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Journal Articles

Estimation of environmental releases of radioactive materials

Chino, Masamichi*; Nagai, Haruyasu

Environmental Contamination from the Fukushima Nuclear Disaster; Dispersion, Monitoring, Mitigation and Lessons Learned, p.50 - 61, 2019/00

Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station accident and their atmospheric dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. We have estimated the atmospheric releases during the accident by comparing measurements with calculations by atmospheric deposition model. UNSCEAR compared several estimated source terms and used our source term for estimating levels of radioactive material in the terrestrial environment and doses to the public. To improve our source term, we recently made detailed source term estimation by using additional monitoring data and WSPEEDI including new deposition scheme.

Journal Articles

Utilization of $$^{134}$$Cs/$$^{137}$$Cs in the environment to identify the reactor units that caused atmospheric releases during the Fukushima Daiichi accident

Chino, Masamichi; Terada, Hiroaki; Nagai, Haruyasu; Katata, Genki; Mikami, Satoshi; Torii, Tatsuo; Saito, Kimiaki; Nishizawa, Yukiyasu

Scientific Reports (Internet), 6, p.31376_1 - 31376_14, 2016/08

 Times Cited Count:10 Percentile:8.68(Multidisciplinary Sciences)

Journal Articles

Reverse estimation of amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere

Terada, Hiroaki; Chino, Masamichi

Kisho Kenkyusho Gijutsu Hokoku, 76 (Internet), p.77 - 80, 2015/10

Japan Atomic Energy Agency has been trying to estimate the source term of iodine and cesium discharged from the Fukushima Daiichi Nuclear Power Station into the atmosphere for the assessment of the radiological dose to the public. The method applied in this estimation is a reverse estimation of source term by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq h$$^{-1}$$). For the source term estimation, environmental monitoring data on air concentrations of iodine and cesium and air dose rates were used. These data were observed over East Japan, almost in Fukushima Prefecture. The SPEEDI (System for Prediction of Environmental Emergency Dose Information) network system and the Worldwide version of SPEEDI (WSPEEDI-II) were used for calculating air concentrations and dose rates. We estimated the release rates and total amounts of $$^{131}$$I and $$^{137}$$Cs from March 12 to April 5, 2011.

Journal Articles

Source term estimation for the Fukushima Daiichi Nuclear Power Station accident by combined analysis of environmental monitoring and plant data through atmospheric dispersion simulation

Nagai, Haruyasu; Terada, Hiroaki; Chino, Masamichi; Katata, Genki; Mikami, Satoshi; Saito, Kimiaki

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.4044 - 4052, 2015/08

JAEA has estimated the atmospheric releases of radionuclide during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric transport and deposition model (ATDM). To improve our source term, we are trying to develop more sophisticated estimation method and use new information from severe accident analysis and observation data. As the first step of new trial, we used $$^{134}$$Cs/$$^{137}$$Cs ratios of inventories in FNPS1 reactors Unit 1 to 3 and those in surface deposition. By considering temporal change in $$^{134}$$Cs/$$^{137}$$Cs ratio of released plume and ATDM simulations, spatial distribution of $$^{134}$$Cs/$$^{137}$$Cs ratio in surface deposition was explained. This result can be used to specify from which reactor the dominant release occurred for each time period, and consequently provide useful information to severe accident analysis for the FNPS1 case.

Journal Articles

Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

Katata, Genki; Chino, Masamichi; Kobayashi, Takuya; Terada, Hiroaki; Ota, Masakazu; Nagai, Haruyasu; Kajino, Mizuo*; Draxler, R.*; Hort, M.*; Malo, A.*; et al.

Atmospheric Chemistry and Physics, 15(2), p.1029 - 1070, 2015/01

 Times Cited Count:88 Percentile:0.81(Environmental Sciences)

We estimated a detailed time trend of atmospheric releases during the Fukushima Dai-ichi Power Station (FNPS1) accident by combining environmental monitoring data with coupling simulation of atmospheric model of WSPEEDI-II, and oceanic dispersion model of SEA-GEARN-FDM. The new scheme of dry and fogwater depositions, in-cloud scavenging, cloud condensation nuclei activity, and wet scavenging by ice phase for radioactive iodine gas and other particles was incorporated into WSPEEDI-II. The results revealed that the major releases of radionuclides occurred in the following periods: afternoon on 12 March when the wet venting and hydrogen explosion at Unit 1, morning on 13 March after the venting event at Unit 3, midnight on 14 March when three-time openings of SRV were conducted at Unit 2, morning and night on 15 March, and morning on 16 March.

Journal Articles

Atmospheric releases of radionuclides, 2.1$$sim$$2.4

Chino, Masamichi; Nagai, Haruyasu

Gempatsu Jiko Osen; Fukushima Daiichi Gempatsu No Chikyu Kagakuteki Sokumen, p.36 - 44, 2014/10

The book to be published is a summary of the latest knowledge on environmental contaminations due to the Fukushima Dai-ichi nuclear accident. Here, we describe the releases of radionuclides into the atmosphere which have been investigated by JAEA until now. Furthermore, it is addressed that the accuracy of estimated source term by comparing with other researches related to the source term, the problem to be solved in future.

Journal Articles

Source term estimation of $$^{131}$$I and $$^{137}$$Cs discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere

Nagai, Haruyasu; Katata, Genki; Terada, Hiroaki; Chino, Masamichi

Radiation Monitoring and Dose Estimation of the Fukushima Nuclear Accident, p.155 - 173, 2014/03

AA2013-0245.pdf:0.62MB

JAEA has been trying to estimate the source term of iodine and cesium discharged from the Fukushima Daiichi Nuclear Power Plant to the atmosphere. As the first step, the source term was preliminary estimated by coupling environmental monitoring data with atmospheric dispersion simulations by SPEEDI and WSPEEDI. Then, detailed analysis on the local atmospheric dispersion has been carried out, and revealed the formation process of high dose rate zone around north-west direction from the plant. With this analysis and further analysis for the early phase of the accident, the release rates and total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere were re-estimated for the period from 12 to 15 March, 2011. Finally, the validity of revised source term was also examined by comparing daily and monthly surface deposition (fallout) over land in eastern Japan between measurements and outputs from the regional scale atmospheric dispersion simulation.

Journal Articles

Report of the Special Symposium on the Transport and Diffusion of Contaminants from the Fukushima Dai-ichi Nuclear Power Plant; Present status and future directions

Kondo, Hiroaki*; Yamada, Tetsuji*; Chino, Masamichi; Iwasaki, Toshiki*; Katata, Genki; Maki, Takashi*; Saito, Kazuo*; Terada, Hiroaki; Tsuruta, Haruo*

Tenki, 60(9), p.723 - 729, 2013/09

AA2013-0745.pdf:0.51MB

no abstracts in English

Journal Articles

Verification! Predicted information provided from SPEEDI during the Fukushima Daiichi Nuclear accident; Accuracy, timeliness and future utilization

Chino, Masamichi

Nippon Genshiryoku Gakkai-Shi, 55(4), p.220 - 224, 2013/04

During the Fukushima Daiichi Nuclear Power Reactor accident, SPEEDI were providing related authorities with predicted information on atompsheric dispersion, but it was accused that the information were not used for contermeasures of evacuation, etc. This paper describes what kind of prediction wer carried out, when these were provided to authoirities and how were the accuracy of these information. Furthermore, on the basis of these investigation, the future effective utilization of SPEEDI is proposed.

Journal Articles

Source term estimation of atmospheric release due to the Fukushima Dai-ichi Nuclear Power Plant accident by atmospheric and oceanic dispersion simulations

Kobayashi, Takuya; Nagai, Haruyasu; Chino, Masamichi; Kawamura, Hideyuki

Journal of Nuclear Science and Technology, 50(3), p.255 - 264, 2013/03

AA2012-0777.pdf:1.24MB

 Times Cited Count:94 Percentile:0.17(Nuclear Science & Technology)

The source term of the atmospheric release of $$^{131}$$I and $$^{137}$$Cs due to the Fukushima Dai-ichi Nuclear Power Plant accident estimated by previous studies was validated and refined by coupling atmospheric and oceanic dispersion simulations with observed $$^{134}$$Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for $$^{134}$$Cs and $$^{137}$$Cs, the sea surface concentration of $$^{134}$$Cs was calculated using the previously estimated source term and was compared with measurement data. The release rate of $$^{137}$$Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of $$^{131}$$I was refined to follow the radioactivity ratio of $$^{137}$$Cs. As a result, the total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.0$$times$$10$$^{17}$$ and 1.3$$times$$10$$^{16}$$ Bq, respectively.

Journal Articles

Atmospheric dispersion simulations of radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant due to accident; Consideration of deposition process

Nagai, Haruyasu; Chino, Masamichi; Terada, Hiroaki; Katata, Genki

NIRS-M-252, p.137 - 149, 2013/03

It is urgent to assess the radiological dose to the public due to the Fukushima Daiichi Nuclear Power Plant accident. JAEA has been undertaking this task by computer simulation of radioactive materials in the environment. The source term of radioactive materials discharged into the atmosphere was estimated. Then, detailed analysis on the local and regional scale dispersion were carried out by WSPEEDI-II simulations. However, there were some discrepancies between calculation and airborne monitoring of surface deposition of $$^{137}$$Cs. The cause of these discrepancies was investigated by carrying out some parametric study with focus on uncertainties due to the deposition process. In these tests, most discrepancies were reduced by modifying wet deposition processes without changing any other conditions. Further examinations are necessary to formulate wet deposition processes properly and to provide more accurate simulation for assessment of the radiological dose to the public.

Journal Articles

Reconstruction of the atmospheric releases of $$^{131}$$I and $$^{137}$$Cs resulting from the Fukushima Daiichi Nuclear Power Plant accident

Chino, Masamichi; Terada, Hiroaki; Katata, Genki; Nagai, Haruyasu; Nakayama, Hiromasa; Yamazawa, Hiromi*; Hirao, Shigekazu*; Ohara, Toshimasa*; Takigawa, Masayuki*; Hayami, Hiroshi*; et al.

NIRS-M-252, p.127 - 135, 2013/03

We estimated the release rates and total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere from March 12 to April 5, 2011. The applied method is a reverse estimation by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq/h). It calculates release rates of radionuclides (Bq/h) by dividing measured air concentrations of $$^{131}$$I and $$^{137}$$Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10$$^{15}$$ Bq/h of $$^{131}$$I, occurred on March 15, following to relatively small releases, 10$$^{13}$$ $$sim$$ 10$$^{14}$$ Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10$$^{14}$$ Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10$$^{11}$$ $$sim$$ 10$$^{12}$$ Bq/h of $$^{131}$$I on the beginning of April. The estimated source term was examined on the point of the time trend, total releases and the ground depositions of $$^{137}$$Cs by using different atmospheric dispersion models with above source term and compared them with observed $$^{137}$$Cs deposition distribution. These examinations showed that the estimated source term was reasonably accurate during the period when the plume flowed over land in Japan.

Journal Articles

Outline of the Fukushima Dai-ichi Nuclear Power Plant accident and process of radioactive contamination

Chino, Masamichi; Nagai, Haruyasu

Sui Kankyo Gakkai-Shi, 36(3), p.74 - 78, 2013/03

no abstracts in English

Journal Articles

Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi Nuclear Power Plant accident, 2; Verification of the source term and analysis of regional-scale atmospheric dispersion

Terada, Hiroaki; Katata, Genki; Chino, Masamichi; Nagai, Haruyasu

Journal of Environmental Radioactivity, 112, p.141 - 154, 2012/10

AA2011-0927.pdf:5.35MB

 Times Cited Count:165 Percentile:1.03(Environmental Sciences)

Regional-scale atmospheric dispersion simulations were carried out to verify source term of $$^{131}$$I and $$^{137}$$Cs estimated by our previous studies and analyze the atmospheric dispersion during the Fukushima Dai-ichi Nuclear Power Plant accident with measurements of daily and monthly surface depositions over land in Eastern Japan from March 12 to April 30, 2011. The prediction accuracy of daily surface deposition by using the refined source term was mostly within a factor of 10 without apparent biases. Therefore, the estimated source term is reasonable during the period when the plume flowed over land in Japan. The analysis of regional-scale atmospheric dispersion suggested that the distribution of a large amount of $$^{137}$$Cs deposition was produced mainly on March 12, 15-16, 20, and 21-23. The ratio of wet deposition to total one varied in wide range depending on the degree of influence by each event.

Journal Articles

Numerical reconstruction of high dose rate zones due to the Fukushima Dai-ichi Nuclear Power Plant accident

Katata, Genki; Terada, Hiroaki; Nagai, Haruyasu; Chino, Masamichi

Journal of Environmental Radioactivity, 111, p.2 - 12, 2012/09

AA2011-0339.pdf:1.57MB

 Times Cited Count:76 Percentile:4.8(Environmental Sciences)

For future planning of preventive measures against possible nuclear accident, it is important to understand how the high dose rate zones was created in the northwest area of the plant during the Fukushima Dai-ichi nuclear reactor accident. Because most of the observation equipment did not work due to the severe earthquakes, temporal information of release rates of radionuclides into the atmosphere and environmental monitoring data were limited to analyze the movements of radioactive plume in a significant release of radionuclides on 15 March, 2011. Here we reconstructed the atmospheric dispersion of radionuclides during the period from 15 to 16 March using computer-based nuclear emergency response system, WSPEEDI-II. We found that high dose rate zones were created by a significant deposition of radionuclides discharged during the afternoon on 15 March and two factors, i.e., rainfall and topography, strongly affected the distribution of surface deposition.

Journal Articles

Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi Nuclear Power Plant accident, 1; Source term estimation and local-scale atmospheric dispersion in early phase of the accident

Katata, Genki; Ota, Masakazu; Terada, Hiroaki; Chino, Masamichi; Nagai, Haruyasu

Journal of Environmental Radioactivity, 109, p.103 - 113, 2012/07

AA2011-0656.pdf:1.56MB

 Times Cited Count:112 Percentile:2.17(Environmental Sciences)

The source term of $$^{131}$$I and $$^{137}$$Cs discharged in early phase of the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident was estimated by combining environmental data with atmospheric dispersion simulations of a computer-based nuclear emergency response system, WSPEEDI-II. Major releases were estimated when air dose rates increased after the hydrogen explosion at Unit 1 during the afternoon on 12 March and during the midnight on 14 March. The high-concentration plumes discharged during these periods caused large deposition to the northwest and south-southwest directions of FNPP1, respectively. The increases of air dose rates observed at the monitoring posts were overall reproduced by WSPEEDI-II using estimated release rates. The simulation indicated that air dose rates significantly increased in the south-southwest region of FNPP1 by dry deposition of the high-concentration plume discharged from the midnight on 14 March to the morning on 15 March.

Journal Articles

How is the future of SPEEDI; Based on the experience of the Fukushima Daiichi Nuclear Power Plant accident

Chino, Masamichi

Nippon Genshiryoku Gakkai-Shi, 54(3), p.210 - 211, 2012/03

no abstracts in English

Journal Articles

Application of numerical simulation to predict the environmental transport of radioactive materials discharged from Fukushima Daiichi Nuclear Power Plant due to accident

Nagai, Haruyasu; Chino, Masamichi; Terada, Hiroaki; Katata, Genki; Nakayama, Hiromasa; Ota, Masakazu

Proceedings of International Symposium on Disaster Simulation & Structural Safety in the Next Generation (DS '11), p.369 - 374, 2011/09

In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Plant accident, the spatial and temporal distribution of radioactive materials in the environment have been and are planning to be analyzed by SPEEDI, WSPEEDI-II, and the numerical simulation system for material transport in the atmospheric, terrestrial, and oceanic environments, SPEEDI-MP. As the first step, the source term of radioactive materials discharged into the atmosphere has been estimated by coupling environmental monitoring data with atmospheric dispersion simulations by SPEEDI and WSPEEDI-II. As the next step, detailed analysis on the local dispersion around the plant by using WSPEEDI-II revealed the mechanism for the formation of high dose rate zone around north-west direction from the plant. Then, we are planning to apply SPEEDI-MP to provide more information on the distribution of radioactive materials in the whole environment.

Journal Articles

Preliminary estimation of release amounts of $$^{131}$$I and $$^{137}$$Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere

Chino, Masamichi; Nakayama, Hiromasa; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki; Yamazawa, Hiromi*

Journal of Nuclear Science and Technology, 48(7), p.1129 - 1134, 2011/07

The release amounts of $$^{131}$$I and $$^{137}$$Cs into the atmosphere due to the Fukushima Daiichi Nuclear Power Plant is preliminary estimated by coupling monitoring data on air concentrations and atmospheric dispersion simulation assuming unit release rate (1 Bq/h). The estimated results show that the large amount of release, the peak value of about 10$$^{16}$$ Bq/h of $$^{131}$$I on March 15, continued for a week after the accident, and, after March 23, the release rates have generally been declining to the order of 10$$^{11}$$ to 10$$^{12}$$ Bq/h. The total amounts of $$^{131}$$I and $$^{137}$$Cs discharged into the atmosphere are estimated about 1.5$$times$$10$$^{17}$$ Bq and 1.2$$times$$10$$^{16}$$ Bq.

Journal Articles

Study on improvement of reliability on inventory assessment in vitrified waste for long-term safety of geological disposal

Ishikawa, Masumi*; Kaneko, Satoru*; Kitayama, Kazumi*; Ishiguro, Katsuhiko*; Ueda, Hiroyoshi*; Wakasugi, Keiichiro*; Shinohara, Nobuo; Okumura, Keisuke; Chino, Masamichi; Moriya Noriyasu*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 8(4), p.304 - 312, 2009/12

Since quality control issues for vitrified waste are defined mainly with the focus on the transport and storage of the waste rather than the long-term safety of geological disposal, they do not cover inventories of long-lived nuclides which are of most interest in the safety assessment of geological disposal. Therefore we suggest a flow chart for assessment of inventories of long-lived nuclides in the vitrified waste focusing on measured value. We started a programme to examine the applicability as well as to improve reliability of nuclide generation/decay code and nuclear data library using liquid waste from spent fuel with clear irradiation history. To solve the issue of quality control for vitrified waste, comprehensive study is needed in aspects not only of geological disposal field but also of operation of nuclear power plant, reprocessing of spent fuel and vitrification of liquid waste. This study is a pioneering study to integrate them.

133 (Records 1-20 displayed on this page)