Digital acoustic model of an NPP pressurizer with WWER

Abstract

It is experimentally proven that the main cause of vibration excitation of equipment and internals of the main circulation circuit (MCC) are acoustic standing waves (ASW) and main circulation pumps (MCP). Usage of an interdisciplinary approach made it possible to create a digital acoustic model of pressurizer system with pipelines attached to it and prove that it is a self-oscillating system capable of generating acoustic standing waves (ASW) similar to simultaneous operation of several Helmholtz resonators. Each Helmholtz resonator in pressurizer is able to suppress a certain frequency of ASW generated by the reactor, which depends on coolant temperature. Determination of natural frequencies of coolant pressure oscillations (NFCPO) in pressurizer using Thomson formula is based on method of electroacoustic analogy. Acoustic compliance of pressurizer and acoustic mass of various combinations of pipelines connected to it make it possible to calculate NFCPO, in the system under consideration, according to the formula presented in the form of acoustic analogues of inductance and capacitance. Acoustic parameters of a system of Helmholtz resonators formed by a pressurizer and a connecting pipeline with hot leg of the third loop in nominal operating mode of NPP with WWER-1000 are calculated. A technology has been developed and verified, advantage of which is usage of a pressurizer for damping ASW, frequencies of which fall within vibration bandwidth of primary circuit structural elements. Calculation and experimental proof of previously unknown ability of pressurizer to damp ASW generated by the reactor in a wide frequency range is given, and possibility of preventing resonances with vibrations of equipment and NPP structures is substantiated.