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Ono, Ayako; Sakashita, Hiroto*; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki
Mechanical Engineering Journal (Internet), 11(4), p.24-00188_1 - 24-00188_12, 2024/07
Japan Atomic Energy Agency (JAEA) is developing the evaluation method for a two-phase flow in the reactor core using simulation codes based on the Volume Of Fluid (VOF) method. JAEA started developing a Simplified Boiling Model (SBM) for the large-scale two-phase flow in the fuel assemblies. In the SBM, the motion and growth equations of the bubble are solved to obtain their diameter and time length at the detachment, of which size scale is within/around the calculation grid size of the numerical simulation. JUPITER calculates the bubble behavior with a scale of more than several 
m. In this study, the convection boiling on a vertical heating surface is simulated using the developed SBM. The comparison between the simulation and experimental results showed good reproducibility of the heat flux and velocity dependency on the passage period of the bubble.
Ono, Ayako; Sakashita, Hiroto*; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 7 Pages, 2022/10
The new prediction method of critical heat flux (CHF) of the fuel assemblies based on the mechanism is proposed in this study. The prediction method of CHF based on the mechanism has been needed for a long time to enhance the safety analysis and reduce the design cost. From several experimental findings of the liquid-vapor behavior near the heating surface from the nucleate boiling to the CHF, the authors consider that the macrolayer dryout model will be appropriate to predict the CHF under the reactor condition. The prediction method of the macrolayer thickness and the passage period of vapor mass in the fuel assemblies are needed to predict CHF from the macrolayer dryout model. In this study, the CHF under the forced convection is evaluated by combining the prediction methods for the macrolayer thickness and passage period of vapor mass, which are proposed by authors. The prediction of the CHF under the forced convection is examined and compared with the experimental data.
Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki
Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-13) (Internet), 12 Pages, 2022/09
Japan Atomic Energy Agency is developing the computational fluid dynamics code, JUPITER, based on the volume of fluid (VOF) method to analyze detailed thermal-hydraulics in a reactor. The detailed numerical simulation of boiling from a heating surface needs a substantial computational cost to resolve the microscale thermal-hydraulic phenomena such as the bubble generation from a cavity and evaporation of a micro-layer. This study developed the simplified boiling model from the heating surface to reduce the computational cost, which will apply to the detailed simulation code based on the surface tracking method such as JUPITER. We applied the simplified boiling model to JUPITER, and compared the simulation results with the experimental data of the vertical heating surface in the forced convection. We confirmed the degree of their reproducibility, and the issues to be modified were extracted.
Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki
Dai-26-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2022/07
JAEA is implementing a simulation of a two-phase flow in the reactor core by TPFIT and JUPITER which are developed by JAEA based on the surface tracking method. However, it is impossible to simulate a boiling on the heating surface in the large-scale domain by this type of simulation method since the simulation of boiling based on the surface tracking method needs the fine mesh which sufficiently resolves the initiation of boiling. Therefore, JAEA started to develop the simplified boiling model applied for the two-phase flow in the fuel assemblies. In this study, the simulation results of the convection boiling on a vertical heating surface and the comparison between the simulation results and experimental results are shown.
Ono, Ayako; Sakashita, Hiroto*; Yoshida, Hiroyuki
Heat Transfer Engineering, 42(21), p.1775 - 1788, 2021/00
Times Cited Count：4 Percentile：24.92(Thermodynamics)In this study, the macrolayer formation model is proposed to predict the critical heat flux in the saturated and subcooled pool boiling based on the macrolayer dryout model. This model concept is based on the results of the previous experiments. In the model, the nucleation site is assumed to distribute based on the Poisson distribution. Combining the proposed macrolayer formation model and macrolayer dryout model, the CHFs up to subcooling 40K were predicted and they are successfully good agreement with the experimental data. Moreover, the concept of the model was confirmed by the numerical simulation using the TPFIT.
Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki
no journal, ,
Understanding the boiling heat transfer characteristics in debris beds is indispensable to assess the coolability of molten debris at severe accident. However, the trigger mechanism of the critical heat flux on the bottom heated debris beds has not been fully elucidated. This study performed the visualization measurements using a transparent heating surface on which small particles are accumulated. The boiling behaviors were observed via a total reflection technique, and effects of particle size on dryout and rewetting process of the heating surface were examined.
Sakashita, Hiroto*; Kawakami, Taira*; Ono, Ayako; Yoshida, Hiroyuki
no journal, ,
This study measured the critical heat flux on a bottom surface for bottom and volume heated particulate beds, where small spherical metal particles were placed on a 75mm diameter heating surface and internally heated by induction heating. The data were obtained by varying the particle size and the volumetric heated rates in the particulate beds. The CHF on the bottom surface decreases with decreasing the particle size and is unaffected by the volumetric heated rates of the particulate beds. The previously proposed CHF correlations, which were derived based on the assumption that the CHF is triggered by hydrodynamic phenomena of liquid and vapor flows through the particulate beds, are not applicable to the CHF for bottom and volume heated particulate beds.
Murata, Tetsuya*; Miwa, Shuichiro*; Sakashita, Hiroto*; Mori, Michitsugu*; Kasahara, Seiji; Yan, X.
no journal, ,
Application of a high temperature gas-cooled reactor (HTGR) for snow melting and district heating in Hokkaido was investigated. Concept design of a heat delivery system, modeling of pipes and a heat exchanger, calculation of heat supply amount from HTGR, and determination of location of the HTGRs were carried out. Sapporo and Ishikari were assumed as a heat demand district. To supply the maximum heat demand 435 MW in a year, 2 GTHTR300s, a kind of design of HTGR, were required. Though the distance from the GTHTR300 site and the heat demand district was 40 km, the temperature of the GTHTR300 waste heat was enough for the district heating. Double pipe for the heat transportation from the GTHTR300 to the district was advantageous for less heat loss and smaller excavation area. This system required 9 double pipes and more that 5000 heat exchangers.
Ono, Ayako; Yamaguchi, Manabu*; Sakashita, Hiroto*; Uesawa, Shinichiro; Shibata, Mitsuhiko; Yoshida, Hiroyuki
no journal, ,
The establishment of the evaluation method of the critical heat flux for light water reactors is needed. However, the boiling phenomena under high pressure remain to be clarified. The measurement system based on detecting the electric capacitance has been developed, which detects the liquid-vapor behavior vicinity of the heating surface in order to clarify the mechanism of the critical heat flux under the higher pressure region. In this study, the detail of the measurement system and the result to confirm the validity of the measurement system are reported.
Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki
no journal, ,
JAEA is implementing a simulation of a two-phase flow in the reactor core by TPFIT and JUPITER which are developed by JAEA based on the surface tracking method. However, it is impossible to simulate a boiling on the heating surface in the large-scale domain by this type of simulation method since the simulation of boiling based on the surface tracking method needs the fine mesh which sufficiently resolves the initiation of boiling. Therefore, JAEA started to develop the simplified boiling model applied for the two-phase flow in the fuel assemblies. In this study, the simulation results of the convection boiling on vertical heating surface and the comparison between the simulation results and experimental results are shown.
Kawakami, Taira*; Sakurada, Keishi*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki
no journal, ,
The effect of height and density of accumulated particles on the critical heat flux was investigated on the heating surface, where the particles were accumulated, in order to investigate the cooling process of debris under the severe accident. The thermal-hydraulic behavior on the heating surface was visualized from the backsides of heating surface made of glass.
Sakurada, Keishi*; Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki
no journal, ,
This study measured the dryout heat fluxes on a bottom surface for bottom and volume heated debris beds, where small spherical metal particles were placed on a 75 mm diameter heating surface and internally heated by induction heating. The data were obtained by varying the particle size and the volumetric heated rate, and compared with the available correlations.
Sakurada, Keishi*; Kawakami, Taira*; Sakashita, Hiroto*; Ono, Ayako; Yoshida, Hiroyuki
no journal, ,
This study measured the dryout heat fluxes for bottom heated debris beds, where small spherical particles were placed on a 75mm diameter heating surface. The data were obtained by varying the particle size in the range of 3 to 10mm, and compared with the predicted results with the one dimensional model proposed by Lipinski.
Ono, Ayako; Sakashita, Hiroto*
no journal, ,
A macrolayer formation model for saturated and subcooled pool boiling is proposed, which is developed based on the visual observation of boiling behavior. The distribution of nucleation sites is assumed to distribute based on Poisson distribution. The predicted macrolayer thicknesses are used for the prediction of CHFs in saturated and subcooled pool boiling based on the macrolayer dryout model. The combination of the macrolayer dryout model and macrolayer formation model is able to predict the CHF well at least up to subcooling 40K.
