# Explain how a chain reaction occurs during nuclear fission.

> Eduqas GCSE Physics — 9.4 Nuclear fission and fusion · Explain · 4 marks

> Nuclear fission is used in nuclear power stations to generate electricity. During fission, uranium-235 nuclei are split apart.

## Mark scheme (4 marks)

1. A neutron is absorbed by a uranium-235 nucleus
2. The nucleus splits / undergoes fission, releasing two or three neutrons
3. These neutrons go on to be absorbed by other uranium nuclei / cause further fission events
4. The reaction is self-sustaining / the number of fissions increases rapidly

## Key terms

- [nuclear fission](https://www.gradenine.co.uk/glossary/nuclear-fission)
- [chain reaction](https://www.gradenine.co.uk/glossary/chain-reaction)

## Related

- [Revision notes for Eduqas GCSE Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-chain-reaction-occurs-fd781848) · Published by Druglandscape Ltd.