Safety evaluation of radiation dose rates in Fukushima Nakadori districts

Abstract

After the TEPCO Fukushima DAIICHI NPP accident, IAEA and ICRP advised accelerating the decontamination work to clean up the living environment of the areas where additional annual radiation exposure doses are beyond 1 mSv per year (i.e., 1 mSv/y) and to diminish radiation worries. However, the advice was not recognized well because it did not contain clearly understandable numerical data. In the present work, the ambient radiation dose rates in the Nakadori district have been investigated to clarify that the doses are lower than 1 mSv/y in the major part where the decontamination was completed. A part of the district and three municipalities in the special decontamination area have doses of 1.0–2.0 mSv/y. The country-averaged annual doses of natural radiation in the world have been evaluated using the basic data taken from the UNSCEAR 2000 report. The result shows that total annual exposure doses containing cesium and natural radiation contributions in Fukushima are 2–4 mSv/y, which are close to the natural radiation doses in Europe. The risk coefficient of the public exposure limits, 1 mSv/y, has also been evaluated to be 4.5 × 10−7 per year. It is lower than that of traffic accidents by two orders of magnitude. These results will be useful to judge how the safety of the Fukushima prefecture is secured.