5MW核供热堆自然循环两相流流动特性分析

ANALYSIS ON TWO PHASE FLOW BEHAVIOR FOR NATURALCIRCULATION SYSTEM IN 5MW NUCLEAR HEATING REACTOR

实验研究在５ＭＷ核供热堆热工水力学模拟系统ＨＲＴＬ－５上进行。计算分析采用带有质量，蒸汽质量，能量及动量守恒方程的一维两相流漂移模型。用Ｃｌａｕｓｉｕｓ－Ｃｌａｐｅｙｒｏｎ方程计算上升段中闪蒸起始点。通过在过冷沸腾区，饱和沸腾区及上升段中推导守恒方程，得到可描述自然循环两相流系统特性的常微分方程组。用时域法求解。研究表明过冷沸腾及空泡的闪蒸对空泡分布，系统循环流量及流动稳定性都有很大影响，且系统压力越低，过冷沸腾及闪蒸的影响越大；在相当宽的两相流动条件下，加热段中只发生过冷沸腾；揭示了两相流不稳定时振荡的传播特性。在５ＭＷ核供热堆条件下理论分析与实验结果吻合得很好。

The experiment was carried out on a test loop HRTL 5 simulating the geometry and system design of the 5MW Nuclear heating reactor,while the analysis was based on a one dimensional two phase flow drift model with conservation equations for mass,steam,energy and momentum.Clausius Clapeyron equation was used for the calculation of flashing front in the riser.A set of ordinary differential equation,describing the behavior of two phase flow in the natural circulation system,was derived through integration of the above conservation equations in subcooled boiling region,bulk boiling region in the heated section and in the riser.The method of time domain was used for the calculation.The results show that,firstly,subcooled boiling in the heated section and void flashing in the riscr have signifiacnt influence on the distribution of the void fraction,mass flow rate and stability of the system,espccially at lower pressure;secondly,in a wide range of two phase flow conditions,only subcooled boiling occurs in the heated section.The propagation behavior of flow oscillation was also studied.Calculated results agree with experimental data well at the 5MW nuclear reactor conditions.