Review Questions
Chapter 4
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students in the 2017 Winter Semester course
EP4P03 Nuclear Plant Systems and Operation.
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True or False
4A.1-a
The CANDU 9 Primary Heat Transport
System Main Circuit layout resembles two
interconnected figure of 8 loops. From the ROH the
coolant flow is to the Steam Generator, from there
the coolant flows to the inlet of the circulating
pumps, and after the pumps it flows to the Reactor
Inlet Header, and finally via a feeder pipe to a
pressure tube.
True
4A.1-a
The CANDU 9 Primary Heat Transport
System Main Circuit layout resembles two
interconnected figure of 8 loops. From the ROH the
coolant flow is to the Steam Generator, from there
the coolant flows to the inlet of the circulating
pumps, and after the pumps it flows to the Reactor
Inlet Header, and finally via a feeder pipe to a
pressure tube.
True or False
4A.1-b
The CANDU 9 Primary Heat Transport
System Main Circuit layout resembles two
interconnected figure of 8 loops. From the ROH the
coolant flow is to the Steam Generator where it
mixes with the light water of the feedwater system,
from there the coolant flows to the inlet of the
circulating pumps, and after the pumps it flows to
the Reactor Inlet Header, and finally via a feeder pipe
to a pressure tube.
False; a correct form of the statement is:
4A.1-b
The heavy water coolant of the primary
circuit and the light water of the feedwater system
are kept separate in the steam generators, they do
not “mix”, only the heat is transferred across the
walls of the tubes in the steam generator.
True or False
4A.2-a
The assignment of pressure tubes to
either of the two loops is random to ensure
maximum redundancy and to allow flexibility in
making the connections between pressure tubes and
feeder pipes.
False; a correct form of the statement is:
4A.2-a
The assignment of the pressure tubes to
one of the two loops is not random, the fuel
channels are connected to the respective outlet
headers so that each loop serves half of the reactor,
on either side of a vertical center-plane.
True or False
4A.2-b
The PHT Main Circuit is designed to
provide cooling of the reactor fuel at all times during
reactor operation and provide for the heavy water
coolant to remove decay heat when the reactor is
shut down.
True
4A.2-b
The PHT Main Circuit is designed to
provide cooling of the reactor fuel at all times during
reactor operation and provide for the heavy water
coolant to remove decay heat when the reactor is
shut down.
True or False
4A.3-a
When the Main Circuit pumps are
turned ON, the flow of heavy water is from the
Reactor Outlet Headers through the Shutdown
Cooling Pumps and Heat Exchangers, to the Reactor
Inlet Headers.
False; a correct form of the statement is:
4A.3-a When the Main Circuit
Pumps are turned ON, the flow of
heavy water is from the Reactor
Inlet Headers through the
Shutdown Cooling Pumps and Heat
Exchangers, to the reactor Outlet
Headers. This is why the Shutdown
Cooling Pumps must not be ON as
long as the Main Circuit Pumps are
ON: the much stronger Main Circuit
Pumps would burn out the
Shutdown Cooling Pump motors.
True or False
4A.3-b
The Shutdown Cooling System is used to
cool the heat transport heavy water below the 177C
limit possible with the steam generators, and has the
capability to indefinitely remove reactor decay heat
following the shutdown of the reactor.
True
4A.3-b
The Shutdown Cooling System is used to
cool the heat transport heavy water below the 177C
limit possible with the steam generators, and has the
capability to indefinitely remove reactor decay heat
following the shutdown of the reactor.
True or False
4A.4-a
The main circuit pressure must be
maintained so that there is adequate saturation
margin in the reactor outlet headers, and that the
required net positive suction head for the circulation
pumps is provided.
True
4A.4-a
The main circuit pressure must be
maintained so that there is adequate saturation
margin in the reactor outlet headers, and that the
required net positive suction head for the circulation
pumps is provided.
True or False
4A.4-b
The Pressurizer is designed to
compensate for the pressure drop that occurs as the
heavy water coolant flows around the Main Circuit.
False; a correct form of the statement is:
4A.4-b
The Pressurizer is designed to maintain
the pressure in the Main Circuit. The Main Circulating
Pumps are designed to compensate for the pressure
drop that occurs as the heavy water coolant flows
around the Main circuit.
True or False
4B.1-a
Under normal operating conditions the
CANDU 9 Heat Transport System Main Circuit ROH
Pressure setpoint is varied as a linear function of
Reactor Power.
False; a correct form of the statement is:
4B.1-a
Under normal operating conditions the
CANDU 9 Heat Transport System Main Circuit ROH
Pressure setpoint is held constant at 10 MPa.
True or False
4B.1-b
The pressure of the Main Circuit must
be maintained at a sufficiently high value so that only
the design amount of boiling takes place in the fuel
channels, and except under specific shutdown
conditions, the inventory of heavy water must keep
the Main Circuit completely filled.
True
4B.1-b
The pressure of the Main Circuit must
be maintained at a sufficiently high value so that only
the design amount of boiling takes place in the fuel
channels, and except under specific shutdown
conditions, the inventory of heavy water must keep
the Main Circuit completely filled.
True or False
4B.2-a
Under normal operating conditions
there is a free flow of heavy water between the
Pressurizer and the Main Circuit that equalizes any
pressure differences between the Main Circuit and
the Pressurizer.
True
4B.2-a
Under normal operating conditions
there is a free flow of heavy water between the
Pressurizer and the Main Circuit that equalizes any
pressure differences between the Main Circuit and
the Pressurizer.
True or False
4B.2-b
“Normal Mode” of unit control requires
“Normal Mode” of Heat Transport Pressure Control.
False; a correct form of the statement is:
4B.2-b
Under “at power normal operating
conditions” OPG’s CANDU units are operated in
“Alternate” mode Overall Unit Control, while the
Heat Transport Pressure Control system is in “Normal
Mode”.
True or False
4B.3-a
Under normal operating conditions the
pressure in the Pressurizer is controlled to the
Pressurizer Pressure Setpoint.
False; a correct form of the statement is:
4B.3-a
Under normal operating conditions the
pressure in the Pressurizer is controlled to the
Reactor Outlet Header Pressure setpoint. Only under
certain shutdown conditions, typically during Heat
Transport System warm-up or cool-down, when the
Pressurizer is isolated from the Main Circuit (i.e.
Main Circuit in Solid Mode Pressure Control) is the
pressure of the Pressurizer controlled to the
Pressurizer Pressure Setpoint.
True or False
4B.3-b
The Pressurizer’s liquid and steam are
kept at saturation, and at a pressure that keeps the
reactor outlet header at its setpoint (10 MPa for
CANDU-9 operating in the “at power” range).
True
4B.3-b
The Pressurizer’s liquid and steam are
kept at saturation, and at a pressure that keeps the
reactor outlet header at its setpoint (10 MPa for
CANDU-9 operating in the “at power” range).
True or False
4B.4-a
The level setpoint in the Pressurizer is
increased automatically so that all the swell resulting
from power increases is stored in the Pressurizer. The
opposite takes place on a reactor power decrease.
The level in the Pressurizer, and therefore the Heat
Transport System inventory, is normally controlled
via the main circuit feed and bleed valves.
True
4B.4-a
The level setpoint in the Pressurizer is
increased automatically so that all the swell resulting
from power increases is stored in the Pressurizer. The
opposite takes place on a reactor power decrease.
The level in the Pressurizer, and therefore the Heat
Transport System inventory, is normally controlled
via the main circuit feed and bleed valves.
True or False
4B.4-b
A Pressurizer level above the setpoint is
an indication of excess heavy water inventory in the
Main Loop, so some bleed is taken into the Main
Circuit from the D2O Storage Tank.
False; a correct form of the statement is:
4B.4-b
A Pressurizer level above the setpoint is
an indication of excess heavy water inventory in the
Main Loop, so some bleed is taken from the Main
Circuit into the D2O Storage Tank.
True or False
4B.5-a
The Overpressure relief valve of the
Bleed Condenser is used to release non-condensable
gases, mostly Nitrogen, which can accumulate in the
Heat Transport coolant.
False; a correct form of the statement is:
4B.5-a
The Overpressure relief Valve of the
Bleed Condenser is used to relieve D2O steam and
liquid from the Bleed Condenser in case of excessive
pressure build-up. Non-condensable gases are
released by opening the degassing valve.
True or False
4B.5-b
The principal purpose of the Bleed
Condenser is to reduce the pressure and temperature
of the heavy water coolant from the Main Circuit and
of the heavy water steam from the Pressurizer. The
Bleed Condenser at normal operating conditions
contains heavy water and steam at saturation
conditions, at a pressure around 1.7 MPa.
True
4B.5-b
The principal purpose of the Bleed
Condenser is to reduce the pressure and temperature
of the heavy water coolant from the Main Circuit and
of the heavy water steam from the Pressurizer. The
Bleed Condenser at normal operating conditions
contains heavy water and steam at saturation
conditions, at a pressure around 1.7 MPa.
True or False
4B.6-a
All CANDU nuclear steam supply systems
use a Pressurizer to control the pressure of the Main
Heat Transport Circuit.
False; a correct form of the statement is:
4B.6-a
While all the operating CANDU 6 and 9
units use a Pressurizer to control the pressure in the
Main Heat Transport Circuit under normal operating
conditions, some of the early CANDU units, such as
the ones at Pickering, use a feed and bleed system for
pressure control (known as “SOLID” mode for CANDU
6 and 9 units).
True or False
4B.6-b
The term “Solid Mode” is used for a feed
and bleed heat transport pressure control system, as
it relies on the tensile strength of the vessels and
piping of the main circuit, and on the very small
compressibility of water.
True
4B.6-b
The term “Solid Mode” is used for a feed
and bleed heat transport pressure control system, as
it relies on the tensile strength of the vessels and
piping of the main circuit, and on the very small
compressibility of water.
True or False
4B.7-a
In “normal mode” the Inventory of heavy
water in the Heat Transport Main Circuit is controlled
by the Pressurizer Level Control system. It is achieved
by feed and bleed, and is designed to compensate for
volume changes as a function of coolant temperature.
True
4B.7-a
In “normal mode” the Inventory of heavy
water in the Heat Transport Main Circuit is controlled
by the Pressurizer Level Control system. It is achieved
by feed and bleed, and is designed to compensate for
volume changes as a function of coolant temperature.
True or False
4B.7-b
The Feed and Bleed system is used for
inventory control of the Primary Heat Transport
System in both “normal mode” and “solid mode”, and
in both modes inventory control is independent of
pressure control.
False; a correct form of the statement is:
4B.7-b
In “solid mode” both inventory and
pressure control of the Primary Heat Transport System
are achieved using the feed and bleed system.
True or False
4B.8-a
All vessels that are under pressure must,
by law, have the appropriate form of over-pressure
protection. To prevent main heat transport high
pressure transients exceeding system limits the Liquid
Relief valves will open to the bleed condenser.
True
4B.8-a
All vessels that are under pressure must,
by law, have the appropriate form of over-pressure
protection. To prevent main heat transport high
pressure transients exceeding system limits the Liquid
Relief valves will open to the bleed condenser.
True or False
4B.8-b
The purification circuit is protected
against high pressures and temperatures by closing
the by-pass valve and opening the inlet and outlet
valves to the Purification System.
False; a correct form of the statement is:
4B.8-b
The
Purification Circuit is
protected against
high pressure and
temperature by
opening the bypass
valve and closing
the inlet and outlet
valves to the
Purification System.