Assessment Model of Radiation Doses from External Exposure to the Public after the Fukushima Daiichi Nuclear Power Plant Accident

Radiation exposure is one of most important factors to manage following a nuclear emergency. Actual measurement is the best way to obtain information concerning the dose received by the people in terms of accuracy and reliability. However, in practice, it is difficult to collect measurements from all people affected by nuclear accidents over the whole period of exposure from past to future. Therefore, probabilistic assessment using a model is needed. An assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rates inside and outside houses in Fukushima City. A survey of behavioral patterns was also performed for the same purpose. In addition to our measurement and survey, we took into account the latest insights from the experiences of the Fukushima Daiichi nuclear power plant accident. Comparisons between the assessed and measured results revealed that the time-dependence of doses and the distribution of doses obtained using the developed models agree well with the results of actual measurements. Thus, our probabilistic approach was validated. Based on both our assessment and on our actual measurements, no participants were observed to receive doses in excess of 1 mSv y as of 8 y after the Fukushima Daiichi nuclear power plant accident in Fukushima City.