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Nguyen, H. H.
Annals of Nuclear Energy, 230, p.112171_1 - 112171_13, 2026/06
This study examined the effects of the moderator-to-fuel volume ratio, fuel debris shape, and the number of damaged fuel assemblies on the neutronic characteristics of a partially damaged reactor model, where the fuel assemblies at the core center melt to fuel debris while the fuel assemblies at the outer region remain intact. The investigations were conducted using the Serpent code and the JENDL-5 library. The results show that when fuel debris is surrounded by intact fuel assemblies, the k
can be classified into two groups based on the shape of the fuel debris. Conversely, in scenarios where the fuel debris is not fully encircled by intact fuel assemblies, the shape of the fuel debris has a negligible impact on the k. Additionally, the relationship between the number of neutrons entering and leaving the fuel debris determines how the shape of the fuel debris affects the k.
Luu, V. N.; Taniguchi, Yoshinori; Udagawa, Yutaka; Tasaki, Yudai; Katsuyama, Jinya
Annals of Nuclear Energy, 230, p.112114_1 - 112114_14, 2026/06
Taniguchi, Yoshinori; Luu, V. N.; Tasaki, Yudai; Udagawa, Yutaka; Katsuyama, Jinya
Annals of Nuclear Energy, 231, p.112177_1 - 112177_16, 2026/06
Takamizawa, Hisashi; Nishiyama, Yutaka
Journal of Pressure Vessel Technology, 148(3), p.031501_1 - 031502_12, 2026/06
Embrittlement of reactor pressure vessel (RPV) steel caused by neutron irradiation has been evaluated using ductile-to-brittle transition temperature (DBTT) derived from surveillance tests (Charpy impact tests) during plant operation. For reliable structural integrity assessment of the RPV, incorporating adequate safety margins which take into account uncertainties inherent in surveillance Charpy impact tests is needed. In this study, a model to evaluate temperature dependence of Charpy absorbed energy variability using approximately 1,900 datasets of unirradiated and irradiated materials manufactured in Japan and United States was developed. Next, probability distribution of Charpy ductile-to-brittle transition temperature at a 41J energy level (
) was evaluated by estimating the probability distribution of Charpy test data using Monte Carlo sampling and Bayesian inference. From the detailed evaluation of the relationship between the number of specimens and uncertainty, uncertainty of was found to be almost the same in materials manufactured in Japan and U.S., and unchanged with neutron irradiation (no clear change in material inhomogeneity). Regarding product form on the other hand, uncertainty of for base metal and weld metal was almost the same, but the heat affected zone was shown to have large uncertainty.
Furuta, Takuya; Hashimoto, Shintaro; Ogawa, Tatsuhiko; Tanimura, Yoshihiko
Nuclear Instruments and Methods in Physics Research A, 1086, p.171320_1 - 171320_8, 2026/06
A new function to incorporate nuclear data libraries with outgoing particles plus residual nuclei in specific excitation states for neutron-induced reactions has been implemented in a Monte Carlo simulation code, Particle and Heavy Ion Transport code System (PHITS). With this function, accurate predictions of outgoing particle spectra and angular distributions according to the nuclear data libraries become possible, while accounting for production of residual nuclei and de-excitation gammas, conserving total energy and momentum in each event. This feature allows users to perform high-precision simulations of detector responses and radiation damage in materials.
Takayanagi, Tomohiro; Ueno, Tomoaki*; Horino, Koki*; Sugita, Moe; Fuwa, Yasuhiro; Shinozaki, Shinichi
IEEE Transactions on Applied Superconductivity, 36(3), p.4900905_1 - 4900905_5, 2026/05
Motegi, Kosuke; Shiotsu, Hiroyuki; Matsumoto, Toshinori; Hibiki, Takashi*; Shibamoto, Yasuteru
International Journal of Heat and Mass Transfer, 258, p.128275_1 - 128275_15, 2026/05
Kreinder, B.; Cox, I.*; Grzywacz, R.*; Nishio, Katsuhisa; 24 of others*
Nuclear Instruments and Methods in Physics Research A, 1085, p.171298_1 - 171298_7, 2026/05
Shiotsu, Hiroyuki
Progress in Nuclear Energy, 195, p.106300_1 - 106300_11, 2026/05
Kondo, Masatoshi*; Kitamura, Yoshiki*; Kawarai, Atsushi*; Saito, Shigeru; Obayashi, Hironari
Corrosion Science, 262, p.113646_1 - 113646_14, 2026/04
The corrosion resistance of FeCrAl alloy APMT (Fe-21Cr-5Al-3Mo) in flowing lead-bismuth eutectic (LBE) was investigated by corrosion tests performed at 723 K using a non-isothermal forced convection loop. The oxygen concentration in flowing LBE was controlled at 1
10
wt%. No severe corrosion or erosion was detected on the specimens exposed to flowing LBE for 2000 h and 4000 h. Multiple oxide layers consisting of Fe-rich, Cr-rich and Al-rich sub-layers were formed in situ on the surface of APMT during the corrosion tests, which effectively suppressed corrosion and erosion. The oxide layers were intentionally removed by gentle abrasion prior to re-immersion and the specimens were then re-immersed in flowing LBE for an additional 2000 h. The oxide layers were spontaneously re-formed in situ on the abraded surface. This behavior indicates a self-healing capability. The results of micro-scratch tests indicated that the in-situ formed multiple oxide layers exhibited high adhesion strength in the shear direction after the 2000 h corrosion test.
Mohamad, A. B.; Chen, J.*; Ioka, Ikuo*; Suzuki, Eriko; Kondo, Keietsu; Abe, Yosuke; Yamashita, Shinichiro; Okubo, Nariaki; Nemoto, Yoshiyuki; Okada, Yuji*; et al.
Journal of Nuclear Materials, 625, p.156513_1 - 156513_9, 2026/04
Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Onizawa, Kunio
Journal of Pressure Vessel Technology, 148(2), p.021504_1 - 021504_10, 2026/04
In the current structural integrity assessment of the reactor pressure vessel, the accurate reference temperature (T
) based on the Master Curve method is necessary. The T can be estimated by using the Mini-C(T) fracture toughness specimen in accordance with ASTM E1921 and JEAC4216, which prescribe the crack straightness criteria. A requirement in ASTM E1921 has been revised in a decade to increase the accuracy and reasonability, and the applicable crack curvature has been varied by applied codes. The crack curvature of the Mini-C(T) specimen might have an impact on the T because of the variation of the plastic constraint. In this work, the effect of the crack curvature on the fracture toughness (K
) evaluation using the Mini-C(T) specimen was quantitatively evaluated by using the finite element analysis (FEA) including the Weibull stress analysis, to discuss the difference in a requirement of the crack straightness in ASTM E1921 and JEAC4216. FEAs showed a possibility that the upper limit curvature would decrease the plastic constraint, and consequently obtain higher K in the Mini-C(T) specimen. Furthermore, if the upper limit curvature according to the ASTM E1921-21 was allowed, the T would be estimated as nonconservative based on the Weibull stress analysis. In contrast, the difference in (T) between the crack with upper limit curvature according to JEAC4216 and the ideal straight crack was not significant.
Yamada, Ippei; Kojima, Kunihiro; Chimura, Motoki
Nuclear Instruments and Methods in Physics Research A, 1084, p.171261_1 - 171261_12, 2026/04
no abstracts in English
Okagaki, Yuria; Hibiki, Takashi*
Progress in Nuclear Energy, 194, p.106267_1 - 106267_23, 2026/04
:Ce using PHITS track-structure simulationsHirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko; Watanabe, Kenichi*; Kato, Takumi*; Kawaguchi, Noriaki*; Yanagida, Takayuki*
Radiation Measurements, 193, p.107651_1 - 107651_8, 2026/04
CaF:Ce has a high potential to be used as a dosimeter due to its high optically stimulated luminescence (OSL) intensity. However, when phosphors such as CaF:Ce are irradiated with swift ions, the OSL intensity per dose decreases due to quenching effects. Traditionally, quenching effects in phosphors have been evaluated based on energy deposition density, using linear energy transfer (LET) as a metric. However, the relationship between quenching effects and LET varies with ion type, complicating unified evaluations. The track structure in PHITS can precisely simulate the radiation interactions. In this study, we simulated the detector response of CaF:Ce irradiated with swift-ions and compared these results with experimental data. The comparison suggests that the quantum yield of OSL is a critical parameter influencing the quenching effect in CaF:Ce. These findings are expected to contribute to the development of improved phosphor detectors.
Mikami, Nao; Aizawa, Kosuke; Kurihara, Akikazu; Ueki, Yoshitaka*
AI Thermal Fluids (Internet), 5, p.100029_1 - 100029_15, 2026/03
Yamane, Towa*; Inatsu, Masaru*; Kawano, Jun*; Sato, Takuto; Kusaka, Hiroyuki*
Agricultural and Forest Meteorology, 379, p.111052_1 - 111052_9, 2026/03
This study aims to obtain fundamental information on birch pollen deposition data by field observation for the high-resolution, accurate pollen modeling. On the peak dispersal day in 2024, simple pollen collectors were installed just below and at three downwind points of an isolated birch tree line in Ebetsu, Hokkaido, Japan. Meteorological observation were also conducted at the site during the days. The birch pollen captured on slide glasses was imaged by a microscope. We first developed the automatic pollen counting technique by applying a machine learning algorithm YOLO to the images. This technique was validated by comparison with subjective counting, and we successfully achieved the automatic counting that has never been done before. The results suggested that the pollen count was highest in the point 200 m downstream from the tree line and diurnal variations were observed at all distances. A simple linear regression analysis of pollen count and meteorological factors revealed a significant positive correlation with temperature. Additionally, a positive correlation with wind speed was also found only at the point just below the tree line. The large-eddy simulation with the pollen advection supported the observation results, though the pollen deposition position was more concentrated near the tree in the simulation.
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：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.
-ray beam measurementsOmer, M.; Shizuma, Toshiyuki*; Koizumi, Mitsuo; Taira, Yoshitaka*; Zen, H.*; Ogaki, Hideaki*; Hajima, Ryoichi*
Radiation Physics and Chemistry, 240, p.113467_1 - 113467_8, 2026/03
Ueno, Katsuhiro; Ouchi, Kazuki; Watanabe, Masayuki
Results in Engineering (Internet), 29, p.109246_1 - 109246_10, 2026/03
