过冷水流经通道的闪蒸临界流模型研究

Flashing Critical Flow Model of Subcooled Water through Channel

反应堆发生失水事故时,破口处的临界流量决定着冷却水系统的装量,影响着堆芯燃料元件温度分布,对事故后果起重要作用。为了更好理解临界流动中各项参数的变化规律及机理,提出了两流体六方程临界流动模型,用来计算初始滞止状态为过冷水通过通道的临界流量。模型中既考虑了两相之间的动力学不均匀,也考虑了相间热力学不平衡。模型中引入了合适的计算闪蒸起始点位置和过热度的公式,并将汽泡增长方程与基本方程联立求解,可比较准确地反映汽泡的增长规律。在较宽的压力和温度范围内、不同长径比情况下,模型预测结果与试验结果符合较好,表明该模型具有较强的通用性。

During the postulated loss of coolant accident of nuclear reactor,the critical flow rate at the break would determine the coolant inventory and energy loss rate,thus dominate the temperature of fuel element in the core and strongly impact the progress of transient.In order to have a better understanding of basic parameter variation law during discharge flow,the general two-fluid model was developed for initially subcooled and saturated water flow in pipe or orifice.In this model,the thermal non-equilibrium between the liquid and vapor bubbles and the interphase relative motion were taken into account.An improved correlation to calculate flashing inception location and surperheat was proposed.The bubble growth equation and governing equations were combined to simulate the bubble diameter change with the quality and the void fraction.The code predicted results agree well with the test data for a wide range of pressure and temperature,and length to diameter ratios,which indicates that the model is a generalized critical flow model.