Uncertainty clouds nuke crisis; work resumes

Updated at 2:06 p.m. Eastern

FUKUSHIMA, Japan - Emergency workers forced to retreat from a tsunami-stricken Japanese nuclear power plant when radiation levels soared prepared to return Wednesday night after emissions dropped to safer levels.

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The pullback cost precious time in the fight to prevent a nuclear meltdown, further escalating a crisis spawned by last week's devastating earthquake and tsunami that pulverized Japan's northeastern coast and likely killed more than 10,000 people.

Officials for Tokyo Electric Power Co., operator of the Fukushima Dai-ichi nuclear plant and also known as Tepco, said at a late night press conference Wednesday that four out of the five vehicles pumping seawater into the plant's reactors are operational. One pump vehicle each has been assigned to reactors No. 1 and No. 3. Reactor No. 2 has two pump vehicles. As of midnight Thursday, a new pump vehicle was being prepared to start working on reactor No. 4.

Meanwhile, the U.N.'s nuclear watchdog confirmed core damage in reactors Nos. 1, 2 and 3 in a news conference Wednesday. International Atomic Energy Agency chief Yukiya Amano called the situation in Japan "very serious" but said the plant's reactor vessels seem intact, the Reuters news agency reports. Amano said he hoped to leave Vienna for Japan Thursday and meet with senior officials.

It was unclear what happened in the nuclear plant's overheating reactors after late morning, when the workers stopped pumping in seawater trying to cool their fuel rods.

In Washington, Energy Secretary Steven Chu told members of a congressional committee that "we don't really know in detail what's happening," CBS News reports. Soon after Chu's testimony, the U.S. embassy in Tokyo urged all Americans within 50 miles of the power plant to evacuate the area or stay indoors. Reuters later reported that the British government advised its citizens in Tokyo and in areas north of the capital to consider leaving the area.

Ryohei Shiomi, of Japan's Nuclear and Industrial Safety Agency, told CBS News in a phone interview that the plant was never completely abandoned. He would not say how many workers remained inside the Fukushima Dai-ichi plant after the government suggested an evacuation was taking place.

Speaking to CBS Radio News' Lucy Craft earlier on Wednesday, a representative from Tepco said all the workers were back on the job.

But conditions at the Fukushima Dai-ichi nuclear plant appeared to be worsening. White steam-like clouds drifted up from one reactor which, the government said, likely emitted the burst of radiation that led to the workers' withdrawal. The plant's operator reported a fire at another reactor for the second time in two days.

"They are up against a wall ... this is not just one Three Mile Island. It's effectively four," Sharon Squassoni, an expert on nuclear issues at the Center for Strategic and International Studies, told CBS' "The Early Show."

At one point, national broadcaster NHK showed military helicopters lifting off to survey radiation levels above the complex, preparing to dump water onto the most troubled reactors in a desperate effort to cool them down. The defense ministry later said those flights were a drill, and it had no plans to make an airborne water drop.

Tepco officials said at their late night news conference that they wanted the military to again try pouring water from a helicopter onto the reactors, Reuters reported.

"The anxiety and anger being felt by people in Fukushima have reached a boiling point," the governor of Fukushima prefecture, Yuhei Sato, fumed in an interview with NHK. He criticized preparations for an evacuation if conditions worsen and said centers already housing people moved from nearby the plant do not have enough hot meals and basic necessities.

Fears are so high, voluntary radiation exams are being administered as far as Niigata on the west coast of Japan. And Japanese nuclear authorities have a history of being less than forthcoming about the safety of their reactors, which only contributes to the confusion and distrust, reports CBS News correspondent Harry Smith.

The nuclear crisis has triggered international alarm and partly overshadowed the human tragedy caused by Friday's 9.0-magnitude earthquake and the subsequent tsunami, a blast of black seawater that pulverized Japan's northeastern coastline. The quake was one of the strongest recorded in history.

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Millions of people struggled for a fifth day with little food, water or heat, and already chilly temperatures turned to snow in many areas. Police say more than 452,000 people are staying in temporary shelters, often sleeping on the floor in school gymnasiums.

Nearly 3,700 people are officially listed as dead, but officials believe the toll will climb over 10,000 since several thousand more are listed as missing.

In an extremely rare address to the nation, Emperor Akihito expressed condolences and urged Japan not to give up.

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"It is important that each of us shares the difficult days that lie ahead," said Akihito, 77, a figure deeply respected across the country. "I pray that we will all take care of each other and overcome this tragedy."

He also expressed his worries over the nuclear crisis, saying: "With the help of those involved I hope things will not get worse."

Since the quake and wave hit, authorities have been struggling to avert an environmental catastrophe at the Fukushima Dai-ichi complex, 140 miles north of Tokyo. The tsunami knocked out the backup diesel generators needed to keep nuclear fuel cool at the plant's six reactors, setting off the atomic crisis.

In the city of Fukushima, about 40 miles inland from the nuclear complex, hundreds of harried government workers, police officers and others struggled to stay on top of the situation in a makeshift command center.

An entire floor of one of the prefecture's office buildings had been taken over by people tracking evacuations, power needs, death tolls and food supplies.

In one room, uniformed soldiers evaluated radiation readings on maps posted across a wall. In another, senior officials were in meetings throughout the day, while nuclear power industry representatives held impromptu briefings before rows of media cameras.

Wednesday's radiation spike was believed to have come from Unit 3, where workers are struggling with a fuel storage pond believed to be leaking radiation, as well as possible damage to the containment vessel -- the thick concrete armor built around the reactor -- that would allow radiation to escape.

"The workers cannot carry out even minimal work at the plant now," Chief Cabinet Secretary Yukio Edano said Wednesday morning at briefing aired on television, as smoke billowed above the complex. "Because of the radiation risk we are on standby."

With no workers on site, efforts to cool the reactors likely ceased altogether, said Michael Friedlander, a former nuclear power plant operator who worked at a General Electric boiling water reactor in the United States similar to the stricken ones in Japan.

"They're in right now is what's called a feed-and-bleed mode. In order to keep the core covered and keep the reactor cool they have to feed in water," said Friedlander, who is currently based in Hong Kong. "It's something that they physically have to be present to do."

Elevated levels of radiation were detected well outside the 20-mile emergency area around the plants. In Ibaraki prefecture, just south of Fukushima, officials said radiation levels were about 300 times normal levels by late morning.

A little radiation was also detected in Tokyo, triggering panic buying of food and water.

To give some perspective on the dangers posed by the radiation, a chest X-ray emits about 1/10th of a millisievert, the unit of measurement for radiation.

Nuclear plant workers are limited to 20 millisieverts a year. One-hundred milisieverts in one dose can increase the risk of cancer, and 100 to 500 can cause bone marrow damage, leading to infection and death.

Reports say radiation levels were as high as 400 millisieverts an hour at the plant Tuesday. But they fell dramatically -- first to 11.9, then to zero-point-six.

For further perspective, in Chernobyl, among people who became sick the radiation dose ranged from 800 to 1.6 million millisieverts - much higher than what's being measured so far in Japan.

Given the reported radiation levels, John Price, an Australian-based nuclear safety expert, said he saw few health risks for the general public so far. He was concerned for the workers, who he said were almost certainly working in full body suits and breathing through respirators. The workers at the forefront of the fight -- a core team of about 180 -- had been regularly rotated in and out of the danger zone to minimize their radiation exposure.

Price said he was surprised by how little information the Japanese were sharing.

"We don't know even the fundamentals of what's happening, what's wrong, what isn't working. We're all guessing," he said. "I would have thought they would put on a panel of experts every two hours."

Edano said the government expects to ask the U.S. military for help, though he did not elaborate. He said the government is still considering whether to accept offers of help from other countries.

There are six reactors at the plant. Units 1, 2 and 3, which were operating last week, shut down automatically when the quake hit. Since then, all three have been rocked by explosions. Compounding the problems, on Tuesday a fire broke out in Unit 4's fuel storage pond, an area where used nuclear fuel is kept cool, causing radioactivity to be released into the atmosphere.

Units 4, 5 and 6 were shut at the time of the quake, but even offline reactors have nuclear fuel -- either inside the reactors or in storage ponds -- that need to be kept cool.

Meanwhile, the Nuclear and Industrial Safety Agency estimated that 70 percent of the rods have been damaged at the No. 1 reactor.

Japan's national news agency, Kyodo, said that 33 percent of the fuel rods at the No. 2 reactor were damaged and that the cores of both reactors were believed to have partially melted.