Partial nuclear meltdown at Fukushima 'no disaster', expert says

Any partial meltdown of nuclear fuel in a quake-hit power plant in Japan "is not a disaster" and a complete meltdown is unlikely, a German industry expert said on Sunday.

Robert Engel, a structural analyst and senior engineer at Switzerland's Leibstadt nuclear power plant, said he believed Japanese authorities would be able to manage the situation at the damaged Fukushima facility north of Tokyo.

Engel was an external member of a team sent by the International Atomic Energy Agency (IAEA) to Japan after a 2007 earthquake that hit the Kashiwazaki-Kariwa plant, until then the largest to affect a nuclear complex.

"I think nobody can say at this time whether there is a small melting of any fuel elements or something like that. You have to inspect it afterwards," he told Reuters by phone.

But a partial meltdown "is not a disaster" and a complete meltdown is not likely, he said, suggesting he believed Japanese authorities were succeeding in cooling down the reactors even though the systems for doing this failed after the quake hit.

"I only see they are trying to cool the reactor, that is the main task, and they are trying to get cooling water from the sea," Engel said, stressing he did not have first-hand information about events at the Fukushima facility.

Normally, he said, the water level inside a reactor core is about 3 to 4 metres above the fuel. If the rods are not covered by water for a longer time then a core melting is possible.

"I think they will be able to manage it ... When the (reactor) containment is intact only a small amount of radioactivity can go out, like in Three Mile Island," he said referring to the 1979 nuclear accident in the United States.

At Three Mile Island, a cooling fault led to a build-up of pressure in the radioactive core and resulted in a relatively small radiation leak.

Japan was working on Sunday to prevent the fuel rods in the plant from overheating after radiation leaked into the air.

The government said a building housing a second reactor was at risk of exploding after a blast on Saturday blew the roof off the facility's No 1 reactor, where there is believed to have been a partial meltdown of the fuel rods.

Experts say the critical issue is what has happened or is happening with the fuel -- which contains nearly all the radioactivity in the plant -- and whether and to what extent it is damaged.

If there is a fuel meltdown, it would release radioactivity, but Engel said there were barriers before it could escape into the atmosphere -- the fuel rods, reactor vessel and containment.