Nuclear fission

• What is nuclear fission?

  The splitting of large, unstable nuclei to form smaller more stable nuclei (+ the emission of spare neutrons).
• Give an example of a fissionable isotope.

  uranium - 235
• What usually needs to happen to induce fission?

  • The unstable nuclei must absorb a neutron
  • spontaneous fission (where no neutron absorption occurs) is rare.
• Alongside two smaller nuclei, what else is emitted in a fission reaction?

  • two or three neutrons
  • gamma rays
  • energy
• What form of energy do all fission products have?

  kinetic energy
• What takes place during a chain reaction in a nuclear reactor?

  • An unstable nucleus absorbs a neutron
  • the nucleus undergoes fission and releases 2 or 3 further neutrons
  • these induce more fission, which results in a chain reaction
• What is the consequence of an uncontrolled chain reaction?

  • The rate of fission events becomes too high and results in the production of too much energy
  • This can lead to a nuclear explosion
• What are the three main components of the core a nuclear reactor?

  • Fuel rods
  • control rods
  • moderator
• What is the role of the moderator in a nuclear reactor?

  To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
• How is the chain reaction in a fission reactor kept under control?

  • Control rods are positioned in between the fuel rods
  • the rate of fission is controlled by moving these rods up and down
  • The lower the rods are inserted, the slower the rate of fission
• What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?

  Fissile nuclei