Pressure-modulated magnetism and negative thermal expansion in the HoFe intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

https://doi.org/10.1021/acs.chemmater.3c00158

Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in HoFe on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.

Design and actual performance of J-PARC 3 GeV rapid cycling synchrotron for high-intensity operation

Yamamoto, Kazami; Kinsho, Michikazu; Hayashi, Naoki; Saha, P. K.; Tamura, Fumihiko; Yamamoto, Masanobu; Tani, Norio; Takayanagi, Tomohiro; Kamiya, Junichiro; Shobuda, Yoshihiro; et al.

Journal of Nuclear Science and Technology, 59(9), p.1174 - 1205, 2022/09

https://doi.org/10.1080/00223131.2022.2038301

In the Japan Proton Accelerator Research Complex, the purpose of the 3 GeV rapid cycling synchrotron (RCS) is to accelerate a 1 MW, high-intensity proton beam. To achieve beam operation at a repetition rate of 25 Hz at high intensities, the RCS was elaborately designed. After starting the RCS operation, we carefully verified the validity of its design and made certain improvements to establish a reliable operation at higher power as possible. Consequently, we demonstrated beam operation at a high power, namely, 1 MW. We then summarized the design, actual performance, and improvements of the RCS to achieve a 1 MW beam.

Development of a supplementary outboard side thruster system for dynamic positioning control of autonomous surface vehicle

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

https://doi.org/10.17736/ijope.2021.jc825

The 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.

Invention of automatic movement and dynamic positioning control method of unmanned vessel for mud mining

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.

Author correction; Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems

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

https://doi.org/10.1038/s43017-020-00119-7

Visualizing cation vacancies in Ce:GdAlGaO scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Fujimori, 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

https://doi.org/10.35848/1882-0786/aba0dd

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:YAlO, 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.

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

https://doi.org/10.14407/jrpr.2019.44.4.128

Dry cleaning process test for fuel assembly of fast reactor plant system, 1; Pilot scale test for fuel pin bundle

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.

Development of ROV system to explore fuel debris in the Fukushima Daiichi Nuclear Power Plant

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

https://doi.org/10.15669/pnst.6.199

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.

Enhancement of oxidation tolerance of graphite materials for high temperature gas-cooled reactor

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.