重力注水过程流动不稳定现象关键影响因素研究

重力驱动注水过程中由于流量较小以及蒸汽的积聚可能导致流动不稳定现象的发生，对核反应堆安全运行具有重要的影响。通过实验研究的方法，搭建了重力注水模拟实验装置，研究了不同蒸汽出口形阻、高位储水箱水位和加热棒初始温度下流动不稳定现象的变化规律。结果表明，重力驱动注水过程流动不稳定现象包含冷却水初次注入阶段、注入水逐出阶段和冷却水再注入阶段等。在一定冷却水初始温度、冷却水入口形阻以及系统压力下，蒸汽排出速度以及实验本体内筒顶部的聚集情况取决于蒸汽出口形阻，减小蒸汽出口形阻可加快蒸汽排放速度，压力峰峰值降低、振荡周期变长，有利于系统稳定；提高高位储水箱水位加快了冷却水注入速率，增加了加热棒被淹没率，降低了流动不稳定现象的发生次数和持续时间；随加热棒初始温度的升高，冷却水流量出现了波动向停滞的转变，流动不稳定现象发生的次数增加且持续时间加长。

Study on Key Influence Factors of Flow Instability during Gravity-driven Reflooding

Flow instability may occur during the reflooding process driven by gravity and may hinder the continuous injection of cooling water because of the small flow rate of cooling water and the accumulation of steam in the pressure vessel, which has an important impact on the safe operation of nuclear reactors. A reflooding experiment device was set up and the variation regularity of flow instability under different resistances of steam outlet, high storage tank water level and initial temperature of the heated rods was studied. The results show that the flow instability includes cooling water initial injection, cooling water expulsion and cooling water re-injection. The steam’s emission rate and accumulation at the top of the experiment body depend on the resistance of steam outlet. Decreasing the resistance of steam outlet accelerates the emission rate of steam and prevents the accumulation of steam at the top of the experiment body. The peak value of pressure shows a drop and oscillation period becomes longer with the decrease of the resistance of steam outlet, which are beneficial to the stability of the system. Raising the water level accelerates the injection flow rate of the cooling water, increases the submerged ratio of the heated rods and reduces the frequency and duration of the flow instability. As the initial temperature of the heated rods increases, the cooling water flow changes from fluctuation to stagnation. The frequency and duration of the flow instability increase.