Assessment model of radiation doses from external exposure to the public after the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo; Iijima, Masashi*; Watanabe, Masatoshi*

Health Physics, 118(6), p.664 - 677, 2020/06

https://doi.org/10.1097/HP.0000000000001176

Assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rate inside and outside of a house in Fukushima city. The survey on behavioral pattern was also carried out under the same purpose. In addition to the actual measurement and survey by ourselves, we also took into account the latest insights from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Comparisons between the assessed results and the measured ones revealed that the time dependences of doses obtained using the developed models were in good agreement with the results of actual measurements. In addition, we were able to reproduce the distribution of doses for indoor and outdoor workers. Therefore, our probabilistic approach was validated. According to our assessment and actual measurement, no participants received 1 mSv/y or higher in Fukushima city in eight years after the FDNPP accident.

Development of an external radiation dose estimation model for children returning to their homes in areas affected by the Fukushima Nuclear Accident

Mori, Airi; Takahara, Shogo; Yoshida, Hiroko*; Sanada, Yukihisa; Munakata, Masahiro

Health Physics, 117(6), p.606 - 617, 2019/12

https://doi.org/10.1097/HP.0000000000001100

Assessment of radiation doses from ingestion pathway to the public in Fukushima prefecture after the Fukushima Dai-ichi Nuclear Power Plant accident

Takahara, Shogo; Watanabe, Masatoshi*

Proceedings of Asian Symposium on Risk Assessment and Management 2019 (ASRAM 2019) (USB Flash Drive), 9 Pages, 2019/09

Internal exposure from ingestion pathway is one of most concerned contributor to the received doses to the public after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. In the present study, we developed the dose prediction model taking into account the ecological half-lives of radionuclides in foodstuffs and the reduction effects on concentration of radionuclides in cooking-process based on the experiences and the latest insights of the FDNPP accident. From comparison of the retrospective assessment results in Fukushima city between our models and the previous models (market bascket, duplicate, sewer sludge method), no contradictions were observed. In addition, it was found that the potential annual effective doses, which were assessed using the developed model, is several tens micro Sieverts in the first year after the FDNPP accident, and subsequent years the doses is also not exceeding several micro Sv for the future in Fukushima city.

Applied research for the establishment of radiation monitoring and evaluation of exposure dose of residence at the zone designated for reconstruction and recovery

Funaki, Hironori; Takahara, Shogo; Sasaki, Miyuki; Yoshimura, Kazuya; Nakama, Shigeo; Sanada, Yukihisa

JAEA-Research 2018-016, 48 Pages, 2019/03

JAEA-Research-2018-016.pdf:29.73MB

Cabinet Office Nuclear Emergency Response Headquarters starts to consider radiation protection in the "specific reconstruction reproduction base area" of which evacuation order will be lifted by 2023. It is essential to grab the present situations of radiation contamination and evaluate exposure dose in the area to realize the plan. Many surveys have evaluated the distributions of air dose rate and exposure dose has been estimated based on the results since the Fukushima Daiichi Nuclear Power Plant accident. Nevertheless, more detailed information on exposure is needed for the areas because its radiation level is relatively high. That is also to help make prudent evaluation plan. This study aimed to evaluate the detailed contamination situation there and estimate exposure dose with considering areal circumstances. Investigations were carried out for (1) airborne survey of air dose rate using an unmanned helicopter (2) evaluation of airborne radiocesium and (3) estimation of external/internal effective doses for typical activity patterns assumed. Additionally, we applied new methods for the airborne survey to evaluate exposure dose. Our study showed a detailed three-dimensional map of air dose rate and clarified the distribution pattern in the areas. Results of effective dose estimation suggested that the internal effective dose due to inhalation accounts for less than 1% of the external effective dose.

Investigation of reduction factor of internal exposure for sheltering in Japan

Hirouchi, Jun; Takahara, Shogo; Komagamine, Hiroshi*; Munakata, Masahiro

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 8 Pages, 2018/10

no abstracts in English

Challenges for enhancing Fukushima environmental resilience, 10; Dose evaluation and risk communication

Saito, Kimiaki; Takahara, Shogo; Uezu, Yasuhiro

Nippon Genshiryoku Gakkai-Shi, 60(2), p.111 - 115, 2018/02

no abstracts in English

Factors affecting the effectiveness of sheltering in reducing internal exposure

Hirouchi, Jun; Takahara, Shogo; Komagamine, Hiroshi*; Watanabe, Masatoshi*; Munakata, Masahiro

Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 11 Pages, 2017/11

no abstracts in English

Evaluation of effective dose coefficient with variation of absorption fraction in gastrointestinal system for ingestion of radiocesium

Pratama, M. A.; Takahara, Shogo; Hato, Shinji*

Hoken Butsuri, 52(3), p.200 - 209, 2017/09

https://doi.org/10.5453/jhps.52.200

The purpose of this study is to identify the significance of the change in the intestinal absorption rate values the ( value) to the change of dose coefficient as well as to provide a list of dose coefficients which each of the value corresponds to a specific intestinal absorption rate and age groups. In the range of 0-1, 10 different values of for 1 year, 5 years old, and adult group were chosen and used in a separate calculation by using, a biokinetic compartment model, DCAL. It was found that the lower values of intestinal absorption rate lead to a significant decrease of the committed effective coefficient for adult. Oppositely for children, the decrease of committed effective coefficient was not as significant. This study also suggests that the significance of dose coefficient change due to the variation of substantially depends on the biological half-life of the radionuclide and the mass of organs and tissues in human body.

Bioaccessibility of Fukushima-accident-derived Cs in soils and the contribution of soil ingestion to radiation doses in children

Takahara, Shogo; Ikegami, Maiko*; Yoneda, Minoru*; Kondo, Hitoshi*; Ishizaki, Azusa; Iijima, Masashi; Shimada, Yoko*; Matsui, Yasuto*

Risk Analysis, 37(7), p.1256 - 1267, 2017/07

AA2015-0445.pdf:0.53MB

https://doi.org/10.1111/risa.12694

Assessment of residual doses to population after decontamination in Fukushima Prefecture

Mori, Airi; Takahara, Shogo; Ishizaki, Azusa; Iijima, Masashi; Sanada, Yukihisa; Munakata, Masahiro

Journal of Environmental Radioactivity, 166(Part 1), p.74 - 82, 2017/01

https://doi.org/10.1016/j.jenvrad.2016.06.023

Large quantities of radioactive materials were released into the environment as a result of the Fukushima Daiichi Nuclear Power Station accident. Many inhabitants residing in the affected areas are now exposed to radiation in their daily lives. In an attempt to manage this radiation dose, an additional radiation dose of 1 mSv/y was adopted as a long-term dosimetric target. An activity level reading of 0.23 Sv/h was then determined as a guidance value to achieve the target by implementing decontamination measures. The objectives of this study are to assess the effects of decontamination based on this guidance value and to predict any possible future problems with the decontamination strategy. Using a probabilistic approach, we assessed the annual effective dose of indoor workers, outdoor workers, and pensioners in the Fukushima Prefecture. Our probabilistic model considers the variabilities in behavioral patterns and Cs-137 surface-activity levels. Five years after the initial contamination, the 95th percentiles of indoor workers and pensioners in 53 of the 59 municipalities were found to receive annual effective doses of below 1 mSv/y (0.026-0.73 mSv/y). However, for outdoor workers in 25 municipalities, the annual doses were over 1 mSv/y (1.0-35 mSv/y). Therefore, the guidance value is effective for indoor workers and pensioners; to determine whether additional countermeasures for outdoor workers should be implemented, a detailed assessment that uses more realistic assumptions is required.