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Journal Articles

Decreasing trend of ambient dose equivalent rates over a wide area in eastern Japan until 2016 evaluated by car-borne surveys using KURAMA systems

Ando, Masaki; Mikami, Satoshi; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Saito, Kimiaki

Journal of Environmental Radioactivity, 192, p.385 - 398, 2018/12

 Percentile:100(Environmental Sciences)

Car-borne surveys using KURAMA systems have been conducted over a wide area in eastern Japan since 2011. The measurement data collected until 2016 was analyzed, and decreasing trend of the dose rates in regions within 80 km of Fukushima Dai-ichi Nuclear Power Plant were examined. The averaged dose rates tended to decrease considerably with respect to the physical decay of radiocaesium, and the ecological half-lives of the fast and slow decay components were estimated. The decrease of the dose rate in the forest was slower than its decrease in other regions, and the decrease of the dose rate in urban area was the fastest. The decrease in the dose rates obtained via the car-borne survey was larger than that obtained on flat ground with few disturbances using survey meters approximately 1.5 y after the accident; hereafter, the decrease in the dose rates obtained via the car-borne survey was same as the latter measurement.

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

 Percentile:100(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.

Journal Articles

Proceeding of 16th Annual Meeting of the Japanese Society of Radiation Management (JRSM) and the 50th Annual Meeting of Japan Health Physics Society (JHPS) (Oita); Oral session-E2 Radiation measurement-2

Mikami, Satoshi

Nippon Hoshasen Anzen Kanri Gakkai-Shi, 16(2), P. 41, 2017/11

I summarized the outline of the oral presentation session where the author served as chairman.

Journal Articles

Measurements of air dose rates in and around houses in the Fukushima Prefecture in Japan after the Fukushima accident

Matsuda, Norihiro; Mikami, Satoshi; Sato, Tetsuro*; Saito, Kimiaki

Journal of Environmental Radioactivity, 166(Part 3), p.427 - 435, 2017/01

 Times Cited Count:1 Percentile:83.76(Environmental Sciences)

Journal Articles

Utilization of $$^{134}$$Cs/$$^{137}$$Cs in the environment to identify the reactor units that caused atmospheric releases during the Fukushima Daiichi accident

Chino, Masamichi; Terada, Hiroaki; Nagai, Haruyasu; Katata, Genki; Mikami, Satoshi; Torii, Tatsuo; Saito, Kimiaki; Nishizawa, Yukiyasu

Scientific Reports (Internet), 6, p.31376_1 - 31376_14, 2016/08

 Times Cited Count:10 Percentile:8.68(Multidisciplinary Sciences)

Journal Articles

In situ $$gamma$$ spectrometry intercomparison in Fukushima, Japan

Mikami, Satoshi; Sato, Shoji*; Hoshide, Yoshifumi*; Sakamoto, Ryuichi*; Okuda, Naotoshi*; Saito, Kimiaki

Hoken Butsuri, 50(3), p.182 - 188, 2015/09

Intercomparison of in situ $$gamma$$ spectrometry was organized at a site contaminated by the radioactive fallout that originated from the Fukushima Dai-ichi Nuclear Power Plant accident. This intercomparison was conducted by eight teams from four different institutions, which have contributed to the government-led project to construct distribution maps of radionuclides deposited on the ground soil. The resultant $$^{134}$$Cs and $$^{137}$$Cs inventories evaluated by the participants agreed within 6% of the coefficient of variation, after correction for inhomogeneous distribution of the air dose rate. The evaluated $$^{40}$$K inventories agreed within 4% of the coefficient of variation. The authors estimated that these results were in good agreement for creating distribution maps of the radionuclide inventory in the ground soil.

Journal Articles

Measurements and evaluations of air dose rates around Fukushima, 5; Characteristics of air dose rate distribution in the environment around the Fukushima Nuclear Power Plant site

Mikami, Satoshi; Matsuda, Norihiro; Ando, Masaki; Kinase, Sakae; Kitano, Mitsuaki; Kawase, Keiichi; Matsumoto, Shinichiro; Yamamoto, Hideaki; Saito, Kimiaki

Radioisotopes, 64(9), p.589 - 607, 2015/09

This article presents the features of regional distributions and temporal changes in air dose rate and radionuclide deposition densities in Fukushima on the basis of analyses on large-scale environmental monitoring results using diverse methods. The continuity of decontamination effects is discussed according to repeated monitoring data after the decontamination model project. Further, some examples are shown on the projection of air dose rates together with the ecological half lives for different land uses.

Journal Articles

Source term estimation for the Fukushima Daiichi Nuclear Power Station accident by combined analysis of environmental monitoring and plant data through atmospheric dispersion simulation

Nagai, Haruyasu; Terada, Hiroaki; Chino, Masamichi; Katata, Genki; Mikami, Satoshi; Saito, Kimiaki

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.4044 - 4052, 2015/08

JAEA has estimated the atmospheric releases of radionuclide during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric transport and deposition model (ATDM). To improve our source term, we are trying to develop more sophisticated estimation method and use new information from severe accident analysis and observation data. As the first step of new trial, we used $$^{134}$$Cs/$$^{137}$$Cs ratios of inventories in FNPS1 reactors Unit 1 to 3 and those in surface deposition. By considering temporal change in $$^{134}$$Cs/$$^{137}$$Cs ratio of released plume and ATDM simulations, spatial distribution of $$^{134}$$Cs/$$^{137}$$Cs ratio in surface deposition was explained. This result can be used to specify from which reactor the dominant release occurred for each time period, and consequently provide useful information to severe accident analysis for the FNPS1 case.

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

The Air dose rate around the Fukushima Dai-ichi Nuclear Power Plant; Its spatial characteristics and temporal changes until December 2012

Mikami, Satoshi; Maeyama, Takeshi*; Hoshide, Yoshifumi*; Sakamoto, Ryuichi*; Sato, Shoji*; Okuda, Naotoshi*; Sato, Tetsuro*; Takemiya, Hiroshi; Saito, Kimiaki

Journal of Environmental Radioactivity, 139, p.250 - 259, 2015/01

 Times Cited Count:22 Percentile:16.37(Environmental Sciences)

Journal Articles

Spatial distributions of radionuclides deposited onto ground soil around the Fukushima Dai-ichi Nuclear Power Plant and their temporal change until December 2012

Mikami, Satoshi; Maeyama, Takeshi*; Hoshide, Yoshifumi*; Sakamoto, Ryuichi*; Sato, Shoji*; Okuda, Naotoshi*; Demongeot, S.*; Gurriaran, R.*; Uwamino, Yoshitomo*; Kato, Hiroaki*; et al.

Journal of Environmental Radioactivity, 139, p.320 - 343, 2015/01

 Times Cited Count:36 Percentile:6.33(Environmental Sciences)

Journal Articles

Measurement of air dose rates over a wide area around the Fukushima Dai-ichi Nuclear Power Plant through a series of car-borne surveys

Ando, Masaki; Nakahara, Yukio; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Takahashi, Fumiaki; Mikami, Satoshi; Kinouchi, Nobuyuki; Sato, Tetsuro*; Tanigaki, Minoru*; et al.

Journal of Environmental Radioactivity, 139, p.266 - 280, 2015/01

 Times Cited Count:24 Percentile:14.05(Environmental Sciences)

A series of car-borne surveys using the KURAMA and KURAMA-II systems was conducted in a wide area in eastern Japan from June 2011 to December 2012 to evaluate the distribution of air dose rates around the Fukushima Dai-ichi Nuclear Power Plant, and to determine the time-dependent trend of decrease in air dose rates. An automated data processing system was established, which enables analyses of large amounts of data obtained with the use of about 100 units of the measurement system in a short time. The initial data for studying the migration status of radioactive cesium was obtained in the first survey, followed by the other car-borne surveys having wider measurement ranges. Comparing the measured air dose rates obtained in each survey, it was found that the decreasing trend of air dose rates measured through car-borne surveys was larger than that expected from the physical decay of radioactive cesium and that measured using NaI (Tl) survey meters around the road.

Journal Articles

Depth profiles of radioactive cesium in soil using a scraper plate over a wide area surrounding the Fukushima Dai-ichi Nuclear Power Plant, Japan

Matsuda, Norihiro; Mikami, Satoshi; Shimoura, Susumu*; Takahashi, Junko*; Nakano, Masakazu; Shimada, Kiyotaka*; Uno, Kiichiro; Hagiwara, Shigetomo; Saito, Kimiaki

Journal of Environmental Radioactivity, 139, p.427 - 434, 2015/01

 Times Cited Count:42 Percentile:4.57(Environmental Sciences)

Journal Articles

Accelerator neutron dosimetry using composite-gas-filled proportional counting tube

Usui, Toshihide; Mikami, Satoshi; Hashimoto, Makoto; Nakayama, Naoto; Suzuki, Chihiro*; Tani, Kotaro*; Yamasaki, Keizo*; Misawa, Tsuyoshi*

KURRI Progress Report 2010, P. 209, 2011/10

no abstracts in English

JAEA Reports

Re-evaluation of a method for monitoring airborne radioiodine discharge and its contribution to development of an advanced method

Koarashi, Jun; Mikami, Satoshi; Miyauchi, Toru; Kozawa, Tomoyasu*; Yokota, Tomokazu*; Nakada, Akira; Akiyama, Kiyomitsu; Momose, Takumaro

JAEA-Technology 2010-039, 34 Pages, 2010/12


The current methodology for monitoring airborne radioiodine at the Tokai reprocessing plant (TRP) was reviewed, and some investigations were made to re-evaluate collection and measurement techniques in the methodology. The investigations focused particularly on: (1) in situ collection efficiency of an iodine sampler for $$^{129}$$I and its dependence on sampling flow rate; (2) evaluation of $$^{129}$$I and $$^{131}$$I activities collected in an activated charcoal cartridge; (3) $$^{129}$$I collection capacity of an activated charcoal cartridge under reprocessing off-gas conditions; and (4) real-time monitoring system for $$^{129}$$I in airborne effluent. The results obtained gave not only the validity of the TRP's monitoring method, but also technical aspects required for establishing a more reliable and effective monitoring method for radioiodine isotopes.

Journal Articles

Rapid detection and estimation of an unexpected atmospheric release of $$^{129}$$I

Koarashi, Jun; Mikami, Satoshi; Akiyama, Kiyomitsu; Takeishi, Minoru

Hoken Butsuri, 43(4), p.366 - 370, 2008/12

A sampling system was designed to detect rapidly an unexpected release of $$^{129}$$I during a weekly batch-sampling of a stack gas. The system consisted mainly of a sampling unit and an iodine monitor with an NaI(Tl) scintillation detector. A relationship between in situ count rate of the monitor and $$^{129}$$I activity collected in the sampling unit was derived from several set of data obtained with the system in the Tokai reprocessing plant. The system and relationship allowed us to estimate the amount of $$^{129}$$I release at an arbitrary time during the batch-sampling. A different iodine monitor with a Ge detector was also tested to overcome a difficulty in selective measurement of $$^{129}$$I with the NaI(Tl) scintillation detector in the presence of $$^{85}$$Kr in the target gas. The test demonstrated a feasibility of the real-time, $$^{85}$$Kr-interference-free monitoring of atmospheric $$^{129}$$I release.

Journal Articles

Monitoring methodologies and chronology of radioactive airborne releases from Tokai reprocessing plant

Koarashi, Jun; Mikami, Satoshi; Nakada, Akira; Akiyama, Kiyomitsu; Kobayashi, Hirohide; Fujita, Hiroki; Takeishi, Minoru

Journal of Nuclear Science and Technology, 45(Suppl.5), p.462 - 465, 2008/06

 Times Cited Count:3 Percentile:70.64(Nuclear Science & Technology)

Tokai reprocessing plant (TRP) has released radionuclides such as $$^{3}$$H, $$^{14}$$C, $$^{85}$$Kr and $$^{129}$$I into the atmosphere since the start of operation in 1977. We have established the monitoring methodologies for these nuclides, to realize an appropriate and continuous radioactive discharge control. The methodologies having various special technical considerations for matching the monitoring of reprocessing off-gas, were summarized in this paper. Briefly, $$^{3}$$H was collected by a cold-trap technique and the concentration was evaluated being independent of the water collection efficiency; $$^{14}$$C was collected by a monoethanolamine bubbler and then measured by liquid scintillation counting without any interferences from $$^{3}$$H and $$^{85}$$Kr; $$^{85}$$Kr was continuously measured by combination of two kinds of detectors to cover very wide range of the concentration; and $$^{129}$$I was collected by a charcoal filter and a charcoal cartridge in series with a relatively high collecting performance.

JAEA Reports

Transfer of $$^{14}$$C discharged from Tokai reprocessing plant into rice plant; Monitoring data and a simple modeling approach

Koarashi, Jun; Fujita, Hiroki; Onuma, Toshimitsu*; Mikami, Satoshi; Akiyama, Kiyomitsu; Takeishi, Minoru

JAEA-Technology 2007-042, 32 Pages, 2007/07


Carbon-14 is one of the most important radionuclides from the perspective of dose estimation due to the nuclear fuel cycle. Japan Atomic Energy Agency (JAEA) has conducted the careful monitoring of $$^{14}$$C in airborne release from Tokai reprocessing plant (TRP), atmospheric CO$$_{2}$$ and rice grains around TRP. This report reviewed the $$^{14}$$C monitoring data obtained over ten years from 1991 to 2001. A simple mathematical model for transfer of TRP-derived $$^{14}$$C into rice plant was tested using the data set. The model-calculated $$^{14}$$C concentrations in atmospheric CO$$_{2}$$ and rice grain agreed well with the observations, suggesting an applicability of the simple modeling approach to environmental assessment for atmospheric $$^{14}$$C discharge under steady-state conditions.

Journal Articles

Consideration on calibration and correction factors of an $$H$$$$_{rm P}$$(10) chamber for different radiation qualities and angles of incidence

Mikami, Satoshi; Iti$'e$, C.*; Texier, C.*

Radiation Protection Dosimetry, 123(1), p.122 - 127, 2007/01

 Times Cited Count:1 Percentile:86.86(Environmental Sciences)

This paper presents the characterization, performed in IRSN (France) of a $$H$$$$_{rm P}$$(10) chamber in terms of calibration factor and correction factors for the radiation qualities of ISO narrow spectrum series. The $$H$$$$_{rm P}$$(10) chamber can measure directly the conventional true value of Hp(10) after a calibration by a reference laboratory, and can by used for transferring reference quantities $$H$$$$_{rm P}$$(10) from a reference laboratory.

Journal Articles

Airborne radioiodine monitoring at Tokai reprocessing plant

Mikami, Satoshi; Koarashi, Jun; Miyauchi, Toru; Akiyama, Kiyomitsu; Kobayashi, Hirohide

Proceedings of 2nd Asian and Oceanic Congress Radiological Protection (AOCRP-2) (CD-ROM), p.308 - 312, 2006/10

As airborne radioiodine effluent monitoring in Tokai reprocessing plant (TRP), not only a weekly evaluation of exact discharged amount of radioiodine ($$^{129}$$I) for assessing environmental impact, but also continuous monitoring of radioiodine being discharged are performed for quick recognition of unexpected effluent tendency. Furthermore, to enhance effluent monitoring activity corresponding to features reprocessing plant, sequential radioiodine monitoring system without interference by the mingled $$^{85}$$Kr has been developed and effectively functioned as an assist during plant operation. The systematic configurations having these functions for airborne radioiodine monitoring corresponding to nuclear fuel reprocessing plant have been established.

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