Impact of decontamination on individual radiation doses from external exposure among residents of Minamisoma City after the 2011 Fukushima Daiichi nuclear power plant incident in Japan: a retrospective observational study

Abstract

Following the Fukushima incident, radiation doses from external exposure accounted for the majority of the total doses. Although countermeasures are being implemented, with the aim of reducing radiation exposure, little information is available on the effects of decontamination on individual doses among the residents of radioactively contaminated areas. To evaluate the effectiveness of the decontamination measures in reducing individual doses, and to examine the influence of the timing of decontamination and the district, data were analysed for 18 392 adults and 3 650 children in Minamisoma City, Fukushima, who participated in a voluntary screening programme using individual radiation dosimeters (Glass Badge) between June 2013 and September 2016. The dose reduction rates (DRR) were calculated for one year by comparing the first and last three-month measurement results between areas with and without decontamination. Using a regression approach and Monte Carlo simulation, the dose reduction rate by decontamination eliminating the effect of physical decay (DRRd′) was also estimated as a function of the timing of the decontamination and the dose at the time of starting the decontamination. The annual DRR in areas with decontamination for both adults and children were significantly higher than those in areas without decontamination, depending on the timing of decontamination: 31%–36% for 2013–14 for adults in decontamination areas and 33%–35% for children in decontamination areas, compared to 12%–23% and 13%–23% for adults and children in areas without decontamination, respectively. There was a positive correlation between DRRd′ and individual doses, and DRRd′ was estimated at 30%–40% for adults and children with doses of 3 mSv y−1 in 2013 and 2014. This study demonstrated that decontamination does lower individual doses from external exposure. The higher the dose at the time of starting the decontamination, the greater the dose reduction rate by decontamination, regardless of the timing of the decontamination. Our study confirms that decontamination was useful for high-dose areas in the later phases of the incident.

ICRP Publication 146: Radiological Protection of People and the Environment in the Event of a Large Nuclear Accident

“…schools) and the environment near to dwellings starts in the intermediate phase, and may continue for some time (several years) during the long-term phase. The Commission recommends that decontamination actions should be carried out in close consultation with the residents and users of dwellings, buildings, gardens, and public and recreational areas to identify the areas that either contribute significantly to exposures or are of primary concern for these people. (201) Decontamination actions notably contribute to reducing external exposure (Tsubokura et al., 2019). In practice, empowerment of people through their involvement in co-expertise processes allows them to better manage their own external exposure by compiling local maps of dose rates at places where they live, work, and relax.…”

“…(201) Decontamination actions notably contribute to reducing external exposure (Tsubokura et al., 2019). In practice, empowerment of people through their involvement in co-expertise processes allows them to better manage their own external exposure by compiling local maps of dose rates at places where they live, work, and relax.…”

Individual Doses to the Public after the Fukushima Nuclear Accident

“…Although it was reported that decontamination decreased ambient dose rate [30], it was not demonstrated whether or not the decontamination surely lowered personal doses. The first report on this appeared in 2019 [31]. The annual DRRs (dose reduction rates for personal dose) in areas that had undergone decontamination for both adults and children were significantly higher than those in areas without decontamination.…”

Review of health risks among decontamination workers after the Fukushima Daiichi Nuclear Power Plant Accident

“…However, the decontamination work required decontaminating large areas over a relatively short span of several years, and saw an influx of workers from the construction industry, coming from outside of the affected areas as a type of migrant worker. Decontamination work is effective in minimizing the exposure of residents in areas where radioactive materials have been dispersed in a nuclear accident, and the personnel involved in this work play an important role for rehabilitation of the exclusion zone after a nuclear disaster (Tsubokura et al, 2019). Therefore, it is imperative to understand and manage their health appropriately, and previous studies have shown that the decontamination workers after the FDNPP accident have been exposed to a wide range of health risks beyond radiation exposure.…”