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Japan Radiation Risks: FAQ

Answers to questions about health risks posed by Japan's damaged Fukushimi Daiichi nuclear power plant.

What does it mean for a nuclear energy plant to melt down? continued...

Three of the six buildings housing Fukushima Daiichi's six reactors had hydrogen explosions. One, on March 14, injured 11 workers and could be felt for miles. However, the internal containment walls appeared to remain intact. The third blast at unit 2 may have caused a small breach in the inner containment vessel, as radioactivity around the plant shot up to dangerous levels before going down. 

On March 14, officials ordered the evacuation of all residents living within 20 kilometers (about 12.5 miles) of the plant. On March 15, they advised people living between 20 kilometers and 30 kilometers (about 18.6 miles) to remain indoors. Many people left the area. On March 25, Japanese officials encouraged people within 19 miles of the plant to leave the area.

Another radiation issue is in reactor 4, which had been shut down before the earthquake. But spent fuel rods were still cooling in the plant's rooftop pool. These fuel rods may have been exposed and may have released radiation.

One of the reactors, reactor 3, is said to be running on mixed-oxide (MOX) fuel. MOX fuel contains plutonium in far greater amounts than regular nuclear fuel and would be more toxic if released into the environment. 

Could the nuclear disaster in Japan happen in the U.S.?

 The U.S. has 23 nuclear reactors at 16 nuclear power plants that are designed exactly like the reactors leaking radiation in Japan.

Back in 1972, a safety official with the U.S. Atomic Energy Commission warned in a memo that the "safety disadvantages" of these reactors outweighed their advantages.

But remember, the nuclear plants in Japan were hit by an earthquake and tsunami of record proportions. This doesn't mean the aging U.S. plants are safe -- but neither does it mean they are an imminent danger.

WebMD senior reporter Daniel J. DeNoon contributed to this report.

Reviewed on April 15, 2011

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