# Nuclear fission reactors: Overview

Splitting atoms for steady, very low-carbon electricity

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

What this tile covers Reactors that split uranium or thorium atoms to make heat for steam turbines. Share of use 5.2% share of world energy supply (2024)

Share of world total energy supply captured or extracted by each method, 2024 (latest year where noted). Denominator is the Energy Institute Statistical Review 2025 total of 592.2 EJ (physical energy content method); electricity from wind, solar, hydro and geothermal is counted at output, nuclear at reactor heat. Heat and biomass flows outside EI's total are set against the same 592.2 EJ. Nuclear 30.74 EJ, counted as reactor heat input, of 592.2 EJ (calculated). Source: [Statistical Review of World Energy 2025 (74th edition)](https://assets.kpmg.com/content/dam/kpmgsites/sg/pdf/2025/08/2025-statistical-review-of-world-energy.pdf), Energy Institute.

#### Key facts

| **Output** | Heat → electricity |
|---|---|
| **Chain** | Nuclear → heat → steam → mechanical → electrical |

#### Included from the reference tables

- Light-water reactors (pressurised, boiling)
- Heavy-water reactors (CANDU, India's PHWRs)
- Fast breeder reactors and thorium fuel cycles
- SMRs, microreactors, molten salt and high-temperature gas reactors
- Naval reactors
- Uranium mining, in-situ leaching and enrichment

#### Linked to the material world
[U Uranium](https://www.materialinsights.org/energy/uranium/)[Zr Zirconium](https://www.materialinsights.org/commodities/zirconium/)[Hf Hafnium](https://www.materialinsights.org/commodities/hafnium/)[H₂O Water](https://www.materialinsights.org/commodities/water/)

#### Also in Fossil and nuclear
[CM Coal mining](https://www.materialinsights.org/energy/e_coal_mining/)[OGw Conventional oil and gas production](https://www.materialinsights.org/energy/e_oil_gas_conv/)[UOG Unconventional oil and gas](https://www.materialinsights.org/energy/e_oil_gas_unconv/)

Explore paths from here
 More on this tile in the tabs above: efficiency, techniques, resources and labour, impact on the biosphere.

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_fission/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)