Reactor Theory
Rx Operational Physics
© Copyright 2016
192008 – Rx Operational Physics
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1. During a nuclear reactor startup, the first reactivity
addition caused the source range count rate to increase
from 20 to 40 cps. The second reactivity addition caused
the count rate to increase from 40 to 160 cps.
Which one of the following statements accurately
compares the two reactivity additions?
Th
er
e
is
an
no
d
te
no
se
co
ug
h
nd
...
...
...
d.
..
ity
nd
co
Th
e
se
fir
st
192008 – Rx Operational Physics
Th
e
© Copyright 2016
fir
st
There is not enough information given to
compare the reactivity values.
ad
D.
ct
iv
The first and second reactivity additions
were equal.
e
C.
25% 25% 25% 25%
Th
The second reactivity addition was larger.
ct
iv
ity
B.
re
a
The first reactivity addition was larger.
re
a
A.
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2. Which one of the following describes the change in
neutron 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.)
192008 – Rx Operational Physics
...
...
pr
om
pt
ju
m
p
in
m
p
ju
e
e
pr
om
pt
Th
e
Th
Th
pr
om
pt
ju
m
p
in
© Copyright 2016
in
...
The prompt jump in count rate will be greater, and
the increase in count rate will be greater with Keff at
0.99.
in
D.
25% 25% 25% 25%
m
p
The prompt jump in count rate will be the same, but
the increase in count rate will be greater with Keff at
0.99.
ju
C.
pr
om
pt
The prompt jump in count rate will be greater with
Keff at 0.99, but the increase in count rate will be the
same.
e
B.
Th
The prompt jump in count rate will be the same, and
the increase in count rate will be the same.
...
A.
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3. 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.
0.5% ΔK/K
B.
1.0% ΔK/K
C.
1.5% ΔK/K
D.
2.0% ΔK/K
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192008 – Rx Operational Physics
OGF - Polling
4. 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?
r
ng
e
lo
on
g
r;
l
ho
r;
s
al
le
al
le
192008 – Rx Operational Physics
sm
sm
© Copyright 2016
te
r;
1.0
gr
ea
D.
25% 25% 25% 25%
er
0.75
or
te
r
C.
sh
0.5
te
r;
B.
gr
ea
0.25
rte
r
A.
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5. During a nuclear reactor startup, as Keff increases
toward 1.0 the value of 1/M...
se
s
0.
..
1.
in
cr
ea
to
w
ar
d
ze
ar
d
ar
d
to
w
to
w
s
se
s
cr
ea
se
192008 – Rx Operational Physics
de
cr
ea
de
© Copyright 2016
se
s
increases toward 1.0.
1.
0.
D.
25% 25% 25% 25%
fin
.
increases toward infinity.
in
C.
to
w
ar
d
decreases toward 1.0.
cr
ea
B.
in
decreases toward zero.
ro
.
A.
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6.
The following data was obtained under stable conditions during a
reactor startup:
Control Rod
Units Withdrawn
0
10
15
20
25
30
Source Range
Count Rate (cps)
180
210
250
300
360
420
Assuming uniform differential rod worth, at what approximate control
rod position will criticality occur?
© Copyright 2016
192008 – Rx Operational Physics
56
to
dr
aw
n
dr
aw
n
65
un
its
w
ith
w
ith
its
its
un
un
55
45
to
to
46
35
w
ith
66 to 75 units withdrawn
its
D.
un
56 to 65 units withdrawn
75
C.
w
ith
46 to 55 units withdrawn
to
B.
66
35 to 45 units withdrawn
dr
aw
n
A.
dr
aw
n
25% 25% 25% 25%
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7. Which one of the following conditions will result in
criticality occurring at a rod position that is lower
than the estimated control rod position?
..
st
e.
.
s.
..
e
of
th
tim
e
dj
us
is
a
M
in
g
th
e
tin
g
...
tin
.
oo
al
fu
n
m
dj
us
192008 – Rx Operational Physics
A
A
© Copyright 2016
su
l
Misadjusting the steam dump (turbine bypass)
controller such that steam pressure is
maintained 50 psig higher than the required noload setting.
tin
g
D.
25% 25% 25% 25%
re
Delaying the time of startup from 10 days to 14
days following a trip from 100% power
equilibrium conditions.
el
ay
C.
ct
or
c
A malfunction resulting in control rod speed
being lower than normal speed
D
B.
re
a
Adjusting reactor coolant system boron
concentration to 50 ppm lower than assumed
for startup calculations
ct
io
n
A.
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8. A reactor is initially 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.
greater; at
B.
greater; greater than
C.
less; at
D.
less; greater than
ve
t
bo
;a
;a
ss
le
ss
le
ov
te
r;
ab
te
r;
192008 – Rx Operational Physics
gr
ea
gr
ea
© Copyright 2016
e
at
25% 25% 25% 25%
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9. 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.
increase and stabilize at the POAH.
B.
quickly stabilize at a power level below the
POAH.
co
nt
in
ue
to
to
de
de
cr
e
cr
e
as
e
as
e
..
...
a.
..
ze
at
e
ili
z
st
ab
an
d
qu
ic
k
ly
se
192008 – Rx Operational Physics
in
cr
ea
© Copyright 2016
nt
in
ue
continue to decrease with an unknown
startup rate until an equilibrium shutdown
neutron level is reached.
bi
li
D.
co
continue to decrease on a -1/3 dpm startup
rate until the shutdown equilibrium
shutdown neutron level is reached.
st
a
C.
..
25% 25% 25% 25%
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10. With a reactor on a constant startup rate, which one
of the following power changes requires the longest
amount of time to occur?
x.
..
6.
0
x.
..
0
5
0
5.
1.
3.
x
10
-7
%
to
1.
5
5.
0
to
to
%
-8
%
-8
10
0
x
10
192008 – Rx Operational Physics
3.
x
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to
3.0 x 10-7 percent to 6.0 x 10-7 percent
%
D.
25% 25% 25% 25%
-7
1.5 x 10-7 percent to 3.0 x 10-7 percent
10
C.
x.
..
5.0 x 10-8 percent to 1.5 x 10-7 percent
3.
0
B.
x
3.0 x 10-8 percent to 5.0 x 10-8 percent
x.
..
A.
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