基于三维CFD分析软件CYCAS的湍流浮力流动模拟研究

Numerical Study on the Turbulent Buoyant Flow based on a 3D CFD Code CYCAS

严重事故中晚期,破口附近或者安全壳隔间之间的湍流浮力流动与安全壳内气体流场相互作用,直接影响安全壳内气体流场分布特性和氢气燃爆风险后果。本文应用一款三维计算流体力学(CFD)分析软件CYCAS,基于大尺寸安全壳台架流动实验PANDA OECD/SETH和PANDA HYMERES实验,开展了复杂湍流浮力流动的模拟和验证研究。结果表明,低速的湍流浮力流可在装置顶部形成分层分布,而射流在障碍物的作用下降低速度、但同时可能增强湍流脉动,有利于对分层分布的消散作用,三维CFD分析软件CYCAS可以有效模拟复杂的湍流浮力流动及其与大气流场的相互作用。在此基础上,基于某三代核电厂开展了安全壳内湍流浮力流动及其与大气流场相互作用的模拟分析。本研究表明,CYCAS软件可应用于压水堆核电厂严重事故安全壳内复杂湍流浮力流动模拟及氢气分布计算分析。

During the late phase of severe accidents,turbulent buoyant flows may occur with long-term depressurization or occur in the apertures between two compartments.These turbulent buoyant flows often interact with the flow field in the containment imposing impacts on the hydrogen distribution and hydrogen combustion risk.Experiments such as PANDA OECD/SETH tests and PANDA HYMERES tests have been performed to study the effects of the turbulent buoyant flows on the hydrogen distribution characteristics.An in-house 3-D computational fluid dynamic(CFD)code CYCAS,which is developed to investigate the thermal-hydraulic phenomena in the containment and applies for the hydrogen risk assessment in severe accidents,is used in this study.The low-momentum turbulent buoyant flow may form hydrogen stratification at the top of the facility.The jet flow velocity is reduced by the obstruction while the turbulence kinetic may be enlarged which is helpful in the break-up/erosion process.The results show that the 3-D CFD code CYCAS can catch well the turbulent buoyant flow and the interaction with the gas flow field.This approves the capabilities of CYCAS on the hydrogen distribution and hydrogen risk analysis in long-term phase of severe accidents.Based on these analyses,the CYCAS code is applied in a 3^(rd) generation nuclear power plant.The study indicates that the CYCAS code is applicable in the turbulent buoyant flow simulation and hydrogen distribution,and the hydrogen risk analysis in the PWR nuclear power plants.