Japan struggles to cool radioactive materials, after helicopter mission ruled unsafe
Toshirharu Kato / GETTY IMAGES - The Japanese government is telling people living within 20 miles to stay indoors with the windows closed because of the possibility of high levels of radiation being released from the Fukushima Diiachi plant.
Japanese officials scrambled Wednesday for ways to cool overheated elements at a damaged nuclear plant that can emit potentially lethal radioactive steam, after aborting a risky mission to use a helicopter to douse part of the plant with water.
Gallery: Japan’s nuclear crisis: Japan battles to prevent a nuclear catastrophe and to care for millions of people without power or water in its worst crisis since World War II.
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Graphic: Track the status of the nuclear crisis in Japan.
As radiation levels in the air above the Fukushima Daiichi plant spiked dangerously for the second consecutive day, a skeleton crew of workers charged with cooling efforts was temporarily relocated.
Within an hour, though, the radiation levels dropped again, and the small group was permitted to return.
In order for them to resume trying to cool the damaged sectors, Japan’s health and welfare minister had to waive the nation’s standard of radiation exposure, increasing the level of acceptable exposure from 100 millisieverts to 250 — five times the level allowed in the United States.
The workers were focusing on the plant’s unit 3 reactor building, where a white plume of smoke was spotted Wednesday morning, and on unit 4, where fires flared up Tuesday and again on Wednesday morning.
The blazes triggered fears that spent uranium fuel sitting in a pool above the reactor was burning. Such a conflagration would generate intense concentrations of cesium-137 and other dangerous radioactive isotopes. But a spokesperson for the Nuclear Energy Institute, an industry lobbying group, said Tokyo Electric Power Co. concluded that the first fire in unit 4 was not in the spent fuel pool, “but rather in a corner of the reactor building’s fourth floor.”
Initially, government spokesman Yukio Edano said the steam coming from the unit 3 reactor building could mean that its containment vessel had ruptured in an earlier explosion — a potentially dire development. A reactor containment vessel in the plant’s unit 2 is believed to have ruptured on Tuesday.
But Edano said Wednesday afternoon that the unit 3 containment vessel was unlikely to have suffered severe damage. The Japanese news agency Kyodo quoted the country’s nuclear disaster task force as saying: “The possibility of the No. 3 reactor having suffered severe damage to its containment vessel is low.”
Still, Edano said officials presumed that the steam coming from unit 3 was indeed radioactive. He said emergency crews were still trying to determine its source .
The rising steam was just the latest problem for the embattled plant, which suffered heavy damage to its cooling systems after Friday’s devastating earthquake and tsunami. Since then, the Japanese government and Tokyo Electric, which owns the facility, have struggled mightily to keep the plant’s six reactors cool. Each day has brought new problems.
Tuesday’s blast at unit 2 was not outwardly visible, but was potentially more dangerous than some of the earlier explosions, because it may have created an escape route for radioactive material bottled up inside the thick steel-and-concrete reactor vessel.
Radiation-laced steam is probably building between the reactor vessel and the building that houses it, experts said, creating pressure that could blow apart the structure, emitting radiation from the core.
“They’re putting water into the core and generating steam, and that steam has to go somewhere. It has to be carrying radiation,” said nuclear engineer Arnie Gundersen, who has 40 years of experience overseeing the Vermont Yankee nuclear facility, whose reactors are of the same vintage and design as those at the Fukushima Daiichi plant.
Such a breach would be the first at a nuclear power plant since the Chernobyl catastrophe 25 years ago in what was then the Soviet Union.
Nuclear experts have repeatedly stressed that radiation releases on the scale of Chernobyl are unlikely or even impossible, given the Japanese plant’s heavier engineering and additional layers of containment. Still, Tokyo Electric said radiation briefly rose to dangerous levels at the plant Tuesday morning and again on Wednesday.
Crews noted a drop in pressure after the blast inside the unit 2 reactor and within a doughnut-shaped structure below, called a suppression pool. The simultaneous loss of pressure in those two places indicates serious damage, nuclear experts said.
The explosion probably happened after the streams of seawater that crews have been pumping into the reactor faltered. The fuel rods were left completely exposed to the air for some time, Tokyo Electric said in a statement. Without water, the rods grew white-hot and possibly melted through the steel-and-concrete tube.
The power company said a skeleton crew of 50 to 70 employees — far fewer than the 1,400 or more at the plant during normal operations — had been working in shifts to keep seawater flowing to the three reactors now in trouble. Their withdrawal on Wednesday temporarily left the plant with nobody to continue cooling operations.
Wednesday afternoon, the Japanese military dispatched two helicopters to the Daiichi plant from Kasuminome Air Base in Sendai. A lead chopper was sent to determine whether radiation levels were low enough to continue with the operation. The second helicopter, a Boeing CH-47, followed behind, a huge bucket of sea water dangling beneath it. The CH-47 was slated to make several passes to drop water onto unit 3. But the crew on the first copter found radiation levels were too high to carry out the risky mission.
Using a helicopter, or fire hoses, to spray water through holes in the breached buildings would be a risky, last-ditch effort to prevent the spent fuel from burning. With the outer containment building at unit 2 primed for a possible explosion, experts said, any fire crews would be in grave peril.
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