Studies aimed at clarifying thermal-hydraulic behavior during the 1F accident; Study of debris-relocation behavior during the 1F accident

Sato, Ikken*; Yamashita, Takuya

Nihon Genshiryoku Gakkai-Shi ATOMO, 68(5), p.306 - 310, 2026/05

https://doi.org/10.3327/jaesjb.68.5_306

Understanding fuel debris behavior during the accident and its final distribution and properties is crucial for fuel debris retrieval at the Fukushima Daiichi Nuclear Power Station (1F). By comprehensively synthesizing existing knowledge, including internal plant investigations, accident-stage plant data, and consistent analytical evaluations, this study estimates the most probable fuel debris behavior for 1F Units 1 to 3. The estimation focuses on the thermal conditions of the debris during each relocation stage from the reactor pressure vessel (RPV) to the pedestal. Finally, we identify key issues for future investigation.

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

Feasibility of individual dosimetry using RT-PHITS for patients with SPECT/CT imaging after Lu-DOTATATE peptide receptor radionuclide therapy

Miwa, Kenta*; Kakino, Ryo*; Sato, Tatsuhiko; Furuta, Takuya; Miyaji, Noriaki*; Yamao, Tensho*; Yamashita, Kosuke*; Terauchi, Takashi*

Physical and Engineering Sciences in Medicine, 48(2), p.949 - 957, 2025/06

https://doi.org/10.1007/s13246-025-01551-z

Radiotherapy package based on Particle and Heavy Ion Transport code System (RT-PHITS) enables to calculate the 3-dimensional dose distribution inside patients using their individual SPECT/CT images coupled with the Monte Carlo radiation transport simulation. The objective of this study is to evaluate the feasibility of individual dosimetry based on RT-PHITS for patients after Lu-DOTATATE peptide receptor radionuclide therapy.

4.1.2 BWR lower head penetration failure test focusing on eutectic melting

Yamashita, Takuya

Fukushima Daiichi Nuclear Power Station Accident Information Collection and Evaluation (FACE) Project Annual Report 2023, p.55 - 62, 2024/11

Fukushima Daiichi Nuclear Power Plant accident analysis considering the thermal stratification and containment leakage

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

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-14) (Internet), 12 Pages, 2024/08

Numerical analysis of melt penetration behavior in the control rod drive housing of Fukushima Daiichi Nuclear Power Station Unit-2

Li, X.; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya; Nagae, Yuji

Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 12 Pages, 2024/05

Development of 3D view application debrisEye for decommissioning of Fukushima Daiichi Nuclear Power Plant

Yamashita, Takuya; Shimomura, Kenta; Nagae, Yuji; Nagai, Eiichi*; Yasumatsu, Tomohiro*; Nakashima, Satoru*; Ogino, Shoya*; Mizokami, Shinya*

Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 11 Pages, 2024/05

https://doi.org/10.5445/IR/1000174165/v2

Summary report in FY2022 of subsidy program for the Project of Decommissioning and Contaminated Water Management "Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy, Thermal behavior Estimation, and Simplified Analysis of Fuel Debris)" started in FY2021

Koyama, Shinichi; Ikeuchi, Hirotomo; Mitsugi, Takeshi; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Tsai, T.-H.; Takano, Masahide; Fukaya, Hiroyuki; Nakamura, Satoshi; et al.

Hairo, Osensui, Shorisui Taisaku Jigyo Jimukyoku Homu Peji (Internet), 216 Pages, 2023/11

https://en.dccc-program.jp/wp-content/uploads/20231117_JAEA.pdf

In FY 2021 and 2022, JAEA perfomed the subsidy program for "the Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy, Thermal Behavior Estimation, and Abbreviated Analysis))" started in FY 2021. This presentation material summarized the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning, Contaminated Water and Treated Water Management.

MPS method simulation for estimating fuel debris distributions under the damaged reactor pressure vessel of 1F Unit-2

Bando, Yamato*; Yamaji, Akifumi*; Yamashita, Takuya

Proceedings of International Conference on Environmental Remediation and Radioactive Waste Management (ICEM2023) (Internet), 9 Pages, 2023/10

https://doi.org/10.1115/ICEM2023-112652

MAAP code analysis focusing on the fuel debris condition in the lower head of the pressure vessel in Fukushima-Daiichi Nuclear Power Station Unit 2

Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Cibula, M.*; Mizokami, Shinya*

Nuclear Engineering and Design, 404, p.112205_1 - 112205_21, 2023/04

https://doi.org/10.1016/j.nucengdes.2023.112205

Based on updated knowledge from plant-internal investigations, experiments and model simulations until now, the in-vessel phase of Fukushima-Daiichi Nuclear Power Station Unit 2 was analyzed using the MAAP code. In Unit 2, it is considered that the core material enthalpy was relatively low when it relocated to the lower plenum of the pressure vessel, then, cooled by the coolant and solidified there. Although the MAAP code tended to underestimate the degree of core-material oxidation during the relocation, this probable underestimation was compensated for by an existing study that was considered more reliable, so that more realistic debris conditions in the lower plenum could be obtained. Basic validity of the former prediction of the Unit 2 accident progression behavior was confirmed and detailed boundary condition for the later phase was provided. This boundary condition should be utilized for future studies addressing debris reheating process leading to lower head failure and debris relocation toward the pedestal.