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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.
Onishi, Takashi; Koyama, Shinichi*; Yokoyama, Keisuke; Morishita, Kazuki; Watanabe, Masashi; Maeda, Shigetaka; Yano, Yasuhide; Oki, Shigeo
Nuclear Engineering and Design, 432, p.113755_1 - 113755_17, 2025/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Ito, Hiromichi*; Ota, Katsu; Kawahara, Hirotaka; Kobayashi, Tetsuhiko; Takamatsu, Misao; Nagai, Akinori
JAEA-Technology 2016-008, 87 Pages, 2016/05
JAEA-Technology-2016-008.pdf:18.11MB
In the experimental fast reactor Joyo, as a part of the restoration work of a partial dysfunction of fuel handling, the replacement of the upper core structure (UCS) was started from March 2014, and was completed in December 2014. In the jack-up test, the UCS was jacked-up to 1000 mm without significant sodium shearing resistance and interference. In the replacement of the UCS, a procedure was prepared with the use of wire-jack equipment assuming the interference. As a result, with the procedure and wire-jack were effectively functioned, the work was successfully completed.
Usami, Shin; Kishimoto, Yasufumi; Taninaka, Hiroshi; Maeda, Shigetaka
Proceedings of International Conference on the Physics of Reactors; Unifying Theory and Experiments in the 21st Century (PHYSOR 2016) (USB Flash Drive), p.3263 - 3274, 2016/05
The present paper describes the validation of the new decay heat evaluation method using FPGS90 code with both the updated nuclear data library and the rational extent of uncertainty, by comparing the results of the decay heat measurement of the spent fuel subassemblies in Joyo MK-II core and by comparing with the calculation results of ORIGEN2.2 code. The calculated values of decay heat (C) by FPGS90 based on the JENDL-4.0 library were coincident with the measured ones (E) within the calculation uncertainties, and the C/E ranged from 1.01 to 0.93. FPGS90 evaluated the decay heat almost 3% larger than ORIGEN2.2, and it improved the C/E in comparison with the ORIGEN2.2 code. Furthermore, The C/E by FPGS90 based on the JENDL-4.0 library was improved than that based on the JENDL-3.2 library, and the contribution of the revision of reaction cross section library to the improvement was dominant rather than that of the decay data and fission yield data libraries.
Nabeshima, Kunihiko; Doda, Norihiro; Ohshima, Hiroyuki; Mori, Takero; Ohira, Hiroaki; Iwasaki, Takashi*
Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.1041 - 1049, 2015/08
Natural circulation is one of the most important mechanisms to remove decay heat in the sodium cooled fast reactors from the viewpoint of passive safety. On the other hand, it is difficult to evaluate plant dynamics accurately under low flow natural circulation condition. In this study, Super-COPD has been validated through the application to the analysis of natural circulation tests in the experimental fast reactor JOYO. Almost all plant components in JOYO including four air-coolers were modeled in Super COPD. Furthermore, the full scale modeling of fuel subassembly was also adopted in this analysis. The natural circulation test after reactor scram from 100 MW full power at JOYO was selected and simulated by Super-COPD. The transient behaviors predicted by Super-COPD showed good agreement with the experimental data.
estimatorSuzuki, Katsuo; Suzudo, Tomoaki; Nabeshima, Kunihiko
Nihon Genshiryoku Gakkai Wabun Rombunshi, 3(1), p.24 - 33, 2004/03
This paper concerns an application of digital optimal H estimator to the detection of faulty reactivity in real-time. The detection system, fundamentally based on the reactivity balance method, is composed of three modules, i.e. the net reactivity estimator, the feedback reactivity estimator and the reactivity balance circuit. H optimal filters are used for these two reactivity estimators, and the nonlinear neutronics are taken into consideration especially for the design of the net reactivity estimator. A series of performance tests of the detection system are conducted by using numerical simulations of reactor dynamics with the insertion of a faulty reactivity for an experimental fast breeder reactor JOYO. The system detects the typical artificial reactivity insertions of 1￠ within a few seconds with the accuracy of 0.1￠, and is satisfactory for its practical use.
Iwai, Takashi; Nakajima, Kunihisa; Kikuchi, Hironobu; Nagashima, Hisao; Kimura, Yasuhiko; Matsui, Hiroki; Arai, Yasuo
JAERI-Research 2002-038, 69 Pages, 2003/01
JAERI-Research-2002-038.pdf:12.46MB
Uranium-plutonium mixed carbide and nitiride fuel pins were fabricated in JAERI and irradiated at fast test rector JOYO based on the JAERI-JNC joint research program. The results of non-destructive and destructive post irradiation examinations cariied out at JNC were reported elsewhere. This report summarizes the results of destructive post irradiation examinations of (U,Pu)C and (U,Pu)N fuel pins carried out at JAERI.
Department of JMTR
JAERI-Conf 97-006, 178 Pages, 1997/03
no abstracts in English
Sasaki, Yuto; Iwamoto, Nobuyuki; Maeda, Shigetaka; Takaki, Naoyuki*
no journal, ,
In Japan, research is being promoted to improve and achieve domestic preparedness for the production of medical radioisotopes (RI) using existing fission reactors. We investigated the efficient production of 
Mo/
Tc by neutron activation with an alternative method of producing Mo that does not use enriched uranium (HEU, LEU) as a raw material, utilizing the neutron moderator filed around the core of the experimental fast reactor Joyo. As a result, we found that 231
33 TBq of Mo can be produced by irradiating the sample for 7 days in an irradiation field using a moderated assembly with a beryllium filling rate of 60%. This amount is enough to meet domestic weekly demand, even if we consider a supply of once every two weeks. However, Joyo has difficulty in continuing production due to annual inspections. Therefore, it would be possible to achieve a stable supply by establishing a supply system that is a best mix of other research reactors and accelerators.
-ray dose rates on the upper core structure of the experimental fast reactor JoyoIto, Chikara; Yamamoto, Takahiro; Maeda, Shigetaka; Ito, Hideaki; Sekine, Takashi
no journal, ,
In the experimental fast reactor Joyo, the upper core structure (UCS) was replaced. We have evaluated -ray dose rates on UCS in order to conduct radiation shielding design of the UCS cask and radiation exposure control in the UCS removal work. The -ray dose rates was calculated using the QAD-CGGP2R and corrected by the measured in-vessel axial distributions of -ray dose rate. In order to verify the -ray dose rate evaluation procedure, we measured spatial distribution of -ray on the surface of the cask, which contained UCS using plastic scintillating optical fiber (PSF) during the UCS removal work. The calculated PSF output values were approximately twice as large as measured through the UCS. Correcting the calculated -ray dose rates on the surface of the cask by results of the comparison has shown appropriate -ray dose rates distribution.
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.
