Water Flow Simulation Test on Flow-Induced Oscillation of Thermowell in Prototype Fast Breeder Reactor "MONJU"

Water flow simulation tests were performed on the flow-induced oscillations of the thermowell in the prototype fast breeder reactor (FBR), MONJU. The displacements of the target cylinder were measured, and the oscillation amplitudes, the frequency characteristics, and the phase relationships were estimated. The estimations showed that the oscillations of the target cylinder had a one-dimensional oscillation region in the in-line direction with symmetric vortices shedding and a two-dimensional oscillation region induced by alternative vortices. The phase estimation, carried out by a methodology using wavelet analysis and statistical analysis, indicated that the effect of the alternative vortices on the in-line oscillation was changed with the flow velocity.