Abstract
Numerous radionuclides were released from the Fukushima Daiichi Nuclear Power Station (F1-NPS) in Japan following the magnitude 9.0 earthquake and tsunami on March 11, 2011. Local residents have been eager to calculate their individual radiation exposure. Thus, absorbed dose rates in the indoor and outdoor air at evacuation sites in the Fukushima Prefecture were measured using a gamma-ray measuring devices, and individual radiation exposure was calculated by assessing the radiation dose reduction efficiency (defined as the ratio of absorbed dose rate in the indoor air to the absorbed dose rate in the outdoor air) of wood, aluminum, and reinforced concrete buildings. Between March 2011 and July 2011, dose reduction efficiencies of wood, aluminum, and reinforced concrete buildings were 0.55±0.04, 0.15±0.02, and 0.19±0.04, respectively. The reduction efficiency of wood structures was 1.4 times higher than that reported by the International Atomic Energy Agency. The efficiency of reinforced concrete was similar to previously reported values, whereas that of aluminum structures has not been previously reported. Dose reduction efficiency increased in proportion to the distance from F1-NPS at 8 of the 18 evacuation sites. Time variations did not reflect dose reduction efficiencies at evacuation sites although absorbed dose rates in the outdoor air decreased. These data suggest that dose reduction efficiency depends on structure types, levels of contamination, and evacuee behaviors at evacuation sites.
Highlights
Numerous radionuclides were released from the Fukushima Daiichi Nuclear Power Station (F1-NPS) following the magnitude 9.0 earthquake and tsunami on March 11, 2011
Absorbed dose rates in the indoor and outdoor air were monitored at each evacuation site in Fukushima for 5 months after the accident, and data were collected to assess the impacts of time, direction, and distance from F1-NPS on the dose reduction efficiency of the structure types at each of these sites
Dose reduction efficiency of structures Dose reduction efficiency is defined as the ratio of the absorbed dose rate in the indoor air to that in the outdoor air
Summary
Numerous radionuclides were released from the Fukushima Daiichi Nuclear Power Station (F1-NPS) following the magnitude 9.0 earthquake and tsunami on March 11, 2011. To support radiation surveying and contamination monitoring of safe shelters immediately after the first hydrogen explosion, Hirosaki University sent many staff members to the temporary safe shelters that were set up around F1-NPS [4]. Almost all of these shelters were public facilities such as schools and exhibition halls, and they had various structure types (e.g., wood, aluminum, or reinforced concrete construction). Absorbed dose rates in the indoor and outdoor air were monitored at each evacuation site in Fukushima for 5 months after the accident, and data were collected to assess the impacts of time, direction, and distance from F1-NPS on the dose reduction efficiency of the structure types at each of these sites
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