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Th as a long-life 
Ac generator using the experimental fast reactor JoyoSasaki, Yuto; Maeda, Shigetaka; Fukasawa, Tetsuo*; Takaki, Naoyuki*
Journal of Nuclear Science and Technology, 63(2), p.154 - 165, 2026/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)In recent years, targeted alpha therapy, which utilizes Ac combined with antibodies or peptides that selectively accumulate in cancer cells, has garnered attention in the field of nuclear medicine. To meet the resulting increasing demand for Ac, exploring alternative production methods is essential. While several researchers, including the authors, have explored production methods using 
Ra as a raw material, challenges remain, such as the limited availability of Ra, difficulties in handling it, and the requirement for regular irradiation. To address these challenges, the authors focused on developing a production strategy for a long-life Ac generator using 
Th as a raw material and the experimental fast reactor Joyo. A detailed investigation was conducted, encompassing chemical processing after irradiation, target availability, and production yields, including the most probable values and associated uncertainties. Results revealed that although enrichment of the raw material and long-term irradiation are required, Ac can be produced in quantities comparable to its current global supply. Furthermore, this research has shown that the THOREX method, which is already in practical use, be applied to effectively separate by-products such as fission products and radioactive materials from thorium during the chemical processing after irradiation, as revealed by a literature survey.
Ac and its uncertainty through the Ra(n,2n) reaction in the experimental fast reactor JoyoSasaki, Yuto*; Sano, Aaru; Sasaki, Shinji; Iwamoto, Nobuyuki; Ouchi, Kazuki; Kitatsuji, Yoshihiro; Takaki, Naoyuki*; Maeda, Shigetaka
Journal of Nuclear Science and Technology, 61(4), p.509 - 520, 2024/04
Times Cited Count：10 Percentile：85.99(Nuclear Science & Technology)Ac is attracting attention as an alpha-emitting medical radioisotope. Since its demand is expected to increase, domestic production of Ac is required from the viewpoint of Japan's medical research and economic security. To establish the technical bases for the Ac production, JAEA has evaluated the radioactivity that can be produced in the experimental fast reactor Joyo and designed the concept that upgrades the existing facilities for transporting the irradiated target from Joyo to a neighboring PIE facility rapidly. Efficient Ac Separation from Ra irradiated in a fast reactor was studied. Ba and La were used as alternatives to Ra and Ac, respectively. By using DGA resin as an adsorbent, it can be expected that Ra and impurities generated by irradiation will be removed and Ac will be isolated. This study has revealed that Joyo can sufficiently produce Ac as a raw material for pharmaceuticals.
Kaneda, Kazuko*; Shirakami, Yoshifumi*; Kadonaga, Yuichiro*; Watabe, Tadashi*; Oe, Kazuhiro*; Yin, X.*; Haba, Hiromitsu*; Shirasaki, Kenji*; Kikunaga, Hidetoshi*; Tsukada, Kazuaki; et al.
International Journal of Molecular Sciences (Internet), 25(2), p.933_1 - 933_14, 2024/01
Times Cited Count：9 Percentile：76.25(Biochemistry & Molecular Biology)Arai, Masaji; Maeda, Shigetaka
Rinsho Hoshasen, 68(10), p.963 - 970, 2023/10
Ac-225 is attracting attention as an alpha-emitting medical radioisotope. Since its demand is expected to increase, domestic production of Ac-225 is required from the viewpoint of Japan's medical research and economic security. To establish the technical bases for the Ac-225 production, JAEA has evaluated the radioactivity that can be produced in the experimental fast reactor Joyo and designed the concept that upgrades the existing facilities for transporting the irradiated target from Joyo to a neighboring PIE facility rapidly. Efficient Actinium-225 Separation from Ra-226 irradiated in a fast reactor was studied. This study has revealed that Joyo can sufficiently produce Ac-225 as a raw material for pharmaceuticals.
Iwahashi, Daiki*; Sasaki, Yuto*; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
Ac-225 is attracting attention as a radioisotope for targeted 
-therapy (TAT) used for the treatment of prostate cancer and the like. Therefore, we investigated a method of loading Ra-226 into the fast reactor Joyo and producing Ac-225 by transmutation. Ac-225 production can be expected by the (n,2n) reaction using fast neutrons in the center of the core and the (3n,
) reaction using thermalized neutrons in the reflector region.
Maeda, Shigetaka
no journal, ,
Ac is attracting attention as an alpha-emitting medical radioisotope. Since its demand is expected to increase, domestic production of Ac is required from the viewpoint of Japan's medical research and economic security. In this presentation, we report on domestic and international efforts, JAEA's efforts, the conceptual study of production using the Ra and Th irradiation methods at the experimental fast reactor Joyo, and evaluation of production amount. In particular, we report on the most probable value and uncertainty evaluations using the Monte Carlo calculation code MCNP, which was established through the past neutron dosimetry examination in Joyo.
Maeda, Shigetaka
no journal, ,
Regarding Actinium-225, which is one of the medical radioisotopes and has been attracting attention today, we will report on the domestic movement toward domestic production, the research and development plan and progress for production of Actinium-225 using the experimental fast reactor Joyo.
Ohshima, Hiroyuki; Maeda, Shigetaka
no journal, ,
Targeted alpha particle therapy is gaining attention in the field of nuclear medicine. This treatment combines short-lived alpha-emitting radionuclides with antibodies or peptides that selectively accumulate in cancer cells. In 2016, the therapeutic efficacy of Actinium-225 (Ac-225) as an alpha-emitting radionuclide for prostate cancer was reported, and its potential application to other cancers is also currently under investigation. As a result, the demand for Ac-225 is rapidly increasing in the world. Internationally, production methods such as generator-based and accelerator-based approaches are being developed. In Japan, domestic production using nuclear reactors and accelerators is being promoted under the Medical and Other Radioisotope Production and Utilization Promotion Action Plan of the Atomic Energy Commission. The fast experimental reactor Joyo, owned by JAEA, holds promise for large-scale production, with plans to demonstrate production by the JFY2026. This presentation will report on the production principles, production demonstration plan, and prospects for producing enough Ac-225 to meet domestic demand in the future.
Maeda, Shigetaka
no journal, ,
The objectives of this study are a production of Actinium-225 in Japan, and the use of the experimental fast reactor, Joyo. In this concept study, the technical bases of the production should be established. This concept study shows that the experimental fast reactor Joyo can produce a sufficient amount of Ac-225. This has been confirmed by calculation. The existing refueling and PIE transfer systems with some modifications can quickly transfer irradiated Ra-226 to the neighboring PIE facility. We have completed the concept design for the modifications. Issues and challenges are procuration of Ra-226, Joyo restart, for which we need take measures to meet the new regulations of NRA, Japan, licensing for RI use, production, and disposal, and, demonstration of Ac-225 production in Joyo.
Sasaki, Yuto; Sano, Aaru; Itagaki, Wataru; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
no abstracts in English
Sasaki, Yuto; Okagaki, Masaki; Maeda, Shigetaka
no journal, ,
The experimental fast reactor Joyo is the only fast neutron spectrum reactor in the OECD member countries. It has been used for demonstration tests of the safety features unique to fast reactors, such as fuel breeding and core cooling by natural circulation of sodium cooling. Currently, work is underway to comply with the new regulatory standards, and it is scheduled to be restarted in JFY2026. After restarting, it is planned to be used for a variety of purposes, such as the development of fast demonstration reactors, irradiation of materials such as fusion materials, and the production of radioactive isotopes for medical use. In particular, the production of medical radioisotopes can be carried out not only using methods that make the most of the fast neutron spectrum unique to fast reactors, such as the (n,2n) reaction necessary for the production of Ac, but also by adjusting the neutron spectrum flexibly using various moderators, making it possible to carry out irradiation in a thermal neutron spectrum environment, such as the (n,
) reaction necessary for the production of 
Mo. At this conference, we will report on the technology for producing medical radioisotopes using the experimental fast reactor Joyo.
Sasaki, Yuto; Maeda, Shigetaka
no journal, ,
Targeted alpha particle therapy is gaining attention in the field of nuclear medicine. This treatment combines short-lived alpha-emitting radionuclides with antibodies or peptides that selectively accumulate in cancer cells. In 2016, the therapeutic efficacy of Actinium-225 (Ac-225) as an alpha-emitting radionuclide for prostate cancer was reported, and its potential application to other cancers is also currently under investigation. As a result, the demand for Ac-225 is rapidly increasing in the world. Internationally, production methods such as generator-based and accelerator-based approaches are being developed. In Japan, domestic production using nuclear reactors and accelerators is being promoted under the Medical and Other Radioisotope Production and Utilization Promotion Action Plan of the Atomic Energy Commission. The fast experimental reactor Joyo, owned by JAEA, holds promise for large-scale production, with plans to demonstrate production by the JFY2026. This symposium will present the principles of Ac-225 production, the details of the demonstration plan, and future prospects for meeting domestic demand. It will also address the required quality specifications for the target nuclide, particularly the ratio of Ra-226 to Ra-228. Ra-226 is a key target in Ac-225 production via both accelerator and reactor methods, and its purity is critical to ensuring the efficiency and safety of the production process.
Ouchi, Kazuki; Kitatsuji, Yoshihiro; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
In previous study, we have studied the purification process for efficient recovery of Ac-225 produced by neutron irradiation of Ra-226 in a fast reactor. In this presentation, the reuse process for re-irradiating Ra-226 after separation of Ac-225 was studied by using Ba and La as alternative elements. By using Ln resin as adsorbent and changing the nitric acid concentration, the conditions under which Ra can be isolated from impurities expected to be produced by irradiation were clarified. We propose a purification process for Ac using DGA resin and a recycling process for Ra using Ln resin.
