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Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Tsubata, Yasuhiro; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; et al.
Journal of Nuclear Science and Technology, 63(8), p.969 - 975, 2026/08
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The effect of temperature on hydrogen generated from radiolysis was investigated to determine the safety implications in nuclear fuel reprocessing. Radiolytic hydrogen production poses a risk due to its flammability, especially when it accumulates in confined spaces without ventilation. Herein, generation of radiolytic hydrogen from an actual nuclear fuel-derived solution is investigated. Compared to previous studies using a plutonium nitric acid solution, this study evaluates radiolytic hydrogen yield under more realistic conditions, reflecting post-irradiation fuel composition. G-values of H
are determined at multiple temperatures, and the impact of alpha, beta, and gamma radiation doses is evaluated using PHITS-based simulations. Findings from this study confirmed a reduction in hydrogen yield due to scavenging effects of high-concentration nitric acid and metal ions dissolved in the solution, and temperature dependence appeared to be minor. A weak decreasing trend of G-values with temperature under agitated conditions might be related to hydrogen consumption by palladium species.
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, 63(3), p.322 - 327, 2026/03
Times Cited Count：2 Percentile：41.98(Nuclear Science & Technology)The 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.
Araki, Shohei; Arakaki, Yu; Maekawa, Tomoyuki; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Tada, Yuta; Sumiya, Masato; Seki, Masakazu; Aizawa, Eiju; et al.
Proceedings of Nuclear Criticality Safety Division 2025 Conference (NCSD 2025) (Internet), p.80 - 89, 2025/09
In order to investigate the effect on criticality characteristics of fuel debris containing concrete composition in the Fukushima Daiichi Nuclear Power Plant, critical experiments loaded concrete rods were conducted in the modified STACY. The experimental cores of the modified STACY were composed of light water, fuel rods, and concrete rods with grid plates with 15.0-mm lattice intervals in the core tank. Each fuel rod consisted of a zirconium alloy clad tube (9.5-mm outer diameter) and UO pellets (8.2-mm diameter) with 4.98wt.% 235U enrichment. Each concrete rod was composed of concrete simulant pellets (7.0-mm diameter) and an aluminum alloy clad tube (9.5-mm outer diameter). The concrete simulant pellets were fabricated using an aggregate-free mortar in order to ensure a uniform composition of the pellets, and the composition was evaluated by chemical analysis. Three experimental cores were configurated with 9, 25 and 69 concrete rods. The critical water level data were obtained. An effect of composition uncertainty of the concrete simulant pellet was estimated by sensitivity analysis using MCNP6.2 with JENLD-4.0. The sensitivity analysis estimated the effect to be less than 3 pcm. The calculation results performed using MCNP6.2 with ENDF/B-VII.1, JENDL-4.0, and JENDL-5 libraries showed a tendency to overestimate the multiplication factor according to increasing the loading amount of the concrete rods.
Ishii, Junichi; Seki, Masakazu; Aizawa, Eiju; Sumiya, Masato; Maekawa, Tomoyuki; Arakaki, Yu; Hasegawa, Kenta; Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi
Proceedings of Nuclear Criticality Safety Division 2025 Conference (NCSD 2025) (Internet), p.39 - 48, 2025/09
The removal of fuel debris is one of the most important and challenging tasks in the decommissioning of power reactors damaged in the 2011 accident at Fukushima Daiichi Nuclear Power Plant (1F). The Japan Atomic Energy Agency (JAEA) has implemented a renewal program of the Static Experiment Critical Facility (STACY), transitioning it from a homogeneous solution system to a heterogeneous water-moderated system, in order to verify the criticality calculations that consider the fuel debris from the 1F accident. The first criticality of the modified STACY was achieved in April 2024. After a series of performance inspections, an experimental campaign for the investigation of fuel debris characteristics was started in August 2024. In this paper, we describe the main equipment of the modified STACY. In addition, the experimental equipment for the debris-simulated core configuration is also introduced.
Hasegawa, Kenta; Seki, Masakazu; Aizawa, Eiju; Sumiya, Masato; Yoshikawa, Tomoki; Maekawa, Tomoyuki; Ishii, Junichi; Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi
Proceedings of Nuclear Criticality Safety Division 2025 Conference (NCSD 2025) (Internet), p.50 - 59, 2025/09
The STACY was modified from a homogeneous solution-fueled reactor to a heterogeneous-core reactor composed of fuel rods and a light water moderator. This modification was undertaken to support research on the criticality characteristics of fuel debris generated by the Fukushima Daiichi Nuclear Power Plant accident. To facilitate these studies, we developed simulant devices that can be inserted into the modified STACY core as components of fuel debris mock-up configurations. From April to June 2024, Authors conducted a series of pre-service inspections on the safety performance of STACY and subsequently received approval from the Nuclear Regulation Authority (NRA) to resume operation. Experimental operations involving the simulant devices were carried out from that point until the end of March 2025. The pre-service inspections included shutdown margin, one-rod stuck margin, and measurements of the reactivity addition rate. All results satisfied STACY's safety limits.
Araki, Shohei; Aizawa, Eiju; Murakami, Takahiko; Arakaki, Yu; Tada, Yuta; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Sumiya, Masato; Seki, Masakazu; et al.
Annals of Nuclear Energy, 217, p.111323_1 - 111323_8, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)JAEA has modified the STACY from a homogeneous system using solution fuel to a heterogeneous system using fuel rods in order to obtain criticality characteristics of fuel debris. The modification of the STACY was completed in December 2023. A series of performance inspections were conducted for the start of experimental operations. A new thermal power calibration is required for the performance inspections in order to operate at less than 200 W, which is the permitted thermal power. However, the thermal power measurement method and calibration data used in the former STACY is no longer available due to the modification of the modified STACY. We measured the thermal power of the STACY using the activation method that was improved to adapt to the measurement condition and calibrated the power meter system. Since the positions where activation foils could be installed were very limited, the thermal power was evaluated using numerical calculations supplemented by experimental data. Neutron flux data at the positions of the activation foil was measured by the activation method. Neutron distribution in the core was calculated by the Monte Carlo code MVP. A response function of the activation foil was calculated using the PHITS. The uncertainty of the thermal power measurement was conservatively estimated to be about 15%. Four operations were conducted for the thermal power measurement. The power meter was calibrated by using three operational data and tested with the one operational data. It was found that the indicated value of the meter adjusted by the STACY before the modification work would tend to overestimate the actual output by about 40%. In addition, the current calibration was able to calibrate the meter to within 3% accuracy.
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.
Kusumoto, Toshiyuki*; Saruta, Koichi; Naoe, Takashi; Teshigawara, Makoto; Futakawa, Masatoshi; Hasegawa, Kazuo*; Tsuboi, Akihiko
Jikken Rikigaku, 23(4), p.310 - 315, 2023/12
Reducing spatter, i.e., melt droplets flown out of the melt pool, is one of the critical issues when laser cutting is employed as a machining tool for radioactive wastes because the ejected droplets can lead to radioactive contamination with potential human exposure. The spattering phenomena are complicated processes that involve multiple physical phenomena, causing difficulty in the determination of laser parameters to minimize the amount of spatter. Here we observe the spatter ejected from 316L stainless steel plates using a high-speed camera and apply a machine learning technique to these captured images on the basis of three distinctive behaviors appeared at specific time intervals of the process of spattering phenomena: (I) a vapor, (II) a liquid film and breakup into droplets, and (III) a liquid capillary. The numerical model established through the machine learning technique predicts the spattering phenomena with an accuracy of 89% and can be used to determine the laser power and beam diameter that reduce the spatter eruption during laser irradiation.
Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Murakami, Takahiko; Yoshikawa, Tomoki; Hasegawa, Kenta; Tada, Yuta; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 4th Reactor Physics Asia Conference (RPHA2023) (Internet), 4 Pages, 2023/10
To conduct integrated thermal power measurements for the performance test of the modified STACY, we re-analyzed the experimental data measured in the solution fuel STACY using the activation method. We validated its feasibility under the limited number of activation detectors. The re-analyzed results of the activation method by using MVP and PHITS with JENDL-4.0 indicated that the effect of the difference of the position between activation detectors was small enough, and the results agreed with that of the fission product analysis within almost 10%. It is conceivable that the activation method could be adopted instead of the fission product analysis.
Misaki, Satoshi*; Miwa, Hiroko*; Ito, Takashi; Yoshida, Takefumi*; Hasegawa, Shingo*; Nakamura, Yukina*; Tokutake, Shunta*; Takabatake, Moe*; Shimomura, Koichiro*; Chun, W.-J.*; et al.
ACS Catalysis, 13(18), p.12281 - 12287, 2023/09
Times Cited Count：12 Percentile：50.51(Chemistry, Physical)-based superconductor LaBiSO
FTamatsukuri, Hiromu; Hasegawa, Takumi*; Sagayama, Hajime*; Mizumaki, Masaichiro*; Murakami, Yoichi*; Kajitani, Joe*; Higashinaka, Ryuji*; Matsuda, Tatsuma*; Aoki, Yuji*; Tsutsui, Satoshi*
Physical Review B, 107(2), p.024303_1 - 024303_8, 2023/01
Times Cited Count：2 Percentile：12.87(Materials Science, Multidisciplinary)Kondo, Yasuhiro; Kitamura, Ryo; Fuwa, Yasuhiro; Morishita, Takatoshi; Moriya, Katsuhiro; Takayanagi, Tomohiro; Otani, Masashi*; Cicek, E.*; Ego, Hiroyasu*; Fukao, Yoshinori*; et al.
Proceedings of 31st International Linear Accelerator Conference (LINAC 2022) (Internet), p.636 - 641, 2022/09
The muon linac project for the precise measurement of the muon anomalous magnetic and electric dipole moments, which is currently one of the hottest issues of the elementary particle physics, is in progress at J-PARC. The muons from the J-PARC muon facility are once cooled to room temperature, then accelerated up to 212 MeV with a normalized emittance of 1.5 
mm mrad and a momentum spread of 0.1%. Four types of accelerating structures are adopted to obtain the efficient acceleration with a wide beta range from 0.01 to 0.94. The project is moving into the construction phase. We already demonstrated the re-acceleration scheme of the decelerated muons using a 324-MHz RFQ in 2017. The high-power test of the 324-MHz Interdigital H-mode (IH) DTL using a prototype cavity was performed in 2021. The fabrication of the first module of 14 modules of the 1296-MHz Disk and Washer (DAW) CCL will be done to confirm the production process. Moreover, the final design of the travelling wave accelerating structure for the high beta region is also proceeding. In this paper, the recent progress toward the realization of the world first muon linac will be presented.
Hayashida, Takeshi*; Uemura, Yohei*; Kimura, Kenta*; Matsuoka, Satoshi*; Hagihara, Masato; Hirose, Sakyo*; Morioka, Hitoshi*; Hasegawa, Tatsuo*; Kimura, Tsuyoshi*
Physical Review Materials (Internet), 5(12), p.124409_1 - 124409_10, 2021/12
Times Cited Count：52 Percentile：87.16(Materials Science, Multidisciplinary)
-Orbital component in the Borromean nucleus 
BYang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.
Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02
Times Cited Count：94 Percentile：97.22(Physics, Multidisciplinary)A quasifree (
,
) experiment was performed to study the structure of the Borromean nucleus B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 
and 
orbitals, and a surprisingly small percentage of 9(2)% was determined for . Our finding of such a small component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B. The present work gives the smallest - or -orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of or orbitals is not a prerequisite for the occurrence of a neutron halo.
Kusumoto, Tamon*; Matsuya, Yusuke; Baba, Kentaro*; Ogawara, Ryo*; Akselrod, M. S.*; Harrison, J.*; Fomenko, V.*; Kai, Takeshi; Ishikawa, Masayori*; Hasegawa, Sumitaka*; et al.
Radiation Measurements, 132, p.106256_1 - 106256_4, 2020/03
Times Cited Count：11 Percentile：64.34(Nuclear Science & Technology)Internal radiation therapy with Cu-64 concentrates energy deposition in tumor cells by virtue of released Auger electrons with low energy. In our previous study, we have attached the solutions at the surface of Fluorescent Nuclear Track Detector (FNTD) and succeeded in measuring the absorbed doses of Auger electrons registered in FNTD. However, because there are several types of radiation emitted from the source, i.e., beta rays, positron etc., the contribution degree of Auger electron to energy concentration remain uncertain. In this study, we quantitatively analyzed the spatial dose distribution in the FNTD based on Monte Carlo simulation with PHITS and GEANT4, and evaluated high dose deposited by Auger electrons. The dose distribution calculated by the PHITS code is exactly equivalent to that by Geant4. Also, the simulations are well agreement with experimental results. If the contribution of Auger electrons is ignored, the significantly high absorbed dose proximal to the source is not properly reduced. These findings demonstrate that Auger electrons work very effectively to kill cancer cells proximal to Cu-64 source while minimizing damage effects on normal cells distal to the source.
Nishikino, Masaharu; Ishino, Masahiko; Ichimaru, Satoshi*; Hatayama, Masatoshi*; Hasegawa, Noboru; Kawachi, Tetsuya
Reza Gakkai Dai-483-Kai Kenkyukai Hokoku; Tanhacho Ryoshi Bimu Hassei To Sono Oyo, p.25 - 28, 2015/12
X-ray ablation has been recently achieved using plasma soft X-ray lasers (SXRLs), laser plasma soft X-rays, and X-ray free electron lasers. In order to study the interactions between picosecond SXRL beams and material and multi-layered structure surfaces were irradiated with SXRL pulse. Following irradiation, the substrate surface was observed using a scanning electron microscope and an atomic force microscope. The surface modifications caused by the SXRL beam were clearly seen. The multi-layered mirror is the important component for the EUV lithography. Then, we have started the damage test of multi-layered structure, and the surface modifications caused by the SXRL pulse irradiations were confirmed.
Takahashi, Hideyuki*; Handa, Nobuo*; Murano, Takanori*; Terauchi, Masami*; Koike, Masato; Kawachi, Tetsuya; Imazono, Takashi; Hasegawa, Noboru; Koeda, Masaru*; Nagano, Tetsuya*; et al.
Microscopy and Microanalysis, 20(Suppl.3), p.684 - 685, 2014/08
A novel wavelength dispersive soft X-ray emission spectrometer (SXES) having a X-ray energy range of 50-210 eV has been developed. One feature is that the SXES is parallel detection of the signals so that it can be used like a conventional energy dispersive spectrometer. The other is a high energy resolution, which is about 0.2 eV at Al-L comparable to those revealed by XPS and EELS. These features enable us to obtain meaningful information about chemical bonding in various bulk samples. The SXES can detect Li-K emission spectrum. In the case of an anode electrode of a lithium ion battery (LIB), two types of lithium peaks are observed: one lower energy peak at 50 eV and the other higher energy peak at 54 eV. It was found that the former peak corresponds to the amount of charging, whereas the latter corresponds to the metallic state of lithium.
Starikov, S. V.*; Faenov, A. Ya.; Pikuz, T. A.; Skobelev, I. Yu.*; Fortov, V. E.*; Tamotsu, Satoshi*; Ishino, Masahiko; Tanaka, Momoko; Hasegawa, Noboru; Nishikino, Masaharu; et al.
Applied Physics B, 116(4), p.1005 - 1016, 2014/02
Times Cited Count：26 Percentile：74.99(Optics)Ishino, Masahiko; Faenov, A.*; Tanaka, Momoko; Pikuz, T. A.; Tamotsu, Satoshi*; Hasegawa, Noboru; Nishikino, Masaharu; Starikov, S. V.*; Stegailov, V. V.*; Norman, G.*; et al.
X-Ray Lasers 2012; Springer Proceedings in Physics, Vol.147, p.121 - 124, 2014/00
Times Cited Count：0 Percentile：0.00(Engineering, Electrical & Electronic)Terauchi, Masami*; Takahashi, Hideyuki*; Handa, Nobuo*; Murano, Takanori*; Koike, Masato; Kawachi, Tetsuya; Imazono, Takashi; Hasegawa, Noboru; Koeda, Masaru*; Nagano, Tetsuya*; et al.
JAEA-Conf 2013-001, p.77 - 80, 2013/09
We have been developing a soft X-ray emission spectroscopy (SXES) instrument for electron microscopes (TEM, EPMA/SEM) with an extension of detectable energy range to 50-4000 eV. An introduction of valence electron spectroscopy with microscopy will supply fruitful information on bonding electrons, which cannot be obtained by EELS and EDS. For extend the lowest (or highest) detection energy upto 50 eV (or 4000 eV), a new laminar-type varied-line-spacing (VLS) grating, JS50XL, (or JS4000) has designed and manufactured. JS50XL and JS4000 having 1200 and 2400 lines/mm as well as coated by Au and a new multilayer-structure of W/B
C for a wide-band energy region of 2000-3800 eV, respectively. Those gratings were installed and tested in a SXES spectrometer attached to a TEM. The extension in lowest detection energy was confirmed by Mg-L emission (JS50XL). The energy resolution was 0.2 eV at Fermi edge of 49.5 eV. It can be also seen a sharp Fermi edge for Li-K emission spectrum of metal-Li. The high energy resolution was confirmed by Te-La emission at 3.8 keV (JS4000). The full width at half maximum of the peak was 27 eV. The detection energy range was successfully extended by using the two new VLS-gratings.
