David Guttenfelder / Pool via EPA, file
A building of the crippled Fukushima Dai-ichi nuclear power station as seen through a bus window in Okuma, Japan, on Nov. 12.
Updated at 6:23 a.m. ET
TOKYO -- The tsunami-devastated Fukushima Dai-ichi nuclear power plant has reached a "cold shutdown" and is no longer leaking substantial amounts of radiation, Japan's prime minister said Friday.
Prime Minister Yoshihiko Noda's announcement marks a milestone nine months after the March 11 tsunami sent three reactors at the plant into meltdowns in the worst nuclear crisis since Chernobyl. It is a crucial step toward lifting evacuation orders and closing the plant.
"Even if unforeseeable incidents happen, the situation is such that radiation levels on the boundary of the plant can now be maintained at a low level," Noda said. "Now that we have achieved stability in the reactors, a major concern for the nation has been resolved."
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However, experts noted that the plant remains vulnerable. Its surroundings are contaminated by radiation and closing the plant safely will take 30 or more years.
'Our battle is not over'
NBC News reported that there are still sporadic reports of leaks of contaminated water from the site.
"There are many issues that remain," Noda added. "Our battle is not over."
Noda's announcement means officials can now start discussing whether to allow some evacuees to return to less-contaminated areas — although a 12-mile zone around the plant is expected to remain off limits for years to come. The crisis displaced some 100,000 people.
A cold shutdown normally means a nuclear reactor's coolant system is at atmospheric pressure and its reactor core is at a temperature below 212 degrees Fahrenheit (100 degrees Celsius), making it impossible for a chain reaction to take place.
According to plant operator TEPCO, temperature gauges inside the Fukushima reactors show the pressure vessel is at around 158 degrees F (70 C). The government also says the amount of radiation now being released around the plant is at or below 1 millisievert per year — equivalent to the annual legal exposure limit for ordinary citizens before the crisis began.
Akira Yamaguchi, a nuclear physicist at Osaka University, said that the government's definition of cold shutdown is disputable.
"But what's most important right now is that there aren't any massive radiation leaks any more," he said.
Putting longer-term issues aside, he warned that much of the backup equipment installed at the plant since the crisis began is makeshift and may break down. He said winter cold could test their strength.
Tamotsu Baba, the mayor of evacuated Naimie town, told a press conference Friday that it was "hard to accept" Noda's declaration.
"We still feel a major distrust towards the government," he added.
Located 150 miles northeast of Tokyo, the plant was wrecked by a huge earthquake and a tsunami that exceeded 45 feet in some areas, which knocked out its cooling systems, triggering meltdowns and radiation leaks.
NBC News reported that the extraction of more than 3,000 fuel rods from the site, most likely involving robotic cranes, is due to begin next year. High-powered water sprays will be used to decontaminate roads and other infrastructure in nearby towns from early next month.
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NBC News' Arata Yamamoto, Reuters and The Associated Press contributed to this report