Spontaneous Fission

• When a larger nuclide splits into two smaller daughter nuclides.
• Only found to occur in nuclides with masses  230.
• Most are extremely slow, e.g.  the half-life for the spontaneous fission of ²³⁸U is 10¹⁶ billion years.
• In order for a nuclide to undergo spontaneous fission, it must overcome the force of the internal barrier.
  • Internal Barrier - An activation energy stronger than the force of repulsion of the positively charged protons which keeps a nuclide from ejecting protons or alpha particles.

Induced Fission

• When a nuclide absorbs a thermal neutron and consequently splits into two smaller daughter nuclides.

• Compared to the efficiency of burning natural gas - 50 kJ/g, ²³⁵U produces 80 million kJ/g when  it undergoes induced fission.

The first artificial nuclear reactor was created with uranium fuel by Enrico Fermi at the University of Chicago on December 2, 1942.

An atomic bomb is a nuclear chain reaction that is left uncontrolled

Critical Mass - The amount of fissionable material necessary  for the chain reaction to sustain itself.

Fertile Nuclide - A nuclide that can be converted into on e that undergoes spontaneous fission

e.g.  ²³⁹U can be converted into ²³⁹Pu.

Nuclear Reactor

• Five basic components:
  1. Fuel rods - Enriched uranium which undergoes the chain reaction.
  2. Moderator - Turns the neutrons that are produced from the fission into thermal neutrons (i.e. slows them down) so that they may be absorbed by more uranium to continue the chain reaction.

     e.g.  water, carbon, beryllium.

  3. Control rods - Move in and out to absorb some of the excess neutrons to prevent the reaction from becoming too fast and uncontrolled.

     e.g. cadmium rods.

  4. Coolant - Water transfers the heat generated by the reaction to a separate water system which turns into steam.  The steam is directed toward turbogenerators which produces electricity.
  5. Shielding - Extremely dense concrete shields are placed around the reactor structure to prevent radiation from escaping to the environment.

Pros and Cons of Nuclear Fission

• Pros
  1. Extremely efficient source of power.
• Cons
  1. Accidents happen
     • e.g.  Chernobyl, USSR in 1986 - A runaway fission reaction at the power plant caused a violent explosion.

       31 people were killed, 15,000 people are estimated to die within the next 50 years from radioactive fallout.

     • e.g.  Three Mile Island, US in 1979 - Partial meltdown.
  2. Nuclear waste:  storage, transportation, etc.

     Not only of used fuel rods, but also the entire reactor structure once the power plant cannot be used.

Next:  "Nuclear Fusion"