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安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介
Nuclear Engineering and Design, 368, p.110785_1 - 110785_14, 2020/11
被引用回数：10 パーセンタイル：75.92(Nuclear Science & Technology)The hydrogen behavior in a nuclear containment vessel is one of the significant issues raised when discussing the potential of hydrogen combustion during a severe accident. Computational Fluid Dynamics (CFD) is a powerful tool for better understanding the turbulence transport behavior of a gas mixture, including hydrogen. Reynolds-averaged Navier-Stokes (RANS) is a practical-use approach for simulating the averaged gaseous behavior in a large and complicated geometry, such as a nuclear containment vessel; however, some improvements are required. We implemented the dynamic modeling for 
based on the previous studies into the OpenFOAM ver 2.3.1 package. The experimental data obtained by using a small scale test apparatus at Japan Atomic Energy Agency (JAEA) was used to validate the RANS methodology. Moreover, Large-Eddy Simulation (LES) was performed to phenomenologically discuss the interaction behavior. The comparison study indicated that the turbulence production ratio by shear stress and buoyancy force predicted by the RANS with the dynamic modeling for was a better agreement with the LES result, and the gradual decay of the turbulence fluctuation in the stratification was predicted accurately. The time transient of the helium molar fraction in the case with the dynamic modeling was very closed to the VIMES experimental data. The improvement on the RANS accuracy was produced by the accurate prediction of the turbulent mixing region, which was explained with the turbulent helium mass flux in the interaction region. Moreover, the parametric study on the jet velocity indicates the good performance of the RANS with the dynamic modeling for on the slower erosive process. This study concludes that the dynamic modeling for is a useful and practical approach to improve the prediction accuracy.
Studer, E.*; 安部 諭; Andreani, M.*; Bharj, J. S.*; Gera, B.*; Ishay, L.*; Kelm, S.*; Kim, J.*; Lu, Y.*; Paliwal, P.*; et al.
Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 16 Pages, 2018/10
Nuclear engineering research groups were interested in the phenomena of the interaction between a rising jet and a stratified layer located above in order to better understand the underlying mechanisms of hydrogen accumulation and dispersion in a nuclear reactor containment. Previous studies were performed with an upward jet of fluid heavier or lighter than the upper stratified layer. However, in real configurations i.e. the inner part of a nuclear containment, obstacles such as pipes, components as pumps or reservoirs and walls are present, and they can dissipate the initial momentum of the gas release. Consequently, the upward flow pattern can be considered "diffuse" and buoyant, neither pure jet nor pure plume. Therefore, this challenging issue was part of a project called HYMERES, which was launched and conducted in the OECD/NEA framework. Dedicated experiments were performed to study the interaction between a diffuse buoyant jet and two-layer stratification. In the large-scale MISTRA facility, the HM1-1 test series were conducted in which the erosive flow pattern came from a horizontal hot air jet impinging on a vertical cylinder. These experimental results were offered for a blind and open benchmark exercise.
Bentaib, A.*; Chaumeix, N.*; Grosseuvres, R.*; Bleyer, A.*; Gastaldo, L.*; Maas, L.*; Jallais, S.*; Vyazmina, E.*; Kudriakov, S.*; Studer, E.*; et al.
Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 11 Pages, 2018/10
In the framework of the French MITHYGENE project, the new highly instrumented ENACCEF2 facility was built at the Institut de Combustion Aerothermique Reactivite et Environnement (ICARE) of the Centre National de la Recherche Scientifique (CNRS) in Orleans (France) to address the flame propagation in hydrogen combustion during a severe accident. The ENACCEF2 facility is a vertical tube of 7.65 m height and 0.23 m inner diameter. In the lower part of the tube, annular obstacles are installed to promote turbulent flame propagation. At the initiative of the MITHYGENE project consortium and the European Technical Safety Organisation Network (ETSON), a benchmark on hydrogen combustion was organised with the goal to identify the current level of the computational tools in the area of hydrogen combustion simulation under conditions typical for safety considerations for NPP. In the proposed paper, the simulation results obtained by participating organizations, using both Computational Fluid Dynamics (CFD) and lumped-parameter computer codes, are compared to experimental results and analysed.
安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介
Nuclear Engineering and Design, 331, p.162 - 175, 2018/05
被引用回数：21 パーセンタイル：91.03(Nuclear Science & Technology)Density stratification and its breakup are important phenomena to consider in the analysis of the hydrogen distribution during a severe accident. Many previous experimental studies, using helium as mimic gas of hydrogen, focused on the stratification breakup by a vertical or horizontal jet. However, in a real containment vessel, the upward flow pattern can be considered diffuse and buoyant neither pure jet nor pure plume. HM1-1 and HM1-1bis tests in the MISTRA facility were performed to investigate such erosive flow pattern created from a horizontal hot air jet impinging on a vertical cylinder. The experimental results indicated that the jet flow was quickly mixed with the surrounding gas in the lower region of the initial stratification, and deaccelerated by buoyancy force therein. Consequently, the erosive process became slower at the upper region of the initial stratification. Those observed behavior was analyzed using the computational fluid dynamics (CFD) techniques focusing on models for turbulent Schmidt and Prndtl numbers. Some previous studies mentioned that these numbers significantly change in the stratified flow. The changes of and 
are very important factor to predict the stratification erosion process. The results have indicated that the simulation can be much improved by using appropriate dynamic models for those numbers. This research is a collaboration activity between CEA and JAEA.
) on density stratification erosion in a small rectangular vessel安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介
Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 13 Pages, 2017/09
Density stratification and its break-up are important phenomena for discussing the containment hydrogen behavior. Turbulence transport phenomenon is one of the important factor in the stratification erosion behavior. A small scale test is a useful approach to develop a physical model for the stratification erosion because of easiness for detailed measurement. Thus, small scale experiments have been carried out in our research project named "ROSA-SA". A rectangular vessel apparatus named VIMES (VIsualization and MEasurement system on Stratification behavior) is one of such facilities, which has a vessel made of acrylic plates for visualizing flow field with the PIV measurement, whose volume is 4.05m
(1.5m(L)
1.5m(W)1.8m(H)). In this paper, we focus on Computational Fluid Dynamics (CFD) analysis on a density stratification erosion with a vertical buoyant jet observed in the VIMES experiments. Comparative study between Large-eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) are also performed to validate the dynamic turbulence Schmidt number () formulation. The results have indicated that the dynamic Sct model is advantageous to predict the observed stratification erosion behavior. This research is a collaboration activity between CEA and JAEA.
安部 諭; Studer, E.*; 石垣 将宏; 与能本 泰介
no journal, ,
シビアアクシデント時の格納容器内水素リスクに関する現象的理解向上を目指してOECD/HYMERESプロジェクトが進められた。本報告では、プロジェクト内で行われたCFDベンチマークテストに関して、乱流シュミット(およびプラントル)数を動的に変化させるモデルを用いた解析結果について発表する。
