Evaluation of Environmental Contamination and Estimated Radiation Exposure Dose Rates among Residents Immediately after Returning Home to Tomioka Town, Fukushima Prefecture

et al. 2020

Sci Rep

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Temporal variations in ambient dose rates in a restricted area designated as "difficult-to-return" for residents of Tomioka Town, Fukushima Prefecture were evaluated in a car-borne survey during 2018-2019. The median dose rates in the "Decontaminated area" in the difficult-to-return zone decreased rapidly from 1.0 μSv/h to 0.32 μSv/h; however, the median dose rates in the "Non-decontaminated area" and "Radioactive waste storage area" fluctuated between 1.1-1.4 μSv/h and 0.46-0.61 μSv/h, respectively. The detected rate of the cesium-137 (137 Cs) (137 Cs-detected points per all measuring points) in the "Decontaminated area" also decreased rapidly from 64% to 6.7%, accompany with decreasing in ambient dose rates. On the other hand, the detection of 137 Cs in the "Radioactive waste storage area" and "Non-decontaminated area" decreased from 53% to 17% and 93% to 88%, respectively. We confirmed that the dose rates in the Decontaminated area dramatically decreased due to decontamination work aiming to help residents return home. Moreover, the estimated external exposure dose of workers during the present survey was 0.66 mSv/y in the Decontaminated area and 0.55 mSv/y in the Radioactive waste storage area, respectively. This case of Tomioka Town within the "difficult-to-return zone" may be the first reconstruction model for evaluating environmental contamination and radiation exposure dose rates due to artificial radionuclides derived from the nuclear disaster. The Great East Japan Earthquake (magnitude 9.0) and subsequent tsunami on March 11, 2011 caused an accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) that resulted in various radionuclides including cesium-134 (134 Cs), cesium-137 (137 Cs) and iodine-131(131 I) being released into the atmosphere and eventually depositing on land and at sea in the surrounding areas 1. The United Nations Scientific Committee on the Effects of Atomic Radiation estimated the total release of 134 Cs (half-life: 2.1 y), 137 Cs (half-life: 30 y) and 131 I (half-life: 8 d) to be 9.0, 8.8 and 120.0 petabecquerels (PBq), respectively 1. The Japanese government, municipalities and private companies have carried out environmental and individual radiation monitoring programs to confirm the radiation levels in the affected areas 2,3. More than 8 years have passed since the accident and it has been confirmed that artificial radionuclides with a relatively long half-life such as 134 Cs and 137 Cs still exist in soil and plant samples collected around the FDNPS 1-3. Environmental monitoring in Fukushima Prefecture have been carried out by many methods (the airborne survey by monitor stations and personnel, vehicle-borne survey, aerial-vehicle survey and radionuclide analysis of the environmental samples such as soils, sediments and foodstuffs) 3-9. These surveys and the collected data are extremely important to precise evaluation of environmental remediation in the affected areas. Following the FDNPS accident, residential areas, farmlands, forests close to residential areas, and roads...

Section: Discussionsupporting

confidence: 66%

“…One car-borne survey in the difficult-to-return zone of Namie Town near Tomioka Town (within the 20 km of the FDNPS) reported absorbed dose rates ranging from 1 to 5 μGy/h in 2017 15 . Our previous handheld measurements showed the median dose rate was 2.3 µSv/h in the difficult-to-return zone of Tomioka Town in 2017 16 .…”

Section: Discussionmentioning

confidence: 96%

Environmental Remediation of the difficult-to-return zone in Tomioka Town, Fukushima Prefecture

Cui

et al. 2020

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“…Limitations of the present study are that the bias associated with the D-SHUTTLE dosimeter positions (investigator) and temperature may be significant; in the present study, the temperature was observed to vary from 17 to 19 °C in October 2019, and from 10 to 13 °C in December 2019 40,41 . In addition, we did not characterize the soils along the Mt Okura hiking trail, although the findings of our previous study showed that dose-forming artificial radiocesium was prevalent in all surface soil samples (0-10 cm) collected in Tomioka Town in 2017 20 . However, in the present study, we used the RADI-PROBE for high and sensitive gamma-ray detection (typically 1400 cps per µSv/h for 137 Cs) 24,25,42 .…”

Section: Discussionmentioning

confidence: 92%

“…In the present study, the reduction of radiocesium was estimated to be only 0.35% from October to December 2019 (Supplementary S2) 26,27 . Thus, the median ambient dose rates along the Mt Okura hiking trail remained relatively stable in 2019 20,24 .…”

Section: Discussionmentioning

confidence: 97%

“…In 2017, we reported that median ambient dose rates around the homes of the residents who had returned to areas where the evacuation order had been lifted in Tomioka Town were 0.20-0.34 µSv/h (1.7-3.0 mSv/y) and the additional radiation exposure dose was estimated at 1.6 mSv/y based on the guidelines from the Ministry of the Environment, Japan 20 . In 2018, we estimated that the median ambient dose rate along the Mt Okura hiking trail was 0.49 μSv/h, and that the individual dose was 0.44 μSv/h (0.42 mSv/y) (Supplementary S1) 24 .…”

Section: Discussionmentioning

confidence: 99%

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Radiocesium levels in contaminated forests has remained stable, even after heavy rains due to typhoons and localized downpours

Yamaguchi

et al. 2020

Sci Rep

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In recent years, Japan has suffered serious damage due to natural disasters such as earthquakes, heavy rains due to tropical storms (typhoons) and localized downpours. To assess the chronological changes in the attenuation of external exposure doses and environmental radiation contamination due to the rainfall associated with typhoons and heavy rains during October to December 2019 in Fukushima, we measured environmental radiation levels in forest areas along the Mt Okura hiking trail in Tomioka Town, Fukushima Prefecture, near the Fukushima Daiichi Nuclear Power Station. We confirmed that (1) current ambient dose rates of 0.38–0.95 μSv/h in most forest areas were 79.9–84.7% higher than in residential areas; (2) the number of sites along the hiking trail where 137Cs was detected was limited (1.1–4.7%); and (3) individual dose rates of 0.21–0.34 μSv/h were lower than ambient dose rates. These findings suggest that radiocesium has remained stable in natural forests that have not been decontaminated even though current levels are low, despite the occurrence of heavy rainfall associated with Super Typhoon Hagibis in 2019 and localized downpours. Hiking while managing exposure to environmental contamination using a personal dosimeter may be the safest model for spending time of leisure activities.

Assessment of localized and resuspended ¹³⁷Cs due to decontamination and demolition in the difficult‐to‐return zone of Tomioka town, Fukushima Prefecture

Integr Envir Assess & Manag

Orita

et al. 2022

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