Japan nuke plants: What happened
The Fukushima Daiichi nuclear plant was designed to withstand the fiercest of earthquakes.
As soon as the plant lost power, diesel generators kicked in, reports CBS News correspondent Nancy Cordes.
Even as workers like Danny Eudy were dodging the crashing debris trying to get out.
"He cut his feet and it slowed him down," said Janie Eudy, his wife from Pineville, La. "He said that was my lucky point, it slowed me down he said or otherwise if I had been a little faster I would have been in the tsunami and washed out to sea."
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But then at least one of the backup generators failed, crippling the cooling system that pumps thousands of gallons of water through one of the plant's six reactors. Heat began building and so did pressure in the form of steam. Plant managers began considering releasing some steam to the reactor's containment unit or even into the air to prevent an uncontrolled leak like the one at Pennsylvania's Three Mile Island in 1979.
Humans can withstand a certain amount of radioactive vapor without any problems.
Map: Color-coded radiation data in Japan
"When you have that vapor released from the site it automatically goes into the atmosphere and spreads out so it's not a significant amount and it's not a concentrated amount," said J. Scott Peterson with the Nuclear Energy Institute.
Still, when radiation levels inside the plan surged to 1,000 times the normal level, the evacuation area was expanded from a 2-mile radius to a 6-mile radius.
Japan's 55 nuclear reactors provide about a third of the nation's power - 11 of them were in the earthquake zone.
"The fact is a dozen of these reactors have shut down and have done what they were designed go do," said Richard Lester, with MIT.
Later, news came that the cooling system has failed at a second nuclear plant. Generators are now being trucked in. Getting a consistent source of power at both plants is going to be key to preventing a meltdown.
