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Cancer Health Center

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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 are the health effects of radiation? continued...

The long-term effects of radiation exposure, Williams says, are the various cancers that can occur. The cancers most commonly associated with radiation are leukemia and cancers of the thyroid, lung, and breast.

In a year, the typical U.S. resident is exposed to 3 millisieverts of radiation, just as part of day-to-day life. By comparison, a chest X-ray is 0.02 to 0.67 millisieverts.

A person who receives a short-term dose of 1,000 millisieverts will experience radiation sickness but probably will survive. Short-term doses of 2,000 to 10,000 millisieverts have an increasing probability of causing a fatal cancer.

Is it safe to visit Japan?

That depends on whom you ask and what areas of Japan you’re talking about.

As of March 30, the U.S. State Department still advised people to defer non-essential travel to a number of regions beyond just the area of the earthquake, tsunami and radiation crisis, including Tokyo and Yokohama.

Other popular destinations, such as Kyoto, Okinawa and Osaka, are “outside the regions of concern,” according to the State Department’s warning. (For an updated alert, go to the State Department's web site.)

On the other hand, experts tell WebMD that they would not hesitate to travel to areas of Japan outside the disaster zone.

“I was supposed to go to Japan next month, but the meeting was cancelled because the organizers understandably have other things to do,” Williams says. “But I was perfectly happy to go, and I’m a bit sad that I’m not because I’ve never been to Japan. I would be absolutely fine to go.”

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

"Meltdown" is not a technical term, but it vividly describes the worst-case scenario for a nuclear reactor.

Nuclear reactors generate power via controlled nuclear fission, which occurs when enough radioactive material is gathered into a critical mass. Control rods can separate the radioactive material, thus ending the nuclear reaction.

That's exactly what happened when the March 11 earthquake hit Japan. Control rods effectively halted the nuclear reactions.

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