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Li, X.; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya
Annals of Nuclear Energy, 214, p.111217_1 - 111217_13, 2025/05
Aoyama, Takahito; Ueno, Fumiyoshi; Sato, Tomonori; Kato, Chiaki; Sano, Naruto; Yamashita, Naoki; Otani, Kyohei; Igarashi, Takahiro
Annals of Nuclear Energy, 214, p.111229_1 - 111229_6, 2025/05
Sasaki, Miyuki; Abe, Yuki*; Sanada, Yukihisa; Torii, Tatsuo*
Nuclear Instruments and Methods in Physics Research A, 1072, p.170207_1 - 170207_12, 2025/03
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.
Matsumura, Taichi; Okumura, Keisuke; Sakamoto, Masahiro; Terashima, Kenichi; Riyana, E. S.; Kondo, Kazuhiro*
Nuclear Engineering and Design, 432, p.113791_1 - 113791_9, 2025/02
Times Cited Count:0Morishita, Yuki; Sagawa, Naoki; Fujisawa, Makoto; Kurosawa, Shunsuke*; Sasano, Makoto*; Hayashi, Masateru*; Tanaka, Hiroki*
Radiation Measurements, 181, p.107371_1 - 107371_5, 2025/02
The effects of different types of radiation on a high-resolution alpha imager developed using an electron multiplying charge-coupled device (EMCCD) camera were investigated. This imager was originally developed to visualize alpha particles from Pu oxide particles at decommissioning sites. Other types of radiation such as beta particles, gamma rays, and neutrons are also present. The purpose of this study is to investigate the effects of these background radiations on the imager and to develop a method to discriminate between alpha particles and other types of radiation. When measuring gamma rays, and neutrons, the sensor of the EMCCD camera generated high intensity signals due to gamma rays and neutrons. These radiations were identified by image processing. The image values were binarized and the findContours function was applied to count the number of alpha particle spots. The results showed that alpha and gamma (neutron) radiation can be discriminated by using differences in intensity. This method will be useful for visualizing alpha particles at decommissioning sites.
Morishita, Yuki; DiPrete, D. P.*; Deason, T.*; Nagaishi, Ryuji
Radiation Measurements, 181, p.107366_1 - 107366_8, 2025/02
Times Cited Count:0Nuclear fuel materials such as Plutonium (Pu) and Neptunium (Np) are produced as by-products of reprocessing operations, necessitating precise understanding of their contamination distribution within controlled areas for radiation protection. This study presents the development and application of an alpha particle imaging detector for on-site detection of Pu and Np contamination. The detector's performance was evaluated using various alpha sources, demonstrating promising energy resolution and spatial resolution. Subsequently, Pu and
Np oxide samples were measured at the Savannah River National Laboratory, showing the detector's effectiveness in on-site applications. The detector enabled simultaneous measurement of radioactivity and energy spectrum of individual particles, facilitating rapid discrimination between
Pu and
Np. The imaging detector has potential for enhancing on-site detection of alpha nuclides in nuclear facilities, aiding in decontamination efforts and environmental monitoring.
Naraha Center for Remote Control Technology Development
JAEA-Review 2024-046, 52 Pages, 2025/01
Naraha Center for Remote Control Technology Development (NARREC) was established in Japan Atomic Energy Agency to promote a decommissioning work of Fukushima Daiichi Nuclear Power Station (Fukushima Daiichi NPS). NARREC consists of a Full-scale Mock-up Test Building and Research Management Building. Various test facilities are installed in these buildings for the decommissioning work of Fukushima Daiichi NPS. These test facilities are intended to be used for various users, such as companies engaged in the decommissioning work, research and development institutions, educational institutions and so on. The number of NARREC facility uses was 113 in FY2022. We participated booth exhibitions and presentations on the decommissioning related events. Moreover, we also contributed to the development of human resources by supporting the 7th Creative Robot Contest for Decommissioning. As a new project, "Narahakko Children's Classroom" was implemented for elementary school students in Naraha Town. This report summarizes the activities of NARREC in FY2022, such as the utilization of facilities and equipment of NARREC, arrangement of the remote-control machines for emergency response, and training for operators by using the machines.
Nakamura, Satoshi; Ishii, Sho*; Kato, Hitoshi*; Ban, Yasutoshi; Hiruta, Kenta; Yoshida, Takuya; Uehara, Hiroyuki; Obata, Hiroki; Kimura, Yasuhiko; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.56 - 64, 2025/01
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)A dissolution method for analyzing the elemental composition of fuel debris using the sodium peroxide (NaO
) fusion technique has been developed. Herein, two different types of simulated debris materials (such as solid solution of (Zr,RE)O
and molten core-concrete interaction products (MCCI)) were taken. At various temperatures, these debris materials were subsequently fused with Na
O
in crucibles, which are made of different materials, such as Ni, Al
O
, Fe, and Zr. Then, the fused samples are dissolved in nitric acid. Furthermore, the effects of the experimental conditions on the elemental composition analysis were evaluated using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), which suggested the use of a Ni crucible at 923 K as an optimum testing condition. The optimum testing condition was then applied to the demonstration tests with Three Mile Island unit-2 (TMI-2) debris in a shielded concrete cell, thereby achieving complete dissolution of the debris. The elemental composition of TMI-2 debris revealed by the proposed dissolution method has good reproducibility and has an insignificant contradiction in the mass balance of the sample. Therefore, this newly developed reproducible dissolution method can be effectively utilized in practical applications by dissolving fuel debris and estimating its elemental composition.
Nakajima, Kunihisa; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.78 - 85, 2025/01
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)At TEPCO's Fukushima Daiichi Nuclear Power Station, it is estimated that considerable amounts of cesium still remain in the reactors from the analysis results using the severe accident analysis codes and the reverse analysis from contaminated water. Since cesium is known to form stable compounds with uranium and zirconium, chemisorption experiments with uranium dioxide pellets and iron-zirconium melts for cesium hydroxide vapor were carried out. As the results, formations of cesium uranate, CsUO
, and cesium zirconate, Cs
ZrO
, were confirmed, indicating that cesium was chemisorbed on both of the uranium dioxide pellets and the iron-zirconium melts in an Ar-H
-H
O flow and an Ar-H
flow, respectively. Therefore, it was considered that cesium released from fuel might be trapped by chemisorption with fuels and/or iron-zirconium melts during light water reactor severe accidents.
Terasaka, Yuta; Sato, Yuki; Furuta, Yoshihiro*; Kubo, Shin*; Ichiba, Yuta*
Nuclear Instruments and Methods in Physics Research A, 1070(2), p.170021_1 - 170021_9, 2025/01
Times Cited Count:0 Percentile:0.00(Instruments & Instrumentation)Takahashi, Yoshio*; Yamaguchi, Akiko; Yomogida, Takumi
Treatise on Geochemistry, 3rd edition, Vol.6, 46 Pages, 2025/00
With the recent development of measurement techniques, new approaches to the environmental geochemistry of radionuclides have been applied for various research targets. In this review article, several topics within the last 10-15 years in the field of environmental geochemistry of radionuclides have been discussed. In particular, this article mainly focused on two topics, (i) studies on the migration of radionuclides emitted by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in 2011 and (ii) the development of X-ray absorption fine structure (XAFS) spectroscopy and its application to the geochemical processes of radionuclides.
Usami, Hiroshi; Ito, Rintaro; Tagawa, Akihiro
JAEA-Review 2024-045, 49 Pages, 2024/12
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 "Conferences 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-9 was held at "Manabi-no-Mori" in Tomioka-machi, Fukushima Prefecture, from March 21-22, 2024. This proceeding compiles the contents of report papers in the conference.
Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*
JAEA-Review 2024-016, 61 Pages, 2024/12
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 FY2022. 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 a high-resolution imaging camera for alpha dust and high-dose rate monitor" conducted in FY2022. The present study aims to develop a high-resolution imaging camera for alpha dust and a high-dose rate monitor. To realize the high-resolution imaging camera for alpha dust, we have developed novel scintillation materials with emission bands of 500-800 nm. Moreover, we have prepared several materials for the camera and software. We have also developed novel scintillation materials with emission bands of 650-1,000 nm, and simulation studies have been conducted for the high-dose-rate monitor system consisting of optical fiber.
Gunji, Satoshi; Araki, Shohei; Izawa, Kazuhiko; Suyama, Kenya
Annals of Nuclear Energy, 209, p.110783_1 - 110783_7, 2024/12
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)Since the compositions and properties of the fuel debris are uncertain, critical experiments are required to validate calculation codes and nuclear data used for the safety evaluation. For this purpose, the Japan Atomic Energy Agency (JAEA) has been modifying a critical assembly called "STACY." The first criticality of the modified STACY is scheduled for spring 2024. This paper reports the consideration results of the specifications of the basic core configurations of the modified STACY at the first criticality. We prepared two types of gird plates with different neutron moderation conditions (their intervals are 1.50 cm and 1.27 cm). However, there is a limitation on the number of available UO fuel rods. The core configurations for the first criticality satisfying these experimental constraints were designed by computational analysis. A cylindrical core configuration with a 1.50 cm grid plate close to the optimum moderation condition needs 253 fuel rods to reach criticality. As to the 1.27 cm grid plate, we considered core configurations with 2.54 cm intervals by using doubled pitches of the grid plate. It will need 213 fuel rods for the criticality. In addition, we considered the experimental core configuration with steel/concrete simulant rods to simulate fuel debris conditions. This paper shows these core configurations and their evaluated specifications.
Miura, Taito*; Miyamoto, Shintoro*; Maruyama, Ippei*; Aili, A.*; Sato, Takumi; Nagae, Yuji; Igarashi, Go*
Case Studies in Construction Materials, 21, p.e03571_1 - e03571_14, 2024/12
Times Cited Count:0 Percentile:0.00(Construction & Building Technology)Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*
Environmental Science & Technology, 194, p.109148_1 - 109148_8, 2024/12
Times Cited Count:0 Percentile:0.00(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.
Niizato, Tadafumi; Kamikawa, Tsutomu*; Oki, Noriko*
Joho Chishitsu, 35(4), p.99 - 108, 2024/12
Extraction of the needs related to countermeasures against radioactive contamination was conducted by access analysis of the "Base Information Q&A Site" operated by JAEA and text mining of stenographic text data from a briefing on R&D by JAEA for local government officials. The results of the access analysis indicated that even after over 10 years had passed since the 1F accident, there were needs for data and information on the concentration of radiocesium in the environment, and agricultural, forestry, and fishery products and air dose rates used as a degree of radioactive contamination and evidence for the lifting of evacuation orders. The text mining results suggested the needs for data and information on radiocesium concentrations and air dose rates for river systems and aquatic products in the northern part of Hamadori, for forested environment and forest products in Nakadori, and for decontamination and air dose rates in forests and reservoirs in the southern part of Hamadori, as well as for monitoring data on changes in air dose rates after decontamination. The needs for information and data based on surveys and monitoring on the current situation of radioactive contamination rather than the future situation were also inferred.
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:0 Percentile:0.00(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 Dai-ichi 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.
Hanari, Toshihide; Nakamura, Keita*; Imabuchi, Takashi; Kawabata, Kuniaki
Journal of Robotics and Mechatronics, 36(6), p.1537 - 1549, 2024/12
This paper describes three-dimensional (3D) reconstruction processes introducing the image selection method for efficiently generating a 3D model from an image sequence. To obtain suitable images for efficient 3D reconstruction, we tried to apply the image selection method to remove the redundant images in the image sequence. By the proposed method, the suitable images were selected from the image sequence based on optical flow measures and a fixed threshold. As a result, the proposed method can reduce the computational cost for the 3D reconstruction processes based on the image sequence acquired by the camera. We confirmed that the computational cost of the 3D reconstruction processes can reduce while keeping the 3D reconstruction accuracy at a constant level.
Maekawa, Akihiro*; Sakuma, Kazuyuki; Fan, S.*; Fukuda, Miho*; Nasu, Koki*; Taniguchi, Keisuke*
KEK Proceedings 2024-6, p.7 - 12, 2024/12
no abstracts in English