# Fusion fuels: Fluctuation in time

Pulses of seconds, and a fuel that decays

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

What this tab covers How availability changes over seconds, days, seasons, years and longer, how predictable it is, and what that means for the plants that use it.

Fusion fuels themselves are stable stocks, except tritium, which decays by about 5.5% a year. The time question is when, and how steadily, fusion machines can run; experimental devices so far operate in pulses lasting seconds or less.

#### Variation by time scale

| Time scale | What happens | How large |
|---|---|---|
| **Nanoseconds to seconds (pulses)** | Laser fusion produces single shots; tokamaks run pulses of seconds to minutes^[8](https://world-nuclear-news.org/articles/new-world-record-set-in-jet-s-final-fusion-experim) | JET sustained high fusion power for 5 seconds; NIF shots last billionths of a second |
| **Years (tritium decay)** | Tritium stockpiles shrink even if unused^[3](https://iaea.org/sites/default/files/fusionenergy.pdf) | Half-life 12.3 years, a loss of about 5.5% a year (calculated) |
| **Years (experimental progress)** | Record yields have climbed since first ignition, though individual shots vary widely^[9](https://lmf.llnl.gov/science/achieving-fusion-ignition) | 3.15 MJ (December 2022), about 5.2 MJ (February 2024), 8.6 MJ (April 2025, still the record); 7.9 MJ in June 2026 |
| **Centuries to millions of years (depletion)** | Deuterium and lithium supply would outlast any foreseeable demand^[4](https://www.ITER.org/sci/fusionfuels) | Land lithium more than 1,000 years for fusion; seawater lithium about 6 million years |

#### How predictable it is

Not yet applicable: there is no operating fusion power plant, so there are no capacity factors. A future plant would in principle run steadily like a fission plant, limited by maintenance of components damaged by neutrons.

Unlike sunlight or wind, the fuels for fusion do not fluctuate; their abundance changes only on geological time scales. Tritium is the exception because it decays, which makes it impractical to stockpile for decades and means the first plants will depend on a small, shrinking inventory until breeding blankets work.

The realistic timeline is set by engineering. ITER, the international tokamak under construction in France, will draw on the global tritium inventory for its operations, and its results will determine whether tritium breeding at scale is feasible.

#### Sources

1. [Fusion Energy: Energy for the future (booklet)](https://iaea.org/sites/default/files/fusionenergy.pdf) International Atomic Energy Agency, 2023
2. [Fusion fuels](https://www.ITER.org/sci/fusionfuels) ITER Organization, 2024
3. [New world record set in JET's final fusion experiments](https://world-nuclear-news.org/articles/new-world-record-set-in-jet-s-final-fusion-experim) World Nuclear News, 2024
4. [Achieving Fusion Ignition](https://lmf.llnl.gov/science/achieving-fusion-ignition) Lawrence Livermore National Laboratory, 2026

## 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)
- [How energy resides](https://www.materialinsights.org/energy/e_fusion_fuels/resides/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_fusion_fuels/abundance/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)