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. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20531 |
| Date | January 2016 |
| Creators | Yu, Changrui |
| Contributors | Luxat, John, Engineering Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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