por admin » Vie Mar 25, 2011 9:52 am
A paso lento pero seguro. Se sigue avanzando en la planta nuclear.
Slow Progress Made at Japan's Reactor
By ANDREW MORSE And MITSURU OBE
TOKYO—Japanese workers failed to restore power to parts of a crippled nuclear power plant but managed Friday to begin dousing fuel rods with fresh water, a development suggesting that the two-week effort to control the disaster continues to inch ahead.
With the crisis at the Fukushima Daiichi power plant entering its third week, almost every day brings some incremental progress along with reminders that the process is painfully slow and fraught with danger.
Workers at the six-reactor Fukushima Daiichi power plant, operated by Tokyo Electric Power Co., had hoped to connect the control room of the No. 2 unit to outside power and start cooling systems at the Nos. 1, 3 and 4 reactors by the end of Friday.
Those efforts failed as workers battled a highly radioactive environment that put three employees in the hospital for possible burns. On Thursday, they stepped in a puddle that contained radiation levels 10,000 times higher than normal.
"The situation at the Fukushima Daiichi nuclear power plant is still very grave," said Prime Minister Naoto Kan at a news conference. "We are still not at a stage where we can be optimistic."
On the positive side, workers switched to fresh water in dousing the stricken Nos. 1 and 3 reactors rather than corrosive sea water, which had been used as an emergency measure to cool overheating fuel rods.
The week ended with the most important piece of business unfinished. Although each unit is hooked up to the outside electrical grid, workers have yet to restore normal cooling systems that would bring volatile nuclear material under control.
."We cannot say with certainty at this point in how many days all the reactors will be brought to a state of cold shutdown," said Hidehiko Nishiyama, a top official at the Nuclear and Industrial Safety Agency, Japan's nuclear regulator. Cold shutdown refers to the cooling of a nuclear reactor to safe levels.
In the days after the March 11 earthquake and tsunami, Fukushima Daiichi experienced explosions and released radiation that affected people as far away as Tokyo, nearly 150 miles distant.
Hironobu Unesaki, a nuclear expert at Kyoto University, said additional major emission of radioactive substances is unlikely, but warned that weary workers may make slips.
"Human error is likely," he said, citing the accidental radiation exposure in the puddle. "Normally, if you hear there is water, you always check and take precautionary measures, but they have forgotten that," he said.
"They're making progress and they're making it as fast as they can," said Murray Jennex, an associate professor at San Diego State University who worked in the commercial nuclear industry for 17 years. "The longer they go without anything major happening, the better."
Japanese officials acknowledged radiation leakage from the accident is greater than initially believed and has slowed the efforts to stabilize the plant.
"Radiation levels in some parts of the facilities are just stunning," said one official at the Japanese regulator. "The work to fix the cooling system was made all the more difficult by the lack of information about where radiation is high inside the complex."
Nearly 30,000 people are dead or missing after the quake, and more than a quarter million people have been evacuated.
On Friday, Chief Cabinet Secretary Yukio Edano warned more evacuees may be coming as workers struggle to get control of Fukushima Daiichi. He said the government is looking for temporary housing for those living between 20 kilometers and 30 kilometers from the plant. Those people are currently being advised to stay indoors.
The U.S. government has recommended a 50-mile (80-kilometer) exclusion zone.
Friday's use of fresh water to cool parts of the plant should help settle some international unease. On Thursday, a U.S. official said the containment vessels at the Fukushima plant were filling up with salt, which could hinder cooling of the vessels.
Japanese Defense Minister Toshimi Kitazawa said Friday the U.S. has offered to provide fresh water for the cooling operations. A U.S. military spokesman in Japan said that as an initial step, the U.S. military plans to ship 525,000 gallons of fresh water on two Navy barges from a base in Yokosuka, south of Tokyo.
Also, the U.S. government has begun distributing potassium iodide tablets to American citizens in Tokyo as a precaution. Potassium iodide can help prevent the absorption of iodide 131, an isotope created in nuclear fission that collects in the thyroid gland.
The Fukushima Daiichi accident is currently rated 5 on a seven-level international scale of nuclear accidents. That is the same as the 1979 Three Mile Island accident, meaning there was a release of radiation to the environment. The 1986 Chernobyl accident was a 7.
Mr. Nishiyama of the nuclear regulator left open the possibility of raising the number after more data are available.
"Five is too low, given the severity of radiation in areas around the nuclear complex," said Masako Sawai of the Citizens' Nuclear Information Center, an antinuclear group in Tokyo. "The government is either underestimating the crisis or avoiding looking at it squarely."
—Chester Dawson and Stephen Power contributed to this article.
More Coverage of the Japan Earthquake