Sub-Scale Versus Full-Scale Testing of Jet Pump Vibration

Time-dependent fluid pressure forces on jet pump components have been observed to cause destructive mechanical vibrations at a number of BWR plants. A test has been proposed for the purpose of studying the fluid-structure interaction phenomena and to determine what design or operational modifications can be imposed to mitigate or remove the vibration problem. Due to multi-system interactions of this problem, a full-scale test of water flow through a jet pump at reactor conditions is recommended over a sub-scale test. Each system to be studied imposes additional constraints to the modeling laws. Acoustic effects, vortex shedding or shear layer instability, and the fundamental beam mode of the jet pump diffuser all have similar characteristics, or response times. The need to maintain the time scale ratios for all systems implies that a full size system at full size structural and fluid parameters is the most likely success path in obtaining accurate and relevant data.