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Luu, V. N.; Taniguchi, Yoshinori; Udagawa, Yutaka; Tasaki, Yudai; Katsuyama, Jinya
Annals of Nuclear Energy, 230, p.112114_1 - 112114_14, 2026/06
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.
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
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
Mikami, Nao; Aizawa, Kosuke; Kurihara, Akikazu; Ueki, Yoshitaka*
AI Thermal Fluids (Internet), 5, p.100029_1 - 100029_15, 2026/03
-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
Yoshimura, Kazuo; Doda, Norihiro; Tanaka, Masaaki; Fujisaki, Tatsuya*; Murakami, Satoshi*
Annals of Nuclear Energy, 226, p.111896_1 - 111896_11, 2026/02
At the Japan Atomic Energy Agency, a multilevel simulation (MLS) methodology which enables consistent evaluation from whole plant behavior to local phenomena in the plant components is being developed to attempt plant design and enhance the safety of sodium-cooled fast reactors. To validate the coupling method in the MLS system, the 1D-CFD coupling method using Super-COPD for 1D plant dynamics analysis and Fluent for multi-dimensional CFD analysis was applied to the analyses of loss of flow tests in EBR-II. It was confirmed that it could predict multi-dimensional thermal-hydraulic phenomena such as thermal stratification in the upper plenum, Z-shaped pipe, and cold pool, holding the whole plant behavior simultaneously. Moreover, the applicability of the 1D-CFD coupling method to the evaluation of the phenomena in natural circulation conditions was confirmed by comparing the results of the 1D-CFD couple analyses and the measured data.
Kawaguchi, Munemichi*; Ikeda, Asuka; Saito, Junichi
Annals of Nuclear Energy, 226, p.111880_1 - 111880_9, 2026/02
Times Cited Count：0Kwon, Saerom*; Konno, Chikara; Honda, Shogo*; Kenjo, Shunsuke*; Sato, Satoshi*
Fusion Engineering and Design, 223, p.115548_1 - 115548_8, 2026/02
In order to evaluate the accuracy of the iron data in the latest nuclear data libraries (FENDL-3.2b, JENDL-5, ENDF/B-VIII.0 and JEFF-3.3) used in the fusion neutron source design, we performed their benchmark tests by using QST/TIARA iron experiment with quasi mono-energy neutrons of 40 and 65 MeV and JAEA/FNS iron experiment with DT neutrons. From the test results, we have found the following issues; (1) The calculation results with FENDL-3.2b underestimate the measured neutron fluxes of the continuous energy range (10-60 MeV) by a factor of 0.6 in the TIARA experiment with 65 MeV neutrons; (2) The calculation results with FENDL-3.2b tend to underestimate the measured neutron flux above 10 MeV by a factor of 0.8 at depth of 70 cm and overestimate the measured ones below 10 keV by a factor of 1.3 up to depth of 40 cm in the FNS experiment. We investigated those issues in detail and clarified their reasons.
Takito, Kiyotaka; Okuda, Yukihiko; Nakamura, Izumi*; Furuya, Osamu*
Haikan Gijutsu, 68(2), p.1 - 7, 2026/02
no abstracts in English
Wang, Z.; Shibamoto, Yasuteru
International Journal of Heat and Mass Transfer, 255(Part 1), p.127701_1 - 127701_16, 2026/02
Times Cited Count：0Sugihara, Kenta; Onodera, Naoyuki*; Idomura, Yasuhiro; Sitompul, Y.; Yamashita, Susumu
Journal of Computational Physics, 547, p.114534_1 - 114534_25, 2026/02
Yoshida, Ryu*; Kurikami, Hiroshi; Nagao, Fumiya; Takahashi, Shigeo*; Sanada, Yukihisa
Journal of Environmental Radioactivity, 293, p.107900_1 - 10790_13, 2026/02
underwater radiation monitoring detectorJi, W.*; Lee, E.*; Ji, Y.-Y.*; Ochi, Kotaro; Yoshimura, Kazuya; Funaki, Hironori; Sanada, Yukihisa
Nuclear Engineering and Technology, 58(2), p.103933_1 - 103933_6, 2026/02
We aimed to validate the performance of an in situ underwater radiation detector, MARK-U1 (Monitoring of Ambient Radiation of KAERI - Underwater), was used to estimate 
Cs activity concentration in river and reservoir sediment at predicted sites of contamination. Additionally, underwater core samples were collected to measure the radioactivity using a high-purity germanium (HPGe) detector. To estimate radioactivity, a conversion factor was derived by comparing the measured spectrum and Cs activity in the sample. A Monte Carlo N-Particle (MCNP) simulation was conducted to determine the effective source geometry for in situ measurement. The simulation results correlated well with the on-site MARK-U1 monitoring results, with a deviation of 31.62%. These findings validate the performance of the in situ detector. This device can therefore be used to estimate Cs activity concentration in the underwater sediment via on-site monitoring, without requiring sample collection.
RhZhang, J. Z.*; Chen, Z. Q.*; Qu, T.*; Wang, Y. K.*; Li, Z. H.*; Orlandi, R.; 62 of others*
Physics Letters B, 873, p.140144_1 - 140144_9, 2026/02
Cs in stream water in forested catchmentsSakuma, Kazuyuki; Yoshimura, Kazuya; Nakanishi, Takahiro; Hayashi, Seiji*; Tsuji, Hideki*; Funaki, Hironori; Iijima, Kazuki
Science of the Total Environment, 1014, p.181397_1 - 181397_9, 2026/02
The Fukushima Daiichi Nuclear Power Plant accident released substantial radiocesium into terrestrial environments in 2011. Understanding the sources of dissolved radiocesium and the factors controlling its seasonal variation in stream water is crucial for assessing and mitigating environmental radioactive contamination. From 2015 to 2021, we investigated dissolved Cs concentrations and dissolved organic carbon (DOC) in stream water, spring water, groundwater, litter leachate, soil pore water, and infiltrated water. In the headwater area, dissolved Cs concentrations increased just after spring compared to the concentrations in the groundwater. During approximately three years of stream water monitoring, dissolved Cs concentrations correlated with water temperature, concentrations of DOC, and K
. A three-component mixture model revealed that stream water composition is derived mainly from groundwater, leaching from forest litter/surface soil, and soil pore water. The soil pore water particularly influenced summer stream water, likely due to the water table fluctuations with precipitation. The leaching water also influenced the summer stream water compared to the winter stream water. These findings suggest that seasonal variations in dissolved Cs are driven by temperature-dependent leaching from surface forest litter/soil and increased contributions from soil pore water. This study is the first to identify the sources and seasonal drivers of dissolved Cs in forested headwater streams.
Tokumitsu, Shun*; Matsumiya, Masahiko*; Sasaki, Yuji
Separation and Purification Technology, 382(Part 2), p.135631_1 - 135631_9, 2026/02
Nakajima, Ryota; Sakai, Tatsuya; Tani, Riku; Handa, Yuichi; Sunaoshi, Mizuho*; Inoue, Hidetaka*; Yamada, Satoshi; Shimizu, Osamu
JAEA-Technology 2025-012, 39 Pages, 2026/01
JAEA-Technology-2025-012.pdf:2.31MB
JAERI's Reprocessing Test Facility (JRTF) has transition to decommissioning since 1996 and inside the facility dismantled equipment and instrument. In the dismantling and removal work of glove boxes and other equipment, starting in October 2022, we prepared a "Manual for Separation of Dismantled Materials of JRTF" and carried out sorting and separation of the generated dismantled waste with the aim of producing waste package that meets the technical standards required for disposal to a landfill facility. This report describes the results and findings of sorting and separating the dismantled waste generated during the dismantling and removal work of glove boxes and other equipment in accordance with the "Manual for Separation of Dismantled Materials of JRTF".
