Yomiuri Shimbun/AFP/Getty Images
This aerial shot shows a Japanese Self Defence Force's CH-47 Chinook helicopter holding more than seven tonnes water each with large buckets from the sea near Natori in Miyagi prefecture on March 17, 2011.
Attempts to get cooling water onto heated nuclear fuel pools by air and ground at Japan's Fukushima Dai-ichi power plant were largely unsuccessful Thursday. A second priority is trying to restore power at the plant, where reactor cooling systems were disrupted by Friday's earthquake and tsunami.
Japanese officials have made little apparent progress bringing the crisis at the Fukushima Dai-ichi nuclear complex under control Thursday.
Neither helicopters nor water cannon trucks have delivered much water to cool overheating nuclear fuel rods at the stricken complex.
Japanese military helicopters made the first attempt. Using tactics similar to those used for fighting wildfires, they tried to dump loads of seawater onto a pool that contains used uranium fuel that is overheating and highly radioactive.
The fuel is supposed to be covered with water, which keeps it cool and contains radiation. But Friday's earthquake and subsequent tsunami disrupted part of the plant's cooling system.
Two CH-47 Chinook helicopters began dumping seawater on the complex's damaged reactor No. 3 at 9:48 a.m. local time (8:48 p.m. EDT), defense ministry spokeswoman Kazumi Toyama said. The choppers dumped at least four loads on the reactor in just the first 10 minutes, though television footage showed much of it appearing to disperse in the wind.
Trucks with water cannons that are normally used to control rioting crowds then started spraying another one of the overheating pools. But Japan's national broadcaster, NHK, reports that one try proved the strategy is futile: Radiation levels are simply too high, and the truck couldn't get close.
Plant operators also said they're racing to finish a new power line that could restore the cooling systems and ease the crisis at the plant on the country's northeast coast.
The state of the pools of used nuclear fuel at reactors No. 3 and No. 4 has emerged as the most urgent problem at the nuclear complex. The reactors themselves are sealed off in steel vessels inside huge concrete containment vessels. So even though some of the fuel inside has melted, most of the radiation is contained. The spent fuel pools, on the other hand, are inside ordinary buildings that are no longer sealed because of explosions and fires.
"We are afraid that the water level at unit No. 4 is the lowest," said Hikaru Kuroda, facilities management official at Tokyo Electric Power Co. But, he added, "because we cannot get near it, the only way to monitor the situation is visually from far away."
The U.S. military has sent an unmanned aerial drone to fly above the complex and take pictures.
'Like Suicide Fighters In A War'
Emergency workers were forced to temporarily retreat from the plant Wednesday when radiation levels soared, losing precious time. While the levels later dropped, they were still too high to let workers get close.
A core team of 180 emergency workers has been at the forefront of the struggle at the plant, rotating in and out of the complex to try to reduce their radiation exposure.
But experts said anyone working close to the reactors was almost certainly being exposed to radiation levels that could at least give them much higher cancer risks.
"I don't know any other way to say it, but this is like suicide fighters in a war," said Keiichi Nakagawa, associate professor of the Department of Radiology at University of Tokyo Hospital.
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.
The Japanese government said it had no plans to expand its mandatory, 12-mile exclusion zone around the plant, while also urging people within roughly 20 miles to stay inside.
The top U.S. nuclear regulatory official gave a far bleaker assessment of the situation and the U.S. ambassador said on Wednesday that the situation was "deteriorating" while warning U.S. citizens within 50 miles of the complex to leave the area or at least remain indoors.
The troubles at the nuclear complex began when last week's magnitude 9.0 earthquake and tsunami knocked out power and destroyed backup generators needed for the reactors' cooling systems.
Four of the plant's six reactors have faced serious crises involving fires, explosions, damage to the structures housing reactor cores, partial meltdowns or rising temperatures in the pools used to store spent nuclear fuel. Officials also announced that temperatures are rising in the spent fuel pools of the last two reactors, though they say at the current rate it will be another week before temperatures in those reactor pools reach critical levels.
Ultimately, the only solution is to restore power to the plant so that cooling systems can begin working again. Everything else is a stop-gap measure.
NPR's Christopher Joyce contributed to this report, which contains material from The Associated Press. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.