Explain why nuclear fusion has not yet been developed as a large-scale commercial energy source, despite the fact that it releases more energy per kilogram of fuel than nuclear fission.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Scientists have been researching nuclear fusion as an energy source for many decades. Fusion powers the Sun and other stars, but producing a controlled fusion reaction on Earth that generates more energy than it consumes has proved extremely difficult.
Model answer (5 marks)
Fusion requires temperatures of millions of degrees to give the nuclei enough kinetic energy to overcome their electrostatic repulsion. At these temperatures matter is a plasma, which cannot be held by any solid material; magnetic or inertial confinement is needed, but no technology yet keeps the plasma stable for long enough.
Even if a plasma is produced, the energy required to heat and confine it is almost as great as the energy released. Break‑even – where the fusion power output equals the input power – has not yet been achieved in a commercial setting.
The fuel – hydrogen isotopes such as deuterium and tritium – is abundant, so the problem is not supply but engineering: creating a sustained, net‑positive energy reaction in a controlled environment.
Thus, despite the high energy yield per kilogram, the extreme temperature, containment, and energy‑balance challenges prevent fusion from becoming a large‑scale commercial power source.
Even if a plasma is produced, the energy required to heat and confine it is almost as great as the energy released. Break‑even – where the fusion power output equals the input power – has not yet been achieved in a commercial setting.
The fuel – hydrogen isotopes such as deuterium and tritium – is abundant, so the problem is not supply but engineering: creating a sustained, net‑positive energy reaction in a controlled environment.
Thus, despite the high energy yield per kilogram, the extreme temperature, containment, and energy‑balance challenges prevent fusion from becoming a large‑scale commercial power source.
Examiner tips
- Show the chain: high T → plasma → containment problem; mention break‑even; note fuel abundance; use terms like electrostatic repulsion, magnetic confinement
Common mistakes
- Confusing fusion with fission energy yield; claiming fuel is scarce; ignoring the need for net‑positive energy output
Mark scheme (5 marks)
- Fusion requires extremely high temperatures (millions of degrees) to occur
- At these temperatures, matter exists as a plasma which is very difficult to contain / no material can withstand these temperatures
- It is difficult to produce more energy from fusion than is put in to start / sustain the reaction (break-even not yet achieved commercially)
- The nuclei being fused must be brought close enough together / must overcome electrostatic repulsion between positively charged nuclei
- Fusion fuel (hydrogen isotopes / deuterium / tritium) is available / the challenge is engineering not fuel supply, making continued research worthwhile
Key terms in this question
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