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Nuclear Energy

Nuclear Energy. Ch. 15. Nuclear Power. President Dwight D. Eisenhower, 1953, “Atoms for Peace” speech Nuclear-powered electrical generators would provide power “too cheap to meter” Between 1970 & 1974, American utilities ordered 140 new reactors for power plants. Nuclear Power.

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Nuclear Energy

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  1. Nuclear Energy Ch. 15

  2. Nuclear Power • President Dwight D. Eisenhower, 1953, “Atoms for Peace” speech • Nuclear-powered electrical generators would provide power “too cheap to meter” • Between 1970 & 1974, American utilities ordered 140 new reactors for power plants

  3. Nuclear Power • After 1975, only 13 orders were placed for new reactors, and all were subsequently cancelled. • In all, 100 of 140 reactors ordered were cancelled. • Construction costs, declining demand, safety fears • Electricity from nuclear power plants was about ½ the price of coal in 1970, but 2x the price of coal in 1990

  4. What Happened to Nuclear Power? Slowest-growing energy source and expected to decline more Why? • Economics • Poor management • Low net yield of energy of the nuclear fuel cycle • Safety concerns • Need for greater government subsidies • Concerns of transporting uranium

  5. Cost of typical nuclear power plant = $14 billion 3X amount national government of Coast Rica spent on EVERYTHING in 2009!

  6. Global Energy Capacity of Nuclear Power Plants Figure 10, Supplement 9

  7. Nuclear Power Plants in the United States Figure 21, Supplement 8

  8. Nuclear Energy Pros Cons Net Energy $$$$ Fear of accidents Long lived radioactive wastes Potential of spreading nuclear weapon technology • Environmental Impact • Accident Risk • Potential energy = 10x106 times more than traditional fuel • No air pollutants if operated correctly • 1/6 CO2 of fossil fuel sources • Low water pollution • Low Disruption of land

  9. How do nuclear power plants work? Relatively simple: boil water to produce steam that spins a turbine and generates electricity

  10. How do nuclear power plants work? • Complex & Costly • BECAUSE – Nuclear Fission

  11. Nuclear Processes

  12. Nuclear fission Uranium-235 Nuclei of isotopes with large mass #s split apart into lighter nuclei when struck by a neutron. Release energy plus 2 or 3 more neutrons Each neutron can trigger an additional fission reaction An ENORMOUS amount of energy is released in chain reactions Energy Fission fragment n n Neutron n n Energy Energy n n Uranium-235 Fission fragment Energy

  13. How do nuclear power plants work? • Complex & Costly • BECAUSE – Nuclear Fission Reaction gives off heat (exothermic). If controlled – the heat that is produced is used to produce steam to turn a turbine If the reaction is not controlled = nuclear explosion An atom splits into two or more smaller nuclei along with by-product particles (neutrons, photons, gamma rays, and beta & alpha particles

  14. Nuclear Fission Chain Reaction*

  15. Nuclear Fission • Takes place in reactor • Most common = light-water reactors (LWRs) • Very inefficient (lose ~ 75% of high quality energy as waste heat) • Net energy loss ~ 92%

  16. Small amounts of radioactive gases Uranium fuel input (reactor core) Control rods * Containment shell Waste heat Heat exchanger Steam Turbine Generator Hot coolant Useful electrical energy about 25% Hot water output Pump Pump Coolant Pump Pump Waste heat Cool water input Moderator Shielding Pressure vessel Coolant passage Water Condenser Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Water source (river, lake, ocean) Fig. 15-20a, p. 387

  17. Nuclear Fission Fuel = uranium ore • Packed as pellets in fuel rods & fuel assemblies

  18. Nuclear Fission Most Common Nuclear Fuels • U-235 • U-238 • Pu =239

  19. Fuel Types U-238 U-235 Pu - 239 1/3 of total energy produced in power plant Can be used for nuclear weapons ½ life = 2.4X104yrs Most naturally occurring isotope Eventually decays into Pu-239 Most depleted uranium ½ life = 4.5x109yrs Used to produce chain reactions Nuclear weapons have >85% Power plants ~3% ½ life = 7X108yrs

  20. What is Half Life? The time taken for the radioactivity of a specified isotope to fall to half its original value

  21. How Do I Calculate Half Life? 250 Radium has a half life of 1500 years. How long will it take for 250kg of Radium to decay down to less than 10kg? 1500 x 5 = 7500 years X 1 Amount Remaining Original Amount = 0.5 2 3 4 X = # of half lives X = Time Half Life 5

  22. How Do Nuclear Power Plants Work? • Uranium ore is mined and refined to enriched U-235 Gas Centrifuge Gaseous Diffusion

  23. How Do Nuclear Power Plants Work? 2. U-235 processed into uranium dioxide pellets (nuclear fuel)

  24. How Do Nuclear Power Plants Work? 3. Inside reactor: U-235 pellets are bombarded by neutrons causing splitting (of nuclei) and chain reaction

  25. How Do Nuclear Power Plants Work? 4. Fission (splitting) releases TONS of energy/heat converting water to steam. • Controlled by control rods (between fuel assemblies) that capture or absorb neutrons. • Cadmium or boron • Control rods can be lowered/raised to change the rate of the reaction.

  26. How Do Nuclear Power Plants Work? * 5. Steam turns turbine to generate electricity

  27. How do Nuclear Power Plants Work? • Reaction is moderated by neutron-absorbing solution (moderator). • Control Rods • Water or other coolant is circulated between fuel rods to remove excess heat.

  28. Parts of a Nuclear Power Plant

  29. Parts of a Nuclear Reactor • Fuel Rods – contain uranium & where fission occurs

  30. Parts of a Nuclear Reactor 2.Reactor Core – Where fission occurs

  31. Parts of a Nuclear Reactor 3.Steam Generator – steam/electricity generated from heat/energy from fission

  32. Parts of a Nuclear Reactor 4. Turbine – uses steam to generate electricity

  33. Parts of a Nuclear Reactor 5.Condenser – Cools steam back to water for use

  34. Two Types of Nuclear Reactors • Pressurized Water Reactor (PWR) • Boiling Water Reactor (BWR)

  35. Two Types of Nuclear Reactors • Pressurized Water Reactor (PWR) • Water in reactor core is isolated from turbine

  36. Two Types of Nuclear Reactors Boiling Water Reactor (BWR) • Same water loop – moderator, coolant & steam source

  37. Safety • Reactor Vessel: steel capsule surrounds structure • Containment building = reinforced concrete • Water = coolant • Containment shell around core = protection • Water filled pools or dry casks for storage of spent fuel rod assemblies

  38. What Is the Nuclear Fuel Cycle? • Mine the uranium • Process the uranium to make the fuel • Use it in the reactor • Safely store the radioactive waste • Decommission the reactor

  39. Decommissioning of reactor Fuel assemblies Reactor Enrichment of UF6 Fuel fabrication (conversion of enriched UF 6 to UO2 and fabrication of fuel assemblies) Temporary storage of spent fuel assemblies underwater or in dry casks Uranium-235 as UF6 Plutonium-239 as PuO2 Conversion of U3O8 to UF6 Spent fuel reprocessing Low-level radiation with long half-life Geologic disposal of moderate- and high-level radioactive wastes Mining uranium ore (U3O8) Open fuel cycle today Recycling of nuclear fuel Running Power Plant = Low Impact Entire Cycle = High Impact Fig. 15-21, p. 388

  40. Trade-Offs: Conventional Nuclear Fuel Cycle Fig. 15-22, p. 389

  41. Trade-Offs: Coal versus Nuclear to Produce Electricity Fig. 15-23, p. 389

  42. Can we develop new & safer types of nuclear reactors? • Advanced Light-Water Reactors (ALWRs) • Pebble Bed Modular Reactor (PBMR) • Breeder Nuclear Fission Reactors

  43. Advanced Light-Water Reactors (ALWRs) • Safer • Built more quickly • Built-in passive safety features

  44. Pebble Bed Modular Reactor (PBMR) • Encapsulate uranium oxide fuel in graphite shell • Rejected • Risk radiation exposure • Terrorist

  45. Breeder Nuclear Fission Reactors • Generate more nuclear fuel than they consume • Create fissionable plutonium and thorium isotopes from stable uranium • Converts non-fissionable Uranium – 238, into fissionable Plutonium – 239

  46. Breeder Nuclear Fission Reactors • USES U-238, Pu – 239 & Th-232 • Uses Na instead of water as a coolant • Na = highly explosive with air/water

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