Chapter 12 Nuclear Energy
o o o o
Introduction to Nuclear Power
•
Overview of Chapter 12
Nuclear Fission Pros and Cons of Nuclear Energy
•
Atoms and radioactivity
Safety Issues at Power Plants
• •
Cost of Nuclear Power
o o
Radioactive Waste Future of Nuclear Power Nuclear energy
•
Three Mile Island & Chornobyl Nuclear Weapons
Introduction to Nuclear Energy
o o
Nuclear fission
•
Energy released by nuclear fission or fusion
o
Nuclear fusion
•
Splitting of an atomic nucleus into two smaller fragments, accompanied by the release of a large amount of energy
Joining of two lightweight atomic nuclei into a single, heavier nucleus, accompanied by the release of a large amount of energy
o o o
Nucleus
•
Atoms and Radioactivity
Electrons (-) orbit around nucleus Neutral atoms
•
Comprised of protons (+) and neutrons (neutral)
Same # of protons and electrons
o
Atomic mass
•
Atoms and Radioactivity
Sum of the protons and neutrons in an atom
o
Atomic number
• •
o
Isotope
• •
Number of protons per atom Each element has its own atomic number
Usually an atom has an equal number of neutrons and protons If the number of neutrons is greater than the number of protons = isotope
o o o o
Unstable isotope Radioactive Decay
•
Radioactive Isotope
Example
•
Emission of energetic particles or rays from unstable atomic nuclei Uranium (U-235) decays over time to lead (Pb-207)
Each isotope decays based on its own half-life
Radioactive Isotope Half-lives
Nuclear Fission
o
Nuclear Fuel Cycle
•
processes involved in producing the fuel used in nuclear reactors and in disposing of radioactive (nuclear) wastes
o o o o o
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
Nuclear Fission
o
A type of nuclear fission in which non-fissionable U-238 is converted into fissionable Pu-239 Pros
How Electricity is Produced Breeder Nuclear Fission
Pros and Cons of Nuclear Energy
o
•
Less of an immediate environmental impact compared to fossil fuels
o
Pros (continued)
• •
Pros and Cons of Nuclear Energy
o
Cons
• • •
Carbon-free source of electricity- no greenhouse gases emitted May be able to generate H-fuel Generates radioactive waste Many steps require fossil fuels (mining and disposal) Expensive
o o o o o
Cost is very high 20% of US electricity is from Nuclear Energy
•
Cost of Electricity from Nuclear Energy
Expensive to build nuclear power plants
•
Affordable due to government subsidies Long cost-recovery time
Fixing technical and safety issues in existing plants is expensive Meltdown
•
Safety Issues in Nuclear Power Plants
o o o
Probability of meltdown or other accident is low Public perception is that nuclear power is not safe Sites of major accidents:
• •
At high temperatures the metal encasing the uranium fuel can melt, releasing radiation
Three Mile Island Chornobyl (Ukraine)
o o
1979- most serious reactor accident in US 50% meltdown of reactor core
• • •
Three-Mile Island
Containment building kept radiation from escaping No substantial environmental damage No human casualties
o
Elevated public apprehension of nuclear energy
•
Led to cancellation of many new plants in US
o o o
1986- worst accident in history 1 or 2 explosions destroyed the nuclear reactor
•
Chornobyl
Spread across large portions of Europe Radiation spread was unpredictable Radiation fallout was dumped unevenly Death toll is 10,000-100,000
Large amounts of radiation escaped into atmosphere
Chornobyl
o o o o o o
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
Low-level radioactive waste•
Nuclear Energy and Nuclear Weapons
Radioactive Waste
o o
High-level radioactive waste•
Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation Radioactive solids, liquids, or gasses that give off large amounts of ionizing radiation
o
Long term solution to waste
• •
Radioactive Wastes
•
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)
Under water storage Above ground concrete and steel casks
o o o o o o
Need approved permanent options soon.
70,000 tons of high-level radioactive waste Tectonic issues have been identified Licensed to operate for 40 years
•
Case-In-Point Yucca Mountain
Decommissioning Nuclear Power Plants
Power plants cannot be abandoned when they are shut down Three solutions
• • •
Several have received 20-year extensions
Storage Entombment Decommissioning (dismantling)
o
Fuel= isotopes of hydrogen
Fusion Fusion
o
Way of the future??
• •
o
Problems
•
Produces no high-level waste Fuel is hydrogen (plenty of it!)
•
o
Scientists have yet to be able to create energy from fusion
It takes very high temperatures (millions of degrees) to make atoms fuse Confining the plasma after it is formed