Annual report for FY2024 on the activities of radiation safety in Nuclear Science Research Institute and so on (April 1, 2024 - March 31, 2025)

Department of Radiation Protection, Nuclear Science Research Institute; Nuclear Facilities Management Section, Aomori Research and Development Center

JAEA-Review 2025-055, 107 Pages, 2026/03

JAEA-Review-2025-055.pdf:2.26MB

This annual report describes the activities in the 2024 fiscal year of Department of Radiation Protection at Nuclear Science Research Institute, Harima Synchrotron Radiation Radioisotope Laboratory, and Nuclear Facilities Management Section at Aomori Research and Development Center. The activities described in this report are environmental monitoring, radiation protection practices in workplaces, individual monitoring, maintenance of monitoring instruments, and research and development of radiation protection. At these institutes, the occupational exposures did not exceed the dose limits. The radioactive gaseous and liquid discharges from the facilities were well below the prescribed limits. The research and development activities in the field of radiological protection were continued.

Effects of irradiation parameters on ' phase precipitation in FeCrAl alloys

Yamashita, Shinichiro; Abe, Yosuke; Okubo, Nariaki; Ukai, Shigeharu; Sasaki, Taisuke*

QST-M-56; QST Takasaki Annual Report 2024, P. 28, 2026/02

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.

Improved prediction of the mass splitting for -wave baryons

Su, N.*; Chen, H.-X.*; Gubler, P.; Hosaka, Atsushi

Physical Review D, 113(1), p.016005_1 - 016005_7, 2026/01

https://doi.org/10.1103/nrl4-2yst

None

Koizumi, Mitsuo; Yogo, Akifumi*

Isotope News, (802), p.11 - 14, 2025/12

https://www.jrias.or.jp/books/cat3/2025/802.html

no abstracts in English

High-speed 3D modeling for nuclear reactor environment based on feature extraction results from video images (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Sapporo University*

JAEA-Review 2025-033, 71 Pages, 2025/11

JAEA-Review-2025-033.pdf:4.48MB

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 "High-speed 3D modeling for nuclear reactor environment based on feature extraction results from video images" conducted in FY2023. The present study aims to develop a 3D model for a workspace that maximizes the amount of information based on the features extracted from video, which is taken when surveying the primary containment vessel and inside the reactor building as part of the decommissioning of 1F, considering within a specified time. In FY2023, we verified extracting effective shooting conditions for obtaining 3D reconstruction based on photogrammetry and the method extracting feature values that can generate 3D restoration results from a small amount of data within a specified time based on deep learning. In addition, we applied point cloud data extracted from video to segmentation and classified it into parts with instance labels.

An Analytical study on Russia's civilian nuclear energy utilization

Kawasaki, Nobuchika

JAEA-Review 2025-043, 74 Pages, 2025/10

JAEA-Review-2025-043.pdf:2.45MB

Russia is one of the most advanced countries in the civilian use of nuclear energy. However, understanding the internal mechanisms of its nuclear program remains difficult due to various reasons. Therefore, this study presents a historical overview of Russia's nuclear energy utilization, fuel supply, fuel manufacturing capabilities, and concepts regarding reprocessing and the nuclear fuel cycle. From this overview, insights have been extracted and analyzed. These insights are then organized under two strategic perspectives: "Strategic diversity and continuity in developments and demonstrations" and "Diversity in utilizations and deployments," with considerations of implications for Japan, as below. Russia's nuclear energy policy strategically utilizes a variety of reactor types and fuel cycle technologies to expand nuclear power generation both domestically and internationally. Currently, nuclear power, centered on light-water reactors (VVER series), accounts for about 20% of Russia's electricity supply, and there are plans to increase this share to 25% by 2045. A wide range of reactors, from large-scale to medium and small modular reactors, are being constructed in Russia. Russia is also actively developing fast reactor technologies, and focusing on the reprocessing and recycling of spent fuel. Internationally, VVER-1200 reactors are under construction in several countries, and cooperation with China is deepening in the field of fast reactors. Notably, Russia offers an integrated, or selectively customizable, package of nuclear technology services on the international stage. These include not only reactor deployment, but also fuel supply, reprocessing, waste management, and even the provision of radioisotopes. Rather than simply exporting products or technology, Russia fosters long-term relationships and trust by flexibly responding to the conditions and needs of partner countries. For this reason, Russia promotes the technology developments in advance within the country in areas anticipated for future overseas deployment. It carefully selects target technologies and services and systematically rolls them out. This flexible strategy, combining "technological diversity" and "strategic consistency", enables cooperation with countries across various geopolitical contexts. For Japan, this strategic approach offers valuable lessons on how to engage in comprehensive international nuclear cooperation, not merely through technology exports, but through integrated approaches that encompass the entire fuel cycle, and by combining elements such as fast reactors and RI supply.

Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; University of Fukui*

JAEA-Review 2025-007, 120 Pages, 2025/09

JAEA-Review-2025-007.pdf:8.13MB

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 FY2021, this report summarizes the research results of the "Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario" conducted from FY2021 to FY2023. The present study aims to clarify the debris formation mechanism and utilize the results to refine the accident scenario. In the backward analysis of oxide debris formation, we prepared simulated fuel particles by the aerodynamic levitation method and ejection of melted oxides from a tungsten pipe with a small hole and summarized the relationship between preparation conditions and the properties of the particles. We also demonstrated the formation of simulated fuel debris obtained by the sampling in 1F and clarified the difference between the experimental results and thermodynamic calculation. From the estimation of mixing, melting and solidified states of metallic debris, it was found that the formation of thin reaction layer suppresses the damage of SUS in spite of Zr content around 1000 C, and we quantify the elution rate of BC and Zircaloy to the melted SUS. We extended reaction rate data between various pressure vessel with SUS and Zr and welding parts and suggested reaction rate equation for large scale experiment. We also estimated the failure behavior of lower plenum of pressure vessel and outflow behavior of melt. Furthermore, we estimated transition behavior of Uranium melt to metallic debris melt in the re-melting process of predropped metallic debris. As the experimental techniques in the future, we prepared the semi-melted debris from oxide and metals and analyzed the reaction products and discussed the formation of simulated debris with a small amount of uranium oxide using a CCIM furnace and the aerodynamic levitation method.

Particle arrangements and optical changes induced by the water swelling of melanin-like polydopamine layers

Watanabe, Taku*; Maejima, Yui*; Ueda, Yuki; Motokawa, Ryuhei; Takabatake, Ai*; Takeda, Shinichi*; Fudoji, Hiroshi*; Kishikawa, Keiki*; Koori, Michinari*

Langmuir, 41(34), p.22762 - 22773, 2025/09

https://doi.org/10.1021/acs.langmuir.5c01855

The assembled structures of melanin particles, i.e., colloidal particles coated with a melanin-like polydopamine (PDA) layer, create vivid structural colors. While the thickness of the PDA layer influences the particle arrangement and optical properties, the underlying mechanism has remained controversial. We demonstrate that the water swelling characteristics of PDA are crucial factors governing the dispersion and aggregation of these particles in solution. Detailed comparisons between dry and wet conditions revealed that the PDA layer readily absorbs water molecules, which leads to significant swelling in the thicker layers. The swelling of the PDA layers determined whether the particles remained dispersed or partially aggregated in the water, ultimately controlling the particle arrangement in the dry state once the water evaporated. These findings provide insights into the self-assembly of colloidal particles and offer a strategy for tuning the periodic particle order. This feature is pivotal for various applications in optical and sensing technologies.

Preliminary study of diffusion and SP3 calculations in unstructured mesh geometry for core deformation reactivity evaluation on SFR

Kato, Shinya; Doda, Norihiro; Yokoyama, Kenji; Tanaka, Masaaki; Endo, Tomohiro*

Proceedings of 2025 International Congress on Advances in Nuclear Power Plants (ICAPP 2025) (Internet), 11 Pages, 2025/09

During a reactor power increase in ULOF and UTOP events in sodium-cooled fast reactors, core deformation due to thermal expansion of core elements is expected to cause a negative feed-back effect to suppress this power increase. An analytical evaluation method of core deformation reactivity for design is being developed in JAEA. However, the neutronics calculation module uses several approximations. This study aims to develop the detailed evaluation method as a reference neutron transport calculation code for confirmation of the validity of the calculated core deformation reactivity. Here, the two-dimensional finite volume method (FVM) code based on simplified P3 (SP3) approximation with unstructured mesh have been developed as the first step of the development. This paper describes the calculation theory of the FVM code, the procedure of introducing SP3 approximation into the code and the verification results of the functions developed.