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Kadowaki, Masanao; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki*; Akari, Shusaku*
Energy Procedia, 131, p.208 - 215, 2017/12
Times Cited Count：4 Percentile：90.81(Energy & Fuels)When radioactive materials are released into the atmosphere due to nuclear accidents, numerical simulations that can reproduce temporal and spatial distribution of radioactive materials are useful to provide the information for emergency responses and radiological dose assessment. In this study, we attempt to improve the atmospheric dispersion simulation using an advanced meteorological data assimilation method and reconstruct the spatiotemporal distribution of radioactive materials released due to the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The atmospheric dispersion simulations were carried out by the Lagrangian particle dispersion model GEARN developed by Japan Atomic Energy Agency. To obtain meteorological fields for GEARN calculation, we used the Weather Research and Forecasting model WRF with meteorological data assimilation using four-dimensional variational method (4D-Var). GEARN calculations of the surface deposition and air concentration of radionuclides were compared with measurements. In the area close to FDNPS, the spatial distribution of the deposition of Cs-137 and I-131 simulated by GEARN agreed with the measured one. The accuracy of modeled deposition in northwest and south directions from FDNPS was particularly improved. This results were mainly attributed to the better reproducibility of wind field by using the meteorological data assimilation with 4D-Var. The improvement of the accuracy of modeled deposition distribution of Cs-137 in the East Japan area was also apparent under the meteorological fields modified by 4D-Var. The information of atmospheric dispersion processes reconstructed in this study is used for updating the existing assessment of radiological dose resulting from the FDNPS accident based on atmospheric simulations by our previous studies. It can also provide useful suggestions to make emergency response plans for nuclear facilities in Japan.
Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Katata, Genki; Ota, Masakazu; Furuno, Akiko; Akari, Shusaku
EPJ Web of Conferences, 153, p.08012_1 - 08012_7, 2017/09
Times Cited Count：3 Percentile：86.43(Nuclear Science & Technology)In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, the spatiotemporal distribution of radioactive materials in the environment are reconstructed by computer simulations. In this study, by refining the source term of radioactive materials and modifying the atmospheric dispersion model (ATDM), the atmospheric dispersion simulation of radioactive materials is improved. Then, a database of spatiotemporal distribution of radioactive materials in the air and on the ground surface is developed from the output of the simulation. This database is used in other studies for the dose assessment by coupling with the behavioral pattern of evacuees from the FDNPS accident. The ATDM simulation was improved to use a new meteorological model and sophisticated deposition scheme. Although the improved ATDM simulations reproduced well the 
Cs deposition pattern in the eastern Japan scale, the reproducibility of deposition pattern was decreased in the vicinity of FDNPS. This result indicated the necessity of further refinement of the source term by optimization to the improved ATDM simulations.
Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Ota, Masakazu; Furuno, Akiko; Akari, Shusaku; Katata, Genki
no journal, ,
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 are reconstructed by computer simulations. In this study, by refining the source term of radioactive materials discharged into the atmosphere and modifying the atmospheric dispersion model, the atmospheric dispersion simulation of radioactive materials is improved. Then, a database of spatiotemporal distribution of radioactive materials in the air and on the ground surface is developed from the output of the simulation, and is used for the dose assessment by coupling with the behavioral pattern of evacuees from the nuclear accident. In this year, (1) investigation of the source term, (2) improvement of atmospheric dispersion simulation, and (3) acquisition and organization of measured data have been conducted.
Kadowaki, Masanao; Nagai, Haruyasu; Terada, Hiroaki; Katata, Genki; Akari, Shusaku*
no journal, ,
When radioactive materials are released into the atmosphere due to nuclear accidents, numerical simulations that can reproduce temporal and spatial distribution of radioactive materials are useful to provide the information for radiological dose assessment. However, the uncertainties in meteorological field predictions to simulate the atmospheric dispersion becomes a major problem. In this study, we attempt to improve the accuracy of atmospheric dispersion simulation for the Fukushima Daiichi Nuclear Power Station accident using WRF. The meteorological fields were simulated by WRF with and without four-dimensional data assimilation. This data assimilation was conducted by WRFDA using four-dimensional variational method (4D-Var). Under the meteorological fields of two runs, the dispersion simulations for radioactive materials were examined by the Lagrangian atmospheric dispersion model GEARN developed by Japan Atomic Energy Agency. The GEARN calculations of the surface deposition and air concentration of Cs-137 were compared with measurements. In this presentation, we will demonstrate the improvement of the accuracy of GEARN simulation when the data assimilation method is applied to WRF.
Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Katata, Genki; Ota, Masakazu; Furuno, Akiko; Kadowaki, Masanao; Akari, Shusaku*
no journal, ,
no abstracts in English
Terada, Hiroaki; Nagai, Haruyasu; Katata, Genki; Tsuzuki, Katsunori; Akari, Shusaku*
no journal, ,
During the Fukushima Daiichi Nuclear Power Station accident which is necessary for accurate estimation of doses to the public, atmospheric dispersion simulations were conducted by using an atmospheric dispersion model underdevelopment Japan Atomic Energy Agency. The simulations were done by a latest meteorological model WRF and a particle dispersion model GEARN which has detailed deposition scheme considering different chemical forms. Surface deposition distribution in east Japan measured by airborne survey was largely reproduced by the simulation using the four-dimensional variational assimilation method (4D-Var) with meteorological observation data near the site and the latest estimated source term. Hereafter, we aim to estimate more accurate source term based on the comparison with the measurements such as air concentrations of Cs, etc.
