27 Nuclear energy
Exam-style questions
AQA Physics
Refer to the Physics data sheet for data, formulae and relationships information.
1
Distinguish between the mass difference and the binding energy of an atomic
nucleus and state how these quantities are related.
(3 marks)
AQA Physics, 2009, Unit 4 (Question 5)
2
a
The principal thermonuclear fusion process by which the Sun produces
energy is a sequence of three separate fusion reactions. This process
effectively combines four protons into one helium nucleus, releasing an
amount of energy that is equivalent to the mass difference between four
1
4
1H atoms and one 2 He atom.
Show that the energy released by the process is about 27 MeV.
mass of 11H atom  1.00783 u
mass of 42 He atom  4.00260 u
(2 marks)
2
b It has been calculated that, in the absence of any atmospheric absorption,
energy from the Sun would reach the Earth at a rate of 1350 W m2.
Show that the mean rate of energy production by the Sun is approximately
4 × 1026 W. Assume that there is no absorption between the Sun and the
Earth.
mean radius of Earth’s orbit  1.50 × 1011 m
(2 marks)
AQA Physics, 2009, Unit 4 (Question 5)
3
a
i
Define the atomic mass unit.
(1 mark)
ii
State and explain how the mass of a 42 He nucleus is different from the
total mass of its protons and neutrons when separated.
(2 marks)
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1
AQA Physics
27 Nuclear energy
Exam-style questions
b Explain why nuclei in a star have to be at a high temperature for fusion to
take place.
(3 marks)
AQA Physics, 2013, Unit 5 (Question 1)
4
a
In the context of nuclear fission, explain what is meant by:
i a chain reaction,
ii
critical mass.
(4 marks)
b Moderation and cooling are essential processes in the operation of a
nuclear power reactor using thermal neutrons. For each process, name a
suitable material that is used to achieve the required effect, and state why it
is suitable.
i Moderation
ii
Cooling
(4 marks)
AQA Physics, 2008, Unit 4 (Question 5)
5
In a nuclear reactor the mean energy produced by each uranium235 nucleus
that undergoes induced fission is 3.0 × 10−11 J. In one pressurised water reactor
(PWR) the fuel rods in the reactor contain 2.0 × 104 kg of uranium235 and 40%
of the energy produced per second is converted to 500 MW of electrical output
power.
molar mass of uranium235  0.235 kg
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This resource sheet may have been changed from the original
2
27 Nuclear energy
Exam-style questions
AQA Physics
5
a
The equation below gives one induced fission reaction that takes place in a
reactor.
235
92
i
U  01X 
n
56
Br 
90
p
Kr  201 X
State the name of the particle represented by X.
(1 mark)
ii
State the proton and nucleon numbers represented by p and n.
p ......................................................................................................
n ......................................................................................................
(2 marks)
b i
Calculate the number of fission reactions that occur in the reactor each
second.
number of fission reactions per second ........................................................
(2 marks)
ii
The reactor fuel rods contain 2.0 × 104 kg of uranium235. Assume that
all this uranium235 could be used.
Calculate the maximum time, in years, for which the reactor could
operate.
time .........................................................years
(4 marks)
iii Suggest why it is not possible to use all the uranium235 in the reactor
fuel rods.
(2 marks)
AQA Physics, 2012, Unit 5 (Question 4)
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This resource sheet may have been changed from the original
3
AQA Physics
6
27 Nuclear energy
Exam-style questions
Figure 1 shows the variation in binding energy per nucleon with nucleon number.
Figure 1
6
a
A uranium235, 235U, nucleus fissions into two approximately equally sized
products.
Use data from the graph to show that the energy released as a result of the
fission is approximately 4 × 10−11 J.
Show on the graph how you have used the data.
(4 marks)
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4
AQA Physics
6
27 Nuclear energy
Exam-style questions
b Using the data below, show that the energy available from the fusion of two
hydrogen2, 2H, nuclei to make a helium4, 4He, nucleus is approximately
3.7 × 10−12 J.
mass of 2H  2.0135 u
mass of 4He  4.0026 u
(4 marks)
6
c
Compare the energy available from the complete fission of 1 kg of
uranium235 with the energy available from the fusion of 1 kg of hydrogen2.
(3 marks)
6
d Fission and fusion reactions release different amounts of energy. Discuss
other reasons why it would be preferable to use fusion rather than fission for
the production of electricity, assuming that the technical problems associated
with fusion could be overcome.
(2 marks)
AQA Physics, 2013, Unit 5 (Question 7)
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5