nuclear fission and fusion

• what is nuclear fission?

  an atom is struck by a neutron causing the nucleus to split into two smaller fragments of nuclei of roughly equal size and to release several neutrons. fission can also happen very rarely without a neutron being absorbed, spontaneous fission.
• what does an atom release after undergoing fission?

  two or three neutrons at high speeds

  energy in the form of gamma radiation plus kinetic energy stored in the fission neutrons and fragment nuclei
• what are chain reactions?

  as two or three neutrons are released in nuclear fission, these neutrons can collide with other nuclei causing a chain reaction of fission.
• what happens inside a nuclear reactor?


  a nuclear reactor has uranium fuel rods spaced out evenly in the reactor core .

  the reactor core contains fuel rods, control rods, and water at a high pressure.

  the fission neutrons are slowed down by collisions with the atoms in water molecules which is vital as fast neutrons don't cause further fission of U-235. the water is a moderator as it slows down fissions.

  control rods in the core absorb surplus neutrons to keep chain reaction under control , depth of rods adjusted to maintain a steady chain reaction.
• what is nuclear fusion?

  spontaneous nuclear fusion happens in stars

  small nuclear fusion into larger ones but the nuclei repel so the temperature and pressure must be very high so that the kinetic energy in the nuclei is then enough too overcome repulsion. the products are mostly stable (not radioactive) and lots of energy is released resulting in stars shining.

  nuclear fusion has a very high energy density and is only spontaneous at high temps and pressures.