Which one of the following conditions describes a reactor that is exactly critical?
A. Keff = 0; delta-K/K = 0
B. Keff = 0; delta-K/K = 1
C. Keff = 1; delta-K/K = 0
D. Keff = 1; delta-K/K = 1
ANSWER: C.
Comment: The question is technically incorrect because it is not necessary to qualify the condition of criticality as "exact." Criticality is a unique condition, in and of itself.
QID: P45 (TOPIC: 192002 KNOWLEDGE: K1.08 [2.6/2.6])
The ratio of the number of neutrons in one generation to the number of neutrons in the previous generation is the:
A. effective multiplication factor.
B. fast fission factor.
C. neutron nonleakage factor.
D. neutron reproduction factor.
ANSWER: A.
Comment: The question is technically incorrect because the "number of neutrons" in any generation is continually diminishing as the life cycle is traversed. In defining keff as a ratio of neutrons in successive generations, it is always necessary to specifically identify the point in the life cycle at which the ratio is taken.
QID: P646 (B1848) (TOPIC: 192002 KNOWLEDGE: K1.09 [2.5/2.7])
Select the equation that defines K-excess (excess reactivity).
A. Keff + 1
B. Keff - 1
C. Keff(1-SDM)
D. 1/(1-Keff)
ANSWER: B.
Comment: This question is technically incorrect because (Keff - 1) does not define K-excess. (Keff - 1) defines delta-K, which can be used to determine the departure from criticality of any off-critical condition. K-excess is a hypothetical reactor condition with all control rods fully withdrawn. (Keff - 1) can be used to calculate the supercritical delta-K for this condition.
QID: P1246 (B2048) (TOPIC: 192002 KNOWLEDGE: K1.09 [2.5/2.7])
Which one of the following is a reason for installing excess reactivity (kexcess) in the core?
A. To compensate for burnout of Xe-135 and Sm-149 during power changes
B. To ensure reactor coolant boron concentration is low enough to ensure a negative moderator coefficient
C. To compensate for the negative reactivity added by the power defect during a power increase
D. To compensate for the conversion of U-238 to Pu-239 over core life
ANSWER: C.
Comment: The question is technically incorrect because the power defect does not "add reactivity." Reactivity is a physical property of the core ... a measure of the nuclear state of one particular reactor condition, in terms of its deviation from criticality. An existing reactivity condition may be altered, or changed, but not by adding "reactivity." In addition, adding "negative" anything is usually considered to be removal or subtraction. As an analogy, an existing core temperature may be altered, or changed, but not by adding "temperature."
The difference between two nuclear states, as in this question, is:
|
and on rearranging terms:
 |
Notice that in moving to a new reactivity condition, rho2, reactivity change, delta-rho, is added to the initial reactivity, rho1. Or, conversely, notice that reactivity, rho, is definitely not added to the initial reactivity. Although use of terminology to indicate reactivity change is preferred, to say that an "increment" of reactivity is added is certainly better than saying reactivity is added.
QID: P127 (TOPIC: 192002 KNOWLEDGE: K1.10 [3.2/3.6])
Shutdown margin is the actual amount of reactivity:
A. inserted by burnable poisons at beginning of life.
B. due to dissolved boron in the reactor coolant system.
C. by which the reactor is subcritical.
D. which would be inserted by shutdown bank rods.
ANSWER: C.
Comment: The question is technically incorrect because shutdown margin is defined for a very specific set of conditions.
QID: P2347 (B2348) (TOPIC: 192002 KNOWLEDGE: K1.10 [3.2/3.6])
Which one of the following core changes will decrease shutdown margin? Assume no operator actions.
A. Depletion of fuel during reactor operation
B. Depletion of burnable poisons during reactor operation
C. Buildup of Sm-149 following a reactor power transient
D. Buildup of Xe-135 following a reactor power transient
ANSWER: B.
Comment: The question is technically incorrect because the indicated correct choice is too general. Depletion of burnable poison is occurring throughout most of the fuel cycle. The positive reactivity change from poison depletion exceeds the negative reactivity change from fuel depletion.
QID: P130 (TOPIC: 192002 KNOWLEDGE: K1.12 [2.4/2.5])
With Keff = 0.985, how much reactivity must be added to make the reactor critical?
A. 1.48% delta-K/K
B. 1.50% delta-K/K
C. 1.52% delta-K/K
D. 1.54% delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as P1246. "Reactivity" is not added; in addition, the four choices are improperly indicated as representing reactivity instead of delta-rho. There are no correct choices.
QID: P446 (B1548) (TOPIC: 192002 KNOWLEDGE: K1.12 [2.4/2.5])
With Keff = 0.987, how much reactivity must be added to make the reactor exactly critical?
A. 1.30% delta-K/K
B. 1.32% delta-K/K
C. 1.34% delta-K/K
D. 1.36% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P1246. "Reactivity" is not added; as per P445, criticality is a very exact condition, and as per P130, the four choices are improperly indicated as representing reactivity instead of delta-rho. There are no correct choices.
QID: P1946 (B648) (TOPIC: 192002 KNOWLEDGE: K1.12 [2.4/2.5])
In a subcritical reactor, Keff was increased from 0.85 to 0.95 by rod withdrawal. Which one of the following is closest to the amount of reactivity that was added to the core?
A. 0.099 delta-K/K
B. 0.124 delta-K/K
C. 0.176 delta-K/K
D. 0.229 delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P1246. "Reactivity" is not added In addition, as per P 130, the four choices are improperly indicated as representing reactivity instead of delta-rho. There is no correct choice.
QID: P2146 (TOPIC: 192002 KNOWLEDGE: K1.12 [2.4/2.5])
With Keff = 0.982, how much positive reactivity is required to make the reactor critical?
A. 1.720% delta-K/K
B. 1.767% delta-K/K
C. 1.800% delta-K/K
D. 1.833% delta-K/K
ANSWER: D.
Comment: This question suffers the same defect as P1246. "Reactivity" is not required; in addition, as per P130, the four choices are improperly indicated as representing reactivity instead of delta-rho. There is no correct choice.
QID: P2447 (B1947) (TOPIC: 192002 KNOWLEDGE: K1.12 [2.4/2.5])
With Keff = 0.985, how much positive reactivity is required to make the reactor exactly critical?
A. 1.487% delta-K/K
B. 1.500% delta-K/K
C. 1.523% delta-K/K
D. 1.545% delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as P1246. "Reactivity" is not required; as P445, criticality is a very exact condition, and as P130, the four choices are improperly indicated as representing reactivity instead of delta-rho. There is no correct choice.
QID: P246 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor at the end of core life has been shut down from 100% power and cooled down to 140F over three days. During the cooldown, boron concentration was increased by 100 ppm. Given the following absolute values of reactivities added during the shutdown and cooldown, assign a (+) or (-) as appropriate and choose the current value of shutdown margin.
Control rods = ( ) 6.918% delta-K/K
Xenon = ( ) 2.675% delta-K/K
Power defect = ( ) 1.575% delta-K/K
Boron = ( ) 1.040% delta-K/K
Temperature = ( ) 0.500% delta-K/K
A. -8.558% delta-K/K
B. -6.358% delta-K/K
C. -3.208% delta-K/K
D. -1.128% delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as P1246. "Reactivity" is not added; in addition, the five contributors to reactivity change are improperly indicated as representing reactivity instead of delta-rho.
QID: P346 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor is operating at steady-state 100% power with all control rods fully withdrawn. Tave is 588F and boron concentration is 1000 ppm. A reactor trip occurs, after which Tave stabilizes at 557F and all control rods are verified to be fully inserted.
Given the following information, select the value of shutdown margin. Assume no operator actions and disregard any reactivity effects of xenon.
Power coefficient = -0.015% delta-K/K/% power
Control/regulating rod worth = -2.788% delta-K/K
Shutdown/safety rod worth = -4.130% delta-K/K
Moderator temperature coefficient = -0.0012% delta-K/K per degree F
A. -5.381% delta-K/K
B. -5.418% delta-K/K
C. -8.383% delta-K/K
D. -8.418% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P246. The power coefficent is incorrectly indicated to represent reactivity/% power, the two rod worths are incorrectly indicated to represent reactivity, and the moderator coefficient is incorrectly indicated to represent reactivity per degree F.
QID: P447 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor is operating at steady-state 90% power with all control rods fully withdrawn and Tave at 580F. A reactor trip occurs, after which Tave stabilizes at 550F and all rods are verified to be fully inserted.
Given the following information, calculate the value of shutdown margin. Assume no operator actions and disregard any reactivity effects of xenon.
Power coefficient = -0.01% delta-K/K/% power
Control/regulating rod worth = -2.788% delta-K/K
Shutdown/safety rod worth = -4.130% delta-K/K
Moderator temperature coefficient = -0.01% delta-K/K per degree F
A. -5.718% delta-K/K
B. -6.018% delta-K/K
C. -7.518% delta-K/K
D. -7.818% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P246. The power coefficient is incorrectly indicated to represent reactivity/% power, the two rod worths are incorrectly indicated to represent reactivity, and the moderator coefficient is incorrectly indicated to represent reactivity per degree F.
QID: P647 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
At the time of a reactor trip from 100% power, shutdown margin was determined to be -5.883% delta-K/K. Over the next 72 hours the reactor coolant system was cooled down and boron concentration was increased. The reactivities affected by the change in plant conditions are as follows:
Reactivity Change (+ or -)
Xenon 2.675% delta-K/K
Moderator temperature 0.5% delta-K/K
Boron 1.04% delta-K/K
What is the shutdown margin 72 hours after the trip? (Assume end of core life.)
A. -1.668% delta-K/K
B. -3.748% delta-K/K
C. -7.018% delta-K/K
D. -9.098% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P246, the xenon, moderator, and boron reactivity changes are incorrectly indicated as representing reactivity.
QID: P747 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor at end of life has been shut down from 100% power and cooled down to 140F over three days. During the cooldown, boron concentration was increased by 100 ppm.
Given the following absolute values of reactivities added during the shutdown and cooldown, assign a (+) or (-) as appropriate and choose the current value of shutdown margin.
Xenon = ( ) 2.5% delta-K/K
Temperature = ( ) 0.5% delta-K/K
Power defect = ( ) 1.5% delta-K/K
Rods = ( ) 7.0% delta-K/K
Boron = ( ) 1.0% delta-K/K
A. -8.5% delta-K/K
B. -6.5% delta-K/K
C. -3.5% delta-K/K
D. -1.5% delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as P246. "Reactivity" is not added. The xenon, temperature, power defect, rods and boron reactivity changes are incorrectly indicated as representing reactivity.
QID: P1047 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor at end of core life has been shut down from 100% power and cooled down to 140F over three days. During the cooldown, boron concentration was increased by 100 ppm.
Given the following absolute values of reactivities added during the shutdown and cooldown, assign a (+) or (-) as appropriate and choose the current value of shutdown margin.
Coolant temperature = ( ) 0.50% delta-K/K
Control rods = ( ) 6.50% delta-K/K
Boron = ( ) 1.50% delta-K/K
Power defect = ( ) 1.75% delta-K/K
Xenon = ( ) 2.75% delta-K/K
A. -0.0% delta-K/K
B. -3.0% delta-K/K
C. -3.5% delta-K/K
D. -8.5% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P246. "Reactivity" is not added. The xenon, temperature, power defect, rods and boron reactivity changes are incorrectly indicated as representing reactivity.
QID: P1446 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor at the beginning of core life has been shut down from 100% power and cooled down to 340F over three days. During the cooldown, boron concentration was increased by 200 ppm.
Given the following absolute values of reactivities added during the shutdown and cooldown, assign a (+) or (-) as appropriate and choose the current value of shutdown margin.
Xenon = ( ) 3.0% delta-K/K
Boron = ( ) 3.5% delta-K/K
Power defect = ( ) 4.0% delta-K/K
Rods = ( ) 7.0% delta-K/K
Cooldown = ( ) 2.0% delta-K/K
A. -1.5% delta-K/K
B. -2.5% delta-K/K
C. -7.5% delta-K/K
D. -9.5% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as P246. "Reactivity" is not added. The xenon, temperature, power defect, rods and boron reactivity changes are incorrectly indicated as representing reactivity.
QID: P1647 (TOPIC: 192002 KNOWLEDGE: K1.13 [3.5/3.7])
A reactor was operating at 100% power for two months when a reactor trip occurred. During the 14 hours since the trip the reactor has been cooled to 340F and boron concentration has been increased by 200 ppm.
Given the following absolute values of reactivities added during the shutdown and cooldown, assign a (+) or (-) as appropriate and choose the current value of shutdown margin.
Xenon = ( ) 2.0% delta-K/K
Boron = ( ) 2.5% delta-K/K
Power defect = ( ) 4.0% delta-K/K
Rods = ( ) 7.0% delta-K/K
Cooldown = ( ) 2.0% delta-K/K
A. -1.5% delta-K/K
B. -3.5% delta-K/K
C. -5.5% delta-K/K
D. -7.5% delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as P246. "Reactivity" is not added. The xenon, temperature, power defect, rods and boron reactivity changes are incorrectly indicated as representing reactivity.