Experimental and Numerical Studies of the Droplet Sizes and Velocities near the Quench Front for Transient Reflood Conditions
Open Access
- Author:
- Garrett, Grant Robert
- Graduate Program:
- Nuclear Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 10, 2021
- Committee Members:
- Justin Watson, Major Field Member
Robert Kunz, Outside Field Member
Fan-Bill Cheung, Chair & Dissertation Advisor
Elia Merzari, Outside Unit Member
Stphen Bajorek, Special Member
Asok Ray, Major Field Member
Arthur Thompson Motta, Program Head/Chair - Keywords:
- Thermal Hydraulics
Core Reflood
TRACE
Nuclear Reactor Safety Analysis
Entrained Droplet Size Measurements
Entrained Droplet Velocity Measurements
Two-Phase Thermal Non-Equilibrium
Post-CHF Flow - Abstract:
- This dissertation presents experimental measurements for droplet sizes and velocities near the quench front for forced bundle reflood flow and corresponding analyses of this unique data. This dissertation also includes numerical studies investigating code performance for core reflood phenomena. In a hypothetical large break loss of coolant accident (LOCA), associated with a break on one of the cold legs, the emergency core cooling system (ECCS) must provide sufficient coolant to the core to remove decay heat and prevent the cladding and/or fuel from exceeding their peak temperature limits. During core reflood, liquid is entrained and impacts the local heat transfer and temperature of the cladding and fuel. The entrainment fraction and droplet size become more significant for post-CHF flows as no liquid is directly in contact with any fuel rods. As entrainment increases, the heat transfer from the cladding to the coolant is enhanced downstream of the quench front, but this increased entrainment delays quenching because the liquid that is entrained out of the vessel decreases the total liquid inventory available to quench the fuel rods. Additionally, the sizes of the droplets contributes to the heat transfer by influencing the interfacial surface area. Also, the relative velocity between the liquid droplets and local vapor phase directly impact the interfacial heat and mass transfer in post-CHF flow regimes. Most droplet experiments to date were conducted with a single heated tube or adiabatic air-water tube. Additionally, previous experiments that were performed in a rod bundle were limited by the measurement capabilities. At the NRC/PSU Rod Bundle Heat Transfer (RBHT) Test Facility, an electrically heated 7x7, 3.66 m rod bundle array has the capability to perform both constant and oscillatory forced flooding rate experiments. The facility is heavily instrumented, equipped with seven spacer grids and optical windows with which to observe the two-phase droplet and heat transfer phenomena during core reflood. Current quench front droplet phenomena models are theoretical due to the inability to measure droplet sizes and velocities at or very close to the quench front. The successful measurement of droplet sizes and velocities near the quench front and numerical studies presented in this dissertation should be very valuable to the engineering community. This dissertation includes the choice of appropriate experimental conditions for the NRC/PSU RBHT Test Facility to measure droplet sizes and velocities at and within a few centimeters of the quench front, along with performing said experiments. To the author's knowledge, this phenomenon has never been experimentally measured. Once unique RBHT data is collected, statistical analysis is performed on the unique data. This dissertation also includes numerical studies that compare thermal hydraulic code predicted results to measured data from RBHT experiments. Results of these numerical studies suggest that the quench front droplet models should be re-evaluated.