TOPIC 8 in a nutshell

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TOPIC 8 in a nutshell
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Why Bother?

• The average world use of energy per person is
  about 300MJ /day (How many kW is that?)
• 3.5 kW (U.S. 10 kW, Africa 0.1 kW)
• This means that the energy demand for the world
  for one year is about 6x1020 J
• The annual world production of energy is
  estimated to be 1.5x1021J.and given the rate at
  which the population is increasing, we are faced
  with a serious problem.

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Energy Sources

• Renewable Solar (wind and wave as a result of
  solar) and tidal
• Non-renewable fossil fuels and nuclear fuels

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World Total Primary Energy Supply
Other includes geothermal, solar, wind, heat,
etc.
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U.S. Energy Flow
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Energy Density

• Coal 30 MJ/kg
• Wood 16 MJ/kg
• Diesel 45 MJ/kg
• Gasoline 47 MJ/kg
• Kerosene 46 MJ/kg
• Natural gas 39 MJ/m3
• Enriched Uranium-235 2100 GJ/kg
• Water in a hydroelectric plant 0.001 MJ/kg

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Fossil Fuels

• Advantages
• Cheap
• High energy density
• Already in use and can be used directly

• Disadvantages
• Non renewable
• Pollutes the environment
• Contributes to the greenhouse effect

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Nuclear Power

• Uses enriched U-235 because it is one of the few
  materials that can undergo induced fission. It
  only makes up 0.7 of the earths Uranium

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How does it work?

• Uranium rods surrounded by a moderator (usually
  water and sometimes graphite) which slows the
  neutrons down so than can be absorbs by the U-235
• Control rods are placed in between the Uranium
  (fuel) rods. These rods absorb neutrons so the
  rate of the fission can be controlled. They can
  be made of Boron

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Why Boron?

• High neutron capture cross section (aka can
  attract neutrons without splitting)
• B-10 isotope is a good example