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.

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://dx.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 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.

Embedded system using a radiation-hardened processor (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Okayama University*

JAEA-Review 2025-022, 51 Pages, 2025/10

JAEA-Review-2025-022.pdf:3.05MB

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 "Embedded system using a radiation-hardened processor" conducted in FY2023. The present study aims to develop a radiation-hardened optoelectronic processor with 10 MGy total-ionizing-dose (TID) tolerance, a radiation-hardened processor with 4 MGy TID tolerance, a radiation-hardened memory with 4 MGy TID tolerance, and a radiation-hardened power supply unit with 1 MGy TID tolerance. Up to now, we have successfully developed a radiation-hardened optoelectronic processor with 10 MGy TID tolerance, a radiation-hardened memory with 4 MGy TID tolerance. Moreover, Japanese research group will support radiation-hardened field programmable gate arrays, power supply units, and radiation-hardened optical systems for radiation-hardened robot systems and radiation sensor systems developed by UK team. Finally, we will provide our radiation-hardened robot system which can identify the intensity and type of radiation.

Establishment of 3-D dose dispersion forecasting method and development of in-structure survey using the transparency difference of each line gamma-ray (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Kyoto University*

JAEA-Review 2025-020, 74 Pages, 2025/10

JAEA-Review-2025-020.pdf:5.85MB

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 FY2022, this report summarizes the research results of the "Establishment of 3-D dose dispersion forecasting method and development of in-structure survey using the transparency difference of each line gamma-ray" conducted in FY2023. We realized an electron track detecting Compton camera (ETCC) that can measure gamma-ray images (linear images) with the bijective projection. In the "Quantitative analysis of radioactivity distribution by imaging of high radiation field environment using gamma-ray imaging spectroscopy" (hereinafter referred to as the previous project) adopted in FY2018, the 1 km square area including the reactor buildings was imaged at once. In FY2021, 3-D dosimetry in the reactor building of the Institute for Integrated Radiation and Nuclear Science was carried out, and 3-D imaging of gamma-rays was successfully obtained. This project will build on the results of the previous project to develop a practical 3-D contaminant dispersion detection and prediction system for sub-mSv/h environments. In addition, a 3-D radiographic Cs distribution measurement method inside the reactor building using highly penetrating Cs gamma-rays will be developed. In FY2023, we fabricated a lightweight and highly effective shielding specifically for the TPC of ETCC based on simulations. In addition, by conducting calibration experiments at the FRS facility, we were also able to repair bugs in the signal processing circuit. Those meticulous advance preparations enabled us to successfully conduct a 3-D experiment within 1F in March 2024.

Horonobe Underground Research Laboratory Project Investigation Program for the Fiscal Year 2025

Nakayama, Masashi; Ishii, Eiichi; Hayano, Akira; Aoyagi, Kazuhei; Murakami, Hiroaki; Ono, Hirokazu; Takeda, Masaki; Mochizuki, Akihito; Ozaki, Yusuke; Kimura, Shun; et al.

JAEA-Review 2025-027, 80 Pages, 2025/09

JAEA-Review-2025-027.pdf:6.22MB

The Horonobe Underground Research Laboratory Project is being pursued by the Japan Atomic Energy Agency to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste through investigating the deep geological environment within the host sedimentary rocks at Horonobe Town in Hokkaido, north Japan. In the fiscal year 2025, we continue R&D on "Study on near-field system performance in geological environment" and "Demonstration of repository design options". These are identified as key R&D challenges to be tackled in the Horonobe underground research plan for the fiscal year 2020 onwards. In the "Study on near-field system performance in geological environment", we continue to obtain data from the full-scale engineered barrier system performance experiment, and work on the specifics of the full-scale engineered barrier system dismantling experiment. As for "Demonstration of repository design options", the investigation, design, and evaluation techniques are to be systemized at various scales, from the tunnel to the pit, by means of an organized set of evaluation methodologies for confinement performance at these respective scales. Preliminary borehole investigations will be conducted within a 500 m gallery, with the objectives of obtaining rock strength and rock permeability data, as well as surveying the extent of the excavation damaged zone surrounding the test tunnel via tomographic analysis. A planning study for the in-situ construction test will be conducted to investigate the construction of backfill material and watertight plugs. The volume of water inflow associated with the excavation of the 500 m gallery will be observed, and its magnitude will be compared with the range of water inflow predicted in the analysis. The test plan to determine the extent of the excavation damaged zone around the pit, which is planned to be constructed in the 500 m gallery, will be studied to determine the in-situ excavation damaged zone. In addition, the investigation and evaluation methods for the amount of water inflow from fractures and the extent of the excavation damaged zone around the pit will be organized. Concerning the construction and maintenance of the subsurface facilities, excavation of the West Access Shaft and the 500 m gallery will continue. It is anticipated that the construction of the facilities will be completed by the end of the fiscal year 2025. In addition, we continue R&D on the following three tasks in the Horonobe International Project; Task A: Solute transport experiment with model testing, Task B: Systematic integration of repository technology options, and Task C: Full-scale engineered barrier system dismantling experiment.

Simulations of magnetic field effects on 3-GeV proton beam brought by magnets for muon beam in future proton beam transport line of J-PARC

Yamaguchi, Yuji; Kondo, Yasuhiro; Meigo, Shinichiro; Shinozaki, Shinichi; Takayanagi, Tomohiro; Fujimori, Hiroshi*; Kawamura, Naritoshi*

Journal of Physics; Conference Series, 3094(1), p.012023_1 - 012023_5, 2025/09

https://doi.org/10.1088/1742-6596/3094/1/012023

The 3-GeV proton beam from the rapid cycling synchrotron (RCS) of J-PARC is transported to the spallation neutron source at Materials and Life Science Experimental Facility (MLF) by a 3-GeV RCS to Neutron facility Beam Transport (3NBT) line. Recently, the first design idea of a new proton beam transport line has been proposed for a future target station of the MLF (TS2). In the present study, proton beam transport is simulated near the TS2 target where a bending magnet and a solenoid are located for muon beam transport. The purposes are to clarify the magnetic field effects on the proton beam by the magnets and to present a method to correct each effect. Orbit deviation by the bending magnet and vertical size expansion due to profile rotation by the solenoid can be corrected by installing additional bending magnets and a solenoid with reversal magnetic field, respectively. The correction method is expected to be effective and also needs to be studied further for detail design.

Applicability of equivalent linear three-dimensional FEM analysis of reactor buildings to the seismic response of a soil-structure interaction system

Ichihara, Yoshitaka*; Nakamura, Naohiro*; Nabeshima, Kunihiko*; Choi, B.; Nishida, Akemi

Nuclear Engineering and Design, 441, p.114160_1 - 114160_10, 2025/09

https://doi.org/10.1016/j.nucengdes.2025.114160

This paper evaluates the applicability of equivalent linear analysis of reinforced concrete model, which uses frequency-independent complex damping with a small computational load, to the seismic design of nuclear power plant reactor buildings. To this end, a three-dimensional finite element method analysis of the soil-structure interaction focusing on nonlinear and equivalent linear seismic behavior of the building embedded in an ideally uniform soil condition was performed for the Kashiwazaki-Kariwa Nuclear Power Plant Unit 7 reactor building. The equivalent linear analysis results correlated well with the nonlinear analysis results of the shear strain, acceleration, displacement, and acceleration response spectrum, demonstrating the effectiveness of the equivalent linear analysis method. Moreover, the equivalent linear analysis results were more conservative than those of nonlinear analysis using the material constitutive law in evaluating the shear strain of the external wall of the reactor building. From this result, equivalent linear analysis method tended to obtain a lower building stiffness than nonlinear analysis under the analysis conditions used in this paper.

Development of a cooperative operation robot system for radiation source exploration (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2025-011, 74 Pages, 2025/08

JAEA-Review-2025-011.pdf:5.31MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science &Z 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 FY2021, this report summarizes the research results of the "Development of a cooperative operation robot system for radiation source exploration" conducted from FY2021 to FY2023. The present study aims to develop a robot system (CORRASE: Cooperative Operation Robot system for RAdiation Source Exploration), realizing radiation source exploration with wide field of view, rapidity, and low cost. In FY2023, our research efforts focused on verification tests for radiation source exploration by summarizing the results of our previous studies. Polyhedral type gamma-ray directional detectors were fabricated from 8 BGO scintillators and shielding bodies. Radiation source exploration experiments were performed by developing a cooperative operation robot system consisting of 3 multi-legged robots carrying the gamma-ray detectors, IMUs (Inertial Measurement Units), and LiDARs (Light Detection And Ranging). An unknown test environment for the radiation source exploration was constructed by placing obstacles and a 10 MBq Cs sealed source as a simulated radioactive contamination source in a room measuring 7.8 5.3 m. The developed system was used to create the environmental map, to formulate the exploration plan, to create the heatmap of the radiation counts, and to image the radiation source from the calculated optimal observation position. The localization of the simulated radioactive contamination source was successfully performed with the cooperation of the 3 robot systems by displaying the image of the radiation source fused on the environmental map. It can be concluded that the initial goal of this study has been successfully achieved by developing the robot system realizing radiation source exploration.

Neutronics/thermal-hydraulics coupling simulation using JAMPAN in a single BWR assembly

Kamiya, Tomohiro; Nagatake, Taku; Ono, Ayako; Tada, Kenichi; Kondo, Ryoichi; Nagaya, Yasunobu; Yoshida, Hiroyuki

Mechanical Engineering Journal (Internet), 12(4), p.24-00461_1 - 24-00461_9, 2025/08

https://doi.org/10.1299/mej.24-00461

JAEA has developed the JAEA Advanced Multi-Physics Analysis platform for Nuclear systems (JAMPAN) to realize high-fidelity neutronics/thermal-hydraulics coupling simulations. We performed a neutronics/thermal-hydraulics coupling simulation for a single BWR fuel assembly in order to confirm that the MVP/JUPITER coupling through JAMPAN is feasible. As a result, we confirmed that the void fraction and the corresponding change in the heat generation distribution are reasonable qualitatively.

Decontamination effectiveness for wiping vehicle in screening during a nuclear emergency

Hiraoka, Hirokazu; Manabe, Kentaro; Hirouchi, Jun; Takahara, Shogo

Proceedings of Asian Symposium on Risk Assessment and Management 2025 (ASRAM 2025) (Internet), p.487 - 494, 2025/08