- Officials working to fix power cable to stricken reactors
- Smoke seen billowing from Unit 2 reactor building
- Tokyo asks U.S. government for technical help
- American nuclear official defends 50-mile evacuation zone
- Head of UN atomic watchdog says he wants to visit site
Japanese engineers raced to restore a power cable to a quake-ravaged nuclear power plant on Friday in the hope of restarting pumps needed to pour cold water on overheating fuel rods and avert a catastrophic release of radiation.
Officials said they hoped to fix the cable to two reactors on Friday and to two others by Sunday, but said work would stop in the morning to allow helicopters and fire trucks to resume pouring water on the Fukushima Dai-ichi plant, about 240 km (150 miles) north of Tokyo.
"Preparatory work has so far not progressed as fast as we had hoped," an official of plant operator Tokyo Electric Power Co. (TEPCO) told a news briefing, adding that engineers had to be constantly checked for radiation levels.
'Unit 3 is our utmost priority'
Smoke billowed from Unit 2 at the plant, and its cause was not known. An explosion hit the building on Tuesday, possibly damaging a crucial cooling chamber that sits below the reactor core.
More urgent, Japan's chief government spokesman said, was the adjacent Unit 3. Fuel rods there may have been partially exposed, and without enough water, the rods may heat further and possibly spew radiation.
"Dealing with Unit 3 is our utmost priority," Chief Cabinet Secretary Yukio Edano told reporters.
Edano said that Tokyo is asking the U.S. government for help and the two are discussing the specifics. "We are coordinating with the U.S. government as to what the U.S. can provide and what people really need," Edano said.
He said crews planned to use fire trucks Friday to spray water more water on Unit 3.
The current evacuation perimeter around the Fukushima plant is appropriate, Edano said.Video: Physicist: Helicopter drops 'like squirt guns against a forest fire'
Emergency workers seemed to try everything they could think of Thursday to douse one of the overheated nuclear reactors: helicopters, heavy-duty fire trucks, even water cannons normally used to quell rioters. But they couldn't be sure any of it was easing the peril at the tsunami-ravaged facility.
Three reactors have had at least partial meltdowns at the Fukushima Dai-ichi plant, where wisps of white steam rose from the stricken units Friday morning. But Japanese and U.S. officials believe a greater danger exists in the pools used to store spent nuclear fuel: Fuel rods in one pool were believed to be at least partially exposed, if not dry, and others were in danger. Without water, the rods could heat up and spew radiation.
It could take days and "possibly weeks" to get the complex under control, U.S. Nuclear Regulatory Commission Chairman Gregory Jazcko said. He defended the U.S. decision to recommend a 50-mile evacuation zone for its citizens, a much stronger measure than Japan has taken.
A senior official with the U.N.'s nuclear safety agency said there had been "no significant worsening" at the nuclear plant but that the situation remained "very serious." Graham Andrew told reporters in Vienna that nuclear fuel rods in two reactors were only about half covered with water, and in a third they were also not completely submerged.
If the fuel is not fully covered, rising temperatures and pressure will increase the chances of complete meltdowns that would release much larger amounts of radioactive material than the failing plant has emitted so far.
Low levels of radiation have been detected well beyond Tokyo, which is 150 miles (240 kilometers) south of the plant, but hazardous levels have been limited to the plant itself. Still, the crisis triggered by last week's earthquake and tsunami has forced thousands to evacuate and drained Tokyo's normally vibrant streets of life, its residents either leaving town or holing up in their homes.
The official death toll from the disasters stood at 5,692 as of Friday morning, with 9,522 missing, the national police agency said.
The International Atomic Energy Agency chief, Yukiya Amano, was in Japan Friday with top Japanese officials and to visit the area struck by the devastating earthquake and tsunami a week ago.
Amano was accompanied by a four-member team of experts. He said: "We see it as an extremely serious accident. The international community is extremely concernced about this issue, and it's important to cooperate in dealing with it."
Obama assures Americans on risks
President Barack Obama appeared on television to assure Americans that officials do not expect harmful amounts of radiation to reach the U.S. or its territories. He also said the U.S. was offering Japan any help it could provide, and said he was asking for a comprehensive review of U.S. nuclear plant safety.
Japanese and American assessments of the crisis have differed, with the plant's owner denying Jazcko's report Wednesday that Unit 4's spent fuel pool was dry and that anyone who gets close to the plant could face potentially lethal doses of radiation. But a Tokyo Electric Power Co. executive moved closer to the U.S. position Thursday.
"Considering the amount of radiation released in the area, the fuel rods are more likely to be exposed than to be covered," Yuichi Sato said.
Another utility official said Wednesday that the company has been unable to get information such as water levels and temperatures from any of the spent fuel pools in the four most troubled reactors.
Workers have been dumping seawater when possible to control temperatures at the plant since the quake and tsunami knocked out power to its cooling systems, but they tried even more desperate measures on Unit 3's reactor and cooling pool.
Helicopters dump water
Two Japanese military CH-47 Chinook helicopters dumped seawater on Unit 3 on Thursday morning, defense ministry spokeswoman Kazumi Toyama said. The choppers doused the reactor with at least four loads of water in just the first 10 minutes, though television footage showed much of it appearing to disperse in the wind.
Chopper crews flew missions of about 40 minutes each to limit their radiation exposure, passing over the reactor with loads of about 2,000 gallons (7,500 liters) of water. Another 9,000 gallons (35,000 liters) of water were blasted from military trucks with high-pressure sprayers used to extinguish fires at plane crashes, though the vehicles had to stay safely back from areas deemed to have too much radiation.
Special police units with water cannons were also tried, but they could not reach the targets from safe distances and had to pull back, said Yasuhiro Hashimoto, a spokesman for Japan's nuclear safety agency.
Unit 3's reactor uses a fuel that combines plutonium, better known as an ingredient in nuclear weapons, and reprocessed uranium. The presence of this mixed oxide fuel, or MOX, means potentially that two very harmful radioactive products could be released into the environment.
Tokyo Electric Power said it believed workers were making headway in staving off a catastrophe both with the spraying and, especially, with efforts to complete an emergency power line to restart the plant's own electric cooling systems. Workers hope to fix a power cable to two reactors on Friday and to two others by Sunday, officials said.
"This is a first step toward recovery," said Teruaki Kobayashi, a facilities management official at the power company. He said radiation levels "have somewhat stabilized at their lows" and that some of the spraying had reached its target, with one reactor emitting steam.
"We are doing all we can as we pray for the situation to improve," Kobayashi said. Authorities planned to spray again Friday, and Kobayashi said: "Choices are limited. We just have to stick to what we can do most quickly and efficiently."
Focus on spent fuel rods
Four of the plant's six reactors have seen fires, explosions, damage to the structures housing reactor cores, partial meltdowns or rising temperatures. Officials also recently said temperatures are rising even in the spent fuel pools of the other two reactors.
The troubles at the nuclear complex were set in motion by last Friday's 9.0-magnitude earthquake and tsunami, which knocked out power and destroyed backup generators needed for the reactors' cooling systems. That added a nuclear crisis on top of twin natural disasters that likely killed well more than 10,000 people and left hundreds of thousands homeless.
Mario V. Bonaca, a physicist sits on an advisory committee to the U.S. Nuclear Regulatory Commission, said he believes the focus of the effort has shifted to the spent fuel pools. "I understand that they've controlled the cooling of the cores," said Bonaca, who said he was basing his understanding on NRC and industry sources.
The storage pools need a constant source of cooling water. Even when removed from reactors, uranium rods are still extremely hot and must be cooled for months, possibly longer, to prevent them from heating up again and emitting radioactivity.
More than 20 at the stricken plant have been injured, more than 20 have been exposed to radiation and two have gone missing during the battle to prevent a nuclear disaster, officials said Thursday.
The top U.S. nuclear regulator has warned that emergency staff at the stricken plant would face potentially "lethal doses" of radiation "in a very short space of time."
Plant workers injured, contaminated
The IAEA released the injury and contamination figures in a statement, saying they were based on information from Japanese authorities.
It said a subcontractor had suffered broken legs, two employees of power company TEPCO had sustained minor injuries and another contractor was in an unknown condition in hospital.
In addition to the two missing, two had been "suddenly taken ill." It also said four people suffered minor injuries in a March 11 explosion and 11 people were hurt in another explosion on March 14.
Quake risk at nuclear plants
Under the heading "radiological contamination," the statement one worker had received exposure and was taken to "an offsite center."
It said 17 workers had got radioactive material on their faces, but were not taken to a hospital because the exposure was low. Two police officers exposed to radiation were decontaminated and authorities were investigating the exposure of a number of firefighters.
Despite the dangers, the Agence France-Presse news agency reported staff from TEPCO and other industry firms were volunteering to join in efforts to stabilize the reactors.
Keiichi Nakagawa, associate professor of the Department of Radiology at University of Tokyo Hospital, put it starkly: "I don't know any other way to say it, but this is like suicide fighters in a war."
Experts note, though, that radiation levels drop quickly with distance from the complex. While elevated radiation has been detected well outside the evacuation zone, experts say those levels are not dangerous.
Some Americans evacuated
U.S. officials were taking no chances. In Washington, the State Department warned U.S. citizens to consider leaving the country and offered voluntary evacuation to family members and dependents of U.S. personnel in the cities of Tokyo, Yokohama and Nagoya.
The first flight left Thursday, with fewer than 100 people onboard, Undersecretary of State Patrick Kennedy said. Plans also call for airlifting several thousand family members of U.S. armed forces personnel as well as nonessential staff stationed in Japan in the coming days.
The U.S. evacuation zone is far bigger than that established by Japan, which has called for a 12-mile zone and has told those within 20 miles to stay indoors. Daniel B. Poneman, U.S. deputy secretary of energy, said at the briefing that his agency agreed with the 50-mile zone — but said Japan's measures were also prudent.
A graphic from another U.N. agency forecasting the possible trajectory of the radioactive cloud shows a moving plume reaching Southern California on Friday after racing across the Pacific and swiping the Aleutian Islands.
But IAEA officials and independent experts emphasized that the radiation level was already low outside of the immediate vicinity of the crippled reactor and would dissipate so strongly by the time it reached the U.S. coastlines that it would pose no health risk whatsoever to residents there.
Any detectable radiation on Friday "could be coming from your own reactors in California," said physics Prof. Paddy Regan at the University of Surrey at Guilfold in Britain. A senior IAEA official who asked for anonymity because he was not authorized to speak to media, noted that even in Tokyo, "radiation was at background levels."
On Friday, the Group of Seven agreed to join in rare concerted intervention to restrain a run-away yen, hoping to calm global markets after a wild week of often panic selling.
Japan's Finance Minister Yoshihiko Noda said the Bank of Japan had begun to sell yen at 12:00 p.m. GMT and other central banks from the G7 would intervene as their markets opened.
The Associated Press and Reuters contributed to this report.