By Yoko Nishikawa
TOKYO (Reuters) - Plutonium found in soil around the crippled Fukushima nuclear complex added to mounting problems on Tuesday in Japan's battle to contain the world's worst atomic crisis since Chernobyl.
Plant operator Tokyo Electric Power Co (TEPCO) said the radioactive material, which is used in nuclear bombs, was traced in soil at five locations at the plant, hit by an earthquake and tsunami on March 11.
The under-pressure company stressed the traces were not at dangerous levels.
"Plutonium found this time is at a similar level seen in soil in a regular environment and it's not at the level that's harmful to human health," TEPCO vice-president Sakae Muto told reporters at a briefing.
Muto said the level was similar to that found in the past in other parts of Japan as a result of nuclear testing abroad. He said it was unclear where the plutonium was from, although it appeared two of the five finds were related to damage from the plant rather than from the atmosphere.
The International Atomic Energy Agency (IAEA), the United Nations nuclear watchdog, said the find was to be expected.
"It is reactor-grade plutonium which is formed into the reactor as far as we can see," IAEA official Denis Flory said. "It means that there is degradation of the fuel, which is not news. We have been saying that consistently for so many days."
The plutonium discovery, from samples taken a week ago, was reported after TEPCO said on Monday highly radioactive water had been leaking from one reactor.
In a growing list of problems, the environmental group Greenpeace said it had detected high levels of radiation outside an exclusion zone.
FIRES, EXPLOSIONS, RADIATION
Fires, explosions and radiation leaks have forced engineers to suspend efforts to stabilize the plant, including at the weekend 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.
TEPCO said later radiation above 1,000 millisieverts per hour had been found in water in concrete tunnels that extend beyond the reactor.
The nuclear crisis has compounded Japan's agony after the magnitude 9.0 quake and huge tsunami devastated its northeast coast, turning towns into apocalyptic landscapes of mud and debris.
More than 11,000 people are confirmed dead and 17,339 are missing. About a quarter of a million people are living in shelters and the cost of damage could top $300 billion, making it the world's costliest natural disaster.
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 130,000 people within a zone extending a further 10 km are advised to stay indoors. They have been encouraged to leave.
Beyond the evacuation zone, traces of radiation have been found tap water in Tokyo and as far away as Iceland.
"POLITICS OVER SCIENCE"
Japanese officials and international experts have generally said the levels away from the plant were not dangerous for people, who in any case face higher radiation doses on a daily basis from natural sources, X-rays or flying.
Greenpeace urged the government to acknowledge the danger and "stop choosing politics over science."
The deputy head of the nuclear safety agency, Hidehiko Nishiyama, said the environmental group's measurement was not reliable and hardly any people were still living in that area.
TEPCO, which has conceded it faces a long 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.
Murray Jennex, a nuclear power plant expert and associate professor at San Diego State University in the United States, 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.
There was good news at least 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.
Although experts said radiation in the Pacific would quickly dissipate, the levels at the site were clearly dangerous, and the 450 or so engineers there have won admiration and sympathy around the world for their bravery and sense of duty.
(Additional reporting by Elaine Lies, Yoko Kubota and Shinichi Saoshiro in Tokyo, David Dolan in Fukushima, Gerard Wynn in London, Alister Doyle in Oslo, Sylvia Westall in Vienna; Writing by Andrew Cawthorne and Robert Birsel; editing by Andrew Dobbie)