A nuclear power station uses a radioactive fuel rod. After the fuel rod is removed from the reactor, it must be stored safely for many years because it contains radioactive waste products. One of these waste products has a very long half-life. Explain why a long half-life makes radioactive waste products more dangerous to store than waste products with a short half-life.

WJEC GCSE Physics (Wales) — 2.8 Half-life · Explain · 4 marks · View as Markdown

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

Radioactive waste from nuclear power stations contains isotopes with a range of different half-lives. Safe storage of this waste is a major challenge for the nuclear industry.

Model answer (4 marks)

A long half‑life means the activity of the waste product decreases very slowly, so it remains dangerously radioactive for a much longer period. Consequently it must be kept in safe storage for a much longer time than a waste product with a short half‑life.

Examiner tips

  • Use the definition of half‑life and link it to activity decrease; explain the storage time implication; keep answer concise and to the point.
  • Mention that a long half‑life keeps the activity high for many years, increasing storage duration.

Common mistakes

  • Confusing half‑life with decay constant or lifetime; not linking slow activity decrease to longer storage time; giving irrelevant details about reactor operation.

Mark scheme (4 marks)

  1. Half-life is the time taken for the number of radioactive nuclei (or activity/count rate) to halve
  2. A long half-life means the activity (or count rate) decreases very slowly over time
  3. The waste product remains dangerously radioactive for a much longer period of time
  4. Therefore it must be kept in safe storage for a much longer time (compared to a short half-life waste product)

Key terms in this question

half-life

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