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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.
Collaborative Laboratories for Advanced Decommissioning Science; Tokai National Higher Education and Research System*
JAEA-Review 2026-018, 141 Pages, 2026/09
JAEA-Review-2026-018.pdf:14.13MB
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 "Pilot study on thermal, physico-chemical, and mechanical behavior of concrete to understand the failure behavior of Fukushima Daiichi Nuclear Power Station reactor pressure vessel pedestals" conducted in FY2024. The present study aims to examine the mechanism of the collapse of only concrete with rebar remaining in the pedestal in the containment vessel (PCV) of 1F. In verifying concrete-specific factors, (1) high-temperature heating experiments were conducted on cement paste, aggregates, and their mixtures to obtain heating behavior. Phase composition changes and melting behavior under high-temperature conditions were analyzed using thermodynamic phase equilibrium calculations, and a numerical analysis method to reproduce water absorption behavior after high-temperature exposure was developed. In addition, (2) exposure experiments simulating the temperature and water injection history of the pedestal were conducted, and time-dependent expansion after heating and expansion behavior induced by water supply were evaluated. In the verification of special external environmental factors, (1) thermal conditions of concrete in the PCV during debris accumulation were evaluated by heat transfer analysis based on accident scenarios. In addition, (2) concrete collapse behavior with and without water vapor was evaluated by small-scale high-temperature holding tests, and concrete damage behavior due to reactions with simulated fuel debris was evaluated by high-temperature reaction tests.
N(
,
)
O reaction rates via the 
F(,
)
F reactionKim, S. H.*; Chae, K. Y.*; Asai, Masato; Hirose, Kentaro; Sato, Tetsuya; Makii, Hiroyuki; Nishio, Katsuhisa; Orlandi, R.; Smallcombe, J.; Suzaki, Fumi; et al.
Journal of the Korean Physical Society, 89(5), p.488 - 493, 2026/09
Times Cited Count：0 Percentile：0.00(Physics, Multidisciplinary)no abstracts in English
Center for Computational Science & e-Systems
JAEA-Evaluation 2026-005, 123 Pages, 2026/08
JAEA-Evaluation-2026-005.pdf:2.02MB
Research on advanced computational science for nuclear applications, based on "the plan to achieve the medium- and long-term goal of the Japan Atomic Energy Agency", has been performed by Center for Computational Science & e-Systems (CCSE), Japan Atomic Energy Agency. CCSE established a committee consisting of external experts and authorities which evaluates and advises toward the future research and development. This report summarizes the results of the R&D performed by CCSE in FY2025 (April 1, 20255March 31, 2026), the interim achievements under the plan to achieve the medium-and long-term goal and their evaluation by the committee.
Omori, Takazumi; Fuyushima, Takumi; Sayato, Natsuki; Saito, Nagatsuki; Takabe, Yugo; Endo, Yasuichi; Inoue, Shuichi; Wojtania, G.*; Migdal, M.*; Takeuchi, Tomoaki; et al.
JAEA-Technology 2026-006, 47 Pages, 2026/06
JAEA-Technology-2026-006.pdf:3.01MB
Japan Materials Testing Reactor (JMTR), which served as the core facility for neutron irradiation research including materials research and radioisotope production, has been decommissioned. As a result, it has become difficult to continue conducting irradiation tests domestically, as well as to transfer the operational expertise and irradiation technologies associated with test reactors, to address these challenges, it was decided to initiate JMTR alternative irradiation, in which foreign irradiation reactors are utilized to partially substitute for JMTR's irradiation capabilities. As a first step, based on the "Arrangement between the National Centre for Nuclear Research and the Japan Atomic Energy Agency for Cooperation in Research and Development on Testing Reactor". The MARIA reactor (30 MW) owned by the National Centre for Nuclear Research (NCBJ) was selected as the neutron irradiation facility, a temperature control system, which is one of JMTR's irradiation technologies, was introduced into the MARIA reactor, and irradiation tests were conducted. The results of this irradiation test confirmed that the combination of the newly introduced temperature control device and the JMTR irradiation test system operates without issues even after an irradiation period exceeding 150 days, it was also demonstrated that the tests could be conducted while continuously measuring the thermocouple temperature inside the capsule during irradiation, as well as the output of the LVDT and SPGD. Furthermore, regarding the constant temperature control of the irradiation capsule at 300
C constant temperature control test, which is highly demanded in materials irradiation testing, was conducted, during reactor power increases, when temperature fluctuations become significant, temperature control was maintained within 
6.3C, while during power decreases, it was controlled within 26.0C. These results indicate that irradiation testing with irradiation temperature control system developed by JMTR, can also be performed in the MARIA reactor, it was confirmed that it can be offered as an alternative irradiation field.
Project 6 Meeting Members for Tsukuba International Strategic Zone*
JAEA-Review 2026-012, 96 Pages, 2026/06
JAEA-Review-2026-012.pdf:20.51MB
In December 2011, the Prime Minister designated Tsukuba and some areas in Ibaraki Prefecture as "Comprehensive Special Zones". In the Tsukuba International Strategic Zone, nine advanced research and development (R&D) projects are underway with the goal of promoting industrialization of life innovation and green innovation utilizing the science and technology in Tsukuba. In these projects, the domestic production of medical radioisotope (Technetium-99m, 
Tc) was certified as a new project in October 2013, and R&D have been performed in collaboration with related organizations with Japan Atomic Energy Agency (JAEA) as the project leader. Japan is the third largest consumer of molybdenum-99 (
Mo) after the United States and Europe, and all Mo are imported. Supply will be insufficient if overseas reactors are shut down due to trouble or if transportation (air and land transportations) is stopped due to volcanic eruptions and some accidents. Thus, early domestic production of Mo is strongly required. This project is a technology development aimed at domestic production of Mo, which is a raw material of Tc used as a diagnostic agent. This report summarizes the activities carried out in the third phase of the domestic production of medical radioisotope (Tc) (here referred to as the "Project 6") in Tsukuba International Strategic Zone (FY2021-2025).
Center for Computational Science & e-Systems
JAEA-Evaluation 2026-003, 41 Pages, 2026/06
JAEA-Evaluation-2026-003.pdf:1.08MB
Research on advanced computational science for nuclear applications, based on "the plan to achieve the medium- and long-term goal of the Japan Atomic Energy Agency", has been performed by Center for Computational Science & e-Systems (CCSE), Japan Atomic Energy Agency. CCSE established a committee consisting of external experts and authorities which evaluates and advises toward the future research and development. This report summarizes the results of the R&D performed by CCSE in FY2024 (April 1st, 2024 - March 31st, 2025) and their evaluation by the committee.
Ta(n,
)
Ta reactionKawamura, Shiori*; Endo, Shunsuke; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kimura, Atsushi; Kitaguchi, Masaaki*; Nakamura, Shoji; Okudaira, Takuya*; Rovira Leveroni, G.; Shimizu, Hirohiko*
JPS Conference Proceedings (Internet), 45, p.011069_1 - 011069_7, 2026/06
La(n,)
La reactionEndo, Shunsuke; Fujioka, Hiroyuki*; Goto, Yu*; Ino, Takashi*; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kawamura, Shiori*; Kimura, Atsushi; Kitaguchi, Masaaki*; Kobayashi, Ryuju; et al.
JPS Conference Proceedings (Internet), 45, p.011056_1 - 011056_8, 2026/06
ionic liquidsEmerson, M. S.*; Fetherolf, J.*; Wu, B.*; Ramati, S.*; Mukhlall, J.*; Fernandez, E. D.*; Gohdo, Masao; Lall-Ramnarine, S. I.*; Castner, E. W. Jr. *; Wishart, J. F.*
Journal of Ionic Liquids (Internet), 6(1), p.100209_1 - 100209_13, 2026/06
Zr(n, )
Zr and 
Zr(n, )
Zr reactions at JRR-3Nakamura, Shoji; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.; Shibahara, Yuji*
Journal of Nuclear Science and Technology, 63(6), p.653 - 666, 2026/06
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Nakamura, Shoji; Shibahara, Yuji*; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.
KURNS Progress Report 2025, P. 101, 2026/06
no abstracts in English
S and 
SBegala, M.*; Elekes, Z.*; Utsuno, Yutaka; 75 of others*
Physical Review C, 113(6), p.064312_1 - 064312_9, 2026/06
Times Cited Count：0no abstracts in English
Kreider, B.; Cox, I.*; Grzywacz, R.*; Allmond, J. M.*; Nishio, Katsuhisa; 23 of others*
Nuclear Instruments and Methods in Physics Research A, 1085, p.171298_1 - 171298_7, 2026/05
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)Alam, M. M.*; Yamakita, Eri*; Tamanna, S.*; Thae, E. P.*; Koarashi, Jun; Atarashi-Andoh, Mariko; Abe, Yukiko; Nakayama, Masataka; Mori, Yuki*; Hiradate, Shuntaro*
Soil Science and Plant Nutrition, 72(3), p.289 - 300, 2026/05
Times Cited Count：1 Percentile：0.00(Plant Sciences)Noseck, U.*; Sch
fer, T.*; Alonso, U.*; Hamamoto, Takafumi*; Havlova, V.*; Hibberd, R.*; Ishidera, Takamitsu; Kitamura, Akira; Klajmon, M.*; Missana, T.*; et al.
Applied Geochemistry, 201, p.106762_1 - 106762_23, 2026/04
Times Cited Count：0 Percentile：0.00(Geochemistry & Geophysics)Thermodynamic benchmark calculations have been performed to better understand the behavior of 
Se(VI), Tc(VII), 
U(VI), 
Np(V), 
Am(III), Th(IV) and 
Pu(IV)) in the evolving geochemical conditions of the Long-term In-situ Test (LIT) at the Grimsel Test Site (GTS) and corresponding mock-up experiment. It also aims to identify the status of the geochemical speciation models and databases for these elements. The experiments are simulating the near-field conditions in some radioactive waste repository concept including a bentonite engineered barrier emplaced in crystalline rock and the findings are contributing to the long-term safety assessment of these facilities.
I neutron capture cross-section in the keV neutron regionRovira Leveroni, G.; Kimura, Atsushi; Nakamura, Shoji; Endo, Shunsuke; Iwamoto, Osamu; Iwamoto, Nobuyuki; Katabuchi, Tatsuya*
Journal of Nuclear Science and Technology, 63(4), p.358 - 369, 2026/04
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Briscoe, A. D.*; Smallcombe, J.; 60 of others*
Physical Review C, 113(4), p.044317_1 - 044317_10, 2026/04
Times Cited Count：0 Percentile：0.00(Physics, Nuclear)Emerson, M. S.*; Lall-Ramnarine, S. I.*; Hatcher-Lamarre, J. L.*; Thomas, M. F.*; Gohdo, Masao; Wu, B.*; Liang, M.*; Ramati, S.*; Wu, F.*; Margulis, C. J.*; et al.
Processes (Internet), 14(8), p.1208_1 - 1208_27, 2026/04
Times Cited Count：0 Percentile：0.00(Engineering, Chemical)Risk Analysis Research Group, Nuclear Safety Research Center
JAEA-Testing 2025-007, 110 Pages, 2026/03
JAEA-Testing-2025-007.pdf:2.57MB
The Japan Atomic Energy Agency's Nuclear Safety Research Center is developing the Level 3 PRA code OSCAAR as part of its research on probabilistic risk assessment (PRA) for nuclear power plant accidents. OSCAAR is a computational code that evaluates the advection, diffusion, and deposition of radioactive materials released into the environment under various meteorological conditions, based on source terms obtained from Level 2 PRA. It can probabilistically assess the radiation doses and health effects to the public caused by these radioactive materials. OSCAAR can account for the dose reduction effects of protective measures implemented during an actual nuclear power plant accident, thereby contributing to the pre-planning of countermeasures and plans to reduce the exposure of residents near nuclear power plants during an accident. This report is a manual for users to create input files and execute the OSCAAR program.
