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.

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

JAEA-Review-2026-020.pdf:6.0MB

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.

Clarification of key input parameters for site boundary dose due to criticality of fuel debris at the Fukushima Daiichi Nuclear Power Plant

Fukuda, Kodai; Shiba, Shigeki*; Iwahashi, Daiki*; Gunji, Satoshi

Journal of Nuclear Science and Technology, 63(9), p.1001 - 1014, 2026/09

https://doi.org/10.1080/00223131.2026.2648997

Radioactive Materials Analysis and Research Facility Laboratory-1 construction report

Shindo, Ryuji; Ichimura, Takahito; Nozawa, Yoshihiko; Komori, Tsuyoshi; Rachi, Reona; Kitahara, Katsumi*; Nakamura, Tomoki*; Koike, Akihiro*

JAEA-Technology 2026-005, 379 Pages, 2026/08

JAEA-Technology-2026-005.pdf:45.42MB

Laboratory-1 of the Radioactive Material Analysis and Research Facility (Laboratory-1) is a facility for analyzing and testing the properties of low and medium radiation dose debris, logging, incinerator ash, and secondary wastes from the decommissioning of the TEPCO HD Fukushima Daiichi Nuclear Power Station (1F) to obtain technical prospects for treatment and disposal measures and their safety. In addition, the ALPS treated water was analyzed by a third party independent of TEPCO HD prior to its discharge into the sea. Laboratory-1 was constructed by the Japan Atomic Energy Agency from January 2017 to June 2022 as part of the 1F Specific Nuclear Facility. The construction work of Laboratory-1 is classified into "building work" for construction of the building by architectural work, electrical equipment work, and mechanical equipment work, and "interior equipment work" for the maintenance of analysis facilities such as iron cells, glove boxes, hoods, etc. This report is a compilation of construction records related to the "building work" that Okuma Construction Office was in charge of. This report is a compilation of construction records and other information related to "building construction" handled by Okuma Construction Office. This report comprehensively summarizes the experience and knowledge from a technical perspective on construction management related to the construction of nuclear facilities, including quality control and construction status for each type of building work, composite coordination, implementation systems and methods for safety and construction quality management, and permits and approvals (such as changes to implementation plans, building permit applications, and forest land development permits). The report also includes a summary of the specific management details such as radiation control for construction in special environments such as construction on the 1F site and construction in a difficult-to-return zone. In the future, we hope that this report will be used as a reference for the development of nuclear facilities such as Laboratory-1, contributing to the identification of issues and rational facility planning.

Development of a 3D-printed two-stage virtual impactor for radioactive aerosol size classification and direct analysis

Laffolley, H.; Tsubota, Yoichi; Kuroe, Ayame; Kato, Tomoaki

ACS Omega (Internet), 11(30), p.45423 - 45438, 2026/08

https://doi.org/10.1021/acsomega.6c04521

Radioactive aerosol size classification is crucial for exposure assessment during nuclear decommissioning. This study presents SPLIT, a two-stage 3D-printed virtual impactor separating aerosols into three aerodynamic classes (10 m, 110 m, and 1 m) while enabling direct analysis on integrated filters. This low-cost, disposable device eliminates hazardous cleaning and metallic waste by allowing incineration after use. Flow paths were optimized via computational fluid dynamics, and prototypes were fabricated by stereolithography. Simulations predicted sharp separation with cutoff diameters of 9.0 m and 1.3 m, despite minor cross-flow particle contamination. Prototype measurements revealed shrinkage and corner rounding, necessitating fabrication compensation. Experiments with incense smoke confirmed submicrometric particles collected mostly in the 1 m class. Tests using Rn-progeny-bearing NaCl particles (1.70 m mean diameter) showed the highest activity on the 110 m filter, confirming the expected classification. These results validate this lightweight, low-cost impactor for simultaneous size classification and direct radioactive particle analysis.

Development of a new measurement method using a portable radiation portal monitor for vehicles to enhance contamination screening efficiency

Hiraoka, Hirokazu; Kawasaki, Kohei*; Kimura, Masanori; Saito, Shota; Ezaki, Iwao*; Kameda, Shuji*; Togawa, Orihiko

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 25(3), p.111 - 121, 2026/08

https://doi.org/10.3327/taesj.J25.007

A method to enable the simultaneous inspection of tires and the wiper area using a portable radiationportal monitor is being developed to improve the efficiency of vehicle inspection during contaminationscreening. To achieve this, we devised an approach to identify whether contamination is located on the tires orin the wiper area. We designed an L-shaped measurement configuration, where detectors are positionedhorizontally near the ground and vertically upright. An identification approach based on this L-shapedconfiguration was evaluated using Monte Carlo simulations. The results showed that the magnitude relation ofcounts measured by the horizontal and vertical detectors varies depending on whether the point source islocated on the tires or in the wiper area. We examined an identification method that utilizes this relationshipto determine the contaminated location. Next, we conducted measurements using a portal monitor (GammaPole, manufactured by Chiyoda Technol) and attempted to identify the contaminated location by the L-shapedmeasurement method. As a result, in the experiment simulating tire contamination, all 30 measurementscorrectly identified the tires as the contaminated location. In contrast, in the experiment simulating wipercontamination, 29 out of 30 measurements correctly identified the wiper area.

Toward the application of atmospheric dispersion analysis in nuclear emergency preparedness

Nagai, Haruyasu

Nihon Genshiryoku Gakkai-Shi ATOMO, 68(8), P. 501, 2026/08

https://doi.org/10.3327/jaesjb.68.8_501

no abstracts in English

BWR RPV lower head penetration failure caused by eutectic reactions with Zr-rich simulated metal; ELSA-3 test

Shimomura, Kenta; Yamashita, Takuya

Proceedings of the 12th European Review Meeting on Severe Accidents Research (ERMSAR2026) (Internet), 11 Pages, 2026/08

https://doi.org/10.5445/IR/1000196279