Workers scramble to cool reactors; official says 2nd blast possible
- "The situation is under control," a prime minister's office spokesman says
- Official: A blast could occur in the building housing a reactor at the Fukushima Daiichi plant
- Authorities say there are no indications of dangerously high radiation levels
- They have not been able to confirm whether a meltdown has occurred
Tune in to CNN tonight at 9 ET for a special edition of "AC360º." Anderson Cooper, Dr. Sanjay Gupta, and Soledad O'Brien report live from Japan on the quake and tsunami's catastrophic effects.
(CNN) -- Japanese efforts to prevent a nuclear meltdown by flooding reactors with seawater are a last-ditch attempt, but do not mean that a nuclear tragedy is imminent, experts said Sunday.
Nuclear experts who have followed the developments at the damaged Fukushima Daiichi nuclear plant in northeastern Japan say that despite several setbacks, the possibility of massive radiation exposure remains low -- at least for now.
Japanese officials are keeping an eye on two nuclear plants that have released radiation beyond normal levels. At the Daiichi plant in Fukushima, in two of the three reactors -- Nos. 1 and 3 -- the Japanese government is assuming, but has not confirmed, that there has been a partial meltdown because of the powerful earthquake and tsunami that struck on Friday. At a second plant, in Onogawa, excessive radiation levels also were recorded, though officials have told the United Nations' atomic watchdog agency that the situation is "under control."
There were reports that there were pressure venting actions at a third nuclear plant -- Fukushima Daini -- but the International Atomic Energy Agency said that such precautions had not taken place at three reactors there, and that a fourth reactor was in a safe, cold shutdown.
An explosion caused by hydrogen buildup Saturday blew the roof off a concrete building housing the Daiichi plant's No. 1 reactor, but the reactor and its containment system were not damaged in the explosion. Officials say the No. 3 reactor would also likely withstand a similar blast, noting that workers had already released gas from the building to try to prevent an explosion.
"I don't think we're really close to a meltdown," said Dale Klein, vice chancellor for special engineering projects at the University of Texas, referring to the Daiichi plant.
There does appear to be some fuel damage to one of the reactors, but the seawater method to keep them cool seems to be working.
"I think when the dust all settles, the death toll from the tsunami and the earthquake will be much more significant than any damage from these reactors," he said.
The use of seawater shows that authorities are giving up future use of the Daiichi plant and are focusing solely on protecting people and the environment, experts said.
"If they are (using seawater), it's because they have no other choice," said James Walsh, a research associate at the security studies program at MIT. "The last thing you want to do is pump seawater and boron into a reactor."
The salt and boron will corrode the reactor, he said.
"Essentially, they are saving the white flag and saying, 'This plant is done,' " Walsh said. "This is a last-ditch mechanism to try to prevent overheating and to prevent a partial or full meltdown."
In addition, danger from any radiation that escapes would vary on a number of factors, including the type of radiation, the amount and geography, he said.
The use of the seawater reflects the seriousness of the damage, said James Acton of the nuclear policy program at The Carnegie Endowment.
"You're only going to do that if you're seriously worried about the possibility of significant core meltdown," he said.
He added that the word "meltdown" can mean a lot of different things, depending on its severity.
"So there's both significant uncertainty about what's going on at the moment, and significant uncertainty about the possible outcomes," Acton said.
A major explosion of a reactor at the Daiichi plant is "almost inconceivable," he said. "I think that worst-case outcome is unbelievably unlikely in this case."
At the Daiichi nuclear plant, workers have been scrambling to cool off fuel rods at both reactors after the massive earthquake and tsunami disabled their cooling systems. Japanese authorities have said there is a "possibility" that a meltdown has occurred in the reactors.
A meltdown is a catastrophic failure of the reactor core, with a potential for widespread radiation release.
Japan's nuclear agency said there was a strong possibility that the radioactive cesium detected by monitors was caused by the melting of a fuel rod at the plant, indicating at least a partial meltdown. High levels of hydrogen inside the reactors -- the element behind the explosion concerns -- is another sign of a potential meltdown.
But Japanese officials stressed that there were no indications of dangerously high radiation levels in the atmosphere around the two reactors at the Fukushima Daiichi nuclear plant in northeastern Japan. They said they were unable to confirm whether a meltdown had occurred because they cannot get close enough to the reactors' cores.
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