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NUCLEAR ENERGY

NUCLEAR ENERGY. Nuclear Energy. The nucleus of an atom is the source of nuclear energy. . Nuclear Energy. When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy.

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NUCLEAR ENERGY

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  1. NUCLEAR ENERGY

  2. Nuclear Energy • The nucleus of an atom is the source of nuclear energy.

  3. Nuclear Energy • When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy. • Nuclear energy is also released when nuclei collide at high speeds and join (fuse). This is called fusion and is how the sun creates its energy.

  4. Nuclear power 6% Geothermal, solar, wind 2.5% Nuclear power 8% Geothermal, solar, wind 1% Hydropower 4.5% Hydropower, 3% Natural gas 23% Natural gas 21% RENEWABLE 18% Biomass 11% Coal 23% Biomass 3% RENEWABLE 7% Coal 22% Oil 39% Oil 33% NONRENEWABLE 82% NONRENEWABLE 93% World United States Fig. 15-3, p. 373

  5. How Does a Nuclear Fission Reactor Work? • Controlled nuclear fission reaction in a reactor A neutron hits the nucleus of an atom which releases more neutrons which hit more nuclei which release more neutrons which hit more…. This is called a chain Reaction.

  6. How Does a Nuclear Fission Reactor Work? • Controlled nuclear fission reaction in a reactor • Light-water reactors • Fueled by uranium ore and packed as pellets in fuel rods and fuel assemblies (U-235) • Control rods absorb neutrons in order to control the rate of the reaction.

  7. How Does a Nuclear Fission Reactor Work? Water is the usual coolant Containment shell around the core for protection Water-filled pools or dry casks for storage of radioactive spent fuel rod assemblies **The objective of a nuclear power plant is to harness the heat energy from fission to make steam

  8. How a reactor works • How nuclear energy works

  9. Light-Water-Moderated and -Cooled Nuclear Power Plant with Water Reactor

  10. 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

  11. Worst Commercial Nuclear Power Plant Accident in the U.S. • Three Mile Island • March 29, 1979 • Near Harrisburg, PA, U.S. • Nuclear reactor lost its coolant (mech. and human error) • The core overheated and suffered a partial meltdown • Unknown amounts of radioactivity escaped • People fled the area-about 100,000 • Increased public concerns for safety • Led to improved safety regulations in the U.S. • $700 million for construction-paid over $1.2 billion in damages and lawsuits

  12. Worst Nuclear Power Plant Accident in the World • Chernobyl April 26, 1986 In Chernobyl, Ukraine • Occurred during a test of the plant when operators disconnected emergency cooling systems and removed the control rods. • The nuclear reactions continued and could not be controlled. (uncontrolled chain reaction) • 31 people died immediately and many others later • Partial meltdown and fire for 10 days • Huge radioactive cloud spread over many countries and eventually the world • 350,000 people left their homes • Effects on human health, water supply, and agriculture

  13. Automatic safety devices that shut down the reactor when water and steam levels fall below normal and turbine stops were shut off because engineers didn’t want systems to “spoil” experiment. Almost all control rods were removed from the core during experiment. Emergency cooling system was turned off to conduct an experiment. Cooling pond Cooling pond Turbines Turbines Radiation shields Radiation shields Reactor Reactor Additional water pump to cool reactor was turned on. But with low power output and extra drain on system, water didn’t actually reach reactor. Reactor power output was lowered too much, making it too difficult to control. Crane for moving fuel rods Steam generator Water pumps Chernobyl Fig. 14.37, p. 350

  14. Remains of a Nuclear Reactor at the Chernobyl Nuclear Power Plant

  15. Possible Methods of Disposal and their Drawbacks • 1. Bury it deep in the ground • 2. Shoot it into space or into the sun • 3. Bury it under the Antarctic ice sheet or the Greenland ice cap • 4. Dump it into descending subduction zones in the deep ocean • 5. Bury it in thick deposits of muck on the deep ocean floor

  16. Nuclear Power Has Advantages and Disadvantages

  17. Coal Nuclear Ample supply Ample supply of uranium High net energy yield Low net energy yield Low air pollution (mostly from fuel reprocessing) Very high air pollution High CO2 emissions Low CO2 emissions (mostly from fuel reprocessing) 65,000 to 200,000 deaths per year in U.S. About 6,000 deaths per year in U.S. High land disruption from surface mining Much lower land disruption from surface mining High land use Moderate land use Low cost (with huge subsidies) High cost (with huge subsidies) Fig. 14.36, p. 349

  18. CO2 Emissions Per Unit of Electrical Energy Produced for Energy Sources

  19. Decommissioning Power Plants • 1/3 of fuel rod assemblies must be replaced every 3-4 years. They are placed in concrete lined pools of water (radiation shield and coolant). • Nuclear wastes must be stored for 10,000 years • After 15-40 years of operation, the plant must be decommissioned by • 1. dismantling it • 2. putting up a physical barrier, or • 3. enclosing the entire plant in a tomb (to last several thousand years)

  20. Small amounts of Radioactive gases Uranium fuel input (reactor core) Containment shell Emergency core Cooling system Control rods Heat exchanger Hot coolant Hot coolant Coolant Coolant Moderator Coolant passage Pressure vessel Shielding Waste heat Electrical power Steam Useful energy 25 to 30% Generator Turbine Hot water output Condenser Pump Pump Cool water input Black Pump Waste heat Water Waste heat Water source (river, lake, ocean) Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Fig. 14.32, p. 346

  21. Ted Talks • Nuclear Power Debate

  22. What do You Remember? • What is the main fuel used in nuclear power plants? • Uranium-235 • List 3 advantages of nuclear power • Low environmental impact • Emits less CO2 than most power sources • Moderate land use and disruption • Large fuel supply • Low risk of accidents • Where is Three Mile Island? • Pennsylvania

  23. List 3 disadvantages of nuclear power. • Expensive • Low net energy yield • High environmental impact if there is an accident • Where to store it for the long term • What is the purpose of nuclear energy as a power source? • To create steam • What helps prevents a runaway chain reaction? • Control rods • What is used to keep the reactor cool? • water

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