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Reactor Operational Physics Flashcards

1
Q

During a reactor startup, the first reactivity addition caused the stable source range count rate to
increase from 20 cps to 40 cps. The second reactivity addition caused the stable count rate to increase
from 40 cps to 160 cps.
Which one of the following statements accurately compares the two reactivity additions?

A

The first reactivity addition was larger.

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2
Q

During a reactor startup, the first positive reactivity addition caused the stable source range count rate
to increase from 20 cps to 30 cps. The second positive reactivity addition caused the stable count rate
to increase from 30 cps to 60 cps. Keff was 0.97 prior to the first reactivity addition.
Which one of the following statements accurately compares the reactivity additions?

A

The first and second reactivity additions were approximately equal.

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3
Q

A nuclear power plant was operating at steady-state 100 percent power near the end of a fuel cycle
when a reactor trip occurred. Four hours after the trip, with reactor coolant temperature at normal
no-load temperature, which one of the following will cause the fission rate in the reactor core to
increase?

A

The operator fully withdraws one bank/group of control rods.

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4
Q

A nuclear power plant was operating at steady-state 100 percent power near the end of a fuel cycle
when a reactor trip occurred. Four hours after the trip, reactor coolant temperature is currently being
maintained at normal no-load temperature in anticipation of commencing a reactor startup.
At this time, which one of the following will cause the fission rate in the reactor core to decrease?

A

An additional 2 hours is allowed to pass with no other changes in plant parameters.

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5
Q

While withdrawing control rods during a reactor startup, the stable source range count rate doubled.
If the same amount of reactivity that caused the first doubling is added again, the stable count rate will
__________; and the reactor will be __________.

A

more than double; critical

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6
Q

A reactor startup is in progress and the reactor is slightly subcritical in the source range. Assuming
the reactor remains subcritical, a short control rod withdrawal will cause the reactor startup rate
indication to increase sharply in the positive direction, and then…

A

gradually decrease and stabilize at zero.

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7
Q

A subcritical reactor has a stable source range count rate of 150 cps with a shutdown reactivity of ˗2.0
%ΔK/K. How much positive reactivity must be added to establish a stable count rate of 300 cps?

A

1.0 %ΔK/K

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8
Q

A subcritical reactor has an initial Keff of 0.8 with a stable source range count rate of 100 cps. If
positive reactivity is added until Keff equals 0.95, at what value will the count rate stabilize?

A

400 cps

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9
Q

During a reactor startup, equal amounts of positive reactivity are being sequentially added, and the
source range count rate is allowed to reach equilibrium after each addition. Which one of the
following statements applies for each successive reactivity addition?

A

The numerical change in equilibrium count rate is greater.

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10
Q

Which one of the following describes the prompt jump and the change in stable source range count
rate resulting from a short control rod withdrawal with Keff at 0.95 as compared to an identical control
rod withdrawal with Keff at 0.99? (Assume the reactivity additions are equal, and the reactor remains
subcritical.)

A

The prompt jump in count rate will be greater with Keff at 0.99, and the increase in stable count rate
will be greater with Keff at 0.99.

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11
Q

A reactor is shut down by 1.8 %ΔK/K. Positive reactivity is added that increases the stable source
range count rate from 15 cps to 300 cps.
What is the current value of Keff?

A

0.999

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12
Q

A subcritical reactor has a stable source range count rate of 150 cps with a shutdown reactivity of ˗2.0
%ΔK/K. Approximately how much positive reactivity must be added to establish a stable count rate
of 600 cps?

A

1.5 %ΔK/K

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13
Q

A subcritical reactor has a stable source range count rate of 60 cps with a shutdown reactivity of -2.0
%ΔK/K. How much positive reactivity must be added to establish a stable count rate of 300 cps?

A

1.6 %ΔK/K

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14
Q

A reactor startup is in progress with the reactor currently subcritical.
Which one of the following describes the change in source range count rate resulting from a short
control rod withdrawal with Keff at 0.95 compared to an identical control rod withdrawal with Keff at
0.98? (Assume the reactivity additions are equal and the reactor remains subcritical.)

A

Both the prompt jump in count rate and the increase in stable count rate will be smaller with Keff at
0.95.

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15
Q

A reactor startup is being performed by adding equal amounts of positive reactivity and waiting for
neutron population to stabilize. As the reactor approaches criticality, the numerical change in stable
neutron population resulting from each reactivity addition will __________; and the time required for
the neutron population to stabilize after each reactivity addition will __________.

A

increase; increase

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16
Q

A reactor startup is being performed with xenon-free conditions. Control rod withdrawal is stopped
when Keff equals 0.995 and source range count rate stabilizes at 1,000 cps. No additional operator
actions are taken.
Which one of the following describes the count rate 20 minutes after rod withdrawal is stopped?

A

1,000 cps and constant.

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17
Q

A reactor startup is in progress. The reactor is slightly subcritical with a constant startup rate of
0.0 DPM. A short control rod insertion will cause the reactor startup rate indication to initially
become negative, and then…

A

gradually become less negative and return to 0.0 DPM.

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18
Q

A reactor startup is being commenced with the initial source range count rate stable at 20 cps. After a
period of control rod withdrawal, count rate stabilizes at 80 cps.
If the total reactivity added by the above control rod withdrawal is 4.5 %ΔK/K, how much additional
positive reactivity must be inserted to make the reactor critical?

A

1.5 %ΔK/K

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19
Q

A xenon-free shutdown nuclear power plant is slowly cooling down due to an unisolable steam leak.
The leak began when reactor coolant temperature was 400°F and the readings on all source range
channels were 80 cps. Currently, reactor coolant temperature is 350°F and all source range channels
indicate 160 cps.
Assume the moderator temperature coefficient remains constant throughout the cooldown, and no
operator action is taken. What will the status of the reactor be when reactor coolant temperature
reaches 290°F?

A

Supercritical, with source range count rate greater than 320 cps.

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20
Q

A reactor startup is in progress with Keff initially equal to 0.90. By what factor will the core neutron
level increase if the reactor is stabilized when Keff equals 0.99?

A

10

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21
Q

A reactor is shutdown with a Keff of 0.96 and a stable source range count rate of 50 cps when a reactor
startup is commenced. Which one of the following will be the stable count rate when Keff reaches
0.995?

A

400 cps

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22
Q

A nuclear power plant is being cooled down from 500°F to 190°F. Just prior to commencing the
cooldown, the source range count rate was stable at 32 cps. After two hours, with reactor coolant
temperature at 350°F, the source range count rate is stable at 64 cps.
Assume the moderator temperature coefficient remains constant throughout the cooldown and reactor
power remains below the point of adding heat.
Without additional operator action, what will the status of the reactor be when reactor coolant
temperature reaches 190°F?

A

Supercritical.

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23
Q

A reactor is critical in the source range during a reactor startup with a core effective delayed neutron
fraction of 0.007. The operator then adds positive reactivity to establish a stable 0.5 DPM startup
rate.
If the core effective delayed neutron fraction had been 0.005, what would be the approximate stable
startup rate after the addition of the same amount of positive reactivity?

A

0.76 DPM

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24
Q

Initially, a nuclear power plant is shut down with a Keff of 0.92 and a stable source range count rate of
200 cps. Then, a reactor startup is initiated. All control rod motion is stopped when Keff equals
0.995. The instant that rod motion stops, source range count rate is 1,800 cps.
When source range count rate stabilizes, count rate will be approximately…

A

3,200 cps

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25
Q

Initially, a nuclear power plant was shut down with a stable source range count rate of 30 cps. Using
many small additions of positive reactivity, a total of 0.1 %ΔK/K was added to the core and the stable
source range count rate is currently 60 cps.
What was the stable source range count rate after only 0.05 %ΔK/K had been added during the above
process?

A

40 cps

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26
Q

A PWR nuclear power plant has been shut down for two weeks and currently has the following stable
conditions:
Reactor coolant temperature = 550°F
Reactor coolant boron concentration = 800 ppm
Source range count rate = 32 cps
A reactor coolant boron dilution is commenced. After two hours, with reactor coolant boron
concentration stable at 775 ppm, the source range count rate is stable at 48 cps.
Assume the differential boron worth (ΔK/K/ppm) remains constant throughout the dilution. Also
assume that reactor coolant temperature remains constant, control rod position does not change, and
no reactor protection actuations occur.
If the reactor coolant boron concentration is further reduced to750 ppm, what will be the status of the
reactor?

A

Subcritical, with a stable source range count rate of approximately 96 cps.

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27
Q

Refer to the drawing that shows a graph of fission rate versus time (see figure below). Both axes have
linear scales.
Which one of the following events, initiated at 0 seconds, could cause the reactor response shown on
the graph?

A

A step addition of positive reactivity to a reactor that is initially subcritical in the source range and
remains subcritical for the duration of the 60-second interval shown.

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28
Q

At the beginning of a reactor startup, Keff was 0.97 and the stable source range count rate was 40 cps.
After several incremental control rod withdrawals, the stable source range count rate was 400 cps.
The next incremental control rod withdrawal resulted in a stable source range count rate of 600 cps.
What is the current Keff?

A

0.998

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29
Q

During a reactor startup, the operator adds 1.0 %ΔK/K of positive reactivity by withdrawing control
rods, thereby increasing the stable source range count rate from 220 cps to 440 cps.
Approximately how much additional positive reactivity is required to raise the stable count rate to 880
cps?

A

0.5 %ΔK/K

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30
Q

Initially, a reactor is subcritical with a Keff of 0.97 and a stable source range count rate of 500 cps.
Which one of the following will be the approximate final steady-state count rate following a rod
withdrawal that adds 1.05 %ΔK/K?

A

750 cps

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31
Q

During a reactor startup, control rods are withdrawn such that Keff increases from 0.98 to 0.99. If the
stable source range count rate before the rod withdrawal was 500 cps, which one of the following will
be the final stable count rate?

A

1,000 cps

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32
Q

As a reactor approaches criticality during a reactor startup, it takes longer to reach an equilibrium
source range count rate after each control rod withdrawal due to the increased…

A

number of neutron generations required to reach a stable neutron level.

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33
Q

During a reactor startup, the first reactivity addition caused the stable source range count rate to
increase from 20 cps to 40 cps. The second reactivity addition caused the stable count rate to increase
from 40 cps to 80 cps. Keff was 0.92 prior to the first reactivity addition.
Which one of the following statements describes the magnitude of the reactivity additions?

A

The first reactivity addition was approximately twice as large as the second.

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34
Q

With Keff at 0.92 during a reactor startup, the stable source range count rate is noted to be 780 cps.
Later in the same startup, the stable count rate is 4,160 cps.
What is the current value of Keff?

A

0.985

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35
Q

Two reactors are currently shut down with reactor startups in progress. The reactors are identical
except that reactor A has a source neutron strength of 100 neutrons per second and reactor B has a
source neutron strength of 200 neutrons per second. The control rods are stationary and Keff is 0.98 in
both reactors. Core neutron levels have stabilized in both reactors.
Which one of the following lists the core neutron levels (neutrons per second) in reactors A and B?

A

Reactor A Reactor B
(n/sec) (n/sec)
5,000 10,000

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36
Q

With Keff at 0.95 during a reactor startup, source range indication is stable at 100 cps. After a number
of control rods have been withdrawn, source range indication stabilizes at 270 cps. What is the
current value of Keff?

A

0.981

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37
Q

A reactor startup is in progress with a current Keff of 0.95 and a stable source range count rate of
120 cps. Which one of the following stable count rates will occur when Keff becomes 0.97?

A

200 cps

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38
Q

A reactor startup is in progress with a current Keff of 0.95 and a stable source range count rate of
150 cps. Which one of the following stable count rates will occur when Keff becomes 0.98?

A

375 cps

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39
Q

With Keff at 0.95 during a reactor startup, source range indication is stable at 120 cps. After a period
of control rod withdrawal, source range indication stabilizes at 600 cps.
What is the current value of Keff?

A

0.99

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40
Q

A reactor is shutdown with a Keff of 0.8. The source range count rate is stable at 800 cps. What
percentage of the core neutron population is being contributed directly by neutron sources other than
neutron-induced fission?

A

20 percent

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41
Q

During a reactor startup, positive reactivity addition X caused the stable source range count rate to
increase from 20 cps to 40 cps. Later in the startup, after several more additions of positive
reactivity, positive reactivity addition Y caused the stable source range count rate to increase from
320 cps to 640 cps.
Which one of the following statements describes how the magnitudes of the two positive reactivity
additions (X and Y) compare?

A

Reactivity addition X was several times greater in magnitude than reactivity addition Y.

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42
Q

A subcritical reactor has a stable source range count rate of 2.0 x 105 cps with a Keff of 0.98. Positive
reactivity is added to the core until a stable count rate of 5.0 x 105 cps is achieved. What is the current
value of Keff?

A

0.992

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43
Q

A reactor is shutdown with a Keff of 0.8. The source range count rate is stable at 800 cps. What
percentage of the core neutron population is being contributed directly by neutron-induced fission?

A

80 percent

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44
Q

A reactor is shutdown with a Keff of 0.96. The source range count rate is stable at 480 cps. What
percentage of the core neutron population is being contributed directly by neutron sources other than
neutron-induced fission?

A

4 percent

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45
Q

During a reactor startup, positive reactivity addition X caused the stable source range count rate to
increase from 15 cps to 30 cps. Later in the startup, after several more positive reactivity additions,
positive reactivity addition Y caused the stable source range count rate to increase from 60 cps to
120 cps.
With the reactor still subcritical, which one of the following statements describes how the magnitudes
of positive reactivity additions X and Y compare?

A

Positive reactivity addition X was greater than positive reactivity addition Y.

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46
Q

As criticality is approached during a reactor startup, equal insertions of positive reactivity result in a
__________ numerical change in the stable source range count rate and a __________ time to reach
each new stable count rate.

A

larger; longer

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47
Q

A reactor startup is in progress with a stable source range count rate and the reactor is near criticality.
Which one of the following statements describes count rate characteristics during and after a 5-second
control rod withdrawal? (Assume the reactor remains subcritical.)

A

The count rate will rapidly increase (prompt jump), then gradually increase and stabilize at a
higher value.

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48
Q

During an initial fuel load, the subcritical multiplication factor increases from 1.0 to 4.0 as the first 100
fuel assemblies are loaded. What is Keff after the first 100 fuel assemblies are loaded?

A

0.75

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49
Q

Refer to the drawing of three 1/M plots labeled A, B, and C (see figure below). Each axis has linear
units.
The least conservative approach to criticality is represented by plot __________; which could possibly
result from recording source range count rates at __________ time intervals after incremental fuel
loading steps as compared to the conditions represented by the other plots.

A

c; shorter

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50
Q

A reactor startup is in progress for a reactor that is in the middle of a fuel cycle. The reactor coolant
system is at normal operating temperature and pressure. The main steam isolation valves are open
and the main turbine bypass (also called steam dump) valves are closed. The reactor is near
criticality.
Reactor startup rate (SUR) is stable at zero when, suddenly, a turbine bypass valve fails open and
remains stuck open, dumping steam to the main condenser. The operator immediately ensures no
control rod motion is occurring and takes no further action. Assume the steam generator water levels
remain stable, and no automatic reactor protective actions occur.
As a result of the valve failure, SUR will initially become __________; and reactor power will
stabilize __________ the point of adding heat.

A

positive; above

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51
Q

Refer to the drawing of a 1/M plot with curves A and B (see figure below). Each axis has linear units.
Curve A would result if each fuel assembly loaded during the early stages of the refueling caused a
relatively __________ fractional change in source range count rate compared to the later stages of the
refueling; curve B would result if each fuel assembly contained equal __________.

A

large; reactivity

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52
Q

During an initial fuel load, the subcritical multiplication factor increases from 1.0 to 8.0. What is the
current value of Keff?

A

0.875

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53
Q

Refer to the drawing of a 1/M plot with curves A and B (see figure below). Each axis has linear units.
Curve A would result if each fuel assembly loaded during the early stages of core refueling caused a
relatively __________ fractional change in stable source range count rate compared to the later stages
of the refueling; curve B would result if each fuel assembly contained equal __________

A

small; reactivity

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54
Q

During a reactor startup, as Keff increases toward 1.0 the value of 1/M…

A

decreases toward zero.

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55
Q

The following data was obtained under stable conditions during a reactor startup:
Control Rod Position Source Range
(units withdrawn) Count Rate (cps)
0 20
10 25
15 28
20 33
25 40
30 50
Assuming uniform differential rod worth, at what approximate control rod position will criticality
occur?

A

46 to 55 units withdrawn

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56
Q

The following data was obtained under stable conditions during a reactor startup:
Control Rod Position Source Range
(units withdrawn) Count Rate (cps)
0 180
10 210
15 250
20 300
25 360
30 420
Assuming uniform differential rod worth, at what approximate control rod position will criticality
occur?

A

46 to 55 units withdrawn

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57
Q

The following data was obtained under stable conditions during a reactor startup:
Control Rod Position Source Range
(units withdrawn) Count Rate (cps)
0 180
5 200
10 225
15 257
20 300
25 360
30 450
Assuming uniform differential rod worth, at what approximate control rod position will criticality
occur?

A

50 units withdrawn

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58
Q

Control Rod Position Source Range
(units withdrawn) Count Rate(cps)
10 360
15 400
20 450
25 514
30 600
35 720
40 900

A

60 units withdrawn

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59
Q

An estimated critical rod position has been calculated for criticality to occur 4 hours after a reactor trip
from steady-state 100 percent power. The actual critical rod position will be lower than the estimated
critical rod position if…

A

the steam dump pressure setpoint is lowered by 100 psi prior to reactor startup.

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60
Q

Which one of the following is not required to determine the estimated critical boron concentration for
a reactor startup to be performed 48 hours following an inadvertent reactor trip?

A

Steam generator levels just prior to the trip

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61
Q

An estimated critical rod position (ECP) has been calculated for criticality to occur 6 hours after a
reactor trip from 60 days of operation at 100 percent power. Which one of the following events or
conditions will result in the actual critical rod position being lower than the ECP?

A

Steam generator pressures are decreased by 100 psi just prior to criticality.

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62
Q

Which one of the following conditions will result in criticality occurring at a rod position that is lower
than the estimated control rod position?

A

Adjusting reactor coolant system boron concentration to 50 ppm lower than assumed for startup
calculations.

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63
Q

An estimated critical rod position (ECP) has been calculated for criticality to occur 15 hours after a
reactor trip from long-term 100 percent power operation. Which one of the following conditions
would cause the actual critical rod position to be higher than the ECP?

A

Reactor criticality is achieved approximately 2 hours earlier than anticipated.

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64
Q

A reactor is subcritical with a startup in progress. Which one of the following conditions will result in
a critical rod position that is lower than the estimated critical rod position?

A

An inadvertent dilution of reactor coolant system boron concentration

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65
Q

Control rods are being withdrawn during a reactor startup. Which one of the following will result in
reactor criticality at a rod position that is higher than the estimated critical rod position?

A

Steam generator pressure increases by 50 psia.

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66
Q

A reactor startup is in progress following a reactor trip from steady-state 100 percent power. Which
one of the following conditions will result in criticality occurring at a rod position that is higher than
the estimated critical rod position?

A

Misadjusting the steam dump (turbine bypass) controller such that steam generator pressure is
maintained 50 psig higher than the required no-load setting.

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67
Q

An estimated critical rod position (ECP) has been calculated for criticality to occur 15 hours after a
reactor trip that ended three months of operation at 100 percent power.
Which one of the following will result in criticality occurring at a rod position that is lower than the
calculated ECP?

A

Using a pretrip reactor power of 90 percent to determine power defect.

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68
Q

A reactor trip has occurred from 100 percent reactor power and equilibrium xenon-135 conditions near
the middle of a fuel cycle. An estimated critical rod position (ECP) has been calculated using the
following assumptions:
$ Criticality occurs 24 hours after the trip.
$ Reactor coolant temperature is 550°F.
$ Reactor coolant boron concentration is 400 ppm.
Which one of the following will result in criticality occurring at a rod position that is higher than the
calculated ECP?

A

Misadjusting the steam dump (turbine bypass) controller such that reactor coolant temperature is
being maintained at 553°F.

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69
Q

A reactor trip has occurred from 100 percent power and equilibrium xenon-135 conditions near the
middle of a fuel cycle. An estimated critical rod position (ECP) has been calculated for the
subsequent reactor startup using the following assumptions:
$ Criticality occurs 24 hours after the trip.
$ Reactor coolant temperature is 550°F.
$ Reactor coolant boron concentration is 400 ppm.
Which one of the following will result in criticality occurring at a control rod position that is lower
than the calculated ECP?

A

Decreasing reactor coolant system boron concentration to 350 ppm

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70
Q

With Keff at 0.985, how much reactivity must be added to make a reactor exactly critical?

A

1.52 %ΔK/K

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71
Q

A reactor is subcritical by 1.0 %ΔK/K when the operator dilutes the reactor coolant system boron
concentration by 30 ppm. If differential boron worth is -0.025 %ΔK/K/ppm, the reactor is currently…

A

subcritical.

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72
Q

When a reactor is critical, reactivity is…

A

0.0 ΔK/K.

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73
Q

During a reactor startup, if the startup rate is constant and positive without any further reactivity
addition, then the reactor is…

A

supercritical.

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74
Q

Initially, a reactor is critical at 10,000 cps in the source range when a steam generator atmospheric
relief valve fails open. Assume end of fuel cycle conditions, no reactor trip, and no operator actions
are taken.
When the reactor stabilizes, the average reactor coolant temperature (Tave) will be __________ than
the initial Tave and reactor power will be __________ the point of adding heat.

A

less; greater than

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75
Q

A reactor startup is being performed following a one-month shutdown period. If the reactor is taken
critical and then stabilized at 10,000 cps in the source range, over the next 10 minutes the count rate
will…

A

remain constant.

76
Q

A reactor startup is in progress following a one-month shutdown. Upon reaching criticality, the
operator establishes a positive 0.5 DPM startup rate and stops control rod motion.
After an additional five minutes, reactor power will be __________ and startup rate will be
__________. (Assume reactor power remains below the point of adding heat.)

A

increasing; constant

77
Q

A reactor is critical at 1.0 x 10-6 percent power. Control rods are withdrawn for 5 seconds and then
stopped, resulting in a stable startup rate (SUR) of positive 0.2 DPM.
If the control rods had been inserted for 5 seconds instead of withdrawn, the stable SUR would have
been: (Assume equal absolute values of reactivity are added in both cases.)

A

less negative than -0.2 DPM because, compared to reactor power increases, reactor power
decreases are more limited by delayed neutrons.

78
Q

A reactor is critical well below the point of adding heat during a plant startup. A small amount of
positive reactivity is then added to the core, and a stable positive startup rate (SUR) is established.
With the stable positive SUR, the following power levels are observed:
Time Power Level
0 sec 3.16 x 10-7 percent
90 sec 1.0 x 10-5 percent

A

3.16 x 10^-5 percent

79
Q

Given:
C Reactors A and B are identical except that reactor A has an effective delayed neutron fraction of
0.0068 and reactor B has an effective delayed neutron fraction of 0.0052.
C Reactor A has a stable period of 45 seconds and reactor B has a stable period of 42 seconds.
C Both reactors are initially operating at 1.0 x 10^-8 percent power.
The reactor that is supercritical by the greater amount of positive reactivity is reactor __________; and
the first reactor to reach 1.0 x 10^-1 percent power will be reactor __________

A

A; B

80
Q

A reactor is currently operating in the source range with a stable positive 90-second period. The core
effective delayed neutron fraction (β�eff) is 0.006. How much additional positive reactivity is needed
to establish a stable positive 60-second period?

A

0.026 %ΔK/K

81
Q

A reactor is critical near the end of a fuel cycle with power level stable at 1.0 x 10-10 percent. Which
one of the following is the smallest listed amount of positive reactivity that is capable of increasing
reactor power level to the point of adding heat?

A

0.001 %ΔK/K

82
Q

Reactors A and B are identical except that reactor A has an effective delayed neutron fraction of 0.007
and reactor B has an effective delayed neutron fraction of 0.006. Initially, both reactors are critical at
1.0 x 10-8 percent power when +0.1 %ΔK/K is simultaneously added to both reactors.
Five minutes after the reactivity additions, reactor _____ will be at the higher power level; and reactor
_____ will have the higher startup rate.

A

B; B

83
Q

Given:
C Reactors A and B are identical except that reactor A has an effective delayed neutron fraction of
0.0055 and reactor B has an effective delayed neutron fraction of 0.0052.
C Reactor A has a stable period of 42 seconds and reactor B has a stable period of 45 seconds.
C Both reactors pass through 1.0 x 10-8 percent power at the same instant.
The reactor that is supercritical by the greater amount of positive reactivity is reactor __________; and
the first reactor to reach 1.0 x 10-1 percent power will be reactor __________

A

A; A

84
Q

Reactors A and B are identical except that reactor A is operating near the beginning of a fuel cycle,
while reactor B is operating near the end of a fuel cycle. Both reactors have the same value for Keff,
which is slightly greater than 1.0.
If both reactors pass through 1.0 x 10-6 percent reactor power at the same time, which reactor, if any,
will reach the point of adding heat (POAH) first, and why?

A

Reactor B, because it has the greater startup rate.

85
Q

A reactor and plant startup is in progress. Reactor power is currently 5.0 x 10^-5 percent and
increasing, with a constant startup rate of 0.2 DPM. Reactivity is not changing.
The reactor is currently __________, at a power level that is __________ the point of adding heat

A

supercritical; less than

86
Q

Which one of the following indicates that a reactor has achieved criticality during a normal reactor
startup?

A

Constant positive startup rate with no rod motion.

87
Q

A reactor startup is in progress. Control rod withdrawal was stopped several minutes ago to assess
criticality. Which one of the following is a combination of indications that together support a
declaration that the reactor has reached criticality?

A

Startup rate is stable at 0.2 DPM; source range count rate is slowly increasing.

88
Q

A reactor has just achieved criticality at 1.0 x 10-8 percent reactor power during a reactor startup from
xenon-free conditions. The operator establishes a 0.5 DPM startup rate to increase power. Over a
period of 10 minutes, startup rate decreases to zero and then becomes increasingly negative.
Which one of the following is a possible cause for these indications?

A

Inadvertent boration of the reactor coolant system

89
Q

During a reactor startup from a xenon-free condition, and after recording critical data, the operator
establishes a positive 0.4 DPM startup rate to increase power. Within 10 minutes, and prior to
reaching the point of adding heat, reactor power stops increasing and begins to slowly decrease.
Which one of the following changes could have caused this behavior?

A

Inadvertent boration of the RCS.

90
Q

After taking critical data during a reactor startup, the operator establishes a positive 1.0 DPM startup
rate to increase power to the point of adding heat (POAH). Which one of the following is the
approximate amount of reactivity needed to stabilize reactor power at the POAH? (Assume that β�eff
= 0.00579.)

A

-0.16 %ΔK/K

91
Q

The point of adding heat can be defined as the power level at which the reactor is producing enough
heat…

A

to cause a measurable temperature increase in the fuel and coolant.

92
Q

After taking critical data during a reactor startup, the operator establishes a positive 0.54 DPM startup
rate to increase reactor 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 β�eff = 0.00579.)

A

-0.10 %ΔK/K

93
Q

A reactor startup is in progress following a one-month shutdown. Upon reaching criticality, the
operator establishes a stable positive 1.0 DPM startup rate and stops rod motion.
After an additional 30 seconds, reactor power will be __________ and startup rate will be
__________. (Assume reactor power remains below the point of adding heat.)

A

increasing; constant

94
Q

A reactor is critical during a xenon-free reactor startup. Reactor power is increasing in the
intermediate range with a stable 0.5 DPM startup rate (SUR).
Assuming no operator action is taken that affects reactivity, SUR will remain constant until…

A

fuel temperature begins to increase, then SUR will decrease.

95
Q

After taking critical data during a reactor startup, the operator establishes a positive 0.75 DPM startup
rate to increase power to the point of adding heat (POAH). Which one of the following is the
approximate amount of reactivity needed to stabilize reactor power at the POAH? (Assume β�eff =
0.0066.)

A

-0.15 %ΔK/K

96
Q

After taking critical data during a reactor startup, the operator establishes a positive 0.52 DPM startup
rate to increase power to the point of adding heat (POAH). Which one of the following is the
approximate amount of reactivity needed to stabilize reactor power at the POAH? (Assume β�eff =
0.006.)

A

-0.10 %ΔK/K

97
Q

During a xenon-free reactor startup, critical data was inadvertently taken two decades below the
required intermediate range (IR) power level. The critical data was taken again at the proper IR
power level with the same reactor coolant temperature and boron concentration.
The critical rod position taken at the proper IR power level is __________ the critical rod position
taken two decades below the proper IR power level.

A

the same as

98
Q

During a xenon-free reactor startup, critical data was inadvertently taken one decade above the
required intermediate range (IR) power level. The critical data was taken again at the proper IR
power level with the same reactor coolant temperature and boron concentration.
The critical rod position taken at the proper IR power level is __________ the critical rod position
taken one decade above the proper IR power level.

A

the same as

99
Q

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
prior to reaching the POAH, reactor power will stabilize…

A

higher than the initial power level but below the POAH.

100
Q

A reactor has just achieved criticality during a xenon-free reactor startup and power is being increased
to take critical data. Instead of stabilizing power at 1.0 x 10^-5 percent per the startup procedure, the
operator inadvertently stabilizes power at 1.0 x 10^-4 percent.
Assuming reactor coolant system (RCS) temperature and RCS boron concentration do not change, the
critical rod height at 1.0 x 10^-4 percent power will be __________ the critical rod height at 1.0 x 10^-5
percent power.

A

equal to

101
Q

A reactor is exactly critical two decades below the point of adding heat when -0.01 %ΔK/K of
reactivity is added. If +0.01 %ΔK/K is added 2 minutes later, reactor power will stabilize at…

A

somewhat lower than the initial power level.

102
Q

Initially, a reactor is critical at 1.0 x 10-5 percent power near the middle of a fuel cycle with manual rod
control when a steam generator relief valve fails open. Assume no operator actions are taken and the
reactor does not trip.
When the reactor stabilizes, average reactor coolant temperature will be __________ the initial reactor
coolant temperature; and reactor power will be __________ the point of adding heat.

A

less than; greater than

103
Q

A reactor is critical at the point of adding heat (POAH) when a small amount of negative reactivity is
added. If the same amount of positive reactivity is added approximately 5 minutes later, reactor
power will…

A

quickly stabilize at a power level below the POAH.

104
Q

A reactor was operating at 1.0 x 10-3 percent power with a positive 0.6 DPM startup rate when an
amount of negative reactivity was inserted that caused reactor power to decrease with a negative
0.4 DPM startup rate.
If an equal amount of positive reactivity is added 5 minutes later, reactor power will…

A

increase and stabilize at the point of adding heat.

105
Q

A reactor is slightly supercritical during a reactor startup. A short control rod withdrawal is
performed to establish the desired positive startup rate. Assume that the reactor remains slightly
supercritical after the control rod withdrawal, and that reactor power remains well below the point of
adding heat.
Immediately after the control rod withdrawal is stopped, the startup rate will initially decrease and
then…

A

stabilize at a positive value.

106
Q

Refer to the figure below for the following question. The axes on each graph have linear scales.
Initially, a reactor is critical in the source range. At 0 seconds, a constant rate addition of positive
reactivity commences. Assume that reactor power remains below the point of adding heat for the
entire time interval shown.
The general response of startup rate to this event is shown on graph _____; and the general response of
reactor power to this event is shown on graph _____. (Note: Either graph may be chosen once, twice,
or not at all.)

A

A; A

107
Q

Refer to the drawing that shows a graph of startup rate versus time (see figure below). Both axes have
linear scales.
Which one of the following events, initiated at 0 seconds, would cause the reactor response shown on
the graph?

A

A constant rate of positive reactivity addition to a reactor that is initially critical in the source range
and remains below the point of adding heat for the duration of the 120-second interval shown

108
Q

During a reactor startup, source range count rate is observed to double every 30 seconds. Which one
of the following is the approximate startup rate?

A

0.6 DPM

109
Q

Refer to the drawing that shows a graph of fission rate versus time (see figure below). Both axes have
linear scales.
Which one of the following events, initiated at 0 seconds, would cause the reactor response shown on
the graph?

A

A step addition of positive reactivity to a reactor that is initially critical in the source range and
remains below the point of adding heat for the duration of the 120-second interval shown.

110
Q

Refer to the drawing that shows a graph of startup rate versus time (see figure below) for a reactor.
Both axes have linear scales.
Which one of the following events, initiated at 0 seconds, would cause the startup rate response shown
on the graph?

A

A controlled constant rate of positive reactivity addition to a reactor that is initially critical in the
source range and remains below the point of adding heat. The positive reactivity addition ends at
120 seconds.

111
Q

A reactor is critical below the point of adding heat (POAH). The operator adds enough reactivity to
attain a startup rate of 0.5 decades per minute. Which one of the following will decrease first when
the reactor reaches the POAH?

A

Startup rate

112
Q

For a slightly supercritical reactor operating below the point of adding heat (POAH), what reactivity
effects are associated with reaching the POAH?

A

An increase in fuel temperature will begin to create a negative reactivity effect.

113
Q

A reactor is operating at a stable power level just above the point of adding heat. To raise reactor
power to a higher stable power level, the operator must increase…

A

steam demand

114
Q

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 and fuel temperature

115
Q

A reactor startup is in progress near the end of a fuel cycle. Reactor power is 5 x 10-2 percent and
increasing slowly with a stable 0.3 DPM startup rate. Assuming no operator action, no reactor trip,
and no steam release, what will reactor power be after 10 minutes?

A

1 percent (point of adding heat)

116
Q

A reactor startup is in progress near the end of a fuel cycle. Reactor power is 5 x 10-3 percent and
increasing slowly with a stable 0.3 DPM startup rate. Assuming no operator action, no reactor trip,
and no steam release, what will reactor power be after 10 minutes?

A

At the POAH.

117
Q

Near the end of a fuel cycle, a reactor required three hours to increase power from 70 percent to 100
percent using only reactor coolant system (RCS) boron dilution at the maximum rate to control RCS
temperature.
Following a refueling outage, the same reactor power change performed under the same conditions
will require a __________ period of time because the rate at which RCS boron concentration can be
decreased at the beginning of a fuel cycle is __________.

A

shorter; faster

118
Q

With a reactor on a constant startup rate, which one of the following power changes requires the
longest time to occur?

A

1.0 x 10^-8 percent to 4.0 x 10^-8 percent

119
Q

With a reactor on a constant startup rate, which one of the following power changes requires the least
amount of time to occur?

A

4.0 x 10^-7 percent to 6.0 x 10^-7 percent

120
Q

With a reactor on a constant startup rate, which one of the following power changes requires the
longest amount of time to occur?

A

5.0 x 10^-8 percent to 1.5 x 10^-7 percent

121
Q

Initially, a reactor is stable at the point of adding heat (POAH) during a reactor startup with the
average reactor coolant temperature at 550°F. Control rods are manually withdrawn a few inches to
increase steam generator steaming rate.
When the reactor stabilizes, reactor power will be __________ the POAH, and average reactor coolant
temperature will be __________ 550°F.

A

greater than; greater than

122
Q

With a reactor on a constant startup rate, which one of the following power changes requires the least
amount of time to occur?

A

3.0 x 10^-8 percent to 5.0 x 10^-8 percent

123
Q

A nuclear power plant is operating at 100 percent power near the end of a fuel cycle with all control
systems in manual. The reactor operator inadvertently adds 100 gallons of boric acid (4 percent by
weight) to the reactor coolant system (RCS).
Which one of the following will occur as a result of the boric acid addition? (Assume a constant main
generator output.)

A

Pressurizer level will decrease and stabilize at a lower value.

124
Q

A nuclear power plant was operating with the following initial steady-state conditions:
Power level = 100 percent
Reactor coolant boron concentration = 620 ppm
Average reactor coolant temperature = 587°F
After a load decrease, the current steady-state conditions are as follows:
Power level = 80 percent
Reactor coolant boron concentration = 650 ppm
Average reactor coolant temperature = 577°F
Given the following information, how much reactivity was added by control rod movement during the
load decrease? (Disregard any changes in fission product poison reactivity.)
Differential boron worth = -1.0 x 10-2 %ΔK/K/ppm
Total power coefficient = -1.5 x 10-2 %ΔK/K/%
Moderator temperature coefficient = -2.0 x 10-2 %ΔK/K/°F

A

0.0 %ΔK/K

125
Q

A nuclear power plant was operating with the following initial steady-state conditions:
Power level = 100 percent
Reactor coolant boron concentration = 630 ppm
Average reactor coolant temperature = 582°F
After a load decrease, the current steady-state conditions are as follows:
Power level = 80 percent
Reactor coolant boron concentration = 640 ppm
Average reactor 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 %ΔK/K/%
Moderator temperature coefficient = -2.0 x 10-2 %ΔK/K/°F
Differential boron worth = -1.5 x 10-2 %ΔK/K/ppm

A

-0.15 %ΔK/K

126
Q

A nuclear power plant was operating with the following initial steady-state conditions:
Power level = 80 percent
Reactor coolant boron concentration = 630 ppm
Average reactor coolant temperature = 582°F
After a normal load decrease, the current steady-state conditions are as follows:
Power level = 50 percent
Reactor coolant boron concentration = 650 ppm
Average reactor 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 %ΔK/K/%
Moderator temperature coefficient = -2.0 x 10-2 %ΔK/K/°F
Differential boron worth = -1.5 x 10-2 %ΔK/K/ppm

A

0.15 %ΔK/K

127
Q

A nuclear power plant was operating with the following initial steady-state conditions:
Power level = 100 percent
Reactor coolant boron concentration = 620 ppm
Average reactor coolant temperature = 587°F
After a load decrease, the current steady-state conditions are as follows:
Power level = 80 percent
Reactor coolant boron concentration = 630 ppm
Average reactor 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 %ΔK/K/%
Moderator temperature coefficient = -2.0 x 10-2 %ΔK/K/°F
Differential boron worth = -1.0 x 10-2 %ΔK/K/ppm

A

-0.2 %ΔK/K

128
Q

One week after a refueling outage, a nuclear power plant is currently operating at 80 percent power
with control rods fully withdrawn. During the outage, the entire core was replaced by new fuel
assemblies, and new burnable poison assemblies were installed at various locations.
Assume reactor power and control rod position do not change during the next week. If no operator
action is taken, how and why will average reactor coolant temperature change during the next week?

A

Decrease slowly, due to fuel burnup and fission product poison buildup.

129
Q

How do the following parameters change during a normal ramp of reactor power from 15 percent to 75
percent?

A

Main Turbine First Reactor Coolant System
Stage Pressure Boron Concentration
Increases Decreases

130
Q

A refueling outage has just been completed, during which one-third of the core was replaced with new
fuel assemblies. A reactor startup has been performed to begin the sixth fuel cycle, and reactor power
is being increased to 100 percent.
Which one of the following pairs of reactor fuels will provide the greatest contribution to core heat
production when the reactor reaches 100 percent power?

A

U-235 and Pu-239

131
Q

A nuclear power plant is operating at 100 percent power near the end of a fuel cycle. The greatest
contribution to core heat production is being provided by the fission of…

A

U-235 and Pu-239.

132
Q

A refueling outage has just been completed, during which the entire core was offloaded and replaced
with new fuel. A reactor startup has been performed and power is being increased to 100 percent.
Which one of the following pairs of reactor fuels will provide the greatest contribution to core heat
production when the reactor reaches 100 percent power

A

U-235 and U-238

133
Q

A reactor is critical at 2.0 x 10^-8 percent power. The operator withdraws rods as necessary to
immediately establish and maintain a positive 0.1 DPM startup rate. How long will it take the reactor
to reach 7.0 x 10^-8 percent power?

A

5.4 minutes

134
Q

A reactor is critical at 3.0 x 10^-8 percent power. The operator withdraws rods as necessary to
immediately establish and maintain a positive 0.1 DPM startup rate. How long will it take the reactor
to reach 7.0 x 10^-8 percent power?

A

3.7 minutes

135
Q

A reactor startup is in progress and criticality has just been achieved. After recording the critical rod
heights, the operator withdraws control rods for 20 seconds to establish a stable positive 0.5 DPM
startup rate (SUR). One minute later (prior to reaching the point of adding heat), the operator inserts
the same control rods for 25 seconds.

A

Prior to the control rods passing through the critical rod height.

136
Q

A reactor startup is in progress with the reactor at normal operating temperature and pressure. With
reactor power stable at the point of adding heat, a control rod malfunction causes an inadvertent rod
withdrawal that results in adding 0.3 %ΔK/K reactivity.
Given:
$ All control rod motion has been stopped.
$ No automatic system or operator actions occur to inhibit the power increase.
$ Power coefficient equals -0.04 %ΔK/K/percent.
$ The effective delayed neutron fraction equals 0.006.
What is the reactor power level increase required to offset the reactivity added by the inadvertent
control rod withdrawal? (Ignore any reactivity effects from changes in fission product poisons.)

A

7.5 percent

137
Q

A reactor startup is in progress with the reactor at normal operating temperature and pressure. With
reactor power level stable at the point of adding heat, a control rod malfunction causes an inadvertent
rod withdrawal that results in adding 0.2 %ΔK/K reactivity.
Given:
$ All control rod motion has been stopped.
$ No automatic system or operator actions occur to inhibit the power increase.
$ Power coefficient equals -0.04 %ΔK/K/percent.
$ The effective delayed neutron fraction equals 0.006.
What is the reactor power level increase required to offset the reactivity added by the inadvertent
control rod withdrawal? (Ignore any reactivity effects from changes in fission product poisons.)

A

5.0 percent

138
Q

A reactor startup is in progress with the reactor at normal operating temperature and pressure. With
reactor power level stable at the point of adding heat, a control rod malfunction causes a short rod
withdrawal that increases reactivity by 0.14 %ΔK/K.
Given:
$ All control rod motion has stopped.
$ No automatic system or operator actions occur to inhibit the power increase.
$ Power coefficient equals -0.028 %ΔK/K/percent.
$ The effective delayed neutron fraction equals 0.006.
What is the reactor power level increase required to offset the reactivity added by the control rod
withdrawal? (Ignore any reactivity effects from changes in fission product poisons.)

A

5.0 percent

139
Q

A reactor startup is in progress with the reactor at normal operating temperature and pressure. With
reactor power stable at the point of adding heat, a control rod malfunction causes an inadvertent
control rod withdrawal that adds positive 0.32 %ΔK/K to the reactor.
Given:
$ All control rod motion has stopped.
$ No automatic system or operator actions occur to inhibit the power increase.
$ Power coefficient equals -0.02 %ΔK/K/percent.
$ The effective delayed neutron fraction equals 0.005.
What is the power level increase required to offset the reactivity added by the control rod withdrawal?
(Ignore any reactivity effects from changes in fission product poisons.)

A

16 percent

140
Q

A reactor is operating at steady-state 80 percent power near the end of a fuel cycle with a symmetrical
axial power distribution peaked at the core midplane. Control rods are in manual control.
If the reactor coolant system (RCS) boron concentration is increased by 10 ppm, the axial power
distribution will shift toward the __________ of the core. Then, if the control rods are repositioned to
return RCS temperatures to normal for 80 percent power, the axial power distribution will shift toward
the __________ of the core.

A

top; top

141
Q

A reactor is operating at steady-state 80 percent power near the end of a fuel cycle with a symmetrical
axial power distribution peaked at the core midplane. Control rods are in manual control.
If the reactor coolant system (RCS) boron concentration is decreased by 10 ppm, the axial power
distribution will shift toward the __________ of the core. Then, if the control rods are repositioned to
return RCS temperatures to normal for 80 percent power, the axial power distribution will shift toward
the __________ of the core.

A

bottom; bottom

142
Q

A nuclear power plant has been operating at 75 percent power for several weeks when a partial main
steam line break occurs that releases 3 percent of rated steam flow. Assuming no operator or
automatic actions occur, reactor power will stabilize __________ 75 percent; and average reactor
coolant temperature will stabilize at a __________ temperature.

A

greater than; lower

143
Q

A reactor is critical at a stable power level below the point of adding heat (POAH). An unisolable
steam line break occurs and 3 percent of rated steam flow is escaping.
Assuming no reactor trip, which one of the following describes the response of the reactor?

A

Reactor coolant average temperature will decrease. The reactor will stabilize at 3 percent power.

144
Q

A nuclear power plant has been operating at 80 percent power for several weeks when a partial steam
line break occurs that releases 2 percent of rated steam flow. Main turbine load and control rod
position remain the same.
Assuming no operator or protective actions occur, when the plant stabilizes reactor power will be
__________; and average reactor coolant temperature will be __________.

A

higher; lower

145
Q

A nuclear power plant is operating at steady-state 85 percent power and 580°F average reactor coolant
temperature (Tave) near the end of a fuel cycle. A failure of the turbine control system opens the
turbine control valves to admit 10 percent more steam flow to the main turbine. No operator actions
occur and no protective system actuations occur. Rod control is in manual.
Following the transient, reactor power will stabilize __________ 85 percent; and Tave will stabilize
__________ 580°F.

A

above; below

146
Q

A nuclear power plant is operating at steady-state 90 percent power near the end of a fuel cycle with
manual rod control when a turbine control system malfunction opens the main turbine steam inlet
valves an additional 5 percent. Reactor power will initially…

A

increase, because the rate of neutron absorption at U-238 resonant energies initially decreases.

147
Q

A nuclear power plant is operating at 100 percent power near the end of a fuel cycle when the main
turbine trips. If the reactor does not immediately trip, reactor power will initially…

A

decrease, due to negative reactivity from the moderator temperature coefficient.

148
Q

A nuclear power plant is operating at steady-state 80 percent power and 580°F average reactor coolant
temperature (Tave) near the end of a fuel cycle with manual rod control. A turbine control system
malfunction partially closes the turbine control valves resulting in 5 percent less steam flow to the
main turbine. No operator actions occur and no protective system actuations occur.
Following the transient, reactor power will stabilize __________ 80 percent; and Tave will stabilize
__________ 580°F.

A

below; above

149
Q

A nuclear power plant is operating at steady-state 60 percent power in the middle of a fuel cycle with
manual rod control when a turbine control system malfunction closes the turbine steam inlet valves an
additional 5 percent. Which one of the following is most responsible for the initial reactor power
decrease?

A

The rate of neutron absorption by the fuel at resonance energies initially increases.

150
Q

A multi-loop nuclear power plant is operating at steady-state 50 percent power with manual rod
control when the main steam isolation valve (MSIV) for one steam generator inadvertently closes.
Assume that no reactor trip or other protective action occurs, and no operator action is taken.
Immediately after the MSIV closure, the cold leg temperature (Tcold) in the reactor coolant loop with
the closed MSIV will initially __________; and the Tcold in a loop with an open MSIV will initially
__________.

A

increase; decrease

151
Q

A nuclear power plant is operating at steady-state 60 percent power in the middle of a fuel cycle with
manual rod control when a turbine control system malfunction opens the main turbine steam inlet
valves an additional 5 percent. Which one of the following is responsible for the initial reactor power
increase?

A

The rate of neutron absorption at U-238 resonance energies initially decreases.

152
Q

Initially, a nuclear power plant is operating at steady-state 100 percent reactor power with the main
generator producing 1,100 MW. Then, a power grid disturbance occurs and appropriate operator
actions are taken. The plant is stabilized with the following current conditions:
• Main generator output is 385 MW.
• Steam dump/bypass system is discharging 15 percent of rated steam flow to the main
condenser.
• All reactor coolant system parameters are in their normal ranges.
What is the approximate current reactor power level?

A

50 percent

153
Q

A high boron concentration is necessary at the beginning of a fuel cycle to…

A

compensate for excess reactivity in the fuel.

154
Q

During a refueling outage, new fuel assemblies with higher enrichments of U-235 were loaded to
prolong the fuel cycle from 12 months to 16 months. What is a possible consequence of offsetting all
the excess positive reactivity of the new fuel assemblies with a higher concentration of boron in the
reactor coolant?

A

An RCS temperature decrease may result in a negative reactivity addition.

155
Q

Shortly after a reactor trip, reactor power indicates 5.0 x 10^-2 percent when a stable negative startup
rate is attained. Approximately how much additional time is required for reactor power to decrease to
5.0 x 10^-3 percent?

A

180 seconds

156
Q

A nuclear power plant has been operating at 100 percent power for several weeks when a reactor trip
occurs. How much time will be required for core decay heat production to decrease to one percent
power following the trip?

A

1 to 8 hours

157
Q

Which one of the following determines the value of the stable negative startup rate observed shortly
after a reactor trip?

A

The longest-lived delayed neutron precursors

158
Q

Shortly after a reactor trip, reactor power indicates 1.0 x 10^-3 percent when a stable negative startup
rate is attained. Reactor power will decrease to 1.0 x 10^-4 percent in approximately _______ seconds.

A

180

159
Q

Following a reactor trip, reactor power indicates 0.1 percent when the typical stable post-trip startup
rate is observed. Approximately how much additional time is required for reactor power to decrease
to 0.05 percent?

A

55 seconds

160
Q

Which one of the following approximates the fission product decay heat produced in a reactor at one
second and one hour following a reactor trip from long-term operation at 100 percent power?

A

One Second One Hour

7 percent 1 percent

161
Q

Reactors A and B are identical and have operated at 100 percent power for six months when a reactor
trip occurs simultaneously on both reactors. All control rods fully insert, except for one reactor B
control rod that remains fully withdrawn.
Which reactor, if any, will have the smaller negative startup rate five minutes after the trip, and why?

A

Both reactors will have the same startup rate because only the longest-lived delayed neutron
precursors will be releasing fission neutrons.

162
Q

Reactors A and B are identical and have operated at 100 percent power for six months when a reactor
trip occurs simultaneously on both reactors. All reactor A control rods fully insert. One reactor B
control rod sticks fully withdrawn.
Which reactor, if any, will have the smaller negative startup rate five minutes after the trip, and why?

A

Both reactors will have the same startup rate because only the longest-lived delayed neutron
precursors will be releasing fission neutrons.

163
Q

Reactors A and B are identical and have operated at 100 percent power for six months when a reactor
trip occurs simultaneously on both reactors. All reactor A control rods fully insert. One reactor B
control rod sticks fully withdrawn, but all others fully insert.
Five minutes after the trip, when compared to reactor B the fission rate in reactor A will be
__________; and the startup rate in reactor A will be __________.

A

smaller; the same

164
Q

A reactor is critical just below the point of adding heat when an inadvertent reactor trip occurs. All
control rods fully insert except for one rod, which remains fully withdrawn. Five minutes after the
reactor trip, with reactor startup rate (SUR) stable at approximately -1/3 DPM, the remaining
withdrawn control rod suddenly drops (fully inserts).
Which one of the following describes the reactor response to the drop of the last control rod?

A

SUR will immediately become more negative, and then return to and stabilize at approximately
-1/3 DPM.

165
Q

A nuclear power plant is operating at steady-state 100 percent power when a reactor trip occurs. As a
result of the trip, the core neutron flux will initially decrease at a startup rate that is much __________
negative than -1/3 DPM; the startup rate will become approximately -1/3 DPM about __________
minutes after the trip

A

more; 3

166
Q 
Refer to the graph of neutron flux versus time (see figure below) for a nuclear power plant reactor that
experienced a reactor trip from extended full power operation at time = 0 seconds.
Which section(s) of the curve has/have a slope that is primarily determined by the production rate of
delayed neutrons?
A

B and C

167
Q

Refer to the graph of neutron flux versus time (see figure below) for a nuclear power plant that
experienced a reactor trip from extended full power operation at time = 0 seconds.
In which section of the curve does the production rate of source neutrons primarily determine the slope
of the curve?

A

D

168
Q

A reactor was operating for several months at 100 percent power when a reactor trip occurred. Which
one of the following is primarily responsible for the startup rate value 2 minutes after the trip?

A

The decay rates of the delayed neutron precursors in the core.

169
Q

Refer to the graph of neutron flux versus time (see figure below) for a nuclear power plant that
experienced a reactor trip from steady-state 100 percent power at time = 0 seconds.
The shape of section A on the graph is primarily determined by a rapid decrease in the production rate
of…

A

prompt fission neutrons.

170
Q

A reactor was operating for several months at steady-state 100 percent power when a reactor trip
occurred. Which one of the following lists the two factors most responsible for the value of the core
neutron flux level one hour after the trip?

A

Keff and the rate of source neutron production.

171
Q

A reactor is critical below the point of adding heat when a fully withdrawn control rod fully inserts into
the core. Assuming no operator or automatic actions, core neutron flux will slowly decrease to…

A

an equilibrium value greater than the source neutron flux

172
Q

A reactor is critical just below the point of adding heat when a single fully withdrawn control rod drops
into the core. Assuming no operator or automatic actions occur, when the plant stabilizes reactor
power will be __________; and average reactor coolant temperature will be __________.

A

lower; the same

173
Q

Initially, a reactor is critical in the source range during a reactor startup when the control rods are
inserted a small amount. Reactor startup rate stabilizes at -0.15 DPM. Assuming startup rate
remains constant, how long will it take for source range count rate to decrease by one-half?

A

2.0 minutes

174
Q

Initially, a reactor was critical just below the point of adding heat during a normal reactor startup when
a reactivity event caused a rapid insertion of negative reactivity. No subsequent changes to reactivity
occurred.
Ten seconds after the completion of the negative reactivity insertion, the startup rate was observed to
be stable at – 0.24 DPM. Was the reactivity event a reactor trip or a dropped fully-withdrawn control
rod, and why?

A

A dropped fully-withdrawn control rod, because a reactor trip will not produce a stable negative
startup rate 10 seconds after the completion of the negative reactivity insertion

175
Q

Which one of the following is the reason for inserting control rods in a predetermined sequence during
a normal reactor shutdown?

A

To prevent abnormally high local power peaks.

176
Q

Which one of the following describes how control rods are inserted during a normal reactor shutdown,
and why?

A

In a bank overlapping sequence, to maintain a relatively constant differential control rod worth.

177
Q

After one month of operation at 100 percent power, the fraction of rated thermal power being produced
from the decay of fission products in a reactor is…

A

greater than 5 percent, but less than 10 percent.

178
Q

The magnitude of decay heat generation is determined primarily by…

A

power history

179
Q

Following a reactor shutdown from three months of operation at 100 percent power, the core decay
heat production rate will depend on the…

A

time elapsed since Keff decreased below 1.0.

180
Q

A nuclear power plant had been operating at 100 percent power for six months when a steam line
rupture occurred that resulted in a reactor trip and all steam generators (SGs) blowing down
(emptying) after approximately 1 hour. The SG blowdown caused reactor coolant system (RCS)
temperature to decrease to 400°F, at which time the SGs became empty and an RCS heatup began.
Given the following information:
Reactor rated thermal power = 3,400 MW
Decay heat rate = 1.0 percent rated thermal power
Reactor coolant pump heat input to the RCS = 15 MW
RCS total heat loss rate = Negligible
RCS specific heat = 1.1 Btu/lbm-°F
RCS inventory (less pressurizer) = 475,000 lbm
What will the average RCS heatup rate be during the 5 minutes immediately after all SGs became
empty?

A

300 to 350 °F/hr

181
Q

A nuclear power plant had been operating at 100 percent power for six months when a steam line
rupture occurred that resulted in a reactor trip and all steam generators (SGs) blowing down
(emptying) after approximately 1 hour. The SG blowdown caused reactor coolant system (RCS)
temperature to decrease to 400°F, at which time the SGs became empty and an RCS heatup began.
Given the following information:
Reactor rated thermal power = 2,400 MW
Decay heat rate = 1.0 percent rated thermal power
Reactor coolant pump heat input to the RCS = 13 MW
RCS total heat loss rate = 2.4 MW
RCS specific heat = 1.1 Btu/lbm-°F
RCS inventory (less pressurizer) = 325,000 lbm
What will the average RCS heatup rate be during the 5 minutes immediately after all SGs became
empty?

A

300 to 400 °F/hr

182
Q

A reactor has been shut down for several weeks when a loss of all AC power results in a loss of forced
coolant flow in the reactor coolant system (RCS).
Given the following information:
Reactor rated thermal power = 2,800 MW
Decay heat rate = 0.2 percent rated thermal power
RCS ambient heat loss rate = 2.4 MW
RCS specific heat = 1.1 Btu/lbm-°F
RCS inventory (less pressurizer)= 325,000 lbm
What will the average reactor coolant heatup rate be during the 20 minutes immediately after forced
coolant flow is lost? Assume the RCS remains in thermal equilibrium and that only ambient losses
are removing heat from the RCS.

A

26 to 50 °F/hour

183
Q

A nuclear power plant has been operating for one hour at 50 percent power following six months of
operation at steady-state 100 percent power. What percentage of rated thermal power is currently
being generated by fission product decay?

A

3 percent to 5 percent

184
Q

A nuclear power plant had been operating at 100 percent power for six months when a reactor trip
occurred. Which one of the following describes the source(s) of core heat generation 30 minutes after
the reactor trip?

A

Fission product decay is the only significant source of core heat generation.

185
Q

A nuclear power plant has been operating at 100 percent power for six months when a reactor trip
occurs. Which one of the following describes the source(s) of core heat generation 1 minute after the
reactor trip?

A

Both fission product decay and delayed neutron-induced fission are capable of increasing fuel
temperature.

RX theory (8 decks)

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