The Numerical Simulation Research of Gas–Liquid Two-Phase Flow in Small-Break Loss-of-Coolant Accidents

Abstract

During small-break loss-of-coolant accidents (LOCA), gas entrainment, which occurs with the lower coolant level, the relief of the loss of coolant, can reduce risk in reactor. Therefore, the gas–liquid two-phase flow through a small hole has become a focal point these years. Considering that the existing researches are mostly about experimental study, and it is difficult to set a limit working condition, this paper simulates and analyzes the flow processes in primary circuit pressure boundary when the small-break LOCA happens by the FLUENT software, on the premise of verifying the computational fluid dynamics model. By means of changing the shape, size, length of break, the gas volume fraction, and the pressure drop, the author discovers that the sharp, long channel break increases the resistance of fluid blowdown and decreases the blowdown velocity, and the loss of coolant is more likely to be reduced in such condition. By simulating the flow processes after flash distillation condition,the author found that in cross section of break, the average blowdown velocity increases with the initial gas volume fraction, while the mass flow rate decreases contrarily considering that the gas volume fraction can meanwhile influence the fluid density. Besides, the larger the initial gas volume is, the earlier the gas entrainment will occur and the loss of coolant will be reduced. According to the results of numerical simulation, the author finds that gas entrainment will decrease the mass flow rate of break, reduce the loss of coolant, and save time for emergency core cooling.