For battered Japan a new threat: nuclear meltdown

A partial meltdown was likely under way at a second nuclear reactor, a top Japanese official said Sunday, as operators frantically tried to prevent a similar threat from a nearby unit at the same facility following a catastrophic earthquake and tsunami that may have killed 1,000 people.

Some 170,000 people have been ordered to evacuate the area covering a radius of 12 miles (20 kilometers) 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.

Chief Cabinet Secretary Yukio Edano told reporters that a partial meltdown in Unit 3 of the Fukushima Dai-ichi power plant is "highly possible."

"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.

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.

Unit 3 is one of the three working reactors at the Fukushima plant that were damaged, losing the cooling functions necessary to keep the fuel rods working properly. The other unit in trouble is called Unit 1. The facility's Unit 2 has not been affected.

On Saturday, an explosion destroyed the walls of Unit 1 as operators desperately tried to prevent it from overheating and melting down.

Edano said cooling operation at Unit 1 was going smoothly after sea water was pumped in. He expressed hope that it would keep the plant under control.

Operators released slightly radioactive air from Unit 3 Sunday, while injecting water into it as an effort to reduce pressure and temperature to save the reactor from a possible meltdown, Edano said.

He 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.

Meanwhile, the government doubled the number of troops pressed into rescue and recovery operations to about 100,000 from 51,000.

Teams searched for the missing along hundreds of miles (kilometers) of the Japanese coast, and thousands of hungry survivors huddled in darkened emergency centers that were cut off from rescuers and aid. At least a million households had gone without water since the quake struck. Large areas of the countryside were surrounded by water and unreachable. Some 2.5 million households were without electricity.

Powerful aftershocks continued to rock the country, including one Sunday with a magnitude of 6.2 that originated in the sea, about 111 miles (179 kilometers) east of Tokyo. It swayed buildings in the capital, but there were no reports of injuries or damage.

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