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Iwamoto, Nobuyuki
Journal of Nuclear Science and Technology, 13 Pages, 2025/10
Tomita, Jumpei; Tomita, Ryohei; Suzuki, Daisuke; Yasuda, Kenichiro; Miyamoto, Yutaka
Journal of Nuclear Science and Technology, 12 Pages, 2025/09
Times Cited Count：0 Percentile：0.00Kondo, Ryoichi; Yamamoto, Akio*; Endo, Tomohiro*
Journal of Nuclear Science and Technology, 12 Pages, 2025/09
Times Cited Count：0 Percentile：0.00The flux distribution tallies using proper orthogonal decomposition, called POD tallies, have been developed to address issues of high-fidelity Monte Carlo simulations. The POD tallies can reduce both dimensionality and statistical error. The present study verifies the applicability of the POD tallies to sub-pin level flux distribution in the two-dimensional C5G7 benchmark. Statistical error estimation is also proposed by applying the circular block bootstrap method to the POD tallies to estimate the statistical error of the flux distribution in a single Monte Carlo calculation. In the verification, the dimensionality of the finely discretized distribution is reduced by more than 90% compared with conventional cell tallies. The statistical error is reduced by more than half as the average value of all tally regions. The proposed approach is confirmed to properly estimate the statistical error of flux distribution considering both the inter-cycle correlation and the correlation between the expansion coefficients of different POD orders.
Sato, Takuto; Nakayama, Hiromasa; Satoh, Daiki
Journal of Nuclear Science and Technology, 17 Pages, 2025/09
Times Cited Count：0 Percentile：0.00We developed a framework for rapid monitoring of radioactive plumes in the vicinity of nuclear facilities based on a quick and practical high-resolution atmospheric dispersion simulation method that combines a large-eddy simulation (LES) model pre-simulation database (pre-sim DB) of wind conditions and onsite meteorological observation results, as proposed by the previous study. However, this framework was not quantitatively demonstrated using measurement data. In this study, we evaluated the performance of the wind condition reproduction and plume dispersion analysis methods. Air dose rates observed at monitoring posts around the stack were compared with the values reproduced by the method using the pre-sim DB, and the reproducibility of both air dose rate and flow field was discussed. The pre-sim DB-based method successfully captured the temporal variation of air dose rates at the monitoring posts, though it tended to overestimate the peak values. Particularly when the vertical wind shear was pronounced, the method using the pre-sim DB could cause significant errors. This is likely because the method relies on wind conditions from a single observation point, which inherently limits its ability to represent vertical wind shear within the pre-sim DB. Despite these limitations, particularly in reproducing complex wind fields, the method utilizing the pre-sim DB offers a valuable and practical tool for rapid dose rate simulation due to its lower computational cost compared to unsteady simulations using an LES model.
Kamiya, Junichiro; Wada, Kaoru*; Htwe, N. T. T.*
Journal of Vacuum Science and Technology B, 43(5), p.054204_1 - 054204_13, 2025/09
Times Cited Count：0 Percentile：0.00Yano, Yasuhide; Miyazawa, Takeshi; Tanno, Takashi; Akasaka, Naoaki; Yoshitake, Tsunemitsu; Kaito, Takeji; Otsuka, Satoshi
Journal of Nuclear Science and Technology, 62(8), p.748 - 755, 2025/08
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The effects of strain rate on tensile properties of irradiated modified 316 stainless steel (PNC316) claddings were investigated. PNC316 claddings were irradiated at the experimental fast reactor Joyo using CRT402 control rod assembly at 400
C up to 25 dpa. Post-irradiation ring tensile tests were carried out at strain rates of 3.3
10
, 3.310
and 3.310
s
at a test temperature of 350C. The results showed no obvious dependence of all strain rates on tensile properties, although a slight decrease in total elongation was observed at the slowest strain rate of 3.310 s. In addition, only a part of fracture surface at the slowest strain rate showed intergranular type region in the inner surface area, although the grain boundary separation occurred on inner surfaces near the fracture region at all strain rates. It is suggested that presence of a high content of helium near the inner surfaces would be related to the fracture behavior.
Sakamoto, Masahiro; Okumura, Keisuke; Kanno, Ikuo; Matsumura, Taichi; Terashima, Kenichi; Riyana, E. S.; Kaneko, Junichi*; Mizokami, Masato*; Mizokami, Shinya*
Journal of Nuclear Science and Technology, 62(8), p.756 - 765, 2025/08
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)
-Al
O
(0001) for use as an adsorbentEntani, Shiro*; Honda, Mitsunori; Takizawa, Masaru*; Koda, Makoto*
Beilstein Journal of Nanotechnology (Internet), 16, p.1082 - 1087, 2025/07
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：1 Percentile：63.96(Materials Science, Multidisciplinary)
Er(n,
)
Er and 
Hf(n,)
Hf reactionsNakamura, Shoji; Shibahara, Yuji*; Endo, Shunsuke; Rovira Leveroni, G.; Kimura, Atsushi
Journal of Nuclear Science and Technology, 62(7), p.617 - 630, 2025/07
Times Cited Count：1 Percentile：78.42(Nuclear Science & Technology)
Co inventory in the core of the Fukushima Daiichi Nuclear Power Plant; Contribution of fuel deposits to the reactor core inventoryUchida, Shunsuke*; Kino, Chiaki*; Karasawa, Hidetoshi; Takahatake, Yoko; Koma, Yoshikazu
Journal of Nuclear Science and Technology, 17 Pages, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Evaluation of radioactive nuclide behavior on and after the accident is important for the estimating radioactive nuclide composition in the wastes. The reactor core inventories have been obtained from the ORIGEN2 analysis, but the inventory of activation products is determined by the amount of their parent nuclides which are impurities contained in the structural materials. The ORIGEN2 does not treat fuel deposits including the impurities. Estimation of the initial Co-60 inventory in accurate is needed on the evaluation of some kinds of radioactive nuclide amount, since it is possible Co-60 is standard in the scaling factor. In this study, contribution of fuel deposits to the reactor core inventory was estimated by comparing the amount of Co-60 and Ni-63 calculated by the amounts of deposition by the microlayer-evaporation and drying-out model (MEDO model) and the result of the ORIGEN2 analysis, and then the method of estimating the reactor core inventory was proposed.
Murakami, Masashi; Yoshida, Yukihiko; Nango, Nobuhito*; Kubota, Shogo*; Kurosawa, Takuya*; Sasaki, Toshiki
Journal of Nuclear Science and Technology, 62(7), p.650 - 661, 2025/07
Times Cited Count：1 Percentile：78.42(Nuclear Science & Technology)
Ho(n,)
Ho reactionsNakamura, Shoji; Shibahara, Yuji*; Endo, Shunsuke; Rovira Leveroni, G.; Kimura, Atsushi
Journal of Nuclear Science and Technology, 14 Pages, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Hayakawa, Kosetsu*; Muraguchi, Masakazu*; Masebo, Yumeno*; Kojima, Yoichiro*; Oda, Masato*; Yabuta, Rina*; Ishii, Hiroyuki*; Honda, Mitsunori
e-Journal of Surface Science and Nanotechnology (Internet), p.2025-041_1 - 2025-041_6, 2025/07
We are developing materials using clay minerals for thermoelectric materials that can be used at high temperatures in environmental friendly applications. We have succeeded in obtaining thermoelectric properties at high temperatures, but we do not know why these properties are exhibited. In order to elucidate the structural changes of weathered biotite under high temperature conditions, we will develop an XAFS analysis method and clarify the local structure of Fe at high temperatures. The local structure analysis of Fe in samples sintered in atmospheric and vacuum environments reveals changes in the chemical bonding state of Fe.
Takei, Hayanori
Journal of Nuclear Science and Technology, 45 Pages, 2025/06
Times Cited Count：0 Percentile：0.00The Japan Atomic Energy Agency is working on the research and development of an accelerator-driven nuclear transmutation system (ADS) for transmuting minor actinides. This system combines a subcritical nuclear reactor with a high-power superconducting proton linear accelerator (JADS-linac). One of the factors limiting the advancement of the JADS-linac is beam trips, which often induce thermal cycle fatigue, thereby damaging the components in the subcritical core. The average beam current of the JADS-linac is 32 times higher than that of the linear accelerator (linac) of the Japan Proton Accelerator Research Complex (J-PARC). Therefore, according to the development stage, comparing the beam trip frequency of the JADS-linac with the allowable beam trip frequency (ABTF) is necessary. Herein the beam trip frequency of the JADS-linac was estimated through a Monte Carlo program using the reliability functions based on the operational data of the J-PARC linac. The Monte Carlo program afforded the distribution of the beam trip duration, which cannot be obtained using traditional analytical methods. Results show that the frequency of the beam trips with a duration exceeding 5 min must be reduced to 27% of the current J-PARC linac level to be below the ABTF.
Uesawa, Shinichiro; Yamashita, Susumu; Sano, Yoshihiko*; Yoshida, Hiroyuki
Journal of Nuclear Science and Technology, 62(6), p.523 - 541, 2025/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Japan Atomic Energy Agency (JAEA) has developed a numerical method with the JUPITER code with a porous medium model to calculate the thermal behavior in PCVs of 1F. In this study, we performed an experiment and numerical simulation of the natural convective heat transfer with the porous medium to validate JUPITER with the porous medium model. In comparison of the temperature and velocity distributions between the experiment and simulation, the temperature distribution in the simulation was in good agreement with the distribution in the experiment except the temperature near the top surface of the porous medium. The velocity distribution also agreed qualitatively with the experimental result. In addition, we also performed the numerical simulations with various effective thermal conductivity models to discuss the effect of the conductivity based on the internal structure of porous media on the natural convective heat transfer. The result indicated that the temperature distribution in the porous medium and the velocity distribution of the natural convection were significantly different for each model, and thus the conductivity of the fuel debris was one of the key parameters of in the thermal behavior analysis in 1F.
Sudo, Ayako; Sato, Takumi; Takano, Masahide
Journal of Nuclear Science and Technology, 62(6), p.573 - 581, 2025/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)During the progression of the severe accident at the Fukushima Daiichi Nuclear Power Station, seawater flowed down and was predicted to react with molten corium and concrete. For the removal and storage of fuel debris, knowing the effects of seawater components on the characteristics of reaction products in the fuel debris is crucial. To understand changes in the microstructure of fuel debris, a reaction test was conducted by introducing sea salt to simulated corium and concrete under a temperature gradient. Among the components of sea salt, sulfur formed iron sulfide during metallic precipitation. Analysis of vaporized species indicated that most of Cl, some Na and K in the sea salt might volatilize during heating rather than react with simulated corium and concrete. Calcium and a small amount of Mg, Na, and K in the sea salt might be trapped in the silicate glass.
Suzuki, Chikashi
Journal of Nuclear Science and Technology, 62(6), p.542 - 551, 2025/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Boron (B) can chemically react with cesium (Cs) to form Cs-B-O compounds and affect the chemical behavior of Cs during severe accidents. The author evaluated the thermal properties of solid Cs-B-O compounds using density functional theory and phonon vibration calculations with CsO and BO as solid reference materials. These evaluations indicate that the calculated thermal properties are in good agreement with the reported ones. The author calculated the reaction enthalpy and Gibbs free energy values of solid CsBO from CsO and BO to obtain fundamental data in solid systems. The deviations between the calculation and the reported data in this study are comparable with those in the previous study. The author estimated the Gibbs free energy values of the CsB
O
reaction from CsBO and boric acid. The differences between these estimations and those in the recent investigation are within the error of the reaction energies in the experiments.
Tsukimori, Kazuyuki; Yada, Hiroki
Journal of Pressure Vessel Technology, 147(3), p.031901_1 - 031901_9, 2025/06
Times Cited Count：0 Percentile：0.00(Engineering, Mechanical)After the accident at the Fukushima Daiichi Nuclear Power Plant, very strict safety measures were implemented for nuclear power plants in Japan. It thus becomes a crucial issue if the safety of a plant is maintained or not at beyond design basis events. In this study, head plates and bellows were examined as components that compose the parts of the boundary of vessels that contain the primary coolant of a prototype fast breeder reactor. The behaviors of buckling, post-buckling deformation, and penetration failure, that is, loss of boundary function of these components with increasing pressure were investigated. The series of this research program started in FY2013 and the research proceeded step by step. The new result in this paper is the application of the proposed criteria to head plates and bellows, and a conservative estimation of penetration failure of these components is obtained.
Hasegawa, Kunio; Yamaguchi, Yoshihito; Udyawar, A.*
Journal of Pressure Vessel Technology, 147(3), p.034501_1 - 034501_7, 2025/06
Times Cited Count：0 Percentile：0.00(Engineering, Mechanical)