Japan fears a nuclear disaster after reactor breach

The cooling problems at Unit 2 represent the most serious development yet in the crisis at the plant, said nuclear specialist Edwin Lyman of the Union of Concerned Scientists.

When the fuel rods get too hot and react with water, they produce hydrogen gas that vents from the reactor into the containment building. When enough hydrogen accumulates, it becomes explosive. Containment buildings around two other reactors at the Fukushima complex already suffered explosions, on Saturday and Monday.

Engineers had begun using fire hoses to pump seawater into the Unit 2 reactor — the third at the plant to receive the last-ditch treatment — after the emergency cooling system failed. Company officials said workers were not paying sufficient attention to the process, however, and let the pump stall, allowing the fuel rods to become partially exposed to the air.

Once the pump was restarted and water flow was restored, another worker inadvertently closed a valve that was designed to vent steam from the containment vessel. As pressure built up inside the vessel, the pumps could no longer force water into it and the fuel rods were once again exposed.

Four officials from Tokyo Electric Power in dark suits and looking somber began their nationally televised news conference hours after the onset of the problems at the Unit 2 reactor by bowing and apologizing for the worry caused.

In something of a contradiction, officials at Japan's Nuclear and Industrial Safety Agency said that, even in a worst-case scenario, the three troubled reactors at Fukushima had been depressurized by the release of radioactive steam, which would decrease the destructiveness of any breach, according to Kyodo News.

But other nuclear experts said it remained possible that an overheated uranium core in any of these reactors could melt down and breach its containment vessel, exposing the environment to a radioactive plume.

The seriousness of the situation was further underscored Monday when the French Embassy in Tokyo advised its citizens to move away from Japan's capital to protect themselves against possible radiation exposure.

A flight ban was imposed within 20 miles of the Fukushima plant because of the radiation danger.

The U.S. Navy's 7th Fleet also said Monday that it had ordered the aircraft carrier Ronald Reagan away from Fukushima after detecting low-level contamination when it was about 100 miles northeast.

Nearly 200,000 Japanese had already been evacuated from a 12-mile zone surrounding the plant, and the company said it had moved 50 emergency workers away from the plant as well.

In the U.S., the Nuclear Regulatory Commission said Monday that it had received a formal request from Japan for assistance and was sending 10 people with expertise in boiling-water reactors. Agency spokesman Scott Burnell said the experts knew that they might have to "undergo radiation doses larger than normal."

Another serious risk involves the more than 200 tons of spent nuclear fuel that is stored in pools adjacent to the reactors, Alvarez said. Those cooling pools depend on continually circulating water to keep the fuel rods from catching fire. Without power to circulate the water, it heats up and potentially boils away, leaving the fuel rods exposed to air.

An aerial image of the Fukushima plant shows the loss of high-capacity cranes needed to move equipment to service the reactor. The photo also appears to show that the spent fuel pool is steaming hot, which may indicate the water is boiling off, Alvarez said.

U.S. nuclear experts said they were particularly concerned about the Unit 3 reactor because it is fueled in part with plutonium, an element used in hydrogen bombs that can be more difficult to control than the enriched uranium normally used to fuel nuclear power plants.

The U.S. Department of Energy activated the National Atmospheric Release Advisory Center at Livermore to create sophisticated computer models of how the radioactive releases from Fukushima No. 1 would disburse into the atmosphere. The center, which was created to deal with contamination in the event of a nuclear war, played a key role in predicting contamination patterns during the 1986 Chernobyl nuclear crisis.

Even before the admission of how serious the problems at the Fukushima complex had become, there were signs that the legendary patience and politeness of Japanese in the face of such adversity was wearing thin. In Natori, north of Tokyo, the top floor of the City Hall was repurposed into a disaster-relief center. There, in an oft-repeated scene, a woman in red pants and a brown coat berated government workers for sitting comfortably in their offices with heat, 24-hour power and water while the rest of the prefecture lacked basic services.

Voice cracking, she said the government had been far too slow in restoring the electricity and repairing roads and basic infrastructure.

"She's complaining that our operation doesn't work so well," said Chizuko Nakajima, a government worker in the senior citizen department, who was helping distribute food as an emergency volunteer. "Actually, it's true. We're so overwhelmed."

Adding to the sense of anxiety, strong aftershocks have rippled across a wide area since Friday's quake, with fresh jolts shaking Tokyo on Tuesday. Japan's Meteorological Agency said Saturday there was a 70% probability of another powerful temblor in coming three days.

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