ZAO, Japan - (AP) - Japanese military helicopters dumped loads ofseawater onto a stricken nuclear reactor Thursday, trying to avoidfull meltdowns as plant operators said they were close to finishinga new power line that could restore cooling systems and ease thecrisis.

U.S. officials in Washington, meanwhile, warned that theFukushima Dai-ichi plant in northeastern Japan may be on the vergeof spewing more radioactive material because water was gone from astorage pool that keeps spent nuclear fuel rods from overheating.

The troubles at several of the plant's reactors were set offwhen last week's earthquake and tsunami knocked out power andruined backup generators needed for their cooling systems, adding amajor nuclear crisis for Japan as it dealt with twin naturaldisasters that killed more than 10,000 people and left hundreds ofthousands homeless.

A Japanese military CH-47 Chinook helicopter began dumpingseawater on the damaged reactor of Unit 3 at the Fukushima complexat 9:48 a.m., said defense ministry spokeswoman Kazumi Toyama. Theaircraft dumped at least four loads on the reactor, though much ofthe water appeared to be dispersed in the wind.

At least a dozen more loads were planned in the 40 minutes thateach crew can operate before switching to limit radiation exposure,the ministry said.

The dumping was intended both to help cool the reactor and toreplenish water in a pool holding spent fuel rods, Toyama said. Theplant's owner, Tokyo Electric Power Co., said earlier that the poolwas nearly empty, which might cause the rods to overheat.

The comments from U.S. officials indicated there were similarproblems at another unit of the Dai-ichi complex.

U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko saidat a congressional hearing in Washington that all the water wasgone from a separate spent fuel pool at the plant's Unit 4.Japanese officials expressed similar worries about that unit, butthat it was impossible to be sure of its status.

Emergency workers were forced to retreat from the plantWednesday when radiation levels soared, losing precious time. Theyresumed work after radiation levels dropped, but much of themonitoring equipment in the plant is inoperable, complicatingefforts to assess the situation.

Japanese officials raised hopes of easing the crisis earlierThursday, saying that they may be close to bringing power back tothe plant and restoring the reactors' cooling systems.

The new power line would revive electric-powered pumps, allowingthe company to control the rising temperatures and pressure thathave led to at least partial meltdowns in three reactors. Thecompany is also trying to repair its existing disabled power line.

Tokyo Electric Power spokesman Naoki Tsunoda said the new powerline to the plant is almost finished and that officials plan to tryit "as soon as possible," but he could not say exactly when.

He urged the Japanese to care for each other and not give uphope. Millions of lives were disrupted by the magnitude 9earthquake and subsequent tsunami, which are believed to havekilled more than 10,000 people.

Other countries have complained that Japan has been too slow andvague in releasing details about its rapidly evolving crisis at thecomplex of six reactors along Japan's northeastern coast.

The 180 emergency workers who were working in shifts to manuallypump seawater into the overheating reactors to cool them and staveoff complete meltdowns were emerging as heroes as they perseveredin circumstances in which no radiation suit could completelyprotect them.

Japan's health ministry made what it called an "unavoidable"change Wednesday, more than doubling the amount of radiation towhich the workers can be legally exposed.

"I don't know any other way to say it, but this is like suicidefighters in a war," said Keiichi Nakagawa, associate professor ofthe Department of Radiology at University of Tokyo Hospital.

The government asked special police units to bring in watercannons - usually used to quell rioters - to spray onto the spentfuel storage pool at unit 4.

Elevated levels of radiation were detected well outside the20-mile emergency area around the plants. In Ibarakiprefecture, just south of Fukushima, officials said radiationlevels were about 300 times normal levels by late Wednesdaymorning. It would take three years of constant exposure to thesehigher levels to raise a person's risk of cancer.

A little radiation has also been detected in Tokyo, triggeringpanic buying of food and water.

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