落棒过程中燃料组件导向管内的流场分析迭代方法

已有落棒计算认为控制棒下落过程中燃料组件导向管各流水孔始终为流出状态,而实际会出现流动反向。为解决此问题,认为每一时刻各流水孔均有流进和流出2种可能状态。对所有流动断面发生突变的位置进行流动能量损失分析,通过引入表征流动状态的流向指标,将所有可能出现的流动状态串联为一套Bernoulli方程和流量守恒方程,进行流向及流量的迭代求解。利用求解获得的流态、压强及速度分布计算控制棒组件上的流体阻力,代入下落运动方程,进行落棒时间计算。结果表明:考虑流动反向的落棒时间为2.133s,而认为所有流水孔始终流出的落棒时间为2.036s;流动反向对落棒时程及落棒时间影响明显,理论分析可采用考虑流动反向的迭代方法。

Iterative Method of Flow Computation in Guide Thimble during Rod Dropping

In the previous rod dropping computation, it was assumed that the flow in the discharge orifices of the guide thimble are all of outflow throughout the rod dropping course, while, in fact, the inflow occurs. To handle this problem, it is assumed that inflow and outflow exist in each discharge orifice. The energy dissipation is analyzed on every flow section, having changes in shape or area. By introducing the flow indexes to represent the flow status of each orifice, a set of equations of the Bernoulli and flow conservation is subsequently developed by accumulating all flow status with these indexes. The flow status, pressure and velocity in the guide thimble are iteratively solved and used to compute the drag force on the control rod assembly. The dropping time is finally solved by substituting the drag force into the equation of dropping motion. The dropping time is obtained as 2.133 s while it is 2.036 s if the flow reversed is neglected and the outflow is assumed. It is indicated that the flow reverse has a significant effect on the dropping course and dropping time. Hence, this iterative method is a preferable choice of the flow computation for the guide thimble.