By Kiyoshi Takenaka and Yoko Kubota
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 27,000 people dead or missing across northeast 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 of radiation at that reactor although Chief Cabinet Secretary Yukio Edano said the radiation had mainly been contained in the reactor building.
TEPCO later said radiation above 1,000 millisieverts per hour was found in water in tunnels used for piping outside 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 (one sievert) is enough to cause hemorrhaging.
TEPCO officials said the underground tunnels did not flow into the sea but the possibility of radioactive water seeping into the ground could not be ruled out.
Greenpeace said its experts had confirmed radiation levels of up to 10 microsieverts per hour in Iitate, a village 40 km (25 miles) northwest of the plant. (One microsievert = one thousandth of a millisievert). 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 are not dangerous for humans, 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: "The authorities must stop choosing politics over science."
On the weekend, the spike in radiation levels 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. "In my humble opinion, this is more important than the Libya no-fly zone."
TEPCO, which has conceded it faces a protracted and uncertain operation to contain the crisis, sought outside help, asking help from French firms including Electricite de France SA and Areva SA, Kyodo reported.
SEA RADIATION DROPS SHARPLY
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, Hidehiko Nishiyama, deputy director general of the Nuclear and Industrial Safety Agency, told a news conference on Monday.
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 to their legs after water seeped over their shoes, and on Sunday, engineers had to abandon reactor No. 2 after the new reading.
One long-term solution may be to entomb the Fukushima reactors in sand and concrete as happened at Chernobyl, Ukraine, after the 1986 disaster that was the world's worst.
The Japan crisis 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.
Asked about Japan's plans for nuclear power, Edano said the priority was to resolve the crisis, then an assessment could be made.
The nuclear crisis has compounded Japan's agony after the magnitude 9.0 quake and massive tsunami devastated its northeast coast, turning whole towns into apocalyptic-looking landscapes of mud and debris.
Residents there have been repeatedly 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 10,804 people, with 16,244 people missing 17 days after the disaster. 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.