抗流致振动的压水堆控制棒导向筒阻流板设计与数值分析

Design and Analysis on Flow-blocking Plate Mounted on the GuideColumn of Control Rod Against Flow-induced Vibration in Pwr

压水堆的堆芯上腔室中的控制棒导向筒可使控制棒在其内平滑地被提出或插入堆芯。堆芯上腔室内掠过控制棒导向筒的横向流从导向筒壁面的流水孔流入导向筒内部,会诱发控制棒的流致振动。流水孔的作用是在控制棒下落时排出导向筒内的水以减少控制棒下落阻力,使控制棒及时落入特定位置从而保证反应堆的安全。如果流水孔的尺寸过大,落棒阻力较小,但控制棒的流致振动会增强;反之亦然。虽然在常规设计中核算了流水孔尺寸以平衡落棒阻力和流致振动,但是压水堆核电厂还是会经常出现由上述问题引发的落棒延迟或控制棒流致振动过大问题。为了解决上述问题,本研究提出了改进设计方案,即在导向筒流水孔的前部设置阻流板,减小通过流水孔进入控制棒导向筒的流体。对控制棒周围的流体进行三维数值模拟,根据计算出的控制棒周围的流速,比较和评估改进设计前后控制棒周围的流动特性。计算结果表明,与改进设计前相比,改进后设计中控制棒周围的横向流动明显减弱。

Guide columns in the upper plenum of pressurized water reactor(PWR)can guide the control rods to rise from or to drop into the core smoothly.Cross flow over the guide columns in the upper plenum of core may invade into the columns through windows opened at wall of the columns,which may cause flow-induced vibration(FIV)of the control rods.Function of the window is to drain the water inside the column to reduce the drag force of the control rod when it drops so that the control rod can drop to the specified position timely for safety of the reactor.If size of the window is so large,the drag force becomes small meanwhile the FIV of the control rods may strong due to the large invading flow,and vice versa.Although a critical size of the window is usually determined to keep the balance between the drag force and FIV in the conventional design,drop time delay or FIV damage of the control rods caused by this kind of unbalance problem occurred in the PWR sometimes.In order to solve above problem,a creative design is proposed in the present research,in which a flow-blocking(or shading)plate is set in front of the window of guide column so that the invading flow is blocked,while the drain flow is kept fluent.Invading flow around the control rods was simulated by a computational fluid dynamics(CFD)code either for the creative design or for the conventional design.According to the calculated out mean flow velocity around the control rods,FIV amplitudes of the control rods in both designs were assessed and compared.Results showed that invading flow around the control rods in the creative design is much weak compared to that in the conventional design.