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Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Tanaka, Masaaki
Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 8 Pages, 2022/08
Development of evaluation method for cover gas entrainment (GE) by vortices generated at free surface in upper plenum of sodium-cooled fast reactor (SFR) is required. GE evaluation tool, named StreamViewer, based on method using numerical results of three-dimensional computational fluid dynamics analysis for loop-type SFRs has been developed. In this study, modification of evaluation method of StreamViewer to rationalize conservativeness in evaluation results was examined by identifying vortex center lines and calculating three-dimensional distribution of pressure decrease along vortex center lines. The applicability of modified method was checked using water experimental result in rectangular open channel where unsteady vortices are generated. As the result, it was indicated that evaluation results on gas core depth which were excessive in current method were improved in modified method, and it is confirmed that modified method may discriminate onset of GE with appropriate criteria.
Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Tanaka, Masaaki
Nihon Kikai Gakkai Kanto Shibu Ibaraki Koenkai 2021-Nendo Koen Rombunshu (Internet), 4 Pages, 2021/08
For evaluation of gas entrainment phenomenon at free surface in reactor vessel of sodium-cooled fast reactor, the gas entrainment evaluation tool named "Stream Viewer" has been developed. In Stream Viewer, depth of surface vortex dimple is predicted by calculating pressure decrease at the vortex center using velocity distribution around the vortex and Burgers vortex model. In this report, a method to identify continuous vortex center lines from a velocity distribution is newly developed. It becomes possible to evaluate three-dimensional distribution of pressure decrease along vortex center line. Then, the method is validated by applying Stream Viewer to an open channel experiment. As the result, it was confirmed that vortex center lines were successfully identified by the improved Stream Viewer. Moreover, it was also shown that the evaluation accuracy of gas entrainment was expected to be improved by considering distribution of pressure decrease along vortex center line.
Ito, Kei*; Ito, Daisuke*; Saito, Yasushi*; Ezure, Toshiki; Matsushita, Kentaro; Tanaka, Masaaki; Imai, Yasutomo*
Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.6632 - 6642, 2019/08
In this paper, a mechanistic model is proposed to calculate the entrained gas flow rate by a free surface vortex. The model contains the theoretical equation of transient gas core elongation and the empirical equation of critical gas core length for gas bubble detachment. Based on those two equations, the entrained gas flow rate is calculated as the portion of the gas core elongated beyond the critical gas core length per unit time. Then, the mechanistic model was applied to the calculation of the entrained gas flow rate in a simple water experiment. As a result, it is confirmed that the entrained gas flow rate grows rapidly when the liquid (water) flow rate, which determine the strength of a free surface vortex, exceeds a certain threshold value.
Imai, Yoshinori*; Takahashi, Hideyuki*; Kitagawa, Kentaro*; Matsubayashi, Kazuyuki*; Nakai, Noriyuki*; Nagai, Yuki; Uwatoko, Yoshiya*; Machida, Masahiko; Maeda, Atsutaka*
Journal of the Physical Society of Japan, 80(1), p.013704_1 - 013704_4, 2011/01
Times Cited Count：36 Percentile：81.82(Physics, Multidisciplinary)no abstracts in English
Kajimoto, Ryoichi; Yokoo, Tetsuya*; Nakajima, Kenji; Nakamura, Mitsutaka; Inamura, Yasuhiro; Maruyama, Ryuji; Soyama, Kazuhiko; Suzuya, Kentaro; Ino, Takashi*; Oyama, Kenji*; et al.
no journal, ,
no abstracts in English
Kajimoto, Ryoichi; Yokoo, Tetsuya*; Nakajima, Kenji; Nakamura, Mitsutaka; Inamura, Yasuhiro; Maruyama, Ryuji; Soyama, Kazuhiko; Suzuya, Kentaro; Ino, Takashi*; Oyama, Kenji*; et al.
no journal, ,
4SEASONS is a chopper-type inelastic neutron spectrometer, and one of the day-one instruments at the spallation neutron source facility in Japan Proton Accelerator Research Complex (J-PARC). The targeted energy range is 5-300meV, and the spectrometer is optimized in intensity in this energy range by moderating the resolutions (
% at 
), by incorporating an efficient beam transport system, and by realizing multi incident energy (
) measurement. The high intensity and efficiency available at 4SEASONS make this spectrometer suitable for study of novel quantum phenomena in high-
superconductors and related systems. In the present paper, we will report the current status of the development and the construction of 4SEASONS, such as construction of the vacuum tank and the shielding, development of the new Fermi chopper for the multi- measurement, 2.5m-long 
He PSDs, and the beam transport system.
Furumoto, Hideyuki*; Usuda, Jitsuo*; Maehara, Sachio*; Imai, Kentaro*; Ishizumi, Taichiro*; Honda, Hidetoshi*; Oka, Kiyoshi; Kajiwara, Naohiro*; Ohira, Tatsuo*; Ikeda, Norihiko*
no journal, ,
no abstracts in English
Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Tanaka, Masaaki
no journal, ,
In safety design of sodium-cooled fast reactor, generation of a cover gas entrainment vortex at free surface in upper plenum is an issue. It is necessary to evaluate gas entrainment vortex by numerical analysis, and gas entrainment amount evaluation tool "Stream Viewer" based on velocity distribution obtained by numerical analysis is developed. In this report, as a part of the development of Stream Viewer, evaluation method to identify vortex center line from free surface is examined to evaluate three dimensional behavior of gas entrainment vortex. The evaluation method was applied to an open channel water test in which an wake vortex is generated unsteadily from the plate. It was confirmed that vortex center line can be identified and a vortex that propagates to downstream and gas core grows can be distinguished from a vortex in which gas core does not grow by evaluation method of the vortex center line.
Nagatsuka, Kentaro*; Sato, Hiroyuki; Imai, Yoshiyuki; Yan, X.
no journal, ,
In order to improve economics of High Temperature gas cooled reactors (HTGR) by means of increasing core power density, HTGR's fuel assembly in which converged coolant flow is adapted is proposed to achieve reduction of fuel temperature during normal operation and heat transfer flow characteristics is estimated with numerical simulation. As a result of estimation, a perspective of fuel temperature reduction is obtained without numbers of fuel enrichment which are required in the conventional method.
Matsushita, Kentaro; Ezure, Toshiki; Fujisaki, Tatsuya*; Imai, Yasutomo*; Tanaka, Masaaki
no journal, ,
Development of evaluation method for cover gas entrainment (GE) by vortices generated at free surface in upper plenum of sodium-cooled fast reactor (SFR) is required. An evaluation method by predicting vortices from flow velocity distribution obtained by 3D CFD analysis is developed, and partial refinement of analysis mesh from the viewpoint of improving efficiency of 3D CFD analysis is examined. In this study, a method of predicting vortex radius that can occur in a system by machine learning and using the predicted value as a reference value for analysis mesh before applying refinement (initial mesh). CFD analysis was performed for cylinder column system where wake vortex occurs by changing parameters such as cylinder diameter and inlet flow velocity, and supervised learning was performed using the obtained variables and vortex radius was predicted. As a result, it was obtained that initial mesh size can be efficiently determined by using the predicted vortex radius as a reference.
Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Tanaka, Masaaki
no journal, ,
Japan Atomic Energy Agency (JAEA) is developing AI-aided advanced reactor life cycle optimization method, ARKADIA, in order to support the development of various reactor systems, including sodium-cooled fast reactors (SFRs). One of the important thermal-hydraulic issues in SFR design is the suppression of cover gas entrainment caused by dip vortices in the free surface of the upper plenum of the reactor, and JAEA is developing gas entrainment evaluation system centered on the gas entrainment evaluation tool, StreamViewer, in ARKADIA. In this report, the overview of gas entrainment evaluation system in ARKADIA and the development status of StreamViewer are reported. In addition, the results of applying StreamViewer to the analysis results of the water flow test system and confirming that it is possible to evaluate the gas entrainment phenomenon are reported.
Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Tanaka, Masaaki
no journal, ,
In the sodium-cooled fast reactors, evaluation of cover gas entrainment (GE) by dip vortices at the free surface in the upper plenum of reactor vessel is important. In this study, GE evaluation model, including the identification of vortex center lines between free surface and suction port from the flow velocity distribution obtained by three-dimensional analysis, the calculation of pressure decrease distribution along vortex center line, and the comparison of pressure decrease and the hydrostatic pressure, was investigated. The analyses for GE experiments in a rectangular flow channel were performed by changing the inlet flow velocity condition, and this evaluation model was applied to the flow velocity distribution obtained from the analysis results. As a result, it was confirmed that the phenomenon in which the occurrence of GE increased as the inlet flow velocity increased was reproduced as in the experimental results.
Matsushita, Kentaro; Ezure, Toshiki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Tanaka, Masaaki
no journal, ,
In sodium-cooled fast reactors, the cover gas is entrained into the coolant due to the dimple vortices generated in the free surface in the upper plenum of the reactor vessel, and gas entrainment (GE) phenomenon may affect core behavior. It is necessary to develop evaluation methods of GE phenomenon. In this study, a GE evaluation model, PVL model (Pressure Vortex Line model) was constructed. The PVL model includes the identification of vortex center lines from the flow velocity distribution obtained by 3-D analysis, the calculation of the 3-D distribution of pressure decrease along the vortex center line and the evaluation of gas core length of vortex by comparing the pressure decrease and the hydrostatic pressure. The PVL model was applied to the analysis results of advective vortex experiments in a rectangular channel system to evaluate GE. As the result, it was confirmed that it was possible to judge the GE occurrence of advective vortices by the application of PVL model.
