Transcript Energy Resources Alternative Sources

Chapter 14
Energy Resources
Alternative Sources
Figure 14.1
Figure 14.2
Figure 14.3
Figure 14.4
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
Figure 14.5 U-235 Nuclear fission and chain reaction
Figure 14.6 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
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
Figure 14.7 the nuclear fuel cycle
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
Figure 14.8 Three Mile Island Reactors
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
Figure 14.9 Locations of U.S. uranium reserves
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
Figure 14.10
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
Figure 14.11 U.S. nuclear power plants
Figure 14.12 Percentage of electricity generated
by nuclear fission varies greatly by country
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
Figure 14.13 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 solarheated water
• Solar Electricity
– Photovoltaic cells
Figure 14.14 Distribution of solar energy
Fig. 14.15 Solar heating
Figure 14.16 A solar cell for the generation of electricity
Figures 14.17 a and b
Figures 14.18 a and b
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
Figure 14.19 Geothermal energy
Figure 14.20 Lone Star Geyser, Yellowstone
Figure 14.21 Geothermal power plants worldwide
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
Figure 14.22 The Geysers geothermal power complex
Figure 14.23 Mammoth Terraces, Yellowstone
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
Figure 14.24
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
Figure 14.25
Figure 14.26
Figure 14.27
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
Figure 14.28 Tidal-power generation
Figure 14.29 Ocean thermal energy conversion
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
Figure 14.30 The windiest places in the United States
Figure 14.31 “Art” driven by wind, Palm Springs, California
Figure 14.32 Wind power capacity
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