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Takamatsu, Kuniyoshi; Funatani, Shumpei*
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 17 Pages, 2023/04
The objectives of this study are as follows: to understand the characteristics, degree of passive safety features for heat removal were compared for RCCSs based on atmospheric radiation and based on atmospheric natural circulation under the same conditions. Therefore, the authors concluded that the proposed RCCS based on atmospheric radiation has the advantage that the temperature of the RPV can be stably maintained against disturbances in the outside air (ambient air). Moreover, methodology to utilize all the heat emitted from the RPV surface for increasing the degree of waste-heat utilization was discussed.
Takano, Kazuya; Oki, Shigeo; Doda, Norihiro; Chikazawa, Yoshitaka; Maeda, Seiichiro
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 7 Pages, 2023/04
The MOX fueled SMR-SFRs with lower linear heat rating of 100 W/cm and 50 W/cm, whereas the linear heat rating at rated power is around 400 W/cm in general, were designed to decrease the fuel temperature during its rated power state in order to pursue the inherent core safety for MOX fueled SMR-SFRs. The transient analyses for Anticipated Transient Without Scram (ATWS) events represented by an Unprotected Loss of Flow (ULOF) accident on the lower linear heat rating cores were performed considering their inherent feedback reactivity. Through the transient analysis, the inherent core safety performances for the lower linear heat rating cores were discussed based on the evaluated maximum coolant temperature and Cumulative Damage Fraction (CDF) as criteria to maintain the core and fuel integrity. The feasible design window for MOX fueled SMR-SFRs with the inherent core safety focusing on the linear heat rating was identified based on the transient analysis results.
Nishida, Akemi; Kawata, Manabu; Choi, B.; Iigaki, Kazuhiko; Shiomi, Tadahiko; Li, Y.
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 10 Pages, 2023/04
Our research and development are aimed at improving the accuracy of the three-dimensional seismic evaluation analysis method for nuclear buildings, which contributes to the probabilistic risk assessment caused by earthquakes (seismic PRA), using actual seismic observation records in collaboration with the Nuclear Regulation Authority since 2019. In this study, we constructed a large-scale observation system that enabled simultaneous measurements at multiple positions during earthquakes or against artificial waves. The accelerometers of the observation system were installed on/in the soil, floors, and on the walls of the nuclear building. This paper presents an outline of the large-scale observation system and the findings obtained from the analysis of the seismic observation records acquired using the system.
Matsuba, Kenichi; Emura, Yuki; Kamiyama, Kenji
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 8 Pages, 2023/04
A series of Fuel-Coolant Interaction (FCI) experiments discharging about 1 kg of molten stainless steel (SS), one of prototypic materials, into a sodium pool (about 30 cm in diameter, about 1 m in depth) has been conducted at the MELT facility of Japan Atomic Energy Agency. X-ray visualization program confirmed that molten SS jets with diameters of about 1 to 2 cm were broken up by FCIs which occurred with sodium vapor expansion at depths near the initial sodium level. Responses of thermocouples suggested that the jets were rapidly cooled near the initial sodium level and became SS fragments before reaching the bottom of the sodium pool. Results of experiments with molten SS jets confirmed that an evaluation methodology for jet breakup under sodium-cooled conditions needs to be developed by taking into account effects of thermal parameters related to sodium vaporization as well as conventional parameters, such as density ratio of a jet and coolant, and jet diameter.
Ishida, Shinya; Fukano, Yoshitaka; Tobita, Yoshiharu; Okano, Yasushi
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 8 Pages, 2023/04
Koike, Akari*; Nemoto, Masaya*; Nakashima, Risako*; Sakai, Takaaki*; Doda, Norihiro; Tanaka, Masaaki
Proceedings of 2023 International Congress on Advanced in Nuclear Power Plants (ICAPP 2023) (Internet), 2 Pages, 2023/04
To evaluate the effect of the operator's recognition of the accident management (AM) necessity on plant safety, the operator's recognition of the AM necessity was modeled as a function of time-dependent success probability, and dynamic PRA analyses were performed for a sodium-cooled fast reactor during abnormal snowfall. The analysis results showed that the operator's recognition of the snowfall can avoid the core damage at an earlier stage after the accident.