Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2024 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2025-013, 206 Pages, 2026/03

JAEA-Technology-2025-013.pdf:34.64MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances conducted in FY2024. Car-borne and walk surveys, a measurement using survey meters, and an unmanned helicopter survey were carried out to obtain air dose rate data on land to create their distribution maps, and temporal changes of those air dose rates were analyzed. In order to confirm the applicability of unmanned aircraft to monitoring in mountainous areas, a basic performance of unmanned aircraft was investigated in mountainous areas. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. These measurement results were published on the WEB site. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated air dose rate distribution data acquired through surveys such as car-borne and walk surveys. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out. Representative life patterns that can be expected after the return to the evacuation-designated restricted area were set, and the cumulative exposure doses were evaluated for the local governments and residents in the area. Score maps to classify the importance of the measurement points were created, and the temporal changes in the score were analyzed. A system to report the tritium concentration level in seawater to the Nuclear Regulation Authority was operated, and the variation of tritium concentration before and after the discharge of ALPS treated water to the ocean was analyzed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until FY2024 was analyzed.

Synthesis report on the R&D for the Horonobe Underground Research Laboratory Project carried out between fiscal years 2020-2024

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

JAEA-Research 2025-016, 141 Pages, 2026/03

JAEA-Research-2025-016.pdf:13.37MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA). The main aim of the project is to enhance the reliability of relevant technologies for the geological disposal of high-level radioactive waste by investigating the deep geological environment within the host sedimentary rocks at Horonobe in Hokkaido, northern Japan. These investigations have been conducted in three phases: "Phase 1: Surface-based investigation", "Phase 2: Construction" (investigation during tunnel excavation) and "Phase 3: Operation" (investigation in subsurface facilities). Since the fiscal year 2020, we have been conducting R&D based on the Horonobe Underground Research Plan for the Fiscal Year 2020 Onwards, which was approved by Hokkaido Prefecture and Horonobe Town. In particular, we are working on the following key tasks with the aim of completing JAEA's 3rd and 4th Mid- and Long-Term Plans: "Study on near-field system performance in geological environments", "Demonstration of repository design options" and "Understanding of buffering behaviour of sedimentary rocks to natural perturbations". This report summarizes the R&D activities on the three above-mentioned key tasks, the goals of which were achieved between fiscal years 2020 and 2024. The results obtained from these tasks will be systematically organized as part of the "Systematic integration of technologies towards EBS emplacement" which has been in progress since fiscal year 2024. This task includes concepts related to the layout of galleries and pits, installation methods for engineered barrier materials, and methods for evaluating their containment performance.

Development of a high-resolution imaging camera for alpha dust and high-dose rate monitor (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tohoku University*

JAEA-Review 2025-048, 56 Pages, 2026/02

JAEA-Review-2025-048.pdf:2.89MB

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 a high-resolution imaging camera for alpha dust and high-dose rate monitor" conducted in FY2023. 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. In addition, we demonstrated this monitoring system, and the dose-rate dynamic range was found to be 20 mSv/h to 1 kSv/h.

Ambient dose rate variation in the Fukushima region visualized using explainable AI techniques

Yoshida, Ryu*; Kurikami, Hiroshi; Nagao, Fumiya; Takahashi, Shigeo*; Sanada, Yukihisa

Journal of Environmental Radioactivity, 293, p.107900_1 - 10790_13, 2026/02

https://doi.org/10.1016/j.jenvrad.2026.107900

Separation of Rh(III) and direct electrodeposition in phosphonium-based ionic liquids with electrochemical and spectroscopic analyses for extracted Rh(III) complex

Tokumitsu, Shun*; Matsumiya, Masahiko*; Sasaki, Yuji

Separation and Purification Technology, 382(Part 2), p.135631_1 - 135631_9, 2026/02

https://doi.org/10.1016/j.seppur.2025.135631

Small-scale experiments on melt spreading and deposition via melt-jet impingement on a dry substrate; Evaluation of empirical correlations for deposition area of continuous layered debris

Iwasawa, Yuzuru; Shibamoto, Yasuteru; Maruyama, Yu

Nuclear Engineering and Design, 446(Part B), p.114599_1 - 114599_16, 2026/01

https://doi.org/10.1016/j.nucengdes.2025.114599

Potential and solution conductivity inside stainless steel crevices in a very dilute bulk solution

Soma, Yasutaka; Komatsu, Atsushi; Igarashi, Takahiro

Corrosion Science, 128, 29 Pages, 2026/00

https://doi.org/10.1016/j.corsci.2026.113812

2D iron oxide at the graphene/SiC(0001) interface

Sakakibara, Ryotaro*; Terasawa, Tomoo; Kawauchi, Taizo*; Fukutani, Katsuyuki; Ito, Takahiro*; Norimatsu, Wataru*

Small Methods, 12 Pages, 2026/00

https://doi.org/10.1002/smtd.202501889

Analysis of deposits inside "X-6 penetration" for the Unit 2 primary containment vessel at Fukushima Daiichi Nuclear Power Station

Yoneyama, Kai; Nitta, Ayako; Tanaka, Yasuyuki; Kodaka, Noriyasu; Kikuchi, Riku; Sakano, Takuma; Furuse, Takahiro; Sato, Soichi; Sambongi, Mitsuru; Tanaka, Kosuke

JAEA-Technology 2025-008, 44 Pages, 2025/12

JAEA-Technology-2025-008.pdf:4.3MB

At the TEPCO's Fukushima Daiichi Nuclear Power Station (1F), an investigation inside the reactors has been carried out. In order to safely carry out the decommissioning work such as fuel debris retrieval and building demolition, it is important to estimate the contamination in primary containment vessel for control the decommissioning planning and the worker radiation exposure levels. Therefore, the analysis of the deposit inside the penetration for the 1F Unit 2 primary containment vessel ("X-6 penetration") was performed to clarify the components and activity. The smears from the deposit were used for the analysis. Non-destructive analysis such as gamma-ray spectrometry, X-ray Fluorescence (XRF) and Scanning Electron Microscope-Energy dispersive X-ray spectroscopy (SEM-EDX) for the smear-samples were performed to determine the gamma-nuclides and the morphology of elements in the deposit. Furthermore, in order to evaluate the nuclides and nuclide composition of the deposit in detail, the smear-samples were dissolved and the quantitative analysis of gamma-nuclides, Sr-90, alpha-nuclides in the dissolved solution were conducted. The results (non-destructive analysis and quantitative analysis) were compared with the results of samples collected at different locations in the X-6 penetration in 2020. In the gamma-ray spectrometry as non-destructive analysis where the smears were analyzed directly, Co-60, Sb-125, Cs-134, Cs-137, Eu-154, Eu-155 and Am-241 were detected. In XRF results, Fe originating from construction material was detected as a major element and small amount of U and Zr originating from the fuel and fuel cladding were also detected. In SEM-EDX results, O and Fe were found as a major element of the deposit and U particles coexisting with Fe, Si, Cr, Ni and Zr were also found. These results were consistent with the SEM-EDX results of the samples collected in 2020. In radioactivity analysis, quantitative values for gamma-nuclides (Co-60, Sb-125, Cs-134, Cs-137, Eu-154, Eu-155), Sr-90, Pu-238, Pu-239+240, Am-241, Cm-244, U-235 and U-238 were obtained. Using the results, the ratios of radioactivity based on Cs-137 and U-238 were calculated. Both sets of the ratios were compared to the calculated value of the Unit 2 fuel composition from ORIGEN.

Challenge for screening of nuclear fuel debris by innovative spectral imaging and its verification by LIBS mapping (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Osaka*

JAEA-Review 2025-040, 111 Pages, 2025/12

JAEA-Review-2025-040.pdf:22.28MB

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 "Challenge for screening of nuclear fuel debris by innovative spectral imaging and its verification by LIBS mapping" conducted in FY2023. The present study aims to develop a remote-sensing technique to identify the in-reactor materials by a combination of Hyper Spectral Imaging (HSI) and Laser Induced Breakdown Spectroscopy (LIBS). HSI analyzes spectral information of more than 100 colors, and is being applied to classify various materials. On the other hand, material composition cannot be directly evaluated by HSI. Therefore, we thought that the combination of HSI and LIBS could be an accurate and wide-ranging visualization technique. In order to demonstrate the HSI and LIBS, it is necessary to prepare standard materials that simulate in-reactor materials, and to acquire and accumulate training data on them. In this study, the University of Osaka is in charge of the preparation of standard materials and HSI data analysis, Nuclear Fuel Development (NFD) is in charge of the preparation of uranium bearing materials and HSI/LIBS measurements, and JAEA is in charge of LIBS development. On the UK side, the Univ. of Strathclyde, National Nuclear Laboratory (NNL), and Lancaster University participate in the joint research project. The compositions of the standard samples were determined from past experiments and thermodynamic calculation results. Several samples such as UO based composites and concrete were prepared. The HSI data were obtained using a hyperspectral camera installed in the NFD. For LIBS, we worked on the automatic optimization of focal distance as part of the development of remote operation technology.