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JAEA Reports

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

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2020-007, 249 Pages, 2020/10

JAEA-Research-2020-007.pdf:15.83MB

The accident of the Fukushima Daiichi Nuclear Power Station, 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, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" 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.

Journal Articles

Estimation of air dose rate using measurement results of monitoring posts in Fukushima Prefecture

Seki, Akiyuki; Mayumi, Akie; Murakami, Haruko*; Saito, Kimiaki; Takemiya, Hiroshi; Idomura, Yasuhiro

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.158 - 164, 2020/10

We developed a method to estimate the temporal change of the air dose rate at the location with sparse (in time) measurements by using the continuous measurement data from the nearby monitoring post. This method determines an observation model from the correlation between sparse data at the target location and dense data at the monitoring post based on a hierarchical Bayesian model. The developed method was validated against the air dose rate measured at the monitoring posts in Fukushima prefecture from 2012 to 2017. The results showed that the developed method can predict the air dose rate at almost all target locations with an error rate of less than 10%.

Journal Articles

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

Sun, D.*; Wainwright, H. M.*; Oroza, C. A.*; Seki, Akiyuki; Mikami, Satoshi; Takemiya, Hiroshi; Saito, Kimiaki

Journal of Environmental Radioactivity, 220-221, p.106281_1 - 106281_8, 2020/09

We have developed a methodology for optimizing the monitoring locations of radiation air dose-rate monitoring. For the method, we use a Gaussian mixture model to identify the representative locations among multiple environmental variables, such as elevation and land-cover types. Next, we use a Gaussian process model to capture and estimate the heterogeneity of air-dose rates across the domain. 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.

Journal Articles

Summary of temporal changes in air dose rates and radionuclide deposition densities in the 80 km zone over five years after the Fukushima Nuclear Power Plant accident

Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Yoshida, Tadayoshi; Sato, Tetsuro*; Seki, Akiyuki; Yamamoto, Hideaki*; et al.

Journal of Environmental Radioactivity, 210, p.105878_1 - 105878_12, 2019/12

 Times Cited Count:7 Percentile:25.42(Environmental Sciences)

Journal Articles

Temporal change in radiological environments on land after the Fukushima Daiichi Nuclear Power Plant accident

Saito, Kimiaki; Mikami, Satoshi; Ando, Masaki; Matsuda, Norihiro; Kinase, Sakae; Tsuda, Shuichi; Sato, Tetsuro*; Seki, Akiyuki; Sanada, Yukihisa; Wainwright-Murakami, Haruko*; et al.

Journal of Radiation Protection and Research, 44(4), p.128 - 148, 2019/12

JAEA Reports

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

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2019-002, 235 Pages, 2019/08

JAEA-Research-2019-002.pdf:21.04MB

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.

Journal Articles

Characterizing regional-scale temporal evolution of air dose rates after the Fukushima Daiichi Nuclear Power Plant accident

Wainwright, H. M.*; Seki, Akiyuki; Mikami, Satoshi; Saito, Kimiaki

Journal of Environmental Radioactivity, 189, p.213 - 220, 2018/09

 Times Cited Count:3 Percentile:67.79(Environmental Sciences)

In this study, we quantify the temporal changes of air dose rates in the regional scale around the Fukushima Daiichi Nuclear Power Plant in Japan, and predict the spatial distribution of air dose rates in the future. We first apply the Bayesian geostatistical method developed by Wainwright et al. (2017) to integrate multiscale datasets including ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. We apply this method to the datasets from three years: 2014 to 2016. The temporal changes among the three integrated maps enables us to characterize the spatiotemporal dynamics of radiation air dose rates.

JAEA Reports

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

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

JAEA-Review 2017-040, 34 Pages, 2018/03

JAEA-Review-2017-040.pdf:9.52MB

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.

Journal Articles

A Multiscale Bayesian data integration approach for mapping air dose rates around the Fukushima Daiichi Nuclear Power Plant

Wainwright, Haruko*; Seki, Akiyuki; Chen, J.*; Saito, Kimiaki

Proceedings of International Waste Management Symposia 2017 (WM 2017) (Internet), 8 Pages, 2017/03

We integrate various types of datasets, such as ground-based walk and car surveys, and airborne surveys, all of which have different scales, resolutions, spatial coverage, and accuracy. This method is based on geostatistics to represent spatial heterogeneous structures, and also on Bayesian hierarchical models to integrate multiscale, multitype datasets in a consistent manner. The Bayesian method allows us to quantify the uncertainty in the estimates, and to provide the confidence intervals that are critical for robust decision-making. We showed the demonstration of Bayesian data integration approach for the Fukushima evacuation zones with high air dose rates.

Journal Articles

A Multiscale Bayesian data integration approach for mapping air dose rates around the Fukushima Daiichi Nuclear Power Plant

Wainwright, H. M.*; Seki, Akiyuki; Chen, J.*; Saito, Kimiaki

Journal of Environmental Radioactivity, 167, p.62 - 69, 2017/02

 Times Cited Count:7 Percentile:51.94(Environmental Sciences)

This paper presents a multiscale data integration method to estimate the spatial distribution of air dose rates in the regional scale around the Fukushima Daiichi Nuclear Power Plant. We demonstrate our approach using three types of datasets collected at the same time over Fukushima City in Japan: (1) coarse-resolution airborne surveys covering the entire area, (2) car surveys along major roads, and (3) walk surveys in multiple neighborhoods. Results show that the method can successfully integrate three types of datasets and create an integrated map (including the confidence intervals) of air dose rates over the domain in high resolution. Moreover, this study provides us with various insights into the characteristics of each data set, as well as radiocaesium distribution. In particular, the urban areas show high heterogeneity in the contaminant distribution due to human activities as well as large discrepancy among different surveys due to such heterogeneity.

Journal Articles

Development of a software platform for providing environmental monitoring data for the Fukushima Daiichi nuclear accident

Seki, Akiyuki; Saito, Osamu; Nago, Harutaka*; Suzuki, Kenta; Tomishima, Katsuya; Saito, Kimiaki; Takemiya, Hiroshi

Radiation Protection Dosimetry, 164(1-2), p.97 - 102, 2015/04

 Times Cited Count:3 Percentile:62.98(Environmental Sciences)

We have developed a software platform which supports working steps for providing large amount of diverse monitoring data. It was found that the platform is effective in reducing the time needed to publish the monitoring data. Reducing the cost and workload for publishing the monitoring data is also important, because monitoring should be continued over a few decades in the case of Fukushima accident. Our platform is expected to help to mitigate the problem, too.

Journal Articles

Measurements and evaluations of air dose rates around Fukushima, 4; Practical aspects of air dose rate measurements in the environment

Tsuda, Shuichi; Yoshida, Tadayoshi; Ando, Masaki; Matsuda, Norihiro; Mikami, Satoshi; Tanigaki, Minoru*; Okumura, Ryo*; Takamiya, Koichi*; Sato, Nobuhiro*; Seki, Akiyuki; et al.

Radioisotopes, 64(4), p.275 - 289, 2015/04

This article provides practically useful information on air dose rate measurements in the environments. The basic requirements for the accurate measurements are described giving actual data. The characteristics and some measured results are shown for reliable methods which are widely used in the environmental radiation measurements. Further, information is given on internet sites where air dose rates and related data obtained by official organizations can be browsed.

Journal Articles

Detailed deposition density maps constructed by large-scale soil sampling for $$gamma$$-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident

Saito, Kimiaki; Tanihata, Isao*; Fujiwara, Mamoru; Saito, Takashi*; Shimoura, Susumu*; Otsuka, Takaharu*; Onda, Yuichi*; Hoshi, Masaharu*; Ikeuchi, Yoshihiro*; Takahashi, Fumiaki; et al.

Journal of Environmental Radioactivity, 139, p.308 - 319, 2015/01

 Times Cited Count:168 Percentile:0.6(Environmental Sciences)

Journal Articles

Development of radionuclide distribution database and map system on the Fukushima nuclear accident

Seki, Akiyuki; Takemiya, Hiroshi; Takahashi, Fumiaki; Saito, Kimiaki; Tanaka, Kei*; Takahashi, Yutaka*; Takemura, Kazuhiro*; Tsuzawa, Masaharu*

Progress in Nuclear Science and Technology (Internet), 4, p.47 - 50, 2014/04

The radionuclide distribution database and map system, which provide basic information for evaluations and countermeasures of the Fukushima nuclear accident, are explained. Due to massive earthquake and tsunami, Fukushima Dai-ichi Nuclear Power Plant has been damaged and had spread out radioactive materials around the Fukushima site. It is necessary to collect, analyze, and provide the information of radioactivity correctly and immediately. We developed two providing systems to identify the current distribution of released radionuclides and support decontamination activities.

JAEA Reports

Construction of a car-borne survey system for measurement of dose rates in air; KURAMA-II, and its application

Tsuda, Shuichi; Yoshida, Tadayoshi; Nakahara, Yukio; Sato, Tetsuro; Seki, Akiyuki; Matsuda, Norihiro; Ando, Masaki; Takemiya, Hiroshi; Tanigaki, Minoru*; Takamiya, Koichi*; et al.

JAEA-Technology 2013-037, 54 Pages, 2013/10

JAEA-Technology-2013-037.pdf:4.94MB

JAEA has been performing dose rate mapping in air using a car-borne survey system KURAMA-II. The KURAMA system is a GPS-aided mobile radiation monitoring system that has been newly developed by Kyoto University Research Reactor Institute in response to the nuclear disaster. The KURAMA system is composed of an energy-compensated scintillation survey meter for measuring dose rate, electric device for controlling both the dose rates and the position data from a GPS module, a computer server for processing and analyzing data from KURAMA, and client PCs for providing for end users. The KURAMA-II has been improved in small-packaging, durability, and automated data transmission. In consequence, dose rate mapping in wide area has become possible in shorter period of time. This report describes the construction of KURAMA-II, its application and a suggestion of how to manage a large number of KURAMA-II.

Journal Articles

Preliminary investigation on material welding simulation by laser irradiation

Takase, Kazuyuki; Muramatsu, Toshiharu; Seki, Akiyuki; Kitamura, Tatsuaki*; Machida, Hiromu*

Nippon Kikai Gakkai Netsu Kogaku Konfarensu 2009 Koen Rombunshu, p.217 - 218, 2009/11

no abstracts in English

JAEA Reports

Development of Radiation Dose Assessment System for Radiation Accident (RADARAC)

Takahashi, Fumiaki; Shigemori, Yuji*; Seki, Akiyuki

JAEA-Data/Code 2009-008, 127 Pages, 2009/07

JAEA-Data-Code-2009-008.pdf:10.5MB

A radiation transport calculation can derive dose distribution in a heavily exposed person for the medical treatment at the case of an accident. Since the accident cannot be prospected, many complicated procedures are needed to make the input file soon after the accident and to inform radiation dose based upon the output files with much information concerning the calculation. Thus, ($underline{Ra}$)diation ($underline{D}$)ose ($underline{A}$)ssessment system for ($underline{R}$)adiation ($underline{Ac}$)cident (RADARAC) was developed to derive effectively radiation dose by the MCNPX or the MCNP code. RADARAC consists of RADARAC_INPUT and RADARAC_DOSE. A user can interactively set up necessary resources to make input files with three programs in RADARAC_INPUT. The results of radiation doses are indicated with tables, graphs and figures depicting dose distribution by RADARAC_DOSE. It is confirmed that RADARAC can make input files with a few thousand lines and indicate more than 20,000 data dose within a few minutes.

Journal Articles

Dose assessment system for a heavily exposed person in radiation facility

Takahashi, Fumiaki; Shigemori, Yuji*; Seki, Akiyuki

Hozengaku, 8(1), p.56 - 61, 2009/04

Failure of safety management system can bring about a heavily exposed person in maintenance of a radiation facility, though such a case is very rare. A method using radiation transport code has advantages in an assessment of dose distribution inside a human body. Complicated procedures, however, are needed to prepare an input-file and to derive radiation dose based upon descriptions of an output-file in a numerical analysis using a radiation transport code. Thus, a system was developed to set up necessary information for an input file and to give radiation dose from an output file by a dialogue method using graphical user interfaces. Dose assessment can be effectively carried out for a radiological accident with this system.

Journal Articles

Accurate dose assessment system for an exposed person utilising radiation transport calculation codes in emergency response to a radiological accident

Takahashi, Fumiaki; Shigemori, Yuji*; Seki, Akiyuki

Radiation Protection Dosimetry, 133(1), p.35 - 43, 2009/01

 Times Cited Count:1 Percentile:88.49(Environmental Sciences)

A system has been developed to assess radiation dose distribution inside a body of exposed persons in a radiological accident by utilizing radiation transport calculation codes - MCNP and MCNPX. The system mainly consists of two parts, pre-processor and post-processor of the radiation transport calculation. Programs for the pre-processor are used to set up a "problem-dependent" input file, which defines the accident condition and dosimetric quantities to be estimated. The developed program for the post-processor part can effectively indicate dose information based upon the output file of the code. All of the programs in the dosimetry system can be executed with a generally used personal computer and accurately give the dose profile to an exposed person in a radiological accident without complicated procedures. An experiment using a physical phantom was carried out to verify the availability of the dosimetry system with the developed programs in a $$gamma$$-ray irradiation field. The dosimetry system with the developed programs can appropriately assess dose distribution inside or on the human body, if the user exactly define the source and human models and their geometric relationship.

JAEA Reports

Solution of large underestimation problem in the Monte Carlo calculation with hard biasing; In case with geometry input data created by CAD/MCNP automatic converter

Iida, Hiromasa; Kawasaki, Nobuo*; Konno, Chikara; Sato, Satoshi; Seki, Akiyuki

JAEA-Research 2008-050, 26 Pages, 2008/04

JAEA-Research-2008-050.pdf:1.98MB

An inconvenient experience was encountered, in which we have different answers depending on applied weight window values, in the nuclear analysis of the benchmark problem for CAD/MCNP interface programs, being developed under the ITER R&D task. Biasing can enhance calculation speed, but should not give different answers. Mechanism of this large underestimation is clarified. It is caused by the combination of the following two facts; (1) When one of particles in a history has got lost, MCNP cancels all tallies calculated during the history and all banked particles are thrown away (never tracked). (2) When we have distributed micro geometry errors in input data, important histories, which give significant contribution to tallies, will have many splitting and have "lost particle" with higher probability in the case of hard biasing. These two facts lead to selective canceling of important histories. An attempt to eliminate this inconvenience has been made, by modifying the subroutine "hstory" of MCNP. The modification has been done very successfully and eliminated the large underestimation, giving the same answer independently from applied weight window values.

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