ADS-4 Pipe Vibration Evaluation During AP1000® Preoperational Testing

Abstract

Preoperational testing of the first AP1000® pressurized water reactors took place in the fall and winter of 2016. This Hot Functional Testing (HFT) included observation of vibrations throughout the piping systems, and is required to be successfully completed before fuel load. During HFT, flow through the hot leg passes many piping intersections where instabilities such as vortex shedding create pressure pulsations. Coupling of the vortex shedding frequency and natural acoustic frequency of the piping sidebranch may lead to acoustic resonance of the system. This resonance condition is understood, but difficult to predict; therefore, the HFT plan included screening for such conditions based on ASME Operation and Maintenance of Nuclear Power Plants vibration monitoring group (VMG). Vibration was observed in the Automatic Depressurization System (ADS) branch off the reactor coolant system hot leg that was potentially in a resonant condition. This paper details the identification, characterization, and analysis of the ADS vibration observed during HFT. Additional instrumentation was employed and data were gathered at varying conditions to determine the nature and extent of the vibrations. Demonstration of acceptable vibration levels in the ADS system was a key engineering accomplishment for AP1000® fuel load.