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Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa; Fujii, Shun*
International Journal of Offshore and Polar Engineering, 31(3), p.316 - 324, 2021/09
Times Cited Count：0The development of a side thruster system (vehicle (ASV)) that can maintain the direction of travel on the autonomous surface will be explained. Currently, we are working on a mud radioactivity survey in collaboration with Japan Agency for Marine-Earth Science and Technology, Japan Atomic Energy Agency, and Tokyo University of Marine Science and Technology. Deposited at the mouth of Fukushima Prefecture, Japan, the main purpose is to collect unmanned mud using ASV. The Mad Collection has developed a side thruster system and implemented it in ASV. We have confirmed the operation of the ASV with the joystick by using the thruster system for operating the ASV by one person using the joystick.
Hirouchi, Jun; Takahara, Shogo; Komagamine, Hiroshi*; Kato, Nobuyuki*; Matsui, Yasuto*; Yoneda, Minoru*
Journal of Radiological Protection, 41(3), p.S139 - S149, 2021/09
Times Cited Count：0 Percentile：0.01(Environmental Sciences)Sheltering is one of the countermeasures for protection against radiation exposures in nuclear accidents. The effectiveness of sheltering is often expressed by the reduction factor, that is the ratio of the indoor to the outdoor cumulative radioactivity concentrations or doses. The indoor concentration is mainly controlled by the air exchange rate, penetration factor, and indoor deposition rate. The penetration factor and indoor deposition rate depend on the surface and opening materials. We investigated experimentally these parameters of I
and particles. The experiment was performed in two apartment houses, three single-family houses, and chambers. The obtained penetration factor ranged 0.3 
1 for particles of 0.3 1 
m and 0.15 0.7 for I depending on the air exchange rate. The indoor deposition rate for a house room ranged 0.007 0.2 h
for particles of 0.31 m and 0.21.5 h for I depending on floor materials.
Fujii, Shun*; Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa
Proceedings of 26th International Symposium on Artificial Life and Robotics (AROB 26th 2021), p.280 - 285, 2021/01
In recent years, autonomously navigating unmanned vessels have been actively studied, and many of these vessels are designed to perform unmanned operations such as observation and transportation. On the other hand, this study uses an unmanned ship with a moon pool that collects seabed mud, which is difficult for ordinary ships. Vessels used since the area are highly turbulent due to wind, so it is necessary to maintain a fixed point and orientation when removing mud. The ship is equipped with side thrusters to maintain a fixed point and bow direction. In this study, the control method was devised to maintain fixed point and orientation, and the control method is based on robust sliding mode control. The proposed control method was verified by simulation, and the desired behavior was confirmed.
Onda, Yuichi*; Taniguchi, Keisuke*; Yoshimura, Kazuya; Kato, Hiroaki*; Takahashi, Junko*; Wakiyama, Yoshifumi*; Coppin, F.*; Smith, H.*
Nature Reviews Earth & Environment (Internet), 1(12), p.644 - 660, 2020/12
Times Cited Count：17 Percentile：81.26(Environmental Sciences)Onda, Yuichi*; Taniguchi, Keisuke*; Yoshimura, Kazuya; Kato, Hiroaki*; Takahashi, Junko*; Wakiyama, Yoshifumi*; Coppin, F.*; Smith, H.*
Nature Reviews Earth & Environment (Internet), 1(12), P. 694_1, 2020/12
Times Cited Count：0 Percentile：0.29(Environmental Sciences)Kato, Tetsu*; Kawamura, Yamato*; Tahara, Junichiro*; Baba, Shoichiro*; Sanada, Yukihisa
Proceedings of the 30th (2020) International Ocean and Polar Engineering Conference (ISOPE 2020) (USB Flash Drive), p.1255 - 1260, 2020/10
AlGaO
scintillators by gamma-ray-induced positron annihilation lifetime spectroscopyFujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
Times Cited Count：1 Percentile：24.67(Physics, Applied)To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAl
O, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg
ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Mo/
Tc generator by (n,
) method, 2Fujita, Yoshitaka; Seki, Misaki; Namekawa, Yoji*; Nishikata, Kaori; Kato, Yoshiaki; Sayato, Natsuki; Tsuchiya, Kunihiko; Sano, Tadafumi*; Fujihara, Yasuyuki*; Hori, Junichi*; et al.
KURNS Progress Report 2019, P. 157, 2020/08
no abstracts in English
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
Nancekievill, M.*; Espinosa, J.*; Watson, S.*; Lennox, B.*; Jones, A.*; Joyce, M. J.*; Katakura, Junichi*; Okumura, Keisuke; Kamada, So*; Kato, Michio*; et al.
Sensors (Internet), 19(20), p.4602_1 - 4602_16, 2019/10
Times Cited Count：4 Percentile：51.67(Chemistry, Analytical)In order to contribute to fuel debris search at the Fukushima Daiichi Nuclear Power Station, we developed a system to search for submerged fuel debris by mounting a sonar on the remotely operated vehicle (ROV). The system can obtain 3D images of submerged fuel debris in real time by using the positioning system, depth sensor, and collected sonar data. As a demonstration test, a simulated fuel debris was installed at the bottom of the water tank facility at the Naraha Center for Remote Control Technology Development, and a 3D image was successfully obtained.
Kudo, Hideyuki*; Otani, Yuichi*; Hara, Masahide*; Kato, Atsushi; Ishikawa, Nobuyuki; Otaka, Masahiko; Nagai, Keiichi; Saito, Junichi; Ara, Kuniaki; Ide, Akihiro*
Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 10 Pages, 2019/05
A next generation SFR in Japan has adopted an advanced dry cleaning system which consists of the argon gas blowing process to reduce the amount of metallic residual sodium remaining on spent fuel assemblies. This paper describes experimental and analytical work focusing on the amount of residual sodium remaining on a fuel pin bundle before and after the argon gas blowing process. The experiments were conducted using a sodium test loop and a short specimen consisting of a 7 pin bundle. The effects of the blowing gas velocity and the blowing time were quantitatively analyzed in the experiments. On the basis of these experimental results, evaluation models predicting the amount of the residual sodium were constructed.
Ide, Akihiro*; Kudo, Hideyuki*; Inuzuka, Taisuke*; Hara, Masahide*; Kato, Atsushi; Ishikawa, Nobuyuki; Otaka, Masahiko; Nagai, Keiichi; Saito, Junichi; Ara, Kuniaki
Proceedings of 2019 International Congress on Advances in Nuclear Power Plants (ICAPP 2019) (Internet), 10 Pages, 2019/05
A next generation SFR in Japan has adopted an advanced dry cleaning system which consists of the following process of argon gas blowing to reduce the amount of metallic sodium, moist argon gas blowing to deactivate the residual sodium, and direct storage in the SFP without using storage containers. This three-step process increases economic competitiveness and reduces waste products. In this Research and Development work, the amount of residual sodium and performance of the dry cleaning process were investigated. This paper describes experimental and analytical work for all parts of a fuel assembly except for a fuel pin bundle.
Kamada, So*; Kato, Michio*; Nishimura, Kazuya*; Nancekievill, M.*; Watson, S.*; Lennox, B.*; Jones, A.*; Joyce, M. J.*; Okumura, Keisuke; Katakura, Junichi*
Progress in Nuclear Science and Technology (Internet), 6, p.199 - 202, 2019/01
As a technology development to investigate the distribution of submerged fuel debris in the primary containment vessel (PCV) of the Fukushima Daiichi Nuclear Power Station, we are conducting development experiments of sonar system to be mounted in a compact ROV. The experiments were conducted in two types of water tanks with different depths, simulating the PCV, using sonar with different sizes, ultrasonic frequencies, and beam scanning method, and simulated fuel debris. As a result, we characterized the shape discrimination performance of the simulated debris, and the noise due to multi-path in narrow closed space.
Shibata, Taiju; Mizuta, Naoki; Sumita, Junya; Sakaba, Nariaki; Osaki, Takashi*; Kato, Hideki*; Izawa, Shoichi*; Muto, Takenori*; Gizatulin, S.*; Shaimerdenov, A.*; et al.
Proceedings of 9th International Topical Meeting on High Temperature Reactor Technology (HTR 2018) (USB Flash Drive), 7 Pages, 2018/10
Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR). Oxidation damage on the graphite components in air ingress accident is a crucial issue for the safety point of view. SiC coating on graphite surface is a possible technique to enhance oxidation resistance. However, it is important to confirm the integrity of this material against high temperature and neutron irradiation for the application of the in-core components. JAEA and Japanese graphite companies carried out the R&D to develop the oxidation-resistant graphite. JAEA and INP investigated the irradiation effects on the oxidation-resistant graphite by using a framework of ISTC partner project. This paper describes the results of post irradiation experiment about the neutron irradiated SiC-coated oxidation-resistant graphite. A brand of oxidation-resistant graphite shows excellent performance against oxidation test after the irradiation.
Mizuta, Naoki; Sumita, Junya; Shibata, Taiju; Osaki, Takashi*; Kato, Hideki*; Izawa, Shoichi*; Muto, Takenori*; Gizatulin, S.*; Sakaba, Nariaki
Tanso Zairyo Kagaku No Shinten; Nihon Gakutsu Shinkokai Dai-117-Iinkai 70-Shunen Kinen-Shi, p.161 - 166, 2018/10
To enhance oxidation resistance of graphite material for in-core components of HTGR, JAEA and four Japanese graphite companies; Toyo Tanso, IBIDEN, Tokai Carbon and Nippon Techno-Carbon, are carrying out for development of oxidation-resistant graphite by CVD-SiC coating. This paper describes the outline of neutron irradiation test about the oxidation-resistant graphite by WWR-K reactor of INP, Kazakhstan through an ISTC partner project. Prior to the irradiation test, the oxidation-resistant graphite by CVD-SiC coating of all specimens showed enough oxidation resistance under un-irradiation condition. The neutron irradiation test was already completed and out-of-pile oxidation test will be carried out at the hot-laboratory of WWR-K.
Nancekievill, M.*; Jones, A. R.*; Joyce, M. J.*; Lennox, B.*; Watson, S.*; Katakura, Junichi*; Okumura, Keisuke; Kamada, So*; Kato, Michio*; Nishimura, Kazuya*
IEEE Transactions on Nuclear Science, 65(9), p.2565 - 2572, 2018/09
Times Cited Count：10 Percentile：87.34(Engineering, Electrical & Electronic)In order to contribute to the development of technology to search fuel debris submerged in water inside the primary containment vessel of the Fukushima Daiichi Nuclear Power Station, we are developing a remotely operated vehicle (ROV) system equipped with a compact radiation detector and sonar. A cerium bromide (CeBr) scintillator detector for dose rate monitoring and ray spectroscopy was integrated into ROV and experimentally validated with a 
Cs source, both in the conditions of laboratory and submerged. In addition, the ROV combined with the IMAGENEX 831L sonar could characterize the shape and size of a simulated fuel debris at the bottom of the water pool facility.
Sato, Junya; Kikuchi, Hiroshi*; Kato, Jun; Sakakibara, Tetsuro; Matsushima, Ryotatsu; Sato, Fuminori; Kojima, Junji; Nakazawa, Osamu
QST-M-8; QST Takasaki Annual Report 2016, P. 62, 2018/03
no abstracts in English
Okabe, Kota; Yamamoto, Kazami; Kamiya, Junichiro; Takayanagi, Tomohiro; Yamamoto, Masanobu; Yoshimoto, Masahiro; Takeda, Osamu*; Horino, Koki*; Ueno, Tomoaki*; Yanagibashi, Toru*; et al.
Proceedings of 14th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.853 - 857, 2017/12
The most important issue is to reduce the uncontrolled beam loss in the high intensity hadron accelerator such as J-PARC proton accelerators. The J-PARC 3 GeV Synchrotron (RCS) has a collimator system which narrows a high intensity beam in the RCS. After startup of RCS in 2007, the collimator system of the RCS worked well. However, in April 2016, vacuum leakage at the collimator system occurred during the maintenance operation. To investigate a cause of the failure, we took apart iron shields of the collimator reducing exposed dose of operators. As a result of inspection, we succeeded to identify the cause of the vacuum leakage failure. In this presentation, we report the failure investigation of the beam collimator system in the RCS.
Miyabe, Masabumi; Oba, Masaki; Jung, K.; Iimura, Hideki; Akaoka, Katsuaki; Kato, Masaaki; Otobe, Haruyoshi; Khumaeni, A.*; Wakaida, Ikuo
Spectrochimica Acta, Part B, 134, p.42 - 51, 2017/08
Times Cited Count：18 Percentile：89.47(Spectroscopy)Spectroscopic properties of atomic species of plutonium were investigated by combining laser ablation and resonance absorption techniques for the analysis of a plutonium oxide sample. For 17 transitions of Pu atoms and ions, the absorbance, isotope shift, and hyperfine splitting were determined via Voigt profile fitting of the recorded absorption spectra. Three transitions were selected as candidates for analytical use. Using these transitions, we investigated the analytical performance that was attainable and determined a correlation coefficient R2 between the absorbance and plutonium concentration of 0.9999, a limit of detection of 30-130 ppm, and a relative standard deviation of approximately 6% for an abundance of 
Pu of 2.4%. These results demonstrate that laser ablation absorption spectroscopy is applicable to the remote isotopic analysis of highly radioactive nuclear fuels and waste materials containing multiple actinide elements.
Kato, Jun; Nakagawa, Akinori; Taniguchi, Takumi; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro
JAEA-Review 2017-015, 173 Pages, 2017/07
JAEA-Review-2017-015.pdf:6.67MB
Various radioactive wastes have been generated at the Fukushima Daiichi Nuclear Power Station (1F). To dispose of the wastes underground, it is necessary to make a suitable waste package by the volume reduction and solidification of the wastes. To plan the future decommissioning of 1F, it is also necessary to estimate feasibility of existing treatment technology for those wastes. Therefore the document survey has been performed about volume reduction and solidification technologies that have domestic or foreign experiences of practical treatment for radioactive wastes to assist selection of suitable treatment of the wastes. This report shows the arranged results. The 1F wastes are classified into two groups, homogeneous particulate and liquid wastes and heterogeneous solid wastes. The needful items for the feasibility study such as a technology name, a fundamental principle, treatment efficiency, and characteristic of solidified waste are summarized in each group.
