Development of RELAP5-3D model for an integrated test facility for advanced reactor systems

Makuuchi, Etsuyo; Aizawa, Kosuke; Imai, Yoshiyuki; Kamiji, Yu; Akasaka, Naoaki; Yan, X.; Sakuma, Wataru*; Tanihira, Masanori*

Nuclear Technology, 11 Pages, 2026/00

https://doi.org/10.1080/00295450.2025.2582351

Investigation on daily load following operation in sodium cooled fast reactor

Aizawa, Kosuke; Chikazawa, Yoshitaka; Morohoshi, Kyoichi*; Kubo, Koji*; Uchita, Masato*

Proceedings of 2025 International Congress on Advances in Nuclear Power Plants (ICAPP 2025) (Internet), 8 Pages, 2025/09

Subcooled-boiling detection by data-driven acoustic diagnosis

Ueki, Yoshitaka*; Hirako, Itsuki*; Tezuka, Kosuke*; Aizawa, Kosuke; Ara, Kuniaki*

Proceedings of 12th International Conference on Multiphase flow (ICMF2025) (Internet), 2 Pages, 2025/05

Study on performance evaluation of self-actuated shutdown system for sodium-cooled fast reactor; Flow field measurement around a curie point electromagnet

Yamasaki, Ryota; Aizawa, Kosuke; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 7 Pages, 2024/11

CNN-based acoustic identification of gas-liquid jet; Evaluation of noise resistance and visual explanation using Grad-CAM

Mikami, Nao*; Ueki, Yoshitaka*; Shibahara, Masahiko*; Aizawa, Kosuke; Ara, Kuniaki*

International Journal of Multiphase Flow, 171, p.104688_1 - 104688_13, 2024/01

https://doi.org/10.1016/j.ijmultiphaseflow.2023.104688

State sensing of bubble jet flow based on acoustic identification of deep learning

Mikami, Nao*; Ueki, Yoshitaka*; Shibahara, Masahiko*; Aizawa, Kosuke; Ara, Kuniaki

Proceedings of 17th International Heat Transfer Conference (IHTC-17) (Internet), 9 Pages, 2023/08

Study on performance evaluation of self-actuated shutdown system for sodium-cooled fast reactor; Investigation on flow field around curie point electromagnet

Aizawa, Kosuke; Hiyama, Tomoyuki; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 6 Pages, 2023/05

Self-actuated shutdown system (SASS) is a passive reactor-shutdown system that utilizes a Curie-point electromagnet (CPEM), which features the characteristic of loss in magnetism when the magnet temperature reaches the Curie point. A control rod with SASS is inserted into the core by gravity without recourse to any active shutdown system. To allow the SASS to effectively function, efficiently guiding high-temperature fluid from the fuel assembly to CPEM is important. Therefore, CPEM features a complicated shape such as having 45 fins, and a flow collector is installed upstream of CPEM to direct the flow from the fuel subassembly outlet to CPEM. In this report, the water experiment was performed on the full-scale model that simulates from the outlets of the fuel assemblies to the SASS flow collector, and flow phenomena around the temperature sensing part was analyzed from the data obtained by PIV measurement.

State sensing of bubble jet flow based on acoustic recognition and deep learning

Mikami, Nao*; Ueki, Yoshitaka*; Shibahara, Masahiko*; Aizawa, Kosuke; Ara, Kuniaki

International Journal of Multiphase Flow, 159, p.104340_1 - 104340_8, 2023/02

https://doi.org/10.1016/j.ijmultiphaseflow.2022.104340

This study covers the accidental generation of bubble jet flow caused by steam generator (SG) tubes damaging in sodium cooled fast reactors (SFRs). The main objective of this study is to develop a novel state sensing method of bubble jet flow based on acoustic recognition and deep learning. Prior to the application of this method to actual SFRs, we utilize air and water as simulant fluids in order to perform the proof of concept. This study is divided into three phases. The first phase is the acquisition and analysis of pipe flow sound and bubble jet flow sound, each of which simulates the normal and anomaly sound from SG tubes in SFRs. The second phase is the preprocessing of acoustic signals and feature extraction. The third phase is the building of deep learning models and performance evaluation. As a result, every of our proposed models could distinguish between pipe flow sound and bubble jet sound with an accuracy of almost 100.00%, and the best model could classify pipe flow sound and three types of bubble jet flow sound with an accuracy of 99.76%. This result suggests that the acoustic recognition with deep learning has great potential to sense the state of bubble jet flow in actual SFRs.

Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 2; Transient behavior under operations of multiple decay heat removal systems

Aizawa, Kosuke; Tsuji, Mitsuyo; Kobayashi, Jun; Kurihara, Akikazu

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10

In sodium-cooled fast reactors (SFRs), optimizing the design and operate decay heat removal systems (DHRSs) is important for safety enhancement against severe accidents. Thus, it is required to evaluate the cooling capability of DHRSs including the natural circulation behavior inside the reactor vessel during heat-removal phase that the fuel debris relocated in the reactor vessel is cooled by DHRSs. In this study, the experiments which simultaneously operations of the dipped-type DHX and the penetrated-type DHX were conducted to investigate the effect of operating multiple decay heat removal system on the natural circulation behavior in the reactor vessel. After achieving the stable conditions by operating the dipped-type DHX or the penetrated-type DHX, the other DHX was operated and the transient behavior was clarified by the temperature measurements. The clear temperature rise in the reactor vessel was confirmed by operating the penetrated-type DHX as second DHX operation under the condition of the dipped-type DHX operation at the beginning and the high heater power of fuel debris on the core catcher. Therefore, it was confirmed that the inhibition of the cooling for the decay heat occurred by operating multiple DHXs.

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.