Development of the best-estimate computer code for reflood transient analysis

Abstract

As an extension work of computer codes QUENID and KREWET developed by previous workers at KAIST, an improved code entitiled BEAR has been developed. The BEAR code is based on mechanistic models developed to analyze bottom reflooding of a single flow channel and its associated fuel rod. From the hydrodynamic point of view the flow channel is divided into a singlephase liquid region, a continuous liquid two-phase region, and a dispersed liquid region. The heat transfer coefficients are the functions of the local flow conditions. The wall temperature history is calculated by solving the time-dependent radial conduction equation. Quench pront propagation is treated separately from the overall heat transfer calculations by models including the effects of axial conduction. Comparison of the predictions of the BEAR code with the PWR-FLECHT experiment data show a relatively good agreement, but further improvement seems to be necessary for low pressure and low flooding rate conditions.