Download Lecture - Chapter 12

Chapter 12
Nuclear Energy
Introduction to Nuclear Energy
 Nuclear energy
–
 Nuclear fission
 Nuclear fusion
–
Atoms and Radioactivity
 Nucleus
–
 Electrons (-) orbit around nucleus
 Neutral atoms
–
 Atomic mass
–
 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 Isotope
 Unstable isotope
 Radioactive Decay
–
–
 Example
–
 Each isotope decays based on its own half-life – time required for one half of the
total amount of a radioactive substance to change to a different element.
Uranium isotopes
 U-238:
 U-235: 0.71% of ore, used in conventional nuclear fission but must be refined to
3% (enrichment) (Bomb grade is 20%)
 U-234:<0.01% of ore. Not used in fission.
 Uranium found predominantly in
Radioactive Isotope Half-lives
Nuclear Fission
 Nuclear Fuel Cycle
–
Nuclear Fission




U-235
The nucleus absorbs neutrons
2-3 neutrons are emitted and bombard another U-235 atom

How Electricity is produced
Breeder Nuclear Fission
 A type of nuclear fission in which non-fissionable U-238 is converted into fissionable
Pu-239
 Plutonium also used in nuclear weapons

Pros
–
Pros and Cons of Nuclear Energy
 Pros (continued)
– Carbon-free source of electricity–
 Cons
–
–
–
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
 Fixing technical and safety issues in existing plants is expensive
Safety Issues in Nuclear Power Plants
 Meltdown
–


 Sites of major accidents:
– Three Mile Island
– Chornobyl (Ukraine)
Three-Mile Island
 1979 50% meltdown of reactor core
–
–
–
 Elevated public apprehension of nuclear energy
– Led to cancellation of many new plants in US
Chornobyl
 1986- Worst accident in history
 1 or 2 explosions destroyed the nuclear reactor
–
 Spread across large portions of Europe


 Death toll is 10,000-100,000
Nuclear Energy and Nuclear Weapons

 These countries have access to spent fuel needed to make nuclear weapons
 Safe storage and handling of these weapons is a concern
Radioactive Waste
 Low-level radioactive waste-
 High-level radioactive waste-
Radioactive Wastes
 Long term solution to waste
– Deep geologic burial –Yucca Mountain (closed)
– As of 2004, site must meet EPA million year standard (compared to previous
10,000 year standard)
– Possibilities:



 Temporary storage solutions
– In nuclear plant facility (require high security)



Case-In-Point Yucca Mountain



70,000 tons of high-level radioactive waste
Tectonic issues have been identified-near earthquake fault line and volcano
Transportation of waste an issue
Decommissioning Nuclear Power Plants
 Licensed to operate for 40 years
–
 Power plants cannot be abandoned when they are shut down
 Three solutions
– Storage –
– Entombment– Decommissioning (dismantling)Fusion


Fuel= isotopes of hydrogen (heavy hydrogen or deuterium)
Combining 2 lighter atoms into one large one producing very large amounts of
energy
Fusion
 Way of the future??
–
–
 Problems

– It takes very high temperatures (millions of degrees) to make atoms fuse
– Confining the plasma after it is formed
super heated ionizing gas (plasma) has a tendency to expand and nuclei aren’t
close together and will lose energy when they hit the container wall.
Scientists have yet to be able to create energy from fusion