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Nuclear Processes - A Level Standard Questions

Q3.

(a) Explain why, after a period of use, the fuel rods in a nuclear reactor become:

(i) less effective for power production,

Power production depends upon the number of fissions in unit time. After a period of time the amount of (fissionable) uranium (235) in fuel decreases because they have undergone fission. Two fission fragments are produced for each completed fission reaction and they absorb neutrons preventing further fission.


(ii) more dangerous.

Fission fragments are in general neutron heavy and therefore radioactive or unstable emitting beta and gamma radiation Some fission fragments have short half-lives or high activities whereas the Uranium has a long half life and a relativeloy low activity compared to the fission products.

(3)

(b) Describe the stages in the handling and processing of spent fuel rods after they have been removed from a reactor, indicating how the active wastes are dealt with.

  • moved by remote control
  • placed in cooling ponds for several months [or to allow short half life isotopes to decay]
  • transport precautions, e.g. impact resistant flasks
  • separation of uranium from active wastes
  • high level waste stored (as liquid)
  • rods are buried deep underground at geologically stable site
  • storage precautions, e.g. shielded tanks or monitoring
  • reference to vitrification Max 5

(5)
(Total 8 marks)