The Oregon State University (OSU) Advanced Plant Experiment (APEX) is a one-fourth height, one-half time scale, reduced pressure integral systems test facility designed to model the long-term cooling capabilities of the emergency core cooling systems of the Westinghouse AP600. This study provides a brief description of the APEX test facility, analyzes the measured flow rates through the simulated break geometry, and compares the data with existing flow models.

The break flow rates of various tests have been measured using state-of-the-art instrumentation: magnetic meters for liquid flows and vortex meters for vapor flows. The flow rate data has been reported with corresponding instrument measurement errors. In addition to the flow meters’ measurements, the liquid-level-depression-rate within the pressurizer was determined for simulated break sizes of one inch or less. Based upon a simple mass balance, the initial break flow rates were calculated using the pressurizer draining rates, and the calculated values were found to be in good agreement with that of the flow meters. The following flow models were also used to predict the initial break flow rates: Homogeneous Equilibrium Model, Equilibrium Rate Model, and Henry-Fauske Subcooled Model. The Henry-Fauske Subcooled Model yielded the most accurate flow predictions when saturated conditions were assumed at a given system pressure.