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McMaster University
Nuclear Power-Plant Systems and Operations - EP4P03
B. Rouben
2017 Jan-Apr.
Identify if the statement is true or false
Adjuster rods are located in the reactor core for the purpose of flattening
the neutron flux and to provide positive reactivity when needed.
If a spurious injection of ECI were to occur, the ion exchange columns in
the Moderator purification system would be used to return the isotopic
purity of the Moderator D2O to 99.96% or higher.
Since the adjuster rods absorb neutrons, a reactor that has adjuster rods
out of the core will be at a higher power level than a reactor with all the
adjuster rods inserted.
For CANDU reactors liquid poison in the Moderator is used to provide
negative reactivity beyond the range of the liquid zones and solid neutron
absorbing reactivity mechanisms.
Changes in the temperature or flow of the condenser cooling water have
no effect on the electrical power output of a nuclear generating station.
All the control logic required for reactor control is programmed in computer
software.
The heat created in the Moderator of a CANDU reactor and rejected to the
cooling water (and ultimately the lake or river used for cooling the plant)
represents the largest source of thermal loss from the power plant.
The average residency time of a fuel bundle in the reactor is approximately
one year.
The Cover Gas System above the free moderator surface prevents
moisture in the air down-grading the heavy water concentration.
The Pressurizer is designed to compensate for the pressure drop that
occurs as the heavy water coolant flows around the Main Circuit.
The two full capability CANDU reactor shutdown systems are functionally
and physically independent, but are actuated by the same protection
system.
The Deaerator in a CANDU plant is used to remove Oxygen to help reduce
corrosion and is located high in the plant to provide a good suction
condition for the Steam Generator Feed Pumps.
At the outlet of the HP Turbine the moisture content of the steam is more
than 15%.
The moisture extracted by the Moisture Separator flows to the main
condenser.
For a Bulk Electric Power System that operates at 50 Hz, a three phase
four pole generator will rotate at 1500 rpm.
Heating of the feedwater system can be accomplished throughout the “at
power” operating range (reactor power above 5%, HT system at operating
temperatures and pressure) by the use of extraction steam.
Both the “Unit Service Transformer” and the “Station Service Transformer”
convert high voltage (230kV or 500 kV) to supply the class IV buses (4 –
14 kV).
The higher the “class” of a power supply at a CANDU station the lower its
reliability.
Class III power supplies loads must be available 100% of the time in order
to ensure the safe removal of heat from the fuel.
Class II supplies uninterruptible AC power and Class I supplies
uninterruptible DC power at a typical CANDU 9 unit.
Boron or Gadolinium is added to the Primary Heat Transport System of a
CANDU reactor for reactivity control when there is insufficient Xenon
concentration in the core following a shutdown of one week duration.
In a CANDU reactor operating in steady state at high power, the higher
concentration of Xe-135 in low-power regions of the core creates a natural
flux-flattening effect.
If a CANDU reactor were allowed to operate in steady state at 200% FP,
the I-135 and Xe-135 concentrations would be double the values at steady
state FP.
At any given power level in steady state, the rate of loss of I-135 and of
Xe-135 is proportional to the I-135 and Xe-135 concentrations
respectively.
Although the Shutdown Rods are withdrawn under the control of the
Reactor Regulating System, their reactor shutdown function remains
independent of the Reactor Regulating System.
The spatial distribution of the flux can be altered both by the liquid zone
control system and by the movement of adjuster rods.
The Reactor Regulating System can raise or lower the water level in each
zone by different relative amounts for the purpose of spatial power control.
The only difference between Adjuster Rods and Mechanical Control
Absorber rods is that the former are normally in the core and the latter are
normally out of the core.
During the initial part of dropping or driving a solid neutron absorber from
its parked position outside the reactor, there will be no significant change
in core reactivity.
The Reactor Regulating System can raise or lower the water level in each
zone only by changing the opening of the compartment inlet valve.
Gadolinium is a strong neutron absorber, and can be either slowly added
to the Moderator for the purpose of reactivity control, or rapidly injected
into the Moderator to shut down the reactor.
At the completion of the “hold power” mode or of the “setback” mode the
Reactor Regulating System is placed into “alternate” mode.
Reactor Setback is the forced reduction of the reactor power setpoint at
specified rates and endpoints, the values of which depend on the condition
that initiated the setback.
The End Shields are filled with steel balls to allow access to the reactor
face during power operations.
The leakage flux that reaches an ion chamber is proportional to the
average flux inside the reactor.
The Log N Rate signal from the ion chambers is used throughout the
power range of operations.
Measuring the coolant flow and temperature change across the CANDU
reactor core will give an accurate but delayed value for the heat
transferred from the fuel to the coolant at all power levels.
All fuel bundles in a CANDU reactor produce an equal amount of heat.
The flow of reactor coolant in adjacent pressure tubes is in opposite
directions, resulting in bi-directional coolant flow through the core.
Refuelling is bi-directional, with new fuel pushed into a channel in the
direction opposite to the flow of coolant.
The CANDU-9 simulator does not model spatial changes in flux.
Identify the correct statement
1.
On a CANDU 9 unit at normal full power operation, which one of the following components
sinks the greatest proportion of reactor thermal power:
A. Turbine Generator (exclusive of the condensers)
B. Moderator Heat Exchangers
C. Condensers
D. End Shield Cooling Heat Exchangers.
2.
When comparing properties of heavy water and light water, which one of the following
statements is true?
A. Their chemical properties are very different, their physical properties are similar and
their nuclear properties are very different.
B. Their chemical properties are essentially identical, their physical properties are very
different and their nuclear properties are very different.
C. Their chemical properties are essentially identical, their physical properties are similar
and their nuclear properties are identical.
D. Their chemical properties are essentially identical, their physical properties are similar
and their nuclear properties are very different.
3.
Which of the following is NOT a function of the Moderator Purification System?
A. To maintain the purity of the heavy water so that the production of deuterium and
oxygen through radiolysis is minimized
B. To minimize the corrosion of system components by removing impurities and
controlling the pD of the system
C. To remove Gadolinium Nitrate that was injected when SDS2 fired
D. To maintain a high isotopic concentration of D2O in the Moderator System
4.
The poison over-ride time available in a CANDU 9 reactor that has experienced a reactor
trip from 100% full power is approximately:
A. 2 hours
B. 45 minutes
C. 36 hours
D. 5 minutes
5.
Which one of the following statements is correct about CANDU fuel?
A. CANDU 9 fuel assemblies use 37 `pencils' to have a large heat transfer surface between
fuel and the PHT coolant
B. The fuel in the CANDU fuel bundle is made of uranium dioxide that contains 1.71% U235
C. Normally on power fuelling moves 12 fuel bundles at a time
D. All fuel bundles in a CANDU reactor produce an equal amount of heat
6.
Which statement is the best description of typical refuelling operations for a CANDU 9
reactor?
E. Replacing any number of fuel bundles for a given channel
F. Shutting down the unit in order to replace any failed fuel bundles
G. Fuel is normally changed during full power operations, using two fuelling machines
connected to the ends of the fuel channel being refuelled
H. Fuel bundles, typically eight at a time, can be loaded manually into the reactor during
shutdown.
7.
Which of the following statements is correct with reference to the use of heavy water
moderator CANDU reactors:
E. The heavy water used in the moderator system is shared with the heavy water used in
the heat transport system
F. The temperature of the moderator is controlled by the use of circulating pumps and the
flow of service water through the heat exchangers
G. The concentration of liquid poison in the moderator is under the control of the Reactor
Regulating System
H. The moderator purification system can only improve the concentration of D2O, and
cannot change the pD of the moderator
8.
If a CANDU is operating in `NORMAL’ mode of Overall Unit Control, and the grid load is lost,
which of the following is correct:
E. Reactor Power will increase
F. Reactor Power will decrease
G. Turbine output will not change
H. Turbine output will increase
9.
With reference to the purpose of the Overall Unit Control System, which of the following
statements is correct:
E. The purpose of overall unit control is to satisfy the electricity needs of the electrical power
system
F. Fluctuations in heat transport temperature and pressure will result in changes to the electrical
output of the generator
G. Steam Generator Pressure error reflects an imbalance between the power produced by
the reactor and that converted by the turbine.
H. The CANDU 9 overall unit control system must be able to respond to frequency changes of the
bulk electric system
10.
Xe-135 is called a Saturating Fission Product because:
A. It saturates the fuel and prevents the production of all other fission products.
B. At the operating temperature of the fuel 135Xe has reached its saturation pressure.
C. Its concentration does not accumulate without limit in a reactor operating at a constant
power level.
D. It reaches a concentration that is independent of the neutron flux in the reactor.
11. A reactor has been operating at 30% FP for a very long time. Power is then raised to 100% FP and
remains at that value. Which one of the following statements correctly describes the sequence of
events?
A. The Xe-135 concentration will increase, go through a maximum, and over many hours return to
its original value.
B. The Xe-135 reactivity will become and remain more negative than initially.
C. The Xe-135 reactivity will first become less negative, but will eventually trend to a value more
negative than its original value.
D. The Xe-135 will burn out more quickly and its concentration will quickly go to 0.
12. Which one of the following statements correctly describes the uses of Adjuster Rods?
A. The Adjuster Rods provide a reserve of positive reactivity that may be sufficient to override
Xenon transients that develop following a reactor trip or other large power level reductions.
B. Adjuster Rod auto out-drive is only initiated by RRS if the average zone level is below 15%.
C. Adjuster Rod auto in-drive is only initiated by RRS if average zone level is above 75%.
D. If the operating point is within the normal range of control for the liquid zones, RRS will not
initiate Adjuster Rod drive movement, and nor should the operator, because it is good operating
practice to leave rods partially in the core.
13. Which one of the following statements correctly describes the characteristics and uses of
Mechanical Control Absorber Rods?
A. The Control Absorber rods are dropped fully into the core every time a SETBACK of reactor
power level is required.
B. Control Absorber rods are normally located completely outside the core. They are driven into
the core to provide negative reactivity when the liquid zones have used up their range of
control.
C. Control Absorber auto in-drive is initiated by RRS whenever the average zone level is above 80%.
D. Control Absorber auto out-drive is initiated by RRS whenever the average zone level is below 75%.
14. If refuelling cannot be performed for a week or more in the CANDU 9:
A.
B.
C.
D.
Adjuster Rods will be withdrawn to keep the reactor at full power.
Adjuster Rods may be withdrawn but the reactor power will be derated.
The reactor will definitely go into shutdown
Reactor power can be increased to burn out some Xe-135 to provide positive reactivity.
15. Xenon oscillations are a potential problem in CANDU-9 and similar sized reactors because:
A. Such large reactors are inherently unstable, particularly in seismically active regions.
B. They can be set off by regional perturbations in the reactor, for example following the
routine refuelling of a channel.
C. The Reactor Regulating System is designed to control the overall power output of the
reactor, and isn’t equipped to control regional variations.
D. Such oscillations can slow down the recovery from a reactor trip, for example if the ion
chamber signals are observed to be fluctuating at power levels below 5%FP.
16. Which of the following statements is the correct one?
A.
B.
C.
D.
Xe-135 changes provide positive feedback following a power increase and negative feedback
following a power decrease
Xe-135 changes provide negative feedback following a power increase and positive feedback
following a power decrease
Xe-135 changes provide positive feedback following any power change
Xe-135 changes provide negative feedback following any power change.
17. Which one of the following statements correctly describes the characteristics of an Ion Chamber?
E. A larger self-powered neutron detector, located outside the reactor that is used during long
outages when other instrumentation has gone off scale low.
F. A detector with an external power supply and a Boron coating inside that produces Alpha
particle induced ionization under neutron irradiation. It is used for indication and control from
very low to high power.
G. A neutron detector with a high voltage anode, good spatial control characteristics, and is
normally located above the reactor to allow access for maintenance and testing.
H. A small self-powered detector that produces Beta particle induced ionization under neutron
irradiation, and is used for indication only at high power.
18. Which one of the following statements correctly describes the characteristics and uses of selfpowered in-core flux detectors:
A. Self-powered in-core flux detectors are used to measure the total neutron flux in the range of
10-5%FP to 120%FP.
B. Self-powered flux detectors work on the principle that neutron and gamma radiation eject
electrons from the emitter, and these electrons travel across the insulator to the collector,
thereby creating a voltage difference.
C. Most flux detectors over-respond to neutrons and to gamma rays, resulting in not enough
prompt response, and too much delayed response as reactor power level changes.
D. The main advantages of the in-core flux detectors are that they give an immediate and linear
response to a change in flux and are the basis of reactor power control from 50%FP to 120%FP.
19. With respect to the use of neutronic and thermal power measurements in the reactor regulating
system, which one of the following statements is true?
A. Thermal power measurements cover the whole range (10-5 %FP to 100%FP) of normal reactor
power control.
B. Neutronic devices are too slow to be used exclusively.
C. Thermal power measurements are used to provide spatial indication of power, neutronics are
only sensitive to bulk power.
D. Thermal power measurements are used to continuously calibrate neutronic measurements at
power levels above 5%FP.
Section 3.Provide short answers to the following questions:
1.
What are the four main methods for measuring the energy generated by a CANDU nuclear
reactor, and indicate for each whether it measures neutron flux or thermal power, and if
the measuring takes place inside or outside the reactor?
2.
A CANDU 9 unit has operated at 100% FP for several weeks when the operator is asked to reduce
station output to 80% FP. Over the next several hours, what adjustments will the Reactor
Regulating System need to make in order to maintain unit output at 80%FP?
3. What are the main parameters that the Unit Power Regulator (UPR) program (i) monitors,
(ii) computes, (iii) controls, and (iv) what is/are the device(s) that respond(s) to the control
signal?
4. What are the main parameters that the Reactor Regulating System (RRS) program (i)
monitors, (ii) computes, (iii) controls, and (iv) what is/are the device(s) that respond(s) to
the control signal?
5. What are the main parameters that the Heat Transport Pressure Control (HTPC) program,
operating with the Pressurizer connected to the main loop, (i) monitors, (ii) computes, (iii)
controls, and (iv) what is/are the device(s) that respond(s) to the control signal?
6.
What are the main parameters that the Steam Generator Pressure Control (SGPC) program
(i) monitors, (ii) computes, (iii) controls, and (iv) what is/are the device(s) that respond(s) to
the control signal?
7.
What are the main parameters that the Steam Generator Level Control (SGLC) program (i)
monitors, (ii) computes, (iii) controls, and (iv) what is/are the device(s) that respond(s) to
the control signal?