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http://hdl.handle.net/11375/20531
Title: | Analysis of Flow Reversal under Two-Phase Natural Circulation in CANDU9 during Small Loss of Coolant Accident with Loss of Class IV Power |
Authors: | Yu, Changrui |
Advisor: | Luxat, John |
Department: | Engineering Physics |
Keywords: | flow reversal;natural circulation |
Publication Date: | 2016 |
Abstract: | A thermal hydraulic analysis has been conducted to investigate the conditions leading to the channel flow reversal and the subsequent effects that may have on the Primary Heat Transfer System(PHTS) thermohydraulic parameters during the natural circulation under the specific accident scenarios for a generic CANDU 900 MW plant model similar to Darlington NGS. The assumed initiating events are the combination of a small Loss Of Coolant Accident (LOCA) with a loss of Class IV power, as well as the unavailability of Emergency Coolant Injection (ECI) system. No makeup inventory is taken into account in this study, and there is no fuel sheath temperature excursion or fuel centerline melting, i.e., the integrity of fuel is always maintained. A one-dimensional quasi-steady state Homogeneous Equilibrium Model(HEM) has been constructed for the study. A specific node-link structure is adopted to represent the primary heat transfer loop: The whole loop and different components in HTS are represented by a series of nodes that have quasi-static thermal hydraulic characteristics such as pressure and enthalpy, etc. Dynamic characteristics are delivered by the links between nodes, e.g., flow rate and pressure drop. The channel powers (decay heat), the secondary side pressure and the pressure at Reactor Inlet Header(RIH) are chosen as boundary conditions to describe the assumed initiating incidents for the iii model. With ongoing loss of inventory and system depressurization, vapor lock occurs in Steam Generator(SG), and it increases the pressure drop from Reactor Outlet Header(ROH) to RIH across SG and forms an increasingly negative RIH-to-ROH pressure differential. Flow reversal occurs in the channel due to the counter force balance between negative RIH-to-ROH pressure difference and the driving force derived from the density difference between the hot and cold legs. It is found that channels in row A have the highest reversal preference, then followed by the channels in row B, and in that order subsequently. Row A reverses when inventory decreases to about 79.5% of initial value, with following boundary conditions: decay heat is 1.5% of Full Power(FP) and secondary side pressure is 5.070 MPa. In addition, it is found that the decrease in channel power accelerates the depressurization process and brings forward the occurrence of flow reversal in fuel channels. |
URI: | http://hdl.handle.net/11375/20531 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Yu_Changrui_201609_MASc.pdf | 5.39 MB | Adobe PDF | View/Open |
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