Neutronic characteristics of a partially damaged reactor model with varying numbers of damaged fuel assemblies

Nguyen, H. H.

Annals of Nuclear Energy, 230, p.112171_1 - 112171_13, 2026/06

https://doi.org/10.1016/j.anucene.2026.112171

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.

Implementation of a new function for handling nuclear data of outgoing particles and residual excitation states in PHITS

Furuta, Takuya; Hashimoto, Shintaro; Ogawa, Tatsuhiko; Tanimura, Yoshihiko

Nuclear Instruments and Methods in Physics Research A, 1086, p.171320_1 - 171320_8, 2026/06

https://doi.org/10.1016/j.nima.2026.171320

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.

Chemical kinetic uncertainty quantification for Reynolds-Averaged Navier-Stokes simulations of turbulent premixed combustion

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

https://doi.org/10.1016/j.ijheatmasstransfer.2025.128275

Analysis of the effect of crack curvature in Mini-C(T) specimen on fracture toughness evaluation

Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Onizawa, Kunio

Journal of Pressure Vessel Technology, 148(2), p.021504_1 - 021504_10, 2026/04

https://doi.org/10.1115/1.4070669

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.

Modeling terminal velocity and aspect ratio of a single bubble in distorted-particle and cap bubble regimes for pool scrubbing simulation

Okagaki, Yuria; Hibiki, Takashi*

Progress in Nuclear Energy, 194, p.106267_1 - 106267_23, 2026/04

https://doi.org/10.1016/j.pnucene.2026.106267

Short-distance dispersion of birch pollen

Yamane, Towa*; Inatsu, Masaru*; Kawano, Jun*; Sato, Takuto; Kusaka, Hiroyuki*

Agricultural and Forest Meteorology, 379, p.111052_1 - 111052_9, 2026/03

https://doi.org/10.1016/j.agrformet.2026.111052

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.

A Fundamental study on clarifying the potential performance of a new rechargeable battery using uranium as an active material

Ueno, Katsuhiro; Ouchi, Kazuki; Watanabe, Masayuki

Results in Engineering (Internet), 29, p.109246_1 - 109246_10, 2026/03

https://doi.org/10.1016/j.rineng.2026.109246

Development of a high-resolution imaging camera for alpha dust and high-dose rate monitor (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2025-048, 56 Pages, 2026/02

JAEA-Review-2025-048.pdf:2.89MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2023. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, 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 FY2022, this report summarizes the research results of the "Development of a high-resolution imaging camera for alpha dust and high-dose rate monitor" conducted in FY2023. The present study aims to develop a high-resolution imaging camera for alpha dust and a high-dose rate monitor. To realize the high-resolution imaging camera for alpha dust, we have developed novel scintillation materials with emission bands of 500-800 nm. Moreover, we have prepared several materials for the camera and software. We have also developed novel scintillation materials with emission bands of 650-1,000 nm, and simulation studies have been conducted for the high-dose-rate monitor system consisting of optical fiber. In addition, we demonstrated this monitoring system, and the dose-rate dynamic range was found to be 20 mSv/h to 1 kSv/h.

Development of 1D-CFD coupling method for natural circulation analyses through benchmark analyses of shutdown heat removal tests in EBR-II

Yoshimura, Kazuo; Doda, Norihiro; Tanaka, Masaaki; Fujisaki, Tatsuya*; Murakami, Satoshi*

Annals of Nuclear Energy, 226, p.111896_1 - 111896_11, 2026/02

https://doi.org/10.1016/j.anucene.2025.111896

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.

Benchmarks of iron nuclear data for fusion neutron sources

Kwon, Saerom*; Konno, Chikara; Honda, Shogo*; Kenjo, Shunsuke*; Sato, Satoshi*

Fusion Engineering and Design, 223, p.115548_1 - 115548_8, 2026/02

https://doi.org/10.1016/j.fusengdes.2025.115548

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.