Chain reactions

• What pairs of atoms can uranium split into?

  Krypton-91 and barium-143
• What is true about the new nuclei formed from uranium fission?

  All these new nuclei are radioactive
• What happens when a uranium atom splits?

  It releases two or three neutrons
• What is a chain reaction in nuclear fission?

  It is when neutrons cause further fissions
• Why must chain reactions in reactors be carefully controlled?

  To prevent uncontrolled energy release
• What do the neutrons released by fission reactions have?

  They have a lot of energy
• What is required for neutrons to cause further fissions?

  They must be moving slowly enough
• What are slow-moving neutrons called?

  Thermal neutrons
• What is the purpose of a moderator in a nuclear reactor?

  To slow down fast-moving neutrons
• What is an example of a moderator?

  Graphite
• What do control rods do in a nuclear reactor?

  They limit the rate of fission
• What material are control rods often made of?

  Boron
• How are control rods used in a reactor?

  They are raised and lowered to control fission
• What does a steady rate of nuclear fission mean?

  One new neutron produces another fission
• What happens if the chain reaction is left unchecked?

  Large amounts of energy are released quickly
• What could a runaway reaction in a nuclear reactor lead to?

  It could lead to an explosion
• What is the relationship between nuclear power stations and steam engines?

  • Nuclear power stations create controlled chain reactions
  • They generate steam to produce electricity