Multiple-Choice Questions

Multiple-Choice Questions
This material is provided for the sole use of students in the 2017 Winter Semester course EP4P03 Nuclear Plant Systems and Operation. This material is not to be copied or shared in either electronic or paper form with anyone not registered in the above class.

1. On a CANDU 9 unit at normal full power operation, which one of the following components sinks (absorbs) 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? Their chemical properties are very different, their physical properties are similar and their nuclear properties are very different. Their chemical properties are essentially identical, their physical properties are very different and their nuclear properties are very different. Their chemical properties are essentially identical, their physical properties are similar and their nuclear properties are identical. Their chemical properties are essentially identical, their physical properties are similar and their nuclear properties are very different.

3. Steam is found in a superheated condition at which one of the following points in a typical CANDU plant: Inlet to the HP Turbine At the outlet of the Reheater Outlet of the LP Turbine in the Condenser In the Deaerator

4. The poison over-ride time available in a CANDU 9 reactor that has experienced a reactor trip from 100% full power is approximately : 2 hours 45 minutes 36 hours 5 minutes

5. Which one of the following statements is correct about CANDU fuel?
CANDU 9 fuel assemblies use 37 `pencils' to have a large heat transfer surface between fuel and the PHT coolant The fuel in the CANDU fuel bundle is made of uranium dioxide that contains 1.71% U235 Normally on power fuelling moves 12 fuel bundles at a time All fuel bundles in a CANDU reactor produce an equal amount of heat

6. After the loss of Class 4 power:
The Primary Heat Transport Pumps start to rotate in the reverse direction as flow reverses in the core. The Primary Heat Transport Pumps continue to run because they are supplied by alternate power supplies. The Primary Heat Transport Pumps stop immediately due to hydraulic inertia in the system. The Primary Heat Transport Pumps slow down over a period of a few minutes because large flywheels store energy to aid in prolonging the coast to a stop period

7. The electrical energy used by a CANDU plant to power the equipment inside the Station that is required to operate the plant is called the Station Service load. For a CANDU 9 nuclear power plant, the Station Service load is approximately : 75 MW 100 MW 55 MW 10 MW

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: Reactor Power will increase Reactor Power will decrease Turbine output will not change Turbine output will increase

9. Which of the following is NOT a function of the Moderator Purification System?
To maintain the purity of the heavy water so that the production of deuterium and oxygen through radiolysis is minimized To minimize the corrosion of system components by removing impurities and controlling the pD of the system To remove Gadolinium Nitrate that was injected when SDS2 fired To maintain a high isotopic concentration of D2O in the Moderator System

10. The garter springs that hold the pressure tubes from making contact with the calandria tubes are made of Inconel. The number typically installed in a channel is: One Two Three Four

1. Which one of the following is a function of control absorbers?
Driving into core on a SDS trip Partially dropping into core on a turbine trip Driving into core when AZL is low Driving into core following a power reduction to offset the Xenon transient (poison override)

2. A channel is fuelled normally on a Darlington reactor
2. A channel is fuelled normally on a Darlington reactor. What is the expected response of the regulating system? The average zone level increases and individual zone levels are changed to control the resultant flux tilt. The average zone level decreases and individual zone levels are changed to control the resultant flux tilt. The average zone level remains constant, but individual zone levels are changed to control the resultant flux tilt. Nothing, normal fueling requires no response from the regulating system.

3. Level in a liquid zone compartment is controlled by:
Adjusting water inflow to the compartment Adjusting water outflow from the compartment Adjusting He pressure in the zone control compartment Adjusting the temperature of the water

4. In Alternate (Reactor-Leading) mode of Overall Unit Control, the power generated by the Turbine-Generator in response to a change in reactor power is modified by: Changing the Steam Generator Pressure Setpoint Controlling the water level in the liquid zone controllers Adjusting the opening of the Governor Valves Changing the Steam Generator Level Setpoint

5. The height of water in each liquid zone-control compartment is measured by:
Measuring the opening of the inflow valve into the compartment Measuring the opening of the outflow valve from the compartment Calculating the difference between the openings of the in-flow and outflow valves Difference in the helium pressure above and below the water

1. Which one of the following statements correctly describes the characteristics of an Ion Chamber?
A larger self-powered neutron detector, located outside the reactor that is used during long outages when other instrumentation has gone off scale low. 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. 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. A small self-powered detector that produces Beta particle induced ionization under neutron irradiation, and is used for indication only at high power.

1. Which one of the following statements correctly describes the characteristics of an Ion Chamber?
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. Power Supply

2. Which one of the following statements correctly describes the characteristics and uses of self-powered in-core flux detectors? Self-powered in-core flux detectors are used to measure the total neutron flux in the range of 10-5%FP to 120%FP. Self-powered flux detectors work on the principle that neutron and gamma radiation eject from the emitter electrons which, after traveling across the insulator to the collector, create a voltage difference. 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. 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.

3. With respect to the use of neutronic and thermal power measurements in the reactor regulating system, which one of the following statements is true? Thermal power measurements cover the whole range (10-5 %FP to 100%FP) of normal reactor power control. Neutronic devices are too slow to be used exclusively. Thermal power measurements are used to provide spatial indication of power, neutronics are sensitive only to bulk power. Thermal power measurements are used to continuously calibrate neutronic measurements at power levels above 5%FP.

3. With respect to the use of neutronic and thermal power measurements in the reactor regulating system, which one of the following statements is true? Thermal power measurements cover the whole range (10-5 %FP to 100%FP) of normal reactor power control. Neutronic devices are too slow to be used exclusively. Thermal power measurements are used to provide spatial indication of power, neutronics are only sensitive to bulk power. Thermal power measurements are used to continuously calibrate neutronic measurements at power levels above 5%FP. (Gradual transfer from Ion Chambers at & below 5% to In-Core Detectors at & above 15%)

4. Which one of the following statements correctly describes the characteristics and uses of adjuster rods: The Adjuster rods provide a reserve of positive reactivity to override any xenon transient that may develop following a reactor trip or other large power level reductions. Adjuster rod auto out-drive is only initiated by RRS if the average zone level is below 15%. Adjuster rod auto in-drive is only initiated by RRS if average zone level is above 75%. If the operating point is within the normal range of control for the liquid zones, RRS will not initiate adjuster drive movement because it is good operating practice to leave rods partially in the core.

4. Which one of the following statements correctly describes the characteristics and uses of adjuster rods: Adjuster rod auto out-drive is only initiated by RRS if the average zone level is below 15%. Adjuster rod auto in-drive is only initiated by RRS if average zone level is above 75%. If the operating point is within the normal range of control for the liquid zones, RRS will not initiate adjuster drive movement because it is good operating practice to leave rods partially in the core.

5. Which one of the following statements correctly describes the characteristics and uses of control absorber rods: The control absorbers are dropped fully into the core when a Stepback of reactor power level is required. 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. Control Absorber auto in-drive is initiated by RRS whenever the average zone level is above 80%. Control Absorber auto out-drive is initiated by RRS whenever the average zone level is below 75%.

5. Which one of the following statements correctly describes the characteristics and uses of control absorber rods: Control Absorber auto in-drive is initiated by RRS whenever the average zone level is above 80%. Control Absorber auto out-drive is initiated by RRS whenever the average zone level is below 75%.

5. Which one of the following statements correctly describes the characteristics and uses of control absorber rods: The control absorbers are dropped fully into the core when a Stepback of reactor power level is required. 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. Control Absorber auto in-drive is initiated by RRS whenever the average zone level is above 80%. Control Absorber auto out-drive is initiated by RRS whenever the average zone level is below 75%.

Sim Ex 2.1 POWER MANEUVER IN “ALTERNATE” MODE: 100% to 50% Power Reduction and Return to Full Power
(a) Explain the changes in Average Zone Level between each operating state or column (8 marks):

1. 135Xe is called a Saturating Fission Product because:
It saturates the fuel and prevents the production of all other fission products. At the operating temperature of the fuel 135Xe has reached its saturation pressure. Its concentration does not accumulate without limit in a reactor operating at a constant power level. It reaches a concentration that is independent of the neutron flux in the reactor.

2. Xenon oscillations are a potential problem in CANDU-9 and similar sized reactors because:
Such large reactors are inherently unstable, particularly in seismically active regions. They can be set off by regional perturbations in the reactor, for example following the routine refuelling of a channel. The Reactor Regulating System is designed to control the overall power output of the reactor, and isn’t equipped to control regional variations. 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.

2. Xenon oscillations are a potential problem in CANDU-9 and similar sized reactors because:
They can be set off by regional perturbations in the reactor, for example following the routine refuelling of a channel.

3. After a reactor trip in the CANDU 9 reactor, which one of the following statements correctly describes the response of the Liquid Zone Control system: All compartments have their levels frozen at the level they were at when the reactor trip occurs so that they don't lower level and introduce positive reactivity to the reactor core. They respond to the signals of the Reactor Regulating System so as to maintain control over spatial flux distribution. They go to the maximum allowed level (95% for CANDU-9) and stay there until the trip is cleared and a request to raise power results in a negative power error. They go to the lowest permissible level (5% in CANDU-9) so as to help override the Xenon poison as it builds up following the reactor trip.

4. Which one of the following statements correctly describes Poison Prevent operation?
Isolating the moderator poison addition system from the moderator Allowing the reactor to poison out following a SDS trip because of insufficient decision and action time Allowing RRS to insert adjusters into core following a power reduction to offset the Xenon reactivity transient Maintaining reactor power high enough following a turbine trip such that a poison out will not occur

5. A reactor has been operating at 30% FP for a very long time
5. 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? The Xe-135 concentration will increase, go through a maximum, and over many hours return to its original value. The Xe-135 reactivity will become and remain more negative than initially. The Xe-135 reactivity will first become less negative, but will eventually tend to a value more negative than its original value. The Xe-135 will burn out more quickly and its concentration will quickly go to 0.

2. A pressurizer steam bleed valve fails open with a CANDU 9 unit operating at full power. Which one of the following is not an expected initial response? The bleed condenser pressure increases The main circuit pressure decreases The pressurizer level decreases. The bleed valves open further.

3. Overpressure protection for the Primary Heat Transport System is provided by:
PHT Bleed Valves that relieve into the Bleed Condenser PHT Liquid Relief Valves that relieve into the Bleed Condenser PHT Bleed Valves that relieve into the Pressurizer PHT Liquid Relief valves that relieve into the Pressurizer

4. The Pressurizer level setpoint is ramped up as reactor power (RP) increases. Which one of the following statements is correct? Increased setpoint accounts for boiling in the Reactor Outlet Headers as RP increases. Increased setpoint accounts for increased boiling in the Pressurizer as RP increases. Increased setpoint accommodates swell in the Main Circuit as RP increases. Increased setpoint allows for transfer of inventory to the Main Circuit as RP increases.

5. If the PHT is operating in `Normal Mode’ of control and a leak develops in the PHT pressure envelope: Pressurizer level will stay constant and D2O storage Tank level will fall Pressurizer level will fall first and then D2O Storage Tank level will begin to fall D2O Storage Tank level will fall first and then Pressurizer level will fall Pressurizer level will fall but D2O Storage Tank level will stay constant

1. In a steam generator at full power the light water at the top of the tube bundle is very wet steam. However steam exits the steam generator towards the turbine at almost 100% quality. Which one of the following statements correctly explains this increase in steam quality? The reheater in the steam generator above the tube bundle adds the remaining heat of vaporization to dry the wet steam. Cyclone separators and then steam scrubbers mechanically remove the liquid water from the wet steam and return the liquid water to the bottom of the steam generator via the downcomer annulus. The wet steam is passed through the pre-heater where the remaining heat of vaporization is added to dry the steam. Cyclone separators and then steam scrubbers mechanically remove the liquid water from the wet steam and this liquid water is discharged to the lake via the blowdown header.

1. In a steam generator at full power the light water at the top of the tube bundle is very wet steam. However steam exits the steam generator towards the turbine at almost 100% quality. Which one of the following statements correctly explains this increase in steam quality? Cyclone separators and then steam scrubbers mechanically remove the liquid water from the wet steam and return the liquid water to the bottom of the steam generator via the downcomer annulus.

2. Which of the following is true about steam generator level:
Level setpoint is ramped up from zero power to full power to accommodate the level increase due to swell. Level setpoint is ramped down from zero power to full power to accommodate the level decrease due to shrink. Level setpoint is ramped up from zero power to full power to minimize volumetric changes in the PHT during power changes. Level setpoint is ramped down from zero power to full power to minimize volumetric changes in the PHT during power changes.

2. Which of the following is true about steam generator level:
Level setpoint is ramped up from zero power to full power to accommodate the level increase due to swell.

3. The Steam Generator Level Control program at Darlington uses a 3-element control scheme at high power. Which one of the following answers correctly identifies the three elements? Steam generator pressure, level and feedwater flow. Steam generator pressure, level and steam flow. Steam generator pressure, feedwater flow and steam flow. Steam generator level, steam flow and feedwater flow.

3. The Steam Generator Level Control program at Darlington uses a 3-element control scheme at high power. Which one of the following answers correctly identifies the three elements? Steam generator level, steam flow and feedwater flow.

4. Which of the following statements is correct in SOLID Mode?
Feed and Bleed flows are regulated according to the difference between Pressurizer Level and Pressurizer Level Setpoint. For pressure control the parameter controlled is Pressurizer Pressure. For inventory control the setpoint is ROH Pressure. All inventory changes are via the Pressurizer and Bleed Condenser.

5. Which of the following statements correctly describes some of the steps in the movement of the feedwater towards the Steam Generators? From Condenser to LP and HP heaters, then to Boiler Feedpumps. From Deaerator to Boiler Feedpumps and to LP and HP heaters. From Condenser to Condensate Extraction Pumps to Boiler Feedpumps to Deaerator. From LP Heaters to Deaerator to Boiler Feedpumps to HP Heaters.

5. Which of the following statements correctly describes some of the steps in the movement of the feedwater towards the Steam Generators? From LP Heaters to Deaerator to Boiler Feedpumps to HP Heaters.

1. A loss of feedheating steam flow to the High Pressure Feedheaters occurs on a CANDU 9 unit operating in “Alternate” OUC mode at high power. Which one of the following best describes the impact on the thermodynamic cycle? Actual steam flow out of the steam generators will increase resulting in lower turbine/generator power (less MWe output) for the same reactor power. Feedwater temperature entering the SGs will increase resulting in less heating needed in the preheater and therefore more heat being used to boil the water. For the same reactor power more steam will be produced resulting in higher turbine power (more MWe output). Feedwater temperature entering the SGs will decrease resulting in more heating required of the preheater and less heat being used to boil the water. For the same reactor power less steam will be produced resulting in lower turbine power (less MWe output). The reduction in feedheating steam flow means less steam is directed to the turbine resulting in higher turbine/generator power (more MWe output) for the same reactor power.

1. A loss of feedheating steam flow to the High Pressure Feedheaters occurs on a CANDU 9 unit operating in “Alternate” OUC mode at high power. Which one of the following best describes the impact on the thermodynamic cycle?

1. A loss of feedheating steam flow to the High Pressure Feedheaters occurs on a CANDU 9 unit operating in “Alternate” OUC mode at high power. Which one of the following best describes the impact on the thermodynamic cycle? Actual steam flow out of the steam generators will increase resulting in lower turbine/generator power (less MWe output) for the same reactor power. Feedwater temperature entering the SGs will increase resulting in less heating needed in the preheater and therefore more heat being used to boil the water. For the same reactor power more steam will be produced resulting in higher turbine power (more MWe output). Feedwater temperature entering the SGs will decrease resulting in more heating required of the preheater and less heat being used to boil the water. For the same reactor power less steam will be produced resulting in lower turbine power (less MWe output). The reduction in feedheating steam flow means less steam is directed to the turbine resulting in higher turbine/generator power (more MWe output) for the same reactor power.

2. Steam is found in a superheated condition at which one of the following points in a typical CANDU plant: Inlet to the HP Turbine Outlet of the LP Turbine in the Condenser In the Deaerator At the outlet of the Reheater

2. Steam is found in a superheated condition at which one of the following points in a typical CANDU plant: At the outlet of the Reheater.

4. A CANDU 9 reactor is operating at full power, when a turbine generator trip occurs. Assuming the unit responds correctly, which of the following describes the expected response of the STEPBACK program and RRS? The Reactor Power alternate mode setpoint is automatically set to 60%FP by the STEPBACK program on a turbine generator trip; RRS then controls the liquid zone levels by raising the levels to reduce reactor power, and the Control Absorber (CA) rods are maintained at their present position following any STEPBACK program action. Reactor power is reduced by the action of the STEPBACK program dropping the CA rods fully into core, and RRS withdraws the CA rods and drain the Liquid Zone levels to restore power back to 60%FP. The CA rods are dropped into core as far as necessary until power is below 60%FP, and RRS controls Liquid Zone levels and withdraws the CA rods to control reactor power to a value determined by the lowest actual power plus the offset of the deviation limiter. The STEPBACK program rapidly reduces reactor power by dropping the CA rods partially into core by a timed opening of the clutch mechanism contacts. RRS then raises the average Liquid Zone level in accordance with the Reactivity Control Diagram.

5. After a loss of Class 4 power:
The Primary Heat Transport Pumps start to rotate in the reverse direction as flow reverses in the core The Primary Heat Transport Pumps continue to run because they are supplied by alternate power supplies Primary Heat Transport Pumps need to be restarted within 3 to 5 minutes or the reactor core will overheat The Primary Heat Transport Pumps slow down over a period of a few minutes because large flywheels store energy to aid in prolonging the coast to a stop period

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