nuclear energy chapter 12. nuclear fuel cycle uranium mines and mills u-235 enrichment fabrication...
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Nuclear Energy
Chapter 12
Nuclear Fuel Cycle
Uranium mines and mills
U-235 enrichment
Fabrication of fuel assemblies
Nuclear power plant
Uranium tailings
Depleted uranium tails
Factory wastes
Low-level wastes
Spent fuel stored on-site
Deep geological disposal
Spent fuel reprocessing
Politics
Enrichment
Enrichment Methods:
• Gaseous & Centrifuge• Both require repeated steps• UF6 (Uranium Hexaflouride) is uranium of all weights mixed with flourine gas
U235 is enriched to 3-5% from 0.7%Enriched U-235 (1 pellet) containing uranium enriched to 3% = one ton of coal
Centrifuges
Georgia Power
Vogle +2Georgia’s Electrical GenerationCoal 74%Nuclear 18% - France 75%Oil & Gas <6%Hydro <3%Renewable
Introduction to the Nuclear Process• Fission – nuclear energy released when atom split• Fusion – nuclear energy released when atoms fused
Fuel Assembly
A fuel assembly consists of a square array of 179 to 264 fuel rods, and 121 to 193 fuel assemblies are loaded into an individual reactor - numbers vary greatly
Fuel Assembly
Nuclear FissionHow Electricity is Produced from Conventional Nuclear Fission
Primary/Secondary/Tertiary water circuits?
Vogtle Power Plant
Cooling Towers
Cooling Towers
Cooling water absorbs heat in the condenser and is pumped to the cooling towers where the water pours over a horizontal grid. Upward airflow cools it off. A minor part of the cold cooling water flows back into the river.
Spent Fuel Storage
Pu-239 Breeder Reactor
• U-235 <1% of worlds uranium• Most available U-238
Issues:•Pu- 239 extremely carcinogenic•Half-life 24,000 years• Sodium coolants are explosively reactive
The plutonium-239 core is surrounded by a layer of uranium-238 – which becomes or is “bred” into U-239
U-235 could run for 200 years at current rates of consumption.
Breeder reactors could match today's nuclear output for 30,000 years
Pros and Cons of Nuclear Energy
Impact Coal Nuclear
Land use 17,000 ac 1,900 ac
Daily fuel requirement
9,000 tons/day 3 kg/day
Air pollutionModerate to severe
Low
Radioactive emissions
1 curie 28,000 curies
Risk from catastrophic accidents
Short-term local risk
Long-term risk over large area
Accidents Can Happen
Three Mile Island
1979, Three Mile Island plant in PAthe most serious nuclear reactor accident in the USA -human error (cooling system failed) -50% meltdown of reactor core
Luckily, containment building kept radioactivity from releasing into the countryside
What caused 3 miles island?
1. Minor malfunction in cooling causes Emergency shutdown
1. Steam relief valve opens but does not close as it should
1. Instruments indicate valve had closed
1. Coolant levels dropped and reactor heated up
1. Later that day hydrogen gas build-up threatened an explosion
Chernobyl Disaster
1986, Ukraine (former Soviet Union)
Worst accident ever (?) to occur at a nuclear power plant
Safety Issues in Nuclear Power Plants
Radioactive fallout from Chernobyl:
What caused Chernobyl?
1. Plant operators ran a safety test of back-up safety systems - specifically the generators that would power coolant
2. Control rods were removed and when “SCRAM” was initiated
1. Control rods jammed 1/3 of the way in as fuel rods warped
1. Explosion was from steam pressure followed y fire as oxygen mixed with heated graphite
Impact• Fire broke out and explosions spread radioactive waste
• 350,000 people relocated
• 4,000 Deaths
• 2 million acres of farmland lost
• 1,700,000 acres of forest lost
•Resurgent animals?•http://www.cnn.com/2011/WORLD/europe/01/14/chernobyl.nature.radiation.debate/index.html
Japan
Tsunami: http://www.youtube.com/watch?feature=player_detailpage&v=w3AdFjklR50
The Future of Nuclear Power
Issues:
• Making nuclear power safer
• Standardizing power plant designs
• Decommissioning Nuclear Power Plants
• Lowering construction costs
• Securing Long Term Waste Storage
• Monitoring storage - weapons
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