A Japanese military helicopter flew towards a radiation-leaking nuclear plant Wednesday afternoon, a bucket of seawater dangling beneath it, the latest desperate attempt to cool overheated materials that are emitting potentially lethal radioactive steam.
But the operation was deemed too dangerous and aborted, because of high radiation levels in the air above the Fukushima Daiichi plant. Officials were left to find another way to address the explosions and leaks at the stricken facility, which have stoked fear and panic across the nation.
Television cameras first spotted plumes of white steam emitting from Unit 3 Wednesday morning. Chief Cabinet Secretary Yukio Edano said officials were trying to determine the source of the steam and presumed it to be radioactive.
As radiation levels rose around the plant, the lone 50 workers charged with cooling efforts were temporarily relocated. Hundreds of other workers had been evacuated Tuesday because conditions were deemed so dangerous.
Within an hour, though, the radiation levels dropped again, and the small group was permitted to continued its big task. 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 levels of acceptable exposure from 100 millisieverts to 250–five times the level allowed in the United States.
Wednesday afternoon, the military dispatched two helicopters from Kasuminome Air Base in Sendai. A lead chopper flew to the plant, less than 150 miles north of Tokyo, to determine whether radiation levels were low enough to continue with the operation.
The second helicopter, a Boeing CH-47 was scheduled to make several passes, dropping seawater onto Unit 3, which had suffered an explosion on Monday that resulted in structural damage that appears to have compromised the reactor. But the crew on the lead chopper found radiation levels were too high to carry out the risky mission.
The rising steam from the breached sector was just the latest problem for the embattled plant. One day earlier, officials were dealing with an explosion at Unit 2.
The Japanese government and Tokyo Electric Power have struggled to keep the six units at the plant cool since last Friday’s devastating earthquake. Officials were still making plans Wednesday afternoon to inject water from the ground on nearby Unit 4, but each day has brought new problems.
The explosion Tuesday in unit 2 probably damaged the main protective shield around the uranium-filled core inside one of the plant’s six reactors. 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.
The explosion, combined with a fire in a different unit and the pulling back of workers marked the deepest setbacks yet in the five-day battle to stabilize the Daiichi facility, which suffered heavy damage to its cooling systems after Friday’s earthquake and tsunami. Other explosions occurred earlier at two of the plant’s reactors.
The blast at unit 2 was not outwardly visible, but was potentially more dangerous, because it may have created an escape route for radioactive material bottled up inside the thick steel-and-concrete reactor tube. Radiation-laced steam is probably building between that tube and the building that houses it, experts said, triggering fears that the pressure would 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,” said said nuclear engineer Arnie Gundersen. Gunderson who has 40 years of experience overseeing the Vermont Yankee nuclear facility, whose re actors are of the same vintage and design as those at the Fukushima Daiichi plant. “It has to be carrying radiation.”
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 Power Co., which operates the Daiichi facility, said radiation briefly rose to dangerous levels at the plant Tuesday morning and again Wednesday. On Wednesday morning, the Japanese government raised the permitted radiation exposure for the few workers still at the plant by 2.5 times, to allow them to work longer, the national television network NHK reported.
After the Tuesday explosion, crews noted a drop in pressure inside the reactor and also 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, Tepco said in a statement. Without water, the rods grew white-hot and possibly melted through the steel-and-concrete tube.
Tepco 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 left the plant with nobody to continue cooling operations.
Also on Tuesday, and again on Wednesday morning, fires temporarily flared up in unit 4, causing fear 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.
A spokesperson for the Nuclear Energy Institute, an industry lobbying group, said that Tepco 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.”
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 and to keep cesium-137 and other radioactive isotopes from being released into the air.
“This is scary,” said Lake Barrett, a nuclear engineer who directed the cleanup of the Three Mile Island nuclear facility in Pennsylvania after the 1979 accident there. “The plans in a severe accident are to just get a fire hose in there, get any kind of water to keep water in the pool above the fuel. ”
With the outer containment building at unit 2 primed for a possible explosion, any fire crews would be in grave peril.
During normal plant operations, uranium fuel rods that can no longer produce enough heat for generating electricity are periodically removed from a reactor and placed into the spent fuel pools above the reactors. These rods continue to generate heat and radioactive isotopes for many years.
Keeping this material covered with water is sufficient to cool it. But water levels may have dropped dramatically during the crisis, exposing fuel rods to the air.
Robert Alvarez, an analyst at the Institute for Policy Studies who has long warned of the dangers of spent fuel pools, said that — unlike the reactors themselves — the fuel pools typically do not have backup pumps to maintain water flow. “They were so overwhelmed,” he said of the workers straining to contain the disaster, that they were unable to maintain enough water in the pool to prevent boiling.
If the fuel pools are exposed to the air, the radiation doses coming from them could be life-threatening up to 50 yards, Alvarez said.
Concerns about the dangers of storing used uranium fuel in relatively poorly shielded pools above reactors increased with the fear of terrorism after the Sept. 11, 2001, attacks, causing industry experts to dispute the design. In 2006, the National Research Council issued a report saying in part that a uranium fuel fire “could result in the release of large amounts of radioactive material.”
The NRC report also recommended that nuclear power plants build “redundant and diverse” coolant systems to keep the fuel underwater during a crisis.
Late Tuesday, Tepco said water levels were “low” in unit 4’s used fuel pool. Japanese officials said Wednesday that the water level in unit 5 was slightly low but that they plan to use a generator to add more.
Satellite photos show steam rising from the facility. The amount of radioactivity carried by the plume is unknown, but small increases in radiation — not enough to affect human health — were reported in Tokyo, about 150 miles to the southwest of the facility, and in other parts of Japan.
In response, NHK television reported that the Japanese government had ordered the country’s 47 prefectures to publicly report recorded radiation levels twice a day.
Wednesday morning, 33 nuclear disaster experts from the U.S. Department of Energy arrived in Japan with 17,000 pounds of gear to help with the crisis. The team also will help the Obama administration decide what to tell Americans in Japan and at home about the crisis, White House spokesman Jay Carney said. In response to questions about whether Japanese officials were providing complete information, Carney said American teams on the ground will make independent assessments of the situation.
When the teams arrive, they will find plenty of work to do. The plant’s reactor cores take about two weeks to lose half of their intense heat, Gundersen said, meaning that the battle between the radioactive cores and Fukushima Daiichi’s badly damaged cooling system will play out for days or weeks to come.
Maese reported from Tokyo. Correspondent Akiko Yamamoto in Tokyo also contributed to this report.