[Maximum number: 2]

This question is about nuclear power production.

(a)

State two advantages of power production using fossil fuels compared to using nuclear fuels.

1.

2.

[ 2 ]

[Maximum number: 9]

This question is about nuclear reactions.

(a)

A reaction that takes place in the core of a particular nuclear reactor is as shown.

{ }_{92}^{235} \mathrm{U}+\mathrm{X} \rightarrow{ }_{56}^{144} \mathrm{Ba}+{ }_{36}^{89} \mathrm{Kr}+3 \mathrm{X}

[ 1 ]

(i)

State one form of energy that is instantaneously released in the reaction.

[ 1 ]

(b)

In the nuclear reactor, $9.5 \times 10^{19}$ fissions take place every second. Each fission gives rise to 200 MeV of energy that is available for conversion to electrical energy. The overall efficiency of the nuclear power station is 32 %.

[ 5 ]

(i)

Determine the mass of U-235 that undergoes fission in the reactor every day.

[ 3 ]

(ii)

Calculate the power output of the nuclear power station.

[ 2 ]

(c)

In addition to the U-235, the nuclear reactor contains graphite that acts as a moderator. Explain the function of the moderator.

[ 3 ]

[Maximum number: 2]

This question is about the use of energy resources.

(a)

Nuclear reactors are also used to generate energy in France. In a particular nuclear reactor, neutrons collide elastically with carbon-12 nuclei $\left({ }_{6}^{12} \mathrm{C}\right)$ that act as the moderator of the reactor. A neutron with an initial speed of $9.8 \times 10^{6} \mathrm{~m} \mathrm{~s}^{-1}$ collides head-on with a stationary carbon-12 nucleus. Immediately after the collision the carbon-12 nucleus has a speed of $1.5 \times 10^{6} \mathrm{~m} \mathrm{~s}^{-1}$ .

[ 2 ]

(i)

Outline why the reduction in energy is necessary for this type of reactor to function.

[ 2 ]

[Maximum number: 5]

This question is about energy sources.

A small island is situated in the Arctic. The islanders require an electricity supply but have no fossil fuels on the island. It is suggested that wind generators should be used in combination with power stations using either oil or nuclear fuel.

(a)

Any nuclear fuel available to the islanders must be enriched before it can be used.

Outline why fuel enrichment is needed.

[ 2 ]

(b)

A nuclear reactor requires both control rods and a moderator to operate. Outline, with reference to neutrons, one similarity and two differences in the function of each of these components.

[ 3 ]

[Maximum number: 1]

A suitable material for use as a moderator in a nuclear reactor is...

A

cadmium.

B

concrete.

C

uranium-238.

D

water.

[Maximum number: 1]

Which two components of a nuclear power station are primarily responsible for ensuring that a controlled chain reaction is maintained?

A

Control rods and heat exchangers

B

Moderators and shielding

C

Shielding and heat exchangers

D

Moderators and control rods

[Maximum number: 1]

A nuclear reactor contains atoms that are used for moderation and atoms that are used for control.

What are the ideal properties of the moderator atoms and the control atoms in terms of neutron absorption?

Ideal moderator atom

Ideal control atom

poor absorber of neutrons

good absorber of neutrons

poor absorber of neutrons

good absorber of neutrons

[Maximum number: 1]

What part of a nuclear power station is principally responsible for increasing the chance that a neutron will cause fission?

A

Moderator

B

Control rod

C

Pressure vessel

D

Heat exchanger

[Maximum number: 1]

What is the function of control rods in a nuclear power plant?

A

To slow neutrons down

B

To regulate fuel supply

C

To exchange thermal energy

D

To regulate the reaction rate

[Maximum number: 1]

In a simple model of a nuclear reactor, four neutrons are emitted per fission on average.

The average number of neutrons absorbed by the control rods is $N_{\mathrm{c}}$ per fission.
The average number of neutrons that are lost through the walls of the reactor is $N_{1}$ per fission.
Any remaining neutrons induce further fissions.
What are possible values for $N_{\mathrm{c}}$ and $N_{1}$ for the reactor to maintain a steady reaction?

$\boldsymbol{N}_{\mathbf{c}}$

$\boldsymbol{N}_{\mathbf{1}}$

1

3

2

1

2