APPROACHES TO MODELING CONDITIONS OF THERMOACOUSTIC INSTABILITY IN NON-EQUILIBRIUM TWO-PHASE COOLANT OF NUCLEAR REACTORS
Abstract
The occurrence of thermoacoustic instability in the non-equilibrium two-phase flow of the coolant can significantly affect the reliability and integrity of the nuclear reactor's internal devices. At present, the development of adequate and justified methods for modeling thermoacoustic instability in the active zone of a nuclear reactor is an urgent issue. The purpose of the study is to develop a criterion method for determining the conditions for the occurrence of TAN in the active zone of nuclear reactors, which will increase operational safety and provide an opportunity to develop an operational system for diagnosing the conditions of TAN in the active zone of high-power reactor installations. For the conditions of transient and emergency modes of nuclear power plants with VVER, the thermodynamic approach of determining the conditions for the occurrence of thermoacoustic instability of a non-equilibrium two-phase coolant is more justified. Based on the thermodynamic approach, the conditions of thermoacoustic instability of the coolant in the active zone of the reactor were obtained. They depend on the defining thermodynamic parameters – reactor power, coolant consumption, pressure and temperature of the coolant at the entrance and exit of the active zone. It was established that in the nominal operating mode of the reactor, the coolant is stable with respect to thermoacoustic fluctuations. Based on the analysis of the well-known resonance approach to modeling the conditions for the occurrence of thermoacoustic instability (on the example of a single condensing bubble), it was established that the resonance effects of the coincidence of the frequency of propagation of acoustic waves and the frequency of condensation of steam bubbles can be significant for relatively short channels (less than 1 m) at relatively low pressures. For the conditions of transient and emergency modes of nuclear power plants with VVER, the thermodynamic approach of determining the conditions for the occurrence of thermoacoustic instability of a non-equilibrium two-phase coolant, based on the regularities of the conditions for the occurrence of oscillatory processes during acoustic perturbations of the thermodynamic parameters of the coolant flow in the active zone of a nuclear reactor, is more justified.
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