Differential microbial roles in the organic layer and mineral soil determine radioactive cesium fate in forest ecosystems

Koarashi, Jun; Nagano, Hirohiko*; Nakayama, Masataka*; Atarashi-Andoh, Mariko; Nagaoka, Mika

Chemosphere, 389, p.144715_1 - 144715_11, 2025/11

https://doi.org/10.1016/j.chemosphere.2025.144715

Radiocesium (Cs) contamination poses a long-term ecological challenge, particularly in forest ecosystems. The role of soil microorganisms in determining its fate remains insufficiently understood. This study presents a dynamic assessment of microbial Cs retention, focusing on the complex interplay among microorganisms, organic matter, and clay minerals within the organic layer-mineral soil system. Our results show that rapid microbial cycling sustains a potentially bioavailable Cs pool in the organic layer. This microbial involvement diminishes as Cs activity concentrations in the organic layer decline. In the mineral soil, minimal microbial Cs retention was observed, suggesting an indirect role in facilitating Cs immobilization by clay minerals. Notably, microbial Cs retention in the organic layer is regulated by Cs availability, independent of region, forest type, and time since deposition. These findings provide a unified explanation for observed differences in Cs persistence in organic layers between European and Japanese forests.

Improving the analysis method of the Compton camera system mounted on the unmanned helicopter by correcting scintillator coordinates data at each event timing

Shikaze, Yoshiaki

Radioisotopes, 74(3), p.273 - 287, 2025/11

https://doi.org/10.3769/radioisotopes.740302

The previous method used the data during the stable period for the position and attitude angles of the unmanned helicopter as a countermeasure to improve the measurement data analysis of the Compton camera system mounted on the unmanned helicopter. However, this reduced the number of events used for analysis, allowing statistical accuracy to be improved in future. Therefore, all event data were corrected and used this time. The scintillator coordinates of two layers fixed in the previous analysis were replaced with those corrected for the ever-changing positions and tilts for each event. I reconstructed gamma-ray images using the corrected events to improve their statistical accuracy and spatial resolution. I compared the ground measurement results to evaluate the improvement in the accuracy of the reconstructed images of gamma-ray intensity. As for the effect of the improved statistics,a decrease in the residual sum of squares (RSS) was noted after improvement, indicating the effectiveness of this method through good correlations with the ground-measured values. Moreover, from the RSS value comparison, compared to changing from the previous method to the improved method, expanding the range of averaging the measured values was confirmed to be more effective, showing better correlations with the ground-measured values.

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.

Establishment of characterization method for small fuel debris using the world's first isotope micro imaging apparatus (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Kogakuin University*

JAEA-Review 2025-013, 111 Pages, 2025/10

JAEA-Review-2025-013.pdf:7.49MB

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 FY2021, this report summarizes the research results of the "Establishment of characterization method for small fuel debris using the world's first isotope micro imaging apparatus" conducted from FY2021 to FY2023. The present study aims to obtain, for the first time in the world, the important data necessary for clarifying the retrieval of small amounts of fuel debris, and to evaluate and examine them. The isotope microimaging apparatus (developed by Kogakuin University) introduced at the JAEA Fuel Monitoring Facility (FMF) can obtain local quantitative data such as isotope composition while processing cross-sections of radioactive micro-samples, which can be used to determine the properties of fuel debris. In FY2021, we improved the isotope microimaging apparatus introduced to the JAEA FMF to accommodate high radiation dose samples. In FY2022, we maintained the isotope microimaging apparatus at the JAEA FMF and succeeded in analyzing real particles containing uranium. In FY2023, we completed development to automate and remotely perform analysis routines using a prototype machine at Kogakuin University. At the JAEA FMF, although manual operations were involved, we succeeded in analyzing each Cs isotope from real particles by resonance ionization. In Nagoya University, we improved the RIMS apparatus to investigate the difference in electronic state caused by ion beam sputtering. And we succeeded in obtaining resonance ionization signals from neutral particles generated by ion beam sputtering. At the JAEA CLADS, they investigated the ionization scheme for important nuclides Nd and Gd. Those proposed ionization schemes were examined at Kogakuin University.

Weathering promotes the sorption of radiocesium in mafic minerals of river sediments in the Fukushima Prefecture, Japan

Hagiwara, Hiroki; Watanabe, Yusuke; Konishi, Hiromi*; Funaki, Hironori; Fujiwara, Kenso; Iijima, Kazuki

Applied Geochemistry, 190, p.106490_1 - 106490_10, 2025/10

https://doi.org/10.1016/j.apgeochem.2025.106490

Improvement of aerosol time-of-flight mass spectrometer for on-line measurement of tiny particles containing alpha emitters (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*

JAEA-Review 2025-019, 95 Pages, 2025/09

JAEA-Review-2025-019.pdf:9.49MB

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 FY2021, this report summarizes the research results of the "Improvement of aerosol time-of-flight mass spectrometer for on-line measurement of tiny particles containing alpha emitters" conducted from FY2021 to FY2023. The present study aims to improve Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) in order to monitor tiny particles containing alpha emitters such as U and Pu which were generated in removing debris from the reactors of 1F. We newly fabricated the improved ATOFMS quipped with a reflectron and carried out measurements for modeled tiny particles containing U. In obtained TOF spectra, ion peaks were observed for Zr, U, and their oxides as well as Zr and U. Mass resolution of the ion peak of U+ was 1,700, which demonstrates that the improved ATOFMS has sufficient mass resolution to distinguish Pu from U. In the development of the apparatus for preparing enriched and enlarged particles, we fabricated the apparatus consisting of PILS, a volume reduction tube, a supersonic atomizer, and an online dryer, and optimized apparatus conditions. In the optimized conditions, enlarged particles with size between 0.4 m and 0.8 m which are detectable with ATOFMS were dominantly produced. By analyzing the enlarged particles, these were produced by taking component elements of the apparatuses used in the enlarged process. The efficiency was evaluated to be 4.5 times. From these developments, the detection concentration limits of the apparatus were evaluated to be 7.010, 4.210, and 1.310 Bq/cm for U, U, and Pu, respectively. These values are below the air concentration limit.

Novel mechanical manipulator for efficient fuel debris retrieval (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

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

JAEA-Review 2025-014, 86 Pages, 2025/09

JAEA-Review-2025-014.pdf:9.38MB

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 FY2021, this report summarizes the research results of the "Novel mechanical manipulator for efficient fuel debris retrieval" conducted from FY2021 to FY2023. The present study aims to the development of a collision-tolerant robotic manipulator with the mechanical variable impedance actuators in an unknown environment. Another research target is the system architecture of an artificial intelligence-based control method for efficient exploration and decommissioning. In addition to conducting an investigation in the area deep inside the aperture, which has been difficult with conventional investigations, we aim to recover pebble-shaped fuel debris at the bottom of the pedestal using a gripper at the tip of the manipulator. We will establish a manipulator mechanism and remote-control system to cope with the environmental constraints inside the pedestal. This year focused on developing a manipulator navigation algorithm, evaluating control performance, and conducting on-site scenario demonstration experiments. Studies included building a driving model, designing a control algorithm, and assessing manipulator control performance, with comparisons to simulation models. Demonstration experiments were conducted at facilities like the JAEA Naraha Center for Remote Control Technology Development. The research was promoted in close collaboration with the UK team and external advisors, including bi-weekly meetings. At the end of the fiscal year, an oral presentation introducing the project was given at an international workshop organized by the University of Tokyo and Technical University of Munich (TUM).

Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; University of Fukui*

JAEA-Review 2025-007, 120 Pages, 2025/09

JAEA-Review-2025-007.pdf:8.13MB

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 FY2021, this report summarizes the research results of the "Clarification of debris formation conditions on the basis of the sampling data and experimental study using simulated fuel debris and reinforcement of the analytical results of severe accident scenario" conducted from FY2021 to FY2023. The present study aims to clarify the debris formation mechanism and utilize the results to refine the accident scenario. In the backward analysis of oxide debris formation, we prepared simulated fuel particles by the aerodynamic levitation method and ejection of melted oxides from a tungsten pipe with a small hole and summarized the relationship between preparation conditions and the properties of the particles. We also demonstrated the formation of simulated fuel debris obtained by the sampling in 1F and clarified the difference between the experimental results and thermodynamic calculation. From the estimation of mixing, melting and solidified states of metallic debris, it was found that the formation of thin reaction layer suppresses the damage of SUS in spite of Zr content around 1000 C, and we quantify the elution rate of BC and Zircaloy to the melted SUS. We extended reaction rate data between various pressure vessel with SUS and Zr and welding parts and suggested reaction rate equation for large scale experiment. We also estimated the failure behavior of lower plenum of pressure vessel and outflow behavior of melt. Furthermore, we estimated transition behavior of Uranium melt to metallic debris melt in the re-melting process of predropped metallic debris. As the experimental techniques in the future, we prepared the semi-melted debris from oxide and metals and analyzed the reaction products and discussed the formation of simulated debris with a small amount of uranium oxide using a CCIM furnace and the aerodynamic levitation method.

Effort of information dissemination of environmental research with Fukushima Comprehensive Environmental Information Site

Nagao, Fumiya; Oki, Noriko*; Sawada, Noriyoshi*; Shidomi, Masaaki*; Maruyama, Renta*; Kamikawa, Tsutomu*; Ito, Satomi; Niizato, Tadafumi; Kurikami, Hiroshi

JAEA-Data/Code 2025-008, 60 Pages, 2025/09

JAEA-Data-Code-2025-008.pdf:3.0MB
JAEA-Data-Code-2025-008-appendix(CD-ROM).zip:351.97MB

The Great East Japan Earthquake and the following tsunami caused the accident at the Fukushima Daiichi Nuclear Power Station. As a result, a large amount of radioactive materials was discharged into the environment. The Japan Atomic Energy Agency (JAEA) started research on the dynamics of radioactive materials in the environment and disseminated the results on the JAEA website "Base Information Q&A Site". A database site "Database for Radioactive Substance Monitoring Data" was also established to collect, form, and consolidate monitoring data on radioactive substances in the environment and air dose rates obtained and disclosed by various organizations, in addition to the environmental dynamics research of JAEA. Subsequently, in order to release the findings obtained through the research and the actual monitoring data as a single entity, they were compiled and operated as the portal site "Fukushima Comprehensive Environmental Information Site" (FaCE!S). With the establishment of the Fukushima Institute for Research, Education and Innovation, F-REI, the environmental dynamics research at JAEA was terminated and transferred to F-REI. Therefore, the Q&A site was also transferred to FREI in FY2025. This report summarizes the efforts of FaCE!S up to FY2024, and archives the Q&A site as of FY2024.