Plutonium find at Japan nuclear plant

Plant operator Tokyo Electric Power Co said the material was discovered at low-risk levels in five places at the facility, which was crippled by a massive earthquake and tsunami on 11 March.

Plutonium is a by-product of atomic reactions and also used in nuclear bombs. It is highly carcinogenic and one of the most dangerous substances on the planet.

Japan's Nuclear and Industrial Safety Agency said while the levels were not harmful to human health, the discovery could mean a breach in the reactor's containment mechanism.

Experts 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 the substance in its fuel mix.

"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 apologise for making people worried," Muto said.

Japanese MPs have attacked the Prime Minister for his handling of the disaster.

Some opposition politicians lambasted Naoto Kan in parliament for not extending an evacuation zone around the plant.

Kan said he was seeking advice on widening the area, which would force 130,000 people to move in addition to 70,000 already displaced.