Security Council," said Najmedin Meshkati, of the University of Southern California.
TEPCO, which has conceded it faces a protracted and uncertain operation to contain the crisis, sought outside help from French firms including Electricite de France SA and Areva SA, a French government minister said.
A spokesman for state-owned nuclear reactor maker Areva said the company was studying the request.
Murray Jennex, a nuclear power plant expert and associate professor at San Diego State University, said "there's not really a plan B" other than to dry out the plant, get power restored and start cooling it down.
"What we're now in is a long slog period with lots of small, unsexy steps that have to be taken to pull the whole thing together," he said by telephone. The good news, he said, was that the reactor cores appeared to be cooling down.
There was good news as well about the radiation levels in the sea just off the plant, which skyrocketed on Sunday to 1,850 times normal. Those had come down sharply, the nuclear safety agency said the next day.
Though experts said radiation in the Pacific would quickly dissipate, the levels at the site are clearly dangerous, and the 450 or so engineers there have won admiration and sympathy around the world for their bravery and sense of duty.
Last week, two workers at Fukushima were injured with radiation burns after water seeped over their shoes, and on Sunday, engineers had to abandon reactor No. 2 after the new reading.
The world's worst nuclear disaster since Chernobyl in 1986 has prompted a reassessment of nuclear power across the world. It had its most direct political impact yet in foreign politics in Germany at the weekend.
Chancellor Angela Merkel's Christian Democrats lost control of Germany's most prosperous state, Baden-Wuerttemberg, as anti-nuclear sentiment benefited her opponents in a regional vote.
Residents of the northeast have been rattled by aftershocks from the strongest earthquake in Japanese history, including a magnitude 6.5 tremor on Monday that triggered a tsunami warning.
"I lived through World War Two, when there was nothing to eat and no clothes to wear. I'll live through this," said Mitsuharu Watanobe, sitting cross-legged on a blanket in an evacuation center in Fukushima city.
"But the scary thing is the radiation. There is a gap between what the newspapers write and what the government is saying. I want the government to tell the truth more."
The latest death toll was 11,004 people, with 17,339 people missing 17 days after the disaster.
(Additional reporting by Elaine Lies, Yoko Kubota and Shinichi Saoshiro in Tokyo, David Dolan in Fukushima, Gerard Wynn in London, Alister Doyle in Oslo; Writing by Robert Birsel; Editing by Alex Richardson)