During a reactor startup, source range indication is stable at 120 cps with Keff at 0.95. After a period of control rod withdrawal, source range indication stabilizes at 600 cps. Which one of the following is the approximate new Keff?
A. 0.96
B. 0.97
C. 0.98
D. 0.99
ANSWER: D.
Comment: This question suffers poor terminology. Restate as, After several control rod withdrawal increments, ... . Use of "period" can be confused with reactor rate.
QID: P267 (TOPIC: 192008 KNOWLEDGE: K1.05 [3.8/3.9])
As criticality is approached during a reactor startup, equal insertions of positive reactivity result in a ____________ absolute change in equilibrium count rate and a ____________ time to reach each new equilibrium.
A. smaller; shorter
B. smaller; longer
C. greater; shorter
D. greater; longer
ANSWER: D.
Comment: This question suffers the same defect as P65. Reactivity is not inserted and a PWR startup does not introduce "equal" reactivity increments. The question does not pose an "operational" situation.
QID: P365 (B365) (TOPIC: 192008 KNOWLEDGE: K1.05 [3.8/3.9])
Which one of the following statements describes count rate characteristics after a 5 second control rod withdrawal with the reactor very close to criticality? (Assume the reactor remains subcritical.)
A. There will be no change in count rate until criticality is achieved.
B. The count rate will rapidly increase (prompt jump) to a stable higher value.
C. The count rate will rapidly increase (prompt jump) then gradually increase and stabilize at a higher value.
D. The count rate will rapidly increase (prompt jump) then gradually decrease and stabilize at the previous value.
ANSWER: C.
Comment: This question suffers the same defect as P1166, a prompt jump in count rate requires a step change in reactivity.
QID: P68 (B123) (TOPIC: 192008 KNOWLEDGE: K1.09 [3.2/3.3])
With Keff = 0.985, how much reactivity must be added to make a reactor exactly critical?
A. 1.54% delta-K/K
B. 1.52% delta-K/K
C. 1.50% delta-K/K
D. 1.48% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho.
QID: P469 (TOPIC: 192008 KNOWLEDGE: K1.09 [3.2/3.3])
A reactor is subcritical by 1.0 % delta-K/K when the operator dilutes the reactor coolant system by 30 ppm boron. Assuming boron worth is -0.025% delta-K/K per ppm and that no other reactivity changes occur, the reactor is:
A. subcritical.
B. critical.
C. supercritical.
D. prompt critical.
ANSWER: A.
Comment: This question suffers the same defect as P266. The boron worth is incorrectly indicated to represent reactivity per ppm.
QID: P2267 (B867) (TOPIC: 192008 KNOWLEDGE: K1.09 [3.2/3.3])
When a reactor is exactly critical, reactivity is:
A. infinity.
B. undefined.
C. 0.0 delta-K/K.
D. 1.0 delta-K/K.
ANSWER: C.
Comment: The question is technically incorrect because of improper terminology. Criticality is an exact condition.
QID: P69 (B269) (TOPIC: 192008 KNOWLEDGE: K1.10 [3.3/3.4])
If, during a reactor startup, the startup rate is constant and positive without any further reactivity addition, then the reactor is:
A. exactly critical.
B. supercritical.
C. subcritical.
D. prompt critical.
ANSWER: B.
Comment: This question suffers the same defect as P565. Reactivity is not added.
QID: P1967 (B68) (TOPIC: 192008 KNOWLEDGE: K1.10 [3.3/3.4])
Assume a reactor is critical at a power level below the point of adding heat. For a 0.01% delta-K/K positive reactivity addition, the reactor period will be:
A. shorter at a higher reactor coolant temperature.
B. longer at a higher reactor coolant temperature.
C. shorter at the end of core life (EOL) than at the beginning of core life (BOL).
D. longer at EOL than at BOL.
ANSWER: C.
Comment: This question suffers the same defect as P565. Reactivity is not added.
QID: P2667 (B2668) (TOPIC: 192008 KNOWLEDGE: K1.10 [3.3/3.4])
A reactor is critical at 10-6% power. Control rods are withdrawn for 2 seconds and then stopped, resulting in a stable 0.2 dpm startup rate (SUR). If control rods were inserted (instead of withdrawn) for 2 seconds with the reactor initially critical at 10-6%, the stable SUR would have been: (Assume equal absolute values of reactivity are added in both cases.)
A. faster than -0.2 dpm, because, compared to power increases, reactor power decreases result in smaller delayed neutron fractions.
B. faster than -0.2 dpm, because, compared to power increases, reactor power decreases are less limited by delayed neutrons.
C. slower than -0.2 dpm, because, compared to power increases, reactor power decreases result in larger delayed neutron fractions.
D. slower than -0.2 dpm, because, compared to power increases, reactor power decreases are more limited by delayed neutrons.
ANSWER: D.
Comment: This question suffers the same defect as P565. Reactivity is not added. In addition, the question is technically incorrect because there are two correct answers. Choice C is correct because the delayed neutron population fraction, represented by (beta - rho), increases with power decrease caused by negative reactivity. Both Choice C and Choice D are correct.
QID: P2968 (B2966) (TOPIC: 192008 KNOWLEDGE: K1.11 [3.8/3.8])
A reactor startup is in progress; control rod withdrawal has just been stopped to assess criticality. Which one of the following is a combination of indications in which each listed indication supports a declaration that the reactor is critical?
A. Stable startup rate equals 0.0 dpm; source range count rate is stable; inverse multiplication (1/M) value equals 1.111.
B. Stable startup rate equals +0.2 dpm; source range count rate is slowly increasing; inverse multiplication (1/M) value equals 1.000
C. Stable startup rate equals 0.0 dpm; source range count rate is stable; inverse multiplication (1/M) value equals 0.111.
D. Stable startup rate equals +0.2 dpm; source range count rate is slowly increasing; inverse multiplication (1/M) value equals 0.000.
ANSWER: D.
Comment: This question is technically incorrect because the mathematical representation for source multiplication is valid only for keff < 1.0.
QID: P767 (TOPIC: 192008 KNOWLEDGE: K1.12 [3.5/3.6])
A reactor has just achieved criticality at 10-8% reactor power during a reactor startup from xenon-free conditions. The operator establishes a 0.5 decade per minute startup rate to increase power. After 10 minutes, startup rate decreases to zero and then becomes increasingly negative. A possible cause for these indications is:
A. inadvertent boration.
B. reaching the point of adding heat.
C. fuel depletion.
D. burnable poison burnout.
ANSWER: A.
Comment: This question suffers the same defect as P2467. Negative is negative.
QID: P670 (B670) (TOPIC: 192008 KNOWLEDGE: K1.13 [3.4/3.6])
After taking critical data during a reactor startup, the operator establishes a stable 1 DPM startup rate to increase power to the point of adding heat (POAH). How much negative reactivity feedback must be added at the POAH to stop the power increase?
Assume: ß = 0.00579
l * = 1.0 x 10-5 seconds
lambdaeff = 0.1 seconds-1
A. 0.16% delta-K/K
B. 0.19% delta-K/K
C. 0.23% delta-K/K
D. 0.29% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho. In addition this question is technically incorrect because the amount of negative reactivity feedback to "stop" the power increase occurs at power turning and is less than the amount of negative reactivity feedback required to establish criticality.
QID: P2370 (B2369) (TOPIC: 192008 KNOWLEDGE: K1.13 [3.4/3.6])
After taking critical data during a reactor startup, the operator establishes a positive 48-second reactor period to increase power to the point of adding heat (POAH). Which one of the following is the approximate amount of reactivity needed to stabilize power at the POAH? (Assume ßeff = 0.00579.)
A. -0.10% delta-K/K
B. -0.12% delta-K/K
C. -0.01% delta-K/K
D. -0.012% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity. In addition, initial conditions should be specified, e.g. ambient heat loss.
QID: P972 (B133) (TOPIC: 192008 KNOWLEDGE: K1.14 [3.1/3.1])
A reactor is critical several decades below the point of adding heat (POAH) when a small amount of positive reactivity is added to the core. If the exact same amount of negative reactivity is then added to the core prior to reaching the POAH, reactor power will stabilize:
A. higher than the initial power level but below the POAH.
B. lower than the initial power level.
C. at the initial power level.
D. at the POAH.
ANSWER: A.
Comment: This question suffers the same defect as P1065. Reactivity is not added. In addition, the wording, "power will stabilize" is poor. The reactor will be "critical" at a power level somewhat higher ...
QID: P1268 (TOPIC: 192008 KNOWLEDGE: K1.14 [3.1/3.1])
A reactor is critical two decades below the point of adding heat when -0.01% delta-K/K of reactivity is added to the core. If +0.01% delta-K/K is then added to the core 2 minutes later, reactor power will stabilize at:
A. the point of adding heat.
B. somewhat lower than the initial power level.
C. the initial power level.
D. the subcritical multiplication equilibrium level.
ANSWER: B.
Comment: This question suffers the same defect as P266. Reactivity is not added.
QID: P2568 (B2568) (TOPIC: 192008 KNOWLEDGE: K1.14 [3.1/3.1])
A reactor is currently at 10-3% power with a positive 60 second reactor period. An amount of negative reactivity is added to the core that places the reactor on a negative 40 second reactor period. If the same amount of positive reactivity is added to the core approximately 5 minutes later, reactor power will:
A. increase and stabilize at the point of adding heat.
B. increase and stabilize at 10-3%.
C. continue to decrease on a negative 40 second period until the equilibrium source neutron level is reached.
D. continue to decrease with an unknown period until the equilibrium source neutron level is reached.
ANSWER: A.
Comment: This question suffers the same defect as P266. Reactivity is not added. In addition, the question is technically incorrect because the initial conditions are not specified. The power will not stabilize at the point of adding heat unless ambient heat loss or steam demand is of the order of at least 0.5% of rated power.
QID: P1070 (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
A reactor is critical at a stable power level below the point of adding heat (POAH) when a small amount of positive reactivity is added. Which one of the following reactivity coefficient(s) will stabilize reactor power at the POAH?
A. Moderator temperature only
B. Fuel temperature only
C. Moderator temperature and fuel temperature
D. Fuel temperature and voids
ANSWER: C.
Comment: This question suffers the same defect as P2568. Reactivity is not added and necessary initial conditions are not provided.
QID: P1172 (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
A reactor near the end of core life is at 5 x 10-2% power with a 0.3 DPM startup rate. With no operator action, what will be the approximate reactor power 10 minutes later? (Assume no protective system actuation.)
A. 100%
B. 50%
C. 10%
D. 1% (point of adding heat)
ANSWER: D.
Comment: This question is technically incorrect because necessary initial conditions are not provided.
QID: P1367 (B1966) (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
A reactor nearing end of core life is at 5 x 10-6amps (5 x 10-2%) with a positive 0.3 DPM startup rate. With no operator action, no reactor trip, and no steam release, what will be reactor power 10 minutes later?
A. Below the point of adding heat (POAH)
B. At the POAH
C. Above the POAH but less than 50%
D. At 50%
ANSWER: B.
Comment: This question is technically incorrect because necessary initial conditions are not provided.
QID: P1470 (B1371) (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
With a reactor on a constant period, which one of the following power changes requires the longest time to occur?
A. 1% power to 4% power
B. 5% power to 15% power
C. 20% power to 35% power
D. 40% power to 60% power
ANSWER: A.
Comment: This question is technically incorrect because a constant period does not occur in the power range.
QID: P1567 (B1570) (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
With a reactor on a constant period of 30 minutes, which one of the following power changes requires the least time to occur?
A. 1% power to 6% power
B. 10% power to 20% power
C. 20% power to 35% power
D. 40% power to 60% power
ANSWER: D.
Comment: This question is technically incorrect because a constant period does not occur in the power range. In addition, reactor period should be specified in seconds.
QID: P2069 (B2072) (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
With a reactor on a constant period of 180 seconds, which one of the following power changes requires the longest amount of time to occur?
A. 3% power to 5% power
B. 5% power to 15% power
C. 15% power to 30% power
D. 30% power to 60% power
ANSWER: B.
Comment: This question is technically incorrect because a constant period does not occur in the power range.
QID: P2770 (B2770) (TOPIC: 192008 KNOWLEDGE: K1.17 [3.3/3.4])
With a reactor on a constant period of 180 seconds, which one of the following power changes requires the shortest amount of time to occur?
A. 3% power to 5% power
B. 5% power to 15% power
C. 15% power to 30% power
D. 30% power to 60% power
ANSWER: A.
Comment: This question is technically incorrect because a constant period does not occur in the power range.
QID: P1071 (TOPIC: 192008 KNOWLEDGE: K1.18 [3.6/3.5])
A reactor is operating with the following initial conditions:
Power level = 100%
Coolant boron = 620 ppm
Coolant temperature = 587 F
After a load decrease reactor conditions are as follows:
Power level = 80%
Coolant boron = 650 ppm
Coolant temperature = 577 F
All parameters were at normal steady-state values before and after the power change. Given the following, how much reactivity was added by control rod movement during the load decrease? (Assume fission product poison reactivity does not change.)
Differential boron worth = -1.0 x 10-2% delta-K/K/ppm
Total power coefficient = -1.5 x 10-2% delta-K/K/%
Moderator temperature coefficient = -2.0 x 10-2% delta-K/K/ F
A. -0.0% delta-K/K
B. -0.2% delta-K/K
C. -0.6% delta-K/K
D. -0.8% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho. In addition, this question is technically incorrect because the differential boron worth, the total power coefficient, and the moderator temperature coefficient are incorrectly indicated to represent reactivity per unit parameter change.
QID: P1871 (TOPIC: 192008 KNOWLEDGE: K1.18 [3.6/3.5])
A reactor is operating with the following stable initial conditions:
Power level = 100%
Coolant boron = 630 ppm
Coolant temperature = 582 F
After a load decrease, stable reactor conditions are as follows:
Power level = 80%
Coolant boron = 640 ppm
Coolant temperature = 577 F
Given the following values, how much reactivity was added by control rod movement during the load decrease? (Assume fission product poison reactivity does not change.)
Total power coefficient = -1.5 x 10-2% delta-k/k/%
Moderator temperature coefficient = -2.0 x 10-2% delta-k/k/ F
Differential boron worth = -1.5 x 10-2% delta-k/k/ppm
A. +0.15% delta-k/k
B. +0.25% delta-k/k
C. -0.15% delta-k/k
D. -0.25% delta-k/k
ANSWER: C.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho. In addition, this question is technically incorrect because the differential boron worth, the total power coefficient, and the moderator temperature coefficient are incorrectly indicated to represent reactivity per unit parameter change.
QID: P1968
(TOPIC: 192008 KNOWLEDGE: K1.18 [3.6/3.5]) A reactor is operating with the following initial conditions:
Power level = 80%
Coolant boron = 630 ppm
Coolant temperature = 582 F
After a normal load decrease reactor conditions are as follows:
Power level = 50%
Coolant boron = 650 ppm
Coolant temperature = 572 F
Given the following values, how much reactivity was added by control rod movement during the load decrease? (Assume fission product poison reactivity does not change.)
Total power coefficient = -1.5 x 10-2% delta-K/K/%
Moderator temperature coefficient = -2.0 x 10-2% delta-K/K/ F
Differential boron worth = -1.5 x 10-2% delta-K/K/ppm
A. -0.5% delta-K/K
B. -0.15% delta-K/K
C. -0.25% delta-K/K
D. -0.35% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho. In addition, this question is technically incorrect because the differential boron worth, the total power coefficient, and the moderator temperature coefficient are incorrectly indicated to represent reactivity per unit parameter change.
QID: P2070 (TOPIC: 192008 KNOWLEDGE: K1.18 [3.6/3.5])
A reactor is operating with the following initial conditions:
Power level = 100%
Coolant boron = 620 ppm
Average coolant temperature = 587 F
After a load decrease reactor conditions are as follows:
Power level = 80%
Coolant boron = 630 ppm
Average coolant temperature = 577 F
Given the following values, how much reactivity was added by control rod movement during the load decrease? (Assume fission product poison reactivity does not change.)
Total power coefficient = -1.5 x 10-2% delta-K/K/%
Moderator temperature coefficient = -2.0 x 10-2% delta-K/K/ F
Differential boron worth = -1.0 x 10-2% delta-K/K/ppm
A. -0.2% delta-K/K
B. +0.2% delta-K/K
C. -0.4% delta-K/K
D. +0.4% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as P266. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity rather than delta-rho. In addition, this question is technically incorrect because the differential boron worth, the total power coefficient, and the moderator temperature coefficient are incorrectly indicated to represent reactivity per unit parameter change.