Development of core technologies for a wireless communication chipset with radiation tolerance (Baseband circuit development) (Contract research); FY2024 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; High Energy Accelerator Research Organization*

JAEA-Review 2026-006, 53 Pages, 2026/07

JAEA-Review-2026-006.pdf:2.98MB

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 FY2024, this report summarizes the research results of the "Development of core technologies for a wireless communication chipset with radiation tolerance (baseband circuit development)" conducted in FY2024. The present study aims to develop a wireless communication system operable within the reactor of 1F, focusing on radiation-hardened circuit technologies. The project is divided into two sub-themes: "High-frequency analog circuit development" and "Baseband circuit development." This study is responsible for the baseband circuit development, designing analog components such as variable gain amplifiers, data converters, phase-locked loops, and clock generators. It also involves designing digital components for error correction, encoding, and radiation-hardened RAM. To validate circuit performance, we will build a software/hardware co-design environment. Additionally, we will develop low-power, high-stability piezoelectric oscillators and measure their radiation tolerance. The ultimate goal is to prototype a wireless communication chipset capable of 2.5 Mbps or higher data rates and withstanding radiation doses exceeding 1 MGy.

Individual external doses and conversion coefficients for outdoor workers after the lifting of evacuation orders in specified reconstruction and revitalization base areas following the Fukushima Daiichi nuclear power station accident

Saisu, Motofumi*; Ochi, Kotaro; Uchiyama, Keizo*; Mizuno, Naruhito*; Yoshida, Masashi*; Sanada, Yukihisa

Journal of Radiological Protection, 46(3), p.031506_1 - 031506_12, 2026/07

https://doi.org/10.1088/1361-6498/ae7d36

After evacuation orders were lifted in Specified Reconstruction and Revitalization Base Areas following the Fukushima Daiichi accident, individual external doses of outdoor workers were measured using personal dosimeters and compared with airborne-derived ambient dose rates. Median hourly doses after lifting were significantly lower than before. The median conversion coefficient from ambient to individual dose was 0.39, below the commonly used value of 0.6, but consistent with previous results. These findings indicate that current government models provide conservative dose estimates and that conversion coefficients remain stable under post-evacuation conditions.

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.

A Study for establishment of passive creep-fatigue test techniques using the difference of thermal expansion coefficients of materials

Wakai, Takashi; Ando, Masanori; Okajima, Satoshi; Toyota, Kodai; Ishigami, Katsuo*; Onuma, Terumitsu*; Takahashi, Ryoya*; Asayama, Tai

Nihon Kikai Gakkai Rombunshu (Internet), 12 Pages, 2026/00

https://doi.org/10.1299/transjsme.26-00004

This paper describes current efforts within the Japan Atomic Energy Agency to develop a new materials surveillance technology for sodium-cooled fast reactors that aims at raising the confidence levels in operating reactors' structural integrity to the ones which could otherwise be achieved only by a vast amount of long-term material test data that needs decades to accumulate. The technology would allow for monitoring on-going materials degradation processes in an actual reactor, namely fatigue and creep-fatigue, by inserting a newly developed specimen for this purpose into the reactor and establishing procedures to observe and evaluate the specimen to get desired information such as the extent of degradation and residual life. To establish the test procedure, a passive creep-fatigue test model was developed in the framework of the "Civil Nuclear Energy Research and Development Working Group (CNWG)", a collaboration agreement between the US and Japan, and a demonstration test was performed under cyclic thermal loads using an electric furnace. Temperature conditions had been determined based on finite element analyses. As a result, the test specimen failed by several hundred thermal cycles. Macroscopic inspection of the specimen after the test showed the test had been performed successfully without buckling. Fracture surface observations suggested that the failure caused probably by fatigue or creep-fatigue.

Development of on-site detection system for concealed nuclear materials

Tanabe, Kosuke*; Komeda, Masao; Toh, Yosuke; Kitamura, Yasunori*; Misawa, Tsuyoshi*

Nihon Genshiryoku Gakkai-Shi ATOMO, 67(3), p.198 - 202, 2025/03

https://doi.org/10.3327/jaesjb.67.3_198

no abstracts in English

Evolution of radionuclide transport and retardation processes in uplifting granitic rocks, Part 2; Modelling coupled processes in uplift scenarios

Metcalfe, R.*; Benbow, S. J.*; Kawama, Daisuke*; Tachi, Yukio

Science of the Total Environment, 958, p.177690_1 - 177690_17, 2025/01

https://doi.org/10.1016/j.scitotenv.2024.177690

Uplifting fractured granitic rocks occur in substantial areas of countries such as Japan. A repository site would be selected in such an area only if it is possible to make a safety case, accounting for the changing conditions during uplift. The safety case must include robust arguments that chemical processes in the rocks around the repository will contribute sufficiently to minimise radiological doses to biosphere receptors. To provide confidence in the safety arguments, numerical models need to be sufficiently realistic, but also parameterised conservatively (pessimistically). However, model development is challenging because uplift involves many complex couplings between groundwater flow, chemical reactions between water and rock, and changing rock properties. The couplings would affect radionuclide mobilisation and retardation, by influencing diffusive radionuclide fluxes between groundwater flowing in fractures and effectively immobile porewater in the rock matrix and radionuclide partitioning between water and solid phases, via: (i) mineral precipitation/dissolution; (ii) mineral alteration; and (iii) sorption/desorption. It is difficult to represent all this complexity in numerical models while showing that they are parameterised conservatively. Here we present a modelling approach, illustrated by simulation cases for some exemplar radioelements, to identify realistically conservative process conceptualisations and model parameterisations.

Multiple knowledge exploration functions for advanced reactor design and safety in knowledge management system implemented in the ARKADIA

Seki, Akiyuki; Kondo, Yuki; Hashidate, Ryuta; Yoshikawa, Masanori; Yokoyama, Kenji; Takaya, Shigeru; Enuma, Yasuhiro; Hazama, Taira; Wakai, Takashi; Asayama, Tai

Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 7 Pages, 2024/11

https://doi.org/10.1115/ICONE31-131784

Development of a non-destructive carbon quantification method in iron by negative muon lifetime measurement

Ninomiya, Kazuhiko*; Kubo, Kenya*; Inagaki, Makoto*; Yoshida, Go*; Takeshita, Soshi*; Tampo, Motonobu*; Shimomura, Koichiro*; Kawamura, Naritoshi*; Strasser, P.*; Miyake, Yasuhiro*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 333(7), p.3445 - 3450, 2024/07

https://doi.org/10.1007/s10967-023-09289-2

Positron annihilation lifetime spectroscopy of FeCr and FeCrAl oxide dispersion strengthened (ODS) alloys

Ukai, Shigeharu; Hirade, Tetsuya; Okubo, Nariaki

Materials Characterization, 211, p.113813_1 - 113813_9, 2024/05

https://doi.org/10.1016/j.matchar.2024.113813

Positron annihilation lifetime spectroscopy (PALS) was performed to characterize the interface nanostructure between the oxide particles and the ferritic matrix for two types of the oxide dispersion-strengthened (ODS) alloys. The spectra were precisely decomposed with two trappings. For the shorter annihilation lifetime (179-194 ps), based on the advanced theoretical work by Kuramoto, it could be ascribed to positron trapping at vacancies and divacancies localized under the misfit dislocations. The longer annihilation lifetime (301-323 ps) could be Ar-filled gas bubbles precipitated at the oxide particle/matrix interfaces. The estimated number density of Ar-filled gas bubbles is the same order of the oxide particle number density measured by HRTEM.

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2022 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2023-024, 176 Pages, 2024/03

JAEA-Technology-2023-024.pdf:22.16MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2022. Car-borne surveys, a measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data to create their distribution maps, and temporal changes of the air dose rates were analyzed. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Score maps to classify the importance of the measurement points were created, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. The range of fluctuation of past tritium concentration data in seawater was determined, and the causes of the fluctuation were discussed. Monitoring data in coastal area performed in 2022 owing to the comprehensive radiation monitoring plan was summarized, and temporal changes in cesium-137 were analyzed. 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 with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2022 were published on the "Database for Radioactive Substance Monitoring Data", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.