Oscillation Excitation of Bunch of Fuel Elements of “VVER” Reactors by Turbulent Flow of Heat Carrier

Experimental data are obtained concerning pressure pulsations in the turbulent water flow at the full-scale mock-up of the fuel element assemblies "VVER-440". Based on multi-point measurements of pressure pulsations along the perimeter and length of a bunch of fuel elements, hydro-dynamical loads are estimated and the appropriate experimental data on vibration displacements are obtained. It is shown that input devices (in part, throttling spacers) creating the flow turbulence exert the substantial influence on the hydro-dynamical loads and vibration levels of the bunch of fuel elements. As diameters of the throttling spacers are decreasing, the hydro-dynamical loads increase at the section of the bunch of fuel elements near the lower supporting grid, and their spectral composition is characterized by low-frequency wide-band resonances. On the basis of data on the longitudinal distributions of pressure pulsations, it is established that the throttling spacers (or some other input devices) effect on the hydro-dynamical loads creation extends to the initial hydro-dynamical section of the heat carrier flow in the bunch, i.e., within the first two-three spans of the bunch.