Estimation of the Early Cs-137 Intake of Evacuees from Areas Affected by the 2011 Fukushima Daiichi Nuclear Power Plant Accident Based on Personal Behavioral Data and the Latest Atmospheric Transport and Dispersion Model Simulation

Abstract

More than nine years have passed since the 2011 nuclear disaster in Fukushima Prefecture, 2 Japan. During this period, much effort has been made on the dose reconstruction for Fukushima 3 residents; however, the estimation of the internal dose due to the potential intake of the short-4 lived radionuclides (mainly, 131 I) has been challenging because of the lack of direct human 5 measurements at the early phase of the accident. Our previous study revealed that the residual 6 cesium body contents observed in delayed whole-body counter (WBC) measurements of 7 residents from Namie-town, one of the most affected municipalities), varied greatly with the 8 timepoint of their evacuations on 12 March 2011 when the first explosive event occurred at the 9 accident site; i.e., the late evacuees had much higher residual Cs body contents compared to the 10 prompt evacuees. The present study thus aimed to clarify this finding by reproducing the 11 exposure situation based on the evacuees' personal behavioral data in combination with the 12 latest atmospheric transport and dispersion model (ATDM) simulation for 356 selected subjects 13 in adult and 15-year (13-17 yrs) age groups. The results demonstrated that the ATDM 14 simulation-based method could reasonably reproduce the subjects' exposure situation, 15supporting the previous finding. However, the residual 137 Cs body contents calculated by this 16 method were only 10%-20% of those in the subjects' WBC measurements. This large 17 discrepancy was considered to be caused by both the present method's underestimation and the 18 overestimation of the subjects' early intake in the WBC measurements due to a conservative 19 intake scenario not assuming potential additional intake. Additional studies are needed to 20 further clarify the reasons for the discrepancy and to evaluate the magnitude of the inhalation

Estimation of the Thyroid Equivalent Doses to Residents in Areas Affected by the 2011 Fukushima Nuclear Disaster Due to Inhalation of 131I Based on Their Behavioral Data and the Latest Atmospheric Transport and Dispersion Model Simulation

“…The significance of our present study is that it obtained evidence supporting the view by Igarashi et al (2020) as well as the companion study (Kim et al 2021), i.e., that some residents of Namie-town could have received considerable exposure to not only Cs but also 131 I during their evacuation due to the hydrogen explosion at the Unit 1 Reactor building on the afternoon of 12 March. The visualization of the locations of individuals on the contour map of the 131 I air concentrations clarified the situation of exposure on that day (Fig.…”

“…A significant discrepancy remains regarding the 137 Cs air concentration between the ATDM predictions and the SPM data. The latest ATDM simulation can overestimate or underestimate the daily 137 Cs intake by several times in general, depending on the location (Kim et al 2021). This would also be true for 131 I.…”

“…For the Adult and 15-y-old groups, we also subdivided the subjects into two groups depending on the direction of their evacuation shortly after the accident; namely, evacuation to the Tsushima area of Namie-town or to Minamisomacity. Details of the grouping of the subjects are described in the paper (Kim et al 2021). The personal behavioral data consist of the time-series of the whereabouts of the individual (the place name and its latitude/longitude); the time he or she spent indoors, outdoors or moving; and the type of building where the individual stayed (e.g., a wooden house, concrete building).…”

“…This finding indicated the possibility of significant exposure among some residents during their evacuation shortly after the accident. The second study attempted to clarify this possibility using the same ATDM-based method as the present study for Cs (Kim et al 2021). Their results demonstrated that the method could reasonably reproduce the subjects’ exposure situations, supporting the possibility of significant exposure, although the method gave underestimations of the Cs dose.…”

“…We describe herein our estimation of the internal thyroid doses by the inhalation of 131 I to residents living in Namie-town, one of the municipalities that was most radiologically affected by the FDNPP accident based on the latest ATDM simulation, coupled with the residents' behavioral data recorded from shortly after the accident. This study was mainly based on two investigations: Igarashi et al (2020) and Kim et al (2021). The first analyzed subjects of Namie town who underwent the WBC measurements and revealed that the late evacuees tended to have higher Cs body contents compared to the prompt evacuees (Igarashi et al 2020).…”