Some Comments on Dose Assessment for Members of the Public After the Fukushima Daiichi NPP Accident
Abstract This chapter describes the importance of dose assessment, either prospectively or retrospectively, for protection of members of the public exposed to radiation after the Fukushima NPP accident. There are three points. The first point is the implication of dose assessment. The International Commission on Radiological Protection (ICRP) has developed a system of radiation protection in which dose is the most important measure of radiological risk. In decision making regarding radiation protection, it is very important to understand the implications of dose assessment and to endeavor suitable protective measures based on the results of dose assessments. The second point is the radiological impact of the Fukushima accident. A large amount of radioactivity was released into the environment, but owing to extensive monitoring and protective measures, doses received by members of the public were fortunately not high, at the level of not causing any immediate health effects. We have much to learn from the accident, which includes (1) establishment of a better strategic system for emergency response, (2) reinforcement of environmental monitoring including in vivo counting of the human body, and (3) enhancement of better communication relevant to the accident. The third point is the effects of radiation exposure of children and infants. The protection of children in the accident aftermath has been a particular concern, and parents were extremely worried about the protection of their offspring. ICRP has provided age-dependent dose coefficients, so it was proposed that UNSCEAR should make the radiation risk of children more clear and that ICRP should revise its recommendation to include radiation protection scheme for children.
Keywords Dose assessment • Dose estimation • Internal dose • External dose • In vivo counting • Environmental monitoring • Infant • Children • Age-dependent dose • Age-dependent risk
On March 11 of 2011, the Great East Japan Earthquake and Tsunami affected the Tohoku District of Japan. In TEPCO's Fukushima Daiichi Nuclear Power Station, the external power supply was lost because of damage to the grid lines caused by the earthquake, and emergency diesel generators were terminated by the tsunami, which eliminated the capability to control radioactivity in reactors and the spent fuel storage pool. Consequently, a large amount of radioactive materials was released into the environment. Immediately after the release there was tremendous difficulty in managing the radioactive materials. It was extremely difficult to maintain communication, to mobilize human resources, and to procure supplies among other areas when addressing the nuclear accident that coincided with a massive natural disaster. Then, environmental radiation monitoring was initiated and various kinds of protective measures were implemented; however, radiation exposure resulted among the residents of Fukushima Prefecture and neighboring areas. Radiation exposure was initially caused by radioisotopes of iodine and short-lived radionuclides and subsequently by radiocesium from both external irradiation and internal irradiation through consumption of foods contaminated with these radionuclides.
Data and information related to dose assessment, such as in air dose rate and the concentration of radioactive materials in various environmental media after the Fukushima accident, have been reported by various organizations and disclosed by news media and the Internet. The International Symposium held on 14 December 2012 by Kyoto University provided an excellent opportunity for the integration of relevant information. Results of dose assessment for various populations have been also reported by various authors. However, no quantified and conclusive results of dose assessment have been reported by the responsible organization so far. The results are still in the process of being finalized for official presentation to the public.
In the present comments, therefore, I start by describing the implication of dose assessment in general, then I will report some results of dose assessment in the Fukushima accident. Finally, I touch on a key point of the present accident, radiation exposure of children, which seems to me extremely important for current radiation protection.