Japan Faces Potential Nuclear Disaster as Radiation Levels Rise

Japan’s nuclear crisis verged toward catastrophe on Tuesday after an explosion damaged the vessel containing the nuclear core at one reactor and a fire at another spewed large amounts of radioactive material into the air, according to statements from Japanese government and industry officials.

In a brief address to the nation at 11 a.m. Tokyo time, Prime MinisterNaoto Kan pleaded for calm, but warned that radiation had already spread from the crippled reactors and there was “a very high risk” of further leakage. Fortunately, the prevailing winds were sweeping most of the plume of radioactivity out into the Pacific Ocean, rather than over populated areas.

The sudden turn of events, after an explosion Monday at one reactor and then an early-morning explosion Tuesday at yet another — the third in four days at the plant — already made the crisis at the Fukushima Daiichi Nuclear Power Station the worst nuclear accident since the Chernobyl reactor disaster a quarter century ago.

Engineers at the plant, working at tremendous personal risk, on Tuesday continued efforts to cool down the most heavily damaged unit, reactor No. 2, by pumping in seawater. According to government statements, most of the 800 workers at the plant had been withdrawn, leaving 50 or so workers in a desperate effort to keep the cores of three stricken reactors cooled with seawater pumped by firefighting equipment, while crews battled to put out the fire at the No. 4 reactor, which they claimed to have done just after noon on Tuesday.

That fourth reactor had been turned off and was under refurbishment for months before the earthquake and tsunami hit the plant on Friday. But the plant contains spent fuel rods that were removed from the reactor, and experts guessed that the pool containing those rods had run dry, allowing the rods to overheat and catch fire. That is almost as dangerous as the fuel in working reactors melting down, because the spent fuel can also spew radioactivity into the atmosphere.

After an emergency cabinet meeting, the Japanese government told people living within about 20 miles of the Daiichi plant to stay indoors, keep their windows closed and stop using air conditioning.

Mr. Kan, whose government was extraordinarily weak before the sequence of calamities struck the nation, told the Japanese people that “although this incident is of great concern, I ask you to react very calmly.” And in fact, there seemed to be little panic, but huge apprehension in a country where radioactivity brings up memories of Hiroshima and Nagasaki, the haunting images of post-war Japan.

Radiation measurements reported on Tuesday showed a spike of radioactivity around the plant that made the leakage significantly worse than it had been, with levels measured at one point as high as 400 millisieverts an hour. Even 7 minutes of exposure at that level will reach the maximum annual dose that a worker at an American nuclear plant is allowed. And exposure for 75 minutes would likely lead to acute radiation sickness.

The extent of the public health risk depends on how long such elevated levels persist, as well as how far and fast the radioactive materials spread, and whether the limited evacuation plan announced by the government proves sufficient.

In Tokyo, 170 miles south of the plant, the metropolitan government said Tuesday it had detected radiation levels 20 times above normal over the city, though it stressed that such a level posed no immediate health threat, and that levels had dropped since then.

The government said later Tuesday that radiation levels at the Fukushima plant also appeared to be falling sharply.

But worryingly, temperatures appeared to be rising in the spent fuel pools at two other reactors at the plant, No. 5 and No. 6, said Yukio Edano, the chief cabinet secretary. Meanwhile, workers continued to pump seawater into the No. 1 and No. 3 reactors, where cooling systems remained unusable.

Japan has officially requested assistance from the United States Nuclear Regulatory Commission, as well as the International Atomic Energy Agency. But on Tuesday, the United States Forces Japan said the Fukushima plant had turned away two fire trucks that had made their way to the plant to offer assistance.

“They said they didn’t need them,” said Sgt. Maj. Steve Valley of the military public affairs office. “So they came right back.”

The succession of problems at Daiichi was initially difficult to interpret, with confusion compounded by incomplete and inconsistent information provided by government officials and executives of the plant’s operator, Tokyo Electric Power Company.

But industry executives in close contact with officials in Japan expressed extreme concern that the authorities were close to losing control over the fuel melting that has been ongoing in three reactors at Daiichi, especially at the crippled No. 2 reactor where the containment vessel was damaged.

Tokyo Electric Power said Tuesday that after the explosion at the No. 2 reactor, pressure had dropped in the “suppression pool” — a section at the bottom of the reactor that converts steam to water and is part of the critical function of keeping the nuclear fuel protected. After that occurred, radiation levels outside No. 2 were reported to have risen sharply.

“We are on the brink. We are now facing the worst-case scenario,” said Hiroaki Koide, a senior reactor engineering specialist at the Research Reactor Institute of Kyoto University. “We can assume that the containment vessel at Reactor No. 2 is already breached. If there is heavy melting inside the reactor, large amounts of radiation will most definitely be released.”

Another executive said the chain of events at Daiichi suggested that it would be difficult to maintain emergency seawater cooling operations for an extended period if the containment vessel at one reactor had been compromised because radiation levels could threaten the health of workers nearby.

If all workers do in fact leave the plant, the nuclear fuel in all three reactors is likely to melt down, which would lead to wholesale releases of radioactive material — by far the largest accident of its kind since Chernobyl.

Even if a full meltdown is averted, Japanese officials have been facing unpalatable options. One was to continue flooding the reactors and venting the resulting steam, while hoping that the prevailing winds did not turn south toward Tokyo or west, across northern Japan to the Korean Peninsula. The other was to hope that the worst of the overheating was over, and that with the passage of a few more days the nuclear cores would cool enough to essentially entomb the radioactivity inside the plants, which clearly will never be used again. Both approaches carried huge risks.

While Japanese officials made no comparisons to past accidents, the release of an unknown quantity of radioactive gases and particles — all signs that the reactor cores were damaged from at least partial melting of fuel — added considerable tension to the effort to cool the reactors.

“It’s way past Three Mile Island already,” said Frank von Hippel, a physicist and professor at Princeton. “The biggest risk now is that the core really melts down and you have a steam explosion.”

The sharp deterioration came after a frantic day and night of rescue efforts focused largely on the No. 2 reactor. There, a malfunctioning valve prevented workers from manually venting the containment vessel to release pressure and allow fresh seawater to be injected into it. That meant that the extraordinary remedy emergency workers had jury-rigged to keep the nuclear fuel from overheating no longer worked.

As a result, the nuclear fuel in that reactor was exposed for many hours, increasing the risk of a breach of the container vessel and more dangerous emissions of radioactive particles.

By Tuesday morning, Tokyo Electric Power said that it had fixed the valve and resumed seawater injections, but that it had detected possible leaks in the containment vessel that prevented water from fully covering the fuel rods.

Then an explosion hit that reactor. After a series of conflicting reports about what level of damage was inflicted on the reactor after that blast, Mr. Edano, the chief cabinet secretary, said, “there is a very high probability that a portion of the containment vessel was damaged.”

The steel containment vessels that protect nuclear fuel in reactors are considered crucial to maintain the integrity of the reactor and the safety of the fuel.

Mr. Edano, however, said that the level of leaking at the No. 2 reactor remained small, raising the prospect that the container was sufficiently intact to protect the nuclear fuel inside.

 

 

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Earthquake, Tsunami Now Nuclear Risk Alerts Japan

Cooling systems have failed at another nuclear reactor on Japan’s devastated coast, hours after an explosion at a nearby unit made leaking radiation, or even outright meltdown, the central threat to the country following a catastrophic earthquake and tsunami.

The Japanese government said radiation emanating from the plant appeared to have decreased after Saturday’s blast, which produced a cloud of white smoke that obscured the complex. But the danger was grave enough that officials pumped sea water into the reactor to avoid disaster and moved 170,000 people from the area.

Japan’s nuclear safety agency reported on Sunday an emergency at another reactor unit, the third in the complex to have its cooling systems malfunction.

“All the functions to keep cooling water levels in No. 3 reactor have failed at the Fukushima No. 1 plant,” plant operator Tokyo Electric Power [Tepco] said, adding that pressure was rising slightly.

Japan’s nuclear safety agency rated the accident at four on the international scale of zero to seven. The 1979 Three Mile Island accident in the United States was rated five, while the 1986 Chernobyl disaster was a seven.

Japan dealt with the nuclear threat as it struggled to determine the scope of the earthquake, the most powerful in its recorded history, and the tsunami that ravaged its northeast on Friday with breathtaking speed and power.

The official count of the dead was 763, but the government said the figure could far exceed 1,000. Media reports said thousands of people were missing or unaccounted for.

 

Preventing meltdown

The explosion at the nuclear plant, Fukushima Dai-ichi, 274km northeast of Tokyo, appeared to be a consequence of steps taken to prevent a meltdown after the quake and tsunami knocked out power to the plant, crippling the system used to cool fuel rods there.
Inside that superheated steel vessel, water was being poured over the fuel rods to cool them formed hydrogen. The blast destroyed the building housing the reactor, but not the reactor itself, which is enveloped by stainless steel 15cm thick.
When officials released some of the hydrogen gas to relieve pressure inside the reactor, the hydrogen apparently reacted with oxygen, either in the air or the cooling water, and caused the explosion.

Officials declined to say what the temperature was inside the troubled reactor, Unit 1. At 1,200 degrees Celsius, the zirconium casings of the fuel rods can react with the cooling water and create hydrogen. At 2,200 C, the uranium fuel pellets inside the rods start to melt, the beginning of a meltdown.

Evacuation order

Chief Cabinet Secretary Yukio Edano said radiation around the plant had fallen, not risen, after the blast but did not offer an explanation.

Virtually any increase in dispersed radiation can raise the risk of cancer, and authorities were planning to distribute iodine, which helps protect against thyroid cancer. Authorities ordered 210,000 people out of the area within 20km of the reactor.
Officials have said that radiation levels at Fukushima were elevated before the blast: At one point, the plant was releasing each hour the amount of radiation a person normally absorbs from the environment each year.It was the first time Japan had confronted the threat of a significant spread of radiation since the greatest nightmare in its history, a catastrophe exponentially worse: the 1945 atomic bombings of Hiroshima and Nagasaki by the United States, which resulted in more than 200,000 deaths from the explosions, fallout and radiation sickness.

The Japanese utility that runs the plant said four workers suffered fractures and bruises and were being treated at a hospital.

Nine residents of a town near the plant who later evacuated the area tested positive for radiation exposure, though officials said they showed no health problems.

Although the government played down fears of radiation leak, Japanese nuclear agency spokesman Shinji Kinjo acknowledged there were still fears of a meltdown, the collapse of a power plant’s systems, rendering it unable regulate temperatures and keep the reactor fuel cool.