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Terada, Hiroaki; Nagai, Haruyasu; Kadowaki, Masanao; Tsuzuki, Katsunori
Journal of Nuclear Science and Technology, 60(8), p.980 - 1001, 2023/08
Times Cited Count：4 Percentile：98.08(Nuclear Science & Technology)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.
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：8 Percentile：82.45(Environmental Sciences)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.
Nagai, Haruyasu; Terada, Hiroaki; Chino, Masamichi*
no journal, ,
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 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. We will discuss the effectiveness of a variety of monitoring data for the source term estimation by reviewing our source term estimation results.
Terada, Hiroaki; Nagai, Haruyasu; Tsuzuki, Katsunori; Furuno, Akiko; Kadowaki, Masanao
no journal, ,
We attempted to estimate source terms of radionuclides discharged into the atmosphere during the Fukushima Daiichi Nuclear Power Station accident by Bayesian inference using multi-scale dispersion simulations and various environmental measurements compositely. To make source-receptor matrix for the Bayesian analysis, we preliminary constructed a database of air concentration and surface deposition from dispersion calculations for multiple scales; several hundred km-square area, East Japan area, and the northern hemisphere area. We used various measurements such as dust sampling data, surface deposition map by airborne monitoring, fallout, hourly air concentration derived by analyzing suspended particulate matter collected at air pollution monitoring stations, and air concentrations at the Comprehensive Nuclear-Test-Ban Treaty Organization stations. We conducted a test estimation using these prototype databases and confirmed the validity and effectiveness of the method.
Nagai, Haruyasu; Terada, Hiroaki
no journal, ,
The Fukushima Daiichi Nuclear Power Station accident in March 2011 released significant amounts of radioactive materials into the atmosphere. In order to evaluate the environmental impacts and resultant radiological doses to the public due to the accident, the source term of radioactive materials discharged into the atmosphere was estimated and updated in a series of research conducted by Japan Atomic Energy Agency (JAEA). In these studies, the source term was reversely estimated from environmental monitoring data with an analysis method using atmospheric dispersion simulations. The atmospheric dispersion model mainly used in these studies was the Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI) developed by JAEA. In this report, the estimation method of source term and analysis results are presented.
Terada, Hiroaki; Nagai, Haruyasu; Tsuzuki, Katsunori; Kadowaki, Masanao
no journal, ,
Terada, Hiroaki
no journal, ,
Furuno, Akiko; Yamamoto, Yoichi; Tomita, Yutaka; Kurihara, Toshiyuki
no journal, ,
This study aims at the source term estimation of Xe-135 observed at the Takasaki Radionuclide Station of CTBT International Monitoring System and at two temporary stations, Horonobe and Mutsu of the Joint Noble Gas Measurement Project with CTBT, from the viewpoint of atmospheric dispersion. Radioactive xenon has been irregularly and frequently observed at these stations, thus it is very important to expose the source of the release areas in order to ensure the detection of nuclear tests. The most frequently observed isotope of radioactive xenon monitored by CTBT is Xe-133; nuclear facilities in Europe may be possible source as well as in East Asia depending on the meteorological conditions due to its relatively long half-life (5.25 days), making it difficult to specific of the source. On the other hand, Xe-135 has a short half-life of about 9 hours, and the possible release areas are limited to a relatively small area. In this presentation, we will focus on the Xe-135 detection events in the past four years and discuss the possible sources that could affect Japan.
