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TOPIC 8 in a nutshell

TOPIC 8 in a nutshell. 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 6x10 20 J

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TOPIC 8 in a nutshell

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  1. TOPIC 8 in a nutshell

  2. 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.

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

  4. World Total Primary Energy Supply **Other includes geothermal, solar, wind, heat, etc.

  5. U.S. Energy Flow

  6. 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

  7. Advantages Cheap High energy density Already in use and can be used directly Disadvantages Non renewable Pollutes the environment Contributes to the greenhouse effect Fossil Fuels

  8. 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 earth’s Uranium

  9. 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

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

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