低干度自然循环流量漂移的特征曲线图谱分析

在5MW低温核供热堆全模拟试验回路(HRTL-5)上,实验观察到了低干度自然循环条件下的流量漂移现象.通过一个考虑了加热段欠热沸腾、上升段冷凝、闪蒸等物理过程的两相流动数学模型,编制了相应的计算程序,获得了自然循环特征曲线图谱及其运行曲线,确定了自然循环分岔图和静态不稳定边界图,进而提出了通过自然循环特征曲线图谱研究流量漂移的分析方法.分析表明:特征曲线图谱方法是研究自然循环静态不稳定的有效手段.增大系统压力、减小热流密度、增加入口单相阻力、减小出口两相阻力有利于避免自然循环流量漂移的发生.     

低干度自然循环两相流动系统的静态分岔特性

基于一维两相四方程漂移流模型，采用数值模拟的方法对5MW低温核供热堆热工模拟回路（HTRL-5）的自然循环进行模拟，分析在自然循环系统中存在的分岔特性及其参数效应。结果表明：在一定条件下低干度自然循环两相流动系统存在静态分岔现象，并且静态分岔点出现在特征曲线的切点上；当压力高到一定程度或热流密度小到一定程度系统的分岔点消失。     

低温核供热堆流动特性分析(英文)

实验研究在5MW核供热反应堆模拟热工水力学实验回路HRTL-5上进行。分析计算基于带有质量,蒸汽质量,能量及动量守恒方程的一维两相流漂移模型。给出了在不同系统压力,进口过冷度及热流密度条件下的稳态和动态分析结果。研究结果表明:加热段中的过冷沸腾及上升段中的闪蒸对空泡份额分布及流动稳定性有重要影响,特别是在低压条件下;在相当宽的两相流条件下,加热段中只发生过冷沸腾;对于沸水设计工况的5MW低温堆,其堆芯出口温度尚未达到饱和。描述了两相流振荡机理,即“零阻降”机理。在进口过冷度相当宽范围内(OK<ΔT<28K),对系统流条件,存在3个区域,即稳定的两相流,整体和过冷沸腾不稳定流和过冷沸腾以及单相稳定流。给出了系统流量在小热流密度扰动下的响应特性。在此基础上给出了稳定边界图的计算和实验值。     

HRTL-5轴向空泡份额计算

基于一维两相四方程漂移流模型,并考虑加热段欠热沸腾、上升段冷凝以及上升段闪蒸的影响,采用数值模拟的方法对5 MW低温核供热堆热工模拟回路(HRTL-5)的轴向空泡分布进行模拟计算,分析HRTL-5轴向参数分布的特性及其参数效应。结果表明:1)在HRTL-5条件下,考虑欠热沸腾、冷凝、闪蒸等因素影响的计算结果更接近实际情况;2)是否考虑加热段的欠热沸腾对于加热段出口的空泡份额以及出口的状态确定有重要影响;3)冷凝过程对于闪蒸区以及自然循环驱动力的计算有一定的影响;4)闪蒸对低压低干度自然循环系统轴向空泡份额的分布有重要影响,尤其在低压情况下。     

低温核供热堆流动特性分析

实验研究在5MW核供热反应堆模拟热工水力学实验回路HRTL-5上进行。分析计算基于带有质量,蒸汽质量,能量及动量守恒方程的一维两相流漂移模型。给出了在不同系统压力,进口过冷度及热流密度条件下的稳态和动态分析结果。研究结果表明:加热段中的过冷沸腾及上升段中的闪蒸对空泡份额分布及流动稳定性有重要影响,特别是在低压条件下;在相当宽的两相流条件下,加热段中只发生过冷沸腾;对于沸水设计工况的5MW低温堆,其堆芯出口温度尚未达到饱和。描述了两相流振荡机理,即“零阻降”机理。在进     

强迫循环并联通道流量漂移现象研究

使用RELAP5程序对垂直并联环隙窄缝通道流量漂移现象进行研究,分析了强迫循环并联通道流量漂移现象的形成过程及其原因,研究了主要运行参数对垂直并联环隙窄缝通道流量漂移现象的影响。结果表明:增大窄缝间隙,降低入口欠热度,增大系统压力,减小热流密度,增加入口单相阻力,减小出口两相阻力均可减小通道压降-流量特性曲线的斜率,从而提高系统的稳定性,避免流量漂移现象的发生。     

启动低温堆过程中流动特性实验研究(英文)

研究了由清华大学核能技术设计研究院研制的自然循环5MW低温堆加热启动过程中的流动特性。实验研究在模拟5MW核供热反应堆的热工水力学实验回路HRTL-5上进行。描述了不同类型的两相流稳定性,即geysering,闪蒸不稳定性及低干度密度波不稳定性对加热启动过程的影响。阐述了闪蒸不稳定性的机理。在此研究基础上,提出低温堆从初始状态向沸水工况的过渡的具体措施。提出用小热流密度,小进口过冷度实现压水-沸水过渡的方法。通过仔细地选择热工参数,可以获得5MW低温堆稳定的加热启动过程。     

窄矩形通道内低压两相自然循环流量漂移实验研究

在自然循环实验台架上进行窄矩形通道自然循环流量漂移实验研究。当加热到一定功率时,系统开始出现自然循环流量漂移,且流量漂移过程中伴随着流量振荡;整个系统的稳定性随着入口流体欠热度、压力、缝隙宽度的增加而增大。通过欠热度数、相变数等参数绘制出系统的稳定性曲线。发现窄矩形通道流量漂移存在4阶段机理,并提出窄矩形自然循环流量漂移起始功率经验关系式。     

低压流动稳定性实验研究(英文)

在5MW核供热反应堆模拟热工水力学实验回路HRTL-5上研究了在低压(P=0.1,0.24MPa)自然循环各种进口过欠热度条件下,单相及两相流流动特性。研究了不同种类的流动不稳定性,如,欠热沸腾不稳定性,欠热沸腾引起的闪蒸不稳定性,纯闪蒸不稳定性,密度波-闪蒸耦合不稳定性及高频流动振荡。研究结果表明:低压自然循环系统在绝大部分进口欠热度条件下,其两相流流动是不稳定的,仅在小进口欠热度条件下可获得稳定的两相流流动;在高进口欠热度条件下,加热段中的欠热沸腾控制流动不稳定,在中进口欠热度条件下,加热段中的欠热沸腾及上升段中的空泡闪蒸控制流动不稳定。     

压水堆自然循环比例模化基本方程及相似准则数的研究

在分析压水堆自然循环特性基础上,以漂移流模型作为两相流模型,从独立的单相和两相方程出发,通过无量纲化处理,获得一组相同的无量纲化方程组,从而获得能够适用于单相和两相的相似准则数.同时,对自然循环现象模拟的本质以及准则数的物理含义进行了分析说明,并就模拟初始数值的选择,流动不稳定性模拟、传热及临界热流密度模拟等方面进行了分析.     

Assessment of Some Cross Section Libraries through Analyses of Coupled-Core Critical Experiments by Monte Carlo Calculations

An experiment was performed on the natural circulation test loop HRTL-5, which simulates the geometry and system design of the 5 MW full power natural circulation nuclear heating reactor. Different flow modes, including density wave oscillation and flow excursion et al., were observed in a wide range of inlet sub-cooling at 1.5MPa. By means of self-developed computational codes, the bifurcation chart has been obtained. Consequently the flow excursion boundary has been determined. Through the analysis on the excursion boundary, the method to avoid the flow excursion during startup has been presented. Analytical results show: (1) with the decreasing heat flux or the increasing system pressure, the static flow excursion occurs at higher inlet temperature and its range in the instability maps becomes narrower correspondingly; (2) to decrease the outlet two-phase resistance or increase the inlet single-phase resistance is beneficial to avoid the flow excursion; (3) by means of increasing the system pressure to start up the reactor with low heat flux, the flow excursion and low steam quality density wave oscillation can be successfully avoided. This investigation is meaningful to the reactor safety and the design of the nuclear heating reactors.     

Numerical study of nuclear coupled two-phase flow instability in natural circulation system under low pressure and low quality

Based on the one-dimension two-phase drift flow model, the numerical simulation of two-phase flow stability characteristic on the test loop (HRTL-5) for 5 MW heating reactor (developed by the Institute of Nuclear and New Energy Technology of Tsinghua University, Beijing) is performed with and without coupled point neutron kinetics. The density wave oscillation instability is analyzed in the system under low pressure at 1.5 MPa and low steam quality less than 10%. The effect of inlet subcooling and heating flux on the system instability is simulated under the system pressure P_sys = 1.5 MPa. The numerical results show that there exist two instability inlet subcooling boundaries at different heat flux. The numerical results show good agreement with the experimental results on HRTL-5 without consideration of point neutron kinetics. If coupled with point neutron kinetics, the system will exhibit little difference on instability boundaries from that without considering the nuclear characteristics. But the amplitude and the phase of the oscillation of the thermal hydraulic parameters of the system will be somehow affected in unstable zone if the system is coupled with point neutron kinetics.     

Mechanism analysis on flow excursion of a natural circulation with low steam quality

Flow excursion was observed on the natural circulation test loop HRTL-5, which simulates the geometry and system design of the 5 MW nuclear heating reactor. By means of self-developed computational codes, a set of tools used for analyzing the flow characteristics of the natural circulation have been presented, including the characteristic curves, operational curve and the bifurcation curve. The two-dimensional disturbance analysis is adopted to explain the mechanism of the flow excursion. Analytical result shows: (1) flow excursion can occur in a natural circulation system at a suitable geometry and thermal–hydraulic conditions. (2) Characteristic curves, operational curve, bifurcation curve, and the two-dimensional disturbance analysis are the available method to analyze the flow excursion of the natural circulation. (3) The flow excursion is prior to the low steam quality density wave oscillation. (4) The onset of the flow excursion is the tangency point of the drive force curve and the flow resistance curve. (5) To operate at low heat flux to increase the inlet temperature is the effectual approach to transfer from the pressurized water state to the boiling water state, in which the flow excursion and the low steam quality density wave oscillation can be avoided.     

低温堆上空腔破口失水后期的流动振荡实验研究

在５ＭＷ低温堆的模拟试验台架ＨＴＲＬ－５上对该低温堆上空腔破口失水事故进行了实验研究。重点研究了事故后期的流动振荡现象,揭示了振荡的发展过程和发生机理。经实验研究,给出了小破口失水闪蒸过程中回路内压力、温度、空泡份额、循环流量等重要参数的变化规律,同时表明了小破口失水过程中由于压力下降引起闪蒸产生大量气泡并引起自然循环流量的变化,这些变化又反过来对各参数产生影响,使循环流量的传热情况发生周期性变化     

低压低干度自然循环流量漂移和热虹吸现象的动态模拟

采用一维两相4方程漂移流模型编制程序,对5MW核供热堆模拟实验回路中发生的流量漂移现象进行数值模拟,同时分析热虹吸的机理,并对其进行动态模拟.结果表明,该程序可以对自然循环系统的静态不稳定性进行模拟,对流量漂移现象的模拟基本与实验相符.     

窄通道自然循环临界热流密度的非线性分析

通过自然循环流动实验,取得5 mm间隙窄矩形通道的自然循环临界热流密度（CHF）发生时的可视化图片,以及流量、壁温和实验段压差信号,并运用非线性分析技术对CHF发生过程进行了定性和定量研究。研究发现：自然循环压差时间序列的功率谱在半对数坐标中呈指数下降;自相关系数逐渐下降;三维吸引子相图表现出奇怪吸引子的特点。这表明了自然循环系统CHF的发生过程具有非线性混沌特性。自然循环CHF发生的初始阶段,由于流量脉动和流型往复变迁,流动和换热表现出一定的周期性;随着热流密度的提高,周期性减小,随机性增大,但总能达到一个确定的状态,体现了混沌运动的特点。     

Flow excursion phenomenon and its mechanism in natural circulation

An experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of a 5-MW nuclear heating reactor. In a wide range of inlet subcoolings, different flow modes, such as single-phase stable flow, subcooled boiling stable flow, subcooled boiling static flow excursion, density-wave oscillation and stable two-phase flow in the natural circulation system have been described. The phenomenon and mechanism of the static flow-excursion, which has never been studied well on this field, is especially interpreted. The experimental results show that, in the process of flow excursion, the mass flow rate and the inlet temperature decreases, while the exit temperature increases smoothly. As the process of the excursion continues for about 1 h, short period dynamic flow oscillation occurs, which can only be seen in the process of this static flow excursion, and has also never been studied well. These static and dynamic flow instabilities combine together and continue for about 2 h, then a point is reached, at which the static flow excursion disappears, but the dynamic flow oscillation continues. The mechanism of the static flow excursion is interpreted through two sets of curves for flow resistance pressure drop and driven head in natural circulation, and one curve for the natural circulation operation under special thermohydraulic condition. The study of the flow excursion and its concerned dynamic flow oscillation is of great significance for the development of the nuclear heating reactor under natural circulation.