Water Hammers in Transonic Modes of Steam-Liquid Flows in NPP Equipment

Abstract

The analysis of well-known studies in modelling conditions for water hammers in equipment and components of pipeline systems has revealed that definition of conditions and parameters of water hammers in the transonic modes of single-and two-phase flows (at a speed of propagation of acoustic disturbances) is the least studied problem.The original method is proposed for determining the conditions and parameters of water hammers in transonic flow modes subject to the transition of the kinetic energy of the flow stagnation into the energy of the water hammer pulse.It was found that the simulated hydrodynamic loads in transonic modes can significantly exceed the corresponding known recommendations of N. Zhukovsky.The proposed method of equations computer modelling served to determine the criteria range for water hammers due to aperiodic thermohydrodynamic instability in transonic flow modes. K e y w o r d s: water hammer, transonic modes, head-flow characteristic.

Criteria and Conditions of Thermal Hydrodynamic Instability in the Circuits of Natural Circulation of Nuclear Power Plants in Case of Leak Accidents

“…The method is based on the fundamental thermodynamic principles of analysis of the influence of fluctuating pressure and flow disturbances in PSS-NC circuits on the conditions and consequences of THI in the process of accidents with circulation circuit leaks. According to these principles, if pressure and mass increase (or decrease) simultaneously and independently of each other in an equilibrium system, the system is unstable [9][10][11][12].…”

“…-Negative consequences for the reliability/safety of NPPs of this type of THI in PSB-PC can be: violation of safety functions for emergency cooling of the active zone of reactors and refueling of steam generators, hydrodynamic and thermal shocks in systems important for safety, etc. [9][10][11][12].…”

“…The THI phenomenon consists in high-amplitude oscillatory or pulsed deviations of thermal hydrodynamic parameters from the established (quasiequilibrium) state of the system. The following types of THI are distinguished: high-frequency (thermoacoustic) THI as a consequence of incomplete heat and mass transfer in acoustic waves of thermally unbalanced twophase flows [9]; low-frequency THI as a consequence of the inertia of the non-porous-cost characteristic of pumps of safety systems in transient modes [10]; pulsed (aperiodic) THI in transsonic two-phase flows [11] and others. It should be noted that, despite the indisputable relevance of the problem, the conditions and consequences of THI in the contours of PSS-NC have not been sufficiently studied.…”

Сriterion Method for Determining the Conditions for Occurrence of Thermoacoustic Instability in the Reactor Core

“…The conditions for the occurrence of thermoacoustic oscillations are significantly influenced by the distribution of heat emissions along the length of the heated channel, the gas saturation of the coolant and other factors. In [6], the question of the conditions for the occurrence of thermohydrodynamic instability in the safety valves of the reactor plant was considered. As a result, the conditions for the occurrence of aperiodic instability due to transonic regimes of two-phase flows of the heat carrier are established; and there are no conditions for the emergence of TAI.…”