Japan’s nuclear emergency turned more dire on Tuesday after the third explosion in four days rocked the seaside Fukushima Daiichi complex and fire briefly raged in a storage facility for spent fuel rods at a fourth, previously unaffected reactor.Officials from Tokyo Electric Power Co., owner of the nuclear complex, said radioactive substances were emitted after a 6:14 a.m. explosion, which took place in the unit 2 reactor. The blast took place near or in the suppression pool, which traps and cools radioactive elements from the containment vessel, officials said. The explosion appeared to have damaged valves and pipes, possibly creating a path for radioactive materials to escape.
A grave Prime Minister Naoto Kan told the nation Tuesday morning that radiation had already spread from the reactors and there was “still a very high risk of further radioactive material escaping.” He advised people within 19 miles of the plant to remain indoors. He urged calm.
Tokyo Electric, which over the weekend said it had 1,400 people working at the complex, said it was evacuating all but 50 workers. Kan hailed those workers, who he said “are putting themselves in a very dangerous situation.”
A no-fly zone was declared covering a 19-mile radius from the facility.
The setbacks came as Tokyo Electric was still wrestling to regain control of ultra-hot fuel rods in two other nuclear units, nos. 1 and 3, by flooding them with seawater.
Tuesday began with a fire that broke out in a pool storing spent fuel rods at the base of unit 4, which had been shut down for inspection before last Friday’s earthquake. Experts said the fire most likely broke out because the pool water had run low or dry, allowing the rods to overheat. Radioactive substances spewed outside from the fire, officials said, because the structure housing the pool was damaged by Monday’s explosion at unit 3.
Half an hour later, the explosion at unit 2 took place. Experts said that, unlike the two previous explosions that destroyed outer buildings, this explosion might have damaged portions of the containment vessel designed to bottle up radioactive materials in the event of an emergency.
The explosion — more serious than the earlier ones — was followed by a brief drop in pressure in the vessel and a spike in radioactivity outside the reactor to levels more than eight times the recommended limit for what people should receive in a year, the company said. Japanese government officials later said it was unclear whether the spent fuel fire or the explosion had caused the spike in radiation.
The new setbacks came on the heels of a difficult Monday at Fukushima Daiichi unit 2, one of six reactors at the site. Utility officials there reported that four out of five water pumps being used to flood the reactor had failed and that the other pump had briefly stopped working. As a result, the company said, the fuel rods, normally covered by water, were completely exposed for 140 minutes.
That could have grave consequences, worsening the partial meltdown that most experts think is underway. By comparison, in the 1979 Three Mile Island, Pa., nuclear plant accident, it took just two hours for half the plant’s nuclear fuel to melt.
According to a report by the Kyodo news agency, the fifth pump was later restarted, and seawater mixed with boron was again injected in a desperate bid to cool the reactor, but the fuel rods remained partially exposed and ultra-hot. On Tuesday morning, Tokyo Electric said that 2.7 meters, or less than half, of the rods were still exposed.
The other four pumps were thought to have been damaged by a blast Monday that destroyed a building at the nearby unit 3 reactor, Kyodo reported. That blast, like one on Saturday at unit 1, was caused by a buildup in hydrogen generated by a reaction that took place when the zirconium alloy wrapped around the fuel rods was exposed to steam at 2,200 degrees Fahrenheit.
The International Atomic Energy Agency reported that injections of seawater into units 1 and 3 had been interrupted because of a low level in a seawater supply reservoir, but the seawater injections were later restored.
A commercial satellite photo of the complex showed piles of debris on top of units 1 and 3, which raised new fears about the condition of the pools where spent fuel is stored, especially at unit 1, where a design by General Electric placed the pool on top of the reactor but below the outer structure that was destroyed. In the satellite photo, there was no sign of a large crane that had been sitting on the roof before the blast. The ability of workers to assess the damage was hindered by fears that another explosion might occur.
In March 2010, 1,760 tons of spent fuel was stored in the six pools — 84 percent of capacity, according to Tokyo Electric.
After Monday’s explosion at unit 3, Japanese government officials were quick to assert that it did not damage the core containment structure, and they said there would be little increase in radiation levels around the plant. But the explosion prompted Japan’s nuclear agency to warn those within 12 miles to stay indoors. The blast also injured 11 people, one seriously.
The string of earthquake- and tsunami-triggered troubles at the Fukushima Daiichi plant began Friday, when a loss of grid power (caused by the earthquake) followed by a loss of backup diesel generators (caused by the tsunami) led to the failure of cooling systems needed to keep reactor cores from overheating.
The IAEA reported that Japan has evacuated 185,000 people from towns near the nuclear complex. The agency said Japan has distributed 230,000 units of stable iodine to evacuation centers from the area around the Fukushima Daiichi and Fukushima Daini nuclear power plants. The iodine has not been administered to residents; the distribution is a precautionary measure. The ingestion of stable iodine can help to prevent the accumulation of radioactive iodine in the thyroid.
The U.S. 7th Fleet said Monday that some of its personnel, who are stationed 100 miles offshore from the Fukushima Daiichi plant, had come into contact with radioactive contamination. The airborne radioactivity prompted the fleet to reposition its ships and aircraft.
Using sensitive instruments, precautionary measurements were conducted on three helicopter aircrews returning to the USS Ronald Reagan after conducting disaster relief missions near Sendai. Those measurements identified low levels of radioactivity on 17 crew members.
The low-level radioactivity was easily removed from affected personnel by washing with soap and water, and later tests detected no further contamination.
The political fallout spread all the way to the United States and Europe. German Chancellor Angel Merkel said Monday that she was suspending a deal that would have extended permits for 17 aging nuclear plants.
Many nuclear experts also called for a tougher scrutiny of U.S. plants, noting that the Japanese nuclear crisis exposed the limits of human ingenuity and imagination and pointed to the possible failure of the best-laid backup plans.
David Lochbaum, a nuclear engineer and director of the Nuclear Safety Program of the Union of Concerned Scientists, said in a conference call that in certain respects, the U.S. nuclear plants are not as prepared as the Japanese ones for a catastrophic power outage. After the earthquake and tsunami knocked out the electrical grid and backup generators, the Japanese engineers switched to batteries that could last for eight hours, he said.
“In this country, most of our reactors are only designed with battery capacity for four hours,” Lochbaum said. “Many of our reactors are in situation where earthquakes, or hurricanes in the gulf, or ice storms in the northeast, or a tree in Cleveland, can cause an extensive blackout,” he said.
The August 2003 blackout that affected 52 million people across the upper Midwest, New York and parts of Canada was triggered when overheated wires sagged into trees in northeastern Ohio. Nine nuclear units switched to diesel backup generators, which are the size of locomotives without wheels.
Despite the cascade of equipment failures at the Fukushima Daiichi complex, some nuclear experts noted on Monday that the fuel rods there, whose temperature could have risen to as high as 4,000 degrees Fahrenheit, would lose some of their heat over the next few days and would probably remain encased, even in the worst-case scenario, in a secondary containment structure with several feet of steel and concrete walls.
But the new explosion raises new questions. With it impossible to see into the reactor vessels, officials were in large part speculating about what is happening inside by using a variety of gauges and indicators.
“Let’s hope they can get these reactors under control,” said Richard Lester, head of the department of nuclear science and engineering at the Massachusetts Institute of Technology. “They’re not there yet.”