Transcript Nuclear Energy Pwrpt

Chapter 12
Nuclear Energy
Overview of Chapter 12
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Introduction to Nuclear Power
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Nuclear Fission
Pros and Cons of Nuclear Energy
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Cost of Nuclear Power
Safety Issues at Power Plants
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Atoms and radioactivity
Three Mile Island & Chornobyl
Nuclear Weapons
Radioactive Waste
Future of Nuclear Power
Introduction to Nuclear Energy
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Nuclear energy
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Nuclear fission
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Energy released by nuclear fission or fusion
Splitting of an atomic nucleus into two smaller
fragments, accompanied by the release of a
large amount of energy
Nuclear fusion
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Joining of two lightweight atomic nuclei into a
single, heavier nucleus, accompanied by the
release of a large amount of energy
Atoms and Radioactivity
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Nucleus
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Comprised of protons
(+) and neutrons
(neutral)
Electrons (-) orbit
around nucleus
Neutral atoms
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Same # of protons and
electrons
Atoms and Radioactivity
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Atomic mass
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Atomic number
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Sum of the protons and neutrons in an atom
Number of protons per atom
Each element has its own atomic number
Isotope
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Usually an atom has an equal number of
neutrons and protons
If the number of neutrons is greater than the
number of protons = isotope
Radioactive Isotope
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Unstable isotope
Radioactive Decay
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Example
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Emission of energetic particles or rays from
unstable atomic nuclei
Uranium (U-235) decays over time to lead (Pb207)
Each isotope decays based on its own halflife
Radioactive Isotope Half-lives
Nuclear Fission
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Nuclear Fuel Cycle
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processes involved
in producing the
fuel used in
nuclear reactors
and in disposing of
radioactive
(nuclear) wastes
Nuclear Fission
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U-235 is
bombarded with
neutrons
The nucleus
absorbs neutrons
It becomes
unstable and
splits into 2
neutrons
2-3 neutrons are
emitted and
bombard another
U-235 atom
Chain reaction
How Electricity is Produced
Breeder Nuclear Fission
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A type of nuclear fission in which nonfissionable U-238 is converted into
fissionable Pu-239
Pros and Cons of Nuclear Energy
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Pros
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Less of an immediate environmental impact
compared to fossil fuels
Pros and Cons of Nuclear Energy
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Pros (continued)
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Carbon-free source of electricity- no
greenhouse gases emitted
May be able to generate H-fuel
Cons
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Generates radioactive waste
Many steps require fossil fuels (mining and
disposal)
Expensive
Cost of Electricity from Nuclear
Energy
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Cost is very high
20% of US electricity is from Nuclear
Energy
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Expensive to build nuclear power plants
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Affordable due to government subsidies
Long cost-recovery time
Fixing technical and safety issues in
existing plants is expensive
Safety Issues in Nuclear Power Plants
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Meltdown
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At high temperatures the metal encasing the
uranium fuel can melt, releasing radiation
Probability of meltdown or other accident
is low
Public perception is that nuclear power is
not safe
Sites of major accidents:
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Three Mile Island
Chornobyl (Ukraine)
Three-Mile Island
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1979- most serious reactor accident in US
50% meltdown of reactor core
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Containment building kept radiation from
escaping
No substantial environmental damage
No human casualties
Elevated public apprehension of nuclear
energy
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Led to cancellation of many new plants in US
Chornobyl
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1986- worst accident
in history
1 or 2 explosions
destroyed the nuclear
reactor
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Large amounts of
radiation escaped into
atmosphere
Spread across large
portions of Europe
Chornobyl
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Radiation
spread was
unpredictable
Radiation
fallout was
dumped
unevenly
Death toll is
10,000100,000
Nuclear Energy and Nuclear Weapons
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31 countries use nuclear energy to create
electricity
These countries have access to spent fuel
needed to make nuclear weapons
Safe storage and handling of these
weapons is a concern
Radioactive Waste
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Low-level radioactive waste•
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Radioactive solids, liquids, or gasses that give off small
amounts of ionizing radiation
High-level radioactive waste•
Radioactive solids, liquids, or gasses that give off large
amounts of ionizing radiation
Radioactive Wastes
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Long term solution to waste
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Deep geologic burial –Yucca Mountain
As of 2004, site must meet EPA million year
standard (compared to previous 10,000 year
standard)
Possibilities:
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Above ground mausoleums
Arctic ice sheets
Beneath ocean floor
Radioactive Waste
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Temporary storage solutions
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In nuclear plant facility (require high security)
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Under water storage
Above ground concrete and steel casks
Need approved permanent options soon.
Case-In-Point Yucca
Mountain
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70,000 tons of highlevel radioactive waste
Tectonic issues have
been identified
Decommissioning Nuclear Power Plants
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Licensed to operate for 40 years
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Several have received 20-year extensions
Power plants cannot be abandoned when
they are shut down
Three solutions
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Storage
Entombment
Decommissioning (dismantling)
Fusion
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Fuel= isotopes of hydrogen
Fusion
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Way of the future??
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Problems
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Produces no high-level waste
Fuel is hydrogen (plenty of it!)
It takes very high temperatures (millions of
degrees) to make atoms fuse
Confining the plasma after it is formed
Scientists have yet to be able to create
energy from fusion