Development of LASSO based optimized scheme for reconstructing radioactive source distributions using monitoring air dose rates

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Okamoto, Koji*

Measurement, 258(Part D), p.119444_1 - 119444_15, 2026/01

https://doi.org/10.1016/j.measurement.2025.119444

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

Separation test of heat generating nuclides from high-level liquid waste

Hotoku, Shinobu; Ban, Yasutoshi; Konda, Miki; Kitatsuji, Yoshihiro

JAEA-Technology 2025-009, 33 Pages, 2025/11

JAEA-Technology-2025-009.pdf:1.9MB

High-level liquid waste (HLLW) produced from reprocessing of spent nuclear fuels contains heat generating nuclides such as Sr-90, Y-90, Cs-137, Ba-137m, and Am-241. Separation and recovery of these nuclides lead to reduce the volume and toxicity of high-level waste. Furthermore, the recovered nuclides and elements could be utilized as resources after purification. In this test, Sr separation by extraction chromatography using Sr resin and Pb resin, Cs separation by co-precipitation using ammonium phosphomolybdate (AMP), and Am separation by solvent extraction using alkyl diamideamine (ADAAM) were carried out, cold tests were performed for the separation of Cs and Sr in a nitric acid solution. Based on the results, hot tests were performed using dissolution solutions of spent fuel at the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF), and each component contained in the separated solution was analyzed. In the Sr separation by extraction chromatography, most of Sr was separated from other elements using 8 mol/L nitric acid for absorption and 0.02 mol/L nitric acid for elution. In the separation of Cs, more than 99.9% of Cs was selectively co-precipitated by adding AMP to the HLLW, in which nitric acid concentration was adjusted to 3.1 mol/L. In solvent extraction of Am by ADAAM, 81.4% of Am-241 was recovered by a single stage batch experiment. Since Sr, Cs, and Am were properly separated and recovered from HLLW, the effectiveness of the present separation method was successfully demonstrated.

Development of inspection technology for pipes in high background radiation environments (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; University of Fukui*

JAEA-Review 2025-036, 88 Pages, 2025/11

JAEA-Review-2025-036.pdf:6.36MB

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 "Development of inspection technology for pipes in high background radiation environments" conducted in FY2023. The following two studies are being conducted with the aim of comprehensively developing technologies to address the three needs indicated in the hearing with TEPCO regarding observation of the inside of piping: (1) Hydrogen content, (2) Presence of precipitates, (3) Presence or absence of / radiation emitting nuclides. First, by downsizing existing nondestructive inspection equipment and developing a dedicated radiation detector capable of nondestructively imaging the inside of piping, we aim to obtain information on the inside of piping by nondestructive inspection using lasers, etc., and to clarify the presence or absence of -nuclides in piping and the internal conditions of piping, etc. In addition, we will develop equipment to visualize -nuclides and discriminate -nuclides in high dose rate environments, as well as technology to investigate the contents of the piping. Deployment of the developed technology is expected to be put into practical use by TEPCO and private companies.

Development of a prototype shielding-free radiation-resistant diamond neutron measurement system (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Hokkaido University*

JAEA-Review 2025-028, 66 Pages, 2025/11

JAEA-Review-2025-028.pdf:3.59MB

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 a prototype shielding-free radiation-resistant diamond neutron measurement system" conducted in FY2023. The present study aims to develop a prototype of a shielding-free neutron measurement system for 1F. The system consists of diamond neutron detectors and radiation-resistant silicon integrated circuits, and has radiation resistance of more than 10 MGy and 4 MGy, respectively, at the component level in terms of integrated dose, and has a track record of stable operation under -ray dose rate environment of 1.5 kGy/h. 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. This development will lead to the completion of system development, development of the actual system in collaboration with the manufacturer, and introduction of the system into 1F decommissioning project.

Corrosion behavior of extra-high-purity Type 316 austenitic stainless steel in a liquid lead-bismuth eutectic with oxygen saturation or low oxygen concentrations

Irisawa, Eriko; Kato, Chiaki

Corrosion Science, 256, p.113173_1 - 113173_16, 2025/11

https://doi.org/10.1016/j.corsci.2025.113173

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.

Development of elemental technologies of hand-foot-cloth monitors for -contamination visualization (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Hokkaido University*

JAEA-Review 2025-021, 63 Pages, 2025/10

JAEA-Review-2025-021.pdf:5.71MB

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 elemental technologies of hand-foot-cloth monitors for -contamination visualization" conducted in FY2023. The present study aims to develop hand-foot-monitors for -contamination visualization and cloth monitors for /-contamination visualization consisting of a portable phoswich detector. ZnS(Ag) thick films by AD method and rare earth complexes have been studied for development of -ray scintillator materials. The scintillator properties of the newly prepared ZnS(Ag) thick films were improved from those prepared in 2022. A rare earth complex shows strong emission intensity under -ray irradiation, which was 12.5 times higher than that of a commercially available plastic scintillator (Saint-Gobain, BC400). By optimizing the manufacturing process conditions (molding die, sintering conditions, cutting process, annealing conditions, grinding/polishing processes) for La-GPS polycrystalline thin plates, the preparing process for 50 mm square La-GPS was established. The prepared La-GPS provided excellent performance for -ray scintillators. The cloth monitors for /-contamination visualization were also improved for the reflection of the actual situation. Furthermore, the basic performance of the prototype cloth monitors was evaluated, and alpha-ray energy and position distribution information were obtained. In an evaluation test of the phoswich detector, a precise discrimination between - and -rays was achieved.

Challenge of novel hybrid-waste-solidification of mobile nuclei generated in Fukushima Nuclear Power Station and establishment of rational disposal concept and its safety assessment (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*

JAEA-Review 2025-016, 143 Pages, 2025/10

JAEA-Review-2025-016.pdf:10.71MB

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 (hereafter referred to "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 "Challenge of novel hybrid-waste-solidification of mobile nuclei generated in Fukushima Nuclear Power Station and establishment of rational disposal concept and its safety assessment" conducted from FY2021 to FY2023. This study aims to establish the rational waste disposal concept of various wastes generated in 1F based on the hybrid-waste-solidification by the Hot Isostatic Press (HIP) method. The ceramics form with target elements, mainly iodine, which is challenging to immobilize, and Minor Actinides such as Am, an alpha emitter and heat source, are HIPed with well-studied materials such as SUS and zircaloy, which make the long-term stability evaluation and safety assessment possible. In 2024, the project's final year, we demonstrated the effectiveness of the hybrid solidification concept by linking all the sub-themes, from waste synthesis to disposal considerations. The compatibility of various wastes, such as ALPS, AREVA sediment wastes, AgI, waste silver adsorbent, ceria adsorbent, and iodine apatite, with metals and oxide matrices was investigated. which involves investigating the HIPed hybrid wastes after exploring the compatibility of various metals and oxide matrices using the rapid sintering method, spark plasma sintering (SPS), proposed in this project. It revealed that hybrid waste solidification with SUS matrix was superior for many wastes. Furthermore, we studied waste disposal concepts based on nuclide migration calculations. Finally, we could connect the waste fabrication to safety assessment for the first time, leading to finding an appropriate waste disposal scenario for 1F decommissioning.

Experimental simulation of high-temperature and high-pressure annular two-phase flow using an HFC134a-ethanol system; Characterization of disturbance wave flow

Zhang, H.*; Umehara, Yutaro*; Horiguchi, Naoki; Yoshida, Hiroyuki; Eto, Atsuro*; Mori, Shoji*

Energy, 335, p.138090_1 - 138090_18, 2025/10

https://doi.org/10.1016/j.energy.2025.138090

Nuclear power is a key low-carbon energy source for a carbon-neutral future. In boiling water reactors (BWRs), steam-water annular flow near fuel rods is crucial for reactor safety, but its high-temperature, high-pressure conditions (285C, 7 MPa) make direct measurement challenges. To address this, we used an HFC134a-ethanol system at lower conditions (40C, 0.7 MPa) to simulate BWR annular flow. Using a high-speed camera and the constant electric current method, we analyzed liquid-film characteristics, wave velocity and frequency. We also examined surface tension and interfacial shear stress effects. Furthermore, we proposed a new correlation for base film thickness.