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Steam interfacial condensation in a core makeup tank was simulated using the code RELAP5/MOD3 version 8.0 to predict the violent pressure oscillation phenomena in a core makeup tank. Six base cases were carried out to study the effects of back pressure and of vacuum conditions produced in the core makeup tank by rapid steam condensation. The effect of varying the liquid conduction thermal layer thickness was studied. In addition, the code's ability to predict condensation heat transfer was evaluated. Violent pressure oscillations were found in the early period of a transient. The violent pressure oscillations had no effect on the total amount of injection water from core makeup tank. The conduction thermal layer thickness was found to only effect the liquid temperature history. The current version of RELAP5/MOD3 was found to be incapable of dealing with the condensation heat transfer problem in which the volume liquid temperature is lower than the temperature of the heat structure which is connected to that hydraulic volume. / Graduation date: 1994

The phenomena of interest in this work is the thermal stratification which occurs during the early stages of a loss of coolant accident (LOCA) in the OSU APEX Thermal Hydraulic Test Facility, which is a scaled model of the Westinghouse AP600 nuclear power plant. Thermal stratification has been linked to the occurrence of pressurized thermal shock (PTS). Analysis of the OSU APEX facility data has allowed the determination of an onset criteria and support for the postulated mechanisms leading to thermal stratification. CFX 4.1, a computational fluid dynamics code, was used to generate a model of the cold legs and the downcomer and the phenomena occurring within them. The following are the accomplishments of the work contained within this report; Determined the causes of thermal stratification in the cold legs of the Westinghouse Advanced Passive 600 MW (AP600) nuclear power plant. Predicted the onset of thermal stratification in the cold legs of the Westinghouse Advanced Passive 600 MW (AP600) nuclear power plant. Modeled the phenomena associated with thermal stratification in the cold legs of the Westinghouse Advanced Passive 600 MW (AP600) nuclear power plant. / Graduation date: 1998

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Bruce William Hagemeier. / M.S.