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Under simulated accident conditions, tees in the primary coolant loop of a Pressurized Water Reactor (PWR) can deviate from their original design purpose and become separators that effectively remove core heat sink capacity. This method of primary coolant removal is a phenomelogical subset of phase separation known as liquid entrainment, whereby liquid is forced from its original path by the inertia of the gas. A comprehensive literature review revealed common deficiencies in previous studies. The Westinghouse AP600 advanced reactor design was chosen to assess the validity of entrainment models. Following a systematic scaling analysis of the prototypic design a model separate effects test was proposed and constructed at Oregon State University. Just under 100 tests were run to fill the deficiencies found in the literature review. New data from the Air-water Test Loop for Advanced Thermal-hydraulic Studies (ATLATS) could not be predicted by published correlations. A new theoretical model for predicting liquid entrainment onset and steady state entrainment was developed. Comparison with all available data shows a marked improvement for predicting the mass flow rate out the vertical branch. / Graduation date: 2003

In the event of a small break loss of coolant accident (SBLOCA) in a nuclear reactor, cold fluid is injected through the reactor system high pressure injector to compensate for the coolant loss. When this flow rate is less than a critical value, however, the hot fluid in the cold leg penetrates into the vertical injection line in a process called buoyant backflow. Because the resulting penetrations induce thermal stresses in the pipe, the presence of backflow in the injection lines is potentially significant. Since these penetrations could potentially damage the pipe, it was the purpose of this study to evaluate the backflow behavior. To this end, both the critical injection conditions and the subcritical penetration depth were experimentally determined through flow simulation in a 1/5 scale model. In addition, the experimental trends wi-re modeled theoretically. By matching the theoretical results to the experimental data, it was determined that backflow began below a critical Froude number of .65 and increased in depth with the negative logarithm of the injection velocity. The agreement between theory and experiment was excellent. For a certain class of reactor systems, the full scale Froude numbers were then compared to the critical value obtained in the analysis. For the systems involved in this comparison, the full scale Froude numbers were shown to be less than .65 for all practical flow rates. As a consequence, buoyant backflow is expected within the injection lines of these reactors, under safety injection conditions. / Graduation date: 1991

The flooding phenomenon can be defined as the maximum attainable flow condition beyond which the well defined countercurrent flow pattern can no longer exist. Thus the countercurrent flow limit (CCFL) or the flooding limit may be thought of as the flow condition at which the strong interaction between the two phases occurs. Considerable effort has been devoted to understanding and analyzing the flooding transition in many fields. For example; the flooding phenomenon is one of the important phenomena encountered in the safety analysis of light water reactors (pressurized water reactors and boiling water reactors). Accurate predictions of flooding behavior are particularly important in the assessment of emergency core cooling system (ECCS) performance. Currently, the postulated loss-of-coolant accident (LOCA) is considered the design basis accident. A physical understanding of the flooding phenomenon will help assess core refill during the course of a LOCA. Understanding the physical mechanisms of the flooding phenomenon might help establish more reliable equations and correlations which accurately describe the thermal hydraulic behavior of the system. The models can provide best-estimate capability to the design codes used in the evaluation of ECCS performance. The primary concern of this study was to: 1. Understand the physical mechanisms involved in the flooding phenomenon in order to derive a suitable analytical model. 2. Show that the combination of: a. Linear Instability Theory b. Kinematic Wave Theory c. Catastrophe Theory can provide a general model for flooding phenomenon. The theoretical model derived using the aforementioned combination of theories indicates good agreement between the experimental and the predicted values. Comparisons have been made using a large volume of air-water flooding data. / Graduation date: 1991

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Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Nuclear Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.

Thesis (Nucl. E.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1977. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Thomas Rodack. / M.S. / Nucl.E.