Nuclear Energy

Chapter 6
Nuclear Physics

6.2 Nuclear Energy

Pupils are able to :

1. Communicate about nuclear reactions:
(i) nuclear fission
(ii) nuclear fusion

2. Describe relationship between energy released during nuclear reaction
and mass defect: E = mc2

3. Solve problems involving nuclear energy due to radioactive decay and
nuclear reactions

4. Describe generation of electrical energy in nuclear reactor

5. Justify the use of nuclear energy as an alternative energy to generate
electrical energy

6.2.1 Communicate about nuclear reactions:
(i) Nuclear Fission
(ii) Nuclear Fusion

Nuclear energy is known as atomic
energy, released during nuclear reactions
such as radioactive decay, nuclear fission
and nuclear fusion.

Nuclear fission Nuclear fusion
‘ split ‘ ‘ combine ‘

Nuclear fission is a nuclear reaction when a heavy nucleus splits
into two or more lighter nuclei while releasing a large amount of
energy.

Nuclear fission involving uranium–235 bombarded by a single neutron

Nuclear fission

1. In the fission reactions, one neutron starts the fission process, but three
neutrons are produced.

2. If one of these neutrons bombards another uranium-235 nucleus then
more fissions will occur, releasing more neutrons. A chain reaction is
produced.

3. A chain reaction is a self-sustaining reaction in which the products of a
reaction can initiate another similar reaction.

4. As uranium atoms continue to split, a significant amount of energy is
released during each reaction. The heat released is harnessed and used
to generate electrical energy.

Example of Chain Reaction

A controlled chain reaction is used in nuclear power stations
(slow down the neutron using water and graphite. Fast neutron

are more likely not captured by uranium nuclei)

An uncontrolled chain reaction is used in nuclear bombs.

Nuclear fusion is a nuclear reaction in which small and light nuclei fuse to
form a heavier nucleus while releasing a large amount of energy. This
nuclear reaction happens under extremely high temperature and pressure.

Other examples:
11 H + 21 H → 32 He + γ + Energy
21 H + 31 H → 42 He + 10 n + Energy
32 He + 32 He → 42 He + 11 H + 11 H + Energy
21 H+ 32 He → 42 He + 11 H + Energy

Nuclear fusion between deuterium and tritium
occurs to form a heavier helium nucleus. Energy
and one neutron is also released.

Nuclear fusion

1. The energy release is much more than in nuclear fission.
2. Occurs when 2 nuclei approach each other at a very high speed to

overcome the force of repulsion.
3. Can only occur at a very high temperature. Fusion of hydrogen -2

nuclei requires a temperature of more than 10 million oC
4. Hydrogen bomb uses the principle of nuclear fusion.
5. Nuclear fusion occurs naturally in the sun and stars as it requires

high temperature to provide enough kinetic energy for the nuclei to
collide and fuse together.

6.2.2 Describe relationship between energy
released during nuclear reaction and mass
defect: E = mc2

Atomic Mass Unit (a.m.u)

❑ Used to measure the masses of atomic particles which are very
small.

❑ 1 a.m.u or 1 u is 1/12 of the mass of carbon-12 atom
❑ The mass of one carbon-12 atom is 1.99 x 10-26 kg

❑ Mass of daughter particles are less than the parent particles.
❑ Loss of mass = Mass defect ↔ Energy released

Mass defect = mass of parent particle – total mass of daughter particle





Nuclear Energy, E Einstein Mass – Energy Equivalent Law

6.2.3 Solve problems involving nuclear
energy due to radioactive decay and
nuclear reactions

1
2

3

1
2







6.2.4 Describe generation of electrical
energy in nuclear reactor











6.2.5 Justify the use of nuclear energy as an
alternative energy to generate electrical energy



Advantages of using nuclear fission

1. It does not produce smoke or carbon dioxide.
It does not contribute to the greenhouse
effect. It produces less waste than fossil fuels.

2. It produces huge amounts of energy from
small amounts of fuel.

3. Nuclear power stations need less fuel than
stations which use fossil fuels

4. Vast reserves of nuclear fuel in the world.

5. Safety procedures in the administration of
nuclear reactors are very advanced and safe

Chernobyl Power Plant Disadvantages of using nuclear fission
The Chernobyl Disaster 1. The initial cost to design and build a
Cause: reactor design flaws and serious
breach of protocol during simulated nuclear power station is very high.
power outage safety test 2. There is always a risk of accidents. If a

chain reaction goes out of control,
explosion or leakage or large amounts of
radioactive substance may happen.
3. Used fuel rods are very hot and highly
radioactive with very long half-lives.
4. Expensive procedures are required to cool
down the rods and store them.
5. The hot water discharged from the nuclear
power stations can cause thermal pollution
6. People who work in the nuclear power
station and those living nearby may be
exposed to excessive radiation.

Nuclear fission is a nuclear reaction when a heavy nucleus splits into two
or more lighter nuclei while releasing a large amount of energy.

Nuclear fusion is a nuclear reaction in which small and light nuclei fuse to
form a heavier nucleus while releasing a large amount of energy. This
nuclear reaction happens under extremely high temperature and pressure.

o In a nuclear reactor, a uranium-235 nucleus is bombarded by a neutron to
form the uranium-236 nucleus which is unstable.

o The unstable uranium-236 nucleus will split to produce lighter and more
stable nuclei such as barium-141 and krypton-92 as well as three new
neutrons.

o The three neutrons released will then bombard three other uranium-235
nuclei to form three heavy unstable uranium-236 nuclei.

o These unstable uranium-236 nuclei will undergo nuclear fission which in
turn produce other neutrons that enable the subsequent nuclear fission.

o The nuclear energy produced increases with the increasing number of
fissions of nuclei.

▪ In a nuclear reactor, fissions occurs when uranium-235 nuclei
are bombarded by neutrons to form a chain reaction.

▪ The resulting nuclear energy boils water to become steam.
▪ High pressure steam is channeled to rotate the turbine.
▪ Rotating turbines with switch on dynamos that generate

electrical energy.



Question 1

Leader Board Results

Multiple Choice Submissions

Details can be found in the Notes section below

Question 2

Leader Board Results

Multiple Choice Submissions

Details can be found in the Notes section below

Question 3

Leader Board Results

Multiple Choice Submissions

Details can be found in the Notes section below

Question 4

Leader Board Results

Multiple Choice Submissions

Details can be found in the Notes section below

Question 5

Leader Board Results