IWAKI, Japan – A partial meltdown was likely under way at a second nuclear reactor, a top Japanese official said Sunday, as authorities frantically tried to prevent a similar threat from nearby unit after a catastrophic earthquake and tsunami.
Some 170,000 people were ordered to evacuate the area covering a radius of 12 miles around the plant in Fukushima near Iwaki. A meltdown refers to a very serious collapse of a power plant’s systems and its ability to manage temperatures. A complete meltdown would release uranium and dangerous byproducts into the environment that can pose serious health risks.
Japan dealt with the nuclear threat as it struggled to determine the scope of the twin disasters Friday, when an 8.9-magnitude earthquake, the most powerful in its recorded history, was followed by a tsunami that ravaged its northeastern coast 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 some 10,000 people were missing or unaccounted for.
The quake and tsunami damaged three reactors at the Fukushima Dai-ichi nuclear plant, which lost their cooling functions necessary to keep the fuel rods functioning properly. At first the Unit 1 reactor was in trouble with an explosion destroying the walls of the room in which it is placed. Later, Unit 3 also began to experience problems.
Chief Cabinet Secretary Yukio Edano said operators released slightly radioactive air from Unit 3 today, while injecting water into it as an effort to reduce pressure and temperature to save the reactor from a possible meltdown.
Still, a partial meltdown in the unit is “highly possible,” he told reporters.
“Because it’s inside the reactor, we cannot directly check it but we are taking measures on the assumption of the possible partial meltdown,” he said.
Edano said radiation levels briefly rose above legal limits, but that it has since declined significantly. Also, fuel rods were exposed briefly, he said, indicating that coolant water didn’t cover the rods for some time. That would contribute further to raising the temperature in the reactor vessel.
The explosion at Fukushima Dai-ichi 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.
The blast destroyed the building housing the reactor, but not the reactor itself, which is enveloped by stainless steel 6 inches thick.
Inside that superheated steel vessel, water being poured over the fuel rods to cool them formed hydrogen. 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.
Nuclear agency officials said Japan was injecting seawater into the core – an indication, Hibbs said, of “how serious the problem is and how the Japanese had to resort to unusual and improvised solutions to cool the reactor core.”
Officials declined to say what the temperature was inside the troubled reactor, Unit 1. At 2,200 degrees Fahrenheit, the zirconium casings of the fuel rods can react with the cooling water and create hydrogen. At 4,000 degrees, the uranium fuel pellets inside the rods start to melt, the beginning of a meltdown.
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.
“Everyone wants to get out of the town. But the roads are terrible,” said Reiko Takagi, a middle-aged woman, standing outside a taxi company. “It is too dangerous to go anywhere. But we are afraid that winds may change and bring radiation toward us.”
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.
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.
The Japanese utility that runs the plant said four workers suffered fractures and bruises and were being treated at a hospital.
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.
Yaroslov Shtrombakh, a Russian nuclear expert, said it was unlikely that the Japanese plant would suffer a meltdown like the one in 1986 at Chernobyl, when a reactor exploded and sent a cloud of radiation over much of Europe. That reactor, unlike the reactor at Fukushima, was not housed in a sealed container.
