Chain Reactions (GCSE Physics)

Chain Reactions

Controlling the Chain Reaction

• Chain reactions can be dangerous. It is very difficult to stop a chain reaction, meaning it can become dangerous very quickly. Many neutrons are produced by each fission reaction, leading to multiple fission reactions.
• Nuclear reactors use control rods and moderators. Inside a nuclear reactor, there are a controlled series of fission reactions occurring. We do this by using control rods inside the reactor. Usually water or carbon are used as moderators, also acting as a coolant.
• Control rods absorb neutrons. By placing control rods into the reactor, we can absorb excess neutrons. We know that neutrons induce fission reactions, so by absorbing some of them, we are limiting the number of fission reactions that occur.
• Nuclear weapons have uncontrolled reactions. Inside a nuclear weapon, there are uncontrolled nuclear fission reactions happening. This means that there is an uncontrolled chain reaction, which ultimately leads to an explosion.
• The reaction must be shielded. A large amount of radiation is produced by nuclear fission, which can be very hazardous. Therefore the reaction should be shielded, absorbing any radiation and reducing the risk of harm.

Representing Nuclear Fission

Below, we can see a representation of nuclear fission. You may be asked to draw a diagram like this in an exam, so here’s how to do it:

1. Draw a neutron. This is essentially a small circle. You can label it ’n’.
2. Draw a large nucleus. As you can see in the diagram below, the nucleus must be made up of smaller particles.
3. Draw 2 more nuclei. Since this is a fission reaction, we need to draw the 2 neutrons that are produced.
4. Draw 2 or 3 neutrons. Fission reactions produce more neutrons, which we need to represent on our diagram as small circles again.
5. Draw more fission reactions. From one of the neutrons, draw an arrow to another nuclei. This is the continuation of the chain reaction.

The end product should look similar to the diagram below:

Generation of Electricity

The chain reaction can be used to provide nuclear power in power stations, to generate electricity.

1. Nuclear energy. Usually, uranium and plutonium are used as nuclear fuels in the chain reaction.
2. Thermal energy. As heat is produced through the chain reaction, water is heated to produce steam in a boiler.
3. Kinetic energy. The steam then turns a turbine, which turns a generator to produce electricity.