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.

International benchmark on radionuclide solubility and speciation for the Long-term In-situ Test (LIT) at Grimsel Test Site (GTS, Switzerland)

Noseck, U.*; Schfer, T.*; Alonso, U.*; Hamamoto, Takafumi*; Havlova, V.*; Hibberd, R.*; Ishidera, Takamitsu; Kitamura, Akira; Klajmon, M.*; Missana, T.*; et al.

Applied Geochemistry, 201, p.106762_1 - 106762_23, 2026/04

https://doi.org/10.1016/j.apgeochem.2026.106762

Thermodynamic benchmark calculations have been performed to better understand the behavior of Se(VI), Tc(VII), U(VI), Np(V), Am(III), Th(IV) and Pu(IV)) in the evolving geochemical conditions of the Long-term In-situ Test (LIT) at the Grimsel Test Site (GTS) and corresponding mock-up experiment. It also aims to identify the status of the geochemical speciation models and databases for these elements. The experiments are simulating the near-field conditions in some radioactive waste repository concept including a bentonite engineered barrier emplaced in crystalline rock and the findings are contributing to the long-term safety assessment of these facilities.

Production of JENDL-5 AMPX libraries

Konno, Chikara

JAEA-Data/Code 2025-019, 70 Pages, 2026/03

JAEA-Data-Code-2025-019.pdf:4.47MB

AMPX format libraries were produced from the evaluated nuclear data library JENDL-5 to make JENDL-5 usable in the US nuclear safety analysis code systems SCALE6.2 and SCALE6.3, which are widely used in Japan. The produced libraries are an AMPX continuous energy library, AMPX multigroup libraries and AMPX covariance libraries. This report explains in detail how to produce the libraries and describes test calculation results for verification of the AMPX libraries.

Cesium sorption onto alkaline activated materials

Hagiwara, Hiroki; Takaku, Atsushi*; Sagawa, Hiroshi*; Kanno, Futoshi*; Ito, Azusa; Ando, Taichi*; Ichihara, Masatsugu*; Watanabe, Yusuke; Koarai, Kazuma; Kato, Jun; et al.

Proceedings of Waste Management Symposia 2026 (WM2026) (Internet), 7 Pages, 2026/03

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.

Validation of underwater radiation monitoring detector

Ji, 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

https://doi.org/10.1016/j.net.2025.103933

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.

Development of an innovative n/ scintillation detection system for simple non-destructive measurements (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2025-046, 70 Pages, 2026/01

JAEA-Review-2025-046.pdf:5.46MB

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 (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 an innovative n/ scintillation detection system for simple non-destructive measurements" conducted in FY2023. At 1F, removal of fuel debris from the primary containment vessel (PCV) is scheduled for FY2023, and a phased expansion of the removal scale is being considered in the future. As a solution to the above problem, this study will develop an innovative scintillation radiation detection system for screening and continuous monitoring during target sample removal. To develop a remote measurement system that contributes to in-vessel investigations for decommissioning of nuclear facilities such as 1F. More specifically, we will develop vertically integrated research into the following elemental technologies: (1) development of innovative high-performance scintillation materials for thermal neutron / gamma-ray discrimination (Tohoku University), (2) downsizing of censer and signal processing system (the University of Tokyo), (3) construction and characterization of various radiation fields (National Institute of Advanced Industrial Science and Technology), and (4) development of a simple non-destructive measurement system and hot cell demonstration test (JAEA). By vertically integrating elemental technologies, R&D on each research item planned in FY2023 was conducted to develop a detector that can discriminate gamma-ray and neutron radiation in environments exceeding 10 Gy/h and simultaneously identify the dose rate and nuclide of each in PCVs and in each acceptance cell.

Mutual separation of Ru, Rh, and Pd via reflux-assisted extraction and reverse-extraction using ion-pair and solvation with S- and amino-N-donor reagents

Sasaki, Yuji; Kaneko, Masashi; Matsumiya, Masahiko*; Kumagai, Yuta

Journal of Molecular Liquids, 441, p.129013_1 - 129013_10, 2026/01

https://doi.org/10.1016/j.molliq.2025.129013

This study determined extraction and back-extraction conditions for the mutual separation of three light PGMs, Ru, Rh, and Pd. Results revealed that reagents containing soft N and S donor atoms efficiently extract and strip Pd through solvation. In comparison, Ru and Rh undergo ion-pair extraction, requiring both anionic metal species and cationic extractants. These essential chlorinated PGM anions and protonated extractants having amino N atoms are present in HCl media. D(Ru) and D(Rh) values of approximately 100 and 10, respectively, were obtained using nitrilo-triacet-amide (NTAamide), which exhibits tetradentate coordination. Refluxing in 3-6 M HCl at 250 C, a condition that promotes the formation of highly chlorinated PGM anionic species, increased D(Ru) and D(Rh). Based on these findings, a flow diagram for the mutual separation of three PGMs was developed.

Experimental study of AESOP code for aerosol removal behavior from a rising gas bubble in water pool and parametric study for application to sodium pool system

Miyahara, Shinya*; Koie, Ryusuke*; Uno, Masayoshi*; Kawaguchi, Munemichi*; Sato, Rika; Seino, Hiroshi

Nuclear Engineering and Design, 446(Part A), p.114523_1 - 114523_14, 2026/01

https://doi.org/10.1016/j.nucengdes.2025.114523

Research and development of remote optical measurement technology for PCV gas-phase leakage location and leakage volume estimation (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Chiba University*

JAEA-Review 2025-038, 84 Pages, 2025/12

JAEA-Review-2025-038.pdf:6.08MB

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 FY2023, this report summarizes the research results of the "Research and development of remote optical measurement technology for PCV gas-phase leakage location and leakage volume estimation" conducted in FY2023. The present study aims to locate leakage points using a remote optical measurement system including Lidar, and to develop a visualization method for leakage at those points. The Lidar can be distance-resolved in the line-of-sight direction and can separate and observe signals from walls and pipes in the building and surrounding gas-phase molecules (nitrogen N, water vapor HO, etc.) and suspended particles (aerosols). In addition, flash Lidar, which combines a laser beam with a high-sensitivity imaging sensor, and high-sensitivity shearography, which uses interference of light waves, are used to image and visualize the leakage location and to estimate the amount of leakage. Through comparison of these methods, we will clarify the positional resolution in locating the leakage point and the lower detection limit of the leakage amount that can be visualized.