Nuclear Fission and Energy

This lesson covers nuclear fission, the process by which heavy nuclei split to release energy, how a chain reaction is sustained and controlled in a nuclear power station, and the advantages, disadvantages and challenges of nuclear energy. This is the final topic in the Particle Model and Radioactivity section of the Edexcel GCSE Combined Science specification (1SC0).

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What Is Nuclear Fission?

Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei (called daughter nuclei or fission fragments), accompanied by the release of:

• Two or three neutrons
• A large amount of energy (as kinetic energy of the fragments and neutrons, and gamma radiation)

The Process

1. A slow-moving (thermal) neutron is absorbed by a large, unstable nucleus (e.g. uranium-235 or plutonium-239).
2. The nucleus becomes even more unstable.
3. The nucleus splits into two smaller daughter nuclei of roughly equal size.
4. Two or three neutrons are released.
5. A large amount of energy is released.

graph LR
    N["Slow neutron"] --> U["Uranium-235<br/>nucleus"]
    U --> F1["Daughter<br/>nucleus 1"]
    U --> F2["Daughter<br/>nucleus 2"]
    U --> N1["Neutron"]
    U --> N2["Neutron"]
    U --> N3["Neutron"]
    U --> E["Energy<br/>(kinetic + gamma)"]