Two-fluid modeling of two-phase flow in BWR cores

Two-fluid modeling of two-phase flow represents the state-of-the-art in the thermal-hydraulic analysis of light water reactors. For example, computer codes such as TRAC and THERMIT have been used for a wide variety of studies ranging from pressurized water reactor core modeling to analysis of flow instability problems in steam generators. An unfortunate consequence of the semi-implicit numerical solution technique which is used, however, is that the maximum time step size ..delta..t is limited by a stability condition. For boiling water reactor transient analysis where there is significant boiling and slip between the phases, this restriction on the time step size may be as small as 10 ms. For this reason, a fully implicit two-fluid, one-dimensional, multi-channel model for analyzing two-phase flow has been developed and is summarized. The intent is the development of a numerically stable solution method which would allow large time step sizes. Emphasis has been placed on steady state and mild transient analysis of boiling water reactor cores.