Mechanism of the Excitation of Vibrations in RBMK Fuel Assemblies

Abstract

It is shown that the high intensity of the vibrations of RBMK fuel assemblies is due to the parametric excitation of oscillations when an axial flow of the coolant interacts with the fuel elements. The periodicity of this coolant action is due to plug-flow regimes of the two-phase coolant, pumped-induced oscillations of the coolant flow rate, and turbulization of the flow by the spacing lattices and fittings. It is shown that an in-reactor experiment must be performed in order to obtain a relation between the steam-content distribution and the vibrations in the RBMK fuel assemblies. For this, it is suggested that the steam-content distribution and the vibrations of the fuel elements be measured by using a standard system of measurements of the thermohydraulic and neutron-physical parameters of RBMK reactors and by analysing the noise in the indications of the sensors monitoring the height distribution of the energy release.