Evaluation of averted doses to infants by tap water restrictions after the Fukushima Daiichi Nuclear Power Plant accident

There has been some concern in reviewing the effectiveness of making decisions on the implementation of protective measures in emergency exposure situations. After the Fukushima Daiichi Nuclear Power Plant accident, temporal changes in the concentration of iodine 131 in tap water were studied using published data from several authorities in Fukushima, Ibaraki, and Tokyo. Averted doses to infants (1-year-old children) due to the intake of iodine 131 through tap water intake restrictions were also evaluated. Consequently, it was found that the apparent half-life of iodine 131 in tap water was 2.8 days. The averted equivalent doses to the thyroids of 1-year-old children were found to have a maximum value of 8.3 mSv in a local area of Fukushima. Hence, the tap water intake restrictions implemented by the authorities were considered to be effective in the early phase of the emergency exposure situation. (author)