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Cancer Health Center

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

FAQ on Radiation Risk From Tsunami-Damaged Nuclear Plants

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

"The scariest outcome from such releases of radiation are the immediate effects, which are going to be only felt by personnel who have to go into the building and shut it down," radiation biologist Jacqueline P. Williams, PhD, tells WebMD. Williams is a researcher in the department of radiation oncology at the University of Rochester, N.Y.

The long-term effects of radiation exposure, Williams says, are the various cancers that can occur.

The most cancers most commonly associated with radiation are leukemia and cancers of the thyroid, lung, and breast.

But it's easy to overestimate the danger, says radiation authority Henry D. Royal, MD, co-director of the Mallinckrodt Institute of Radiology at Washington University, St. Louis. Royal was co-leader of the international team that studied the health effects of the Chernobyl nuclear disaster.

"In Chernobyl, people living within 1 to 2 kilometers of the plant, who stayed indoors, received about 50 millisieverts of radiation -- equivalent to about five CT scans," Royal tells WebMD. "And in Fukushima, we are not talking about Chernobyl. This may be worse than Three Mile Island, but nothing like Chernobyl."

The worst nuclear disaster ever was in 1986 at the Chernobyl nuclear plant in northern Ukraine. This wasn't the same kind of disaster as in Japan, as it was caused by a series of human and mechanical failures. The result was a series of explosions that shot a plume of radioactive materials into the air.

Fallout from Chernobyl fell heavily on Belarus, Russia, Ukraine, Finland, Norway, Sweden, Austria, and Bulgaria.

"The Chernobyl cloud technically covered a huge area. It did follow the jet stream and everything else," Williams says. "But radioactive particles have substance, they have weight. The bigger the particle, the quicker it falls out of the cloud. So the contamination area where you have risks from contamination are relatively close to the disaster site. As far as I am aware, the cancers from Chernobyl radiation occurred in and around Chernobyl itself."

However, radioactive iodine from the Chernobyl cloud fell on fields where it was absorbed by grass, eaten by cows, and drunk as milk by children. Until 1998, there was a significant increase in thyroid cancer among children in the affected areas. Despite over 5,000 cases of thyroid cancer, there have been fewer than 20 deaths to date.

A meltdown in Japan would be devastating to the local environment. Should there be a release of radiation, and should winds blow in the wrong direction, residents of Japan would be affected to some degree. But the effects almost certainly will not go far beyond the borders of Japan.

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