Nuclear power
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  • 1. Electricity from Nuclear
  • 2. Advantages of Nuclear Power
    • Nuclear electricity is reliable and relatively cheap (with an average generating cost of 2.9 cents per kW/h) once the reactor is in place and operating.
    • Large reserves of Uranium in United States - Fuel for nuclear power plants will not run out for tens of thousands of years
    • Nuclear power plants contribute no greenhouse gasses and few atmospheric pollutants
  • 3. Disadvantages of Nuclear Power
    • Uranium is ultimately a nonrenewable resource.
    • Nuclear power plants are extremely costly to build.
    • The slight possibility that nuclear power plants can have catastrophic failures.
    • Large environmental impact during the mining and processing stages of uranium are numerous.
    • Nuclear waste (Spent nuclear fuel) is extremely hazardous and must be stored safely for thousands of years.
  • 4. Comparing Uranium to Coal
    • *1 kg of uranium-235 will generate as much energy as 3,000 tons of coal without CO 2 emissions
  • 5. Comparing Uranium to Coal
  • 6. Coal Power Plant Environmental Concerns
  • 7. Nuclear Power Plant Environmental Concerns
  • 8. Nuclear Power in the U.S.
    • The U.S. has 104 nuclear power plants (more than any other country)
    • Combined, these reactors produce about 100 billion watts of electricity (20% of the total)
  • 9. Nuclear Power in the U.S.
    • No new reactors have been completed in the U.S. since 1979.
    • Why???
      • High Operating Costs
      • Liability Problems
      • Wastes
      • Health Concerns
      • Terrorism
      • Public Misconceptions
  • 10. Illinois Nuclear Power
    • Nuclear power typically accounts for nearly one-half of Illinois electricity generation and more than one-tenth of all the nuclear power generated in the United States.
    • With 11 operating reactors at six nuclear power plants, Illinois ranks first among the States in nuclear generation.
    • The growth of the Illinois nuclear industry is due largely to State government initiatives, which began encouraging nuclear power development in the 1950s
  • 11. Illinois Nuclear Power
    • The origin of all of the commercial and military nuclear industries in the world can be traced back to December 2, 1942 at the University of Chicago.
    • On that day, a team of scientists under Dr. Enrico Fermi initiated the first controlled nuclear chain reaction.
  • 12. Illinois Nuclear Power
    • There are 6 operating nuclear power plants in Illinois: Braidwood, Byron, Clinton, Dresden, LaSalle, and Quad Cities.
    • With the sole exception of the single-unit Clinton plant, each of these facilities has two reactors.
    • The two reactors at Braidwood and both reactors at Byron are pressurized light water reactors (PWR).
    • The reactors at the other facilities (Clinton, Dresden, LaSalle, and Quad Cities are boiling water reactors (BWR).
  • 13. Fission and Fusion
    • Fission: A heavy nucleus is split into smaller nuclei, releasing energy
    • Fusion: Two light nuclei fuse into a heavy nucleus, releasing energy
      • Fusion generates much more energy than fission
      • Fusion of hydrogen into helium is what provides power to the sun (and thus to the Earth)
  • 14. Energy from Fission
    • When a neutron strikes a uranium-235 nucleus, it splits into two nuclei, releasing energy
    • Example: n + 235 U -> 93 Kr + 141 Ba + 2n
    • One neutron goes in, two neutrons come out
  • 15. Chain Reactions
    • If at least one neutron from each fission strikes another nucleus, a chain reaction will result
    • An assembly of uranium-235 that sustains a chain reaction is critical
  • 16. Power Plants and Bombs
    • Natural uranium contains 99.3% uranium-238 and 0.7% uranium-235
    • Only uranium-235 can create fission chain reactions
      • Nuclear power plants use uranium that has been enriched to 3% uranium-235
      • Nuclear bombs use uranium that has been enriched to 95% uranium-235
    • 3% enriched uranium can never explode!
  • 17. Nuclear Bombs
    • Since neutrons initiate fission, and each fission creates more neutrons, there is potential for a chain reaction
  • 18. Nuclear Bombs
    • Have to have enough fissile material around to intercept liberated neutrons
    • Critical mass for 235 U is about 15 kg, for 239 Pu it’s about 5 kg
    • Bomb is dirt-simple: separate two sub-critical masses and just put them next to each other when you want them to explode!
      • difficulty is in enriching natural uranium to mostly 235 U
  • 19. Nuclear Fuel Cycle
  • 20. Mining and Milling
    • Uranium is usually mined by either surface (open cut) or underground mining techniques, depending on the depth at which the ore body is found.
    • From these, the mined uranium ore is sent to a mill which is usually located close to the mine.
  • 21. Mining and Milling
    • At the mill the ore is crushed and ground to a fine slurry which is leached in sulfuric acid to allow the separation of uranium from the waste rock.
    • It is then recovered from solution and precipitated as uranium oxide (U 3 0 8 ) concentrate.
      • Sometimes this is known as "yellowcake“
  • 22. Conversion
    • Because uranium needs to be in the form of a gas before it can be enriched, the U 3 0 8 is converted into the gas uranium hexafluoride (UF 6 ) at a conversion plant.
  • 23. Enriching
    • Need to enrich uranium to at least 3% U-235 for a power plant
    • Gaseous Diffusion Method
      • UF 6 (hexafluoride) gas heated
      • U-238 is heavier than U-235
      • Hexafluoride Gas can be separated into two streams
        • Low velocity U-238
        • High Velocity U-235
    • Centrifuge Method
      • Gas spun in centrifuge
      • Lighter U-235 will separate from heavier U-238
  • 24. Fuel Conversion
    • Enriched Uranium transported to a fuel fabrication plant where it is converted to uranium dioxide (UO 2 ) powder and pressed into small pellets.
    • These pellets are inserted into thin tubes, usually of a zirconium alloy (zircalloy) or stainless steel, to form fuel rods.
    • The rods are then sealed and assembled in clusters to form fuel assemblies for use in the core of the nuclear reactor.
  • 25. Fuel Packaging in the Core
    • Rods contain uranium enriched to ~3% 235 U
    • Need roughly 100 tons per year for a 1 GW plant
    • Uranium stays in three years, 1/3 of the fuel rods are cycled annually
  • 26. The Reactor Core
    • The reactor core consists of fuel rods and control rods
      • Fuel rods contain enriched uranium
      • Control rods are inserted between the fuel rods to absorb neutrons and slow the chain reaction
    • Control rods are made of cadmium or boron, which absorb neutrons effectively
  • 27. Moderators
    • Neutrons produced during fission in the core are moving too fast to cause a chain reaction
      • Note: This is not an issue with a bomb, where fissile uranium is so tightly packed that fast moving neutrons can still do the job.
    • A moderator is required to slow down the neutrons
    • In Nuclear Power Plants water (light or heavy) or graphite acts as the moderator
      • Graphite increases efficiency but can be unstable (Chernobyl)
  • 28. Light vs. Heavy Water
    • 99.99% of water molecules contain normal hydrogen (i.e. with a single proton in the nucleus)
    • Water can be specially prepared so that the molecules contain deuterium (i.e. hydrogen with a proton and a neutron in the nucleus)
    • Normal water is called light water while water containing deuterium is called heavy water
    • Heavy water is a much better moderator but is very expensive to make
  • 29. Boiling Water Reactor (BWR)
    • Heat generated in the core is used to generated steam through a heat exchanger
    • The steam runs a turbine just like a normal power plant
  • 30. Pressurized Water Reactor (PWR)
  • 31. Pressurized Water Reactor (PWR)
    • Water in the core heated top 315 ° C but is not turned into steam due to high pressure in the primary loop.
    • Heat exchanger used to transfer heat into secondary loop where water is turned to steam to power turbine.
    • Steam used to power turbine never comes directly in contact with radioactive materials.
  • 32. PWR vs. BWR
  • 33. Spent Nuclear Storage
    • Fuel rods must be replaced every 3 years.
    • Spent Fuel Rods are temporarily stored in special ponds which are usually located at the reactor site.
    • The water in the ponds serves the dual purpose of acting as a barrier against radiation and dispersing the heat from the spent fuel.
  • 34. Spent Fuel Rods Radiation
    • Spent fuel assemblies taken from the reactor core are highly radioactive
    • Contain plutonium-239, which is radioactive.
    • Forms from the reaction of U-238 and neutrons in the core
  • 35. Fate of Spent Fuel
    • There are two alternatives for spent fuel:
    • Reprocessing to recover the usable portion of it
    • Long-term storage and final disposal without reprocessing.
  • 36. Uranium Reprocessing
    • Spent fuel still contains approximately 96% of its original uranium, of which the fissionable U-235 content has been reduced to less than 1%.
    • About 3% of spent fuel comprises waste products and the remaining 1% is plutonium produced while the fuel was in the reactor
    • Reprocessing extracts useable fissile U-238 and Plutonium from the spent fuel rods
  • 37. Uranium Reprocessing
    • Most of the spent fuel can be reprocessed but isn’t in the U.S.
    • Federal law prohibits commercial reprocessing because it will produce plutonium (which can be used both as a fuel and in constructing bombs)
  • 38. Nuclear Waste Disposal
    • In the U.S., no high-level nuclear waste is ever disposed of --it sits in specially designed pools resembling large swimming pools (water cools the fuel and acts as a radiation shield) or in specially designed dry storage containers. 
    • Spent nuclear fuel must be isolated for thousands of years
    • After 10,000 years of radioactive decay, according to EPA standards, the spent nuclear fuel will no longer pose a threat to public health and
  • 39. Yucca Mountain
    • The United States Department of Energy's long range plan is for this spent fuel to be stored deep in the earth in a geologic repository, at Yucca Mountain, Nevada. 
  • 40. Concerns about Yucca Mountain
    • Possible health risks to those living near Yucca Mountain and transportation routes
    • Eventual corrosion of the metal barrels containing the waste
    • Located in an earthquake region and contains many interconnected faults and fractures
      • These could move groundwater and any escaping radioactive material through the repository to the aquifer below and then to the outside environment
  • 41. Reactor Safety
    • These are the only major accidents (Three Mile Island and Chernobyl) to have occurred in more than 12,700 cumulative reactor-years of commercial operation in 32 countries. 
    • The risks from nuclear power plants, are minimal compared with other commonly accepted risks
  • 42. Breeder Reactor
    • In a fission reactor, both uranium-235 and plutonium-239 can be used as nuclear fuel
    • Most of the uranium in a typical reactor is uranium-238, which cannot be used as nuclear fuel
    • When a high-energy neutron collides with the nucleus of uranium-238, plutonium-239 is sometimes produced
    • Could a nuclear reactor create more fuel while it generates energy? Yes, this is a breeder reactor
  • 43. Breeder Reactor
    • To convert uranium-238 to plutonium-239, you need fast neutrons
    • Therefore, water (which acts as a moderator) cannot be used as the coolant
    • Liquid sodium or high pressure gasses are used instead
    Uranium-238 only captures fast (high-energy) neutrons
  • 44. The Core of a Breeder Reactor
    • A breeder reactor core consists of a normal uranium-235 reactor (moderated by graphite rods) surrounded by a jacket of uranium-238
    • The uranium-238 will be converted to plutonium-239 by neutrons escaping from the core
    Orange: uranium-238 Green: enriched uranium-235 Blue: graphite rods
  • 45. A Typical Breeder Reactor
    • Because liquid sodium becomes radioactive, it is separated from the rest of the power plant using a heat exchanger
    • High pressure gas-cooled reactors are also being researched
  • 46. Comments on Breeder Reactors
    • Breeder reactors must be tightly controlled, because plutonium-239 can be used to build atomic weapons
    • Liquid sodium is extremely reactive (and dangerous) thus high-pressure gasses are preferred as the coolant
    • Only France and Japan are actively pursuing breeder reactor technology
    • Breeder reactors are Illegal in the united States due to safety and terrorist concerns.