The head of the U.N.'s nuclear energy agency called the effort to cool overheating reactors at Japan's crippled power plant a race against the clock that demands global cooperation Friday, and Japan reached out to the U.S. for help in reining in the crisis.
Japan's nuclear safety agency raised the severity rating of the disaster at the Fukushima Dai-ichi plant from Level 4 to Level 5 on the seven-level International Nuclear Event Scale, putting it on par with the Three Mile Island accident in Pennsylvania in 1979, said agency spokesman Ryohei Shiomi.
The scale defines a Level 4 incident as having local consequences and a Level 5 incident as having wider consequences. A partial meltdown at Three Mile Island also was ranked a Level 5. The Chernobyl accident of 1986, which killed at least 31 people with radiation sickness, raised long-term cancer rates, and spewed radiation for hundreds of miles, was ranked a Level 7. France's Nuclear Safety Authority has been saying since Tuesday that the crisis in northeastern Japan should be ranked Level 6 on the scale.
At the stricken complex, military fire trucks sprayed the troubled reactor units for a second day Friday, with tons of water arcing over the facility in desperate attempts to douse the units and prevent meltdowns that could spew dangerous levels of radiation.
"The whole world, not just Japan, is depending on them," Tokyo office worker Norie Igarashi, 44, said of the emergency teams at the plants.
Last week's magnitude 9.0 quake and tsunami in Japan's northeast set off the nuclear problems by knocking out power to cooling systems at the Fukushima Dai-ichi plant on the northeast coast. Since then, four of the troubled plant's six reactor units have had fires, explosions or partial meltdowns.
The unfolding crises have led to power shortages in Japan, forced factories to close, sent shockwaves through global manufacturing and triggered a plunge in Japanese stock prices.
"We see it as an extremely serious accident," Yukiya Amano, the head of the U.N.'s International Atomic Energy Agency, told reporters Friday just after arriving in Tokyo. "This is not something that just Japan should deal with, and people of the entire world should cooperate with Japan and the people in the disaster areas."
"I think they are racing against the clock," he said of the efforts to cool the complex.
One week after the quake and tsunami — which left more than 6,500 dead and over 10,300 missing — emergency crews are facing two challenges in the nuclear crisis: cooling the reactors where energy is generated, and cooling the adjacent spent fuel pools where used nuclear fuel rods are stored in water.
Both need water to keep their uranium cool and stop them from emitting radiation, but with radiation levels inside the complex already limiting where workers can go and how long they can remain, it's been difficult to get enough water inside.
Water in at least one fuel pool — in the complex's Unit 3 — is believed to be dangerously low, exposing the stored fuel rods. Without enough water, the rods may heat further and spew out radiation.
"Dealing with Unit 3 is our utmost priority," Chief Cabinet Secretary Yukio Edano told reporters.
Officials also reported that temperature levels in pools at Units 5 and 6 have gone up but not enough to cause immediate concern.
Edano said Friday that Tokyo is asking the U.S. government for help and that 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.
A U.S. military fire truck was used to help spray water into the crippled Unit 3, according to Air Force Chief of Staff Shigeru Iwasaki, though the vehicle was apparently driven by Japanese workers.
The U.S. vehicle was used alongside six Japanese military fire trucks normally used to extinguish fires at plane crashes.
The fire trucks allowed emergency workers to stay a relatively safe distance from the radiation, firing the water with high-pressure cannons. The firefighters also are able to direct the cannons from inside the vehicle.
Officials shared few details about the Friday operation, which lasted nearly 40 minutes, though Iwasaki said he believed some water had reached its target.
The U.S. also is sending specialized aircraft to help determine the scope of the nuclear contamination. The converted Boeing C-135 plane, called Constant Phoenix or "the Sniffer," will fly over Japan's nuclear plants and take samples from the atmosphere. Another Air Force plane, a drone called Global Hawk, is already circling above the plants. Its infrared sensors can detect heat and help determine the effectiveness of attempts to cool the reactors.
Low levels of radiation have been detected well beyond Tokyo, which is 140 miles south of the plant, but hazardous levels have been limited to the plant itself. Still, the crisis 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 Japanese government has been slow in releasing information on the crisis, even as the troubles have multiplied. In a country where the nuclear industry has a long history of hiding its safety problems, this has left many people in Japan and among governments overseas confused and anxious.
At times, Japan and the U.S. — two very close allies — have offered starkly differing assessments over the dangers at Fukushima. U.S. Nuclear Regulatory Commission Chairman Gregory Jazcko said Thursday that it could take days and "possibly weeks" to get the complex under control. He defended the U.S. decision to recommend a 50-mile evacuation zone for its citizens, wider than the 30-mile band Japan has ordered.
Crucial to the effort to regain control over the Fukushima plant is laying a new power line to the plant, allowing operators to restore cooling systems. The operator, Tokyo Electric Power Co., missed a deadline late Thursday but said Friday that workers hoped to complete the effort in 10 to 15 hours, said nuclear safety agency spokesman Minoru Ohgoda.
But the utility is not sure the cooling systems will still function. If they don't, electricity won't help.
President Obama appeared on television to assure Americans that officials do not expect harmful amounts of radiation to reach the U.S. or its territories.
"When we see a crisis like the one in Japan, we have a responsibility to learn from this event and to draw from those lessons to ensure the safety and security of our people," Obama said Thursday. He also said the U.S. is offering Japan any help it could provide.
On Friday, Obama called on the Nuclear Regulatory Commission to conduct a "comprehensive review" of the safety of all U.S. nuclear plants.
At the Fukushima Dai-ichi plant, a core team of 180 emergency workers has been rotating out of the complex to minimize radiation exposure.
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.
