Nuclear fuel inside the crippled reactors at the Fukushima Daiichi power plant has partially melted and settled in granular form at the bottom of pressure vessels, according to an analysis by the Atomic Energy Society of Japan made public by Friday.

As the nation's worst nuclear crisis drags on more than a month after it was triggered by the March 11 quake and tsunami, small amounts of plutonium have been detected for the third time in soil samples taken at the complex.

Also Friday, the plant operator, Tokyo Electric Power Co., said it will pay up to 1 million yen to residents of each of the roughly 50,000 households within 30 kilometers of the plant who have been forced to evacuate their homes or remain indoors, as provisional compensation for the damage caused by the crisis.

The academic body's panel on nuclear energy safety has said the melted fuel at the Nos. 1 to 3 reactors has been kept at a relatively low temperature, discounting the possibility that a large amount of melted fuel has already built up at the bottom of the reactor vessels given the temperature readings there.

A large buildup of melted nuclear fuel could transform into a molten mass so hot that it could damage the critical containers and eventually leak huge amounts of radioactive materials.

The panel has also said that the fuel grains with a diameter of between several millimeters and 1 centimeter are believed to have settled evenly at the bottom of the vessels, leaving almost no possibility of a nuclear chain reaction called ''recriticality.''

Takashi Sawada, deputy chairman of the group, assessed that even if the current stabilization efforts proceed smoothly, it would take at least two to three months for the fuel to be stabilized with few if any radioactive emissions.

The panel also found that the fuel rods in the Nos. 1 to 3 reactors have been damaged after analyzing data made public by the plant operator, known as TEPCO, and the Nuclear and Industrial Safety Agency, which comes under the wing of the Ministry of Economy, Trade and Industry.

The panel has assumed that the fuel has slowly melted and become granular as it was quenched when it fell into the cooling water and then settled at the bottom of the reactor pressure vessels.

Parts of the fuel rods in the Nos. 1 and 2 reactors have apparently been exposed, while those in the No. 3 reactor have been completely submerged in water, according to the panel.

Meanwhile, small amounts of plutonium believed to have been released as a result of the ongoing disaster have been detected in soil samples taken at the nuclear complex in Fukushima Prefecture, according to TEPCO.

It is the third time that traces of plutonium have been found in soil samples taken at the plant. The latest samples were taken on March 31 and April 4. The levels of plutonium in the samples were around the same levels observed in Japan following nuclear bomb tests conducted by other countries, according to the utility.
On Friday, workers continued their efforts to bring the reactors under control and stop radioactive leaks from the coastal plant, injecting more nitrogen gas into the No. 1 reactor and installing more steel plates near a seawater intake for the No. 2 reactor.

TEPCO said it will throw sandbags containing zeolite, a mineral that absorbs radioactive materials, into the sea near the plant, possibly on Friday, to reduce the levels of contamination in the Pacific Ocean.

The nitrogen injection is aimed at preventing a hydrogen explosion at the No. 1 reactor. At a news conference on Friday, spokesman Hidehiko Nishiyama said his agency is also considering injecting nitrogen into the two other troubled reactors soon.

The agency said, meanwhile, that pressure inside the No. 1 reactor has dropped somewhat, an indication that air inside the reactor has leaked outside, but that no major changes in radiation levels have been detected.

The utility has pumped out around 660 tons of highly radioactive water from a tunnel connected to the No. 2 reactor's turbine building into a container inside the building.

The operation resulted in a lower water level in the vertical part of the tunnel, but the agency said that as of Friday morning the level had risen back to the same level as before the water transfer started on Tuesday.

The water filling the tunnel is feared to have come from the reactor, into which TEPCO has been injecting fresh water to keep fuel rods inside from overheating.

Removing the highly contaminated water that has flooded the basements of the Nos. 1 to 3 reactor turbine buildings and adjacent tunnels is seen as key to restoring critical cooling systems for the damaged reactors, which were lost in the March 11 earthquake and tsunami.

The utility plans to divert the tainted water to a plant facility for nuclear waste disposal, but plumbing work was still being conducted there to ensure there would be no leaks in pipes.

''I'm hoping that work to stop water leaks at the (facility) is finished as soon as possible to start channeling the water there,'' said industry minister Banri Kaieda at a news conference on Friday.

The accumulated water is believed to be an unintended side effect of TEPCO's stopgap measure of injecting water into the reactors and their spent nuclear fuel pools to prevent them from overheating.