Transcript Energy Resources Alternative Sources

Chapter 15
Photo from State of Indiana
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
U-235 Nuclear fission and chain reaction
Conventional nuclear fission reactor
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 fissionreactors
 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
The nuclear fuel cycle
Concerns Related Nuclear Reactor Safety
 Nuclear reactor safety is a serious undertaking
 Controlled release of very minor amounts of radiation
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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
U.S. nuclear power plants
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
One nuclear fusion reaction
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
Passive solar heating
A solar cell for the generation of electricity
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 energy
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
The Geysers geothermal power complex
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
 Damming streams, though, changes their ecosystem,
often in a negative way
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
Tidal-power generation
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
The windiest places in the United States
“Art” driven by wind, Palm Springs, California
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