Nuclear Fission & Fusion (Edexcel GCSE Physics)

Fusion and fission are nuclear reactions in which large amounts of energy are released.

i) In a fusion reaction, two hydrogen nuclei are forced together to form a helium nucleus.

Explain why a very high temperature is needed for this reaction to happen.

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ii) In a fusion reaction, the combined mass of the two small nuclei is greater than the mass of the resulting nucleus.

This decrease in mass, m, appears as energy, E, according to the equation.

E = mc²

c is the speed of light = 3.0 × 10⁸ m/s.

The energy released in one fusion reaction is 4.5 × 10⁻¹² J.

Calculate the decrease in mass.

         decrease in mass = ........................................ kg[3]

Nuclear fission is used in nuclear reactors in some power stations.

In the reactor, a fission chain reaction is maintained and controlled to produce a supply of energy to generate electricity.

Figure 14 is a diagram of a nuclear reactor.

Figure 14

Explain how the graphite core and the movable rods are used to maintain and control the chain reaction.

This question is about nuclear reactions.

When a uranium-235 (U-235) nucleus absorbs a neutron, the nucleus splits into smaller parts.

This reaction is called nuclear fission.

How many daughter nuclei are produced from the fission of one nucleus of uranium-235 (U-235)?

i) When a uranium-235 (U-235) nucleus splits, neutrons are also emitted.

The neutrons may start a chain reaction.

Describe what is meant by a chain reaction.

You may draw a diagram to help with your answer.

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ii) In the nuclear reactor of a power station, the chain reaction has to be controlled.

Explain the action of a moderator in a nuclear reactor.

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iii) In a nuclear reactor there are 2.0 × 10¹⁷ fission reactions each second.

Each fission reaction releases 4.0 × 10^–11 J of energy.

Calculate the energy released in 1 second.

energy released in 1 second = ..................................... J[2]

Nuclear fusion is a nuclear reaction that takes place in the Sun.

Describe what happens during a nuclear fusion reaction.

Figure 8 shows a helium nucleus.

Figure 8

Two of the particles in the helium nucleus are neutrons.

State the name of the other two particles in the helium nucleus.

i) Describe the difference between a fusion reaction and a fission reaction.

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ii) Nuclear fusion does not happen at low temperatures because of electrostatic repulsion between

☐ A beta particles

☐ B electrons

☐ C neutrons

☐ D protons

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The energy released per kilogram of fuel in a fusion reaction is 845 000 GJ.

The energy released per kilogram of fuel in burning oil is 0.0394 GJ.

i) Calculate the ratio of the energy released in fusion compared with the energy released in burning oil. Use the equation

ratio = ..............................................................[2]

ii) State two advantages of using a fusion reactor rather than burning oil in a power station.

1 ..................................................................

2 ...................................................................

[2]

iii) State two of the difficulties that need to be overcome to produce a fusion reactor.

1 .................................................................

2 .................................................................

[2]

Figure 1 shows the main parts of a nuclear reactor.

Figure 1

State the function of: 

(i) The control rods

[1]

(ii) The coolant

[1]

(iii) The fuel rods

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(iv) The shielding

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The uranium fuel has a nuclear energy store.

State the name of the energy store that energy is usefully transferred to during a fission reaction.

Explain the role of the moderator in a fission reactor.

Explain what is meant by controlled nuclear fission.

Refer to neutrons in your answer.

Nuclear fission occurs in nuclear reactors.

Describe the process of nuclear fission, including the material used in the fuel rod.

Explain what happens to the energy released. 

Explain how a chain reaction can occur in the reactor.

Scientists in France are currently developing a nuclear fusion reactor called ITER for research into fusion technology.

Nuclear fusion uses isotopes of hydrogen called deuterium and tritium.

Deuterium can be reasonably easily extracted from seawater, and is naturally occurring.

Table 1 below shows the energy released from 1kg of deuterium and 1kg of uranium-235 used as the fuel in a fission power station.

 Table 1

Suggest two advantages of using a nuclear fusion reactor rather than a nuclear fission reactor.

State and explain the conditions for nuclear fusion to occur.

Use words from the box to complete the sentences about nuclear fission of uranium‐235 (U‐235).

A neutron hits a nucleus of U‐235 and causes the nucleus to ......................................

Each fission releases energy, two daughter nuclei and some ....................................... .

In a nuclear reactor, one fission can set off a controlled ............................... reaction.

Both U‐235 and oil can be used as energy sources for generating electricity.

1 kg of natural uranium can result in the generation of 45 000 units of electricity.

1 kg of oil can result in the generation of 5.0 units of electricity.

Calculate the mass of oil needed to generate the same amount of electricity as 1 kg of natural uranium.

mass of oil = .............................................................. kg

Both using nuclear fuel and burning oil produce harmful waste products.

State one harmful waste product from each process.

using nuclear fuel...................................................................

burning oil...............................................................................

Figure 14 shows a household smoke alarm that uses radioactivity to detect smoke.

Figure 14

The radioactive source in the smoke detector is americium–241.

The table in Figure 15 shows some information about americium–241 and two other radioactive sources.

Figure 15

Explain why americium‐241 is the best of these three sources to use in this smoke detector.

Use information from Figure 15 and your own knowledge about radiation. Your answer should refer to

• properties of alpha and gamma radiation

• half‐life.

A kettle is used to heat water.

Figure 11 shows a graph of temperature against time for the water in the kettle.

Calculate the rate of increase in temperature at a time of 150 s, by drawing a tangent to the curve in Figure 11 at a time of 150s.

.............................................................. °C/s

The kettle has an efficiency of 91% in supplying energy to the water.

The thermal energy of the water increases by 3.3 × 10⁵ J in 200 s.

Calculate the total amount of energy supplied to the kettle in the 200 s.

Use the equation

total amount of energy supplied = ...................................... J

c) The global demand for electricity is increasing.

There is a debate about whether nuclear power generation should or should not contribute to meeting this increasing demand.

Discuss the arguments for and against using nuclear power to meet the increasing global demand for electricity.

Nuclear fission occurs in nuclear reactors.

An example of a nuclear reactor is shown in Figure 1. 

Figure 1

Describe the process of nuclear fission in the reactor shown in Figure 1, including the material used in the fuel rod.

Explain what happens to the energy released. 

Explain how a chain reaction can occur in the reactor.

Explain the energy transfer taking place in this chain reaction.