Japan's worst nuclear accident has been brought under control, Prime Minister Yoshihiko Noda declared on Dec. 16, but some experts and the Fukushima governor took issue, saying much remains to be done.
"We concluded that the accident has been brought under control within the (Fukushima No. 1 nuclear power) plant," Noda told a news conference.
The government's nuclear disaster response headquarters, headed by Noda, concluded the same day that the Step 2 goals of the road map for bringing the accident under control have been completed.
But Noda's statement was immediately challenged by Fukushima Governor Yuhei Sato.
"The accident has not been brought under control," Sato told reporters, saying prefectural residents are worried about increasing contaminated water and other problems at the plant.
The primary goal of Step 2 was to achieve a cold shutdown of the crippled reactors at the plant.
For the accident, the government defines a cold shutdown as a condition in which temperatures at the bottom of pressure vessels of the No.1 to No. 3 reactors have been kept at 100 degrees or lower on a stable basis and the release of radioactive materials has been contained.
By emphasizing the plant's safety, the government hopes to dispel lingering concerns about the accident at home and abroad.
But some experts criticized the government for rephrasing the process of achieving a cold shutdown to mean bringing the accident under control.
Fumiya Tanabe, director of the Sociotechnical Systems Safety Research Institute, said a cold shutdown is being used as a political message that the most difficult part is over in resolving the nuclear crisis.
"A cold shutdown is usually used to indicate that a reactor has been shut down on a stable basis in a normal operation control," said Tanabe, who worked as a researcher at the former Japan Atomic Energy Research Institute. "I feel uncomfortable with the phrase being used when nuclear fuel has not maintained its original form."
Tokyo Electric Power Co., operator of the plant, has not been able to explain in what conditions melted fuel remains in the reactors or keep radioactive materials from being released outside the plant premises.
Noda also acknowledged that key challenges still remain outside the plant, most notably removing large amounts of radioactive materials released from the plant in wide parts of Japan and enabling residents who evacuated from areas around the plant to return to their hometowns.
"Tasks remain off the plant site, and our response to the accident has yet to be completed," Noda said.
He said the government plans to spend more than 1 trillion yen on removing radioactive materials, including funds to be allocated in the fiscal 2012 budget, and also to mobilize more than 30,000 workers for decontamination work by April.
At a meeting of the nuclear disaster response headquarters on Dec. 16, it was reported that temperatures of the No. 1 to No. 3 reactors have been below 100 degrees since late September and were at 38 to 68 degrees as of Dec. 15.
Levels of radioactive materials released outside the plant have declined to 60 million becquerels per hour, one-13 millionth of the levels at the time when the accident occurred.
Additional radiation levels at the plant borders have fallen to a maximum of 0.1 millisievert per year, below the government target of 1 millisievert.
"We have confirmed that radiation will be kept at sufficiently low levels outside the plant should a problem occur," Noda said at the news conference.
Decommissioning of the crippled reactors was described as a mid- to long-term task that will be dealt with separately from bringing the accident under control.
The government's Japan Atomic Energy Commission said it will take more than 30 years to decommission the reactors.
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