Last year's accident at the Fukushima No. 1 nuclear power plant exposed local residents to whole-body radiation doses of up to 50 millisieverts, well below the safety threshold, the World Health Organization has estimated.

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Nowhere did the whole-body dose estimate exceed the 100-millisievert limit, which poses enhanced risks of dying from cancer.

The thyroid gland dose estimate was the largest, at 100-200 millisieverts, for infants in Namie, Fukushima Prefecture. That level was lower than the average of 490 millisieverts for evacuees from the Chernobyl nuclear power plant accident of 1986, which caused thyroid cancer in many evacuees.