Assessment of iodine gas decontamination in sodium pool for advanced reactors

Kam, D. H.*; Grabaskas, D.*; Okano, Yasushi; Uchibori, Akihiro; Starkus, T.*

Nuclear Technology, 212(2), p.347 - 364, 2026/02

https://doi.org/10.1080/00295450.2025.2507534

Evaluation of the flow rate of leachate from near surface waste disposal facilities of radioactive wastes from research, industrial and medical facilities based on the latest knowledge

Kitatani, Hikari; Ozone, Kenji; Nakata, Hisakazu

JAEA-Technology 2025-011, 57 Pages, 2025/12

JAEA-Technology-2025-011.pdf:5.32MB

Japan Atomic Energy Agency is responsible for near-surface disposal of research-related low-level radioactive waste and is considering two types of facilities: trench and concrete-pit. In safety assessment of such facilities, dose evaluation requires data on infiltration water. Evaluating infiltration involves uncertainties due to waste conditions and disposal environment. Therefore, in this report, a reference model was established based on the conceptual design conditions of near-surface disposal facilities, and leachate from the facilities was estimated by groundwater flow analysis, using applications by prior operators as reference and reflecting the latest knowledge for safety assessment. This allowed evaluation of how the hydraulic conductivity of each facility layer and surrounding soil affects leachate. Specifically, the 2D FEM groundwater flow code MIG2DF was used: trench facilities were evaluated assuming cover degradation, and concrete-pit facilities assuming salt effects in waste packages. Results showed that in trench facilities, deterioration of clay hydraulic conductivity increased inflow to the waste layer, especially when drainage layer conductivity decreased, as horizontal flow paths failed and infiltration into clay was promoted. In concrete-pit facilities, clay fracturing increased local flow and water through the waste layer. These results quantitatively demonstrate how changes in hydraulic conductivity of each layer affect leachate, providing useful insights for scenario development in safety assessment and for facility management.

Fukushima Daiichi Nuclear Power Plant Unit 2 Accident analysis considering the thermal stratification and containment leakage

Nakamura, Yuki*; Kojima, Yoshihiro*; Yamashita, Takuya; Shimomura, Kenta; Mizokami, Shinya

Journal of Nuclear Science and Technology, 62(12), p.1226 - 1230, 2025/12

https://doi.org/10.1080/00223131.2025.2570371

Estimation of the beam trip frequency of a proton linear accelerator for an accelerator-driven nuclear transmutation system and comparison with the allowable beam trip frequency

Takei, Hayanori

Journal of Nuclear Science and Technology, 62(11), p.1051 - 1070, 2025/11

https://doi.org/10.1080/00223131.2025.2523023

The Japan Atomic Energy Agency is working on the research and development of an accelerator-driven nuclear transmutation system (ADS) for transmuting minor actinides. This system combines a subcritical nuclear reactor with a high-power superconducting proton linear accelerator (JADS-linac). One of the factors limiting the advancement of the JADS-linac is beam trips, which often induce thermal cycle fatigue, thereby damaging the components in the subcritical core. The average beam current of the JADS-linac is 32 times higher than that of the linear accelerator (linac) of the Japan Proton Accelerator Research Complex (J-PARC). Therefore, according to the development stage, comparing the beam trip frequency of the JADS-linac with the allowable beam trip frequency (ABTF) is necessary. Herein the beam trip frequency of the JADS-linac was estimated through a Monte Carlo program using the reliability functions based on the operational data of the J-PARC linac. The Monte Carlo program afforded the distribution of the beam trip duration, which cannot be obtained using traditional analytical methods. Results show that the frequency of the beam trips with a duration exceeding 5 min must be reduced to 27% of the current J-PARC linac level to be below the ABTF.

Uncertainty reduction of the FPs transport mechanism and debris degradation behavior and evaluation of the reactor contamination of debris state on the basis of the accident progression scenario of Fukushima Daiichi Nuclear Power Station Unit 2 and 3 (Contract research); FY2023 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Institute of Science Tokyo*

JAEA-Review 2025-012, 96 Pages, 2025/10

JAEA-Review-2025-012.pdf:3.99MB

JAEA/CLADS had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project. 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). Among the adopted proposals in FY2021, this report summarizes the research results of the "Uncertainty reduction of the FPs transport mechanism and debris degradation behavior and evaluation of the reactor contamination of debris state on the basis of the accident progression scenario of Fukushima Daiichi Nuclear Power Station unit 2 and 3" conducted from FY2021 to FY2023. The present study aims to elucidate the cause of the high dosage under shield plug by clarification of to the cesium behavior of migration, adhesion to structure and deposition as well as evaluate the properties of metal-rich debris predeceasing melted through the materials science approach based on the most probable scenario of accident progression of Unit 2 and 3. Through three years investigation, chemi-absorption configuration of Cs has been elucidated to change with acidity of steel surface during oxidation in humid atmosphere and CsO trapping compound as well as penetration depth have found to be importantly considered. For metallic debris, solid oxidation was found to be controlled by FeO formation and molten state was found to tend to preferentially yield ZrO resulting in formation of slate structure during solidification. Present findings obtained are contributing to better improve the accuracy of accident progression scenario in FDNPP in viewpoint of backward analysis.

Fabrication of low-O/M fast reactor MOX fuel and analysis on its oxygen potential behaviors

Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke

Proceedings of TopFuel 2025; Nuclear Reactor Fuel Performance Conference (Internet), 10 Pages, 2025/10

Reducing the oxygen-to-metal (O/M) ratio in MOX fuels plays an important role in suppressing the corrosion depth in the cladding due to fuel-cladding chemical interaction (FCCI), which is the key to determining the lifetime of fast reactor MOX fuels. Owing to a number of irradiation and post-irradiation experiments, a clear decreasing trend in the corrosion depth with lower O/M ratio in the as-fabricated MOX pellet was reported, whereas a significant redistribution of the O/M ratio in a pellet driven by the radial temperature gradient during irradiation could supply a higher oxygen potential near the pellet periphery where the FCCI should occur. The reduction of the O/M ratio in the MOX pellet fabrication processes can be achieved by heat treatment by taking high temperature, longer time, and lower oxygen partial pressure in the gas into account; the properties governing the reduction are not sufficiently studied. This study demonstrated the variation of O/M ratio in MOX pellets and the in-situ O/M ratio during the heat treatment was analyzed by using a thermogravimeter, which revealed a decreasing behavior during heating and dwell as well as an increasing behavior in the O/M ratio during the cooling step. Furthermore, the redistribution of O/M ratio, analyzed by Sari's model, was discussed to investigate the O/M ratio and the oxygen potential near the pellet periphery which is likely to have a more direct influence on the FCCI than the as-fabricated O/M ratio. By using the recent oxygen potential data on MOX, it is found that the oxygen potential profile in the radial direction is especially drastic near the pellet periphery and is sensitive to the as-fabricated O/M ratio.

Study on estimation of radioactivity concentration of biological shielding at Fukushima Daiichi Nuclear Power Station (Contract Research)

Collaborative Laboratories for Advanced Decommissioning Science; NAIS*

JAEA-Research 2025-004, 102 Pages, 2025/08

JAEA-Research-2025-004.pdf:3.33MB

For planning radioactive waste management at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company Holdings, Incorporated, estimation of radioactivity is essential with considering both contamination from the damaged fuel and activation during reactor operation; with regard to the latter, biological shielding is an important object due to its large amount. It is difficult to conduct field investigations or collect analysis samples at the site, hence the radioactivity should be estimated by calculative analysis with considering the actual conditions of the constituent materials, especially for activation of minor components and water, which affects the neutron flux. Besides it is important to assess the uncertainties involved in the calculation analysis. In this study, the trace composition and water content in the biological shielding concrete were investigated, and a three-dimensional computational model was constructed for the Unit 2 reactor building at the site to estimate the radioactivity concentration. In order to evaluate the uncertainty in the results, the factors contributing to the uncertainty were extracted and the uncertainty resulted from those factors on the calculation results, i.e. the influence of the diversity of the calculation model the parameters used in the calculation model. Based on the results, the dominant factors contributing to the uncertainty were extracted, and the handling as radioactive waste was discussed.

Ingestion doses from radionuclides in seafood before and after the Fukushima Daiichi Nuclear Power Plant accident

Mori, Airi; Johansen, M. P.*; McGinnity, P.*; Takahara, Shogo

Communications Earth & Environment (Internet), 6, p.356_1 - 356_11, 2025/05

https://doi.org/10.1038/s43247-025-02338-6

Reduction and phase transformation of Ce-doped zirconolites

Hayashizaki, Kohei; Hirooka, Shun; Yamada, Tadahisa*; Sunaoshi, Takeo*; Murakami, Tatsutoshi; Saito, Kosuke

Ceramics (Internet), 8(1), p.24_1 - 24_12, 2025/03

https://doi.org/10.3390/ceramics8010024

Assessment of individual external exposure doses based on environmental radiation in areas affected by the Fukushima Daiichi Nuclear Power Station accident

Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*

Environment International, 194, p.109148_1 - 109148_8, 2024/12

https://doi.org/10.1016/j.envint.2024.109148

Assessment of individual external doses from ambient dose equivalents is used for predictive and retrospective assessments where personal dosimeters are not applicable. However, it tends to contain more errors than assessment by personal dosimetry due to various parameters. Therefore, in order to accurately assess the individual dose from ambient dose equivalents, a model that estimates effective doses considering life patterns and the shielding effects by buildings and vehicles, were developed in this study. The model parameters were examined using robust datasets of environmental radiation measured in the areas affected by the Fukushima Daiichi Nuclear Power Station accident in 2020 to 2021. The accuracy of the model was validated by comparison with 106 daily personal doses measured in Fukushima Prefecture in 2020. The measured personal dose was well reproduced by the model-estimated effective dose, showing that the model can be used to assess the individual exposure dose, similar to personal dosimetry. Furthermore, this model is an effective tool for radiation protection, as it can estimate the individual dose predictively and retrospectively by using environmental radiation data.