# A nuclear power station uses uranium as its fuel. Explain how a chain reaction is set up inside the reactor and why engineers must be able to control the rate at which the chain reaction proceeds.

> OCR A-Level Physics B: Advancing Physics (H557) — 6.2 Electric and magnetic fields · Explain · 5 marks

> Nuclear power stations generate electricity by harnessing the energy released during nuclear fission. Uranium nuclei are used as the fuel because they are large and unstable.

## Mark scheme (5 marks)

1. A uranium nucleus absorbs a neutron and becomes unstable / splits into two smaller nuclei
2. The fission of uranium releases further neutrons (and energy / gamma radiation)
3. The released neutrons go on to be absorbed by other uranium nuclei, causing them to split in turn
4. This creates a self-sustaining chain reaction in which each split causes further splits, releasing increasing amounts of energy
5. If the chain reaction is not controlled, the rate of fission (and energy release) increases uncontrollably, which could be dangerous / cause a meltdown

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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/a-nuclear-power-station-uses-uranium-3254fe6a) · Published by Druglandscape Ltd.