开式自然循环流动不稳定性的频域法分析

开式自然循环流动不稳定性的频域法分析

李军;李晓明;刘长亮

【摘要】The passive containment cooling system may serve to remove the heat from the containment after some accidents by means of natural circulation.However,it may also suffer from the two-phase flow instability during the operation.The mathematical model and constitutive relationships were set up for an open natural circulation system. The conservation equations were linearized by using the perturbation method.The transfer function of the mass flow rate of the system was derived in terms of the enthal-py change of the heating section through Laplace transformation.Based on the Nyquist stability criterion,the influence of thermal-hydraulic parameters on the stability of the natural circulation system was analyzed.The results show that the flow stability of the system is mainly dominated by the relationship between the void fraction and the quality of the two-phase flow.In the studied range,with the increase of the quality,the sensi-tivity of the void fraction to the quality is weakened,and the system tends to be stable.%非能动安全壳热量导出系统依靠自然循环导出事故后排入安全壳内的热量,但在运行过程中也可能发生流动不稳定性现象.本文以某开式自然循环非能动安全壳热量导出系统为对象,建立了描述该系统行为的数学模型和本构关系,运用小扰动法对守恒方程进行线性化,通过Laplace变换获得系统质量流速随加热段进口焓变化的传递函数.基于Nyquist稳定性判据,分析了热工参数变化对该自然循环系统稳定性的影响.结果表明:系统的流

动稳定性本质上受空泡份额随质量含气率的变化关系的制约,在一定范围内,随着质量含气率的增大,空泡份额对质量含气率的敏感性减弱,系统趋于稳定.

【期刊名称】《原子能科学技术》

【年(卷),期】2017(051)010

【总页数】6页(P1800-1805)

【关键词】开式自然循环;频域法;不稳定性分析

【作者】李军;李晓明;刘长亮

【作者单位】哈尔滨工程大学核安全与仿真技术国防重点学科实验室,黑龙江哈尔滨 150001;华龙国际核电技术有限公司,北京 100037;中国核工业集团公司,北京100840;中国核电工程有限公司,北京 100840

【正文语种】中文

【中图分类】TL333

Abstract: The passive containment cooling system may serve to remove the heat from the containment after some accidents by means of natural circulation. However, it may also suffer from the two-phase flow instability during the operation. The mathematical model and constitutive relationships were set up for an open natural circulation system. The conservation equations were linearized by using the perturbation method. The transfer function of the mass flow rate of the system was derived in terms of the enthalpy change of the heating section through Laplace transformation. Based on the Nyquist stability criterion, the influence of

thermal-hydraulic parameters on the stability of the natural circulation system was analyzed. The results show that the flow stability of the system is mainly dominated by the relationship between the void fraction and the quality of the two-phase flow. In the studied range, with the increase of

the quality, the sensitivity of the void fraction to the quality is weakened, and the system tends to be stable.

Key words： open natural circulation; frequency domain method; instability analysis

自核电投入商业运行以来，人类历史上发生了3次严重核事故。特别是2011年福岛核事故以后，新一代的核反应堆在设计时均强调了非能动安全的理念[1-3]。当

核反应堆发生某些事故后，例如冷却剂丧失事故(LOCA)或主蒸汽管道破裂(MSLB)事故，安全壳内会由于热量和工质(水、水蒸气以及氢气等)的大量排入而升温升压。如果不能及时导出这部分热量，则有可能使安全壳超过设计压力而失效，甚至引起放射性外泄。为此，针对大型干式混凝土式安全壳，提出一种开式安全壳热量导出系统概念，采用全自然循环方式运行。然而，无论是实验结果还是数值模拟，都发现在某些参数条件下，该类系统可能会经历流动不稳定性[4-6]。

流动不稳定性可能导致流量振荡，从而影响系统传热性能，还会导致系统承受交变的机械和热应力[7]。采用频域法可较好地预测两相流动系统中发生流动不稳定性

的边界[8-9]，为此，本文以该开式自然循环系统为研究对象，采用频域法确定该

系统的不稳定性边界，并探讨诱发该系统发生不稳定性现象的原因。

开式自然循环系统示意图如图1所示。系统加热段为1组布置于安全壳内的换热器，当系统投入运行后，加热段内的流体被安全壳内的热量加热升温，密度降低。由于下降段与加热段及上升段内流体的平均密度差，形成驱动压头，驱动流体流动，从而实现自然循环，在此过程中不断排走安全壳内的热量。