Nuclear Processes - A Level Standard Questions

Q1.

Natural uranium consists of 99.3% and 0.7% . In many nuclear reactors, the fuel consists of enriched uranium enclosed in sealed metal containers.

(a)

(i) Explain what is meant by enriched uranium.

In enriched uranium the proportion of U-235 is greater than in natural uranium

 

(ii) Why is enriched uranium rather than natural uranium used in many nuclear reactors?

Induced fission more probable with U-235 than with U-238

(2)

(b)

(i) By considering the neutrons involved in the fission process, explain how the rate of production of heat in a nuclear reactor is controlled.

  • For a steady rate of fission, one neutron per fission is required to go on to produce further fission.
  • On average each fission produces two or three neutrons.
  • Some neutrons escape the reaction vessel or are absorbed by U-238 without fission occuring
  • Control rods are inserted into the reaction vessel to a depth so that they absorb sufficient neutrons to maintain steady rate of fission.

(ii) Explain why all the fuel in a nuclear reactor is not placed in a single fuel rod.

  • To maximise efficiency the moderator needs to be interspersed between the fuel. Neutrons need to pass through a moderator to slow them (in order to cause further fissions or prevent U-238 absorbing them) - this can be inserted between fuel rods.
  • It makes it easier to replace the fuel in stages

(MAX 5)
(Total 7 marks)