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Uesawa, Shinichiro; Hiramatsu, Natsuki*; Ono, Koji*; Yoshida, Hiroyuki
Dai-53-Kai Kashika Joho Shimpojiumu Koen Rombunshu (Internet), 3 Pages, 2026/08
To realize the early practical application of innovative reactors, it is essential to utilize numerical simulations as alternatives to large-scale mock-up tests. To clarify the validity, we are developing measurement techniques capable of capturing instantaneous and local gas-liquid interface information. In this study, a measurement technique based on deep learning is being developed to obtain instantaneous and local bubble characteristics, such as bubble diameter, bubble velocity, and aspect ratio, for validating detailed two-phase flow simulations. This presentation introduces visualization results in a rod bundle flow channel for acquiring bubble characteristics. To enable visualization of the entire flow channel, a 4
4 rod bundle test section was fabricated using perfluoroalkoxy (PFA) tubes with a refractive index close to that of water as simulated fuel rods. Bubble behavior was captured using two high-speed video cameras arranged orthogonally. The three-dimensional distribution of bubbles was reconstructed from the images obtained from the two viewing directions. In addition, void fraction measurements were conducted under the same conditions using a wire-mesh sensor, and the validity and applicability of the present experimental method were examined through comparisons with the visualization measurement results.
Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*
JAEA-Review 2026-003, 173 Pages, 2026/06
JAEA-Review-2026-003.pdf:12.5MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2024, this report summarizes the research results of the "Human resource development for research based on fuel debris study and SEEM-ology buildup" conducted in FY2024. The present study aims to buildup of "Severe Engineering Management (SEEM)-ology" that enables more rational decision-making in an uncertain and severe environment, and at the same time, to develop research personnel supporting the academic foundation of the extraction, long-term storage, treatment and disposal of fuel debris, which is a central issue in the decommissioning of 1F. Experts in different fields promote multiple research and human resource development tasks in organic collaboration. In the first fiscal year of this study, it was necessary to clarify specific research methods and set the direction in the [SEEM Fields] [Specialized Fields 1
2] and [Common Engineering Fields 13], as well as to prepare various conditions for necessary tests and analyses. It was also necessary to promote the operation of educational programs related to nuclear decommissioning and the planning of SEEM-related courses. For this reason, the purpose of this fiscal year was to obtain the prescribed results by examining specific research methods and making various preparations for conducting necessary tests, preparing various conditions, building and analyzing some measurement systems, and examining human resource development. Based on this objective, we set the performance targets and implementation methods for this fiscal year as an operational plan, implemented them as planned, and were able to achieve the targeted results in each technical field and education and human resource development activities.
Kreider, B.; Cox, I.*; Grzywacz, R.*; Allmond, J. M.*; Nishio, Katsuhisa; 23 of others*
Nuclear Instruments and Methods in Physics Research A, 1085, p.171298_1 - 171298_7, 2026/05
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)
-containing porous hydrogel via freeze-crosslinking for efficiency and salt-robust dye DecolorizationSugita, Tsuyoshi; Ueda, Yuki; Nakabe, Rintaro; Mori, Masanobu*; Nankawa, Takuya; Sekine, Yurina
Journal of Photochemistry and Photobiology A; Chemistry, 473, p.116773_1 - 116773_9, 2026/04
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)We developed a WO-embedded hydrogel (WFG) by freeze-cross-linking that retained high activity even in the presence of coexisting salts. Confocal laser scanning microscope revealed interconnected channels < 200 
m. ensuring good water permeability, and contrast-matching small-angle neutron scattering showed that the secondary particle size of embedded WO (~300 nm) matched that in aqueous suspension. Under visible-light irradiation, WFG decolorized indigo carmine (INC) 1.5-fold increase in rate than suspended WO and 3.7-fold increase in rate than a WO-coated glass plate. Coexisting salts (NaNO, NaCl, Na
SO
, NaHPO) altered the decolorization efficiency; NaNO and NaSO enhanced, whereas Cl
and HPO suppressed the reaction, indicating that ionic strength and anion-species affect contact efficiency and charge transfer.
Department of HTTR
JAEA-Review 2025-053, 86 Pages, 2026/02
JAEA-Review-2025-053.pdf:3.06MB
This report summarizes the activities carried out in the fiscal year 2024 about the operation and maintenance of the High Temperature Engineering Test Reactor (HTTR), the R&Ds using the HTTR and so on. The HTTR is the first Japanese test reactor of High Temperature Gas-cooled Reactor (HTGR) type with 30MW in thermal power and whose maximum outlet coolant temperature achieved 950
C. HTGRs are regarded as the promising candidates of the Next Generation Nuclear Plants conformed to the future decarbonized society because of the inherent safety characteristics as well as high temperature heat supply capability for not only power generation but for wide-ranging industrial uses such as hydrogen production and so on. The HTTR achieved its reactor outlet coolant temperature of 950C under full thermal power of 30MW on April 19, 2004. And since then, HTTR has had a lot of experience of HTGRs' operation and maintenance throughout rated power operations, safety demonstration tests, long-term high temperature operations and demonstration tests relevant to HTGRs' R&Ds. In the fiscal year 2024, we conducted heat load variation tests simulating heat load fluctuations due to equipment abnormalities at thermal utilization facilities (hydrogen production facilities) planned to be connected to HTTR, as well as radioactive iodine quantitative evaluation tests to assess the amount of radioactive iodine deposited in the pipes, assuming a primary double-pipe high temperature gas duct rupture accident of the HTGR. Additionally, to confirm hydrogen production technology using the high-temperature gas reactor, we applied to Nuclear Regulation Authority for a reactor installation change permit to connect a hydrogen production facility to HTTR.
Iwasawa, Yuzuru; Shibamoto, Yasuteru; Maruyama, Yu
Nuclear Engineering and Design, 446(Part B), p.114599_1 - 114599_16, 2026/01
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Fei, Y.*; Wang, Y.*; Zhang, J.*; Liu, J.*; Zhao, Z.*; Hattori, Takanori; Abe, Jun*; Dong, X.*; Mao, H.-K.*; Zheng, H.*; et al.
Chemistry; A European Journal, p.e71096_1 - e71096_11, 2026/00
Times Cited Count：0 Percentile：0.00(Chemistry, Multidisciplinary)We systematically investigated the high-pressure polymerization of naphthalene, the simplest polycyclic aromatic hydrocarbons (PAHs), using multiple cutting-edge methods. Naphthalene molecules were stacked in herringbone style, and underwent [4+2] cycloaddition reactions along the a-b direction above 20 GPa, yielding one-dimensional Carbon nanothreads (CNThs). In contrast to the formation of many CNThs, the nucleation of the CNThs occurs during compression while their growth proceeds during decompression, which is likely prevalent among herringbone-stacked aromatics. The unit cell of the obtained CNTh crystal is determined and the possible structure of the CNTh product is also proposed. Our research reveals the polymerization characteristics of naphthalene under high pressure, highlighting the fact that the slip-angle plays an important role in governing the polymerization pathway.
Fujii, Daisuke; Tanaka, Mitsuru*
Physics Letters B, 870, p.139872_1 - 139872_7, 2025/11
Times Cited Count：4 Percentile：70.29(Astronomy & Astrophysics)We investigate how the QCD scale anomaly contributes to the internal pressure structure of hadrons, employing the decomposition of the energy-momentum tensor into its trace and traceless parts. By utilizing recent model-independent results for gravitational form factors, we analyze the pressure distributions of both pions and nucleons in the instant form and the light-front form. Our analysis reveals that, in all examined cases, the confining pressure is predominantly driven by the scale anomaly. This indicates that the dominance of the scale anomaly in generating internal pressure is a robust and universal feature, regardless of the specific hadron, theoretical model, or form used in the analysis.
Sakaba, Nariaki; Ohashi, Hirofumi; Sato, Hiroyuki
Nihon Genshiryoku Gakkai-Shi ATOMO
, 67(10), p.593 - 597, 2025/10
no abstracts in English
demand and HTGR development potential in the industrial complex in JapanNoguchi, Hiroki; Ishii, Katsunori; Ono, Masato; Kasahara, Seiji; Sato, Hiroyuki; Sakaba, Nariaki
Proceedings of World Hydrogen Technologies Convention 2025 (WHTC 2025) (Internet), p.50 - 52, 2025/10
Achieving carbon neutrality in Japan in 2050, hydrogen is expected to be used as an alternative to fossil fuels in the hard-to-abate sectors. In steelmaking, hydrogen-based reduction process has been developed as a substitute for the conventional blast furnace steelmaking process, which involves the reduction of iron ore by coke. In chemical industry, a novel olefin production process has been developed using hydrogen and CO, through methanol as an intermediate chemical. A large amount of hydrogen is required for these novel processes. Nuclear energy is well-suited to large-scale low-carbon hydrogen production. High temperature gas cooled reactor (HTGR) is a type of nuclear reactor featuring extraction of high temperature heat. The heat can be applicable to hydrogen production. This study predicts hydrogen demand in five industrial complexes in Japan in 2050 and estimates the potential for introducing HTGR to meet the demand. The introduction of HTGR could be a promising solution for decarbonizing industrial complexes due to their large-scale hydrogen supply capacity.
Ishii, Katsunori; Ono, Masato; Noguchi, Hiroki; Shimizu, Atsushi; Nomoto, Yasunobu; Sato, Hiroyuki; Sakaba, Nariaki
Proceedings of World Hydrogen Technologies Convention 2025 (WHTC 2025) (Internet), p.26 - 28, 2025/10
Department of HTTR
JAEA-Review 2025-032, 75 Pages, 2025/09
JAEA-Review-2025-032.pdf:3.15MB
This report summarizes the activities carried out in the fiscal year 2023 about the operation and maintenance of the High Temperature Engineering Test Reactor (HTTR), the R&Ds using the HTTR, and so on. The HTTR is the first Japanese test reactor of High Temperature Gas-cooled Reactor (HTGR) type with 30 MW in thermal power and whose maximum outlet coolant temperature achieved 950 C. HTGRs are regarded as the promising candidates of the Next Generation Nuclear Plants conformed to the future decarbonized society because of the inherent safety characteristics as well as high temperature heat supply capability for not only power generation but for wide-ranging industrial uses such as hydrogen production, and so on. The purpose of the HTTR is establishment of basic HTGR technologies, demonstration of HTGR safety characteristics, and so on. The HTTR has had a lot of experience of HTGRs' operation and maintenance throughout rated power operations, safety demonstration tests, long-term high temperature operations and demonstration tests relevant to HTGRs' R&Ds. In the fiscal year 2023, the HTTR was confirmed its inherent safety of HTGR due to carry out the safety demonstration test (Loss of forced cooling test at the 100% power) as the international joint research of Organization for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA).
Hasegawa, Toshinari; Nagasumi, Satoru; Kubo, Shinji; Iigaki, Kazuhiko; Shinohara, Masanori; Nakagawa, Shigeaki; Shimazaki, Yosuke; Nakajima, Kunihiro; Sakurai, Yosuke
Proceedings of 2025 International Congress on Advances in Nuclear Power Plants (ICAPP 2025) (Internet), 6 Pages, 2025/09
JAEA has planned a hydrogen production test using the High-Temperature Engineering Test Reactor (HTTR) to demonstrate hydrogen production utilizing the heat from a high-temperature gas-cooled reactor (HTGR). To realize the coupling of a hydrogen production facility with an HTGR, one of the key issues is to confirm the effect of thermal load fluctuations in the facility on the reactor. In this study, a thermal load fluctuation test was conducted during HTTR operation to investigate the reactor's response. The test was performed at 90% reactor power, during which the reactor inlet coolant temperature was increased by 11C to simulate a thermal load fluctuation. As a result, the reactor outlet coolant temperature remained almost unchanged, and the heat corresponding to the inlet temperature increase was absorbed by the core graphite blocks. Furthermore, due to the negative reactivity feedback effect associated with the rise in graphite block temperature, the reactor power decreased to 88% and stabilized without any control rod operation. These findings indicate that disturbances in the reactor inlet coolant temperature are mitigated by the heat storage capacity of the core graphite blocks.
Hasegawa, Toshinari; Nagasumi, Satoru; Ishitsuka, Etsuo; Egashira, Keiichiro*; Furuya, Aoi*; Ando, Ryota*; Sakaguchi, Akira*; Sakurai, Yosuke; Nakano, Yumi*; Iigaki, Kazuhiko
JAEA-Technology 2025-004, 20 Pages, 2025/07
JAEA-Technology-2025-004.pdf:1.67MB
Four people from three universities participated in the 2024 summer holiday practical training with the theme of "Technical development on HTTR". The participants practiced the analysis of the HTTR core, the analysis of 
Cs deposition behavior in the primary cooling system, and the feasibility study of nuclear rockets using HTGR. In the questionnaire after this training, there were comments from participants that it was beneficial as a work experience and that it was meaningful because of many opportunities to communicate with staff. These impressions suggest that this training was generally evaluated as good.
Iwasawa, Yuzuru; Matsumoto, Toshinori; Moriyama, Kiyofumi*
JAEA-Data/Code 2025-001, 199 Pages, 2025/06
JAEA-Data-Code-2025-001.pdf:9.71MB
A steam explosion is defined as a phenomenon that occurs when a hot liquid comes into contact with a low-temperature cold liquid with volatile properties. The rapid transfer of heat from the hot liquid to the cold liquid results in a chain reaction of the explosive vaporization of the cold liquid and fine fragmentation of the hot liquid. The explosive vaporization of the cold liquid initiates the propagation of shock waves in the cold liquid. The expansion of the hot and cold liquid mixture exerts mechanical forces on the surrounding structures. In severe accidents of light water reactors, the molten core (melt) is displaced into the coolant water, resulting in fuel-coolant interactions (FCIs). The explosive FCI, referred to as a steam explosion, has been identified as a significant safety assessment issue as it can compromise the integrity of the primary containment vessel. The JASMINE code is an analytical tool developed to evaluate the mechanical forces imposed by steam explosions in nuclear reactors. It performs numerical simulations of steam explosions in a mechanistic manner. The present report describes modeling concepts, basic equations, numerical solutions, and example simulations, as well as instructions for input preparation, code execution, and the use of supporting tools for practical purpose. The present report is the updated version of the "Steam Explosion Simulation Code JASMINE v.3 User's Guide, JAEA-Data/ Code 2008-014". The present report was compiled and updated based on the latest version of the code, JASMINE 3.3c, with corrections for minor errors of the distributed code JASMINE 3.3b, and conformance to recently widely used compilers on UNIX-like environments such as the GNU compiler. The numerical simulations described in the present report were obtained using the latest version JASMINE 3.3c. The latest parameter adjustment method for a model parameter proposed by the previous study is employed to conduct the numerical simulations.
Fukushima, Masahiro; Ando, Masaki; Nagaya, Yasunobu
Nuclear Science and Engineering, 199(6), p.1029 - 1043, 2025/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Yamazaki, Dai; Maruyama, Ryuji; Aoki, Hiroyuki; Hanashima, Takayasu*; Akutsu-Suyama, Kazuhiro*; Miyata, Noboru*; Soyama, Kazuhiko
Quantum Beam Science (Internet), 9(2), p.20_1 - 20_12, 2025/06
Schury, P.*; Ito, Yuta; Wada, Michiharu*
Nihon Butsuri Gakkai-Shi, 80(2), p.72 - 78, 2025/02
The multi-reflection time-of-flight mass spectrograph has recently become of great utility in the study of superheavy nuclei. The device efficiently uses each ion and its operation is amenable to the inclusion of a decay detector being coupled into the time-of-flight (TOF) ion impact detector. In this way, TOF-decay correlation can be measured to unambiguously differentiate low-yield radioactive ions from stable molecular ions or dark counts. This will eventually allow the technique to be applied to the study of extremely low-yield nuclei such as those of 
Nh and 
Mc isotopes.
Katsumura, Kosuke*; Takagi, Junichi*; Miyahara, Naoya*; Uchida, Shunsuke*; Koma, Yoshikazu; Karasawa, Hidetoshi; Miwa, Shuhei; Satou, Yukihiko; Nagai, Haruyasu; Kurata, Masaki; et al.
Nihon Genshiryoku Gakkai-Shi ATOMO, 67(2), p.128 - 132, 2025/02
no abstracts in English
Sr/Y inside the Fukushima Daiichi Nuclear Power Station Unit 3 reactor building using a liquid light guide Cherenkov counterTerasaka, Yuta; Sato, Yuki; Furuta, Yoshihiro*; Kubo, Shin*; Ichiba, Yuta*
Nuclear Instruments and Methods in Physics Research A, 1070, Part 2 , p.170021_1 - 170021_9, 2025/01
Times Cited Count：2 Percentile：41.12(Instruments & Instrumentation)