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Kokubun, Yuji; Nakada, Akira; Seya, Natsumi; Koike, Yuko; Nemoto, Masashi; Tobita, Keiji; Yamada, Ryohei*; Uchiyama, Rei; Yamashita, Daichi; Nagai, Shinji; et al.
JAEA-Review 2023-046, 164 Pages, 2024/03
The Nuclear Fuel Cycle Engineering Laboratories conducts environmental radiation monitoring around the reprocessing plant in accordance with the "Safety Regulations for Reprocessing Plant of JAEA, Part IV: Environmental Monitoring". This report summarizes the results of environmental radiation monitoring conducted during the period from April 2022 to March 2023 and the results of dose calculations for the surrounding public due to the release of radioactive materials into the atmosphere and ocean. In the results of the above environmental radiation monitoring, many items were affected by radioactive materials emitted from the accident at the Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company, Incorporated (changed to Tokyo Electric Power Company Holdings, Inc. on April 1, 2016), which occurred in March 2011. Also included as appendices are an overview of the environmental monitoring plan, an overview of measurement methods, measurement results and their changes over time, meteorological statistics results, radioactive waste release status, and an evaluation of the data which deviated of the normal range.
Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 8 Pages, 2024/03
In this study, we propose failure mitigation methods by application of passive safety structures. The idea of the passive safety structures was applied to next generation fast reactors under high temperature conditions and excessive earthquake conditions.
Morishita, Yuki; Miyamura, Hiroko; Sato, Yuki; Oura, Masatoshi*
Radiation Measurements, 171, p.107064_1 - 107064_7, 2024/02
Times Cited Count:0 Percentile:0.08(Nuclear Science & Technology)The detection of alpha and beta contamination locations is important for decontaminating nuclear facilities. In the high radiation dose rate environment at the decommissioning sites, the contamination measurement by the workers is not effective. Thus, we developed a remote automatic contamination measurement system using a new scintillator-based detector. A 50 mm 100-m-thick YAlO(Ce)(YAP:Ce) scintillator was coupled with a flat panel-type multianode photomultiplier tube. The detector was installed downwards at the bottom of a robot. It has an energy measurement capability, and the energy measurement could discriminate the alpha particles from the beta and Rn alpha particles. With the energy information, alpha and beta particles could be identified and mapped simultaneously. In addition, a slow-moving robot could be used to obtain statistically sufficient counts in a single run measurement, allowing the evaluation of surface contamination density using only alpha particles. The remote automatic contamination measurement system will be useful in visualizing the contamination distribution in environments that are inaccessible to workers.
Fujimori, Shinichi; Kawasaki, Ikuto; Takeda, Yukiharu; Yamagami, Hiroshi; Sasabe, Norimasa*; Sato, Yoshiki*; Shimizu, Yusei*; Nakamura, Ai*; Maruya, A.*; Homma, Yoshiya*; et al.
Electronic Structure (Internet), 5(4), p.045009_1 - 045009_7, 2023/11
Saha, P. K.; Harada, Hiroyuki; Yoneda, Hitoki*; Michine, Yurina*; Sato, Atsushi*; Shibata, Takanori*; Kinsho, Michikazu
Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.59 - 63, 2023/11
Nagayama, Shota; Harada, Hiroyuki; Shimogawa, Tetsushi*; Sato, Atsushi*; Yamada, Ippei; Chimura, Motoki; Kojima, Kunihiro; Yamamoto, Kazami; Kinsho, Michikazu
Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.526 - 530, 2023/11
We have been developing "Non-destructive electrostatic septum" for a slow extraction. This septum has multiple electrodes placed around the region without the beam hitting and separate the beam by its electric field. To evaluate its electric field, we have built a prototype septum and a test machine, which consists of an electron gun and monitors. This test machine can measure the electric field indirectly by using a narrow electron beam. The experiment results of prototype septum is good agreement with the calculation one. However, this electric field distribution is not enough to separate the beam. A step function-like electric field distribution is ideal for the beam separation with minimal negative effect on the beam. We have studied to improve the electrode configuration to match the beam shape. In this paper, we present the result of the electric field measurements and the septum improvement. Additionally, we describe the future plan of this development.
Yamashita, Susumu; Sato, Takumi; Nagae, Yuji; Kurata, Masaki; Yoshida, Hiroyuki
Journal of Nuclear Science and Technology, 60(9), p.1029 - 1045, 2023/09
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)Shirasu, Noriko; Sato, Takumi; Suzuki, Akihiro*; Nagae, Yuji; Kurata, Masaki
Journal of Nuclear Science and Technology, 60(6), p.697 - 714, 2023/06
Times Cited Count:1 Percentile:68.31(Nuclear Science & Technology)Interaction tests between UO and Zr were performed at precisely controlled high temperatures between 1840 and 2000 C to understand the interaction mechanism in detail. A Zr rod was inserted in a UO crucible and then heat-treated at a fixed temperature in Ar-gas flow for 10 min. After heating in the range of 1890 to 1930 C, the Zr rod was deformed to a round shape, in which the post-analysis detected the significant diffusion of U into the Zr region and the formation of a dominant -Zr(O) matrix and a small amount of U-Zr-O precipitates. The abrupt progress of liquefaction was observed in the sample heated at around 1940 C or higher. The higher oxygen concentration in the -Zr(O) matrix suppressed the liquefaction progress, due to the variation in the equilibrium state. The U-Zr-O melt formation progressed by the selective dissolution of Zr from the matrix, and the selective diffusion of U could occur via the U-Zr-O melt.
Umeda, Maki; Chudo, Hiroyuki; Imai, Masaki; Sato, Nana; Saito, Eiji
Review of Scientific Instruments, 94(6), p.063906_1 - 063906_8, 2023/06
Times Cited Count:0 Percentile:0(Instruments & Instrumentation)Sato, Yohei*; Egusa, Daisuke*; Miyazaki, Hidetoshi*; Kimura, Koji*; Itakura, Mitsuhiro; Terauchi, Masami*; Abe, Eiji*
Materials Transactions, 64(5), p.950 - 954, 2023/05
Times Cited Count:1 Percentile:48.82(Materials Science, Multidisciplinary)Dilute Mg-Zn-Y alloy with a mille-feuille structure (MFS) exhibits a mechanical strength comparable to Mg-Zn-Y alloy with long period stacking/ordered (LPSO) structure through kink deformation. In order to deepen understanding the thermal stability of the MFS-type Mg alloys, it is required to clarify the solute cluster structures composed of Zn and Y in solute enriched stacking faults (SESFs). In this study, electron energy-loss and energy dispersive X-ray spectroscopy based on scanning transmission electron microscopy (STEM-EELS/EDS) were conducted to investigate the electronic structure and composition of Zn and Y in the SESFs of the MFS-Mg alloy. Zn-L2,3 spectra indicated that the valence charges of Zn in the dilute Mg alloy were different from that of the LPSO-type Mg-Zn-Y alloy. In addition, the intensity ratio of L3/L2 in Y-L2,3 spectrum of the dilute MFS-Mg alloy was larger than that of the LPSO-Mg alloy, reflecting the electron occupancies of 4d3/2 and 4d5/2 orbitals of Y atoms were different from those of the LPSO-Mg alloys. STEM-EELS analysis of the SESF composition in the dilute MFS-Mg alloy indicated that the Zn/Y ratio should be lower than that of the LPSO-Mg alloy, which was confirmed also by STEM-EDS measurements. These results indicate that the cluster structure in the SESFs of the dilute MFS-Mg alloy should be different from the ideal Zn6Y8 cluster in the LPSO-type Mg-Zn-Y alloys.
Sanada, Yukihisa; Tokiyoshi, Masanori*; Nishiyama, Kyohei*; Sato, Rina; Yoshimura, Kazuya; Funaki, Hironori; Abe, Tomohisa; Ishida, Mutsushi*; Nagamine, Haruo*; Fujisaka, Motoyuki*
Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(2), p.87 - 96, 2023/04
Since the accident at the Fukushima Daiichi Nuclear Power Plant, many decontamination works have been carried out, but it is difficult to say that much data on workers' exposure has necessarily been analyzed in detail. In this paper, based on the GPS location information carried by the workers together with their personal dosimeters, the air dose rate in the work area and the characteristics of each type of work were analyzed. The results showed that more than 50% of the measured actual doses were more than twice the median planned dose calculated from the air dose rate and actual working hours. Furthermore, as a result of the analysis by work type, it was found that the exposure doses of demolition workers tended to be high, and that this was due to the fact that most of the work was carried out before the work was carried out to reduce the dose at the work site. In addition, when the conversion from air dose to effective dose was taken into account, there were many cases of underestimation where the planned values were lower than the measured values, and it is considered important for management to set appropriate working factor.
Nakada, Akira; Kanai, Katsuta; Seya, Natsumi; Nishimura, Shusaku; Futagawa, Kazuo; Nemoto, Masashi; Tobita, Keiji; Yamada, Ryohei*; Uchiyama, Rei; Yamashita, Daichi; et al.
JAEA-Review 2022-078, 164 Pages, 2023/03
Environmental radiation monitoring around the Tokai Reprocessing Plant has been performed by the Nuclear Fuel Cycle Engineering Laboratories, based on "Safety Regulations for the Reprocessing Plant of Japan Atomic Energy Agency, Chapter IV - Environmental Monitoring". This annual report presents the results of the environmental monitoring and the dose estimation to the hypothetical inhabitant due to the radioactivity discharged from the plant to the atmosphere and the sea during April 2021 to March 2022. In this report, some data include the influence of the accidental release from the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Co., Inc. (the trade name was changed to Tokyo Electric Power Company Holdings, Inc. on April 1, 2016) in March 2011. Appendices present comprehensive information, such as monitoring programs, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes. In addition, the data which were influenced by the accidental release and exceeded the normal range of fluctuation in the monitoring, were evaluated.
Yoshimura, Kazuya; Sanada, Yukihisa; Sato, Rina; Nakayama, Mariko*; Tsubokura, Masaharu*
Journal of Radiation Research (Internet), 64(2), p.203 - 209, 2023/03
Times Cited Count:1 Percentile:0.01(Biology)After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, individual exposure doses to residents have been assessed by many municipalities, governments and research institutes. Various methods including measurements with personal dosimeters and simulations have been used for this evaluation depending on purposes, but the information of assessments and methods has not been systematically organized. A comprehensive review of the knowledge and experiences of individual exposure doses assessments accumulated so far and understanding the characteristics of the assessment methods will be very useful for radiation protection and risk communication, following to governmental policy planning. We reviewed the efforts made by the Japanese government and research institutes to assess radiation doses to residents after the FDNPS accident in Part1. On the other hand, each method of assessing individual exposure doses includes uncertainties and points to be considered for the appropriate assessment. These knowledge and experiences are important for the assessment implementation and applying the assessment results to the governmental policy planning, and are summarized in Part2 of this article.
Iwamoto, Osamu; Iwamoto, Nobuyuki; Kunieda, Satoshi; Minato, Futoshi; Nakayama, Shinsuke; Abe, Yutaka*; Tsubakihara, Kosuke*; Okumura, Shin*; Ishizuka, Chikako*; Yoshida, Tadashi*; et al.
Journal of Nuclear Science and Technology, 60(1), p.1 - 60, 2023/01
Times Cited Count:75 Percentile:99.99(Nuclear Science & Technology)Sanada, Yukihisa; Yoshimura, Kazuya; Sato, Rina; Nakayama, Mariko*; Tsubokura, Masaharu*
Journal of Radiation Research (Internet), 64(1), p.2 - 10, 2023/01
Times Cited Count:0 Percentile:0.06(Biology)The evacuation orderareas established due to the accident at the Tokyo Electric Power Company Holdings' (TEPCO) Fukushima Daiichi Nuclear Power Plant (FDNPP) have been reorganized according to the decrease in ambient dose rates and the decontamination progress. The Japanese government decided to decontaminate the difficult-to-return areas and lift the evacuation order by 2030. This radiation protection strategy can be optimized by examining emergency exposure situations to date and the existing exposure after the accident. This article reviews the methods that can determine the individual radiation doses of residents who should return to their homes when the evacuation order is lifted in the specific reconstruction reproduction base area and the difficult-to-return areas outside this base area and summarizes the points to be considered when implementing these methods. In Part 1 of this article, we review the efforts made by the Japanese government and research institutes to assess radiation doses to residents after the FDNPP accident.
Saha, P. K.; Harada, Hiroyuki; Kinsho, Michikazu; Yoneda, Hitoki*; Michine, Yurina*; Sato, Atsushi*; Shibata, Takanori*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.272 - 276, 2023/01
Kobayashi, Aine*; Toyama, Takeshi*; Nakamura, Takeshi*; Shobuda, Yoshihiro; Ishii, Koji*; Tomizawa, Masahito*; Takeuchi, Yasunao*; Sato, Yoichi*
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.19 - 23, 2023/01
In the J-PARC main ring, density modulation due to longitudinal beam instability occurs during the debunching process of coasting beams. This leads to the generation of an electron cloud, which in turn causes transverse beam instabilities. The transverse beam instability causes beam loss and the electron cloud is assumed to cause vacuum degradation, both of which hinder the beam intensity enhancement, so it is essential to clarify the causes and countermeasures. In particular, the longitudinal impedance of several hundred MHz has been investigated as relevant, and measures to reduce the impedance of individual devices are underway. The Eddy-current type septum magnet, newly installed this year, was found to have a large impedance by simulation. Therefore, we are investigating a method to reduce the impedance by a flange loaded with SiC radio wave absorber, which can be applied to locations where there is no spatial margin to install a taper. In this report, we will discuss the characterization of SiC to be used in actual devices, impedance simulation reflecting the results of SiC evaluation, and evaluation of the effect of impedance countermeasures by impedance measurement using the wire method, and progress in evaluating the effect on the beam by beam simulation and beam study.
Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Radiation Physics and Chemistry, 202, p.110590_1 - 110590_6, 2023/01
Times Cited Count:3 Percentile:66.21(Chemistry, Physical)Because of their different charge states, positrons and positronium (Ps) behave quite differently in macromolecules. The behavior of positively charged positrons is strongly influenced by electrostatic interactions. In nonpolar macromolecules such as polyethylene, energetic positrons, if not incorporated into Ps, fall into a delocalized state. These positrons are sensitively trapped by polar groups, if any. On the other hand, charge-neutral Ps is localized in a free volume regardless of the macromolecule's chemical structure. In this study, we discuss the behavior and annihilation characteristics of positrons and Ps in various macromolecules, emphasizing their differences.
Sato, Takumi; Nagae, Yuji; Kurata, Masaki; Quaini, A.*; Guneau, C.*
CALPHAD; Computer Coupling of Phase Diagrams and Thermochemistry, 79, p.102481_1 - 102481_11, 2022/12
Times Cited Count:0 Percentile:0.01(Thermodynamics)Kataoka, Ryuho*; Sato, Tatsuhiko; Kato, Chihiro*; Kadokura, Akira*; Kozai, Masayoshi*; Miyake, Shoko*; Murase, Kiyoka*; Yoshida, Rihito*; Tomikawa, Yoshihiro*; Munakata, Kazuoki*
Journal of Space Weather and Space Climate (Internet), 12, p.37_1 - 37_11, 2022/11
Times Cited Count:1 Percentile:20.65(Astronomy & Astrophysics)Solar modulation of galactic cosmic rays around the solar minimum in 2019-2020 looks different in the secondary neutrons and muons observed at the ground. To compare the solar modulation of primary cosmic rays in detail, we have to remove the possible seasonal variations caused by the atmosphere and surrounding environment. As such surrounding environment effects, we evaluate the snow cover effect on neutron count rate and the atmospheric temperature effect on muon count rate both simultaneously observed at Syowa Station in the Antarctic (69.01 S, 39.59 E). The corrected muon count rate starts decreasing in late 2019, earlier than the corrected neutron count rate which starts decreasing in early 2020, possibly indicating the rigidity dependent solar modulation in the heliosphere.