Japanese military helicopters dumped loads of seawater onto a stricken nuclear reactor today, trying to avoid full meltdowns as plant operators said they were close to finishing a new power line that could restore cooling systems and ease the crisis.
U.S. officials in Washington, meanwhile, warned that the Fukushima Dai-ichi plant in northeastern Japan may be on the verge of spewing more radioactive material because water was gone from a storage pool for spent nuclear fuel rods.
The troubles at several of the plant's reactors were set off when last week's earthquake and tsunami knocked out power and ruined backup generators needed for their cooling systems, adding a major nuclear crisis for Japan as it dealt with twin natural disasters that killed more than 10,000 people and left hundreds of thousands homeless.
A Japanese military CH-47 Chinook helicopter began dumping seawater on the damaged reactor of Unit 3 at the Fukushima complex, said defense ministry spokeswoman Kazumi Toyama. The aircraft dumped at least four loads on the reactor, though much of the water appeared to be dispersed in the air.
The dumping was intended to help cool the reactor and replenish water in a pool holding spent fuel rods, Toyama said.
The plant's owner, Tokyo Electric Power Co., said earlier that the pool was nearly empty, which might cause the rods to overheat.
The comments from U.S. officials indicated there were similar problems at another unit of the Dai-ichi complex.
U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko said at a congressional hearing in Washington that all the water was gone from a separate spent fuel pool at the plant's Unit 4. Japanese officials expressed similar worries about that unit but said that it was impossible to be sure of its status.
If Jaczko is correct, it would mean there's nothing to stop the used fuel rods from getting hotter and ultimately melting down. The outer shells of the rods could also ignite with enough force to propel the radioactive fuel inside over a wide area.
He said the information was coming from NRC staff in Tokyo who are working with the utility in Japan. Emergency workers were forced to retreat from the plant Wednesday when radiation levels soared, losing precious time. They resumed work after radiation levels dropped, but much of the monitoring equipment in the plant is inoperable, complicating efforts to assess the situation.
"We are afraid that the water level at unit 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."
Japanese officials raised hopes of easing the crisis, saying early today that they may be close to bringing power back to the plant and restoring the reactors' cooling systems.
The new power line would revive electric-powered pumps, allowing the company to control rising temperatures and pressure that led to at least partial meltdowns in three reactors. The company is also trying to repair its existing disabled power line.
Tokyo Electric Power spokesman Naoki Tsunoda said the new power line to the plant is almost finished and that officials plan to try it "as soon as possible," but he could not say exactly when.
Other countries have complained that Japan has been too slow and vague in releasing details about its rapidly evolving crisis at complex of six reactors along Japan's northeastern coast, which was ravaged by Friday's magnitude 9.0 earthquake and subsequent tsunami.
Yukiya Amano, chief of the U.N. nuclear agency, said he would go to Japan to assess what he called a "very serious" situation and urged Tokyo to provide better information to his organization.
Several countries have advised their citizens to consider leaving Tokyo and earthquake-affected areas.
About 180 emergency workers have been working in shifts to manually pump seawater into the reactors to stave off complete meltdowns.
Japan's health ministry made what it described as an "unavoidable" change, more than doubling the amount of radiation to which the workers can be legally exposed.
"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 the University of Tokyo Hospital.
Government officials said they asked special police units to bring in water cannons — normally used to quell rioters — to spray water onto the spent fuel storage pool at Unit 4.
The nuclear crisis has partly overshadowed the human tragedy caused by the earthquake. Millions of Japanese have been with little food and water in heavy snow and rain.
More than 4,300 people are officially listed as dead, but officials believe the toll will climb to well over 10,000.