Explain why nuclear fusion is considered a potentially more desirable energy source for the future than nuclear fission, despite fusion not yet being used in power stations.

1. Fusion releases far more energy per unit mass of fuel than fission, so a small amount of fuel can generate a large amount of power.
2. The fuel for fusion – hydrogen isotopes such as deuterium and tritium – is abundant and can be extracted from seawater or produced from lithium, making it readily available.
3. Fusion reactions produce little or no long‑lived radioactive waste; the by‑products are short‑lived and less hazardous than the high‑level waste from fission.
4. However, fusion requires extremely high temperatures and pressures that are currently difficult and expensive to maintain, so it has not yet been achieved on a practical power‑station scale.