Gravity Reflood Oscillations In A Pressurized Water Reactor

Author : Faith Rose Beck
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (11 download)

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Download or read book Experimental and Theoretical Study of Oscillatory Two-Phase Flows with Heat and Mass Transfer written by Faith Rose Beck and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents experimental and theoretical analyses of oscillatory two-phase flows with heat and mass transfer on liquid carryover behavior during refloodof a simulated nuclear reactor core. In a hypothetical large break loss of coolantaccident (LBLOCA), associated with a break in one of the hot- or cold-legs, theemergency core cooling system (ECCS) must provide sufficient coolant to the coreto remove decay heat and prevent the cladding from exceeding 1477.6 K. Duringreflood, flow to the core is gravity-driven, resulting in an oscillatory delivery ofcoolant. These oscillations have been attributed to vapor generation in the coreand a dynamic response of the downcomer water level. Nearly all reflood simulation experiments have been conducted with constant reflood rates, and have not considered the effect of oscillations on rod bundle thermal-hydraulics. The few studies that have been conducted with oscillating flow indicated enhanced entrainment and carryover of liquid from the quench front. While higher entrainmentcan provide precursory cooling ahead of the quench front, it can also expel morecoolant out of the system during oscillatory reflood. The amount of liquid entrained can be significant because, in an accident scenario, the quench rate will beslowed, and it can take longer to fully recover the core. At the Nuclear Regulatory Commission (NRC)/Penn State University (PSU) Rod Bundle Heat Transfer(RBHT) Test Facility, an electrically heated 77, 3.66 m (full-length) rod bundlearray has the capability of performing both constant and oscillatory forced floodingrate experiments. The facility is heavily instrumented, equipped with seven spacergrids with which to analyze droplet and heat transfer phenomena. The system canvary the oscillation period (2 to 10 s), magnitude (0.0254 to 0.0762 m/s), systempressure (0.14 to 0.41 MPa), and subcooling (5 to 55 C) in order to study theentrained droplet dynamics and heat transfer under constant and oscillatory flowconditions.This dissertation includes the analysis of forced oscillatory reflood experiments, which concentrate on the effects of flow (frequency, magnitude, and nominal flooding rate) and system parameters (pressure, subcooling, and bundle fouling) on heat transfer and entrained droplet dynamics. Major findings from the experimental work include: 1) decreasing the oscillation period decreases the peak cladding temperature and the steam temperatures, as well as enhances the liquid carryoverwhen compared with constant reflood experiments; 2) decreasing the system pres-sure enhances the effect of flow oscillations; and 3) the presence of bundle foulingimproves cooling and decreases the amount of liquid carryover. To the authorsknowledge, experiments with the parameters varied in this work, coupled with therod bundle geometry, have not been explored previously.This dissertation utilizes the unique dataset collected at the NRC/PSU RBHT to perform a stability analysis of oscillatory two-phase flows. The governing equations established for this flow incorporate Floquet and viscous-potential flow theories. From the analysis, it is found that the stability at the two-phase interface is highly dependent on the flow orientation and heat transfer to the system. Inaddition, a correlation is developed for the liquid carryover that uses parameters derived from the stability analysis to predict the carryover during oscillatory reflood. The correlation is the first of its kind to include the effects of a moving quench front on the liquid carryover. The carryover model is validated using NRC/PSU RBHT data, as well as other relevant rod bundle data, and the NRCs TRACE code.