Nuclear energy and decay

• Fission


  Fission reactions take place in nuclear reactors to produce energy
• Fission reaction


  1. Slow-moving neutron is absorbed by a uranium-235 nucleus

  2. Nucleus splits into 2 smaller nuclei

  3. 2 or 3 fast moving neutrons are released
• Control rods


  • They absorb 2 out of the 3 neutrons released from each fission reaction, allowing only 1 neutron to cause a reaction
• Moderator


  • Slows the neutrons released to ensure they can be absorbed by the uranium nuclei to cause another reaction
• Fission chain reaction


  1. One neutron starts the reaction

  2. 2 or 3 more neutrons are released

  3. These neutrons can go on to cause another reaction

  4. If uncontrolled, can cause a meltdown
• Nuclear equations for fission or fusion follow the same rules as in unit 2.7, with the sum of nucleon numbers and proton numbers equal before and after the reaction
• The symbol for a neutron, 1 n, is often used in these equations
• Fusion


  Two small nuclei are fused together to create one larger nucleus, requiring a lot of energy to overcome repulsion
• Control rods can be raised or lowered into the reactor to absorb neutrons
• Concrete shield ensures no radiation escapes
• Graphite moderator slows the neutrons so they can be absorbed by the uranium nuclei