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Group for Fukushima Mapping Project
JAEA-Technology 2023-024, 176 Pages, 2024/03
JAEA-Technology-2023-024.pdf:22.16MB
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2022. Car-borne surveys, a measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data to create their distribution maps, and temporal changes of the air dose rates were analyzed. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Score maps to classify the importance of the measurement points were created, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. The range of fluctuation of past tritium concentration data in seawater was determined, and the causes of the fluctuation were discussed. Monitoring data in coastal area performed in 2022 owing to the comprehensive radiation monitoring plan was summarized, and temporal changes in cesium-137 were analyzed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated air dose rate distribution data acquired through surveys such as car-borne and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2022 were published on the "Database for Radioactive Substance Monitoring Data", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Kim, M.; Malins, A.*; Machida, Masahiko; Yoshimura, Kazuya; Saito, Kimiaki; Yoshida, Hiroko*
Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(4), p.156 - 169, 2023/11
Dose reduction factor of a Japanese house is important information in the external exposure estimation of returning residents. In 2019, a total of 19 wooden houses were surveyed in Iitate Village and Namie Town using a gamma plotter that can continuously measure the air dose rate. In addition, the characteristics of the reduction factor were investigated from the measured air dose rate. In the vicinity of houses, uncontaminated areas exist underneath houses and, the ratio of paved surfaces such as asphalt roads is relatively high; furthermore, the pavement has a tendency for the radiation source to decay quickly. Therefore, the air dose rate near the house showed a relatively low value in common at all sites. Air dose rates above unpaved surfaces showed higher values and larger variations than those above paved surfaces within a radius of 50 m form the center of a house. The reduction factor was widely distributed even for one house, if the ratio of every air dose rate observed inside and outside the house is considered. It is suggested that a realistic reduction factor may not be obtained when the reduction factor is obtained based on the measured values at a small number of points that do not have the representativeness of the radiation field to be measured.
Group for Fukushima Mapping Project
JAEA-Technology 2022-026, 152 Pages, 2023/01
JAEA-Technology-2022-026.pdf:20.14MB
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2021. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data to create air dose rate distribution maps, and temporal changes of the air dose rates were analyzed. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Score maps to classify the importance of the measurement points were created for Fukushima Prefecture and the 80 km zone from the FDNPS, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until 2020 was summarized, and temporal changes in cesium-137 were analyzed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained in this project with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2021 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Kobayashi, Hikaru*; Suto, Masahito*; Otsuki, Kentaro*; Yoshimura, Kazuya; Yoshida, Hiroko*
Japan Architectural Review (Internet), 6(1), p.e12353_1 - e12353_12, 2023/00
Group for Fukushima Mapping Project
JAEA-Technology 2021-025, 159 Pages, 2022/01
JAEA-Technology-2021-025.pdf:46.66MB
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2020. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring for classifying the importance of measurement points, a score map was created for Fukushima Prefecture and the 80 km zone from the FDNPS, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2020 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Group for Fukushima Mapping Project
JAEA-Technology 2020-014, 158 Pages, 2020/12
JAEA-Technology-2020-014.pdf:23.82MB
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2019. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring to classify the importance of measurement points, we created a score map of Fukushima Prefecture and that within 80 km from the FDNPS based on the "score" method developed in 2018. The way of monitoring radioactive materials in land area was examined and the representativeness of monitoring points was proposed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2019 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Ando, Masaki; Sasaki, Miyuki; Saito, Kimiaki
Journal of Nuclear Science and Technology, 57(12), p.1319 - 1330, 2020/12
Times Cited Count：4 Percentile：45.45(Nuclear Science & Technology)Air dose rates measured by car-borne surveys within 80 km range of Fukushima Dai-ichi Nuclear Power Plant using KURAMA systems from 2011 up to 2018 were analyzed, and decreasing trends and ecological half-life were evaluated. The decreasing speed of air dose rates became 0.08 over a period of seven years, indicating a much more rapid decrease than estimated by the physical decay of radiocesium (0.3). The fast components of the ecological half-lives evaluated in entire the evacuation order area were about 2 to 3 y, and were considerably larger than those outside the evacuation order area (0.4 to 0.5 y). To model the acceleration in the decrease of air dose rates observed in evacuation order areas, we modified the bi-exponential curve formula of ecological half-life and introduced the two-group model. The fast decreasing components of the ecological half-life evaluated using the two-group model after 2013 were 0.5 to 1 y, and were much shorter than those up to 2013, at 2 to 3 y.
Group for Fukushima Mapping Project
JAEA-Technology 2019-019, 135 Pages, 2020/03
JAEA-Technology-2019-019.pdf:22.01MB
After the accident at TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS), distribution situation survey on radioactive materials have been conducted with financially supported by the Ministry of Education, Culture, Sports, Science and Technology (later the Nuclear Regulatory Agency) from June 2011 to FY2018. Results obtained in the project in FY2018 are presented in this report. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of air dose rate were analyzed. Regarding radiocesium deposition in the soil, depth profile survey in the soil and in-situ measurement were performed. Based on these measurement results, effective half-life of the air dose rate and the deposition were evaluated. Considering radiation monitoring data obtained in previous surveys and the installation positions of existing monitoring posts, we tried to make the "score" of the importance of measurement points. Using the Bayesian hierarchical modeling approach, we obtained a map that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys for the entire region within 80 km from the FDNPS. The measurement results for FY2018 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and environmental sample analysis owing to the comprehensive radiation monitoring plan were carried out.
Yamashita, Takuya; Sawada, Noriyoshi*
JAEA-Research 2019-010, 227 Pages, 2020/03
JAEA-Research-2019-010.pdf:21.44MBJAEA-Research-2019-010(errata).pdf:0.5MB
In order to support the decontamination activities proceeded by the national government and municipalities in terms of technology, we have developed a simulation system "RESET" which predicts the effect of decontamination. We also developed a "two-component model" for the purpose of predicting long-term changes in the air dose rate. We use these tools to perform decontamination simulation and predictive analysis of the air dose rate after decontamination, and provide information to the national government and municipalities aiming for reconstruction. In this report, the verification result of the prediction methods implemented using actual measurement data obtained in the "Decontamination model demonstration project in difficult-to-return zone" and "Survey result on transition of air dose rate after decontamination model demonstration project" conducted by Ministry of the Environment. In addition, the decontamination simulation conducted for the entire difficult-to-return area and the results of future prediction of the air dose rate after decontamination are shown.
Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*
Journal of Environmental Radioactivity, 210, p.105803_1 - 105803_10, 2019/12
Times Cited Count：4 Percentile：16.8(Environmental Sciences)To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of 
rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The 
Cs and 
Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.
Sato, Tetsuro*; Ando, Masaki; Sato, Masako*; Saito, Kimiaki
Journal of Environmental Radioactivity, 210, p.105973_1 - 105973_7, 2019/12
Times Cited Count：9 Percentile：36.49(Environmental Sciences)A method was devised for estimation of external doses of Fukushima residents expected to return to their homes after evacuation orders are lifted. 211 residents expected to return to six towns and villages were surveyed in FY 2014, FY 2015, and FY2016. Interviewing returning residents about their expected life patterns after returning, air dose rate were measured along the reported personal trails representing their patterns of movement in daily life. Excluding 15 residents from whose homes we were unable to take air dose rate measurements, the maximum external effective dose and the average external effective dose were estimated respectively as 4.9 mSv/y and 0.86 mSv/y. Although the mean values and dispersion of external effective doses differ depending on the evacuation level, for 93.3% of all residents, the estimated external effective doses were less than 2 mSv/y. The average exposure dose at home accounts for 66.8% of the annual exposure dose.
Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Yoshida, Tadayoshi; Sato, Tetsuro*; Seki, Akiyuki; Yamamoto, Hideaki*; et al.
Journal of Environmental Radioactivity, 210, p.105878_1 - 105878_12, 2019/12
Times Cited Count：33 Percentile：80.62(Environmental Sciences)Mikami, Satoshi; Tanaka, Hiroyuki*; Matsuda, Hideo*; Sato, Shoji*; Hoshide, Yoshifumi*; Okuda, Naotoshi*; Suzuki, Takeo*; Sakamoto, Ryuichi*; Ando, Masaki; Saito, Kimiaki
Journal of Environmental Radioactivity, 210, p.105941_1 - 105941_12, 2019/12
Times Cited Count：21 Percentile：67.06(Environmental Sciences)The deposition densities of radiocesium and the air dose rates were repeatedly measured in a large number of undisturbed fields within the 80km zone that surrounds the Fukushima Dai-ichi Nuclear Power Plant site between 2011 and 2016, and features of their temporal changes were clarified. The average air dose rate excluding background radiation in this zone decreased to about 20% of the initial value during the period from June 2011 to August 2016, which was essentially a result of the radioactive decay of Cs with a half-life of 2.06y. The air dose rate reduction was faster than that expected from the decay of radiocesium by a factor of about two, with most of this reduction being attributed to the penetration of radiocesium into the soil. The average deposition densities of Cs and Cs in fields that were not decontaminated were found to have decreased nearly according to their expected radioactive decay, which indicated that the movement of radiocesium in the horizontal direction was relatively small. The effect of decontamination was apparently observed in the measurements of air dose rates and deposition densities. Nominally, the average air dose rates in the measurement locations were reduced by about 20% by decontamination and other human activities, of which accurate quantitative analysis is and continue to be a challenge.
Ando, Masaki; Yamamoto, Hideaki*; Kanno, Takashi*; Saito, Kimiaki
Journal of Environmental Radioactivity, 190-191, p.111 - 121, 2018/10
Times Cited Count：17 Percentile：52.92(Environmental Sciences)Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 around the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months, which was beyond that attributable to the physical decay. The air dose rates decreased depending on the level of the evacuation areas, and the decrease was slightly larger in populated areas where humans are active. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground. The air dose rates measured by the walk surveys decreased quickly compared with the air dose rate from the flat ground measurement.
Saito, Kimiaki; Takahara, Shogo; Uezu, Yasuhiro
Nihon Genshiryoku Gakkai-Shi ATOMO
, 60(2), p.111 - 115, 2018/02
no abstracts in English
Miyahara, Kaname
Transactions of the American Nuclear Society, 117(1), p.51 - 52, 2017/10
This presentation highlights JAEA's challenges for contributing to recovering the previous life of residents and the development of resilient communities in Fukushima Prefecture based on considering needs of local people on the environmental restoration categorized by the state of evacuation orders and the lifting of such orders.
Saito, Kimiaki; Nagai, Haruyasu; Kinase, Sakae; Takemiya, Hiroshi
Nihon Genshiryoku Gakkai-Shi ATOMO, 59(6), p.40 - 44, 2017/06
no abstracts in English
Ando, Masaki; Kanno, Takashi; Saito, Kimiaki
JAEA-Technology 2015-060, 40 Pages, 2016/03
JAEA-Technology-2015-060.pdf:50.1MB
The ratios of air dose rate averaged in prefecture-wise measured by car borne surveys in wide area has been performed by with the use of the KURAMA and KURAMA-II systems were investigated. The changes in air dose rate from the first (June 2011) car borne survey to the fourth (September 2012) and seventh (November 2013) car borne surveys in Fukushima Prefecture was similar to those in Tochigi Prefecture, and the ratio in Miyagi Prefecture showed quicker decay than those in the other prefectures in the groups of less than 0.5
Sv/h. Distribution maps of the ratios of air dose rate obtained in 100m mesh wise in Fukushima, Tochigi and Miyagi prefectures showed that the ratios (i.e. decreasing rates) were depending on the area or road. Further, decreasing in the air dose rate was quicker than the physical decay in the big cities where population is big and the traffic is huge.
Saito, Kimiaki; Kurihara, Osamu*; Matsuda, Norihiro; Takahara, Shogo; Sato, Tetsuro*
Radioisotopes, 65(2), p.93 - 112, 2016/02
Late information is introduced on dose evaluation due to external exposures which employ an important role in the exposures due to the Fukushima accident. First, merits and demerits of the currently used two methods, that is the estimation based air dose rates and the measurements using personal dosimeters, are discussed indicating some basic data after a fundamental concept of external dose evaluation is provided. Next, main activities are summarized on external dose measurements and evaluations after the accident. Finally, a new trial on dose evaluation in introduced.
Mikami, Satoshi; Matsuda, Norihiro; Ando, Masaki; Kinase, Sakae; Kitano, Mitsuaki; Kawase, Keiichi; Matsumoto, Shinichiro; Yamamoto, Hideaki; Saito, Kimiaki
Radioisotopes, 64(9), p.589 - 607, 2015/09
This article presents the features of regional distributions and temporal changes in air dose rate and radionuclide deposition densities in Fukushima on the basis of analyses on large-scale environmental monitoring results using diverse methods. The continuity of decontamination effects is discussed according to repeated monitoring data after the decontamination model project. Further, some examples are shown on the projection of air dose rates together with the ecological half lives for different land uses.
