An assessment of radiation doses at an educational institution 57.8 km away from the Fukushima Daiichi nuclear power plant 1 month after the nuclear accident

Abstract

Objectives On 11 March 2011, the Great East Japan Earthquake occurred. Due to this earthquake and subsequent tsunami, malfunctions occurred at the Fukushima Daiichi nuclear power plant. Radioactive material even reached the investigated educational institution despite being 57.8 km away from the power station. With the goal of ensuring the safety of our students, we decided to carry out a risk assessment of the premises of this educational institution by measuring radiation doses at certain locations, making it possible to calculate estimated radiation accumulation. Methods Systematic sampling was carried out at measurement points spaced at regular intervals for a total of 24 indoor and outdoor areas, with 137 measurements at heights of 1 cm and 100 cm above the ground surface. Radiation survey meters were used to measure environmental radiation doses. Results Radiation dose rates and count rates were higher outdoors than indoors, and higher 1 cm above the ground surface than at 100 cm. Radiation doses 1 cm above the ground surface were higher on grass and moss than on asphalt and soil. The estimated radiation exposure for a student spending an average of 11 h on site at this educational institution was 9.80 lSv. Conclusions Environmental radiation doses at our educational institution 57.8 km away from the Fukushima Daiichi nuclear power plant 1 month after the accident were lower than the national regulation dose for schools (3.8 lSv/h) at most points. Differences in radiation doses depending on outdoor surface properties are important to note for risk reduction.

Radiation survey on Fukushima Medical University premises about four years after the Fukushima nuclear disaster

“…Data were obtained in first and second snowfall events. Radiation survey at FMU and FMU Hospital field and parking areas in the northernmost part of the FMU premises, the air -kerma rates of 2.18 -2.54 μGy h -1 (ambient dose equivalent rates : 2.72 -3.18 μSv h -1 ) on April 11, 2011 (noted as a track field in Tsuji et al 6) ) decreased to 0.06 -0.16 μGy h -1 . These areas were developed after the nuclear disaster, which probably caused the significant decreases in the air -kerma rates.…”

“…One month after the nuclear disaster, the airkerma rates were observed to be 0.66 -2.54 μGy h -1 (ambient dose equivalent rates : 0.82 -3.18 μSv h -1 ) on the FMU premises 6,8) . In this study, it was determined that they had decreased to 0.04 -0.52 μGy h -1 about four years later.…”

“…The climate factors are considered to be wash -off by rainfall and resuspension by wind 33 -36) . In addition, these factors are more effective on paved surfaces, resulting in lower radiocesium concentrations (and air -kerma rates) on paved surfaces than on unpaved surfaces 6,7,37,38) . In this study, the air -kerma rates were found to be higher on grass and soil than asphalt (Fig.…”

“…One month after the nuclear disaster, Tsuji et al 6) estimated the effective dose of the university student to be 9.8 μSv over 10.3 h (spending 7 h in buildings and 3.3 h on the athletic field and a parking area). At present it remarkably decreases by about 90% although the estimation conditions are slightly different between Tsuji et al 6) and this study. Our estimated values include the contributions of natural radionuclides.…”

“…1). The univer sity organized a team who conducted radiation measurements on the university premises about one month after the nuclear disaster 6,7) . These surveys were repeated twice a month for the first year, once a month for the second year, and every two months for the third year, and currently, they are repeated every three months, though fewer points are measured than those in the previous surveys 8) .…”