Explain why nuclear fusion has not yet been used as a commercial source of energy, despite being capable of releasing large amounts of energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Scientists have been researching nuclear fusion as a potential energy source for several decades. In fusion, two small, light nuclei join to form a larger, heavier one and release energy.
Model answer (4 marks)
Fusion requires temperatures of millions of kelvin so that the nuclei have enough kinetic energy to overcome their electrostatic repulsion. Such temperatures can only be achieved in a plasma, which must be confined for a sufficient time. Containing a plasma at these temperatures is extremely difficult and expensive, usually requiring magnetic or inertial confinement. Consequently, the energy input needed to maintain the plasma exceeds the energy produced, so a net positive energy output has not yet been achieved.
Examiner tips
- Use the term ‘plasma’ and ‘electrostatic repulsion’
- Explain why high temperature is needed for overcoming Coulomb barrier
- Mention confinement difficulty and cost
- State that net energy output has not been reached
Common mistakes
- Saying fusion is impossible instead of ‘not yet achieved net output’
- Forgetting to mention the need for plasma confinement
- Using ‘high pressure’ instead of ‘high temperature’
Mark scheme (4 marks)
- Fusion requires extremely high temperatures to occur
- High temperatures are needed so that the nuclei have enough energy / speed to overcome the electrostatic repulsion between them
- It is very difficult / expensive to contain a plasma or material at such high temperatures
- More energy is currently needed to sustain the reaction than the reaction releases / engineers have not yet achieved a sustained net energy output
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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