Japan tackles hydrogen buildup, cumulative radiation concerns
UPDATED @ 11:14:31 AM 07-04-2011
April 07, 2011
 A US military barge carrying pure water (bottom) leaves the quay near Tokyo Electric Power Co.’s Fukushima Daiichi Nuclear Power Plant to refill with pure water in Fukushima on April 6, 2011. — Reuters pic
TOKYO, April 7 — Japan pumped nitrogen gas into a crippled nuclear reactor today, 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 nitrogen 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-reactor 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 litres (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.
Safety concerns in Asia In Vienna, the head of a UN 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 risks 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.
Neighbouring South Korea and China, however, are worried about radioactive fallout. China’s health ministry found traces radioactivity in spinach in three Chinese provinces and South Korean media are reporting fears about contaminated rainfall. Immigration data reflected wider foreign fears about the crisis, with international arrivals in Tokyo from March 11-31 down 75 per cent for the same period in 2010, local media said.
The government is preparing to raise the legal radiation limits to adjust to the fact that people near the plant are sustaining cumulative exposure. The original policy was set to cover reactor workers briefly sustaining high doses in an accident. Workers are struggling to restart cooling pumps — which recycle the water — in four damaged reactors.
Until those are fixed, they must pump in water to prevent overheating and meltdowns, but have run out of storage capacity for the seawater when it becomes contaminated.
Radioactive iodine detected in the sea has been recorded at 4,800 times the legal limit, but has since fallen to about 600 times the limit. The water remaining in the reactors has radiation five million times legal limits.
Martin Virgilio, a top official for the US Nuclear Regulatory Commission, said at a House of Representatives hearing that the NRC did not believe that the core of Fukushima’s reactor No. 2 had melted down.
Earlier, a Democratic lawmaker had said the NRC informed him the core had become so hot it had probably melted through the reactor pressure vessel. Lawmakers also grilled the NRC on whether the US nuclear power industry was doing enough to ensure American reactors can withstand worst-case scenarios.
The NRC is conducting special inspections at two Illinois nuclear plants operated by Exelon Corp after routine checks in February found a problem with backup pumps that would be used to remove heat from the reactors in case of an accident.
Cooling reactors key Japan is facing its worst crisis since World War Two after the 9.0 magnitude earthquake and tsunami left nearly 28,000 people dead or missing and thousands homeless, and rocked the world’s third-largest economy.
The quake shifted the seabed near the epicentre in northern Japan by a record 24m, the coastguard said.
To help fund its extra budget for disaster relief, Japan, the world’s No. 5 donor, is considering cutting foreign aid by 20 per cent this fiscal year, local media reported.
It will likely take months to finally cool down the reactors and years to dismantle those that have been damaged. TEPCO has said it will decommission four of the six reactors.
Two Fukushima plants together provide 4 per cent of Japan’s electric power and local politicians warn that reopening them will be politically difficult.
The key to bringing the reactors under control is the extent of damage to the plant’s cooling system, said analysts. — Reuters | 
Post time 6-4-2011 05:42 PM
[/url] [url=]
..
... China yg sama2 ada gempa bumi pon siap bantu bagi 20K tan petrol & diesel lagi buat Jepun .. duit plak sebayak 30 million yuan (4.57 million U.S. dollars) 
[/url]
[/url] 2011年04月06日 ありがとう！米海兵隊 気仙沼市・大島
[/url] 2011年04月06日 東京で桜が満開
[/url] 2011年04月06日 訪日外国人４分の１に急減 観光・小売業にダメージ 東京入国管理局調べ
[/url] 2011年04月07日 プライバシーが少しは守られる
[/url] 2011年04月07日 急がれる仮設住宅建設
