Energy Resources Alternative Sources

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Energy ResourcesAlternative Sources

• Chapter 15

Photo from State of Indiana
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Nuclear Power - Fission

• Fission splitting apart the atom releases
  energy
• Currently commercially feasible
• Uranium-235 fuels most fission reactors
• A controlled chain reaction occurs with
  continuous and moderate release of energy
• The energy release heats water within the core of
  a reactor
• This heat is transferred through heat exchangers
  to outer loops where steam generation is possible
  for generating power or propulsion

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U-235 Nuclear fission and chain reaction
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Conventional nuclear fission reactor
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Geology of Uranium

• 95 of uranium found in sedimentary (or
  metasedimentary) rocks
• Generally found in sandstones
• Uranium is weathered from other rocks and
  deposited by migrating ground water
• Minor amounts of uranium are present in many
  crustal rocks
• Granitic rocks and carbonates may be rich in
  uranium
• Uranium oxide (U3O8) yellowcake

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Extending the Nuclear Fuel Supply

• Uranium-235 is not the only fuel useful for
  fission-reactors
• It is the most plentiful naturally occurring one
• Uranium-238 can absorb a neutron and converts to
  plutonium-239 and is fissionable
• U-238 makes up 99.3 of natural uranium
• Used for over 90 of reactor grade enriched
  uranium
• Breeder reactor can maximize the production of
  other radioactive fuels
• Expensive and complex

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The nuclear fuel cycle
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Concerns Related Nuclear Reactor Safety

• Nuclear reactor safety is a serious undertaking
• Controlled release of very minor amounts of
  radiation occur
• Major concerns are with accidents and sabotage
• Loss of coolant in the core could produce a core
  meltdown
• This event could allow the fuel and core
  materials to melt into an unmanageable mass and
  then migrate out of the containment structure
• Could result in a catastrophic release of
  radiation into the environment
• Reactors must be located away from active faults

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Three Mile Island Reactors
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Concerns Related to Fuel Handling

• Mining and processing of uranium ore is a
  radioactive hazard
• Miners are exposed to higher levels of
  radioactivity than the general population
• Tailings piles are exposed to weather and the
  uranium is mobilized into the environment
• Plutonium is both radioactive and chemically
  toxic
• Easy to convert into nuclear weapons material
• Uranium (enriched) is serious security problem

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Locations of U.S. uranium reserves
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Radioactive Wastes

• Energy produced by nuclear fission produces
  radioactive wastes
• Difficult to treat
• No long-term, permanent storage or disposal sites
  in operation
• Nuclear power plants are decommissioned once
  operations cease
• Expensive to decommission these plants
• Abundant radioactive contaminated material
  associated with these plants that must be
  permanently stored somewhere and safely

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Risk Assessment and Risk Projection

• No energy source is risk-free with acceptable
  risk
• 8 of U.S. energy is supplied by nuclear power in
  2002
• Nuclear-plant cancellation is not without its
  costs
• Nuclear plants have lower fueling and operating
  costs than coal-fired plants
• Reliance on nuclear power varies widely
• Different people weigh the pros and cons of
  nuclear fission power in different ways

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U.S. nuclear power plants
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Percentage of electricity generated by nuclear
fission varies greatly by country
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Nuclear Power - Fusion

• Nuclear fusion is the opposite of nuclear fission
• Sun is a gigantic fusion reactor
• Fusion is a cleaner form nuclear power than
  fission
• Fusion involves combining smaller nuclei to
  form larger ones
• Can produces abundant energy
• Hydrogen is plentiful and is the raw material
  required
• Fusion difficult to achieve given current
  technology
• Theoretical not yet economically attained

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One nuclear fusion reaction
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Solar Energy

• Abundant solar energy reaches the earths surface
• Be dissipated in various ways
• Solar energy is free, clean, and a renewable
  resource
• Limitations are latitude and climate
• Solar Heating
• Passive solar heating no mechanical assistance
• Active solar heating mechanical circulation of
  solar-heated water
• Solar Electricity
• Photovoltaic cells

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Distribution of solar energy
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Passive solar heating
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A solar cell for the generation of electricity
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Geothermal Power

• The earth contains a great deal of heat, most of
  it left over from its early history, some
  generated by decay of radioactive elements in the
  earth
• Interior of the earth is very hot
• Abundant source of heat and hot water
• Magma rising into the crust bring abundant heat
  up into the crust as geothermal energy
• Heat escaping from the magma heats water and the
  water convectively circulates

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Geothermal energy
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Lone Star Geyser, Yellowstone
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Geothermal power plants worldwide
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Geothermal Power

• Applications of Geothermal Energy
• Circulating geothermal water (not steam yet)
  through buildings to heat them
• Use the hot geothermal water to raise the
  temperature of other water to reduce cost of
  heating that water
• Geothermal water can be used to run electric
  generators by direct contact with turbines, or by
  converting a secondary fluid to vapor for driving
  turbines (binary geothermal power plant).
• Environmental Considerations
• Some locations have sulfur gases in the
  geothermal fluids
• Other chemical (caustic) elements may be present
  that can clog geothermal circulation systems

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The Geysers geothermal power complex
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Mammoth Terraces, Yellowstone
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Alternative Geothermal Sources

• Many areas away from plate boundaries have high
  geothermal gradients
• These areas contain hot-dry-rock type geothermal
  resources
• Deep drilling into such rocks may produce
  appreciable amounts of geothermal energy

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Hydropower

• Falling or flowing water has long been used to
  produce energy for humans
• Hydroelectric power produces less than 5 of U.S.
  energy requirement
• Typically, a stream is dammed and the discharge
  is regulated to produce electricity
• Hydropower is clean and non-polluting
• Hydropower is renewable as long as streams have
  water flowing in them
• Damming streams, though, changes their ecosystem,
  often in a negative way

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Limitations on Hydropower Development

• Reservoirs tend to
• Silt up
• Increase surface area exposed to evaporation
• Destroy habitats
• Encourage earthquakes
• Expensive to build
• Reservoirs are stationary power sources

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Tidal Power and Ocean Thermal Energy Conversion

• Limited energy production possible
• Not enough difference in high-tide versus
  low-tide displacement of water (only about 1
  meter difference)
• Most economic potential requires about 5 meters
  difference
• Ocean thermal energy conversion (OTEC) is another
  clean, renewable technology. It exploits the
  temperature difference between warm surface water
  and the cold water at depth

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Tidal-power generation
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Ocean thermal energy conversion
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Wind Energy

• The winds are ultimately powered by the sun, and
  thus wind energy can be viewed as a variant of
  solar energy
• Clean and renewable energy resource
• Many technological improvements have increased
  the energy production from windmills
• Areas of best wind generation potential tend to
  be far from population centers that would benefit
  from them
• Wind Farms are large scale operations producing
  about 1 megawatt per windmill
• Abundant small scale windmills involve small wind
  turbines lifting water on a ranch or farm

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The windiest places in the United States
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Art driven by wind, Palm Springs, California
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Wind power capacity
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Biomass

• Biomass refers to the total mass of all the
  organisms living on earth
• Biomass energy uses discarded waste material that
  is burned as a fuel to produce energy
• Biomass fuels include wood, paper, crop waste,
  and other combustible waste
• Alcohol, as a fuel, is produced from grains, such
  as corn
• Mixed with gasoline to form gasohol
• Qualifies as a renewable resource