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Radiation exposure: How big is the threat in Japan?

Radiation exposure: Adding to the monumental losses after a Japanese earthquake and tsunami, problems at four nuclear reactors have residents near and far concerned about radiation exposure.

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On Sunday, Fukushima reactor 3 was vented again at which point there is believed to have been a partial meltdown in the reactor. A company spokesman stated that the radiation released thus far did not pose a health risk to humans. Later that day the cooling system in reactor 2 failed, and more radioactive steam was control-released.

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The concern is that that radioactive steam will eventually fall back to earth and contaminate food and water supplies.

On Monday, reactor 3 experienced a hydrogen explosion that blew the roof off its containment building. On Tuesday, a fire broke out at the fourth reactor and there were reports that the storage pond, holding spent fuel rods, had boiled over. The fire was extinguished, but Chief Cabinet Secretary Yukio Edano said that more radiation was released as a result and that "now we are talking about levels that can damage human health."

Edano went on to warn, "Please do not go outside. Please stay indoors. Please close windows and make your homes airtight. Don't turn on ventilators. Please hang your laundry indoors."

With radiation close to the reactors measuring four times higher than the maximum allowable limit of 100,000 microsieverts per hour, according to the International Atomic Energy Agency, residents are asking: How dangerous it is around Fukushima?


As of Monday, the plant was emitting as much radiation in one hour as it normally would in six months, but government spokesman, Yukio Edano, said "The possibility that a large amount of radiation has been released is low."

Matthew Bunn, co-principal investigator of the Managing the Atom Project at Harvard’s Belfer Center for Science and International Affairs noted that one risk is the release of "a very modest amount of cesium and other fission products" from partial meltdowns, such as those we have seen in reactor 1 and 3. Mr. Bunn went on to say another possibility is a complete nuclear meltdown. If the fuel in the reactors overheats and melts through the bottom of the steel containment vessel, it may reach an underground water source and create much more dangerous radioactive steam.


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