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

Abstract

The effectiveness of urgent protective measures such as tap water restrictions and bottled water supplies in the early stage of an emergency exposure situation was studied after the Fukushima Daiichi nuclear power plant accident. Temporal changes in the concentration of an important radionuclide –iodine 131– in tap water were analyzed using published data in Fukushima, Ibaraki and Tokyo. Averted doses to members of the public due to chronic intakes of iodine 131 through tap water restrictions were also evaluated using an internal dose calculation code, DSYS-chronic code. In addition, the costs of bottled water supplies were calculated approximately. Consequently, it was found that the apparent half-life of iodine 131 in tap water was 2.8±1.2 days. The averted equivalent doses to the thyroid of members of the public–1-year-old children– were found to have a maximum value of 8.2 mSv in a local area of Fukushima. In comparison with Fukushima, the bottled water supplies might be a large sum of money regardless of the low doses in Tokyo. In conclusion, apart from the bottled water supplies, the tap water restrictions implemented by the authorities would be effective after the Fukushima Daiichi nuclear power plant accident.