Compare nuclear fusion and nuclear fission as energy sources. In your answer, refer to the fuels used, the conditions required, and the type of waste produced.

Eduqas A-Level Physics — 3.6 Nuclear energy · Compare · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

Fusion uses light nuclei such as hydrogen isotopes (deuterium, tritium) as fuel, whereas fission uses heavy nuclei such as uranium‑235 or plutonium‑239.

Fusion requires extremely high temperatures (≈10^7–10^8 K) and pressures to overcome the Coulomb barrier, whereas fission can occur at much lower temperatures and is initiated by a neutron striking a heavy nucleus.

Fission produces long‑lived radioactive waste that remains hazardous for thousands of years. Fusion produces little or no long‑lived waste; the main products are helium and short‑lived isotopes that decay quickly.

Examiner tips

  • Use the exact terms ‘light nuclei’ and ‘heavy nuclei’ to show understanding of fuel types.
  • Mention the temperature requirement for fusion and the neutron‑induced trigger for fission to hit the conditions point.
  • State the waste difference clearly – long‑lived vs. short‑lived/none – to secure the waste point.
  • Keep each point concise to fit the 5‑mark limit.

Common mistakes

  • Confusing the temperature requirement for fission with that of fusion.
  • Saying fusion produces ‘no waste’ instead of ‘little or no long‑lived waste’.
  • Using vague terms like ‘heavy elements’ without specifying uranium or plutonium.

Mark scheme (5 marks)

  1. Fusion uses light nuclei (e.g. hydrogen isotopes) as fuel whereas fission uses heavy nuclei (e.g. uranium) as fuel
  2. Fusion requires extremely high temperatures (and pressures) to occur
  3. Fission can occur at much lower temperatures / fission is triggered by a neutron striking a nucleus
  4. Fission produces radioactive waste that remains dangerous for a long time
  5. Fusion produces little or no long-lived radioactive waste (products are largely helium / non-radioactive)

Key terms in this question

nuclear fusion · nuclear fission

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