Three-dimensional compressible two-fluid model and its application

Reliable prediction of the behavior of a compressible gas-liquid two-phase flow is important for the integrity assessment of power plants. A numerical method for the extended two-fluid model for highly compressible gas-liquid two-phase flow has been developed. The extended two-fluid model can treat the behavior of the interface between gas and liquid because of its accurate discontinuous void fraction transport calculations. The Riemann invariance, related to discontinuities of pressure and velocity in compressible flow, is taken into consideration by the Godunov scheme, originally developed for single-phase compressible flow. The numerical method was implemented in a computer program which was applied to predict integrity of the suppression pool structures during operation of SRVs (Safety Relief Valves) in BWRs (Boiling Water Reactors). If the pressure of the RPV (Reactor Pressure Vessel) becomes higher, SRVs are opened and excessive gas flows into the exhaust pipes to the suppression pool. The present method was applied to predict the transient pressure field caused by large bubble oscillation near the quencher site in the suppression pool. The results showed that the peak pressure changed according to the depth of water in the pool and the pressure propagation was attenuated as time passed. (authors)