Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Futemma, Akira; Ochi, Kotaro; Sasaki, Miyuki; Nakama, Shigeo; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Yamada, Tsutomu*; et al.
JAEA-Technology 2025-016, 253 Pages, 2026/03
JAEA-Technology-2025-016.pdf:20.16MB
Aerial Radiation Monitoring (ARM) has been used to quickly and widely measure radiation distribution caused by the TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS) accident resulted from the tsunami accompanying the Pacific coast of Tohoku Earthquake on March 11, 2011. Since the accident, As a commissioned project of the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) has continuously conducted ARM around FDNPS. This report summarizes the results of the 2024 monitoring activities, evaluates temporal changes in ambient dose rates, and identifies factors contributing to these changes. A terrain-corrected analysis was applied to improve dose rates conversion accuracy, and results with and without this correction were compared. A radon-progeny discrimination method was also used to assess its impact on manned-helicopter measurements. Furthermore, development of unmanned airplane monitoring technologies was advanced to enhance the efficiency of wide-area surveys.
Futemma, Akira; Ochi, Kotaro; Sasaki, Miyuki; Nakama, Shigeo; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; Matsunaga, Yuki*; Sanada, Yukihisa; et al.
JAEA-Technology 2025-015, 171 Pages, 2026/03
JAEA-Technology-2025-015.pdf:11.43MB
On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake and tsunami caused the Fukushima Daiichi Nuclear Power Station accident, releasing radioactive material. Since then, Aerial Radiation Monitoring (ARM) with manned helicopters has been used to assess radiation distribution quickly. In FY2024, the Japan Atomic Energy Agency (JAEA), under commission from the Nuclear Regulation Authority, conducted ARM around the Shimane Nuclear Power Station, producing background dose rate maps validated against ground and other data. During a nuclear emergency drill, UAV training flights complemented manned monitoring, confirming the effectiveness of real-time communication and rapid mapping. The UAV data system was developed and demonstrated for real-time analysis and multi-platform use. Skill training for multicopters was also conducted to strengthen operational capability. Additionally, joint monitoring with the U.S., France, South Korea, and Canada provided insights into international technologies and practices, emphasizing the value of information sharing. This report summarizes the results and technical challenges from these FY2024 activities, contributing to the advancement of emergency radiation monitoring.
Misono, Toshiharu; Shiribiki, Takehiko*; Urabe, Yoshimi*; Sanada, Yukihisa
JAEA-Research 2025-014, 88 Pages, 2026/03
JAEA-Research-2025-014.pdf:7.52MB
An accident occurred at the TEPCO's Fukushima Daiichi Nuclear Power Station (1F) in 2011 and a large amount of radioactive materials were deposited around the 1F. Japan Atomic Energy Agency has continued to conduct research on the dynamics of radioactive materials after the accident. This report summarizes the results of the survey conducted in FY 2022 on the status of marine monitoring survey on radioactive substances. Furthermore, in order to evaluate the inflow of radioactive Cs from the river, the horizontal distribution of the radioactive Cs concentration on the surface sediment in front of the rivers was measured. As basic information on the effects of radioactive materials on marine products, the distribution status of fish was investigated. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.
Usami, Hiroshi; Ito, Rintaro; Sanada, Yukihisa
JAEA-Review 2025-050, 57 Pages, 2026/02
JAEA-Review-2025-050.pdf:17.19MB
The decommissioning of the TEPCO's Fukushima Daiichi Nuclear Power Station is a long-term project, and the training of young engineers and researchers who will be responsible for future decommissioning is a necessary and urgent task. Since 2016, Collaborative Laboratories for Advanced Decommissioning Science has been continuously organizing "Conference for R&D Initiative on Nuclear Decommissioning Technology by the Next Generation (NDEC)" for students who are engaged in research activities for decommissioning. NDEC is a forum for students to present their research for the purpose of human resource development and networking among young researchers, and to increase their motivation for decommissioning research. NDEC-10 was held at "Plaza-Bansho" in Tsuruga-City, Fukui Prefecture, from February 26 - 27, 2025. This proceeding compiles the contents of report papers in the conference.
Yoshida, Ryu*; Kurikami, Hiroshi; Nagao, Fumiya; Takahashi, Shigeo*; Sanada, Yukihisa
Journal of Environmental Radioactivity, 293, p.107900_1 - 10790_13, 2026/02
Times Cited Count：0 Percentile：0.00(Environmental Sciences)
underwater radiation monitoring detectorJi, 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
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)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.
Ji, Y.-Y.*; Ji, W.*; Kim, K.*; Kim, M. J.*; Ochi, Kotaro; Morishita, Yuki; Sanada, Yukihisa
Radiation Physics and Chemistry, 244, p.113781_1 - 113781_12, 2026/02
UAV-based airborne gamma-ray spectrometry enables rapid radiation mapping, but accurate estimation of ground-level ambient dose rates is difficult because of altitude attenuation, detector field-of-view effects, heterogeneous contamination, and terrain variability. We developed a practical method combining hovering-flight calibration and ground-based validation near the Fukushima Daiichi Nuclear Power Plant. Altitude correction factors were derived using a dual-exponential model and compared with tripod and backpack measurements. Results showed that heterogeneous contamination and terrain introduce systematic biases if correction factors are derived under non-uniform conditions, while calibration at uniform sites improves agreement. The proposed approach demonstrates that UAV airborne surveys can reliably estimate spatial dose-rate distributions when site-dependent corrections are applied.
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
Times Cited Count：0 Percentile：0.00(Environmental Sciences)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.
Woloszczuk, K.*; Maik, P.*; Safronov, A.*; Wieczorek, A.*; Morishita, Yuki; Sanada, Yukihisa; Szklarski, L.*
Zeszyty Naukowe SGSP, 2(96), p.105 - 121, 2025/12
Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
Radiation Measurements, 188, p.107502_1 - 107502_7, 2025/11
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)The decommissioning of the Fukushima Daiichi Nuclear Power Station requires thorough inspection of piping for contamination, including alpha nuclides. Since external alpha particle measurements are impractical, detection relies on gamma-rays emitted by the alpha nuclides. Therefore, a phoswich detector for detecting low-energy gamma-rays was developed and experimentally validated. The detector was designed with consideration of energy deposition characteristics and consists of YAP:Ce or HR-GAGG scintillators in combination with BGO scintillators, employing a photomultiplier tube for signal amplification. Validation procedures included Monte Carlo simulations and measurements using actual radiation sources. Both measurement and simulation results demonstrate a correlation in scintillator energy depositions across different gamma-ray energies. Pulse Shape Discrimination (PSD) plots effectively differentiate between low-energy and high-energy gamma-rays, thereby confirming the predictions from simulations. These results suggest promising potential for developing a sensitive low-energy gamma-ray detector utilizing various scintillator combinations. The phoswich detector shows promise for effectively detecting low-energy gamma-rays emitted by alpha nuclides in piping.
Joung, S.*; Ji, Y.-Y.*; Choi, Y.*; Lee, E.*; Ji, W.*; Sasaki, Miyuki; Ochi, Kotaro; Sanada, Yukihisa
Journal of Instrumentation (Internet), 20(4), p.P04027_1 - P04027_10, 2025/04
Times Cited Count：1 Percentile：59.09(Instruments & Instrumentation)Morishita, Yuki; Peschet, L.; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
Radiation Measurements, 183, p.107414_1 - 107414_6, 2025/04
Times Cited Count：1 Percentile：68.76(Nuclear Science & Technology)In the decommissioning nuclear facilities, it is crucial to inspect piping for contamination to prevent worker exposure to alpha-emitting nuclides. Traditional methods using gamma rays and neutrons are inadequate for detecting small amounts of alpha nuclides due to the short range (approximately 4 cm) of alpha particles in air. To address this, we developed a compact detector capable of distinguishing between alpha particles for direct measurement within pipes. This detector, comprising a ZnS(Ag) scintillator for alpha particles and a plastic scintillator for beta particles (gamma rays), was coupled to a small photomultiplier tube. The system demonstrated high accuracy in differentiating between alpha and beta radiation through pulse shape discrimination (PSD). Monte Carlo simulations and empirical measurements confirmed the detector's effectiveness, achieving a 51.3% detection efficiency for alpha particles with negligible sensitivity to beta and gamma radiation. This innovation presents a significant advancement for direct alpha contamination measurement in environments with high beta and gamma backgrounds, such as the Fukushima Daiichi Nuclear Power Plant decommissioning site.
Futemma, Akira; Sanada, Yukihisa; Nakama, Shigeo; Sasaki, Miyuki; Ochi, Kotaro; Sawahata, Yoshiro*; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Haginoya, Masashi*; et al.
JAEA-Technology 2024-022, 170 Pages, 2025/03
JAEA-Technology-2024-022.pdf:15.09MB
On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake caused a tsunami that led to the Fukushima Daiichi Nuclear Power Station accident, releasing radioactive material into the environment. Since then, Aerial Radiation Monitoring (ARM) using manned helicopters has been employed to measure radiation distribution. As a commissioned project from the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) utilizes this technology for emergency monitoring during nuclear facility accidents, aiming to provide prompt results by pre-arranging information on background radiation, topography, and control airspaces around nuclear power plants nationwide. In fiscal year 2023, the commissioned project included conducting ARM around the Sendai Nuclear Power Station and preparing related information. To enhance effectiveness during emergencies, ARM and the first domestic training flight of Unmanned Aerial Vehicles (UAVs) were conducted during the FY2023 Nuclear Energy Disaster Prevention Drill. Furthermore, UAVs radiation monitoring technology was advanced by selecting UAVs and investigating their performance. This report summarizes the results and technical issues identified providing insights to improve emergency preparedness.
Futemma, Akira; Sanada, Yukihisa; Nakama, Shigeo; Sasaki, Miyuki; Ochi, Kotaro; Nagakubo, Azusa; Sawahata, Yoshiro*; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; et al.
JAEA-Technology 2024-021, 232 Pages, 2025/03
JAEA-Technology-2024-021.pdf:25.79MB
The 2011 off the Pacific coast of Tohoku Earthquake on March 11, 2011, caused a tsunami that led to the TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS) accident, releasing a large amount of radioactive material into the surrounding environment. Since the accident, Aerial Radiation Monitoring (ARM) has been used to quickly and widely measure radiation distribution. As a commissioned project from the Nuclear Regulation Authority, the Japan Atomic Energy Agency (JAEA) has continuously conducted ARM around FDNPS using manned and unmanned helicopters. This report summarizes the monitoring results for fiscal year 2023, evaluates changes in dose rate from past results, and discusses the factors contributing to these changes. Additionally, an analysis considering terrain undulation was conducted to improve accuracy for converting ARM data into dose rate. Furthermore, a method to discriminate airborne radon progeny was applied for ARM results to evaluate its impact. Moreover, to perform wide-area monitoring more efficiently, we advanced the development of unmanned airplane monitoring technology.
Sasaki, Miyuki; Abe, Yuki*; Sanada, Yukihisa; Torii, Tatsuo*
Nuclear Instruments and Methods in Physics Research A, 1072, p.170207_1 - 170207_12, 2025/03
Times Cited Count：1 Percentile：68.76(Instruments & Instrumentation)We have developed an omnidirectional radiation imager with fractal geometry named the FRIE system. This paper presents the development and evaluation of the FRIE system, designed to accurately estimate radioactivity distribution within decommissioning environments, such as the Fukushima Daiichi Nuclear Power Station. The FRIE system is a unit of tetrahedral radiation sensors; 16 sensors are arranged in a Sierpinski tetrahedron shape, and the space between the sensors is filled with tungsten-based alloy for radiation shielding. This study assessed the performance of the FRIE system in estimating radiation distribution through simulations and actual measurement tests. From the results of the simulations and experimental data, it was confirmed that by maintaining a measurement density of at least 2 points/m
, limiting the positional error to within 
10 cm, and the angular error to within 10 degrees, it is possible to estimate the source location with an angular resolution of approximately 30 degrees. Future improvements in the arrangement of the FRIE system's crystals and shielding should enhance the performance metrics. This research signifies a pioneering implementation of fractal-based radiation imaging technology, offering a new direction in radiation measurement.
Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*
Environment International, 194, p.109148_1 - 109148_8, 2024/12
Times Cited Count：5 Percentile：56.45(Environmental Sciences)Assessment of individual external doses from ambient dose equivalents is used for predictive and retrospective assessments where personal dosimeters are not applicable. However, it tends to contain more errors than assessment by personal dosimetry due to various parameters. Therefore, in order to accurately assess the individual dose from ambient dose equivalents, a model that estimates effective doses considering life patterns and the shielding effects by buildings and vehicles, were developed in this study. The model parameters were examined using robust datasets of environmental radiation measured in the areas affected by the Fukushima Daiichi Nuclear Power Station accident in 2020 to 2021. The accuracy of the model was validated by comparison with 106 daily personal doses measured in Fukushima Prefecture in 2020. The measured personal dose was well reproduced by the model-estimated effective dose, showing that the model can be used to assess the individual exposure dose, similar to personal dosimetry. Furthermore, this model is an effective tool for radiation protection, as it can estimate the individual dose predictively and retrospectively by using environmental radiation data.
Sakuma, Kazuyuki; Kurikami, Hiroshi; Wainwright, Haruko*; Tanimori, Soichiro*; Nagao, Fumiya; Ochi, Kotaro; Sanada, Yukihisa; Saito, Kimiaki
Journal of Environmental Radioactivity, 280, p.107554_1 - 107554_11, 2024/12
Times Cited Count：7 Percentile：69.23(Environmental Sciences)In this study, we created the integrated radiation air dose rate maps in the Fukushima region during 2011-2022 using multiple types of surveys such as air-borne, car-borne and walk surveys as well as fixed-location measurements. We applied the Bayesian geostatistical method developed by Wainwright et al. (2017, 2019) to the 80 km radius of the Fukushima Daiichi Nuclear Power Plant and the whole of Fukushima Prefecture while considering the history of the lifting of the evacuation zone in Fukushima. The integrated maps fixed the bias to underestimate air dose rates in forest areas, and successfully created more reproducible integrated maps with a wider area and time series than the previous studies. It is highly expected that the results of this study will be used to evaluate detailed exposure doses to the general public.
Sanada, Yukihisa; Urabe, Yoshimi*; Saito, Madoka*; Shiribiki, Takehiko*; Misono, Toshiharu; Funaki, Hironori
Kankyo Gijutsu, 53(4), p.188 - 193, 2024/07
no abstracts in English
Saisu, Motofumi*; Ando, Tadahiko*; Uchiyama, Keizo*; Ueno, Toshihiro*; Takizawa, Koichi*; Endo, Yuji*; Yoshimura, Kazuya; Sanada, Yukihisa
Journal of Radiological Protection, 44(2), p.021518_1 - 021518_16, 2024/06
Times Cited Count：0 Percentile：0.00(Environmental Sciences)Morito, Makoto*; Fujii, Shun*; Yoshimura, Koki*; Sanada, Yukihisa; Baba, Shoichiro*; Matsunaga, Hiroshi*; Mori, Takami*; Sato, Keiichiro*; Tahara, Junichiro*
Proceedings of 34th International Ocean and Polar Engineering Conference (ISOPE-2024), p.3754 - 3761, 2024/06
This study proposes a method that combines sliding mode control and neural networks as a control method for unmanned surface vehicle to measure radiation in submarine soil. Sliding mode control is used as the base of control input, and corrective inputs are added using a neural network controller so that one of the parameters of sliding mode control, 
, and its rate of change are reduced. After producing a control system using this method, we conducted simulation tests and sea area tests to evaluate whether the survey could be conducted using this method.
