Search

Your search keyword '"Takemiya, Hiroshi"' showing total 15 results
Start Over Author "Takemiya, Hiroshi" Search Limiters Available in Library Collection
15 results on '"Takemiya, Hiroshi"'

1. Spatial and temporal prediction of radiation dose rates near Fukushima Daiichi Nuclear Power Plant

Author

Sun, Dajie, Wainwright, Haruko, Suresh, Ishita, Seki, Akiyuki, Takemiya, Hiroshi, and Saito, Kimiaki

Subjects
Environmental Sciences, Soil Sciences, Life on Land, Air Pollutants, Radioactive, Cesium Radioisotopes, Fukushima Nuclear Accident, Japan, Nuclear Power Plants, Radiation Dosage, Radiation Monitoring, Dose-rate time-series, Spatial-temporal prediction, Fukushima daiichi nuclear power plant, Modified Kalman filter, Gaussian process model, Chemical Sciences, Biological Sciences, Biological sciences, Chemical sciences, Environmental sciences
Abstract

In this paper, we have developed a methodology to estimate the spatiotemporal distribution of radiation air dose rates around the Fukushima Daiichi Nuclear Power Plant (FDNPP). In our exploratory data analysis, we found that (1) the temporal evolution of dose rates is composed of a log-linear decay trend and fluctuations of air dose rates that are spatially correlated among adjacent monitoring posts; and (2) the slope of the log-linear environmental decay trend can be represented as a function of the apparent initial dose rates, coordinate position, land-use type, and soil type. From these observations, we first estimated the log-linear decay trend at each location based on these predictors, using the random forest method. We then developed a modified Kalman filter coupled with a Gaussian process model to estimate the dose-rate time series at a given location and time. We applied this method to the Fukushima evacuation zone (as of March 2017), which included 17 monitoring post locations (with monitoring datasets collected between 2014 and 2018) and generated a time series of dose-rate maps. Our results show that this approach allows us to produce accurate spatial and temporal predictions of radiation dose-rate maps using limited spatiotemporal measurements.

Published
2022

2. Optimizing long-term monitoring of radiation air-dose rates after the Fukushima Daiichi Nuclear Power Plant.

Author

Sun, Dajie, Wainwright, Haruko M, Oroza, Carlos A, Seki, Akiyuki, Mikami, Satoshi, Takemiya, Hiroshi, and Saito, Kimiaki

Subjects
Cesium Radioisotopes, Air Pollutants, Radioactive, Bayes Theorem, Radiation Monitoring, Japan, Nuclear Power Plants, Fukushima Nuclear Accident, Dose rate, Fukushima, Long-term monitoring, Machine learning, Network optimization, Air Pollutants, Radioactive, Chemical Sciences, Environmental Sciences, Biological Sciences
Abstract

Radiation air dose rates near the Fukushima Daiichi Nuclear Power Plant (FDNPP) have been steadily decreasing over the past eight years since the release of radioactive elements in March 2011. Currently, the radiation monitoring program is expected to transition to long-term monitoring after most of the remediation activities are completed. The main long-term monitoring objectives are to (1) confirm the continuing reduction of contaminant and hazard levels, (2) provide assurance for the public, (3) accumulate the basic datasets for scientific knowledge and future preparation, and (4) detect changes or anomalies in contaminant mobility (if they occur), or any unexpected processes or events. In this work, we have developed a methodology for optimizing the monitoring locations of radiation air dose-rate monitoring. Our approach consists of three steps in order to determine monitoring locations in a systematic manner: (1) prioritizing the critical locations, such as schools or regulatory requirement locations, (2) diversifying locations that cover the key environmental controls that are known to influence contaminant mobility and distributions, and (3) capturing the heterogeneity of radiation air-dose rates across the domain. For the second step, we use a Gaussian mixture model to identify the representative locations among multiple environmental variables, such as elevation and land-cover types. For the third step, we use a Gaussian process model to capture and estimate the heterogeneity of air-dose rates across the domain. Employing an integrated dose-rate map derived from Bayesian geostatistical methods as a reference map, we distribute the monitoring locations in such a way as to capture the heterogeneity of the reference map. Our results have shown that this approach allows us to select monitoring locations in a systematic manner such that the heterogeneity of air dose rates is captured by the minimal number of monitoring locations.

Published
2020

3. Fields of View for Environmental Radioactivity

Author

Malins, Alex, Okumura, Masahiko, Machida, Masahiko, Takemiya, Hiroshi, and Saito, Kimiaki

Subjects
Physics - Medical Physics, Physics - Instrumentation and Detectors
Abstract

The gamma component of air radiation dose rates is a function of the amount and spread of radioactive nuclides in the environment. These radionuclides can be natural or anthropogenic in origin. The field of view describes the area of radionuclides on, or below, the ground that is responsible for determining the air dose rate, and hence correspondingly the external radiation exposure. This work describes Monte Carlo radiation transport calculations for the field of view under a variety of situations. Presented first are results for natural 40K and thorium and uranium series radionuclides distributed homogeneously within the ground. Results are then described for atmospheric radioactive caesium fallout, such as from the Fukushima Daiichi Nuclear Power Plant accident. Various stages of fallout evolution are considered through the depth distribution of 134Cs and 137Cs in soil. The fields of view for the natural radionuclides and radiocaesium are different. This can affect the responses of radiation monitors to these nuclides if the detector is partially shielded from the ground within its field of view. The field of view also sets the maximum reduction in air dose rates that can be achieved through local decontamination or remediation measures. This maximum efficiency can be determined quickly from the data presented here for the air dose rate versus the spatial extent of radioactive source on the ground., Comment: 6 pages, 6 figures, Author Accepted Manuscript for Proceedings of the 2015 International Symposium on Radiological Issues for Fukushima's Revitalized Future

Published
2015

11. Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018)

Author

Nagao, Fumiya, Niizato, Tadafumi, Sasaki, Yoshito, Ito, Satomi, Watanabe, Takayoshi, Dohi, Terumi, Nakanishi, Takahiro, Sakuma, Kazuyuki, Hagiwara, Hiroki, Funaki, Hironori, Tsuruta, Tadahiko, Misono, Toshiharu, Yoshimura, Kazuya, Nakama, Shigeo, Kurikami, Hiroshi, Machida, Masahiko, Yamada, Susumu, Itakura, Mitsuhiro, Malins, A., Okumura, Masahiko, Kim, M., Liu, X., Yamaguchi, Masaaki, Ishii, Yasuo, Muto, Kotomi, Tagomori, Hisaya, Saito, Hiroshi, Takemiya, Hiroshi, Seki, Akiyuki, Kitamura, Akihiro, and Iijima, Kazuki

Abstract

2011年3月11日に発生した太平洋三陸沖を震源とするマグニチュード9.0の東北地方太平洋沖地震とそれに伴って発生した津波により、東京電力福島第一原子力発電所の事故が発生し、その結果、環境中へ大量の放射性物質が放出され、その大部分が森林に沈着している。これに対し、面積が広大であり大量の除去土壌等が生じる、多面的な森林の機能が損なわれる可能性があるなどの問題があり、生活圏近傍を除き、汚染された森林の具体的な除染計画はない。そのため、未除染の森林から放射性セシウムが流出し、既に除染された生活圏に流入することに対する懸念があり、避難住民の帰還や産業再開の妨げとなる可能性があった。原子力機構では、環境中に放出された放射性物質、特に放射性セシウムの移動挙動に関する「長期環境動態研究」を2012年11月より実施している。この目的は、自治体の施策立案を科学的側面から補助する、住民の環境安全に関する不安を低減し、帰還や産業再開を促進するといった点にある。本報告書は、原子力機構が福島県で実施した環境動態研究におけるこれまでの研究成果について取りまとめたものである。, The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Published
2019

12. Comprehensive evaluation system for environmental remediation of Fukushima; Toward integration of three components as a whole system

Author

Saito, Hiroshi, Nozawa, Takashi, Takemiya, Hiroshi, Seki, Akiyuki, Matsubara, Takeshi, Saito, Kimiaki, and Kitamura, Akihiro

Abstract

平成23年3月11日に福島第一原子力発電所の事故が発生し環境中へ大量の放射性物質が放出された。これらは自然の駆動力によって移動、生活圏に到達し健康等に影響を及ぼす可能性が懸念されており、事故状況の把握や影響評価や対策のため調査研究が多く行われている。原子力機構は、取得データと関係省庁等が取得した公開データを収集・整理し「環境モニタリングデータベース」として公開している。また、これらデータ及び既存または開発した計算コードを用いて「統合解析支援環境」の中で事故後の状況再現や将来予測のため解析を行っている。また、これら知見は他研究機関の成果とあわせ「環境回復知識ベース」として一般の方々が理解できるよう公開ウェブサイトにQ\&A方式で公開している。これら三要素を包含し「福島の環境回復に係る包括的評価システム」と呼ぶ。これらは本来は相互に関連し一システムとして機能すべきところ、現状では独立して機能している。また、十分にオープンで理解しやすい形で外部に発信されているとは言えない。そこで、データや成果に対しより理解を深めることができ求める情報に容易にたどり着けるよう、当システム全体及び各要素の整備を行っていく。, The accidents at Fukushima Daiichi Nuclear Power Station on March 11th 2011, released significant amount of radionuclide to the environment. It has migrated to the human habitation and raised concerns of possible effect on human health, and for that a lot of researches have been performed. JAEA created and opened "Database for Radioactive Substance Monitoring Data" for usage of obtained data. For accurate modelling and future forecast using numerical code and the data, "Supporting Environment for Processing Simulation Codes" has been operated. In addition, research results have been opened as Q\&A style "Knowledge Base for Environmental Remediation" in JAEA's website. The "Comprehensive Evaluation System" composed of these components, should act more interrelated and integrated as one system. Besides, information dissemination is not enough to the outside. The report summarizes the current status, remaining issues and expected improvement of each component and the system.

Published
2018

13. Application Integration Control System for Multi-Scale and Multi-PhysicsSimulation

Author

KINO, Chiaki, TATEKAWA, Takayuki, TESHIMA, Naoya, KIM, Guehee, SUZUKI, Yoshio, ARAYA, Fumimasa, NISHIDA, Akemi, and TAKEMIYA, HIroshi

Subjects
Grid System, Multi-scale and multi physics simulation, Japan Atomic Energy Agency, Fault tolerant API, Seismic Analysis
Abstract

In the case of long-period and large-scale simulation, unexpected stop which is caused by execution time excess, outage of computers, outage of a network during file transfer and so on, become major issues. To avoid the stop of job execution and file transfer, we have developed Task Flow Control System that is a new control system for application integration with a fault tolerant API. If the computer is outage, the system designates an alternate computer, gathers necessary files and submits a new job. Each scheduler, file transfer and job condition can be flexibly defined in XML. This time, we applied the system to fluid-structure interaction analysis simulation. The result indicates that the system enables a user to easily execute multi-scale and multi-physics simulation using application integration.

Published
2010

Catalog

Books, media, physical & digital resources
See catalog results