反应堆堆内构件流致振动特性研究

以某新型工程试验堆为研究对象,采用试验分析与仿真计算相结合的手段探索该试验堆堆内构件流致振动特性。在流致振动试验中,根据相似准则建立了1/2的缩比试验模型,并在整体水力模拟台架上开展了100%额定流量工况下的堆内构件流致振动试验,测量了吊篮组件和二次支承组件在流体作用下的动力响应;根据吊篮组件和二次支承组件所受激励的不同,结合试验结果分别采用不同的计算方法得到了流体力作用下结构的动力响应,分别获得了100%额定流量工况下的最大应力值。     

燃料组件流致振动试验研究

采用试验的方法对燃料组件的振动特性和流致振动响应进行研究,获得了燃料组件的固有振动特性;各稳态工况的流致振动响应规律:响应随流量的增加而增加;瞬态工况下振幅、频率与时间(流量)的三维瀑布图以及定位格架的运动轨迹。试验所获得的完整、可靠的数据为燃料组件的设计、安全分析和磨蚀试验提供重要的输入参数,为最终的安全评审提供依据。     

控制棒导向管外流道旁流特性实验研究

冷却剂流经核反应堆堆芯时，绝大部分通过燃料组件内部流过，带走裂变能量。另外一小部分作为旁流经过燃料组件外侧流道、控制棒导向管外侧及内侧流道流出。为确保反应堆在正常运行工况下的安全性，必须限制堆芯旁流流量。本文通过开展导向管外侧流道阻力特性实验研究，在不同流量工况下获得了分段压差，并进一步拟合了雷诺数与阻力系数的关系式。实验结果表明，导向管外侧流道压力损失主要集中在堆芯下栅格板处，当反应堆额定工况运行时，单组导向管外侧流量仅为0.196 m³/h。     

板型燃料组件额定流速流致振动实验研究

针对贫铀叠层板型燃料组件,采用了一种新的软测量方法,进行了其在经受冷却剂额定流速冲刷时的振动实验。获得了该组件在额定流速6 m/s下的流致振动动态响应时间域和频率域结果,并对实验结果进行了分析。     

六边形组件流致振动响应数值分析

工程堆用六边形组件受到冷却剂的作用会发生流致振动,采用数值分析方法对六边形组件的振动特性和流致振动响应进行分析研究,通过数值仿真计算了六边形组件在空气中和静水中的一阶固有频率及相应振型,并结合试验结果运用流致振动响应计算方法研究了流体力作用下结构的动力响应,获得了响应的最大应变值。计算结果和试验结果精度在同量级,验证了本文数值分析方法在六边形组件流致振动响应研究的可行性。     

CN-1515Ti辐照容器组件流量分配方法研究

CN-1515Ti辐照容器组件的水力特性研究是组件入堆前的重要准备工作,其合理的流量分配对快堆堆芯的安全非常重要,而节流装置的尺寸是影响流量分配的关键因素。本文以中国实验快堆的实际运行参数为要求,以MOX组件水力实验回路为工具,进行了CN-1515Ti辐照容器组件的流量分配实验。结果确定了辐照容器组件节流装置的尺寸为对边距17.2 mm,并形成了可用于相关实验的经验数据。     

凸台约束对快堆组件流致振动特性影响的实验研究

流致振动引起的组件相互碰撞以及流体持续冲刷导致的结构疲劳损伤,会威胁堆芯安全,有必要对快堆组件开展流致振动行为的研究和评价。采用有无固定凸台约束两种方式都会给组件的振动特性带来一定的不确定度。为研究凸台约束对快堆组件流致振动特性的影响,定量评价有无固定凸台约束对组件振动特性带来的不确定度,本文采用实验方法研究了组件上端自由和有0.3 mm间隙的固定凸台约束两种条件下组件的流致振动特性。实验结果表明,组件在有无固定凸台约束条件下最大振幅均方根（RMS）间的相对偏差为6.1%,对于最靠近凸台处测点的幅值,有无凸台约束的最大振幅RMS间的相对偏差为17.4%。本文实验结果对该种复杂支撑条件下组件流致振动行为的分析与评价具有一定的参考价值。     

脉动流下棒束通道内相位差及瞬态流场研究

事故条件及海洋条件下反应堆处于非稳态工况,堆芯燃料组件内热工水力行为具有瞬变及多因素耦合特性,对反应堆的安全提出更高挑战,因此有必要对燃料组件内瞬态特性进行研究。本文通过测量棒状燃料组件内压降和流量之间延迟时间开展棒束通道脉动流条件下相位差研究,对比了相位差在不同振幅、不同流动状态下的变化特性,并分析了定位格架对脉动流相位差的作用特点。另外,基于粒子图像测速(PIV)技术开展了脉动流条件下棒束通道内流场分布特性研究,对比了相同流量条件下稳态工况与瞬态工况下流场分布差异,分析了主流具备不同加速度时棒束通道内流场分布特征。实验结果表明:定位格架可减小脉动流下棒束通道内相位差;棒束通道内流场演化滞后于主流量变化。实验结果有助于揭示燃料组件在非稳态条件下瞬态特性,并为燃料组件的设计和优化奠定基础。     

反应堆压力容器上部堆内支承构件的流致振动分析

核电厂运行工况下,反应堆压力容器(RPV)上部堆内支承构件处在一个高速的横向流流场中。在横向流作用下,RPV上部堆内支承构件产生明显的振动。这类振动行为体现在涡旋导致的结构振动和流弹不稳定。研究RPV上部堆内支承构件在横向流作用下的振动行为特性,并根据ASME规范对其进行流致振动分析评定。研究结果表明:特定结构在冷启堆或冷停堆时更容易产生流致振动,而非在满功率运行工况下。     

矩形通道中两端固定柔性单板湍流微振的研究

平行板燃料组件的流致振动特性研究对于保证核反应堆的安全可靠运行具有重要意义。本文将平行板燃料组件简化成一个在矩形通道中两端固定的柔性单板结构,研究其振动机理,为研究平行板燃料组件的流致振动特性奠定基础。利用加速度传感器等测得实验用铝板的固有频率和弹性模量,使用应变片和激光位移传感器测量平板在不同流速下的振动频率和位移。结果表明：在目前的实验条件下,平板的振动表现为一种由于湍流引起的复杂的随机振动;平板在水中的振动位移随流速的增大而变大;随着流速的增大,平板振动加剧,振动表现为低频成分减少,高频成分增加。     

A study on mechanical properties and flow-induced vibrations of coil-shaped holddown spring

The fuel assemblies used in the OPR1000s in Korea employ four coil-shaped hold-down springs to exert compressive load at the top of fuel assembly so that the assemblies may not be damaged by preventing its hydraulic-induced lifting-off from its lower seating surface. However, the coolant flow generates the flow-induced vibration at the coil-shaped hold-down springs which may cause wear on the spring surfaces. A hold-own spring may be fractured if torsional stress acting on its worn area exceeds a stress limit, resulting in the loss of hold-down spring force of the fuel assembly. In this paper, flow-induced vibration tests were performed for standard and improved coil type hold-down springs to investigate the effects of these two hold-down spring designs on flow-induced vibration wear. In parallel, a wide spectrum of mechanical tests was performed to obtain vibration-related characteristics of these two hold-down springs, which can be used as input data for the fuel assembly static and dynamic analysis. It is found that the improved hold-down spring design is better against flow-induced vibration wear than the standard one. With the use of the three-dimensional Solidwork model, the stress-related design lifetime of the improved hold-down spring was estimated by extrapolating its wear data measured from the flow-induced vibration tests, which indicates that the improved HD spring design will maintain integrity during the fuel design lifetime in OPR1000s in Korea.     

Grid-to-rod flow-induced impact study for PWR fuel in reactor

Dynamic contact impact from hydraulic flow-induced fuel assembly vibration is the source for grid-to-rod fretting in a pressurized water nuclear reactor (PWR). To support grid-to-rod fretting wear mitigation research, finite element analysis (FEA) was used to evaluate the hydraulic flow-induced impact intensity between the fuel rods and the spacer grids. Three-dimensional FEA models, with detailed geometries of the dimple and spring of the actual spacer grids along with fuel rods, were developed for flow impact simulation. The grid-to-rod dynamic impact simulation provided insights of the contact phenomena at grid-rod interface. It is an essential and effective way to evaluate contact forces and provide guidance for simulative bench fretting-impact tests.     

The study on grid-to-rod fretting wear models for PWR fuel

The fretting wear is found to be generated at grid-to-rod contact areas by flow-induced vibration. This flow-induced grid-to-rod fretting wear may be initiated at a certain critical grid-to-rod gap that strongly depends on the extent of flow-induced vibration and grid spring designs. Three fretting wear excitation mechanisms acting on the grid-to-rod fretting wear are summarized. In order to examine the impact of grid spring designs on the fretting wear rate, the fretting wear tests for three kinds of grid spring designs were carried out for 500 h, simulating the reactor flow conditions. In parallel, three grid-to-rod fretting wear models that include constant work rate model, constant work density rate model and linear work density rate model have been developed. The three fretting wear models were used to predict the fuel rod perforation times with the use of the fretting wear test results. It is said that the constant work density rate model or the linear work density rate model is quite effective in predicting the grid-to-rod fretting-induced rod failure time observed in commercial nuclear power plants.     

换热器管束流体激振研究的新思路

提出了一种快速简便地求解非定常粘性流方程的方法、以得到换热器管束复杂流道内作用于振动管子上的流体激振力。简述了如何将管束流动的流体弹性稳定性分析与工程实际的振动疲劳破坏相联系，以及怎样在求解流动基本方程的基础上分析管束复杂流道内的振荡压力传播。将求解复杂流动的快速方法—参数多项式方法与流体激振的全功能分析及振荡压力传播理论结合起来，为管束流体激振研究开拓了一个新的途径。     

Effect of flow-induced vibration on local flow parameters of two-phase flow

A preliminary study was conducted experimentally in order to investigate the effect of flow-induced vibration on flow structure in two-phase flow. Two kinds of experiments were performed, namely ‘reference’ (no vibration) and ‘vibration’ experiments. In the reference experiment, an experimental loop was fixed tightly by three structural supports, whereas the supports were loosen a little in the vibration experiment. In the vibration experiment vibration was induced by flowing two-phase mixture in the loop. For relatively low superficial liquid velocity, flow-induced vibration promoted the bubble coalescence but liquid turbulence energy enhanced by the vibration might not be enough to break up the bubble. This leaded to the marked increase of Sauter mean diameter, and the marked decrease of interfacial area concentration. Accordingly, flow-induced vibration changed the void fraction profile from ‘wall peak’ to ‘core peak’ or ‘transition’, which increased distribution parameter in the drift-flux model. For high superficial liquid velocity, shear-induced liquid turbulence generated by two-phase flow itself might be dominant for liquid turbulence enhanced by flow-induced vibration. Therefore, the effect of flow-induced vibration on local flow parameters was not marked as compared with that for low superficial liquid velocity. Since it is anticipated that flow structure change due to flow-induced vibration would affect the interfacial area concentration, namely interfacial transfer term, further study may be needed under the condition of controlled flow-induced vibration.     

核承压热交换器两相流流致振动现象研究

为保障核承压热交换器的安全运行,采用数值模拟以及软件计算相结合的方法,对核承压热交换器两相流流致振动现象及减振措施进行了探究。研究结果表明:基于流致振动发生机理,热交换器横流速度、固有频率、卡门旋涡脱落频率以及紊流抖振频率为重点分析因素;由公式得出流量、换热管直径、换热管壁厚、管束排列等对流致振动有直接影响,无支撑跨距是影响管束流致振动较大因素;最易发生流致振动的部位包括入口区域、出口区域、折流板缺口区域以及无支撑跨距大管束;设计中,应在流量、换热管直径、壁厚、无支撑跨距、管束排列及入口防冲挡板设置等方面优化,以减小流致振动危害。     

输流管网流致振动特性数值模拟研究

为研究管路系统流质振动特性以优化管路设计,本文以典型输液管网系统为对象,基于Ansys Workbench平台开展了不同流体激励下的管路双向流固耦合模拟计算,获得了管路结构流致振动特性,分析讨论了激励类型、介质温度、流场结构及结构固有频率对管内流致振动特性的影响。结果表明,脉动流量激励下的管路结构振幅显著大于恒定流量激励下的结构振幅,当流体激励频率较接近管路结构固有频率时,结构和流体将趋于共振,导致结构振动加剧。通过在管道适当位置施加约束支撑,使结构固有频率远离流体激励频率,可有效减小管道的振动。此外,介质温度和流速对结构振幅有较大影响。