2. Advantages of Nuclear Power
• Nuclear electricity is reliable and relatively cheap
(with an average generating cost of 2.9 cents
per kW/h) once the reactor is in place and
operating.
• Large reserves of Uranium in United States -
Fuel for nuclear power plants will not run out for
tens of thousands of years
• Nuclear power plants contribute no greenhouse
gasses and few atmospheric pollutants
3. Disadvantages of Nuclear Power
• Uranium is ultimately a nonrenewable resource.
• Nuclear power plants are extremely costly to
build.
• The slight possibility that nuclear power plants
can have catastrophic failures.
• Large environmental impact during the mining
and processing stages of uranium are numerous.
• Nuclear waste (Spent nuclear fuel) is extremely
hazardous and must be stored safely for
thousands of years.
4. Comparing Uranium to Coal
*1 kg of uranium-235 will generate as much energy
as 3,000 tons of coal without CO2 emissions
8. Nuclear Power in the U.S.
• The U.S. has 104
nuclear power plants
(more than any other
country)
• Combined, these
reactors produce
about 100 billion
watts of electricity
(20% of the total)
9. Nuclear Power in the U.S.
• No new reactors have been completed in
the U.S. since 1979.
• Why???
– High Operating Costs
– Liability Problems
– Wastes
– Health Concerns
– Terrorism
– Public Misconceptions
10. Illinois Nuclear Power
• Nuclear power typically accounts for nearly
one-half of Illinois electricity generation and
more than one-tenth of all the nuclear power
generated in the United States.
• With 11 operating reactors at six nuclear power
plants, Illinois ranks first among the States in
nuclear generation.
• The growth of the Illinois nuclear industry is due
largely to State government initiatives, which
began encouraging nuclear power development
in the 1950s
11. Illinois Nuclear Power
• The origin of all of the
commercial and military
nuclear industries in the
world can be traced back
to December 2, 1942 at
the University of Chicago.
• On that day, a team of
scientists under Dr. Enrico
Fermi initiated the first
controlled nuclear chain
reaction.
12. Illinois Nuclear Power
• There are 6 operating nuclear power plants in
Illinois: Braidwood, Byron, Clinton, Dresden,
LaSalle, and Quad Cities.
• With the sole exception of the single-unit Clinton
plant, each of these facilities has two reactors.
• The two reactors at Braidwood and both reactors
at Byron are pressurized light water reactors
(PWR).
• The reactors at the other facilities (Clinton,
Dresden, LaSalle, and Quad Cities are boiling
water reactors (BWR).
13. Fission and Fusion
• Fission: A heavy nucleus is split into
smaller nuclei, releasing energy
• Fusion: Two light nuclei fuse into a
heavy nucleus, releasing energy
– Fusion generates much more energy
than fission
– Fusion of hydrogen into helium is what
provides power to the sun (and thus to
the Earth)
14. Energy from Fission
• When a neutron strikes a uranium-235 nucleus,
it splits into two nuclei, releasing energy
• Example: n + 235
U -> 93
Kr + 141
Ba + 2n
• One neutron goes in, two neutrons come out
15. Chain Reactions
• If at least one
neutron from each
fission strikes
another nucleus, a
chain reaction will
result
• An assembly of
uranium-235 that
sustains a chain
reaction is critical
16. Power Plants and Bombs
• Natural uranium contains 99.3% uranium-238
and 0.7% uranium-235
• Only uranium-235 can create fission chain
reactions
– Nuclear power plants use uranium that has
been enriched to 3% uranium-235
– Nuclear bombs use uranium that has been
enriched to 95% uranium-235
• 3% enriched uranium can never explode!
17. Nuclear Bombs
• Since neutrons initiate fission, and each
fission creates more neutrons, there is
potential for a chain reaction
18. Nuclear Bombs
• Have to have enough fissile material
around to intercept liberated neutrons
• Critical mass for 235
U is about 15 kg, for
239
Pu it’s about 5 kg
• Bomb is dirt-simple: separate two sub-
critical masses and just put them next to
each other when you want them to
explode!
– difficulty is in enriching natural uranium to
mostly 235
U
20. Mining and Milling
• Uranium is usually mined by
either surface (open cut) or
underground mining
techniques, depending on the
depth at which the ore body is
found.
• From these, the mined uranium
ore is sent to a mill which is
usually located close to the
mine.
21. Mining and Milling
• At the mill the ore is crushed and
ground to a fine slurry which is
leached in sulfuric acid to allow the
separation of uranium from the
waste rock.
• It is then recovered from solution
and precipitated as uranium oxide
(U308) concentrate.
– Sometimes this is known as
"yellowcake“
22. Conversion
• Because uranium
needs to be in the
form of a gas before it
can be enriched, the
U308 is converted into
the gas uranium
hexafluoride (UF6) at
a conversion plant.
23. Enriching
• Need to enrich uranium to at least 3% U-235 for
a power plant
• Gaseous Diffusion Method
– UF6 (hexafluoride) gas heated
– U-238 is heavier than U-235
– Hexafluoride Gas can be separated into two streams
• Low velocity U-238
• High Velocity U-235
• Centrifuge Method
– Gas spun in centrifuge
– Lighter U-235 will separate from heavier U-238
24. Fuel Conversion
• Enriched Uranium transported to a fuel
fabrication plant where it is converted to
uranium dioxide (UO2) powder and
pressed into small pellets.
• These pellets are inserted into thin tubes,
usually of a zirconium alloy (zircalloy) or
stainless steel, to form fuel rods.
• The rods are then sealed and assembled
in clusters to form fuel assemblies for use
in the core of the nuclear reactor.
25. Fuel Packaging in the Core
• Rods contain uranium
enriched to ~3% 235
U
• Need roughly 100 tons
per year for a 1 GW plant
• Uranium stays in three
years, 1/3 of the fuel rods
are cycled annually
26. The Reactor Core
• The reactor core consists
of fuel rods and control
rods
– Fuel rods contain enriched
uranium
– Control rods are inserted
between the fuel rods to
absorb neutrons and slow
the chain reaction
• Control rods are made of
cadmium or boron, which
absorb neutrons effectively
27. Moderators
• Neutrons produced during fission in the core
are moving too fast to cause a chain reaction
– Note: This is not an issue with a bomb, where
fissile uranium is so tightly packed that fast moving
neutrons can still do the job.
• A moderator is required to slow down the
neutrons
• In Nuclear Power Plants water (light or
heavy) or graphite acts as the moderator
– Graphite increases efficiency but can be unstable
(Chernobyl)
28. Light vs. Heavy Water
• 99.99% of water molecules contain normal
hydrogen (i.e. with a single proton in the
nucleus)
• Water can be specially prepared so that the
molecules contain deuterium (i.e. hydrogen with
a proton and a neutron in the nucleus)
• Normal water is called light water while water
containing deuterium is called heavy water
• Heavy water is a much better moderator but is
very expensive to make
29. Boiling Water Reactor (BWR)
• Heat generated in
the core is used
to generated
steam through a
heat exchanger
• The steam runs a
turbine just like a
normal power
plant
31. Pressurized Water Reactor (PWR)
• Water in the core heated top 315°C but is
not turned into steam due to high pressure
in the primary loop.
• Heat exchanger used to transfer heat into
secondary loop where water is turned to
steam to power turbine.
• Steam used to power turbine never comes
directly in contact with radioactive
materials.
33. Spent Nuclear Storage
• Fuel rods must be replaced every 3 years.
• Spent Fuel Rods are temporarily stored in
special ponds which are usually located at
the reactor site.
• The water in the ponds serves the dual
purpose of acting as a barrier against
radiation and dispersing the heat from the
spent fuel.
34. Spent Fuel Rods Radiation
• Spent fuel
assemblies taken
from the reactor
core are highly
radioactive
• Contain
plutonium-239,
which is radioactive.
• Forms from the
reaction of U-238
and neutrons in the
core
35. Fate of Spent Fuel
There are two alternatives for spent fuel:
2. Reprocessing to recover the usable portion of it
3. Long-term storage and final disposal without
reprocessing.
36. Uranium Reprocessing
• Spent fuel still contains approximately 96%
of its original uranium, of which the
fissionable U-235 content has been
reduced to less than 1%.
• About 3% of spent fuel comprises waste
products and the remaining 1% is plutonium
produced while the fuel was in the reactor
• Reprocessing extracts useable fissile U-238
and Plutonium from the spent fuel rods
37. Uranium Reprocessing
• Most of the spent fuel can be reprocessed
but isn’t in the U.S.
• Federal law prohibits commercial
reprocessing because it will produce
plutonium (which can be used both as a
fuel and in constructing bombs)
38. Nuclear Waste Disposal
• In the U.S., no high-level nuclear waste is ever
disposed of--it sits in specially designed pools
resembling large swimming pools (water cools the
fuel and acts as a radiation shield) or in specially
designed dry storage containers.
• Spent nuclear fuel must be isolated for thousands
of years
• After 10,000 years of radioactive decay, according
to EPA standards, the spent nuclear fuel will no
longer pose a threat to public health and
39. Yucca Mountain
• The United States Department of Energy's
long range plan is for this spent fuel to be
stored deep in the earth in a geologic
repository, at Yucca Mountain, Nevada.
40. Concerns about Yucca Mountain
• Possible health risks to those living near
Yucca Mountain and transportation routes
• Eventual corrosion of the metal barrels
containing the waste
• Located in an earthquake region and
contains many interconnected faults and
fractures
– These could move groundwater and any
escaping radioactive material through the
repository to the aquifer below and then to the
outside environment
41. Reactor Safety
• These are the only
major accidents (Three
Mile Island and
Chernobyl) to have
occurred in more than
12,700 cumulative
reactor-years of
commercial operation
in 32 countries.
• The risks from nuclear
power plants, are
minimal compared with
other commonly
accepted risks
42. Breeder Reactor
• In a fission reactor, both uranium-235 and
plutonium-239 can be used as nuclear fuel
• Most of the uranium in a typical reactor is
uranium-238, which cannot be used as nuclear
fuel
• When a high-energy neutron collides with the
nucleus of uranium-238, plutonium-239 is
sometimes produced
• Could a nuclear reactor create more fuel while it
generates energy? Yes, this is a breeder
reactor
43. Breeder Reactor
• To convert
uranium-238 to
plutonium-239, you
need fast neutrons
• Therefore, water
(which acts as a
moderator) cannot be
used as the coolant
• Liquid sodium or high
pressure gasses are
used instead Uranium-238 only captures
fast (high-energy) neutrons
44. The Core of a Breeder Reactor
• A breeder reactor core
consists of a normal
uranium-235 reactor
(moderated by graphite
rods) surrounded by a
jacket of uranium-238
• The uranium-238 will be
converted to
plutonium-239 by
neutrons escaping from
the core
Orange: uranium-238
Green: enriched
uranium-235
Blue: graphite rods
45. A Typical Breeder Reactor
• Because liquid sodium becomes radioactive, it is
separated from the rest of the power plant using a heat
exchanger
• High pressure gas-cooled reactors are also being
researched
46. Comments on Breeder Reactors
• Breeder reactors must be tightly controlled,
because plutonium-239 can be used to build
atomic weapons
• Liquid sodium is extremely reactive (and
dangerous) thus high-pressure gasses are
preferred as the coolant
• Only France and Japan are actively pursuing
breeder reactor technology
• Breeder reactors are Illegal in the united States
due to safety and terrorist concerns.