On the numerical approach for simulating reactor thermal hydraulics under seismic conditions

Abstract

The motions of bubbles and free interfaces in oscillating two-phase flow fields are simulated numerically to assess the methodology for simulating reactor thermal hydraulics under seismic conditions. Two numerical methods are compared: one is to model the oscillating flow filed directly using the moving grid of the ALE method, and the other is to simulate the effect of oscillation using an external force acting on the fluid in a stationary grid. The two-phase flow field is simulated by the level set method. The theoretical back ground and the limitation of the two methods are discussed, and the calculated results using the external force are shown to coincide with those using the moving grid. It is found that the interfacial area between liquid and gas phases, which is one of the most important parameters for the nuclear reactor safety analysis, is affected largely by the oscillation.