Date post: | 25-Dec-2015 |
Category: |
Documents |
Upload: | daniela-hart |
View: | 218 times |
Download: | 3 times |
13.2 - Terms and Definitions
• Fission: a large atom of one element is split to produce two different smaller elements
• Fusion: two small atoms combine to form a larger atom of a different element
• Isotope: different (mass number) forms of the same element
Fission, Fusion, or Both?
• Energy is released• Begins with U235• Produces radioactive byproducts• Produces free neutrons
Both
Fission
Fission
Both
Fission, Fusion, or Both?
• Splits a larger atom into smaller atoms
• Fuses smaller atoms into one larger atom
• Begins with H2 and H3
• Produces helium
Fission
Fusion
Fusion
Fusion
Terms and Definitions
• Fuel rods: rods full of U235 pellets• Moderator: fluid (water) coolant that
slows down neutrons• Control rods: moderate rate of the
chain reaction by absorbing neutrons
A Nuclear Reactor Is Designed To
• Sustain a continuous chain reaction.• Prevent amplification into a nuclear
explosion.• Consist of an array of fuel and control
rods.• Make some material intensely hot.
A Nuclear Power Plant Is Designed To
• Use steam to drive turbo generators• Convert steam into electricity• Produce super-heated water in a
reactor vessel• Prevent meltdown
Comparing Nuclear Power with Coal Power
• Requires 3.5 million tons of raw fuel• Requires 30 tons of raw material
• Emits over 7 million tons of CO2 into the atmosphere
• Emits no CO2 into the atmosphere
C
N
C
N
Comparing Nuclear Power with Coal Power
• Emits over 300 thousand tons of SO2 into the atmosphere
• Emits no acid forming pollutants• Produces about 100 thousand tons of
ash• Produces 250 tons of radioactive waste• Possible meltdown
C
N
N
N
C
13.3 - Terms and Definitions
• Radioisotopes: unstable isotopes of the elements resulting from the fission process
Terms and Definitions
• Radioactive emissions: subatomic particles (neutrons) and high-energy radiation (alpha, beta, and gamma rays)
• Radioactive wastes: materials that become radioactive by absorbing neutrons from the fission process
Consequences of Radiation Exposure
• High Dose – results in death quickly• Block cell division• Radiation sickness
• Low Dose – may or may not result in death; slower• Damage biological tissues and DNA• Cancer• Birth defects
Disposal of Radioactive Wastes (200 Thousand Tons) • Finding long-term containment sites• Transport of highly toxic radioactive wastes
across the United States• The lack of any resolution to the radioactive
waste problem• Environmental racism• Cost ($60 billion to 1.5 trillion)
Disposal of Radioactive Wastes
• To be safe, plutonium-239 would require 240,000 years (10 half-lives) of containment!
• Implications of this in terms of disposal of radioactive wastes.
• Yucca mountain in southwestern Nevada = the nation’s nuclear waste repository
Nuclear Power Accidents
• Three Mile Island• 1979• Harrisburg, PA• Loss of coolant in reactor vessel• Damage so bad, reactor shut down
permanently• Unknown amount of radioactive waste
released into atmosphere.
How Chernobyl Blew Up
• Loss of water coolant perhaps triggered the accident. When the water-circulation system failed, the temperature in the reactor core increased to over 5,000 oF, causing the uranium fuel to begin melting and producing steam that reacted with the zirconium alloy cladding of the fuel rod to produce hydrogen gas.
How Chernobyl Blew Up
• A second reaction between steam and graphite produced free hydrogen and carbon oxides. When this gas combined with oxygen, a blast blew off the top of the building, igniting the graphite. The burning graphite threw a dense cloud of radioactive fission products into the air.
Safety and Nuclear Power
• Passive rather than active safety features
• New generations of reactors • Terrorism and nuclear power: dirty
bombs or outright attacks.
Economic Problems with Nuclear Power
• Energy demand estimates were unrealistic.
• Costs increase (5X) to comply with new safety standards.
• Withdrawal of government subsidies to nuclear industry.
• Public protests delayed construction.• Any accident financially ruins the utility.
Main Yankee Nuclear Power Plant
• Decommissioned in 2003• 200,000 tons of solid waste removed by
rail, truck, and barge• Site now consists of 200 acres of
conservation land• 400 acres for economic development• 12 acres of secured storage for spent
nuclear fuel
Breeder, Fusion, or Both
• Creates more fuel than it consumes• Raw material is U238• Splits atoms• Fuses atoms• Releases energy• Raw material is deuterium and tritium• Source of unprecedented thermal
pollution
Breeder
Breeder
Breeder
Fusion
Both
Fusion
Fusion
Opposition
• General distrust of technology• Skepticism of management• Doubt overall safety claims about
nuclear power plants• Nuclear power plants are prime targets
to terrorist attacks• Nuclear waste disposal problems