# Nuclear fission reactors

Reactors that split uranium or thorium atoms to make heat for steam turbines.

Source page: https://www.materialinsights.org/energy/e_fission/

Capture · Fossil and nuclear · No. 46

- Capture
- Output: Heat → electricity
 Capture · Fossil and nuclear · Foundation · Energy

Today's reactors use less than 1% of the energy locked in mined uranium, yet still make about 9% of world electricity.

Chart: Illustration: Nuclear fission reactors

##### Where it comes from

Chart: Map of where it comes from

Uranium is mined or, for 55% of output, dissolved in place by solutions pumped through the ore. Centrifuges then enrich it from 0.7% U-235 to 3-5% for light-water reactors.

##### Three things to know

1. Fukushima's radiation killed one person, while the evacuation was linked to 2,313 deaths.
2. Life-cycle emissions are only about 5.1-6.4 g CO2e/kWh, among the lowest of any electricity source.
3. In October 2026 Finland granted Onkalo the world's first operating licence for a deep geological repository for spent fuel.

##### The journey

1. 1 **Uranium ore**Mined, or dissolved in place underground
2. 2 **Enrichment**Centrifuges raise U-235 to 3-5%
3. 3 **Fuel**Oxide pellets sealed in metal tubes
4. 4 **Reactor**Splitting atoms boils water
5. 5 **Turbine**Steam makes electricity at 33-37%
6. 6 **Spent fuel**Cooled, stored, sometimes reprocessed

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## Other sections

- [Overview](https://www.materialinsights.org/energy/e_fission/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_fission/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_fission/efficiency/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_fission/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_fission/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_fission/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_fission/links/index.md)