Measuring and assessing individual external doses during the rehabilitation phase in Iitate village after the Fukushima Daiichi nuclear power plant accident

Abstract

After the Fukushima Daiichi nuclear power plant accident in 2011, Iitate village was placed under an evacuation order because the level of radioactive materials drifting from the nuclear plant to the village was above a government-set level for allowing residents to live in the area. The evacuation advisory for most of the village was lifted on 31 March 2017. For displaced residents deciding whether or not to return to their homes, it is important to correctly understand and estimate the realistic individual external doses they will receive after returning to the village. In this study, with the support of residents of the village, we used a personal dosimeter (D-Shuttle) coupled with a global positioning system device to measure and thus understand realistic individual external doses while the residents were in Iitate village and to project the individual external doses for different administrative districts as of 1 April 2017. The measured individual external doses measured by D-Shuttle for 38 study participants showed that the doses measured during time spent inside the village were higher and more widely distributed than the doses measured during time spent outside the village. The exposure ratio (ER) was defined as the ratio of additional individual external dose measured by D-Shuttle to the additional ambient dose based on an airborne monitoring survey. The medians of the average ERs were 0.13 (min-max 0.06-0.27) for time spent at home and 0.18 (min-max 0.08-0.36) for time spent outdoors. Projected additional annual individual external doses as of 1 April 2017 for different administrative districts in the village were calculated using ERs obtained in this study. Assuming that individuals spent 8 h per day on outdoor activities and 16 h on indoor activities, additional annual individual external doses were estimated to be below 3 mSv using the mean of the average ERs for most districts in the village, and these values were well below the individual external doses estimated using the approach taken by the central government. The results of this study provide valuable information both for understanding realistic radiological situations in the village and for those who want to know their future individual external dose in order to make a decision on whether or not to live in the village.

Parallel Measurement of Ambient and Individual External Radiation in Iitate Village, Fukushima

“…Some studies have reported the relationship between ambient dose obtained from airborne monitoring and individual dose (Ishikawa et al 2016;Naito et al 2017;Miyazaki and Hayano 2017a, b). We doubt the relevancy of using airborne monitoring data in relation to individual dose, as was done, for example, for the Date City's glass badge monitoring (Miyazaki and Hayano 2017a, b).…”

Internal radiation dose estimation using multiple D‐shuttle dosimeters for positron emission tomography (PET): A validation study usingNEMAbody phantom

“…One should note that the manufacturer has customized the dosimeter for obtaining sufficient dose data in 2 min intervals. Various D‐shuttle dosimeter features described by the manufacturer are listed in Table . Čemusová et al tested the dosimetric characteristics of D‐shuttle related to Hp(10) measurements, energy dependency, angular dependency, etc., and reported that most of the results were in agreement with the manufacturer's specifications.…”

“…Here, we propose a technique for estimating cumulative radioactivity in the source organ of a patient using D‐shuttle dosimeters. D‐shuttle is a semiconductor dosimeter which has been used for continuous long‐term personal dose monitoring of residents in the area affected by the Fukushima Daiichi nuclear power plant accident in 2011, which was caused by the great east Japan earthquake and tsunami . A small number of D‐shuttle dosimeters will be attached to the patient body surface to obtain dose information from several source organs.…”

“…D-shuttle is a semiconductor dosimeter which has been used for continuous long-term personal dose monitoring of residents in the area affected by the Fukushima Daiichi nuclear power plant accident in 2011, which was caused by the great east Japan earthquake and tsunami. [29][30][31] A small number of D-shuttle dosimeters will be attached to the patient body surface to obtain dose information from several source organs. Radioactivities in the source organs will be calculated by solving the dose-radioactivity formula iteratively using body surface doses as measured by the D-shuttle dosimeter and R-matrix.…”

The role of radiological protection experts in stakeholder involvement in the recovery phase of post-nuclear accident situations: Some lessons from the Fukushima-Daïchi NPP accident

“…Several publications have shown that actual individual doses could be 4 to 5 times lower than those estimated with the representative dose rates of the areas. (Naito et al, 2016(Naito et al, , 2017ICRP, 2016).…”