energy resources alternative sources chapter 14. figure 14.1
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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
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”
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
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
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
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
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
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
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
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
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 (stream) can be used to run electric generators
• Environmental Considerations– Some locations have sulfur gases in the geothermal
fluids– Other chemical (caustic) elements may be present
that can clog geothermal circulation systems
Limitations on Geothermal Power
• First, most geothermal fields have limited life times and taper off
• Second, geothermal fields are stationary – not mobile
• Third, not many geothermal sites are suitable for energy production
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
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
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
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
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
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