(An) advanced numerical method with fully-implicit two-fluid model for a real-time accident simulator

Abstract

A new computational method is implemented in FISA-2 (Fully Implicit Safety Analysis-2 code) to simulate LWR operational transients in a real-time accident simulator. The basic field equations of FISA-2 consist of the mixture continuity equation, void propagation equation, two phasic momentum equations, and two phasic energy equations. The fully-implicit scheme is used to eliminate a time-step limitation for simulating slow transients. The phasic energy equations written in the nonconservation form is solved after they are set up to be decoupled from other field equations. The void propagation equation is solved to obtain the void fraction. Spatial acceleration terms in the phasic momentum equations are manipulated with the continuity equations so that pseudo-phasic mass flux may be expressed in terms of pressure only. Putting the pseudo-phasic mass flux into the mixture continuity equation, we finally obtain linear equations with pressure variables only as unknowns. Reasonable accuracy and no stability limitation with fast-running are proved by comparing results from FISA-2 with analytical solutions, experimental data, and results from other codes.