(Corrects name spelling in 12th paragraph and water measure in 14th of story first published on Dec. 16.)
Japan’s Prime Minister Yoshihiko Noda said the Fukushima nuclear reactors have been brought to a state of cold shutdown, a disputed milestone that will likely allow the return of some evacuees and eventual dismantling of the plant.
Speaking at his office in Tokyo, Noda said today that the government and Tokyo Electric Power Co. (9501) had contained the nuclear crisis that occurred after the reactors in northeast Japan were crippled by the March 11 earthquake and tsunami.
“A stable condition has been achieved, and we can consider the accident itself contained,” Noda said.
Cold shutdown describes a reactor’s cooling system operating at atmospheric pressure and below 93 degrees Celsius (200 degrees Fahrenheit), according to the U.S. Nuclear Regulatory Commission. The utility has released data showing it meets these criteria at Fukushima, the site of the worst nuclear accident since the 1986 Chernobyl disaster, though some nuclear scientists say the term doesn’t apply to melted reactors.
“Achieving cold shutdown does not change the condition of the reactors,” Tadashi Narabayashi, a former reactor safety researcher at Toshiba Corp. (6502) and now a nuclear engineering professor at Hokkaido University, said by phone. “It does mean the government will start reviewing evacuation zones and perhaps lifting restrictions depending on extent of contamination.”
While the status of the reactors is in dispute, it remains that swathes of land, towns and villages in Fukushima are highly contaminated by radiation fallout and are likely to be uninhabitable for two decades or more.
Radiation has forced the evacuation of about 160,000 people and the government has yet to say how many can return and when.
“We want to make a united effort for them to return home as soon as possible and rebuild their livelihoods,” Noda said.
Tokyo Electric has battled explosions, aftershocks, equipment breakdowns and leaks of contaminated water after the March 11 earthquake and tsunami hit the plant and knocked out power to reactor cooling systems. Three reactor cores subsequently melted, causing the biggest civilian nuclear disaster since Chernobyl in 1986.
The utility, known as Tepco, said in September it had restored stable cooling of the three reactors at the Dai-Ichi plant and reduced their temperatures below 100 degrees Celsius. Last month, it assessed the radiation exposure at the plant’s boundaries at 0.1 millisievert a year, below its target of 1 millisievert a year.
The drop in radiation was the second of two criteria imposed by the country’s Nuclear and Industrial Safety Agency before the watchdog would consider the plant stable.
It’s an achievement to have restored cooling and gotten water temperatures to 100 degrees, said Arnie Gundersen, a Vermont-based nuclear engineer who has testified to the U.S. Nuclear Regulatory Commission on Fukushima, said in a phone interview.
“But I don’t know why they choose to say cold shutdown because that’s an affront to those in the industry who really know what the term means,” he said. “That nuclear core is still in a configuration where the center is extraordinarily hot.”
Besides maintaining stable cooling of the reactors and spent-fuel pools at the plant, Tepco has to manage storage tanks holding thousands of metric tons of contaminated water.
‘Hardest Part Starts’
“Now the hardest part starts, which is the cleanup,” said Najmedin Meshkati, a professor of civil engineering at the University of Southern California, who worked as a consultant on decommissioning Chernobyl.
Experiences in other countries show the scale of the task still facing Tepco as it begins decommissioning the reactors, and cleaning contaminated waste, even without the complications posed by the damage at Fukushima.
Cold War weapons production in the U.S. left the country with “a significant nuclear cleanup legacy, including high- level waste, contaminated soil and groundwater,” Daniel Poneman, the U.S. Deputy Secretary at the Department of Energy, said in Tokyo yesterday.
The Hanford Site in Washington State and the Savannah River Site in South Carolina have more than 90 million gallons of liquid waste in tanks the government is working to convert into more stable forms that do not threaten the environment, he said.
Japan’s government has requested support from the U.S. to decommission the Fukushima Dai-Ichi plant as well as managing the site from an environmental perspective, he said.
“Work on decommissioning is a long way off. For now, they have to focus on making robots to remove melted fuel and developing new technologies to demolish facilities,” said Narabayashi at Hokkaido University.
In addition, there are about 7 kilometers of plastic pipe in the makeshift cooling system that will need to be replaced with metal versions, he said.
Gundersen said that declaring the cold shutdown at Fukushima risks further eroding people’s faith in the government’s ability to regulate the nuclear power industry.
“I actually think it’s going to blow up in their face,” he said. “In the eyes of the Japanese public, the last thing they need to do is exaggerate. And this is an exaggeration.”
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