Abstract
Traditionally, the "added hydrodynamic mass" approach was widely used for the flow-induced vibration analysis of nuclear power plant reactors and reactor internals. The added hydrodynamic mass method is simple and effective for structures with regular geometries. Over the years, efforts have been made to account for the fluid-structural interaction among the reactor vessel, core barrel, thermal shield, and core shroud using mass-spring representation of the fluid. These efforts were generally benchmarked against test data to generate conservative results for a specific application. More recently, fluid elements have been developed to model the fluid in a structural finite element analysis. A study was performed herein to evaluate the effectiveness and the accuracy of using different fluid elements to model fluid-structural interaction of reactors and reactor internals. Several different fluid elements were used, including a contained fluid element and an acoustic fluid element. First, the fluid elements were used to model submerged beams and submerged concentric cylinders. The results were compared to empirical equations or available test data. The behaviors of these fluid elements were evaluated. The desirable fluid elements were chosen for further study of their behavior in modeling the actual reactor and reactor internals. The fluid elements were used to develop a reactor equipment system model of a Westinghouse three-loop reactor. The fluid elements transfer the fluid-structural interactions among the reactor vessel, thermal shield, core barrel, and core shroud. The reactor system dynamic analysis results were compared to the plant hot functional test data. Fluid elements, when carefully chosen and properly used, are superior to traditional methods to calculate flow-induced vibration responses because they can be adapted to very complicated geometry and they provide a unique hydrodynamic response for each mode shape requested. Fluid element capacities and how they shall be used in modeling with application to reactors and reactor internals are summarized herein. Using fluid elements and the approach herein, the dynamic response of the reactor equipment system can be calculated more accurately. This method is a powerful tool in the dynamic design of new reactor components. It also yields more realistic acceptance criteria for inspections which will benefits plant aging management programs. The fluid element application can be extended to calculate the dynamic responses of reactor and reactor internals due to operating basis earthquake, safe shutdown earthquake, and loss-of-coolant accident.
