Chapter 20

Report
Lecture Outlines
Chapter 20
Environment:
The Science behind the
Stories
4th Edition
Withgott/Brennan
© 2011 Pearson Education, Inc.
This lecture will help you understand:
• Reasons for seeking
alternative fuels
• Contributions to world
energy by alternative
fuels
• Nuclear energy
• The social debate over
nuclear power
• Bioenergy
• Hydroelectric power
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Central Case: Sweden’s search for
alternative energy
• In 1980, Sweden’s people
voted to phase out nuclear
energy
• The government has
promoted hydroelectric,
biomass, and wind power
• Sweden will still use nuclear
power instead of fossil fuels
• Public support for nuclear
power has increased
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Alternatives to fossil fuels
• Our global economy is powered by fossil fuels
- These fuels also power ⅔ of electricity generation
• Fossil fuels are limited and pollute
- We need to shift to resources that are less easily
depleted and environmentally gentler
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Conventional alternatives
• We have alternatives to fossil fuels
- They are renewable and less polluting and harmful
• But they are more expensive in the short term when
external costs are not included in market prices
• The most widely used “conventional alternatives” to
fossil fuels:
- Nuclear, hydroelectric, and biomass energy
• They exert less environmental impact
- These are intermediates along a continuum of
renewability
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The U.S. relies on fossil fuels
• The U.S. relies more on fossil
fuels and nuclear power than
other countries
• Conventional alternatives
play minor, yet substantial,
roles
• The use of conventional
alternatives has been
growing more slowly than
fossil fuels
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Nuclear power
• Nuclear energy occupies an odd and conflicted position
in our debate over energy
• It is free of air pollution produced by fossil fuels
- Yet it has been clouded by weaponry, waste disposal,
and accidents
• Public safety concerns have led to limited development
• The U.S. generates the most electricity from nuclear
power
- But only 20% of U.S. electricity comes from nuclear
- France gets 76% of its electricity from nuclear power
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Fission releases nuclear energy
Nuclei of large atoms are
bombarded with neutrons,
releasing energy and neutrons
• Nuclear energy = the energy that holds together protons
and neutrons within the nucleus of an atom
• Nuclear fission = the splitting apart of atomic nuclei
- The reaction that drives the release of nuclear energy
in power plants
• This chain reaction keeps a constant output of energy
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Nuclear energy comes from uranium
• Nuclear reactors = facilities
within nuclear power plants
• Nuclear fuel cycle = the process
that begins when uranium is
mined
• Radioisotopes = emit subatomic
particles and high-energy
radiation as they decay into
lighter radioisotopes
- They become stable isotopes Uranium is used for
• Uranium-235 decays into lead- nuclear power because
it is radioactive
207
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Nuclear reactors use uranium-235
• Over 99% of uranium occurs as uranium-238 (238U)
- It does not emit enough neutrons for a chain reaction
- So we use 235U, with a half-life of 700 million years
• 235U is enriched to 3% and formed into pellets (UO2)
- Which are incorporated into fuel rods used in nuclear
reactors
• After several years in a reactor, uranium is depleted
- The fuel no longer generates enough energy
• Spent fuel can be reprocessed, but it is expensive
- So it is disposed of as radioactive waste
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Fission in reactors generates electricity
• A moderator = a substance (water or graphite) that slows
the neutrons bombarding uranium
- Allows fission to begin in a nuclear reactor
- Excess neutrons must be soaked up
• Control rods = a metallic alloy that absorbs neutrons
- They are placed into the reactor among the waterbathed fuel rods
- They are moved into and out of the water to control
the rate of the reaction
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A nuclear power plant
• The reactor core is housed in a reactor vessel
- The vessel, steam generator, and plumbing are located
in a containment building
• Containment buildings are constructed to prevent leaks of
radioactivity due to accidents or natural catastrophes
- Not all nations require containment buildings
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A typical light water reactor
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Breeder reactors make better use of fuel
• Breeder reactors use 238U (normally a waste product)
- A neutron is added to 238U to form 239Pu (plutonium)
• They make better use of fuel, generate more power, and
produce less waste
• But breeder reactors are more dangerous than
conventional reactors
- Its highly reactive coolant raises the risk of explosions
- Plutonium can be used in nuclear weapons
- They also are more expensive
• Most of the world’s breeder reactors have been closed
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Fusion remains a dream
Tremendous energy is
released when
deuterium and tritium
are fused to form helium
• Nuclear fusion = forces together small nuclei of
lightweight elements under extremely high temperature
and pressure
• Drives the sun’s output of energy and hydrogen
(thermonuclear) bombs
• If we could control fusion, we could produce vast
amounts of energy from water
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Nuclear power delivers energy cleanly
• Nuclear power helps us avoid emitting 600 million
metric tons of carbon each year
• Power plants pose fewer health risks from pollution
- They are safer for workers than coal-fired plants
• Uranium mining damages less land than coal mining
• Drawbacks of nuclear power:
- Nuclear waste is radioactive
- If an accident or sabotage occurs, the consequences
can be catastrophic
• The world has 436 operating nuclear plants in 30 nations
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Coal versus nuclear power
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Nuclear power poses small risks, but…
• It poses the possibility of catastrophic accidents
• The most serious accident in the U.S. = Three Mile
Island in Pennsylvania in 1979
• Meltdown = coolant water
drained from the reactor
• Temperatures rose inside the
reactor core …
• Melting the metal surrounding
the fuel rods …
• Releasing radiation
The emergency could
have been far worse
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Chernobyl was the worst accident yet
• 1986 explosion at the Chernobyl plant in Ukraine
- The most severe nuclear plant accident ever seen
- It was due to human error and unsafe design
• For 10 days, radiation escaped while crews tried to put
out the fire
- More than 100,000 residents were evacuated
• The landscape for 19 miles still remains contaminated
• The accident killed 31 people directly
- Thousands more became sick or developed cancer
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The Chernobyl accident
The destroyed reactor was encased in a massive concrete
sarcophagus, which is still leaking radioactive material
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Radioactivity from Chernobyl spread widely
Atmospheric currents carried radioactive fallout from
Chernobyl across much of the Northern Hemisphere
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Smaller-scale accidents have occurred
• Western reactors are safer than Chernobyl
- But smaller accidents have occurred
- A 1999 accident in Japan killed two workers and
exposed 400 others to radiation
• Aging plants require more maintenance and are less safe
- Recent terrorist attacks raised fears that similar attacks
could be carried out against nuclear plants
- Or stolen radioactive material could be used in attacks
• The U.S. “megatons to megawatts” program buys
radioactive material from the former Soviet Union
- Using it in power plants
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Waste disposal remains a problem
• Spent fuel rods and all other waste must
be put in a safe location
- Where leaking radioactivity will not
harm future generations
• Waste is held in temporary storage
- Spent rods are stored in water
• U.S. plants are running out of room
- Waste is now stored in thick barrels
of steel, lead, and concrete
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U.S. storage of high-level radioactive waste
• Waste is held at 125 sites in 39 states
• 161 million citizens live within 75 miles of nuclear waste
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Waste storage at Yucca Mountain, Nevada
• It is safer to store all waste in a central repository
- It can be heavily guarded
• Yucca Mountain, Nevada was chosen for this site
- President Obama’s administration does not support it
• So waste will remain at its current locations
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Yucca Mountain, Nevada
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Benefits of storing waste at Yucca Mountain
• It is remote and unpopulated
• It has minimal risk of earthquakes that could damage
the tunnels and release radioactivity
• Its dry climate reduces chances of groundwater
contamination
• The water table is deep underground, making
groundwater contamination less likely
• It is on federal land that can be protected from sabotage
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Concerns with Yucca Mountain as a site
• Some argue that earthquakes and volcanoes could
destabilize the site’s geology
• Fissures in the rock could allow rainwater to seep into
the caverns
• Nuclear waste will need to be transported there
- From current storage areas, and from future nuclear
plants and military installations
- Shipments by rail and truck over thousands of miles
could cause a high risk of accident or sabotage
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Dilemmas slow nuclear power’s growth
• Concerns over waste disposal, safety, and costs have
affected nuclear power’s growth
• It is enormously expensive to build, maintain, operate,
and ensure the safety of nuclear facilities
- Decommissioning plants can be more expensive than
construction
• Power plants serve less than half their expected lifetimes
• Electricity costs more than from coal and other sources
- Governments must subsidize nuclear power
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The future of nuclear energy
• 75% of nuclear power plants in Western Europe will be
retired by 2030
- But some nations are rethinking this because of
concerns over climate change
• Asian nations are increasing nuclear capacity
- 56 plants are under construction
• The U.S. nuclear industry has stopped building plants
- Expanding nuclear capacity would decrease reliance on
fossil fuels and cut greenhouse gas emissions
- Engineers are planning ways to make nuclear power
plants safer and less expensive
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Bioenergy
• Bioenergy (biomass energy) = energy obtained from
organic material that makes up organisms
- Wood, charcoal, agricultural crops, manure
• Bioenergy has great potential for addressing our energy
challenges
Over 1 billion people
use wood for heat,
cooking, and light
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Overharvesting and developing new sources
• Biomass is only renewable if it is not overharvested
- Overharvesting causes deforestation, erosion, and
desertification
- Heavily populated arid regions are most vulnerable
- Cooking produces indoor air pollution
• New biomass sources are being developed
• Biopower = biomass sources are burned in power plants
- Generating heat and electricity
• Biofuels = liquid fuels used to power automobiles
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Biopower generates electricity
Many types of biomass are combusted to generate electricity
• Waste products of industries or
processes
- Woody debris, crop residues
• Specifically grown crops (fastgrowing willow trees, bamboo)
• Co-firing combines biomass and
coal
• Gasification turn biomass to steam
• Pyrolysis produces a liquid fuel
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Scales of production
• Farmers, ranchers, or villages use manure, wood waste,
or biogas from digestion to generate electricity
- Small household biodigesters work in remote areas
• The U.S. has dozens of biomass-fueled power plants
• Biomass power increases efficiency and recycling
- It reduces CO2 emissions and dependence on imported
fossil fuels
- It is better for health and supports rural economies
• But burning crops deprives the soil of nutrients
- Relying only on bioenergy is not a sustainable option
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Ethanol can power automobiles
• Ethanol = a biofuel made by
fermenting carbohydrate-rich
crops
- Ethanol is added to U.S.
gasoline to reduce emissions
• In 2009, 10 billion gallons were
made in the U.S. from corn
• Congressional mandates will
increase ethanol production
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Cars can run on ethanol
• Flexible-fuel vehicles run on
E-85
- 85% ethanol, 15% gasoline
- 8 million cars are in the U.S.
- Most gas stations do not yet
offer this fuel
• Bagasse = crushed sugarcane
residue used to make ethanol
- 50% of new Brazilian cars
are flexible-fuel vehicles
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Ethanol may not be sustainable
• Environmental scientists don’t like corn-based ethanol
• Growing corn impacts ecosystems
- Pesticides, fertilizers, irrigation
- Takes up land that could be left unfarmed
• Ethanol competes with food and drives up food prices
- As farmers shifted to ethanol, corn for food dropped
- Mexicans could not afford tortillas, and so they rioted
• Growing corn requires energy for equipment, pesticides,
and fertilizers
• Its EROI ratio is about 1.5:1, so it is inefficient
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Biodiesel powers engines
• Biodiesel = produced from
vegetable oil, cooking grease,
or animal fats
• Vehicles can run on 100%
biodiesel
- B20 = 20% biodiesel
• Biodiesel reduces emissions
• Its fuel economy is good
• It costs a bit more than gasoline
• Crops are specially grown
- Using land, deforestation
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Novel biofuels are being developed
• Algae produce lipids that can be converted to biodiesel
- Their carbohydrates can be fermented to make ethanol
• It can be grown in ponds, tanks, or photobioreactors
• Algae grows fast and can be harvested every few days
- It can use wastewater, ocean or saline water
- It can capture CO2 emissions to speed its growth
• Biofuels from algae are currently expensive
• Cellulosic ethanol = produced from structural plant
material (e.g., corn stalks) that has no food value
- Switchgrass provides ethanol, habitat, and high EROI
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Two novel biofuels
Algae is a candidate for a
next-generation biofuel
Switchgrass provides fuel
now and may provide
cellulosic ethanol
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Is bioenergy carbon-neutral?
• In principle, biomass energy releases no net carbon
- Photosynthesis removes carbon that is released when
biomass is burned
• Burning biomass is not carbon-neutral:
- If forests are destroyed to plant bioenergy crops
- If we use fossil fuel energy (tractors, fertilizers, etc.)
• The Kyoto Protocol gives incentives to destroy forests for
biofuel crops
- Only emissions from energy use (not land-use
changes) are “counted” toward controlling emissions
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Hydroelectric power (hydropower)
• Hydropower = uses the kinetic energy of moving
water to turn turbines to generate electricity
• Storage technique = water stored in reservoirs
behind dams passes through the dam and turns
turbines
• Run-of-river approach generates electricity without
disrupting the river’s flow
- Flow water over a small dam that does not impede
fish passage
- Useful in areas away from electric grids
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A typical dam
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A run-of-river system
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Hydroelectric power is widely used
• Hydropower accounts for 2.2% of the world’s energy
supply
- And 15.6% of the world’s electricity production
• Nations with large rivers and economic resources have
used dams
• However, many countries have dammed their large rivers
- People want some rivers left undammed
• The U.S. government built dams to employ people and
help end the economic depression of the 1930s
- Engineers exported their dam-building techniques
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Hydropower is clean and renewable
• Hydropower has two clear advantages over fossil fuels
for producing electricity:
- It is renewable: as long as precipitation fills rivers we
can use water to turn turbines
- It is clean: no carbon dioxide is emitted
• Hydropower is efficient
- It has an EROI of 10:1
- As high as any modern-day energy source
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Hydropower has negative impacts
• Damming rivers destroys wildlife habitats
- Upstream areas are submerged
- Downstream areas are starved of water
• Natural flooding cycles are disrupted
- Downstream floodplains don’t get nutrients
• Downstream water is shallower and warmer
• Periodic flushes of cold reservoir water can kill fish
• Dams block passage of fish, fragmenting the river and
reducing biodiversity
• Large dams can cause earthquakes or collapse
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Hydropower may not expand much more
• China’s Three Gorges Dam is the world’s largest dam
- It displaced 1 million people
- Generates as much electricity as dozens of coal-fired
or nuclear plants
• Most of the world’s large rivers have already been
dammed
• People have grown aware of the ecological impact of
dams and resist more construction
• Developing nations with rivers will increase hydropower
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Conclusion
• With limited fossil fuel supplies, nations are trying to
diversify their energy portfolios
• Nuclear power showed promise
- But high costs and public fears stalled its growth
• Biomass energy sources include wood and newer biofuels
- They can be carbon-neutral but are not strictly
renewable
• Hydropower is a renewable, pollution-free alternative
- But it is nearing maximal use and can involve
substantial ecological impacts
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QUESTION: Review
Conventional alternative fuels:
a) Exert less environmental impact than fossil fuels but
are currently not feasible
b) Are intermediate sources of fuel that can help us on
our path towards sustainability
c) Are final sources of fuel that will give us energy
independence
d) Are no longer available for widespread use
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QUESTION: Review
The reaction that drives the release of energy in today’s
nuclear power plants is:
a)
b)
c)
d)
Nuclear fission
Nuclear fusion
Control rods
Nuclear emergencies
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QUESTION: Review
Why have nuclear power plants not been popular in the
United States?
a)
b)
c)
d)
Fears about accidents or sabotage
Storage of nuclear waste is still not solved
High costs of building and maintaining plants
All are issues regarding nuclear energy
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QUESTION: Review
Ethanol in the United States is made mainly from ______,
and is used to ______.
a)
b)
c)
d)
Soybeans, heat homes
Sugarcane, drive cars
Corn, drive cars
Willow trees, make electricity
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QUESTION: Review
Which of the following is an interesting future biofuel?
a)
b)
c)
d)
Corn
Algae
Nuclear
Shale oil
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QUESTION: Review
Which of the following forms of hydropower is least
environmentally destructive?
a)
b)
c)
d)
The storage approach
Run-of-river approach
Bend-of-river approach
All of these are destructive forms and none should be
used.
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QUESTION: Weighing the Issues
Given the choice of living next to a coal-burning power
plant or nuclear plant, which would you choose?
a) The nuclear plant, because it’s cleaner.
b) The coal plant, because it won’t be as likely a target
for terrorists.
c) Neither one; I’d move to another place.
d) Either one; I don’t care.
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QUESTION: Interpreting Graphs and Data
If ethanol in the United States continues to be produced
from corn, a drawback suggested from this graph could be:
a) More corn is available
for ethanol.
b) More competition
between food and fuel.
c) Less land planted in
corn.
d) None of these.
© 2011 Pearson Education, Inc.

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