The quantification of mass lost through a pressurized system rupture is important to full understanding of the depressurization behavior of a wide variety of boiler systems. Of particular interest is the effect of system depressurization on the integrated safety systems of Westinghouse’s next generation nuclear power plant, the AP600. The Oregon State University (OSU) Advanced Plant Experiment (APEX) test facility is designed to model the AP600 small break loss of coolant accidents’ (LOCA) long-term cooling behaviors. An important aspect of the test matrix is the quantification of primary mass inventory losses through simulated system ruptures. This thesis describes the methods used to analyze the break flow measurements obtained in the OSU APEX test facility, and the objectives of this study include the following:

• Evaluate the instrumentation to accurately measure the initially subcooled break flow rates and time-dependent saturated break flow rates for various test configurations.
• Compare the initial break flow rates with the predictions of several well-known critical flow models.
• Compare the time-dependent integrated mass exiting the break measured by the BAMS with the predictions of an integrated mass model.
• Present the results in terms of non-dimensional quantities.

Chapter two presents a brief review of two-phase fluid critical flow models. Chapter three presents a description of the APEX test facility. Chapter four presents an evaluation of the APEX break flow measurement system during subcooled depressurization. Chapter five presents an integrated mass method for collapsing the measured critical flow data onto a single dimensionless plot, and chapter six presents the conclusions of this research.