TOKYO - Japan is poised to declare its crippled nuclear plant virtually stable nine months after a devastating tsunami, but the facility still leaks some radiation, remains vulnerable to earthquakes, and shows no prospect of cleanup for decades.

Prime Minister Yoshihiko Noda said last week that temperatures inside the Fukushima Dai-ichi plant's three melted reactor cores were almost consistently below the boiling point and that radiation leaks had significantly subsided - two key conditions in a hoped-for "cold shutdown."

Officials say the government is expected to hold a news conference Friday to declare something close to cold shutdown, though experts caution it will be, at best, a tenuous stability.

The declaration would mark a step forward for the much-maligned operator, Tokyo Electric Power Co., which has struggled to control the plant after it was damaged in a huge earthquake and tsunami March 11, unleashing the worst nuclear accident since Chernobyl.

'The biggest goal'

"Until now, this has been the biggest goal," TEPCO spokesman Masao Yamaguchi said. "It would be a milestone."

The announcement is expected to refer to cold shutdown "conditions" - less definitive phrasing than a cold shutdown. That's partly because the operator cannot measure temperatures of melted fuel in the damaged reactors in the same way as with normally functioning ones, although the company believes they have reached a stable state.

In any case, experts caution that the progress so far at Fukushima should not be overstated and that problems could still crop up.

"TEPCO and the government are anxious to bring a certain closure to the crisis," said Kazuhiko Kudo, a nuclear physicist at Kyushu University. "It would be a problem if the announcement gives an impression that the plant has received an official safety certificate."

The announcement would mark the end of the second phase of the government's lengthy road map to completely decommission the plant, a process that could take about 30 years, authorities have said.

Food worries

In the next phase, officials may start discussing whether to allow some evacuated residents who lived in areas with lesser damage from the plant to return home - but that could still be months or years away. Many of the more than 100,000 residents evacuated from around the plant remain in limbo, living with relatives or in temporary housing.

Food concerns also persist. The Fukushima plant disaster, which spewed an estimated one-fifth the amount of radiation as the 1986 accident at Chernobyl, has caused contamination of rice, vegetables, and beef from around the region. Recently, even trace amounts of cesium were found in baby formula.

The complex still faces many concerns, including the vulnerability of the spent-fuel pools, which sit on the top floor of the damaged reactor buildings, and the vast amount of contaminated water that has collected in the reactor basements and nearby storage areas.