APPROACHES TO MODELING CONDITIONS OF THERMOACOUSTIC INSTABILITY IN NON-EQUILIBRIUM TWO-PHASE COOLANT OF NUCLEAR REACTORS

Abstract

The consequences of thermoacoustic instability of the coolant in the active zone of nuclear reactors can be high-amplitude, high-frequency dynamic loads on the internal structures and a violation of the tightness of the TVEL shells. However, until now, there are no reactor control/diagnostic systems and operational instructions for managing accidents in conditions of thermoacoustic instability of the coolant in the reactor core. The main reason for this situation is the lack of substantiated methods for modeling the criteria and conditions for the occurrence of thermoacoustic instability in the active zone. The purpose of the work is the development of a criterion method for modeling the conditions of thermoacoustic instability of the coolant in the active zone of the reactor to substantiate the appropriate reactor control systems and symptom-oriented emergency instructions. An original method of determining the criteria and conditions of thermoacoustic instability of the coolant in the active zone depending on the determining parameters of the thermodynamic state of the reactor plant has been developed.. Based on the thermodynamic approach, which takes into account the level of completion of interphase heat and mass transfer processes in acoustic pressure waves, the criteria and area of thermoacoustic instability of the coolant in the reactor core are determined. The established area of thermoacoustic instability of the coolant in the reactor core was verified on the basis of known experimental data obtained at the experimental installation, which meets the criteria of thermodynamic similarity to the core of the VVER-1000 core. Based on the developed criterion method, the main provisions and requirements for the relevant reactor control/diagnostic systems and symptom-oriented instructions for managing accidents in conditions of thermoacoustic instability of the coolant in the active zone of the reactors are defined.