Chapter 12
Nuclear Energy
Overview of Chapter 12*
o
Introduction to Nuclear Power
•
o
o
Nuclear Fission
Pros and Cons of Nuclear Energy
•
o
•
o
Cost of Nuclear Power
Safety Issues at Power Plants
•
o
Atoms and radioactivity
Three Mile Island & Chornobyl
Nuclear Weapons
Radioactive Waste
Future of Nuclear Power
How do we make Electricity?
o
Need fuel source to …
How do we make Electricity?
o
Need fuel source –
•
•
•
•
to boil water
to make steam
to turn a turbine
to convert mechanical energy into electrical
energy
o
Fuel sources = fossil fuels, nuclear
o
Exceptions
•
•
solar – converts solar energy into electrical
energy
wind – turns turbine itself
How Burning Coal Produces Electricity
How Nuclear Fission Produces
Electricity
Introduction to Nuclear Energy
o
Nuclear energy
•
o
Nuclear fission
•
•
o
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
Process used by nuclear power plants
Nuclear fusion
•
•
Joining of two lightweight atomic nuclei into a
single, heavier nucleus, accompanied by the
release of a large amount of energy
Process that powers the sun
Atoms and Radioactivity
o
Nucleus
•
o
o
Comprised of protons
(+) and neutrons
(neutral)
Electrons (-) orbit
around nucleus
Neutral atoms
•
Same # of protons and
electrons
Atoms and Radioactivity
o
Atomic mass
•
o
Atomic number
•
•
o
Sum of the protons and neutrons in an atom
Number of protons per atom
Each element has its own atomic number
Isotope (Greek for “at the same place”)
•
Different forms of the same element
•
•
•
have same number of protons
have different number of neutrons
Some isotopes are radioactive
Examples of Isotope
o
Carbon
• Carbon-12: 6 protons & 6 neutrons (stable)
• Carbon-14: 6 protons & 8 neutrons (radioactive)
o
Uranium
• Uranium-235: 92 protons & 143 neutrons (radioactive)
• Uranium-238: 92 protons & 146 neutrons (radioactive)
Elements which
contain at least one
stable isotope;
Radioactive elements:
the most stable
isotope is very longlived, with half-life of
over four million years;
Radioactive elements:
the most stable
isotope has half-life
between 800 and
34,000 years;
Radioactive elements: the most stable isotope has half-life
between one day and 103 years;
Highly radioactive elements: the most stable isotope has half-life
between one minute and one day;
Extremely radioactive elements: the most stable isotope has halflife less than a minute. Very little is known about these elements
due to their extreme instability and radioactivity.
Radioactive Isotope
Radioactive Decay
• Emission of energetic particles or rays from
unstable atomic nuclei
o
Alpha Decay
•
•
•
o
Loss of 2 protons and 2 neutrons
Lose four mass units
Lose two atomic numbers – so move to the left
2 spaces on the periodic table
Beta Decay
•
•
•
Loss of electron from a neutron
Gain one atomic number - so move right 1 space
on the periodic table
Gain no mass units
Half-life
o
o
o
o
o
o
o
TIME it takes for half of a radioactive element’s
atoms to decay, or change, into a more stable element.
range from a fraction of a second to billions of years –
4.5 billion for uranium 238.
the longer the half-life, the less intense the radiation
each isotope decays based on its own half-life
example: Uranium (U-235) decays over time to Lead
(Pb-207)
Parent Material = original radioactive material
Daughter Product = new, stable material
Radioactive Isotope Half-lives
Calculating Half Lives
DRAW PICTURE FIRST
Half-life l Starting Point ex: 200g of X
1
l
100g
2
l
50g
3
l
25g
Half-life l Starting Point ex: what percent…?
1
l
50%
2
l
25%
3
l
12.5%
Half Life Calculations
1. How many half-lives will pass by the time a
100g sample of Au-198 to decay to 6.25g?
2. How many half-lives will pass by the time a
60g sample of Co-60 decays to 7.5g?
3. How many half-lives does it take a 180g
sample of Au-198 to decay to 1/8 its
original mass?
4. If a 700g sample of I-131 undergoes 4
half-lives, how much material remains?
5. What is the half-life of a radioisotope if
1/16 of it remains after 4 days?
6. If 5 half-lives pass, what percent remains
of the original radioisotope?
7. What is the half-life of a radioactive
isotope if a 500g sample decays to 62.5g in
24.3 hours?
8. How many years would it take for a 1g
sample of Krypton-85 with a half-life of
10.4 years to decay to about 31.25mg?
Released Question from Exam
A.
B.
C.
D.
E.
Uranium-235 has a half-life of 710 million years.
If it is determined that a certain amount of
stored U-235 will be considered safe only when
its radioactivity has dropped to 0.10 percent of
the original level, approximately how much time
must the U-235 be stored securely to be safe?
7.1 x 106 years
7.1 x 107 years
7.1 x 108 years
7.1 x 109 years
7.1 x 1010 years
STOP HERE
Nuclear Fuel Cycle
processes involved in:
o producing the fuel
used in nuclear
reactors and
o disposing of
radioactive
(nuclear) wastes
Pros and Cons of Nuclear Energy
o
Pros
•
Less of an immediate environmental impact
compared to fossil fuels
Pros and Cons of Nuclear Energy
o
Pros (continued)
•
•
o
Carbon-free source of electricity- no
greenhouse gases emitted
May be able to generate H-fuel
Cons
•
•
•
Generates radioactive waste
Many steps require fossil fuels (mining and
disposal)
Expensive
Cost of Electricity from Nuclear
Energy
o
o
Cost is very high
20% of US electricity is from Nuclear
Energy
•
o
Expensive to build nuclear power plants
•
o
Affordable due to government subsidies
Long cost-recovery time
Fixing technical and safety issues in
existing plants is expensive
Radioactive Waste
o
Low-level radioactive waste•
o
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
o
Long term solution to waste
•
•
•
Deep geologic burial –Yucca Mountain
As of 2004, site must meet EPA million year
standard (compared to previous 10,000 year
standard)
Possibilities:
•
•
•
Above ground mausoleums
Arctic ice sheets
Beneath ocean floor
Radioactive Waste
o
Temporary storage solutions
•
In nuclear plant facility (require high security)
•
•
o
Under water storage
Above ground concrete and steel casks
Need approved permanent options soon.
Case-In-Point Yucca
Mountain
o
o
70,000 tons of highlevel radioactive waste
Tectonic issues have
been identified
Types of Waste*
High-Level Waste
•The most dangerous radioactive
waste
•Spent fuel comes from nuclear
reactors (52,000 tons)
• liquid and solid waste from
plutonium production (91 million
gallons).
•About 70 percent of the available
storage space is now filled with used
fuel assemblies at Turkey Point.
Types of Waste*
Transuranic Waste
o
Includes clothing, tools,
and other materials
contaminated with
plutonium, neptunium,
and other synthetic
elements heavier than
uranium. (11.3 million
cubic feet)
Types of Waste*
Low and Mixed Low-Level Waste
o
Includes radioactive and hazardous wastes from
hospitals, research institutions, and decommissioned
power plants (472 million cubic feet)
o
Turkey Point produced annually on average about
2,500 cubic feet of low-level waste. This amount of
waste could be contained within an area about the
size of a 30'x30' room.
Types of Waste*
Uranium Mill Tailings
•Residues left from the extraction
of uranium ore (265 million tons).