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Nagasumi, Satoru; Hasegawa, Toshinari; Iigaki, Kazuhiko; Nakagawa, Shigeaki; Kubo, Shinji; Shimazaki, Yosuke; Nakajima, Kunihiro; Sakurai, Yosuke; Shinohara, Masanori; Saito, Kenji; et al.
Nuclear Engineering and Design, 446, p.114542_1 - 114542_14, 2026/01
To demonstrate HTGR's safety features, a loss-of-forced-cooling (LOFC) test was conducted using the HTTR. In this test, the forced cooling in the reactor core was intentionally lost by shutting down all helium gas circulators (HGCs) without reactor scram. During steady-state operation at 100% reactor power (30 MW), after the LOFC, the reactor power spontaneously decreased. This power reduction occurred due to the negative reactivity feedback effect triggered by an increase in core temperature. The power stabilized at a lower value of 1.2% after re-criticality. Additionally, the measured radioactivity concentration in the primary coolant remained nearly unchanged during this LOFC operation and during an immediately subsequent HTTR operation. This indicates no failure of the coated particle fuel, even after the increase in core temperature associated with the LOFC event. These results provide experimental evidence of the safety features of HTGRs.
Nagai, Takayuki; Aoyama, Yusuke; Okamoto, Yoshihiro; Shibata, Daisuke*; Asakura, Kiyotaka*; Hasegawa, Takehiko*; Sato, Seiichi*; Fukaya, Akane*; Kikuchi, Tetsuya*; Hatakeyama, Kiyoshi*
JAEA-Research 2025-009, 122 Pages, 2025/11
JAEA-Research-2025-009.pdf:20.77MB
XAFS measurements in the soft X-ray region are suitable for evaluating the chemical state of the surface layer of a measurement sample because the X-ray transmittance is low. This study measured the K-edges of the glass-forming elements boron (B), oxygen (O), sodium (Na), and silicon (Si), as well as the L
-edge of the waste component cerium (Ce), to verify the differences between the coagulated layer and the inside of simulated waste glasses made from raw glass compositions with increased alumina concentration. As a result, from the B K-edge XANES spectra, the proportion of B-O tetracoordinate sp
structures (BO
) on the surface layer of the coagulated glass samples was higher than that on the cut surface inside the glass samples. On the other hand, the O K-edge XANES spectra showed differences by measuring points for each glass sample, but the trends of those differences varied between the glass samples. The reason is that the molten raw glass with increased alumina concentration has a high viscosity, making it impossible to produce waste glasses with a uniform composition. The Na and Si K-edge spectra showed no differences between the coagulated layer and the inside of glass samples. In addition, the Ce L-edge XANES spectra confirmed that the Ce valence in the coagulated layer of glass samples was more oxidized compared to that in the inside of glass samples.
Okita, Hidefumi; Adachi, Kyosuke; Tamura, Fumihiko; Nomura, Masahiro; Shimada, Taihei; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Sugiyama, Yasuyuki*; Hasegawa, Katsushi*; et al.
Journal of Physics; Conference Series, 3094, p.012027_1 - 012027_7, 2025/09
no abstracts in English
Nagasumi, Satoru; Hasegawa, Toshinari; Nakagawa, Shigeaki; Kubo, Shinji; Iigaki, Kazuhiko; Shinohara, Masanori; Saikusa, Akio; Nojiri, Naoki; Saito, Kenji; Furusawa, Takayuki; et al.
JAEA-Research 2025-005, 23 Pages, 2025/07
JAEA-Research-2025-005.pdf:2.68MB
A safety demonstration test under abnormal operating conditions using the HTTR (High Temperature Engineering Test Reactor) was conducted to demonstrate safety features of the HTGRs (High Temperature Gas-cooled Reactors). Under a simulation of a control rod shutdown failure, all primary helium gas circulators were intentionally stopped during a steady-state operation at 100% reactor thermal power (30 MW), temporal changes of the reactor power and temperatures around the reactor pressure vessel (RPV) were obtained after the complete loss of forced heat removal from the reactor core. After the event (primary coolant flow stopped), the reactor power quickly decreased due to the negative reactivity feedback associated with the core temperature rise, and then the reactor power spontaneously shifted to a stable state of low power (about 1.2%) even after a recriticality. Heat dissipation from RPV surface to a surrounding vessel cooling system (water-cooled panels) ensured the amount of heat removal required to maintain the reactor temperature constant in the low power state. In this way, the transition from the event occurrence to the stable and safety state, i.e., inherent safety features of HTGRs, were demonstrated in the case of core forced cooling loss without active shutdown operations.
catalyst condition at J-PARC cryogenic moderator systemAriyoshi, Gen; Tatsumoto, Hideki*; Teshigawara, Makoto; Hasegawa, Takumi*; Shiro, Yuki*; Horikawa, Yuka*
IOP Conference Series; Materials Science and Engineering, 1327(1), p.012155_1 - 012155_6, 2025/05
The Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory in the United States of America, which operates at 1.4 MW of high-power proton beam, has recently measured "back conversion production" in which parahydrogen, a nuclear spin isomer, is converted to orthohydrogen in an intense neutron field in a liquid hydrogen circulation system not installing any catalyst, for the first time in the world. The amount of para-to-orthohydrogen back conversion was 0.374 [m/MW/day]. Comparing parahydrogen and orthohydrogen, the total neutron cross section differs more than two orders of magnitude, so the increase in orthohydrogen has a significant impact on the generated neutron performance. Therefore, in the J-PARC hydrogen circulation system, a catalyst is introduced to maintain the parahydrogen state. However, at present, methods have not been developed yet to directly diagnose catalyst performance and/or degradation in-situ. In this study, we devised a new method to easily and intentionally change the amount of orthohydrogen in the J-PARC hydrogen circulation system, and attempted to evaluate catalyst kinetics by intentionally introducing an increase in orthohydrogen equivalent to back conversion into the circulation system. This method has the potential to contribute to the in-situ diagnostic catalyst characterization and to the calculation of neutron performance that depends on the ortho-to-parahydrogen ratio.
Arai, Yoichi; Watanabe, So; Nakahara, Masaumi; Funakoshi, Tomomasa; Hoshino, Takanori; Takahatake, Yoko; Sakamoto, Atsushi; Aihara, Haruka; Hasegawa, Kenta; Yoshida, Toshiki; et al.
Progress in Nuclear Science and Technology (Internet), 7, p.168 - 174, 2025/05
The Japan Atomic Energy Agency (JAEA) has been conducting a project named "Systematic Treatment of RAdioactive liquid waste for Decommissioning (STRAD)" project since 2018 for fundamental and practical studies for treating radioactive liquid wastes with complicated compositions. Fundamental studies have been conducted using genuine liquid wastes accumulated in a hot laboratory of the JAEA called the Chemical Processing Facility (CPF), and treatment procedures for all liquid wastes in CPF were successfully designed on the results obtained. As the next phase of the project, new fundamental and practical studies on primarily organic liquid wastes accumulated in different facilities of JAEA are in progress. This paper reviews the representative achievements of the STRAD project and introduces an overview of ongoing studies.
Taguchi, Miki*; Miyata, Noboru*; Miyazaki, Tsukasa*; Aoki, Hiroyuki; Ozawa, Satoru*; Hasegawa, Ryuichi*; Morimitsu, Yuma*; Kawaguchi, Daisuke*; Yamamoto, Satoru*; Tanaka, Keiji*
Polymer Journal, 7 Pages, 2025/03
Times Cited Count：0 Percentile：0.00(Polymer Science)Nagai, Takayuki; Okamoto, Yoshihiro; Shibata, Daisuke*; Kojima, Kazuo*; Hasegawa, Takehiko*; Sato, Seiichi*; Fukaya, Akane*; Hatakeyama, Kiyoshi*
JAEA-Research 2024-014, 54 Pages, 2025/02
JAEA-Research-2024-014.pdf:7.02MB
XAFS measurements in the soft X-ray region are suitable for evaluating the chemical state of the surface layer of a measurement sample because the X-ray transmittance is low. In this study, the purpose of the study was to confirm the difference between the coagulated surface layer and the inside of the simulated waste glasses by measuring the K-edge of the glass constituent elements boron, oxygen, sodium, and silicon, and the L edge of the waste component cerium. As a result, the B K-edge XANES spectra showed that the proportion of B-O tetracoordinate sp structures (BO) on the surface layer of the coagulated glass samples was higher than that on the cut surface inside the glass samples, which is expected to improve the water resistance of the coagulated surface. On the other hand, the O K-edge XANES spectra suggested that the O abundance in the coagulated surface layer was lower than that in the cut surface inside the glass samples, and that alkali metal elements may be concentrated in the coagulated surface layer. However, no difference was observed in the Na K-edge XANES spectra between the coagulated surface layer and the cut surface, and no difference was observed in the Si K-edge XANES spectra between the solidified surface and the inside of glass samples. In addition, the Ce L-edge XANES spectra confirmed that the Ce valence in the surface layer of coagulated glass samples were oxidized compared to the inside of glass samples.
Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; Nakano, Masanao*; et al.
Journal of Nuclear Science and Technology, 6 Pages, 2025/00
Times Cited Count：0 Percentile：0.00The effect of temperature on hydrogen production generated from radiolysis was investigated to determine the associated implications for nuclear fuel reprocessing safety. The hydrogen yield from radiolysis of plutonium nitric acid solution was measured at temperatures up to the boiling temperature of the solution. The results showed no notable temperature dependence even under boiling conditions. The impact of solution agitation on hydrogen production was also assessed, which revealed minor differences in the hydrogen yield between static and agitated conditions at room temperature. These findings suggest that high temperatures or boiling the solution do not considerably enhance hydrogen generation, and provide crucial information for accurately modeling hydrogen risks under severe accidents.
Hasegawa, Yuta; Idomura, Yasuhiro; Onodera, Naoyuki
EPJ Web of Conferences, 302, p.03005_1 - 03005_9, 2024/10
Times Cited Count：0 Percentile：0.00(Computer Science, Interdisciplinary Applications)We implemented the ensemble data assimilation (DA) method, the local ensemble transform Kalman filter (LETKF), into the mesh-refined lattice Boltzmann method (LBM) for turbulent flows. Both the LETKF and the mesh-refined LBM were fully implemented on GPUs, so that they are efficiently computed on modern GPU-based supercomputers. We examined the DA accuracy against the flow around a cylinder. The result showed that our method enabled accurate DA with spatially- and temporarily-sparse observation data; the error of the assimilated velocity field with the observation interval of 
and the observation resolution 
(1.56% of the total computational grids) was smaller than the amplitude of the observation noise, where 
is the period of the K
rmn vortex and 
is diameter of the square cylinder.
Aoki, Takeshi; Hasegawa, Takeshi; Kurahayashi, Kaoru; Nomoto, Yasunobu; Shimizu, Atsushi; Sato, Hiroyuki; Sakaba, Nariaki
Proceedings of 11th International Topical Meeting on High Temperature Reactor Technology (HTR 2024), 6 Pages, 2024/10
Japan Atomic Energy Agency (JAEA) is planning to perform a test named HTTR heat application test coupling HTTR (High temperature engineering test reactor) and a hydrogen production plant. The present study reports results of the safety design and safety analysis for HTTR heat application test facility. As a safety design, safety classification of structures, systems, and components was defined in the test facility based on their safety functions. As a preliminary safety analysis, a thermal-hydraulic analysis was performed with RELAP5 code. The safety analysis revealed that newly identified events for HTTR heat application test facility except for the rupture of heat transfer tube of steam generator was enveloped by the licensing basis events in conventional HTTR. The preliminary analysis proved that the safety criteria is satisfied in the candidate of licensing basis event.
Adachi, Kyosuke; Tamura, Fumihiko; Nomura, Masahiro; Shimada, Taihei; Miyakoshi, Ryosuke*; Okita, Hidefumi; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Hara, Keigo*; et al.
Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.543 - 546, 2024/10
no abstracts in English
Okita, Hidefumi; Tamura, Fumihiko; Yamamoto, Masanobu; Miyakoshi, Ryosuke*; Nomura, Masahiro; Shimada, Taihei; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Hara, Keigo*; et al.
Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.765 - 769, 2024/10
no abstracts in English
Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Okita, Hidefumi; Miyakoshi, Ryosuke*; Seiya, Kiyomi*; Yoshii, Masahito*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; et al.
Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.85 - 88, 2024/10
no abstracts in English
Tamura, Fumihiko; Sugiyama, Yasuyuki*; Okita, Hidefumi; Yamamoto, Masanobu; Yoshii, Masahito*; Omori, Chihiro*; Seiya, Kiyomi*; Nomura, Masahiro; Shimada, Taihei; Hasegawa, Katsushi*; et al.
Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.774 - 776, 2024/10
The 3GeV RCS of J-PARC accelerates proton beams with a maximum beam intensity of 8e13 ppp, utilizing the features of magnetic alloy (MA) cavities. The beam is extracted in a single turn by kicker magnets, and immediately after the beam is extracted, a short voltage jump occurs in the cavity. This is due to a delay in the voltage control feedback, which takes a certain amount of time to respond to the step-like decrease of beam current upon single-turn extraction. In a wideband (Q=2) MA cavity, this response delay is observed as a voltage jump. This voltage jump can cause damage to the cavity system if the voltage at the time of extraction is high. Therefore, we prepared a logic to suppress the output synchronously with the beam extraction as a function of the LLRF control system. The details of the function and test results are reported.
C
reaction at 1.8 GeV/
with the Superconducting Kaon spectrometerIchikawa, Yudai; Fujita, Manami; Hasegawa, Shoichi; Imai, Kenichi*; Nanamura, Takuya; Naruki, Megumi; Sato, Susumu; Sako, Hiroyuki; Tamura, Hirokazu; Tanida, Kiyoshi; et al.
Progress of Theoretical and Experimental Physics (Internet), 2024(9), p.091D01_1 - 091D01_13, 2024/09
Times Cited Count：1 Percentile：32.23(Physics, Multidisciplinary)Machida, Masahiko; Yamada, Susumu; Kim, M.; Tanaka, Satoshi*; Tobita, Yasuhiro*; Iwata, Ayako*; Aoki, Yuto; Aoki, Kazuhisa; Yanagisawa, Kenichi*; Yamaguchi, Takashi; et al.
RIST News, (70), p.3 - 22, 2024/09
Inside the Fukushima Daiichi Nuclear Power Plant (1F), there are many locations with high radiation levels due to contamination by radioactive materials that leaked from the reactor. These pose a significant obstacle to the smooth progress of decommissioning work. To help solve this issue, the Japan Atomic Energy Agency (JAEA), under a subsidy from the Ministry of Economy, Trade, and Industry's decommissioning and contaminated water management project, is conducting research and development on digital technologies to improve the radiation environment inside the decommissioning site. This project, titled "Development of Technology to Improve the Environment Inside Reactor Buildings (Enhancing Digital Technology for Environment and Source Distribution to Reduce Radiation Exposure)," began in April of FY 2023. In this project, the aim is to develop three interconnected systems: FrontEnd, Pro, and BackEnd. The FrontEnd system, based on the previously developed 3D-ADRES-Indoor (prototype) from FY 2021-2022, will be upgraded to a high-speed digital twin technology usable on-site. The Pro system will carry out detailed analysis in rooms such as the new office building at 1F, while the BackEnd system will serve as a database to centrally manage the collected and analyzed data. This report focuses on the FrontEnd system, which will be used on-site. After point cloud measurement, the system will quickly create a 3D mesh model, estimate the radiation source from dose rate measurements, and refine the position and intensity of the estimated source using recalculation techniques (re-observation instructions and re-estimation). The results of verification tests conducted on Unit 5 are also presented. Furthermore, the report briefly discusses the future research and development plans for this project.
Arai, Yoichi; Hasegawa, Kenta; Watanabe, So; Watanabe, Masayuki; Minowa, Kazuki*; Matsuura, Haruaki*; Hagura, Naoto*; Katsuki, Kenta*; Arai, Tsuyoshi*; Konishi, Yasuhiro*
Journal of Radioanalytical and Nuclear Chemistry, 333(7), p.3585 - 3593, 2024/07
Times Cited Count：1 Percentile：18.87(Chemistry, Analytical)Watanabe, Tsutomu*; Ishikawa, Shuhei*; Kawashima, Masayuki*; Shimoyama, Ko*; Onodera, Naoyuki; Hasegawa, Yuta; Inagaki, Atsushi*
Journal of Wind Engineering and Industrial Aerodynamics, 250, p.105783_1 - 105783_17, 2024/07
Times Cited Count：3 Percentile：52.28(Engineering, Civil)This paper presents simulations of drifting snow using a Lagrangian particle dispersion model coupled with a large-eddy simulation code. The model accurately replicates observed features such as mass transport rate dependency on flow velocity and variations in particle size distribution. It also shows that the saltation layer height increases monotonically with flow velocity, contrary to conventional estimates. Additionally, the study confirms the transition from saltation to suspension near the estimated saltation layer height and finds that dense snow streamers are linked to small-scale low-speed streaks in near-surface flows.
Nemoto, Takahiro; Fujiwara, Yusuke; Arakawa, Ryoki; Choyama, Yuya; Nagasumi, Satoru; Hasegawa, Toshinari; Yokoyama, Keisuke; Watanabe, Masashi; Onishi, Takashi; Kawamoto, Taiki; et al.
JAEA-Technology 2024-003, 17 Pages, 2024/06
JAEA-Technology-2024-003.pdf:1.91MB
In order to investigate the cause of the increase in differential pressure in the primary helium circulator filter that occurred during the RS-14 cycle, a clogged filter was investigated. As a result of the investigation, deposits caused by silicone oil were confirmed on the surface of the filter element. These results revealed that the cause of filter clogging was silicone oil mixed into the primary system due to performance deterioration of the charcoal filter in the gas circulator of primary helium purification system. As a measure to prevent the recurrence of this event, in addition to the conventional management based on operating hours for replacing of charcoal filter in the gas circulator of primary helium purification system, we have established a new replacement plan for every three years.
