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.
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
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). 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 I and Cs from March 12 to April 5, 2011.
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 Cs/Cs ratios of inventories in FNPS1 reactors Unit 1 to 3 and those in surface deposition. By considering temporal change in Cs/Cs ratio of released plume and ATDM simulations, spatial distribution of Cs/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.
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
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.
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.
Nagai, Haruyasu; Katata, Genki; Terada, Hiroaki; Chino, Masamichi
Radiation Monitoring and Dose Estimation of the Fukushima Nuclear Accident, p.155 - 173, 2014/03
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 I and 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.
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
no abstracts in English
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.
Kobayashi, Takuya; Nagai, Haruyasu; Chino, Masamichi; Kawamura, Hideyuki
Journal of Nuclear Science and Technology, 50(3), p.255 - 264, 2013/03
The source term of the atmospheric release of I and 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 Cs in seawater collected from the Pacific Ocean. By assuming the same release rate for Cs and Cs, the sea surface concentration of Cs was calculated using the previously estimated source term and was compared with measurement data. The release rate of Cs was refined to reduce underestimation of measurements, which resulted in a larger value than that previously estimated. In addition, the release rate of I was refined to follow the radioactivity ratio of Cs. As a result, the total amounts of I and Cs discharged into the atmosphere from 5 JST on March 12 to 0 JST on March 20 were estimated to be approximately 2.010 and 1.310 Bq, respectively.
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 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.
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 I and 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 I and Cs into calculated ones at sampling points. The estimated temporal variation of releases indicates that the significant release, over 10 Bq/h of I, occurred on March 15, following to relatively small releases, 10 10 Bq/h, but the release rates from March 16 are estimated to be rather constant on the order 10 Bq/h until March 24. The release rates have decreased with small day-to-day variations to the order of 10 10 Bq/h of 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 Cs by using different atmospheric dispersion models with above source term and compared them with observed 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.
Chino, Masamichi; Nagai, Haruyasu
Sui Kankyo Gakkai-Shi, 36(3), p.74 - 78, 2013/03
no abstracts in English
Terada, Hiroaki; Katata, Genki; Chino, Masamichi; Nagai, Haruyasu
Journal of Environmental Radioactivity, 112, p.141 - 154, 2012/10
Regional-scale atmospheric dispersion simulations were carried out to verify source term of I and 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 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.
Katata, Genki; Terada, Hiroaki; Nagai, Haruyasu; Chino, Masamichi
Journal of Environmental Radioactivity, 111, p.2 - 12, 2012/09
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.
Katata, Genki; Ota, Masakazu; Terada, Hiroaki; Chino, Masamichi; Nagai, Haruyasu
Journal of Environmental Radioactivity, 109, p.103 - 113, 2012/07
The source term of I and 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.
Nippon Genshiryoku Gakkai-Shi, 54(3), p.210 - 211, 2012/03
no abstracts in English
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.
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 I and 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 Bq/h of 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 to 10 Bq/h. The total amounts of I and Cs discharged into the atmosphere are estimated about 1.510 Bq and 1.210 Bq.
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.