# Fusion fuels: How energy resides

How joining tiny nuclei releases enormous energy

Source page: https://www.materialinsights.org/energy/e_fusion_fuels/resides/

What this tab covers The physical form in which the energy is held or carried, where it comes from, the chain of transformations that put it there, and how concentrated it is.

Fusion fuels hold energy as nuclear binding energy that is released when very light nuclei are forced together, the process that powers the Sun. The practical fuels are deuterium from seawater and tritium bred from lithium; helium-3 is a rarer alternative found mainly on the Moon.
 Form Nuclear binding energy in light nuclei (hydrogen isotopes, lithium, helium-3) Origin Nuclear (deuterium and lithium made in the Big Bang and in stars; helium-3 deposited on the Moon by the solar wind)

#### How it got there
 Big Bang and stellar processes make deuterium and lithium Deuterium dissolved in the oceans as heavy water; lithium in brines, rocks and seawater Lithium bombarded by fusion neutrons in a reactor blanket yields tritium Deuterium and tritium heated to about 150 million degrees C as a plasma Nuclei fuse into helium plus a fast neutron Neutron energy captured as heat

#### How concentrated it is

| Measure | Value | Note |
|---|---|---|
| **Energy per deuterium-tritium reaction** | 17.6 MeV^[2](https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusion) | 14.1 MeV (80%) carried by the neutron, the rest by the helium nucleus |
| **Energy per kilogram of fuel versus chemical fuels** | nearly 4 million times x oil or coal^[3](https://iaea.org/sites/default/files/fusionenergy.pdf) | And about four times fission per kilogram; a few grams of D-T fuel could yield a terajoule |
| **Fuel for a 1,000 MW fusion plant** | about 250 kg per year^[4](https://www.ITER.org/sci/fusionfuels) | Half deuterium, half tritium; a coal plant of the same size burns about 2.7 million tonnes a year |
| **Deuterium in seawater** | 33 g per m3^[4](https://www.ITER.org/sci/fusionfuels) | Present in all seawater at this concentration |

Fusion releases energy because a helium nucleus is more tightly bound than the deuterium and tritium that form it. The difficulty is that nuclei repel each other electrically, so fuel must be heated to about 150 million degrees C (ITER's target) and held long enough for reactions to outpace losses. Deuterium-tritium is the easiest reaction to ignite, which is why almost all reactor designs use it.

Tritium is radioactive and decays with a half-life of 12.3 years, so it barely exists in nature. A power plant must make its own by surrounding the plasma with a lithium 'blanket': neutrons from fusion split lithium-6 into tritium and helium. In effect the fuels are deuterium and lithium. Helium-3 fusion with deuterium releases almost all its energy as charged particles rather than neutrons, but helium-3 is extremely scarce on Earth.

#### Sources

1. [Deuterium-tritium fusion](https://en.wikipedia.org/wiki/Deuterium%E2%80%93tritium_fusion) Wikipedia, 2025
2. [Fusion Energy: Energy for the future (booklet)](https://iaea.org/sites/default/files/fusionenergy.pdf) International Atomic Energy Agency, 2023
3. [Fusion fuels](https://www.ITER.org/sci/fusionfuels) ITER Organization, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_fusion_fuels/index.md)
- [Overview](https://www.materialinsights.org/energy/e_fusion_fuels/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_fusion_fuels/correlation/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_fusion_fuels/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/e_fusion_fuels/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/e_fusion_fuels/geography/index.md)
- [Impact on nature](https://www.materialinsights.org/energy/e_fusion_fuels/nature/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_fusion_fuels/links/index.md)