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Journal Articles

Dependency of the source term estimation method for radionuclides released into the atmosphere on the available environmental monitoring data and its applicability to real-time source term estimation

Terada, Hiroaki; Nagai, Haruyasu; Kadowaki, Masanao; Tsuzuki, Katsunori

Journal of Nuclear Science and Technology, 22 Pages, 2023/00

 Times Cited Count:0

It is essential to establish a method for reconstructing the source term and spatiotemporal distribution of radionuclides released into the atmosphere due to a nuclear accident for emergency countermeasures. We examined the dependency of a source term estimation method based on Bayesian inference using atmospheric dispersion simulation and environmental monitoring data on the availability of various monitoring data. Additionally, we examined the applicability of this method to a real-time estimation conducted immediately after an accident. A sensitivity analysis of the estimated source term during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident for combinations of various monitoring data indicated that using monitoring data with a high temporal and spatial resolution and the concurrent use of air concentration and surface deposition data is effective for accurate estimation. A real-time source term estimation experiment assuming the situation of monitoring data acquisition during the FDNPS accident revealed that this method could provide the necessary source term for grasping the overview of surface contamination in the early phase and evaluating the approximate accident scale. If the immediate online acquisition of monitoring data and regular operation of an atmospheric dispersion simulation are established, this method can provide the source term in near-real time.

Journal Articles

Estimation of children's thyroid equivalent doses in 16 municipalities after the Fukushima Daiichi Nuclear Power Station accident

Suzuki, Gen*; Ishikawa, Tetsuo*; Oba, Takashi*; Hasegawa, Arifumi*; Nagai, Haruyasu; Miyatake, Hirokazu*; Yoshizawa, Nobuaki*

Journal of Radiation Research (Internet), 63(6), p.796 - 804, 2022/11

 Times Cited Count:1 Percentile:0.01(Biology)

To elucidate the association between radiation dose and thyroid cancer after the 2011 Fukushima Daiichi Nuclear Power Station (FDNPS) accident, it is essential to estimate individual thyroid equivalent doses (TEDs) to children. In a previous study, we reported a methodology for reconstructing TEDs from inhalation based on individual behavioural survey sheets combined with a spatiotemporal radionuclides database constructed by an atmospheric transport, diffusion, and deposition model (ATDM). In the present study, we further refined our methodology and estimated the combined TEDs from inhalation and ingestion among children in 16 municipalities around the nuclear power station utilizing 3,256 individual whereabouts questionnaire survey sheets. Distributions of estimated TEDs were similar to estimates based on direct thyroid measurements in 1080 children in Iwaki City, Kawamata Town, Iitate Village, and Minamisoma City. Mean TEDs in 1-year-old children ranged from 1.3 mSv in Date City to 14.9 mSv in Odaka Ward in Minamisoma City, and the 95th percentiles varied from 2.3 mSv in Date City to 28.8 mSv in Namie Town. In the future, this methodology can be useful for a case-control study of thyroid cancer after the FDNPS accident.

Journal Articles

Development of local-scale high-resolution atmospheric dispersion and dose assessment system

Nakayama, Hiromasa; Onodera, Naoyuki; Satoh, Daiki; Nagai, Haruyasu; Hasegawa, Yuta; Idomura, Yasuhiro

Journal of Nuclear Science and Technology, 59(10), p.1314 - 1329, 2022/10

 Times Cited Count:2 Percentile:71.47(Nuclear Science & Technology)

We developed a local-scale high-resolution atmospheric dispersion and dose assessment system (LHADDAS) for safety and consequence assessment of nuclear facilities and emergency response to nuclear accidents or deliberate releases of radioactive materials in built-up urban areas. This system is composed of pre-processing of input files, main calculation by local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) and real-time urban dispersion simulation model based on a lattice Boltzmann method (CityLBM), and post-processing of dose-calculation by simulation code powered by lattice dose-response functions (SIBYL). LHADDAS has a broad utility and offers superior performance in (1) simulating turbulent flows, plume dispersion, and dry deposition under realistic meteorological conditions, (2) performing real-time tracer dispersion simulations using a locally mesh-refined lattice Boltzmann method, and (3) estimating air dose rates of radionuclides from air concentrations and surface deposition in consideration of the influence of individual buildings and structures. This system is promising for safety assessment of nuclear facilities as an alternative to wind tunnel experiments, detailed pre/post-analyses of a local-scale radioactive plume dispersion in case of nuclear accidents, and quick response to emergency situations resulting from deliberate release of radioactive materials by a terrorist attack in an urban central district area.

Journal Articles

Evaluation of uncertainties derived from meteorological forecast inputs in plume directions predicted by atmospheric dispersion simulations

Yoshida, Toshiya; Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Sawa, Hiroki*

Journal of Nuclear Science and Technology, 59(1), p.55 - 66, 2022/01

 Times Cited Count:1 Percentile:0.01(Nuclear Science & Technology)

Atmospheric transport, dispersion, and deposition models (ATDMs) can support decision-making during nuclear emergencies; however, uncertainties in the ATDM results need to be carefully evaluated. To investigate the uncertainties derived from meteorological forecast inputs, we conducted three-day forecast simulations every day for one year with hypothetical releases of radionuclides (one-hour releases every 6 h) from a nuclear facility. The forecast outputs were compared with the analysis outputs during the same period. The difference between the outputs is treated as the uncertainty in the forecasts and is represented as an angle based on the discrepancy in the plume directions between the analysis and forecast outputs. Using meteorological inputs made by Japan Meteorological Agency, the discrepancy angle (Ang) increased by approximately 10$$^circ$$ per day on an annual average basis. Meanwhile, the Ang values were occasionally 4-5 times higher than the annual average during short time periods. Since the Ang time series show seasonal and diurnal changes, the statistical characteristics likely depend on the geographical and meteorological conditions, as well as the types of meteorological inputs. Additionally, a main factor in the uncertainty is the wind-direction difference between the analysis and forecast outputs on scales of more than or less than 100 km.

JAEA Reports

Consideration on utilization of atmospheric dispersion models for a nuclear emergency preparedness and response

Togawa, Orihiko; Okura, Takehisa; Kimura, Masanori; Nagai, Haruyasu

JAEA-Review 2021-021, 61 Pages, 2021/11


Triggered by the Fukushima Daiichi Nuclear Power Station accident, there have been a lot of arguments among various situations and levels about utilization of atmospheric dispersion models for a nuclear emergency preparedness and response. Most of these arguments, however, were alternative and extreme discussions on whether predictions by computational models could be applied or not for protective measures in a nuclear emergency, and it was hard to say that these arguments were politely conducted, based on scientific verification in an emergency response. It was known, on the other hand, that there were not a few potential users of atmospheric dispersion models and/or calculation results by the models within the Japan Atomic Energy Agency (JAEA) and outside. However, they seemed to have a lack of understanding and a misunderstanding on proper use of different kinds of atmospheric dispersion models. This report compares an outline of models and calculation method in atmospheric dispersion models for a nuclear emergency preparedness and response, with a central focus on the models which have been developed and used in the JAEA. Examples of calculations by these models are also described in the report. This report aims at contributing to future consideration and activities for potential users of atmospheric dispersion models within the JAEA and outside.

Journal Articles

Validity of the source term for the Fukushima Dai-ichi Nuclear Power Station accident estimated using local-scale atmospheric dispersion simulations to reproduce the large-scale atmospheric dispersion of $$^{137}$$Cs

Kadowaki, Masanao; Furuno, Akiko; Nagai, Haruyasu; Kawamura, Hideyuki; Terada, Hiroaki; Tsuzuki, Katsunori; El-Asaad, H.

Journal of Environmental Radioactivity, 237, p.106704_1 - 106704_18, 2021/10

 Times Cited Count:1 Percentile:0(Environmental Sciences)

The source term of $$^{137}$$Cs for the Fukushima Daiichi Nuclear Power Station (FDNPS) accident was estimated from the results of local-scale atmospheric dispersion simulations and measurements. To confirm the source term's validity for reproducing the large-scale atmospheric dispersion of $$^{137}$$Cs, this study conducted hemispheric-scale atmospheric and oceanic dispersion simulations. In the dispersion simulations, the atmospheric-dispersion database system Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI)-DB and oceanic dispersion model SEA-GEARN-FDM were used. Compared with the air concentrations of $$^{137}$$Cs measured by the Comprehensive Nuclear-Test-Ban Treaty Organization, overall, the WSPEEDI-DB simulation reproduced the measurements with some overestimation. Furthermore, the deposition amounts of $$^{137}$$Cs was investigated using concentrations of $$^{137}$$Cs in seawater. The simulated seawater concentrations of $$^{137}$$Cs were underestimated regionally in the North Pacific. The overestimation and underestimation could be improved without contradiction between the air and seawater concentrations of $$^{137}$$Cs using more realistic precipitation in atmospheric dispersion simulations. This shows that the source term validated in this study could reproduce the spatiotemporal distribution of $$^{137}$$Cs because of the FDNPS accident in both local and large-scale atmospheric dispersion simulations.

Journal Articles

Development of local-scale high-resolution atmospheric dispersion model using Large-Eddy Simulation, 6; Introduction of detailed dose calculation method

Nakayama, Hiromasa; Satoh, Daiki; Nagai, Haruyasu; Terada, Hiroaki

Journal of Nuclear Science and Technology, 58(9), p.949 - 969, 2021/09

 Times Cited Count:5 Percentile:78.24(Nuclear Science & Technology)

We introduced a detailed dose calculation method considering building shielding effects into LOcal-scale High-resolution atmospheric DIspersion Model using LES (LOHDIM-LES). To estimate quickly and accurately dose distributions considering shielding effects of buildings, we employed the calculation method using dose-response matrices which were evaluated by photon transport simulations with Particle and Heavy-Ion Transport code System (PHITS). Compared to the air dose rate data obtained from monitoring posts in an actual nuclear facility, it was shown that the calculated dose rate is reasonably simulated well. It is concluded that LOHDIM-LES equipped with the calculation method using dose-response matrices can reasonably estimate the air dose rates considering shielding effects of individual buildings and structures.

Journal Articles

Atmospheric dispersion simulations for the assessment of radiological dose to the public; Reassessment of the atmospheric concentration distribution of radioactive materials in the immediate aftermath of the accident at the Fukushima Daiichi Nuclear Power Plant

Nagai, Haruyasu

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vo.2; Environmental Effects and Remediation for Restoration, p.37 - 46, 2021/07

Radioactive materials were released into the environment due to the accident that occurred at the Fukushima Daiichi Nuclear Power Plant, which is operated by the Tokyo Electric Power Company. This release immediately led to the performance of an internal exposure dose assessment of iodine and other nuclides with a short halflife. To determine the necessary dose estimation, the spatial-temporal distribution of the atmospheric concentration of radioactive materials was reassessed by performing dispersion simulations with $$^{131}$$I, $$^{133}$$I, $$^{132}$$Te, and $$^{137}$$Cs with due consideration given to their contribution to the internal exposure doses. A database of the spatial-temporal distribution of the concentration was developed based on the results obtained from the calculations performed for each defined time at a horizontal interval of 3 km near the ground surface.

Journal Articles

5.4.3 Source term estimation by atmospheric dispersion simulation

Nagai, Haruyasu

Fission Product Behavior under Severe Accident, p.112 - 116, 2021/05

no abstracts in English

Journal Articles

Global budget of atmospheric $$^{129}$$I during 2007-2010 estimated by a chemical transport model: GEARN-FDM

Kadowaki, Masanao; Terada, Hiroaki; Nagai, Haruyasu

Atmospheric Environment; X (Internet), 8, p.100098_1 - 100098_17, 2020/12

The behaviors of atmospheric $$^{129}$$I and the global cycle of $$^{129}$$I remain incompletely understood because the spatiotemporal resolution of monitoring is insufficient and few measurement-based models have been reported. This study aims to quantitatively understand the global budget of $$^{129}$$I. When quantifying, we conduct global atmospheric $$^{129}$$I dispersion simulations covering from 2007 to 2010. To achieve this goal, the present study newly incorporated the iodine chemistry processes of two gas-phase chemical reactions, six photolysis reactions, and two heterogeneous reactions into an existing atmospheric $$^{129}$$I transport model (GEARN-FDM). Besides the aerial release of $$^{129}$$I from nuclear fuel reprocessing facilities, the model includes the volatilization processes of $$^{129}$$I compounds from Earth's surface. The net $$^{129}$$I exchange fluxes from the atmosphere to the Earth's surface of land and ocean were estimated as 18.0 GBq/y and 5.3 GBq/y, respectively. The global $$^{129}$$I emission from oceans was estimated as 7.2 GBq/y, nearly half of the emission totals were emitted from the English Channel (3.2 GBq/y). In addition, the global $$^{129}$$I emission from land was estimated as 1.7 GBq/y. The remarkable $$^{129}$$I emission from land was mainly appeared in Europe, Russia, and North America, and the emission distribution is impacted by the activities of the past and ongoing nuclear fuel reprocessing facilities. The total $$^{129}$$I emission from ocean and land is lower than the $$^{129}$$I emission from the model-included nuclear fuel reprocessing facilities (23.3 GBq/y), showing that the aerial release of nuclear fuel reprocessing facilities in operation is still an important $$^{129}$$I source.

JAEA Reports

Practical guide on soil sampling, treatment, and carbon isotope analysis for carbon cycle studies

Koarashi, Jun; Atarashi-Andoh, Mariko; Nagano, Hirohiko*; Sugiharto, U.*; Saengkorakot, C.*; Suzuki, Takashi; Kokubu, Yoko; Fujita, Natsuko; Kinoshita, Naoki; Nagai, Haruyasu; et al.

JAEA-Technology 2020-012, 53 Pages, 2020/10


There is growing concern that recent rapid changes in climate and environment could have a significant influence on carbon cycling in terrestrial ecosystems (especially forest ecosystems) and could consequently lead to a positive feedback for global warming. The magnitude and timing of this feedback remain highly uncertain largely due to a lack of quantitative understanding of the dynamics of organic carbon stored in soils and its responses to changes in climate and environment. The tracing of radiocarbon (natural and bomb-derived $$^{14}$$C) and stable carbon ($$^{13}$$C) isotopes through terrestrial ecosystems can be a powerful tool for studying soil organic carbon (SOC) dynamics. The primary aim of this guide is to promote the use of isotope-based approaches to improve our understanding of the carbon cycling in soils, particularly in the Asian region. The guide covers practical methods of soil sampling; treatment and fractionation of soil samples; preparation of soil samples for $$^{13}$$C (and stable nitrogen isotope, $$^{15}$$N) and $$^{14}$$C analyses; and $$^{13}$$C, $$^{15}$$N, and $$^{14}$$C measurements by the use of isotope ratio mass spectrometry and accelerator mass spectrometry (AMS). The guide briefly introduces ways to report $$^{14}$$C data, which are frequently used for soil carbon cycling studies. The guide also reports results of a case study conducted in a Japanese forest ecosystem, as a practical application of the use of isotope-based approaches. This guide is mainly intended for researchers who are interested but are not experienced in this research field. The guide will hopefully encourage readers to participate in soil carbon cycling studies, including field works, laboratory experiments, isotope analyses, and discussions with great interest.

Journal Articles

Development of a user-friendly interface IRONS for atmospheric dispersion database for nuclear emergency preparedness based on the Fukushima database

El-Asaad, H.*; Nagai, Haruyasu; Sagara, Hiroshi*; Han, C. Y.*

Annals of Nuclear Energy, 141, p.107292_1 - 107292_9, 2020/06

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Atmospheric dispersion simulations can provide crucial information to assess radioactive plumes in the environment for nuclear emergency preparedness. However, it is a difficult and time-consuming task to make simulations assuming many possible scenarios and to derive data from a vast number of results. Therefore, an interface was developed to assist users in conveying characteristics of plumes from simulation results. The interface uses a large database that contains WSPEEDI-II simulations for the first 20-days of radioactive release from the Fukushima Daiichi Nuclear Power Plant, and it displays essential quantitative data to the user from the database. The user may conduct sensitivity analysis with the help of the interface by changing release condition to generate many different case scenarios.

Journal Articles

Atmospheric-dispersion database system that can immediately provide calculation results for various source term and meteorological conditions

Terada, Hiroaki; Nagai, Haruyasu; Tanaka, Atsunori*; Tsuzuki, Katsunori; Kadowaki, Masanao

Journal of Nuclear Science and Technology, 57(6), p.745 - 754, 2020/06

 Times Cited Count:6 Percentile:67.23(Nuclear Science & Technology)

We have estimated source term and analyzed processes of atmospheric dispersion of radioactive materials released during the Fukushima Daiichi Nuclear Power Station (FDNPS) accident by the Worldwide version of System for Environmental Emergency Dose Information. On the basis of this experience, we developed an dispersion calculation method that can respond to various needs in a nuclear emergency and provide useful information for emergency-response planning. By this method, if a release point is known, it is possible to immediately obtain the prediction results by applying provided source term to the database of dispersion-calculation results prepared in advance. With this function, it is easy to compare results by applying various source term with monitoring data, and to find out the optimum source term, which was applied for the source term estimation of the FDNPS accident. By performing this calculation with past meteorological-analysis data, it is possible to immediately get dispersion-calculation results for various source term and meteorological conditions. This database can be used for pre-accident planning, such as optimization of a monitoring plan and understanding of events to be supposed in considering emergency countermeasures.

Journal Articles

Refinement of source term and atmospheric dispersion simulations of radionuclides during the Fukushima Daiichi Nuclear Power Station accident

Terada, Hiroaki; Nagai, Haruyasu; Tsuzuki, Katsunori; Furuno, Akiko; Kadowaki, Masanao; Kakefuda, Toyokazu*

Journal of Environmental Radioactivity, 213, p.106104_1 - 106104_13, 2020/03

 Times Cited Count:38 Percentile:93.57(Environmental Sciences)

In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station accident in Japan, the spatial and temporal distribution of radioactive materials in the environment is necessary to be reconstructed by computer simulations with the atmospheric transport, dispersion and deposition model (ATDM) and source term of radioactive materials discharged into the atmosphere is essential. In this study, we carried out refinement of the source term and improvement of ATDM simulation by using an optimization method based on Bayesian inference with various measurements (air concentration, surface deposition, and fallout). We also constructed the spatiotemporal distribution of some major radionuclides in the air and on the surface (optimized dispersion database) by using the optimized release rates and ATDM simulations which is used for the comprehensive dose assessment by coupling with the behavioral pattern of evacuees from the accident.

Journal Articles

Reconstruction of residents' thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi Nuclear Power Station accident

Oba, Takashi*; Ishikawa, Tetsuo*; Nagai, Haruyasu; Tokonami, Shinji*; Hasegawa, Arifumi*; Suzuki, Gen*

Scientific Reports (Internet), 10(1), p.3639_1 - 3639_11, 2020/02

 Times Cited Count:13 Percentile:84.63(Multidisciplinary Sciences)

Internal doses of residents after the Fukushima Daiichi Nuclear Power Station accident have been reconstructed. In total 896 behaviour records in the Fukushima Health Management Survey were analysed to estimate thyroid doses via inhalation, using a spatiotemporal radionuclides concentration database constructed by atmospheric dispersion simulations. After a decontamination factor for sheltering and a modifying factor for the dose coefficient were applied, estimated thyroid doses were close to those estimated on the basis of direct thyroid measurement. The median and 95th percentile of thyroid doses of 1-year-old children ranged from 1.2 to 15 mSv and from 7.5 to 30 mSv, respectively.

Journal Articles

Intercomparison of numerical atmospheric dispersion prediction models for emergency response to emissions of radionuclides with limited source information in the Fukushima Dai-ichi Nuclear Power Plant accident

Iwasaki, Toshiki*; Sekiyama, Tsuyoshi*; Nakajima, Teruyuki*; Watanabe, Akira*; Suzuki, Yasushi*; Kondo, Hiroaki*; Morino, Yu*; Terada, Hiroaki; Nagai, Haruyasu; Takigawa, Masayuki*; et al.

Atmospheric Environment, 214, p.116830_1 - 116830_11, 2019/10

 Times Cited Count:5 Percentile:29.03(Environmental Sciences)

The utilization of numerical atmospheric dispersion prediction (NDP) models for accidental discharge of radioactive substances was recommended by a working group of the Meteorological Society of Japan. This paper is to validate the recommendation through NDP model intercomparison in the accidental release from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Emission intensity is assumed to be constant during the whole forecast period for the worst-case scenario unless time sequence of emission is available. We expect to utilize forecasts of surface air contaminations for preventions of inhalations of radioactive substances, and column-integrated amounts for mitigation of radiation exposure associated with wet deposition. Although NDP forecasts have ensemble spread, they commonly figure out relative risk in space and time. They are of great benefit to disseminating effective warnings to public without failure. The multi-model ensemble technique may be effective to improve the reliability.

Journal Articles

Dispersion modelling of radioactive materials

Nagai, Haruyasu; Yamazawa, Hiromi*

Environmental Contamination from the Fukushima Nuclear Disaster; Dispersion, Monitoring, Mitigation and Lessons Learned, p.230 - 242, 2019/08

An overview of SPEEDI is provided in the context of it development, functions, and role in the framework of nuclear emergency management. Thereafter, we examine how it was used and how it should be used for the Fukushima Daiichi Nuclear Power Station accident from a system developer perspective. We believe that our review can provide lessons or tasks for improving the prediction system and for considering better utilization of the system; it is also beneficial to consider reconstructing the framework of nuclear emergency management. Furthermore, we hope this review will prove useful in understanding and effectively using the atmospheric dispersion predictions from the system in the case of a similar accident in the future.

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

 Times Cited Count:6 Percentile:85.87

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

Model intercomparison of atmospheric $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident; Simulations based on identical input data

Sato, Yosuke*; Takigawa, Masayuki*; Sekiyama, Tsuyoshi*; Kajino, Mizuo*; Terada, Hiroaki; Nagai, Haruyasu; Kondo, Hiroaki*; Uchida, Junya*; Goto, Daisuke*; Qu$'e$lo, D.*; et al.

Journal of Geophysical Research; Atmospheres, 123(20), p.11748 - 11765, 2018/10

 Times Cited Count:32 Percentile:83.83(Meteorology & Atmospheric Sciences)

A model intercomparison of the atmospheric dispersion of $$^{137}$$Cs emitted following the Fukushima Daiichi Nuclear Power Plant accident was conducted by 12 models to understand the behavior of $$^{137}$$Cs in the atmosphere. The same meteorological data, horizontal grid resolution, and an emission inventory were applied to all the models to focus on the model variability originating from the processes included in each model. The multi-model ensemble captured 40% of the observed $$^{137}$$Cs events, and the figure-of-merit in space for the total deposition of $$^{137}$$Cs exceeded 80. Our analyses indicated that the meteorological data were most critical for reproducing the $$^{137}$$Cs events. The results also revealed that the differences among the models were originated from the deposition and diffusion processes when the meteorological field was simulated well. However, the models with strong diffusion tended to overestimate the $$^{137}$$Cs concentrations.

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