Ando, Masaki; Mikami, Satoshi; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Saito, Kimiaki
Journal of Environmental Radioactivity, 192, p.385 - 398, 2018/12
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.
Tsuda, Shuichi; Tanigaki, Minoru*; Yoshida, Tadayoshi; Saito, Kimiaki
Hoshasen, 44(3), p.109 - 118, 2018/11
JAEA has started to perform dose rate monitoring using a car-borne survey system KURAMA to rapidly produce the dose rate mappings of the deposited radionuclides in the environment after the Fukushima Dai-ichi Nuclear Power Plant accident. KURAMA is a car-borne survey system developed by Kyoto University to perform dose rate monitoring in a wide area in detail with rapidity. By improving KURAMA with continuous dose rate monitoring, the 2nd generation of KURAMA (KURAMA-II) succeeded in downsizing, durability and automated transmission of data so that enable detailed dose rate mapping in wide area in shorter period of time. This paper reports the radiation characteristics and the simulation analysis of KURAMA-II on the special issue of Hoshasen, the journal of Ionization Radiation Division in the Japan society of applied physics.
Ando, Masaki; Yamamoto, Hideaki*; Kanno, Takashi*; Saito, Kimiaki
Journal of Environmental Radioactivity, 190-191, p.111 - 121, 2018/10
Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 around the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months, which was beyond that attributable to the physical decay. The air dose rates decreased depending on the level of the evacuation areas, and the decrease was slightly larger in populated areas where humans are active. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground. The air dose rates measured by the walk surveys decreased quickly compared with the air dose rate from the flat ground measurement.
Wainwright, H. M.*; Seki, Akiyuki; Mikami, Satoshi; Saito, Kimiaki
Journal of Environmental Radioactivity, 189, p.213 - 220, 2018/09
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.
Yoshida-Ouchi, Hiroko*; Matsuda, Norihiro; Saito, Kimiaki
Journal of Environmental Radioactivity, 187, p.32 - 39, 2018/07
Saito, Hiroshi; Nozawa, Takashi; Takemiya, Hiroshi; Seki, Akiyuki; Matsubara, Takeshi; Saito, Kimiaki; Kitamura, Akihiro
JAEA-Review 2017-040, 34 Pages, 2018/03
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.
Tsuda, Shuichi; Tanigaki, Minoru*; Yoshida, Tadayoshi; Okumura, Ryo*; Saito, Kimiaki
Nippon Genshiryoku Gakkai Wabun Rombunshi, 17(1), p.11 - 17, 2018/03
Environmental dose rate monitoring has been performed using scintillation detectors since the Fukushima Dai-ichi Nuclear Power Plant accident happened. After the accident, various scintillation detectors with directional dependence are used in the measurement, though detectors with superior directional dependence are needed because photons come from various direction in the environment. To investigate the influence of crystal configurations on indicated values of dose rates, pulse height spectra were measured using scintillation-based detectors with different crystal configurations and ambient dose rates were obtained using a spectrum - dose conversion operator (G(E) function). It is found that the dose rate for a rectangular-parallelepiped crystal is 40% than that for a cylindrical one at the maximum. However, the values agreed within 10% among all the detectors irrespective of the crystal shapes, using G(E) functions determined in a rotational irradiation geometry.
Saito, Kimiaki; Takahara, Shogo; Uezu, Yasuhiro
Nippon Genshiryoku Gakkai-Shi, 60(2), p.111 - 115, 2018/02
no abstracts in English
Kinase, Sakae; Takahashi, Tomoyuki*; Saito, Kimiaki
Journal of Nuclear Science and Technology, 54(12), p.1345 - 1354, 2017/12
Yoshimura, Kazuya; Saito, Kimiaki; Fujiwara, Kenso
Journal of Environmental Radioactivity, 178-179, p.48 - 54, 2017/11
Saito, Kimiaki; Nagai, Haruyasu; Kinase, Sakae; Takemiya, Hiroshi
Nippon Genshiryoku Gakkai-Shi, 59(6), p.40 - 44, 2017/06
no abstracts in English
Kurikami, Hiroshi; Malins, A.; Takeishi, Minoru; Saito, Kimiaki; Iijima, Kazuki
Journal of Environmental Radioactivity, 171, p.99 - 109, 2017/05
A modified diffusion-sorption-fixation model (mDSF) is proposed to describe the vertical migration of radiocesium in soils following fallout. The model introduces kinetics for reversible sites, meaning that the exponential-shape radiocesium distribution can be reproduced immediately following fallout. The initial relaxation mass depth of the distribution is determined by the diffusion length, which depends on the distribution coefficient, sorption rate and dispersion coefficient. The model captures the long tails of the radiocesium distribution at large depths. These tails are caused by different rates for kinetic sorption and desorption.
Ando, Masaki; Matsuda, Norihiro; Saito, Kimiaki
Nippon Genshiryoku Gakkai Wabun Rombunshi, 16(2), p.63 - 80, 2017/05
In order to discriminate the contribution of radioactive cesium due to the Fukushima Dai-ichi Nuclear Power Plant accident to the air dose rates measured by the car-borne surveys, natural background radiation was evaluated for eastern Japan area as the municipality averaged values. The window count method for distinction between natural and artificial radioactive nuclides was applied to the car-borne surveys using the KURAMA-II. Distribution of the evaluated natural background radiation showed geological feature, and it was found that the radiations measured along paved roads were reflecting the distribution of terrestrial -rays. The effect of the radioactive cesium as of 2014 for the municipalities designated as the Intensive Contamination Survey Area was beyond the uncertainty of the natural background radiation. That for the other municipalities, however, was found to be almost negligible.
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.
Wainwright, H. M.*; Seki, Akiyuki; Chen, J.*; Saito, Kimiaki
Journal of Environmental Radioactivity, 167, p.62 - 69, 2017/02
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.
Tsuda, Shuichi; Saito, Kimiaki
Journal of Environmental Radioactivity, 166(Part 3), p.419 - 426, 2017/01
Air dose rate monitoring in the environment has been performed since the Fukushima Dai-ichi Nuclear Power Plant accident happened. In the measurement, NaI(Tl) and CsI(Tl) scintillation detectors are used, which are usually used in nuclear power plants and calibrated in a uniform irradiation condition in a radiation calibration field. In general, however, the detector responses are dependent on incident direction and in reality, the incident direction of the photons is not uniform in the environment. In this study, to evaluate the dependence of dose on the photon incident direction, the spectrum - dose conversion operator (G(E) function) for air kerma in a semi-infinite radiation field were obtained using the PHITS code for commonly used NaI(Tl) and CsI(Tl) scintillation detectors. The results indicate that the commonly used scintillation detectors overestimate the doses by a maximum of 40% for mono-energetic photons but under the real environment, one could obtain the dose in the semi-infinite radiation field within 20%.
Matsuda, Norihiro; Mikami, Satoshi; Sato, Tetsuro*; Saito, Kimiaki
Journal of Environmental Radioactivity, 166(Part 3), p.427 - 435, 2017/01
Yagmur, A.*; Uchida, Kenichi*; Ihara, Kazuki*; Ioka, Ikuo; Kikkawa, Takashi*; Ono, Madoka*; Endo, Junichi*; Kashiwagi, Kimiaki*; Nakashima, Tetsuya*; Kirihara, Akihiro*; et al.
Applied Physics Letters, 109(24), p.243902_1 - 243902_4, 2016/12
Thermoelectric devices based on the spin Seebeck effect (SSE) were irradiated with gamma () rays with the total dose of around 310 Gy in order to investigate the -radiation resistance of the devices. To demonstrate this, Pt/NiZnFeO/Glass and Pt/BiYFeO/GdGaO SSE devices were used. We confirmed that the thermoelectric, magnetic, and structural properties of the SSE devices are not affected by the -ray irradiation. This result demonstrates that SSE devices are applicable to thermoelectric generation even in high radiation environments.
Yoshimura, Kazuya; Fujiwara, Kenso; Saito, Kimiaki
KEK Proceedings 2016-8, p.67 - 71, 2016/10
This study evaluated the Cs inventory (Bq m) on urban surfaces for eleven buildings and building lots in evacuation zone, and relative Cs inventory was obtained by dividing with the initial inventory on plane permeable field around the studied building. The relative Cs inventory was highest at plane permeable field (0.92), followed by paved ground (0.28) on January 13, 2015. Other surfaces such as roof, wall and window showed obviously small values less than 0.1, indicating that the contamination level of buildings was limited four years after the Fukushima Dai-ichi Nuclear Power Plant accident. Roof and paved ground showed different relative Cs inventories from those in the case of Europe after the Chernobyl Nuclear Power Plant accident, suggesting the importance of local parameterization considering the factors affects to the variation of relative Cs inventory.
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