NUCLEAR ENERGY
CHAPTER 12
NUCLEAR POWER PLANT SALEM, NEW
JERSEY
Overview of Chapter 12
• Introduction to Nuclear Power
– Atoms and radioactivity
• Nuclear Fission
• Pros and Cons of Nuclear Energy
– Cost of Nuclear Power
• Safety Issues at Power Plants
– Three Mile Island & Chornobyl
– Nuclear Weapons
• Radioactive Waste
• Future of Nuclear Power
Introduction to nuclear energy
• It is the energy released by nuclear fission or
fusion.
• Fission: the splitting of atomic nucleus into
two smaller fragments, accompanied by the
release of large amounts of energy.
• Fusion: the joining of two lightweight atomic
nuclei into a single heavier nucleus,
accompanied by the release of a large amount
of energy.
Atoms and Radioactivity
• Nucleus
– Comprised of protons (+)
and neutrons (neutral)
• Electrons (-) orbit
around nucleus
• Neutral atoms
– Same # of protons and
electrons
Atoms and Radioactivity
• Atomic mass
– Sum of the protons and neutrons in an atom
• Atomic number
– Number of protons per atom
– Each element has its own atomic number
• Isotope
– 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 decay
• The emission of energetic particles or rays
from unstable atomic nuclei; includes
positively charged alpha particles, negatively
charged beta particles, and high-energy,
electromagnetic gamma rays.
• Forms of a single element that differ in atomic
mass are known as isotopes. The unstable
isotopes are called radioisotopes.
Contd..
• Radioisotopes are radioactive because they spontaneously
emit radiation, a form of energy consisting of particles. As a
radioactive element emits radiation, its nucleus changes
into the nucleus of a different, more stable element. This
process is called radioactive decay.
• For example, the radioactive nucleus of one isotope of
uranium, U-235, decays over time into lead (Pb-207).
• The time taken required for one half of the total amount of
a radioactive substance to change into a different material
is called its radioactive half-life.
• Each isotope decays based on its own half-life years, days,
hours, minutes
Radioactive Isotope Half-lives
Uranium Ore
• Non renewable resource found in limited
amounts in sedimentary rocks in Earth’s crust.
• The processes involved in producing the fuels
used in nuclear reactors and in disposing of
radioactive (nuclear) wastes is known as
nuclear fuel cycle.
• In the United States uranium is found in
Wyoming, Texas, Colorado, New Mexico, and
Utah.
Uranium
CANADA
South Africa
Nuclear Fuel cycle
Deep geologic disposal of spent fuel is currently under study in several
countries including the United States.
• Nuclear Fuel Cycle
– processes involved
in producing the
fuel used in nuclear
reactors and in
disposing of
radioactive
(nuclear) wastes
* Enriched Uranium
Enrichment
• The process by which uranium ore is refined after
mining to increase the concentration of
fissionable U-235 is called enrichment.
• After enrichment, the uranium ore is processed
into small pellets of uranium dioxide, each pellet
contains the energy equivalent of a ton of coal.
• Nuclear Reactor: A device that initiates and
maintains a controlled nuclear fission chain
reaction to produce energy for electricity
Which country generates the highest % of its electricity
from nuclear power plants?
•
•
•
•
•
•
•
France 79%
Lithuania 70%
Slovakia 56%
Belgium 56%
Ukraine 49%
Sweden 47%
S Korea, Bulgaria, Slovenia, Finland, Hungary all above
33%
• Nuclear Power: Second largest source of USA
electricity, what % does it supply? 20% of USA
Electricity
Nuclear Fission
The fission of U-235 releases an enormous amount of heat, used to transform
water into steam, the steam is used to generate electricity. Production of
electricity is possible because the fission reaction is controlled.
Nuclear bombs make use of uncontrolled fission reactions.
If the control mechanism in a nuclear power plant
were to fail, will a bomb like explosion take place?
• It will not take place because nuclear fuel only
has 3-5% U-235, whereas bomb grade material
contains at least 20% and is usually about 85 to
90% U-235.
• In the highly unlikely event of an uncontrolled
fission reaction, an immense amount of heat
could be generated. However, the reactor vessel
and massive concrete containment building are
designed to contain the heat along with the
attendant radioactivity.
NUCLEAR FISSION REACTORS
Pellets placed inside 12’ Fuel Rods
The fuel rods are then grouped into square fuel assemblies. (200)
Can be 50,000+ fuel rods per Nuclear Rector
Fuel Rods
Replaced every 3 years
103 Nuclear Power Plants
103 x 50000 rods
5, 000,000 spent fuel rods
produced every 3 years.
How Electricity is Produced
P
A
R
T
S
REACTOR CORE
TURBINE
ENERGY vid
STEAM GENERATOR
CONDENSOR
How electricity is produced from
conventional Nuclear Fission
• Four main parts of a typical nuclear power plant
• The reactor core (fission occurs here)
• The steam generator(heat produced by fission is
used to produce steam from liquid water in the
steam generator)
• The turbine (uses the steam to generate
electricity
• The condenser – cools the steam and converts it
back to liquid.
Role of control rods in the nuclear
reactor
• The reactor core contains the fuel assemblies.
Above each assembly is a control rod, made of a
special metal alloy that absorbs neutrons.
• The plant operator signals the control rod to
move up or down into the fuel assembly.
• If the control rod is out of the fuel assembly, free
neutrons collide with uranium atoms in the fuel
rods, and fission takes place. If the control rod is
completely lowered into the fuel assembly, it
absorbs the free neutrons, and fission of uranium
no longer occurs.
Refer to page numbers 263 and 264 to know more about water circuit in the
How Electricity is Produced
P
A
R
T
S
REACTOR CORE
TURBINE
ENERGY vid
STEAM GENERATOR
CONDENSOR
kWh
A 100 watt light bulb left on continuously for an entire year
consumes 876 kWh.
To produce 876 kWh requires
876
lbs. of COAL
377
lbs. of natural gas
508
lbs. of oil
0.0007
lbs. of enriched Uranium
Breeder Nuclear Fission
• A type of nuclear fission in which nonfissionable U-238 is converted into fissionable
Pu-239
Risk involved
Refer page
264,265
Because it can use U-238, plutonium based breeder fission can generate much
larger quantities of energy from uranium ore than nuclear fission using U-235
Mixed oxide fuel (MOX) and Spent fuel
• MOX: a reactor fuel that contains a
combination of uranium oxide and plutonium
oxide. The plutonium can come from
reprocessed spent fuel or from other
plutonium stockpiles, including dismantled
weapons.
• Spent fuels: the used fuel elements that were
irradiated in a nuclear reactor.
Pros and Cons of Nuclear Energy
• Pros
– Less of an immediate environmental impact
compared to fossil fuels
Pros and Cons of Nuclear Energy
• Pros (continued)
– Carbon-free source of electricity- no greenhouse
gases emitted
– May be able to generate H-fuel
• Cons
– Generates radioactive waste(spent fuel, radioactive
coolant fluids and other gases in the reactor which are
radioactive)
– Many steps require fossil fuels (mining and disposal)
– Expensive
Cost of Electricity from Nuclear Energy
• Cost is very high……….
• 20% of US electricity is from Nuclear Energy
– Affordable due to government subsidies
• Expensive to build nuclear power plants
– Long cost-recovery time
• Fixing technical and safety issues in existing
plants is expensive
Safety Issues in Nuclear Power Plants
Probability of
meltdown or other
accident is low
Public perception is
that nuclear power
is not safe
Sites of major
accidents:
Three Mile
Island
Chernobyl
(Ukraine)
At high temperatures the metal encasing the uranium fuel melts, releasing
radiation; this is known as a meltdown.
The water used in a nuclear reactor to transfer heat can boil away during
an accident, contaminating the atmosphere with radioactivity.
NUCLEAR POWER PLANT SAFETY
Three mile island
Chernobyl
Three-Mile Island
• 1979- most serious reactor accident in US
• 50% meltdown of reactor core
– Containment building kept radiation from
escaping
– No substantial environmental damage
– No human casualties
• Elevated public apprehension of nuclear
energy
– Led to cancellation of many new plants in US
http://video.google.com/videoplay?docid=251372048648239449
Chernobyl
• 1986- worst accident in
history
• 1 or 2 explosions
destroyed the nuclear
reactor
– Large amounts of
radiation escaped into
atmosphere
• Spread across large
portions of Europe
Chernobyl
• Radiation
spread was
unpredictable
• Radiation
fallout was
dumped
unevenly
• Death toll is
10,000-100,000
http://www.youtube.com/watch?v=bSRC1_OZPIg Chernobyl disaster.
Video clip
Nuclear Energy and Nuclear Weapons
• 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
The bomb of about 50
megatons was code named
Ivan by its developers. This
bomb is tested in Novaya
Zemlya an island in the Arctic
Sea on October 30, 1961
IVAN
Radioactive Waste
• Low-level radioactive waste– 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
Nuclear waste/Radioactive waste
• 1982 Nuclear Waste Safety Act
• Find a site to store waste and make
operational by 1998.
• The Low Level Radioactive Waste Policy Act,
passed in 1980, specified that all states are
responsible for the waste they generate, and it
encouraged states to develop facilities to
handle low-level wastes by 1996.
Read public and expert attitude towrd nuclear energy Page number 274
Case-In-Point Yucca Mountain
• In 1987 Congress identified
Yucca Mountain in Nevada.
• 70,000 tons of high-level
radioactive waste
• Tectonic issues have been
identified
WHY YUCCA MOUNTAIN
Radioactive Waste
• Temporary storage solutions
– In nuclear plant facility (require high security)
• Under water storage
• Above ground concrete and steel casks
• Need approved permanent options soon.
Decommissioning Nuclear Power
Plants
• Three options exist when a nuclear power plant is
closed: a) storage, b) entombment, and c)
decomissioning.
• If an old plant is put into storage, the utility
company guards it for 50 to 100 years, while
some of the radioactive materials decay.
• Permanently encasing the entire power plant in
concrete, a viable option, a the tomb would have
to remain intact for at least 1000 years.
• To dismantle an old nuclear power plant after it
closes is called decommission.
MEDICINE
largest man-made source of radiation is
medical diagnosis and treatment
(includes X-rays, nuclear medicine and cancer treatment)
More than 28,000 American doctors use radiation
virtually every U.S. hospital has some form of nuclear medicine unit
10 million nuclear medicine patient procedures each year
One radioactive isotope, molybdenum-99, is used about
40,000 times each day, to diagnose cancer and illnesses
Food Processing and Preservation
Irradiation kills bacteria, parasites and insects in food—including listeria, salmonella and
potentially deadly E. coli—and retards non-microbial spoilage of certain foods, increasing their
shelf life.
The World Health Organization in 1992 called food irradiation a "perfectly sound foodpreservation technology."
The head of the group's food safety unit said irradiation is "badly needed in a world where foodborne diseases are on the increase and where between one-quarter and one-third of the global
food supply is lost post-harvest."
The United States is among more than 35 countries that permit irradiation of certain foods.
Since the 1960s, NASA has included irradiated food on its space flights.
In 1963, the U.S. Food and Drug Administration approved the irradiation of wheat, flour and
potatoes; in 1983, spices and seasonings; in 1985, pork; in 1986, fruits and vegetables; in 1990,
poultry; and in 1997, red meat.
Industrial Applications
Most Common Human Exposure
to Radiation??
Terrestrial Radiation
Carbon -14
Thorium-223
Uranium-238
Cosmic Radiation
High energy photons
Higher the altitude the
Higher the exposure
Polonium-218
Radon-222
Other Exposures: bricks, stones, cement,(all sources of radon and uranium ores)
then there is tobacco….
Fusion
• Fuel= isotopes of hydrogen
Fusion
• Way of the future??
– Produces no high-level waste
– Fuel is hydrogen (plenty of it!)
• Problems
– It takes very high temperatures (millions of degrees) to
make atoms fuse
– Confining the plasma after it is formed. At extremely high
temperatures, a gas separates into negative electrons and
positive nuclei. This superheated, ionized gas, called
plasma.
• Scientists have yet to be able to create energy from
fusion