By Chizu Nomiyama and Kazunori Takada
TOKYO (Reuters) - Plutonium found in soil at the Fukushima nuclear complex heightened alarm on Tuesday over Japan's battle to contain the world's worst atomic crisis in 25 years, as pressure mounted on the prime minister to widen an evacuation zone around the plant.
Some opposition lawmakers blasted Naoto Kan in parliament for his handling of the disaster and for not widening the exclusion zone. Kan said he was seeking advice on such a step, which would force 130,000 people to move in addition to 70,000 already displaced.
The drama at the six-reactor facility has compounded Japan's agony after an earthquake and tsunami on March 11 left more than 28,000 people dead or missing in the devastated northeast.
In a gesture of support, France said it had sent two nuclear experts to Japan to help contain the accident and French President Nicolas Sarkozy will visit on Thursday for a meeting with Kan.
France is the world's most nuclear-dependent country, producing 75 percent of its power needs from 58 nuclear reactors, and selling state-owned Areva's reactors around the world. Sarkozy will be the first foreign leader to visit since the earthquake.
In the latest blow to hopes authorities were gradually getting the plant under control, operator Tokyo Electric Power Co said plutonium was found at low-risk levels in soil samples at the facility.
A by-product of atomic reactions and also used in nuclear bombs, plutonium is highly carcinogenic and one of the most dangerous substances on the planet, experts say.
They believe some of the plutonium may have come from spent fuel rods at Fukushima or damage to reactor No. 3, the only one to use plutonium in its fuel mix.
Japan's Nuclear and Industrial Safety Agency said while the plutonium levels were not harmful to human health, the discovery could mean the reactor's containment mechanism had been breached.
"Plutonium is a substance that's emitted when the temperature is high, and it's also heavy and so does not leak out easily," agency deputy director Hidehiko Nishiyama told a news conference.
"So if plutonium has emerged from the reactor, that tells us something about the damage to the fuel. And if it has breached the original containment system, it underlines the gravity and seriousness of this accident."
Sakae Muto, a Tokyo Electric vice-president, said the traces of plutonium-238, 239 and 240 were in keeping with levels found in Japan in the past due to particles in the atmosphere from nuclear testing abroad.
"I apologize for making people worried," Muto said.
With towns on the northeast coast reduced to apocalyptic landscapes of mud and debris following the quake and tsunami, more than a quarter of a million people are homeless. The event may be the world's costliest natural disaster, with estimates of damage topping $300 billion.
Workers at Fukushima may have to struggle for weeks or months under extremely dangerous conditions to re-start cooling systems vital to control the reactors and avert total meltdown.
On Monday, highly contaminated water was found in concrete tunnels extending beyond one reactor, while at the weekend radiation hit 100,000 times over normal in water inside another.
That poses a major dilemma for Tokyo Electric, which wants to douse the reactors to cool them, but not worsen the spread of radiation.
Japan's nuclear safety agency said fuel rods in the plant's reactors 1, 2 and 3 were damaged and there was a high possibility of some leakage from their containment vessels.
The crisis, the worst nuclear accident since Chernobyl in 1986, has contaminated vegetables and milk from the area, as well as the surrounding sea. U.S. experts said groundwater, reservoirs and the sea all faced "significant contamination".
A Tokyo Electric official told a briefing he could not rule out the possibility that radioactive water could still be entering the sea, though there was no continuous flow.
Tokyo Electric has sought help from French companies including Electricite de France SA and Areva SA.
French Ecology Minister Nathalie Kosciusko-Morizet said on Tuesday that experts from Areva and nuclear research body CEA had been sent to Japan "to share our experience on pumping and the treatment of radioactive water".
As well as seeking help from France, Japan is also consulting the United States.
The government has declined to outline any specific plan for its nuclear energy policy but said renewable energy would play an important role in future.
EVACUATION ZONE DILEMMA
Experts have said the lack of information and some inconsistent data made it hard to understand what was happening at Fukushima, which appears to have moved from a core-meltdown phase to one in which management of released radioactivity is paramount.
Another pressing concern has been the well-being of people living near the plant. More than 70,000 people have been evacuated from within 20 km (12 miles) of the facility.
But opposition MP Yosuke Isozaki blasted Kan for not ordering people living between 20 km and 30 km (12-19 miles) from the plant to also leave.
"Is there anything as irresponsible as this?" Isozaki asked.
The 130,000 people living inside the wider zone have been encouraged -- but not ordered -- to leave.
Environmental group Greenpeace has urged an extension of the 20-km evacuation zone while the United States has recommended its citizens who live within 80 km (50 miles) of the plant to leave or shelter indoors.
Kan, leading Japan during its worst crisis since World War Two, was already deeply unpopular and under pressure to resign when the crisis began.
He repeatedly defended his decision to fly over the stricken nuclear site a day after the quake, saying it had been important to see it for himself. His top spokesman on Monday denied the visit had delayed operations to cool the reactors, as some media had reported.
The crisis has also put enormous pressure on Tokyo Electric, criticised for safety lapses and a slow disaster response. Its boss, Masataka Shimizu, has barely been seen.
The government might nationalize Tokyo Electric to deal with the crisis, National Strategy Minister Koichiro Gemba said. Its shares have fallen almost 75 percent since the quake including a 19 percent tumble on Tuesday to a 47-year low.
Beyond the evacuation zone, traces of radiation have been found 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 human beings, who in any case face higher radiation doses on a daily basis from natural sources, X-rays or flying.
(Additional reporting by Linda Sieg, Mayumi Negishi, Yoko Nishikawa, leika Kihara and Phil Smith in Tokyo, Timothy Gardner in Washington, Sylvia Westall in Vienna, David Sheppard in New York, Eileen O'Grady in Houston, Alister Doyle in Oslo, Deborah Zabarenko in Washington; Writing by Bill Tarrant; Editing by Dean Yates and Jeremy Laurence)