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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.
Gu, G. H.*; Jeong, S. G.*; Heo, Y.-U.*; Harjo, S.; Gong, W.; Cho, J.*; Kim, H. S.*; 4 of others*
Journal of Materials Science & Technology, 223, p.308 - 324, 2025/07
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Hamdani, A.; Soma, Shu; Abe, Satoshi; Shibamoto, Yasuteru
Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07
Times Cited Count：0Shi, W.*; Machida, Masahiko; Yamada, Susumu; Okamoto, Koji
Progress in Nuclear Energy, 184, p.105710_1 - 105710_10, 2025/06
Very recently, Least Absolute Shrinkage and Selection Operator (LASSO) has been proposed as a scheme capable to inversely estimate radioactive source distributions inside reactor building rooms from air dose rate measurements together with the predicted lower bound of the measurement numbers for successful reconstructions. However, no one has ever analyzed how the uncertainty of input data including the measurement errors influences the accuracy of the inverse estimation results. In this paper, we therefore perform uncertainty analysis of the LASSO scheme and suggest an uncertainty estimation function derived based on the theory of Candes. We actually demonstrate in two types of numerical tests with different input uncertainties obtained by using Monte Carlo code, Particle and Heavy Ion Transport code System (PHITS) that the calculated errors obey the proposed uncertainty estimation function. Thus, the LASSO scheme allows to successfully estimate radioactive distributions within the predicted uncertainty.
Kinoshita, Junichi; Sakamoto, Yu; Suzuki, Ichiro; Nakajima, Ryota; Morita, Yusuke; Irie, Hirobumi
JAEA-Technology 2024-027, 55 Pages, 2025/05
JAEA-Technology-2024-027.pdf:8.49MB
The Waste Treatment Facility No.2 has equipment that can process solid waste with relatively high radioactive levels generated within the Japan Atomic Energy Agency. This facility had been constructed under the old Building Standards Act. Seismic evaluation based on a new regulatory requirements enforced in December 2013 was executed, thereby, it was found that the seismic resistance requirements was insufficient according to the current Building Standards Act. Therefore, seismic reinforcement works was carried out from November 2018 to February 2020. In this report, seismic reinforcement design, works, test and inspection was complied.
Katano, Ryota; Abe, Takumi; Cibert, H.*
JAEA-Research 2024-019, 22 Pages, 2025/05
JAEA-Research-2024-019.pdf:1.03MB
An accelerator-driven system (ADS) dedicated to transmutation of minor actinides (MAs) is driven in subcritical states. It is important for establishment of the subcriticality control of ADS to predict the burnup reactivity. To validate the prediction accuracy, the burnup reactivity, especially at the first cycle, must be measured with sufficient accuracy. In this study, we focus on Current-To-Flux (CTF) method. We have simulated the burnup reactivity monitoring during the ADS normal operation with the CTF method by performing fixed-source-burnup calculations using a continuous energy Monte Carlo code SERPENT2 with some tallies that models in-core fission chambers and have estimated its measurement uncertainty. We have clarified that the 10% biases of measure burnup reactivities appear independently of the burnup duration and their detector position dependence is particularly small in the outer region of the system.
Li, X.; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya
Annals of Nuclear Energy, 214, p.111217_1 - 111217_13, 2025/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Aoyama, Takahito; Ueno, Fumiyoshi; Sato, Tomonori; Kato, Chiaki; Sano, Naruto; Yamashita, Naoki; Otani, Kyohei; Igarashi, Takahiro
Annals of Nuclear Energy, 214, p.111229_1 - 111229_6, 2025/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Uesawa, Shinichiro; Ono, Ayako; Nagatake, Taku; Yamashita, Susumu; Yoshida, Hiroyuki
Journal of Nuclear Science and Technology, 62(5), p.432 - 456, 2025/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)We performed electrostatic simulations of a wire-mesh sensor (WMS) for a single spherical bubble and bubbly flow to clarify the accuracy of the WMS. The electrostatic simulation for the single bubble showed the electric current density distribution and the electric current path from the excited transmitter to receivers for various bubble locations. It indicated systematic errors based on the nonuniform current density distribution around the WMS. The electrostatic simulation for the bubbly flow calculated by the computational fluid dynamics code, JAEA Utility Program for Interdisciplinary Thermal-hydraulics Engineering and Research (JUPITER), indicated that the WMS had difficulty in quantitatively measuring the intermediate values of the instantaneous void fraction between 0 and 1 because they cannot be estimated by previous transformation methods from the WMS signal to the void fraction, such as linear approximation or Maxwell's equation, and have a significant deviation of the void fraction of 
0.2 for the WMS signal. However, the electrostatic simulation indicated that the time-averaged void fractions around the center of the flow channel can be estimated using linear approximation, and the time-averaged void fraction near the wall of the flow channel can be estimated using Maxwell's equation.
Takahatake, Yoko; Watanabe, So; Watanabe, Masayuki; Sano, Yuichi; Takeuchi, Masayuki
Progress in Nuclear Science and Technology (Internet), 7, p.195 - 198, 2025/05
Extraction chromatgraphy technology for trivalent minor actinide (MA(III) ; Am(III) and Cm(III)) recovery from the solution generated by an extraction process in reprocessing of spent nuclear fuel has been developed. A fine particle is generated in the solution. The fine particle must be removed before MA recovery operation, because that leads clogging of the extraction chlomatography column. In order to prevent clogging the column, filtration system utilizing porous silica beads packed column has been designed. In this study, a fine particle trapping system was developed and particle removal performance of the system was experimentally evaluated using alumina particles as simulated fine particle. Column experiments revealed that the fine particle with the particle size from 0.12 to 15 
m is cause of clogging of the filtration column. Since simulated fine particles were trapped on filtration experiments, a filtration system using the porous silica beads column is practical,
Myagmarjav, O.; Tanaka, Nobuyuki; Noguchi, Hiroki; Kamiji, Yu; Ono, Masato; Nomura, Mikihiro*; Takegami, Hiroaki
Progress in Nuclear Science and Technology (Internet), 7, p.235 - 242, 2025/05
hydridosilicate at high pressures; A Bridge to BaSiH
polyhydrideBeyer, D. C.*; Spektor, K.*; Vekilova, O. Y.*; Grins, J.*; Barros Brant Carvalho, P. H.*; Leinbach, L. J.*; Sannemo-Targama, M.*; Bhat, S.*; Baran, V.*; Etter, M.*; et al.
ACS Omega (Internet), 10(15), p.15029 - 15035, 2025/04
Times Cited Count：0Hydridosilicates featuring SiH octahedral moieties represent a rather new class of compounds with potential properties relating to hydrogen storage and hydride ion conductivity. Here, we report on the new representative BaSiH obtained from reacting the Zintl phase hydride BaSiH
with H
fluid at pressures above 4 GPa and subsequent decompression to ambient pressure. It consists of complex SiH
ions, which are octahedrally coordinated by Ba
counterions. The arrangement of Ba and Si atoms deviates only slightly from an ideal fcc NaCl structure. IR and Raman spectroscopy showed SiH bending and stretching modes in the ranges 800-1200 and 1400-1800 cm
, respectively. BaSiH is thermally stable up to 95
C above which decomposition into BaH and Si takes place. DFT calculations indicated a direct band gap of 2.5 eV. The discovery of BaSiH consolidates the compound class of hydridosilicates, accessible from hydrogenations of silicides at gigapascal pressures (
10 GPa). The structural properties of BaSiH suggest that it presents an intermediate (or precursor) for further hydrogenation at considerably higher pressures to the predicted superconducting polyhydride BaSiH.
neutron diffraction studyIto, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.
Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Endo, Akira
ESI-News, 43(2), p.37 - 41, 2025/04
The International Commission on Radiation Units and Measurements (ICRU) published ICRU Report 95 in 2020, revising the operational quantities for external exposure. This article provides an overview of the developments in the discussions within the ICRU, the International Commission on Radiological Protection (ICRP), and experts from Japan, and explores the background and process that led the ICRU to revise the operational quantities, as well as future responses and challenges. The article aims to enhance the understanding of the experts of the new operational quantities and to contribute to their smooth implementation in the future.
Wada, Yuki; Shibamoto, Yasuteru; Hibiki, Takashi*
International Journal of Heat and Mass Transfer, 239, p.126598_1 - 126598_18, 2025/04
Times Cited Count：1 Percentile：30.78(Thermodynamics)Pandian, K.*; Neikter, M.*; Ekh, M.*; Harjo, S.; Kawasaki, Takuro; Woracek, R.*; Hansson, T.*; Pederson, R.*
JOM, 77(4), p.1803 - 1815, 2025/04
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Sato, Yuki; Terasaka, Yuta; Ichiba, Yuta*
Journal of Nuclear Science and Technology, 62(4), p.389 - 400, 2025/04
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)
Tamatsukuri, Hiromu; Uchihara, Takeru*; Mitsuda, Setsuo*; Ishii, Yuta*; Nakao, Hironori*; Takehana, Kanji*; Imanaka, Yasutaka*
Physical Review B, 111(13), p.134403_1 - 134403_9, 2025/04
Times Cited Count：0
under hydrostatic pressure; A Combined neutron, X-ray, Raman, and first-principles calculation studyEfthimiopoulos, I.*; Klotz, S.*; Kunc, K.*; Baptiste, B.*; Chauvigne, P.*; Hattori, Takanori
Physical Review B, 111(13), p.134103_1 - 134103_13, 2025/04
Times Cited Count：0We present a comprehensive study of the high pressure behaviour of ReO using X-ray and neutron diffraction, Raman scattering and first-principles calculations to 15 GPa. We show that the ambient pressure 
structure converts at 0.7 GPa in a continuous phase transition directly to a cubic phase with space group 
and rhombohedral 
structures in this pressure range are an artifact due to an alteration of the sample by high-flux synchrotron X-ray radiation. The structural pressure dependence of the 
O samples are presented. The data shed light onto the unusual transition and densification mechanism due to progressive tilting of essentially rigid ReO octahedra.
Morishita, Yuki; Peschet, L.; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
Radiation Measurements, 183, p.107414_1 - 107414_6, 2025/04
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)In the decommissioning nuclear facilities, it is crucial to inspect piping for contamination to prevent worker exposure to alpha-emitting nuclides. Traditional methods using gamma rays and neutrons are inadequate for detecting small amounts of alpha nuclides due to the short range (approximately 4 cm) of alpha particles in air. To address this, we developed a compact detector capable of distinguishing between alpha particles for direct measurement within pipes. This detector, comprising a ZnS(Ag) scintillator for alpha particles and a plastic scintillator for beta particles (gamma rays), was coupled to a small photomultiplier tube. The system demonstrated high accuracy in differentiating between alpha and beta radiation through pulse shape discrimination (PSD). Monte Carlo simulations and empirical measurements confirmed the detector's effectiveness, achieving a 51.3% detection efficiency for alpha particles with negligible sensitivity to beta and gamma radiation. This innovation presents a significant advancement for direct alpha contamination measurement in environments with high beta and gamma backgrounds, such as the Fukushima Daiichi Nuclear Power Plant decommissioning site.
