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Nguyen, H. H.
Annals of Nuclear Energy, 240, p.112711_1 - 112711_14, 2027/01
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)This study employed the external source mode of the Serpent code to evaluate the individual contributions of the fuel debris region and the intact fuel region to the neutronic characteristics of the two-region damaged reactor model, as well as to analyze the interactions between these two regions. It also examined how factors such as system temperature, boron concentration in the moderator, and the number of damaged assemblies influenced the outcomes. The results indicate that variations in system temperature or boron concentration do not affect the patterns of source parameters. However, these factors influence the coupling strength between the two regions. Furthermore, an increase in the number of damaged assemblies leads to a decrease in the coupling strength between the fuel debris and intact fuel regions.
Cs behavior in the ocean around Fukushima considering multiphase interaction processesIkenoue, Tsubasa; Nakanishi, Takahiro; Kawamura, Hideyuki
Marine Pollution Bulletin, 232, p.120110_1 - 120110_9, 2026/11
Times Cited Count：0 Percentile：0.00(Environmental Sciences)The accident at the Fukushima Daiichi Nuclear Power Plant caused a large-scale migration of radionuclides, including cesium-137 (Cs), into the marine environment. Cesium-137 in the ocean exists in four phases (dissolved, suspended, seabed sediment, and biota), and the interactions between these phases have a great impact on its long-term behavior. Therefore, this study developed an oceanic dispersion model considering multiphase behavior and evaluated the impact of interphase interactions on the long-term behavior of Cs during the decade after the accident. The model sufficiently reproduced the oceanographic conditions and the behavior of planktons, suspended particles, and Cs. The results were consistent with previous studies, suggesting that the dissolved phase and seabed sediment phase played a central role in the Cs behavior within the first three months after the accident and thereafter, respectively. Within 10 years after the accident, the concentrations of all phases in offshore waters (deeper than 25 m) returned to pre-accident levels, but those in coastal waters (shallower than 25 m) were still at high levels due to the long-term source from seabed sediment to other phases, which is attributed to the retention of high concentrations in the seabed sediment phase. The quantitative analysis of interphase interactions made it possible to confirm that this retention was caused by a large proportion of fine-grained particles (bay area), riverine inputs (northern Fukushima), and high accumulation in the surface layers in the early stage of the accident and vigorous vertical mixing (southern Fukushima).
Collaborative Laboratories for Advanced Decommissioning Science; Hokkaido University*
JAEA-Review 2026-017, 78 Pages, 2026/09
JAEA-Review-2026-017.pdf:5.67MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2023, this report summarizes the research results of the "Development of a prototype shielding-free radiation-resistant diamond neutron measurement system" conducted in FY2024. The present study aims to develop a prototype shielding-free neutron measurement system for 1F. The system consists of diamond neutron detectors and radiation-resistant silicon integrated circuits, and future applications are expected to include neutron detectors for debris investigation, criticality proximity monitoring monitors, and neutron detectors for dry tube investigation in pressure vessels. In this development, a prototype consisting of 100 diamond detector elements of 5 mm square will be developed to obtain system construction technology and to evaluate system performance. In addition, a subcriticality evaluation method will be developed. In FY2024, Hokkaido Univ. made progress in establishing mass-production technology for self-supporting diamond detector elements. At AIST, the search for deposition conditions of multilayer films for detectors using the CVD method advanced. At KEK, the operation of the improved ASIC was confirmed, and using a wiring printing device, detector elements were mounted on signal processing circuit boards, followed by neutron measurement tests. The development of a criticality proximity monitoring method, led mainly by Nagoya Univ., advanced in its fundamental studies, and an evaluation test of the diamond neutron measurement system at UTR-KINKI is planned. At Kyushu Univ. and JAEA, evaluations of the diamond neutron measurement system in gamma-ray irradiation fields and thermal neutron isotropic fields proceeded as scheduled.
under high temperatures and various water vapor concentrationsMohamad, A. B.; Nakajima, Kunihisa; Imoto, Jumpei*; Takano, Masahide
Journal of Nuclear Materials, 631, p.156826_1 - 156826_12, 2026/09
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Fukuda, Kodai; Shiba, Shigeki*; Iwahashi, Daiki*; Gunji, Satoshi
Journal of Nuclear Science and Technology, 63(9), p.1001 - 1014, 2026/09
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Liu, X.*; Funatani, Shumpei*; Takamatsu, Kuniyoshi
Proceedings of the 15th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-15) (Internet), 13 Pages, 2026/09
A fundamental study on a new passive radiation cooling system for HTGRs has been conducted. A heat transfer test equipment called 'a scale model' generates natural convection and radiation inside the scale model. The heat flux (approximately 3 kW/m
) needs to be removed from the RPV as heat loss during rated operation for practical HTGRs with a maximum thermal reactor power of 600 MWt. The experimental results demonstrated that the passive radiation cooling system effectively removed heat dissipation from the RPV, confirming its feasibility. Additionally, downsizing the passive radiation cooling system by shortening the overall length did not significantly affect its performance. Shortening the overall length increases its temperature; therefore, the overall length should be adjusted to stay within the structural temperature limits. Moreover, an increase of outside temperature surrounding the passive radiation cooling system did not significantly affect the performance.
CsKobayashi, Hikaru*; Ma, X.*; Suto, Masahito*; Yamamori, Ryo*; Furuta, Takuya
Radiation Measurements, 197, p.107743_1 - 107743_13, 2026/09
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Monte Carlo photon transport simulations are widely used to predict indoor dose distributions from Cs-137 ground deposition, but their computational cost can be high. To improve efficiency, we propose the fluence boundary method (FBM), which accounts for contributions from distant sources by applying analyzed photon fluence profiles at near-site boundaries surrounding a building. These profiles are defined according to the land-cover type adjacent to each boundary. The method was validated by comparing FBM results with full simulations, demonstrating that FBM achieved a maximum absolute percentage error below 5% across indoor dose distributions. The feasibility of representing fluence boundaries using land-cover types was further examined by evaluating the impact of uncertainties in relaxation mass depth (
) for paved and soil surfaces. The normalized indoor dose distributions showed weak dependence on within a reasonable range, indicating that indoor dose distributions can be reliably predicted using representative values when doses are normalized to measurements.
Gil, J.; Itakura, Mitsuhiro; Kobayashi, Keita
Computational Materials Science, 273, p.114924_1 - 114924_10, 2026/08
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Accurate impurity thermodynamics is important for modeling corrosion and mass transport in liquid metals, but direct first-principles simulations are computationally expensive. We combined SCAN-family density-functional calculations with machine-learning molecular dynamics to evaluate oxygen solution enthalpy in liquid sodium. Machine-learning interatomic potentials trained on SCAN, rSCAN, and rSCAN data enabled extensive liquid-state sampling at near-first-principles accuracy. The calculated values agreed with experimental estimates without empirical corrections to molecular oxygen. This suggests that the main error in the conventional PBE method arises from the gas-phase oxygen reference rather than the liquid-state description. The results demonstrate an accurate and scalable approach to impurity thermodynamics in liquid metals.
Jing, Z.*; Yamaguchi, Toshio*; Hattori, Takanori; Yamada, Takeshi*; Tamatsukuri, Hiromu; Matsuura, Masato*; Zhou, Y.*
Journal of Physical Chemistry Letters (Internet), 17(29), p.8419 - 8428, 2026/07
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)We conducted high-pressure neutron diffraction and quasielastic neutron scattering on a series of aqueous alkaline chloride solutions and clarified that the pressure- and ion-induced modifications to the water structure and diffusion originate from distinct physical mechanisms. Applying gigapascal pressure transforms the tetrahedral hydrogen-bonded network structure of water into a dense random packing, due to the collapse of the second and third coordination shells and an increase in the number of interstitial water molecules, regardless of the ion species. On the contrary, dissolved ions disturb the second shell but preserve the inherent tetrahedral network structure of water at ambient pressure. The anomalous trend of water diffusion from Li
to Cs under the ambient conditions disappears under the gigapascal pressure, and all the ions show a behavior of structure-making ions.
Nguyen, H. H.
Annals of Nuclear Energy, 230, p.112171_1 - 112171_13, 2026/06
Times Cited Count：2 Percentile：95.64(Nuclear Science & Technology)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.
Gubarevich, A.*; Kubo, Ryotaro*; Arisaka, Makoto; Osugi, Takeshi; Yoshida, Katsumi*; Takeshita, Kenji*
Journal of Nuclear Science and Technology, 63(6), p.667 - 676, 2026/06
Times Cited Count：3 Percentile：37.36(Nuclear Science & Technology)To immobilize and solidify carbonate-based Advanced Liquid Processing System (ALPS) sediment wastes, this study introduces a chemical transformation process that converts these wastes into calcium and magnesium phosphate phases, followed by densification using a novel cold sintering press (CSP) technique. Simulated calcium-magnesium carbonate slurries were treated with phosphoric acid to synthesize calcium and magnesium phosphates, which were then sintered at 300-500
C using CSP. The effects of the calcium-to-magnesium ratio, strontium incorporation, and sodium chloride addition on phase composition and CSP densification were investigated. Dense bulk samples were successfully fabricated and characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and the Archimedes method. The results showed that the chemical transformation process led to the formation of whitlockite and newberyite, with the calcium-to-magnesium ratio determining the relative proportions of these phases. Strontium was effectively incorporated into the whitlockite crystal structure, while newberyite enhanced densification through a dehydration-driven process. Sodium chloride had no effect on chemical transformation and was not found in the final solid product. These results show that direct conversion of calcium-magnesium carbonate slurries to whitlockite-based phosphate ceramics, followed by CSP, enables stable solidification, making this method promising for ALPS sediment waste management.
Tada, Kenichi
Kaku Deta Nyusu (Internet), (144), p.17 - 29, 2026/06
This document provides an overview of the international conference on reactor physics, Physor2026, and explains research presentations related to nuclear data for the Japanese nuclear data community.
Hagiwara, Hiroki; Kosuge, Atsushi; Saito, Junichi; Namie, Masanari; Kisohara, Naoyuki; Minehara, Eisuke*; Tsuboi, Akihiko; Ishimori, Yuu
Next Research (Internet), 8, p.101581_1 - 101581_9, 2026/06
Fukuda, Kodai; Obara, Toru*
Nuclear Technology, 212(6), p.1567 - 1578, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)
I seawater concentrations off Fukushima and potential of 129I as an oceanographic tracer for ALPS-treated waterSuzuki, Takashi; Otosaka, Shigeyoshi*; Takata, Hyoe*; Kuwabara, Jun; Nakanishi, Takahiro; Ikenoue, Tsubasa
Environmental Science & Technology, 60(17), p.13123 - 13131, 2026/05
Times Cited Count：0 Percentile：0.00(Engineering, Environmental)As a results of the 2011 Fukushima Daiichi Nuclear Power Plant accident, long-lived radioactive I has been released into the environment, with additional releases beginning in 2023 through ALPS-treated water. To study its long-term variation and potential as an oceanographic tracer, I concentrations in seawater off Fukushima were measured from 2012 to 2024. The highest concentration, 445
10
Bq/L, was observed in 2013 near the plant. Levels have since declined toward the pre-accident value of 1.7610 Bq/L. Spatial and temporal changes in the I/Cs ratio indicate the influence of small water masses and support its use as a tracer in areas with complex ocean circulation.
Shiotsu, Hiroyuki
Progress in Nuclear Energy, 195, p.106300_1 - 106300_11, 2026/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Batsaikhan, M.; Oba, Hironori*; Karino, Takahiro; Akaoka, Katsuaki; Wakaida, Ikuo*; Iwata, Yoshihiro; Sakamoto, Kan*
Journal of Analytical Atomic Spectrometry, 41(4), p.1324 - 1335, 2026/04
Times Cited Count：0 Percentile：0.00(Chemistry, Analytical)8 pin bundleLiong, C.*; Endo, Tomohiro*; Tada, Kenichi; Yamamoto, Akio*
Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04
A Deep Neural Network (DNN) is applied to predicting pin-wise coolant void and temperature distributions in a BWR 88 bundle for the neutronics/thermal-hydraulics multi-physics coupling simulation. The calculation results, obtained through precise neutronics and thermal-hydraulics simulations on a Boiling Water Reactor (BWR) 88 bundle under with and without control blade conditions, serve as the training data for the DNN model. In the DNN model, the pin-wise coolant void fraction and temperature radial distributions at the lower axial mesh, and the pin power radial distribution at the current axial mesh, are used to predict the coolant void fraction and temperature radial distributions at the current axial mesh. The DNN model makes accurate predictions for void fraction and temperature distributions at the no control blade case, although slight biases are observed in the control blade insertion case.
Moribe, Taiyo*; Ohashi, Ryonosuke*; Hirota, Ryoga*; Yamamoto, Akio*; Endo, Tomohiro*; Araki, Shohei; Gunji, Satoshi
Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04
Tada, Kenichi; Kondo, Ryoichi; Kamiya, Tomohiro; Fukuda, Takanari; Fukuda, Kodai; Ono, Ayako; Nagaya, Yasunobu; Yoshida, Hiroyuki
Proceedings of International Conference on the Physics of Reactors (PHYSOR 2026) (Internet), 8 Pages, 2026/04
High-fidelity multi-physics simulations are important for the verification of core design codes. JAEA is developing a high-fidelity multi-physics platform JAMPAN to couple many single-physics codes. This paper demonstrates the BWR whole core neutronics and thermal-hydraulics coupling simulation using the continuous energy Monte Carlo calculation code MVP and the three-field subchannel code NASCA. The initial loading core of Peach Bottom Unit 2 obtained from the OECD/NEA Peach Bottom turbine trip benchmark was used for the BWR core calculations. The k-effective value and the axial fission rate distribution in each assembly converged in about 20 seconds (10 iterations) from the initial state. The axial fission rate distribution in each assembly is physically reasonable. These calculation results indicate that JAMPAN appropriately couples the neutronics and thermal-hydraulics calculations for the BWR whole core geometry.
