Verification of digital models of coolant self-oscillation of NPP with VVER

Abstract

The results of verification of VVER-440 digital acoustic model are presented. The vibration control system of the main equipment, named SÜS, which is used in normal operation of nuclear power plants (NPP), is used to measure coolant pressure pulsations and mechanical vibrations. The method of calculation of acoustic standing waves (ASW) generated in the equipment is developed; the calculated values of ASW frequencies are in agreement with the results of measurements of signals from pressure pulsation sensors. It is proved that in the nominal and start-up modes, as a result of transformation of stochastic random pulsations caused by turbulence and vortex formation into ordered oscillations, acoustic waves appear. It is shown that the frequencies of acoustic waves depend on the operating conditions and can coincide with the vibration frequencies of the equipment. It is proved that the acoustic properties of a nuclear reactor, regardless of the number of coolant circulation loops, are similar to the properties of a group of simultaneously used Helmholtz resonators. The use of the acoustic model of the reactor allows optimizing design and engineering solutions by creating equipment capable of minimizing unwanted cyclic loads. This capability is the most important to ensure long - term operation in manoeuvrable modes of small modular reactors.