Structural transformation of zinc in metakaolin-based potassium-geopolymer as revealed by X-ray absorption spectroscopy

Prihutami, P.*; Toda, Kanako*; Chaerun, R. I.; Oya, Yusuke*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Saito, Takumi*

Applied Clay Science, 292, p.108330_1 - 108330_9, 2026/11

https://doi.org/10.1016/j.clay.2026.108330

Limited understanding of zinc (Zn) immobilization in altered geopolymers limits prediction of waste-form durability. This study examined the local structure and retention mechanism of Zn in a metakaolin-based potassium geopolymer by X-ray absorption spectroscopy (XAS). Zn-bearing samples were prepared from metakaolin, zinc chloride (ZnCl) solution, potassium silicate, and potassium hydroxide, cured at 40C and 25C for 48 h, and leached in deionized water for up to 90 days. Zn release was only 0.14%, with limited Al, Si, and Cl release. The main geopolymer framework was preserved after leaching. XAS showed that Zn was initially tetrahedrally coordinated with oxygen and linked to Si or Al tetrahedra. After leaching, Zn changed to octahedral coordination and formed a brucite-like Al-bearing co-precipitate, indicating strong Zn retention despite local structural alteration.

Applications of plastic scintillator fibers for the decommissioning of nuclear facilities

Morishita, Yuki; Abe, Tomohisa; Sasaki, Miyuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Sanada, Yukihisa

Radiation Measurements, 198, p.107772_1 - 107772_11, 2026/11

https://doi.org/10.1016/j.radmeas.2026.107772

Accurate and rapid measurement of beta surface contamination is essential during the decommissioning of nuclear facilities. However, conventional Geiger Muller (GM) survey meters have limited detection areas and cannot measure contamination inside piping, resulting in significant labor and measurement inefficiency. In this study, we developed several plastic scintillation fiber (PSF) based detectors designed for wide-area surface monitoring, in-pipe contamination measurement, and drainage-channel monitoring. The PSF enables radiation detection along its entire length, allowing large-area scanning and insertion into narrow spaces. For surface measurements, a 10-m PSF arranged in a zigzag configuration was mounted under a cart, enabling efficient mapping of beta contamination over asphalt floor surfaces in Fukushima (demonstration up to 5 m 5 m). For piping applications, thin and flexible PSF probes were developed, enabling direct insertion into pipes with an inner diameter of 8 mm and achieving detection limits below the regulatory threshold of 4 Bq/cm; within one minute. Additionally, a waterproof PSF system was developed for monitoring radioactive contamination in drainage channels and successfully detected temporal fluctuations, including rainfall-induced increases in radioactivity. Overall, the developed PSF systems provide practical, versatile, and highly efficient alternatives to conventional survey meters for contamination monitoring in nuclear decommissioning environments.

Interactions between U-Zr-O and concrete near the melting range of concrete

Sudo, Ayako; Sato, Takumi; Nagae, Yuji

Journal of Nuclear Materials, 632, p.156936_1 - 156936_16, 2026/10

https://doi.org/10.1016/j.jnucmat.2026.156936

Current molten corium concrete interaction codes are based on large-scale tests in which core materials interact with concrete and the initial temperature of the molten pool is below 2000C. Suboxides such as U-Zr-O may react with concrete at lower temperatures near the melting range of concrete. Investigating the reactions between core materials and concrete near the melting range of concrete is essential for advancing severe accident analyses. As a result of small-scale reaction tests between concrete and U-Zr-O under an Ar atmosphere at 1200C and 1300C, held for 2 hours, a Si-Zr-U-O layer was formed at the reaction interface. At 1500C, held for 2 hours, three layers were formed: (i)Si-Zr-U-O layer, (ii) (U,Zr)O and concrete, and (iii) Si-Zr metallic precipitates. The thermodynamic analysis, indicate that Ca dissolves in (U,Zr)O, whereas U is not predicted to be present in the Si-Zr-U-O layer. These discrepancies arise because the calculations assume complete mixing of the core materials and concrete. The present study demonstrated that, within the temperature range of 1200C-1500C, the reaction layer formed between U-Zr-O and concrete became thicker with increasing temperature, and that the composition of the reaction layer could not be adequately predicted by thermodynamic calculations alone.

Analysis of 1F Waste at Laboratory-1, Okuma Analysis and Research Center (Annual Activity Report, FY2024)

Okuma Analysis and Research Center

JAEA-Technology 2026-007, 82 Pages, 2026/09

JAEA-Technology-2026-007.pdf:8.05MB

This report summarizes the objectives, methods, and results of analyses of Fukushima Daiichi (1F) waste (hereinafter 1F waste) conducted in FY 2024 at the Radioactive Material Analysis and Research Facility (hereinafter Laboratory-1) of the Okuma Analysis and Research Center. The waste samples analyzed included rubble concrete, soil, incineration ash, secondary wastes obtained from wastewater treatment (e.g., carbonate slurry and iron co-precipitation slurry), rubble metal, and decommissioning debris. Ten key radionuclides in the analysis plan specified by TEPCO - Co-60, Cs-137, Sr-90, Ni-63, Pu-238, Am-241, Cl-36, Tc-99, I-129, and C-14 - were quantified. Since 2024 was the first full year of routine operation at Laboratory-1, the analyses aimed not only to obtain data needed for understanding waste characteristics and supporting safety assessments of waste treatment and disposal, but also to verify the applicability of analytical methods to diverse sample matrices. Accordingly, this report evaluates both analytical results and the effects of sample matrix differences on analytical method performance. Since its establishment and commencement of operations, the Okuma Analysis and Research Center has developed rapid analytical methods for 1F waste and initially validated the developed methods using concrete as the primary waste matrix. In FY 2024, these methods were applied to a broader range of samples. Method validation confirmed that the developed analyses were not affected by co-existing radionuclides and that the achieved detection limits aligned with the regulatory concentration requirements for trench disposal. All sample types satisfied the validity criteria, demonstrating the applicability of the developed methods to the targeted sample matrices. Accordingly, matrix effects were assessed by evaluating chemical separation recovery and its reproducibility, which was expressed as standard deviations. The obtained results showed that for most matrices and radionuclides, the developed methods resulted in good recovery and reproducibility, comparable to concrete, except for the reduced recovery of Cl-36 in soil and incineration ash. Although the detection limits can be improved to a certain level by lengthening the measurement time, such improvements may not always meet low-level detection requirements; therefore, the need to improve these analytical methods was discussed.

High-speed 3D modeling for nuclear reactor environment based on feature extraction results from video images (Contract research); FY2024 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Sapporo University*

JAEA-Review 2026-020, 81 Pages, 2026/09

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. 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 FY2023, this report summarizes the research results of the "High-speed 3D modeling for nuclear reactor environment based on feature extraction results from video images" conducted in FY2024. The present study aims to develop a methodology for 3D modeling of workspaces using video footage captured during surveys of the reactor containment vessel and reactor building at 1F. Based on features extracted from the video within a specified timeframe, the method selects a high-information-content 3D reconstruction approach while augmenting the surrounding contextual information. In fiscal year 2024, we developed a methodology to achieve high-precision photogrammetry-based 3D reconstruction within a specified time limit, using a single video sequence obtained from simulation as input. We also devised a 3D modeling algorithm based on structural grouping and concurrently implemented an optimization algorithm to reduce computation time for 3D reconstruction, thereby accelerating the overall modeling process. Furthermore, we quantitatively evaluated the generation accuracy of moving image data using generative models and continued to enhance both hardware construction and software development to further improve computational efficiency.

Development of a prototype shielding-free radiation-resistant diamond neutron measurement system (Contract research); FY2024 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Hokkaido University*

JAEA-Review 2026-017, 78 Pages, 2026/09

JAEA-Review-2026-017.pdf:5.67MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), has been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") from FY2019. 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 FY2023, this report summarizes the research results of the "Development of a prototype shielding-free radiation-resistant diamond neutron measurement system" conducted in FY2024. The present study aims to develop a prototype shielding-free neutron measurement system for 1F. The system consists of diamond neutron detectors and radiation-resistant silicon integrated circuits, and future applications are expected to include neutron detectors for debris investigation, criticality proximity monitoring monitors, and neutron detectors for dry tube investigation in pressure vessels. In this development, a prototype consisting of 100 diamond detector elements of 5 mm square will be developed to obtain system construction technology and to evaluate system performance. In addition, a subcriticality evaluation method will be developed. In FY2024, Hokkaido Univ. made progress in establishing mass-production technology for self-supporting diamond detector elements. At AIST, the search for deposition conditions of multilayer films for detectors using the CVD method advanced. At KEK, the operation of the improved ASIC was confirmed, and using a wiring printing device, detector elements were mounted on signal processing circuit boards, followed by neutron measurement tests. The development of a criticality proximity monitoring method, led mainly by Nagoya Univ., advanced in its fundamental studies, and an evaluation test of the diamond neutron measurement system at UTR-KINKI is planned. At Kyushu Univ. and JAEA, evaluations of the diamond neutron measurement system in gamma-ray irradiation fields and thermal neutron isotropic fields proceeded as scheduled.

Development of a particle-tracking model for explosive release and its coupling with the atmospheric dispersion model

Irie, Kenta; Terada, Hiroaki; Kawamura, Hideyuki; Takano, Masahide

Journal of Environmental Radioactivity, 299, p.108140_1 - 108140_20, 2026/09

https://doi.org/10.1016/j.jenvrad.2026.108140

This study develops an Explosive-release Particle Tracking Model (EPTM) and couples it with the Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI) to explicitly represent the explosion-induced initial condition in atmospheric dispersion simulation. The developed model is designed to resolve the particle dynamics immediately after an explosive release and to provide a physically based initial condition for subsequent atmospheric transport simulations. To demonstrate the capability and impact of EPTM, numerical experiments were conducted under the idealized meteorological field. The results show that the impact of explosion-induced initial motion on concentration and surface deposition is substantial near the explosion point but diminishes with transport distance. Immediately after explosive release, the explosive case produces a rapid vertical redistribution of radioactive materials. This vertical redistribution increases concentration near the surface and increases surface deposition near the release point compared with the non-explosive case. As a result, air concentration maxima and surface deposition patterns near the explosion point are controlled by the explosion-driven initial conditions represented by EPTM. In contrast, in the downwind area, differences in air concentration and surface deposition between the explosive and non-explosive cases become small because horizontal advection and turbulent diffusion govern the spatial distribution of the concentration and deposition, reducing the relative influence of the initial explosion as the plume evolves. Consequently, increasing explosive energy amplifies the contrast of air concentration and surface deposition near the explosion point while exerting limited influence on downwind concentration and deposition distributions.

Diffusion and sorption of Cs in the mudstone matrix at the Horonobe URL; Comparative experimental and modeling analysis between in situ and laboratory conditions

Takeda, Masaki; Ono, Hirokazu; Ito, Tsuyoshi*; Yotsuji, Kenji*; Fukatsu, Yuta; Sato, Tomofumi*; Tachi, Yukio

Journal of Nuclear Science and Technology, 63(9), p.1071 - 1085, 2026/09

https://doi.org/10.1080/00223131.2026.2659269

Upper limit of temperature-gradient--induced internal magnetic field in tellurium revealed by muon spin rotation

Imai, Masaki; Araki, Yasufumi; Ono, Ryota; Ito, Takashi; Isshiki, Hironari; Kikkawa, Takashi; Funato, Takumi; Haga, Yoshinori; Arisawa, Hiroki*; Saito, Eiji; et al.

Journal of the Physical Society of Japan, 95(9), p.093703_1 - 093703_4, 2026/09

https://doi.org/10.7566/JPSJ.95.093703

Bulk modulus and electron density distribution of high-pressure polymorphs of Fe-Ti-O minerals

Yamanaka, Takamitsu*; Hattori, Takanori

Physics and Chemistry of Minerals, 53(3), p.21_1 - 21_11, 2026/09

https://doi.org/10.1007/s00269-026-01350-2

Bulk modulus and electron density distribution of high-pressure polymorphs of Fe-Ti-O minerals (FeO magnetite, FeTiO ulvspinel, FeTiO ilmenite, FeTiO pseudobrokite) are investigated by X-ray and neutron diffraction. The vacant sites in the unit cell have much larger volumes than cation sites in the all structures. Cation site partly occupied by Ti atom shows a smaller than that of only Fe atom and the compressibility of unit cell increases with increasing Ti content. The compressibility of the vacant sites is close to that of unit cells, but are much smaller than that of the cation site. The structure changes such as high-low electron spin transition, Jahn-Teller effect and hybridization in the Fe-O bonds are elucidated by present high-pressure experiments. The hybridization in the octahedral cation site was observed by molecular orbital calculation and it brings the deformation of the octahedral cation site, which triggers structure changes in the high-pressure polymorphs.