Radioactive cesium can cause more damage long-term, including cancer and lung problems, Williams said.
Workers at the crippled plant continued Tuesday to desperately try to avoid a complete meltdown at the reactors -- the melting of the radioactive core -- that could release radioactive contaminants into the environment and pose major, widespread health risks, the AP reported.
According to The New York Times, workers -- at great personal peril -- continued to pump seawater into the reactors in an attempt to keep them cool. The last-ditch effort was needed because Friday's twin disasters had knocked out conventional cooling systems and backup generators. Most of the 800 workers at the plant had been removed, with a skeleton crew of about 50 or so workers still on hand, while crews battled a fire at one of the reactors.
A "meltdown" isn't a technical term, but instead a layman's description of a serious collapse of a power plant's systems and ability to control temperatures, the AP reported.
Still, even a meltdown would not necessarily mean catastrophe, experts said: it depends on the amount and type of radioactive materials. Donald Olander, professor emeritus of nuclear engineering at the University of California, Berkeley, said even the much higher levels of radiation reported on Tuesday are "not a health hazard," the AP reported.
Experts put the situation in Japan in context to the two biggest nuclear reactor scares in the past -- 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 small that it did not threaten health, the AP said.
At Chernobyl, where there was no containment vessel like those in Japa
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