ESTIMATION OF THE EARLY 137CS INTAKE OF EVACUEES

More than nine years have passed since the 2011 nuclear disaster in Fukushima Prefecture, Japan. During this period, much effort has been made on the dose reconstruction for Fukushima residents; however, the estimation of the internal dose due to the potential intake of the short-lived radionuclides (mainly, 131I) has been challenging because of the lack of direct human measurements at the early phase of the accident. Our previous study revealed that the residual cesium body contents observed in delayed whole-body counter (WBC) measurements of residents from Namie-town, one of the most affected municipalities), varied greatly with the timepoint of their evacuations on 12 March 2011 when the first explosive event occurred at the accident site; i.e., the late evacuees had much higher residual Cs body contents compared to the prompt evacuees. The present study thus aimed to clarify this finding by reproducing the exposure situation based on the evacuees\u27 personal behavioral data in combination with the latest atmospheric transport and dispersion model (ATDM) simulation for 356 selected subjects in adult and 15-year (13–17 yrs) age groups. The results demonstrated that the ATDM simulation-based method could reasonably reproduce the subjects\u27 exposure situation, supporting the previous finding. However, the residual 137Cs body contents calculated by this method were only 10%–20% of those in the subjects\u27 WBC measurements. This large discrepancy was considered to be caused by both the present method\u27s underestimation and the overestimation of the subjects\u27 early intake in the WBC measurements due to a conservative intake scenario not assuming potential additional intake. Additional studies are needed to further clarify the reasons for the discrepancy and to evaluate the magnitude of the inhalation dose in the accident