Численное моделирование гидродинамического воздействия на трубки парогенератора реактора «БРЕСТ-300» при аварии «межконтурная неплотность»

Abstract

The article considers the flashing of water in liquid lead and the hydrodynamic processes caused by this phenomenon initially in the emergency mode involving primary-to-secondary leak in the steam generator used as part of the «BREST-OD-300» fast-neutron lead-cooled nuclear reactor plant. The analysis was carried out using an integral equilibrium thermodynamic model for water describing the flashing of a single droplet. In the analysis, uniform distributions of the physical parameters (pressure, void fraction, etc.) inside the droplet are assumed. The liquid lead hydrodynamics is described by a system of nonsteady equations of continuity and motion for ideal incompressible fluid in a spherical system of coordinates. Mathematical descriptions of the “equilibrium” model and semi-implicit numerical method for solving the differential equations used in the model are given. Time dependences of the droplet expansion radius and droplet pressure are obtained. Spatial distributions of lead velocity and pressure for different moments of time are calculated and presented. Transitions of one kind of energy to another are analyzed. The numerical results obtained from the equilibrium model are compared with similar results calculated from an “explosion” model, the main assumption of which is that the initial excess energy of the droplet instantaneously transforms into the liquid lead mechanical energy. The article presents a short description of the explosion model developed proceeding from generalization of the model of instantaneous point energy release (explosion) in ideal incompressible liquid for the case of instantaneous energy release in a finite volume. The liquid lead velocity field is calculated, based on which the hydrodynamic force applied to the steam generator tube located in close vicinity of the rupture place is estimated. The calculation results have shown that this force is insufficient for causing damage to the nearest steam generator tubes. It has been shown that the hydrodynamic impact force calculated taking into account a finite rate of energy transfer from the droplet to the lead (the equilibrium model) is lower than that obtained from using the explosion model.