PCCS系统自然循环流动特性研究

发布时间：2018-03-25 16:10

本文选题：自然循环　切入点：流动特性　出处：《哈尔滨工程大学》2014年硕士论文

【摘要】：安全壳作为核电站最后一道屏障,可以在严重事故情况下承受事故产生的内压力,防止放射性物质外泄。在新一代核电站中,非能动安全壳冷却系统(PCCS)是防止安全壳在事故条件下超压超温受损的一项重要设施。PCCS系统利用自然循环的方式将热量导出,自然循环流动特性影响着PCCS系统的安全运行,开展对自然循环流动特性的研究具有重要意义,因此,本文设计了 PCCS简化系统,以对PCCS的自然循环特性进行初步研究。在低压、低含气率条件下,对系统的自然循环启动、稳态运行时的流动特性进行了实验研究。实验表明自然循环系统在启动运行过程中经历了三个阶段一单相区、过渡区和稳态运行区;其中过渡区又可分为过渡一区和过渡二区。过渡一区内的流量振荡是由间歇泉不稳定引起的。过渡二区的流动不稳定性在不同加热功率下有不同的表现形态:低加热功率时,间歇泉不稳定和闪蒸引发了流量振荡;高加热功率时,闪蒸和饱和沸腾引发了流量振荡。稳态运行时,系统内存在5种行为模式:周期性闪蒸伴随喷泉、闪蒸伴随周期性沸腾喷发、持续性闪蒸、周期性沸腾喷发和稳定气液两相流动。研究表明,闪蒸和沸腾喷发是影响流动特性的两个主要因素,两者对流动主导作用权重的变化是流动模式随功率发生演变的根本原因。实验获得的流动模式分布图可为自然循环系统的运行提供参考。在考虑驱动压头、回路阻力、过冷沸腾、闪蒸和散热的基础上,建立了自然循环稳态运行时平均流量的计算模型,计算结果和实验值符合良好,表明用平均稳态的流动代替不稳定的流动来研究自然循环流动特性的思路是可行的。由该模型预测了高功率下自然循环平均流量的变化趋势和流量静态漂移,给出了系统由不稳定流动过渡为稳定气液两相流动的判断标准和稳定边界的确定方法,分析了复杂实验回路对自然循环平均流量及流量静态漂移的影响。
[Abstract]:Containment, as the last barrier for nuclear power plants, can withstand the internal pressure caused by accidents in case of serious accidents and prevent the leakage of radioactive materials. In the new generation of nuclear power plants, Non-active containment cooling system (PCCSs) is an important facility to prevent the containment from being damaged by overpressure and overtemperature under the accident condition. The heat is derived by natural circulation. The characteristics of natural circulation flow affect the safe operation of the PCCS system. It is of great significance to study the characteristics of natural circulation flow. Therefore, a simplified PCCS system is designed to study the natural circulation characteristics of PCCS. Under the condition of low pressure and low gas content, the natural circulation of the system is started. The experimental results show that the natural circulation system has experienced three stages: single phase region, transition zone and steady operation area. The flow oscillation in the transition zone is caused by geysers instability. The flow instability in the transition zone has different forms under different heating power: when the heating power is low, the flow instability in the transition zone can be divided into two areas: when the heating power is low, the flow instability in the transition zone is caused by the instability of geysers. The instability and flash of geysers cause flow oscillations, while at high heating power, flash and saturated boiling trigger flow oscillations. Flash is accompanied by periodic boiling eruption, continuous flash eruption, periodic boiling eruption and stable gas-liquid two-phase flow. The change of the weight of the flow leading action is the fundamental reason for the evolution of the flow mode with power. The flow pattern distribution map obtained by the experiment can provide a reference for the operation of the natural circulation system. Considering the driving pressure head, the loop resistance, On the basis of subcooled boiling, flash evaporation and heat dissipation, the calculation model of average flow rate in steady state operation of natural circulation is established. The calculated results are in good agreement with the experimental data. The results show that it is feasible to use the average steady flow instead of the unstable flow to study the flow characteristics of the natural cycle. The model is used to predict the variation trend of the average flow rate and the static drift of the flow under the high power condition. The criterion of the system transition from unstable flow to stable gas-liquid two-phase flow and the method to determine the stable boundary are given. The influence of complex experimental loop on the natural circulation average flow and flow static drift is analyzed.
【学位授予单位】：哈尔滨工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM623;TL364.3

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