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    Nuclear Meltdown in Japan: What's the Risk of Radiation?

    FAQ on Radiation Risk From Tsunami-Damaged Nuclear Plants

    How much radiation has escaped Japan's damaged nuclear plants? continued...

    By comparison, a chest X-ray is 0.02 to 0.67 millisieverts. In a year, the typical U.S. resident is exposed to 3 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.

    Radiation levels in Tokyo are reported to be 20 times above normal but still not in the danger zone. However, a no-fly zone has been imposed for an 18-mile radius around the nuclear plant.

    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. News reports indicate many of these residents are fleeing the area instead. Some 100,000 people are reported to be in the area.

    Another radiation issue is in reactor 4, which had been shut down before the earthquake. Spent fuel rods still were cooling in the plant's rooftop pool. That cooling system appears to be in trouble, as a fire was reported in the plant. Should these fuel rods become exposed, a large amount of radiation will be released. As of March 18, plant officials had used helicopter drops and water cannons to try refill the pool, which may be leaking.

    For now, the chief radiation danger is to plant workers desperately trying to mitigate the disaster. Only a skeleton crew remains on site, threatened by radiation, fire, and hydrogen explosions.

    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.

    How dangerous is the radiation from the damaged Japanese nuclear reactors?

    So far, the only radiation injuries from Japan's nuclear disaster have been to workers trying to end the situation.

    Some of the workers trying to prevent a meltdown have already suffered radiation sickness and injury from explosions related to hydrogen buildup outside the reactor core. At least two others had their feet exposed to dangerously radioactive water.

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