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Fears about health risks rose dramatically in Japan Tuesday with news of a greater radiation release and renewed warnings to remaining residents within 20 miles to stay indoors.
Japanese officials said that more radiation was released at a nuclear plant disastrously damaged by last week's tsunami. Prime Minister Naoto Kan said radiation had spread from four reactors.
"The level seems very high, and there is still a very high risk of more radiation coming out," he said.
Thyroid cancer is the most immediate risk, and the Japanese government made plans to distribute potassium iodide pills to prevent it. Worse case scenarios — lots of radioactive fallout — can lead to other cancers years later.
Even a meltdown would not necessarily mean medical doom, experts said. It depends on the amount and type of radioactive materials.
Donald Olander, professor emeritus of nuclear engineering at the University of California at Berkeley, said even the much higher levels of radiation are "not a health hazard."
The world has seen two big nuclear reactor scares — in 1986 at the Chernobyl plant in the Ukraine, and in 1979 at the Three Mile Island plant in Pennsylvania.
At Three Mile Island, even though a quarter of the reactor core melted, the steel containment structure held. The radiation released was so minuscule that it did not threaten health - the equivalent of a chest X-ray to local folks.
At Chernobyl, where there was no containment vessel, far more radioactive material was released, and of a more dangerous type than at Three Mile Island. It stayed in soil and got into plants in the Ukraine, contaminating milk and meat for decades. Thousands of children developed thyroid cancer from radiation exposure, and scientists are still working to document other possible health problems.
The lessons have not been lost on the Japanese as they grapple with the Fukushima Dai-ichi power plant, whose cooling systems failed after a power outage from the massive earthquake last week.
They have evacuated 180,000 people from areas near the troubled reactors, where relatively minimal fallout was mostly confined at first. They've told people still in the area to wear masks, which can keep radioactive particles from being inhaled.
