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Flashcards in Neutron Life Cycle Deck (57):
1

QID: P44 (B186)

A reactor is initially subcritical with the effective multiplication factor (Keff) equal to 0.998. After a brief withdrawal of control rods, Keff equals 1.002. The reactor is currently...

A. prompt critical.

B. supercritical.

C. exactly critical.

D. subcritical.

B

2

QID: P445 (B247)

Which one of the following conditions describes a reactor that is exactly critical?

A. Keff = 0; ΔK/K = 0

B. Keff = 0; ΔK/K = 1

C. Keff = 1; ΔK/K = 0

D. Keff = 1; ΔK/K = 1

C

3

QID: P45

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. nonleakage factor.

D. reproduction factor.

A

4

QID: P1346 (B1447)

The effective multiplication factor (Keff) can be determined by dividing the number of neutrons in the third generation by the number of neutrons in the __________ generation.

A. first

B. second

C. third

D. fourth

B

5

QID: P1846 (B847)

The effective multiplication factor (Keff) describes the ratio of the number of fission neutrons at the end of one generation to the number of fission neutrons at the __________ of the __________ generation.

A. beginning; next

B. beginning; previous

C. end; next

D. end; previous

D

6

QID: P2647 (B2647)

A thermal neutron is about to interact with a U-238 nucleus in an operating reactor. Which one of the following describes the most likely interaction and its effect on Keff?

A. The neutron will be scattered, thereby leaving Keff unchanged.

B. The neutron will be absorbed and the nucleus will fission, thereby decreasing Keff.

C. The neutron will be absorbed and the nucleus will fission, thereby increasing Keff.

D. The neutron will be absorbed and the nucleus will decay to Pu-239, thereby increasing Keff.

A

7

QID: P3046 (B3147)

A nuclear power plant is currently operating at steady-state 80 percent power near the end of its fuel cycle. During the next 3 days of steady-state power operation, no operator action is taken. How will core Keff be affected during the 3-day period?

A. Core Keff will gradually increase during the entire period.

B. Core Keff will gradually decrease during the entire period.

C. Core Keff will tend to increase, but inherent reactivity feedback will maintain Keff at 1.0.

D. Core Keff will tend to decrease, but inherent reactivity feedback will maintain Keff at 1.0.

D

8

QID: P6424 (B6424)

A 1.5 MeV neutron is about to interact with a U-238 nucleus in an operating reactor. Which one of the following describes the most likely interaction and its effect on Keff?

A. The neutron will be scattered, thereby leaving Keff unchanged.

B. The neutron will be absorbed and the nucleus will fission, thereby decreasing Keff.

C. The neutron will be absorbed and the nucleus will fission, thereby increasing Keff.

D. The neutron will be absorbed and the nucleus will decay to Pu-239, thereby increasing Keff.

A

9

QID: P546

During reactor refueling, burnable poisons are often installed in the core to help control Kexcess. Why are more burnable poisons installed for the first fuel cycle than for subsequent fuel cycles?

A. Control rod worth is lower at the beginning of subsequent fuel cycles.

B. More fuel reactivity is present at the beginning of subsequent fuel cycles.

C. More fission product poisons are present at the beginning of subsequent fuel cycles.

D. Reactor coolant boron concentration is higher at the beginning of subsequent fuel cycles.

C

10

QID: P646 (B1848)

Which one of the following defines K-excess?

A. Keff - 1

B. Keff + 1

C. (Keff - 1)/Keff

D. (1-Keff)/Keff

A

11

QID: P946

The following are combinations of critical conditions that exist for the same reactor operating at the point of adding heat at different times in core life.

Which one of the following combinations indicates the most amount of excess reactivity present in the core?

Control Rod Position   --     RCS Boron Concentration

A. 25% inserted   --  500 ppm

B. 50% inserted  --  500 ppm

C. 25% inserted  --  1,000 ppm

D. 50% inserted  --  1,000 ppm

D

12

QID: P1147

The following are combinations of critical conditions that exist for the same reactor operating at the point of adding heat at different times in core life.

Which one of the following combinations indicates the least amount of excess reactivity present in the core?

Control Rod Position    --    RCS Boron Concentration

A. 25% inserted  --  500 ppm

B. 25% inserted  --  1,000 ppm

C. 50% inserted  --  500 ppm

D. 50% inserted  --  1,000 ppm

A

13

QID: P1246 (B2048)

Which one of the following is a reason for installing excess reactivity (Kexcess) in a reactor?

A. To compensate for the conversion of U-238 to Pu-239 over core life.

B. To compensate for burnout of Xe-135 and Sm-149 during power changes.

C. To ensure the fuel temperature coefficient remains negative throughout core life.

D. To compensate for the negative reactivity added by the power coefficient during a power increase.

D

14

QID: P2847 (B2747)

A reactor is operating at full power at the beginning of a fuel cycle. A neutron has just been absorbed by a U-238 nucleus at a resonance energy of 6.7 electron volts. Which one of the following describes the most likely reaction for the newly formed U-239 nucleus and the effect of this reaction on Kexcess?

A. Decays over several days to Pu-239, which increases Kexcess.

B. Decays over several days to Pu-240, which increases Kexcess.

C. Immediately undergoes fast fission, which decreases Kexcess.

D. Immediately undergoes thermal fission, which decreases Kexcess.

A

15

QID: P3547 (B3547)

Which one of the following is a benefit of installing excess reactivity (Kexcess) in a reactor?

A. Ensures that sufficient control rod negative reactivity is available to shut down the reactor.

B. Ensures that the reactor can be made critical during a peak xenon condition after a reactor trip.

C. Ensures that positive reactivity additions result in controllable reactor power responses.

D. Ensures that the U-235 fuel enrichment is the same at the beginning and the end of a fuel cycle.

B

16

QID: P127

Shutdown margin can be defined as the amount of reactivity...

A. inserted by burnable poisons at beginning of a fuel cycle.

B. added by boron in the reactor coolant system.

C. by which the reactor is subcritical.

D. that would be inserted by shutdown bank rods.

C

17

QID: P245 (B248)

When determining the available shutdown margin for an operating reactor, how many control rods are assumed to remain fully withdrawn?

A. A single control rod of the highest reactivity worth.

B. A symmetrical pair of control rods of the highest reactivity worth.

C. A single control rod of average reactivity worth.

D. A symmetrical pair of control rods of average reactivity worth.

A

18

QID: P345

With a reactor initially operating at steady-state 85 percent power with manual rod control, the operator borates the reactor coolant system an additional 10 ppm. During the boration, the available shutdown margin will...

A. decrease and stabilize at a lower value.

B. decrease, then increase to the original value as coolant temperature changes.

C. increase and stabilize at a higher value.

D. increase, then decrease to the original value as coolant temperature changes.

C

19

QID: P746

With a reactor initially operating at steady-state 75 percent power with manual rod control, the operator dilutes the reactor coolant system boron concentration by 5 ppm. During the dilution, the available shutdown margin will...

A. increase and stabilize at a higher value.

B. increase, then decrease to the original value as coolant temperature changes.

C. decrease and stabilize at a lower value.

D. decrease, then increase to the original value as coolant temperature changes.

C

20

QID: P1747

A nuclear power plant is operating with the following initial conditions: · Reactor power is 50 percent. · Rod control is in manual. · Reactor coolant system (RCS) boron concentration is 600 ppm. Disregarding the effects of fission product poisons, which one of the following will result in a decrease in the available shutdown margin once the plant stabilizes?

A. Reactor power is reduced to 45 percent with final RCS boron concentration at 620 ppm.

B. Reactor power is increased to 55 percent with final RCS boron concentration at 580 ppm.

C. Control rods are withdrawn 3 inches with no change in steady-state reactor power or RCS boron concentration.

D. Control rods are inserted 3 inches with no change in steady-state reactor power or RCS boron concentration.

B

21

QID: P2347 (B2348)

Which one of the following changes will decrease the available shutdown margin in a reactor? (Assume no operator actions.)

A. Depletion of fuel during reactor operation.

B. Depletion of burnable poisons during reactor operation.

C. Buildup of samarium-149 following a reactor power transient.

D. Buildup of xenon-135 following a reactor power transient.

B

22

QID: P2546

A reactor is operating at steady-state 100 percent power with manual rod control about three months from the end of a fuel cycle. During the next two weeks of operation at 100 percent power, the available shutdown margin will... (Assume no operator actions are taken.)

A. continuously increase.

B. continuously decrease.

C. initially increase, and then decrease.

D. initially decrease, and then increase.

A

23

QID: P46

Reactivity is defined as the fractional change in...

A. reactor power per second.

B. neutron population per second.

C. reactor period from criticality.

D. the effective multiplication factor from criticality.

D

24

QID: P846

Which term is described by the following? "The fractional change of the effective multiplication factor from criticality."

A. 1/M

B. Keff

C. Reactor period

D. Reactivity

D

25

QID: P130

With Keff equal to 0.985, how much reactivity must be added to make the reactor critical? (Round answer to the nearest 0.01 %ΔK/K.)

A. 1.48 %ΔK/K

B. 1.50 %ΔK/K

C. 1.52 %ΔK/K

D. 1.54 %ΔK/K

C

26

QID: P446 (B1548)

With Keff equal to 0.987, how much reactivity must be added to make the reactor critical? (Round answer to the nearest 0.01 %ΔK/K.)

A. 1.01 %ΔK/K

B. 1.03 %ΔK/K

C. 1.30 %ΔK/K

D. 1.32 %ΔK/K

D

27

QID: P1946 (B648)

In a subcritical reactor, Keff was increased from 0.85 to 0.95 by rod withdrawal. Which one of the following is the approximate amount of reactivity that was added to the core?

A. 0.099 ΔK/K

B. 0.124 ΔK/K

C. 0.176 ΔK/K

D. 0.229 ΔK/K

B

28

QID: P2146 (B2848)

With Keff equal to 0.982, how much positive reactivity is required to make the reactor critical? (Round answer to the nearest 0.01 %ΔK/K.)

A. 1.72 %ΔK/K

B. 1.77 %ΔK/K

C. 1.80 %ΔK/K

D. 1.83 %ΔK/K

D

29

QID: P2447 (B1947)

With Keff equal to 0.985, how much positive reactivity is required to make the reactor critical? (Round answer to the nearest 0.01 %ΔK/K.)

A. 1.49 %ΔK/K

B. 1.50 %ΔK/K

C. 1.52 %ΔK/K

D. 1.55 %ΔK/K

C

30

QID: P3347 (B748)

With Keff equal to 0.983, how much positive reactivity must be added to make the reactor critical? (Round answer to the nearest 0.01 %ΔK/K.)

A. 1.70 %ΔK/K

B. 1.73 %ΔK/K

C. 3.40 %ΔK/K

D. 3.43 %ΔK/K

B

31

QID: P7647 (B7647)

A reactor was initially shutdown at a stable power level of 2.0 x 10-5 percent. After a small positive reactivity addition, the current stable power level is 3.0 x 10-5 percent. If the initial Keff was 0.982, what is the current Keff?

A. 0.988

B. 0.992

C. 0.996

D. Cannot be determined without additional information.

A

32

QID: P246

A reactor near the end of a fuel cycle has been shut down from 100 percent power and cooled down to 140°F 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 core reactivity.

Control rods = ( ) 6.918 %ΔK/K

Xenon = ( ) 2.675 %ΔK/K

Power defect = ( ) 1.575 %ΔK/K

Boron = ( ) 1.040 %ΔK/K

Cooldown = ( ) 0.500 %ΔK/K

A. -8.558 %ΔK/K

B. -6.358 %ΔK/K

C. -3.208 %ΔK/K

D. -1.128 %ΔK/K

C

33

QID: P346

A reactor was operating at steady-state 100 percent power with all control rods fully withdrawn and average reactor coolant temperature (Tave) at 588°F when a reactor trip occurred. After the trip, Tave stabilized at the no-load temperature of 557°F and all control rods were verified to be fully inserted. Given the following information, select the current value of core reactivity. (Assume no operator actions and disregard any reactivity effects of xenon.)

Power coefficient = -0.015 %ΔK/K/percent

Control rod worth = -6.918 %ΔK/K

Moderator temperature coefficient = -0.0012 %ΔK/K/°F

A. -5.381 %ΔK/K

B. -5.418 %ΔK/K

C. -8.383 %ΔK/K

D. -8.418 %ΔK/K

B

34

QID: P447

A reactor is operating at steady-state 90 percent power with all control rods fully withdrawn and average reactor coolant temperature (Tave) at 580°F. A reactor trip occurs, after which Tave stabilizes at the no-load temperature of 550°F and all control rods are verified to be fully inserted. Given the following information, calculate the current value of core reactivity. (Assume no operator actions and disregard any reactivity effects of changes in xenon-135.)

Power coefficient = -0.01 %ΔK/K/percent

Control rod worth = -6.918 %ΔK/K

Moderator temperature coefficient = -0.01 %ΔK/K/°F

A. -5.718 %ΔK/K

B. -6.018 %ΔK/K

C. -7.518 %ΔK/K

D. -7.818 %ΔK/K

B

35

QID: P647

A reactor was operating at steady-state 100 percent power near the end of a fuel cycle when a reactor trip occurred. Immediately after the trip, shutdown margin was determined to be -5.883 %ΔK/K. Over the next 72 hours, the reactor coolant system was cooled down and reactor coolant boron concentration was increased. The reactivities affected by the change in plant conditions are as follows: Reactivity Change (+) or (-)

Xenon = ( ) 2.675 %ΔK/K

Moderator temperature = ( ) 0.5 %ΔK/K

Boron = ( ) 1.04 %ΔK/K

What is the value of core reactivity 72 hours after the trip?

A. -1.668 %ΔK/K

B. -3.748 %ΔK/K

C. -7.018 %ΔK/K

D. -9.098 %ΔK/K

B

36

QID: P747

A reactor near the end of a fuel cycle has been shut down from 100 percent power and cooled down to 140°F over three days. During the cooldown, reactor coolant 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 core reactivity.

Xenon = ( ) 2.5 %ΔK/K

Moderator temperature = ( ) 0.5 %ΔK/K

Power defect = ( ) 1.5 %ΔK/K

Control rods = ( ) 7.0 %ΔK/K

Boron = ( ) 1.0 %ΔK/K

A. -8.5 %ΔK/K

B. -6.5 %ΔK/K

C. -3.5 %ΔK/K

D. -1.5 %ΔK/K

C

37

QID: P1047

A reactor near the end of a fuel cycle has been shut down from 100 percent power and cooled down to 140°F over three days. During the cooldown, reactor coolant 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 core reactivity.

Moderator temperature = ( ) 0.50 %ΔK/K

Control rods = ( ) 6.50 %ΔK/K

Boron = ( ) 1.50 %ΔK/K

Power defect = ( ) 1.75 %ΔK/K

Xenon = ( ) 2.75 %ΔK/K

A. -0.0 %ΔK/K

B. -3.0 %ΔK/K

C. -3.5 %ΔK/K

D. -8.5 %ΔK/K

B

38

QID: P1446

A reactor near the middle of a fuel cycle has been shut down from 100 percent power and cooled down to 340°F over three days. During the cooldown, reactor coolant 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 core reactivity.

Xenon = ( ) 3.0 %ΔK/K

Boron = ( ) 3.5 %ΔK/K

Power defect = ( ) 4.0 %ΔK/K

Control rods = ( ) 7.0 %ΔK/K

Moderator temperature = ( ) 2.0 %ΔK/K

A. -1.5 %ΔK/K

B. -2.5 %ΔK/K

C. -7.5 %ΔK/K

D. -9.5 %ΔK/K

A

39

QID: P1647

A reactor near the middle of a fuel cycle was operating at 100 percent power for two months when a reactor trip occurred. During the 14 hours since the trip, the reactor has been cooled to 340°F and reactor coolant 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 core reactivity.

Xenon = ( ) 2.0 %ΔK/K

Boron = ( ) 2.5 %ΔK/K

Power defect = ( ) 4.0 %ΔK/K

Control rods = ( ) 7.0 %ΔK/K

Moderator temperature = ( ) 2.0 %ΔK/K

A. -1.5 %ΔK/K

B. -3.5 %ΔK/K

C. -5.5 %ΔK/K

D. -7.5 %ΔK/K

C

40

QID: P5224

A reactor near the middle of a fuel cycle was initially operating at steady-state 100 percent power when it was shut down and cooled down to 200°F over a three-day period. During the cooldown, reactor coolant boron concentration was increased by 80 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 core reactivity.

Control rods = ( ) 6.75 %ΔK/K

Xenon = ( ) 2.50 %ΔK/K

Power defect = ( ) 2.00 %ΔK/K

Boron = ( ) 1.25 %ΔK/K

Moderator temperature = ( ) 0.50 %ΔK/K

A. -0.5 %ΔK/K

B. -3.0 %ΔK/K

C. -7.0 %ΔK/K

D. -8.0 %ΔK/K

B

41

QID: P124

Which one of the following plant parameter changes will increase the shutdown margin for a shutdown reactor near the end of a fuel cycle?

A. Reactor coolant boron concentration is decreased by 100 ppm.

B. One control rod is fully withdrawn for a test.

C. Xenon has decayed for 72 hours following shutdown.

D. The reactor coolant system is allowed to heat up 30°F.

D

42

QID: P547

A nuclear power plant is operating at steady-state 70 percent power with manual rod control. Which one of the following events will increase the shutdown margin? (Assume that no unspecified operator actions occur and the reactor does not trip.)

A. Reactor coolant boron concentration is decreased by 10 ppm.

B. A control rod in a shutdown bank (safety group) drops.

C. Power is decreased to 50 percent using boration.

D. The plant experiences a 3 percent load rejection.

C

43

QID: P2046

A reactor is shutdown with the reactor vessel head removed for refueling. The core is covered by 23 feet of refueling water at 100°F with a boron concentration of 2,000 ppm. Which one of the following will increase core Keff?

A. An unrodded spent fuel assembly is removed from the core.

B. Refueling water temperature is increased to 105°F.

C. A new neutron source is installed in the core.

D. Excore nuclear instrumentation is repositioned to increase source range count rate.

B

44

QID: P2247

A reactor is operating at 80 percent power when the operator adds 10 gallons of boric acid to the reactor coolant system (RCS). Over the next several minutes, the operator adjusts control rod position as necessary to maintain a constant reactor coolant average temperature. When the plant stabilizes, the shutdown margin will be __________; and axial power distribution will have shifted toward the __________ of the core.

A. the same; top

B. the same; bottom

C. larger; top

D. larger; bottom

C

45

QID: P2547

A nuclear power plant malfunction requires a rapid reactor power decrease from 100 percent to 90 percent. The crew performs the downpower transient using control rod insertion when necessary. Reactor coolant boron concentration is not changed. If the shutdown margin at 100 percent power was 3.5 %ΔK/K, which one of the following describes the shutdown margin at the lower power level? (Ignore any changes in core fission product reactivity.)

A. Less than 3.5 %ΔK/K due only to the power defect.

B. Greater than 3.5 %ΔK/K due only to the insertion of control rods.

C. Less than 3.5 %ΔK/K due to the combined effects of control rod insertion and power defect.

D. Equal to 3.5 %ΔK/K regardless of the reactivity effects of control rod insertion and power defect.

D

46

QID: P2746

A reactor is shutdown with the reactor vessel head removed for refueling. The core is covered by 23 feet of refueling water at 105°F with a boron concentration of 2,200 ppm. Which one of the following will increase core Keff?

A. A new neutron source is installed in the core.

B. Refueling water temperature is decreased to 100°F.

C. A spent fuel assembly is replaced with a new fuel assembly.

D. Excore nuclear instrumentation is repositioned to increase source range count rate.

C

47

QID: P2747

Reactors A and B are identical except that reactor A is operating at steady-state 80 percent power while reactor B is operating at steady-state 100 percent power. Initial control rod positions are the same for each reactor. How will the shutdown margins (SDM) compare for the two reactors following a reactor trip? (Assume no post-trip operator actions are taken that would affect SDM.)

A. Reactor A will have the greater SDM.

B. Reactor B will have the greater SDM.

C. When sufficient time has passed to allow both cores to become xenon-free, the SDMs will be equal.

D. Within a few minutes after the trips, when all parameters have returned to normal post-trip conditions, the SDMs will be equal.

A

48

QID: P2947

A reactor is operating at steady-state 50 percent power. A plant test requires a 4°F decrease in reactor coolant system (RCS) average temperature (T-avg). The operator accomplishes this temperature decrease by adjusting RCS boron concentration. No other operator actions are taken. If the initial shutdown margin was 3.0 %ΔK/K, which one of the following describes the shutdown margin at the lower RCS T-avg with the reactor still at steady-state 50 percent power?

A. Less than 3.0 %ΔK/K, because RCS T-avg is lower.

B. More than 3.0 %ΔK/K, because RCS boron concentration is higher.

C. Equal to 3.0 %ΔK/K, because the reactivity change caused by the change in RCS T-avg offsets the reactivity change caused by the change in RCS boron concentration.

D. Equal to 3.0 %ΔK/K because shutdown margin in an operating reactor will not change unless control rod position changes.

B

49

QID: P3647 (B3648)

A reactor is initially operating at steady-state 60 percent power near the end of a fuel cycle when a fully withdrawn control rod suddenly inserts completely into the core. No operator action is taken and the plant control systems stabilize the reactor at a power level in the power range. Compared to the initial available shutdown margin (SDM), the current available SDM is __________; and compared to the initial core Keff, the current core Keff is __________.

A. the same; smaller

B. the same; the same

C. less negative; smaller

D. less negative; the same

B

50

QID: P3747 (B3748)

A nuclear power plant has just completed a refueling outage. Based on the expected core loading, reactor engineers have predicted a control rod configuration at which the reactor will become critical during the initial reactor startup following the refueling outage. However, the burnable poisons scheduled to be loaded were inadvertently omitted. Which one of the following describes the effect of the burnable poison omission on achieving reactor criticality during the initial reactor startup following the refueling outage?

A. The reactor will become critical before the predicted critical control rod configuration is achieved.

B. The reactor will become critical after the predicted critical control rod configuration is achieved.

C. The reactor will be unable to achieve criticality because the fuel assemblies contain insufficient positive reactivity to make the reactor critical.

D. The reactor will be unable to achieve criticality because the control rods contain insufficient positive reactivity to make the reactor critical.

A

51

QID: P4224

A reactor is shutdown with the reactor vessel head removed for refueling. The core is covered by 23 feet of refueling water at 100°F with a boron concentration of 2,000 ppm. Which one of the following will decrease core Keff?

A. An unrodded spent fuel assembly is removed from the core.

B. Refueling water temperature is increased to 105°F.

C. A depleted neutron source is removed from the core.

D. Refueling water boron concentration is decreased by 5 ppm.

A

52

QID: P4924

Reactors A and B are identical except that reactor A is operating near the beginning of a fuel cycle (BOC) and reactor B is operating near the end of a fuel cycle (EOC). Both reactors are operating at 100 percent power with all control rods fully withdrawn. If the total reactivity worth of the control rods is the same for both reactors, which reactor will have the smaller Keff five minutes after a reactor trip, and why?

A. Reactor A, because the power coefficient is less negative near the BOC.

B. Reactor A, because the concentration of U-235 in the fuel rods is higher near the BOC.

C. Reactor B, because the power coefficient is more negative near the EOC.

D. Reactor B, because the concentration of U-235 in the fuel rods is lower near the EOC.

A

53

QID: P5324

A reactor is shutdown with the reactor vessel head removed for refueling. The core is covered by 23 feet of refueling water at 105°F with a boron concentration of 2,000 ppm. Which one of the following will decrease Keff?

A. Refueling water temperature decreases by 5°F.

B. A depleted neutron source is removed from the core.

C. A spent fuel assembly is replaced with a new fuel assembly.

D. Refueling water boron concentration decreases by 5 ppm.

A

54

QID: P6224

Reactors A and B are identical except that reactor A is operating near the beginning of a fuel cycle (BOC) and reactor B is operating near the end of a fuel cycle (EOC). Both reactors are operating at 100 percent power with all control rods fully withdrawn. If the total reactivity worth of the control rods is the same for both reactors, which reactor will have the greater Keff five minutes after a reactor trip, and why?

A. Reactor A, because the pre-trip reactor coolant boron concentration is lower near the BOC.

B. Reactor A, because the power coefficient adds less positive reactivity after a trip near the BOC.

C. Reactor B, because the pre-trip reactor coolant boron concentration is higher near the EOC.

D. Reactor B, because the power coefficient adds more positive reactivity after a trip near the EOC.

D

55

QID: P6624

A nuclear power plant was initially operating at steady state 70 percent power near the middle of a fuel cycle when a control rod dropped into the core. Consider the following two possible operator responses:

  • Response 1: An operator adjusts the reactor coolant system (RCS) boron concentration to restore the initial reactor coolant temperatures.
  • Response 2: An operator withdraws some of the remaining control rods to restore the initial reactor coolant temperatures.

In a comparison between the two responses, which response, if any, will result in the greater shutdown margin (SDM) when the plant is stabilized at 70 percent power, and why?

A. Response 1, because a smaller (than response 2) amount of positive reactivity will be added by the RCS cooldown that occurs immediately after a reactor trip.

B. Response 2, because a larger (than response 1) amount of negative reactivity will be added by the control rods upon a reactor trip.

C. The SDM is the same for both responses because the plant is stabilized at the same initial steady state power level.

D. The SDM is the same for both responses because the same amount of positive reactivity is added in both responses.

B

56

QID: P7124

A reactor is shutdown with the reactor vessel head removed for refueling. The core is covered by 23 feet of refueling water at 120°F with a boron concentration of 2,000 ppm. Source range instrumentation indicates 100 cps. How will source range indication be affected if refueling water temperature decreases to 100°F?

A. Indication will increase because the effect of increased Keff more than offsets the effect of decreased neutron leakage from the core.

B. Indication will increase because of the cooperative effects of increased neutron leakage from the core and increased Keff.

C. Indication will decrease because the effect of decreased neutron leakage from the core more than offsets the effect of increased Keff.

D. Indication will decrease because of the cooperative effects of decreased Keff and decreased neutron leakage from the core.

D

57

QID: P7224

A nuclear power plant was initially operating at equilibrium 100 percent power just prior to a refueling outage. The plant was shut down, refueled, restarted, and is currently operating at equilibrium 100 percent power. Assume the 100 percent power fission rate did not change. Which one of the following describes the current plant status as compared to the conditions just prior to the refueling?

A. The reactor shutdown margin is greater.

B. The reactor coolant boron concentration is smaller.

C. The equilibrium core Xe-135 concentration is smaller.

D. The difference between the reactor coolant hot leg and cold leg temperatures is greater.

A