Analysis of Upper Plenum Level Oscillatory Phenomena by TRAC-BD1

Upper plenum level oscillatory phenomena were observed in boiling water reactor upper plenum mixing experiments. These phenomena were due to the multidimensional interaction of a highly subcooled spray water injected into the upper plenum with a twophase mixture and vapor. Analysis of these phenomena was performed by TRAC-BD1, which is based on a multidimensional, nonhomogeneous, nonequilibrium, two-phase flow model to assess its predictive capability. It was found that TRAC-BD1 can predict upper plenum level oscillatory phenomena by using a simple upper plenum model that accounts for the interaction of a highly subcooled spray with vapor and a two-phase mixture.