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.

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.

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.

Performance of UAV-based airborne gamma-ray spectrometry for wide-area radiation monitoring of contaminated sites

Ji, Y.-Y.*; Joung, S.*; Ji, W.*; Ochi, Kotaro; Sasaki, Miyuki; Sanada, Yukihisa

Journal of Radiological Protection, 45(4), p.042501_1 - 042501_11, 2025/12

https://doi.org/10.1088/1361-6498/ae0cd4

This study reports the development and field validation of KAERI's UAV-based gamma-ray spectrometry system equipped with LaBr(Ce) detectors. Joint surveys with JAEA near Fukushima Daiichi Nuclear Power Plant (FDNPP) showed reliable dose rate estimation after applying altitude based attenuation correction, through discrepancies occurred in sloped terrain. Incorporating terrain data is recommended to enhance accuracy for emergency response applications.

Development of nuclear security technologies for a large public event (Collaboration research)

Takahashi, Tone; Mochimaru, Takanori*; Koizumi, Mitsuo; Yoshimi, Yuki*; Yamanishi, Hirokuni*; Wakabayashi, Genichiro*; Ito, Fumiaki*

JAEA-Review 2025-039, 34 Pages, 2025/11

JAEA-Review-2025-039.pdf:2.18MB

To prevent acts of terrorism involving nuclear or radioactive materials at major public events, it is required to have surveillance technologies that either prevent these materials from being brought in or detect quickly if somebody brings them in secretly. Setting radiation gate monitors to survey pedestrians and vehicles is one of the effective methods. However, considering the possibility of individuals bypassing these monitors, complementary technologies are needed to continuously survey areas inside the gates. To survey extensive areas, radiation mapping is effective. By using multiple detectors and aggregating the data, the survey becomes much more efficient. We have developed mobile detectors capable of simultaneously measuring location data and radiation levels outdoors, with the ability to aggregate measurement results via a network and immediately visualize them on a map. For indoor environments, we have developed a technology that integrates radiation measurement results with environmental mapping created using SLAM (Simultaneous Localization and Mapping) to produce 3D maps of the surveyed areas. Additionally, we have been working on the development of a source search technology using a fast neutron detector to quickly detect neutron sources, including nuclear materials. In this report, we describe a concept of the wide area survey system and report technology development results so far.

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.

Optimising sodium incorporation into potassium-activated metakaolin-based alkali-activated materials

Chaerun, R. I.; Sato, Junya; Hiraki, Yoshihisa; Yoshida, Yukihiko; Sato, Tsutomu*; Osugi, Takeshi

Construction and Building Materials, 500, p.144270_1 - 144270_10, 2025/11

https://doi.org/10.1016/j.conbuildmat.2025.144270

Alkali-activated materials (AAMs), particularly those derived from metakaolin, have gained significant attention as sustainable binders for hazardous waste immobilisation, owing to their dense microstructure and chemical durability. Their amorphous aluminosilicate framework enables effective encapsulation of hazardous materials and reduces environmental risks. However, maintaining the stability of this amorphous network is challenging, particularly when sodium (Na)-rich precursors are used, as excess Na) promotes crystallisation and compromises matrix integrity. This study systematically investigates the influence of Na) concentration on the structural stability of metakaolin-based AAMs activated primarily with potassium (K)). The objective is to identify the threshold Na incorporation level that preserves the amorphous structure and maintains chemical stability. Transmission electron microscopy (TEM), Raman spectroscopy, and thermodynamic modelling were employed to examine the structural evolution of K-AAMs across a range of Na:K molar ratios. The results reveal that higher Na:K ratios induce nanopore formation and early crystallisation of Na-rich zeolitic phases, which can reduce matrix stability. In contrast, an optimal Na:K ratio was identified that maintains the amorphous network and preserves the aluminosilicate framework. These findings provide valuable insights into optimising K-AAMs for advanced, durable waste encapsulation technologies.

Sampling of radioactive materials remaining in JMTR Reactor Facility

Ouchi, Takuya; Nagata, Hiroshi; Shinoda, Yuya; Yoshida, Hayato; Inoue, Shuichi; Chinone, Marina; Abe, Kazuyuki; Ide, Hiroshi; Watahiki, Shunsuke

JAEA-Technology 2025-006, 25 Pages, 2025/10

JAEA-Technology-2025-006.pdf:1.59MB

In the future, radioactive waste which generated from nuclear research facilities in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. It is necessary to establish the method to evaluate the radioactivity concentrations of the radioactive wastes. Therefore, at the Oarai Nuclear Engineering Institute, in order to contribute to the study of methods for evaluating radioactivity concentrations of the radioactive wastes from nuclear research facilities, samples were taken from radioactive waste that are expected to be buried in the future and radiochemical analysis is used to obtain data on the radioactivity concentration of each nuclide contained in the radioactive waste. This report presents the concept of selecting sample collection targets and summarizes the sampling of radioactive materials conducted at the JMTR reactor facility in fiscal years 2023 and 2024 to obtain data on radioactivity concentrations.

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.

Influence of steam flow rate on oxidation kinetics of silicon carbide at 1400-1600 C

Pham, V. H.; Kurata, Masaki; Nagae, Yuji; Ishibashi, Ryo*; Sasaki, Masana*

Corrosion Science, 255, p.113098_1 - 113098_9, 2025/10

https://doi.org/10.1016/j.corsci.2025.113098