Development of the three-dimensional CFD analysis model of helium heat exchanger type steam reformer for hydrogen production by nuclear heat

Ishii, Katsunori; Ono, Masato; Noguchi, Hiroki; Shimizu, Atsushi; Nomoto, Yasunobu; Sato, Hiroyuki; Sakaba, Nariaki

Proceedings of World Hydrogen Technologies Convention 2025 (WHTC 2025) (Internet), p.26 - 28, 2025/10

https://www.whtc2025.com/conference-proceedings

Experiments on Concrete-loaded core in the modified STACY

Araki, Shohei; Arakaki, Yu; Maekawa, Tomoyuki; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Tada, Yuta; Sumiya, Masato; Seki, Masakazu; Aizawa, Eiju; et al.

Proceedings of Nuclear Criticality Safety Division 2025 Conference (NCSD 2025) (Internet), p.80 - 89, 2025/09

In order to investigate the effect on criticality characteristics of fuel debris containing concrete composition in the Fukushima Daiichi Nuclear Power Plant, critical experiments loaded concrete rods were conducted in the modified STACY. The experimental cores of the modified STACY were composed of light water, fuel rods, and concrete rods with grid plates with 15.0-mm lattice intervals in the core tank. Each fuel rod consisted of a zirconium alloy clad tube (9.5-mm outer diameter) and UO pellets (8.2-mm diameter) with 4.98wt.% 235U enrichment. Each concrete rod was composed of concrete simulant pellets (7.0-mm diameter) and an aluminum alloy clad tube (9.5-mm outer diameter). The concrete simulant pellets were fabricated using an aggregate-free mortar in order to ensure a uniform composition of the pellets, and the composition was evaluated by chemical analysis. Three experimental cores were configurated with 9, 25 and 69 concrete rods. The critical water level data were obtained. An effect of composition uncertainty of the concrete simulant pellet was estimated by sensitivity analysis using MCNP6.2 with JENLD-4.0. The sensitivity analysis estimated the effect to be less than 3 pcm. The calculation results performed using MCNP6.2 with ENDF/B-VII.1, JENDL-4.0, and JENDL-5 libraries showed a tendency to overestimate the multiplication factor according to increasing the loading amount of the concrete rods.

Integrated thermal power measurement in the modified STACY for the performance inspections

Araki, Shohei; Aizawa, Eiju; Murakami, Takahiko; Arakaki, Yu; Tada, Yuta; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Sumiya, Masato; Seki, Masakazu; et al.

Annals of Nuclear Energy, 217, p.111323_1 - 111323_8, 2025/07

https://doi.org/10.1016/j.anucene.2025.111323

JAEA has modified the STACY from a homogeneous system using solution fuel to a heterogeneous system using fuel rods in order to obtain criticality characteristics of fuel debris. The modification of the STACY was completed in December 2023. A series of performance inspections were conducted for the start of experimental operations. A new thermal power calibration is required for the performance inspections in order to operate at less than 200 W, which is the permitted thermal power. However, the thermal power measurement method and calibration data used in the former STACY is no longer available due to the modification of the modified STACY. We measured the thermal power of the STACY using the activation method that was improved to adapt to the measurement condition and calibrated the power meter system. Since the positions where activation foils could be installed were very limited, the thermal power was evaluated using numerical calculations supplemented by experimental data. Neutron flux data at the positions of the activation foil was measured by the activation method. Neutron distribution in the core was calculated by the Monte Carlo code MVP. A response function of the activation foil was calculated using the PHITS. The uncertainty of the thermal power measurement was conservatively estimated to be about 15%. Four operations were conducted for the thermal power measurement. The power meter was calibrated by using three operational data and tested with the one operational data. It was found that the indicated value of the meter adjusted by the STACY before the modification work would tend to overestimate the actual output by about 40%. In addition, the current calibration was able to calibrate the meter to within 3% accuracy.

Estimation of H demand and HTGR development potential in the industrial complex in Japan

Noguchi, Hiroki; Ishii, Katsunori; Ono, Masato; Kasahara, Seiji; Sato, Hiroyuki; Sakaba, Nariaki

Proceedings of World Hydrogen Technology Convention 2025 (WHTC 2025) (Internet), p.50 - 52, 2025/00

Achieving carbon neutrality in Japan in 2050, hydrogen is expected to be used as an alternative to fossil fuels in the hard-to-abate sectors. In steelmaking, hydrogen-based reduction process has been developed as a substitute for the conventional blast furnace steelmaking process, which involves the reduction of iron ore by coke. In chemical industry, a novel olefin production process has been developed using hydrogen and CO, through methanol as an intermediate chemical. A large amount of hydrogen is required for these novel processes. Nuclear energy is well-suited to large-scale low-carbon hydrogen production. High temperature gas cooled reactor (HTGR) is a type of nuclear reactor featuring extraction of high temperature heat. The heat can be applicable to hydrogen production. This study predicts hydrogen demand in five industrial complexes in Japan in 2050 and estimates the potential for introducing HTGR to meet the demand. The introduction of HTGR could be a promising solution for decarbonizing industrial complexes due to their large-scale hydrogen supply capacity.

Sustainable thermoelectric materials; Utilizing Fukushima weathered biotite via molten salt treatment

Honda, Mitsunori; Kaneta, Yui; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Goto, Takuya*

AIP Advances (Internet), 14(5), p.055034_1 - 055034_6, 2024/05

https://doi.org/10.1063/5.0206317

This study examines the utilization of Fukushima weathered biotite(WB)as an alternative to conventional thermoelectric materials traditionally derived from rare and toxic substances. WB underwent milling, classification, and subsequent heat treatment via molten-salt treatment to produce crystals exhibiting conductivity akin to semiconductors within from 650C to 850C range. Evaluation of WB and the derived crystal's electrical conductivity and Seebeck coefficient showcased their viability for high-temperature thermoelectric applications. Consequently, WB attained a dimensionless figure of merit (ZT) of 0.015, signaling its potential as a thermoelectric material that surpasses 650C.

Development plan for coupling technology between high temperature gas-cooled reactor HTTR and hydrogen production facility, 1; Overview of the HTTR heat application test plan to establish high safety coupling technology

Nomoto, Yasunobu; Mizuta, Naoki; Morita, Keisuke; Aoki, Takeshi; Okita, Shoichiro; Ishii, Katsunori; Kurahayashi, Kaoru; Yasuda, Takanori; Tanaka, Masato; Isaka, Kazuyoshi; et al.

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 7 Pages, 2023/05

Machine learning sintering density prediction model for MOX fuel pellet

Kato, Masato; Nakamichi, Shinya; Hirooka, Shun; Watanabe, Masashi; Murakami, Tatsutoshi; Ishii, Katsunori

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(2), p.51 - 58, 2023/04

https://doi.org/10.3327/taesj.J22.008

Uranium and Plutonium mixed oxide (MOX) pellets used as fast reactor fuels have been produced from several raw materials by mechanical blending method through processes of ball milling, additive blending, granulation, pressing, sintering and so on. It is essential to control the pellet density which is one of the important fuel specifications, but it is difficult to understand relationships among many parameters in the production. Database for MOX production was prepared from production results in Japan, and input data of eighteen types were chosen from production process and made a data set. Machine learning model to predict sintered density of MOX pellet was derived by gradient boosting regressor, and represented the measured sintered density with coefficient of determination of R=0.996

Sodium-cooled Fast Reactors

Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

https://shop.elsevier.com/books/sodium-cooled-fast-reactors/morishita/978-0-12-824076-2

This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.

On-line rapid purification of [N]N gas for visualization of nitrogen fixation and translocation in nodulated soybean

Yin, Y.-G.*; Ishii, Satomi*; Suzui, Nobuo*; Igura, Masato*; Kurita, Keisuke; Miyoshi, Yuta*; Nagasawa, Naotsugu*; Taguchi, Mitsumasa*; Kawachi, Naoki*

Applied Radiation and Isotopes, 151, p.7 - 12, 2019/09

https://doi.org/10.1016/j.apradiso.2019.05.034

Accurate analysis of N fixation in leguminous crops requires determination of N utilization within an intact plant however, most approaches require tissue disassembly. We developed a simple and rapid technique to generate high-purity and high-yield [N]N gas and obtained real-time images of N fixation in an intact soybean plant. The purification efficiency was 81.6% after decay correction.

Study on source of radioactive material in primary coolant of HTTR

Ishii, Toshiaki; Shimazaki, Yosuke; Ono, Masato; Fujiwara, Yusuke; Ishitsuka, Etsuo; Hamamoto, Shimpei

Proceedings of 9th International Topical Meeting on High Temperature Reactor Technology (HTR 2018) (USB Flash Drive), 3 Pages, 2018/10