A U.S. military barge carrying pure water (bottom) leaves the quay near the Fukushima Daiichi Nuclear Power Plant to refill with pure water, April 6, 2011.
Credit: Reuters/Japan Maritime Self-Defence Force
By Chizu Nomiyama and Shinichi Saoshiro
TOKYO | Wed Apr 6, 2011 7:41pm EDT
(Reuters) - Japan pumped nitrogen gas into a crippled nuclear reactor on Thursday, trying to prevent an explosive buildup of hydrogen gas as the world's worst nuclear disaster in 25 years stirred atomic safety debate and inspections in the United States.
Engineers worked through the night injecting nitrogen into the containment vessel of reactor No.1 at Fukushima Daiichi power plant, following success in stopping highly radioactive water leaking into the sea at another reactor in the complex.
"It is necessary to inject nitrogen gas into the containment vessel and eliminate the potential for a hydrogen explosion," an official of plant operator Tokyo Electric Power (TEPCO) told a news briefing.
The possibility of another hydrogen explosion like those that ripped through reactors No.1 and No.3 early in the crisis, spreading high levels of radiation into the air, was "extremely low," he said.
But TEPCO suspected that the outside casing of the reactor vessel was damaged, said the official.
"Under these conditions, if we continue cooling the reactors with water, the hydrogen leaking from the reactor vessel to the containment vessel could accumulate and could reach a point where it could explode," he added.
A second TEPCO official said 6,000 cubic metres of hydrogen gas would be pumped into reactor No.1 and the utility was preparing nitrogen gas injections for reactors No.2 and No.3 in the six-rector plant as a safety precaution.
Although TEPCO succeeded after days of desperate efforts to plug the leak at reactor No.2, they still need to pump 11.5 million liters (11,500 tonnes) of contaminated water back into the ocean because they have run out of storage space at the facility. The water was used to cool overheated fuel rods.
Nuclear experts said the damaged reactors were far from being under control almost a month after they were hit by a massive earthquake and tsunami on March 11.
In Vienna, the head of a U.N. scientific body said the Fukushima accident is not expected to have any serious impact on people's health, based on the information available now.
Wolfgang Weiss, chairman of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), also said the Fukushima disaster was less dramatic than Chernobyl in 1986 but "much more serious" than Three Mile Island in 1979.
Asked what health consequences he expected from Fukushima, he said: "From what I know now, nothing, because levels are so low."
"We have seen traces of iodine in the air all over the world now but they are much, much, much lower than traces we have seen at similar distances after Chernobyl," Weiss added.
Growing concerns in nearby South Korea and China over radioactive fallout from Japan were underscored when China's health ministry reported trace amounts of radioactive iodine in spinach in three Chinese provinces.
The government is preparing to revise guidelines for legal radiation levels, designed for brief exposure to high levels of radiation in emergencies and not cumulative absorption, for people living near the damaged plant.
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