Vibration of fuel bundles subjected to combined axial and localized cross-flow

核燃料组件在运行期间主要暴露于高速轴向流。在轴向流动条件下，燃料组件经历由流动湍流引起的随机振动。由此产生的湍流激发是很好理解的，并且在燃料组件的设计阶段已经考虑到，从而确保燃料的机械完整性。对于某些设计和/或操作条件，燃料组件可能暴露于更复杂的流动条件，这导致明显更高的振动，并且在某些情况下导致燃料棒微动磨损和故障。最严重的情况是燃料组件经受横向于燃料组件的纵向轴线的（部分）交叉流。例如，在较老的电厂中，横向流动可能是由于堆芯挡板分离造成的。其结果是强烈的局部横流，特别是在燃料棒束周边。由于电厂继续运行超过40年的阈值，由局部横流引起的栅-棒微动磨损引起了重大关注。对于某些电厂，特定的设计特征也可能在燃料棒束中引入交叉流。为了在发生失水事故（LOCA）时减轻极端压力，在反应堆堆芯中加入了战略性定位的LOCA孔或槽，从而引入了横向于燃料棒的高速射流。本文研究了轴向/横向混合流引起的燃料棒束振动问题。该项目的主要目标是了解圆形横截面的横向射流以及通过垂直于燃料棒束的槽的平面射流的燃料棒束动力学。更广泛地说，该项目旨在揭示这些复杂的轴向/横向流动的燃料振动和不稳定性的基本机制。预期的基本成果的重要性超出了核领域。高速复杂流动在从能源生产到化学工业的广泛工业环境中遇到。因此，预计研究结果将在更广泛的应用中为加拿大工业做出重大贡献。************

Nuclear fuel assemblies are exposed to primarily high speed axial flow during operation. Under axial flow conditions, the fuel assembly undergoes random vibration induced by the flow turbulence. The resulting turbulence excitation is well understood and has been accounted for at the design stage of the fuel assemblies thus ensuring fuel mechanical integrity. For certain design and/or operating conditions, the fuel assemblies can be exposed to more complex flow conditions which have led to significantly higher vibrations and in some cases fuel rod fretting wear and failure. Most serious is the case where the fuel assembly is subjected to (partial) cross-flow transverse to the longitudinal axis of the fuel assembly. Transverse flow may, for instance, result from core baffle plate separation in older plants. The result is strong localized cross-flow particularly for fuel rods in the bundle periphery. The grid-rod fretting wear induced by the localized cross-flow is of significant concern as plants continue to operate beyond their 40 year threshold. For some plants specific design features may also introduce cross-flow in the fuel bundles. To mitigate extreme pressures in the case of a Loss of Coolant Accident (LOCA), strategically located LOCA holes or slots have been incorporated in the reactor core, which introduces a high speed jet flow transverse to the fuel rods. The present project addresses the problem of fuel bundle vibration induced by combined axial/transverse flow. The primary goal of the project is to develop an understanding of the fuel bundle dynamics for transverse jet flows of circular cross-section as well as planar jets through slots normal to the fuel bundle. More broadly, the project aims to uncover the fundamental mechanisms underlying fuel vibration and instabilities for these complex axial/transverse flows. The importance of the expected fundamental results goes beyond the nuclear field. High speed complex flows are encountered in a wide range of industrial settings ranging from energy generation to chemical industries. The research results are therefore expected to significantly contribute to Canadian industries in this wider range of applications. ************