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論文

Density stratification breakup by a vertical jet; Experimental and numerical investigation on the effect of dynamic change of turbulent Schmidt number

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

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 $$Sc_{t}$$ 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 $$Sc_{t}$$ 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 $$Sc_{t}$$ on the slower erosive process. This study concludes that the dynamic modeling for $$Sc_{t}$$ is a useful and practical approach to improve the prediction accuracy.

論文

Experimental investigation of density stratification behavior during outer surface cooling of a containment vessel with the CIGMA facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 367, p.110790_1 - 110790_15, 2020/10

 被引用回数:0

シビアアクシデント時の格納容器(CV)内の流体や構造物を冷却するための有効なアクシデントマネジメントとして、CVの外面冷却が期待されている。一方、以下のような可能性も考えられる。第一に、シビアアクシデント時に水-ジルコニウム反応により水素ガスが発生し、外表面冷却により水素を含む非凝縮性ガスが蓄積し、密度成層が形成される可能性がある。第二に、非凝縮性ガスの蓄積は熱伝達を低下させ、CVの冷却を阻害する可能性がある。これらの課題については、これまで多くの研究が行われてきた。しかし、外表面冷却によって生じる密度成層挙動や成層崩壊の条件に着目した体系的な検討は十分に行われていない。また、水素の蓄積による伝熱劣化を定量的に評価していない。そこで、実験設備CIGMA(Containment InteGral effects Measurement Apparatus)を構築し、CIGMA設備を用いて容器外面冷却時の格納容器熱流動挙動の実験的研究を行った。さらに、安定な密度成層が維持できる条件を考慮することで、自然対流が密度成層化挙動に与える影響を議論した。

論文

Unsteady natural convection in a cylindrical containment vessel (CIGMA) with external wall cooling; Numerical CFD simulation

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Energies (Internet), 13(14), p.3652_1 - 3652_22, 2020/07

 被引用回数:0

In the case of a severe accident, natural convection plays an important role in the atmosphere mixing of nuclear reactor containments. In this case, the natural convection might not in the steady-state condition. Hence, instead of steady-state simulation, the transient simulation should be performed to understand natural convection in the accident scenario within a nuclear reactor containment. The present study, therefore, was aimed at the transient 3-D numerical simulations of natural convection of air around a cylindrical containment with unsteady thermal boundary conditions (BCs) at the vessel wall. For this purpose, the experiment series was done in the CIGMA facility at Japan Atomic Energy Agency (JAEA). A 3-D model was simulated with OpenFOAM, applying the unsteady Reynolds-averaged Navier-Stokes equations (URANS) model. Different turbulence models were studied, such as the standard k-$$varepsilon$$, standard k-$$omega$$, k-$$omega$$ shear stress transport (SST), and low-Reynolds-k-$$varepsilon$$ Launder-Sharma. The results of the four turbulence models were compared versus the results of experimental data.

論文

CFD analysis of the CIGMA experiments on the heated JET injection into containment vessel with external surface cooling

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5463 - 5479, 2019/08

The present study introduces thermal mixing and stratification produced by heated air jet located at the bottom level of the containment vessel. The investigation was carried out experimentally and numerically in the large containment vessel called CIGMA (Containment InteGral effects Measurement Apparatus). The experiments were conducted with external surface cooling and various air jet inlet temperatures. The containment cooling was done by flooding the water on the external side of half-upper of a vessel. To identify their influence on the thermal mixing and stratification phenomena, the investigation focuses on mixing convection which occurred in the cooled region of a containment vessel. Temperature distribution and jet velocity were measured by thermocouple and Particle Image Velocimetry (PIV) respectively. Numerical simulation was performed using Computational Fluid Dynamics (CFD) code OpenFOAM to investigate the detail effects of external cooling on the fluid flow and thermal characteristics in the test vessel. CFD results showed a good agreement with experimental data on both temperature and velocity. Both temperature and velocity of hot air jet decayed rapidly downstream jet nozzle. Thermal stratification was observed by visualization of temperature contour maps over a cross-section in the containment vessel. Vigorous mixing was also noticed in the upper region of the containment vessel. Effect of external cooling on mixing and the thermal stratification were presented and discussed.

論文

Experiment on density stratification behavior by containment venting using CIGMA Facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5927 - 5940, 2019/08

格納容器ベントシステムはシビアアクシデント時における格納容器の過圧を防止するための手段として適用される。ベント時に発生する現象の理解と最適な運用という観点から、格納容器ベント時の水素挙動に関する研究は十分ではない。そこで本研究では大型格納容器実験装置CIGMAを用いて格納容器ベントに関する基礎的な実験を実施した。特に、ベントによる水素輸送に対するベント流量及び初期ガス分布の影響について調査を行った。水素の代替ガスであるヘリウム,蒸気,空気を用いて、初期に容器内に成層を形成し、下部ベントラインからベントを実施した。ベントにより初期に容器下部に存在する蒸気・空気のみが排出され、ヘリウム成層が下方へと拡大していく挙動が観察された。この間、上部のヘリウム濃度は一定であった。最終的には容器内のガス濃度分布は均質化した。今回実施した実験条件では、ベントによる容器内のガスの顕著な混合は観察されなかった。また異なる初期濃度分布に対してもヘリウム成層の挙動に大きな差は見られなかった。

論文

Experiments on collapse of density stratification by outer surface cooling of containment vessel; CC-PL-12 and CC-PL-24 experiments at CIGMA

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 11 Pages, 2018/10

シビアアクシデント時における格納容器内熱水力挙動は安全上重要な課題の1つである。本研究では大型格納容器実験装置CIGMAを用いて、格納容器内の水素挙動および自然循環挙動に対する格納容器を外部から冷却した際の影響について検討した。本実験では2つの冷却手法を適用した実験を行った。1つは上部プールに蓄えた冷却水による冷却と上部プール・中段ジャケットへの流下液膜による冷却である。容器内に水素の模擬物質としてヘリウムを注入し、さらに蒸気と空気を注入し、容器上部にヘリウム成層を形成した際の成層挙動について計測を行った。冷却手法に応じて、異なる成層挙動が観測された。

論文

Influence of grating type obstacle on stratification breakup by a vertical jet

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

At Japan Atomic Energy Agency (JAEA), small scale experiment, named VIMES (VIsualization and MEasurement system on stratification behavior) experiment, has been performed since 2014. In this paper, we introduce the influence of grating type obstacle to the VIMES experiment. Two types of grating obstacle were constructed based on the aperture area ratio. The obstacles were placed at the intermediate position between the jet nozzle exit and bottom of the initial stratification. Experimental results showed that the vertical jet was strongly affected by the grating obstacle. Due to the rectifying effect, the radial spreading was suppressed and the velocity magnitude on the jet center line became larger than that in case without the grating obstacle. Meanwhile, due to the resistance effect, the integral momentum flux of the vertical jet was decayed with decrease of the aperture area ratio. It means that in case with the grating obstacle the integral jet penetration strength was decayed, although the local jet penetration to the stratification was stronger than that in case without the grating obstacle. Also, the slower stratification breakup could be observed with decrease of the aperture area ratio, indicating that stratification breakup rate to be discussed in detail considering every possible effect of a jet penetration.

論文

Stratification break-up by a diffuse buoyant jet; A CFD benchmark exercise

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.

論文

Stratification breakup by a diffuse buoyant jet; The MISTRA HM1-1 and 1-1bis experiments and their CFD analysis

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:5 パーセンタイル:26.29(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 $$Sc_{t}$$ and $$Pr_{t}$$ 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.

論文

RANS analysis with a dynamic model for turbulent Schmidt number ($$Sc_{t}$$) 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$$^{3}$$ (1.5m(L)$$times$$1.5m(W)$$times$$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 ($$Sc_{t}$$) 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.

論文

Experimental study on outer surface cooling of containment vessel by using CIGMA

柴本 泰照; 石垣 将宏; 安部 諭; 与能本 泰介

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 14 Pages, 2017/09

The present paper introduces the recent outcome from the CIGMA experiments regarding containment vessel cooling, in which an external side of a vessel upper head was flooded by water. The test vessel was initially pressurized by steam and noncondensable gas (air and/or helium), and was subsequently cooled by pouring water to the outside of the vessel top. Similar experiments were performed by authors using air-steam binary system in the previous study, which showed several characteristic phenomena such as inverse temperature stratification. The experimental conditions were extended systematically in this study to investigate the effects of initial gas composition and distribution in a vessel. The measurement results indicated that natural circulation was significantly affected by distributions of each gas species. In particular, it was enhanced when the gas density became heavier after condensation on the vessel inner wall, while it was suppressed when the gas density became lighter, creating density stratification with helium-rich gas in the upper region. The results are explained by the simplified model.

論文

Influence of mesh non-orthogonality on numerical simulation of buoyant jet flows

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 314, p.326 - 337, 2017/04

 被引用回数:1 パーセンタイル:100(Nuclear Science & Technology)

本研究では浮力が支配的なジェット流れに対するメッシュの非直交性の影響を調査した。解析には三角形要素のメッシュと四角形要素のメッシュを用い、CFDコードOpenFOAMを適用した。非直交性補正を適用しない場合、三角形要素メッシュを用いて解析したジェットでは四角形要素メッシュを用いた場合よりも流れの不安定性が過大評価されることが分かった。一般に非直交補正によりメッシュの非直交性の影響は緩和されるが、計算時間が増大する。そこで、非直交補正を用いずにメッシュの非直交性の影響を緩和するための改良型ソルバを提案した。

論文

CFD simulation of a CIGMA experiment CC-PL-04 on the containment thermal hydraulics affected by the outer surface cooling

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 10 Pages, 2016/11

原子力機構ではシビアアクシデント時の格納容器内熱水力挙動把握のため、大型格納容器実験装置CIGMAを製作し、実験を行っている。本発表では、蒸気及び空気の混合気体を封入した容器における外面冷却実験CC-PL-04についてCFDコードOpenFOAMにより解析した結果を報告する。

論文

Outcome of first containment cooling experiments using CIGMA

柴本 泰照; 与能本 泰介; 石垣 将宏; 安部 諭

Proceedings of 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-11) (USB Flash Drive), 10 Pages, 2016/10

The Japan Atomic Energy Agency (JAEA) initiated the ROSA-SA project in 2013 for the purpose of studying thermal hydraulics relevant to over-temperature containment damage, hydrogen risk, and fission product transport. For this purpose, the JAEA newly constructed the Containment InteGral Measurement Apparatus (CIGMA) in 2015 for the experiments addressing containment responses, separate effects, and accident managements. Recently, we successfully conducted first experiments using CIGMA to characterize the facility under typical experimental conditions. Among these experiments, the present paper focuses on the results of containment cooling tests, for which an upper part of the vessel outer surface was cooled by spray water. Several distinctive phenomena were observed in the tests, including inverse temperature stratification in the vessel due to the cooling in the upper region. The RELAP5 analysis result was also presented to roughly indicate the prediction capability of the best-estimate two-phase flow code in predicting the containment thermal hydraulics.

論文

Experimental and numerical study on density stratification erosion phenomena with a vertical buoyant jet in a small vessel

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 303, p.203 - 213, 2016/07

 被引用回数:5 パーセンタイル:36.45(Nuclear Science & Technology)

The Japan Atomic Energy Agency has started the ROSA-SA project to investigate thermal hydraulic phenomena in a reactor containment vessel during a severe accident. The hydrogen distribution in the vessel is one of significant safety issues in discussing a potential of hydrogen combustion in the containment. This paper focuses on a density stratification erosion and break-up mechanism with a vertical buoyant jet promoting the turbulent helium transport. Small scale experiment and computational fluid dynamics (CFD) analyses were carried out for investigating this phenomena. In the experiment, a rectangular vessel made with acrylic plates with a width of 1.5m, a length of 1.5 m and a height of 1.8 m was used for visualizing flow field with particle image velocimetry system. The quadrupole mass spectrometer system with a multiport rotating valve was applied for measuring gaseous concentration at 20 elevation points. In CFD analysis with OpenFOAM, two typical well-used turbulence models were used: low-Reynolds number type k-$$varepsilon$$ model and SST k-$$omega$$ model, with a turbulence model modification to consider the buoyant effect in the stratification. As a result, the stratification erosion in the CFD analyses with the modified turbulence model agreed well with the experimental data, indicating importance of the turbulence damping by the buoyant effect.

論文

First experiments at the CIGMA facility for investigations of LWR containment thermal hydraulics

柴本 泰照; 安部 諭; 石垣 将宏; 与能本 泰介

Proceedings of 24th International Conference on Nuclear Engineering (ICONE-24) (DVD-ROM), 9 Pages, 2016/06

There has been an extensive reorientation of the light water reactor research in Japan since the Fukushima Dai-ichi Nuclear Power Station accident, which focuses on severe accidents and accident managements. The Japan Atomic Energy Agency (JAEA) initiated the ROSA-SA project in 2013 for the purpose of studying thermal hydraulics relevant to over-temperature containment damage, hydrogen risk, and fission product transport. For this purpose, the JAEA newly constructed the Containment InteGral Measurement Apparatus (CIGMA) in 2015 for the experiments addressing containment responses, separate effects, and accident managements. Recently, we successfully conducted first experiments using CIGMA to characterize the facility under typical experimental conditions investigating basic phenomena such as buildup of pressure by steam injection, containment cooling and depressurization by internal or external cooling, and density stratified layer mixing by impinging jet. This paper provides an overview of the research programs, the brief description of the facility specification and the outcomes obtained from the first experiments.

論文

RANS analyses on erosion behavior of density stratification consisted of helium-air mixture gas by a low momentum vertical buoyant jet in the PANDA test facility, the third international benchmark exercise (IBE-3)

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 289, p.231 - 239, 2015/08

 被引用回数:9 パーセンタイル:23.88(Nuclear Science & Technology)

Density stratification in the reactor containment vessel is an important phenomenon on an issue of hydrogen safety. The Japan Atomic Energy Agency (JAEA) has started the ROSA-SA project on containment thermal hydraulics. As a part of the activity, we participated in the third international CFD benchmark exercise (IBE-3) focused on density stratification erosion by a vertical buoyant jet in containment vessel. This paper shows our approach for the IBE-3, focusing on the turbulence transport phenomena in eroding the density stratification and introducing modified turbulence models for improvement of the CFD analyses. For this analysis, we modified the CFD code OpenFOAM by using two turbulence models; the Kato and Launder modification to estimate turbulent kinetic energy production around a stagnation point, and the Katsuki model to consider turbulence damping in density stratification. As a result, the modified code predicted well the experimental data. The importance of turbulence transport modeling is also discussed using the calculation results.

論文

Thermal hydraulic safety research at JAEA after the Fukushima Dai-ichi Nuclear Power Station accident

与能本 泰介; 柴本 泰照; 竹田 武司; 佐藤 聡; 石垣 将宏; 安部 諭; 岡垣 百合亜; 孫 昊旻; 栃尾 大輔

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.5341 - 5352, 2015/08

This paper summarizes thermal-hydraulic (T/H) safety studies being conducted at JAEA based on the consideration of research issues after the Fukushima Dai-Ichi Nuclear Power Station accident. New researches have been initiated after the accident, which are related to containment thermal hydraulics and accident management (AM) measures for the prevention of core damage under severe multiple failure conditions. They are conducted in parallel with those initiated before the accident such as a research on scaling and uncertainty of the T/H phenomena which are important for the code validation. Those experimental studies are to obtain better understandings on the phenomena and establish databases for the validation of both lumped parameter (LP) and computational fluid dynamics (CFD) codes. The research project on containment thermal hydraulics is called the ROSA-SA project and investigates phenomena related to over-temperature containment damage, hydrogen risk and fission product (FP) transport. For this project, we have designed a large-scale containment vessel test facility called CIGMA (Containment InteGral Measurement Apparatus), which is characterized by the capability of conducting high-temperature experiments as well as those on hydrogen risk with CFD-grade instrumentation of high space resolution. This paper describes the plans for those researches and results obtained so far.

論文

A Study on improvement of RANS analysis for erosion of density stratified layer of multicomponent gas by buoyant jet in a containment vessel

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Journal of Energy and Power Engineering, 9(7), p.599 - 607, 2015/07

格納容器内での多成分ガスで形成される密度成層を精度よく解析することはシビアアクシデントの安全評価の上で重要である。日本原子力研究開発機構は格納容器内熱水力現象調査を目的としてROSA-SAプロジェクトを開始した。このプロジェクトの一環として、我々は浮力ジェットによる密度成層の侵食および崩壊についれ数値流体力学(CFD)解析を実行した。その解析では、既往研究でよく使われているが密度成層の侵食・崩壊を過大予測するRANS解析の改善を試みた。具体的には、低Re型k-$$varepsilon$$モデルをベースとして、ジェットの成層への貫入部分での乱流エネルギーを適切に評価、密度成層内での乱流抑制効果を再現するための改良をほどこした。RANS解析の結果は、計算コストは莫大になるものの精度が高いとされるLES解析と比較をおこなった。その結果、密度成層の侵食・崩壊について、本研究で適用した改良型のモデルは従来モデルよりもLES解析とのよく一致した。

論文

A Study on improvement of RANS analysis for erosion of density stratified layer of multicomponent gas by buoyant jet in a containment vessel

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 10 Pages, 2014/12

The analysis on a density stratification layer consisting of multiple gases in the reactor containment vessel is important for the safety assessment of sever accidents. The Japan Atomic Energy Agency (JAEA) has started the project on the containment thermal hydraulics. We carried out Computational Fluid Dynamics (CFD) analyses in order to investigate the erosion of the density stratification layer by a vertical buoyant jet under this project. We used the Reynolds averaged numerical simulation (RANS) and Large eddy simulation (LES) models to analyze the erosion of a density stratification layer by a vertical buoyant jet in a small vessel which represents a containment vessel. This numerical study calculates the turbulent mixing of a two-component (air and helium) gas mixture. The turbulence models used for the RANS analyses are two types of k-$$varepsilon$$ model models. The first model is the low Reynolds number k-$$varepsilon$$ model developed by Launder and Sharma. The second model is revised from the first model in order to accurately consider the turbulent production and damping in a stratification layer. The results have indicated that both the RANS and LES models simulate almost the same behavior of the erosion of the density stratification layer. While the erosion rate calculated by the low-Re k-$$varepsilon$$ model was faster than that of the LES model, the modified k-$$varepsilon$$ model could calculate the erosion rate similar to the LES result.

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