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Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
Experimental Thermal and Fluid Science, 151, p.111095_1 - 111095_15, 2024/02
Times Cited Count：7 Percentile：72.01(Thermodynamics)Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05
When liquid sodium leaks as a liquid jet from piping in a sodium-cooled fast reactor, the jet impinges with structures to produce splashing droplets which can cause significant combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impingement. In the present work, a nozzle with a sudden contraction in the cross-sectional area was designed to reproduce a supposed pipe leakage, and the breakup behavior of jet discharged from this nozzle was observed. The result shows that the breakup of jet was accelerated until the jet transformed into a particularly stable state when the jet velocity exceeded a certain value. Once the jet has transformed, it will not turn back unless turning down the flow rate to a very low value. The stable jet after the transformation has a longer breakup length than that before the transformation in the same flow rate.
Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 6 Pages, 2022/08
When a liquid sodium leakage accident occurs in a sodium-cooled fast reactor, the injected sodium collides with structures to produce splashing droplets, which can result in a violent combustion. According to previous studies on circular nozzles, the amount of splash is affected by the state of the jet at the moment of impact. However, the outlet shape of damaged area is hardly to be circular; and meanwhile it influences the flow pattern of jet a lot. Considering about this, in the present work, high-speed cameras were used to observe the jet discharged from oval nozzles vertically downward to investigate the falling process of the jet. The result shows that surface wave appears on the jet and within a certain range of flow velocity it can be observed obviously, meanwhile accelerate the breakup of jet.
Okawa, Tomio*; Mori, Shoji*; Liu, W.*; Ose, Yasuo*; Yoshida, Hiroyuki; Ono, Ayako
Nihon Genshiryoku Gakkai-Shi ATOMO
, 63(12), p.820 - 824, 2021/12
The evaluation method of the critical heat flux based on the mechanism is needed for the efficient design and development of fuel in reactors and the appropriate safety evaluation. In this paper, the current researches relating to the mechanism of the critical heat flux are reviewed, and the issue to be considered in the future are discussed.
Zhan, Y.*; Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 126, p.110402_1 - 110402_8, 2021/08
Times Cited Count：8 Percentile：52.12(Thermodynamics)Zhan, Y.*; Kuwata, Yusuke*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 120, p.110249_1 - 110249_12, 2021/01
Times Cited Count：13 Percentile：74.58(Thermodynamics)Zhan, Y.*; Kuwata, Yusuke*; Maruyama, Kiyotaka*; Okawa, Tomio*; Enoki, Koji*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 112, p.109953_1 - 109953_8, 2020/04
Times Cited Count：17 Percentile：73.76(Thermodynamics)Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Experimental Thermal and Fluid Science, 98, p.86 - 94, 2018/11
Times Cited Count：17 Percentile：67.20(Thermodynamics)Kuwata, Yusuke*; Zhan, Y.*; Enoki, Koji*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Takata, Takashi
Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 10 Pages, 2018/10
This study aims improvement of safety analysis for sodium fire accidents in sodium-cooled fast reactors. In the experiment, effect of viscosity on liquid jet impact on solid surface was studied.
Zhan, Y.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi
Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 6 Pages, 2017/07
It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments are performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It is shown that the splash ratio can be correlated well as a function of the impact Weber number and dimensionless impact frequency.
Yi, Z.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro; Takata, Takashi
Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 7 Pages, 2016/11
It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments were performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It was shown that the splash ratio can be correlated well as a function of the impact Weber number, the Strouhal number and the Ohnesorge number of the droplets impinging the liquid film.
Yi, Z.*; Oya, Naoki*; Enoki, Koji*; Okawa, Tomio*; Ohno, Shuji; Aoyagi, Mitsuhiro
Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 7 Pages, 2016/06
It is important to set the amount of sodium droplet mechanistically for appropriate numerical evaluations of sodium leak and fire behavior in a sodium-cooled fast reactor plant. In the present work, fundamental experiments were performed to measure the splash ratio during the vertical water jet impact onto a horizontal wall. It was shown that the splash ratio can be correlated well as a function of the impact Weber number and the Strouhal number of the droplets impinging the liquid film.
Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Takata, Takashi; Aoyagi, Mitsuhiro
no journal, ,
no abstracts in English
Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
no journal, ,
no abstracts in English
Sun, G.*; Zhan, Y.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
no journal, ,
no abstracts in English
Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
no journal, ,
no abstracts in English
Ono, Ayako; Okawa, Tomio*; Yoshida, Hiroyuki
no journal, ,
We are developing a new prediction method for a departure from nucleate boiling (DNB) in the fuel assemblies, which will contribute to the design and safety evaluation for the new-generation reactors. In our project, we consider that the formation of a large vapor mass on the heating surface is the first trigger of the DNB. Therefore, we decided to predict the heat flux to form the large vapor mass by combining a two-phase flow CFD and the large vapor mass formation model based on the mechanism. In this presentation, the concept of the model for the large vapor mass forming and the result of the preliminary analysis are discussed.
Sun, G.*; Okawa, Tomio*; Aoyagi, Mitsuhiro; Uchibori, Akihiro; Okano, Yasushi
no journal, ,
no abstracts in English
Shirakata, Takaaki*; Yamashita, Susumu; Okawa, Tomio*
no journal, ,
The purpose of this study is to elucidate the process of crown formation and the effect of gravity on droplet/film impact phenomena using numerical analysis. The effects of varying the gravitational acceleration on the time evolution of the crown height and crown radius are investigated and correlations are developed. The correlation equation, including the gravity term, clarifies the process of crown formation, and provides a better understanding of secondary droplet formation, which has adverse effects in various industrial fields. It is expected that this study will provide new insights into the generation of splashes in the same phenomenon.
Sun, G.*; Yamashita, Susumu; Okawa, Tomio*; Yoshida, Hiroyuki
no journal, ,
When coolant leak occurs in sodium-cooled fast reactors, liquid sodium jet ejected from damaged piping can impact solid surfaces such as floors, generating splashing droplets. These droplets significantly increase the contact area between sodium and atmosphere, thereby intensifying combustion reactions. The quantity and size of splashing droplets, which influence the contact area, depend on the state of the jet during impact. Therefore, understanding the falling behavior of the jet is crucial. In this study, the breakup characteristics were analyzed to investigate the applicability of the numerical fluid dynamics simulation code JUPITER to the falling behavior of liquid sodium jets. The simulation results were similar to the extrapolated values from the empirical equations obtained from the experimental results with alternative fluids. Prospects for applying JUPITER to the analysis of sodium jet falling behavior were obtained.
