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Chapter 13

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Chapter 13

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  1. Chapter 13 Energy from Nuclear Power

  2. Introduction • Read the intro to CH. 13 (on page 331) and be able to answer the following ?s: • What was the cause and effect of the accident in Japan? • How much of Japan’s electricity is supplied by nuclear power?

  3. 13.1 Nuclear energy in perspective

  4. The Nuclear Age • In the 1960s and early 70s, utility companies moved ahead with plans for numerous nuclear power plants • Research to use nuclear power to generate electricity to prevent the pollution formed by fossil fuels and to solve the problem of resource limitations • Perception of nuclear power plans was one of optimism

  5. Curtailed • 1975 utilities stopped ordering nuclear power plants and existing orders were canceled • The perception of nuclear power has been one of pessimism • Public opinion has the greatest impact on future developments of nuclear energy

  6. Since the early 1970s, when orders for plants reached a peak, few utilities called for new plants and many canceled earlier orders. Nevertheless, the number of plants in service increased steadily as plants under construction were completed. The number of operating plants peaked at 112 and is holding steady at 103

  7. The Shoreham Nuclear Plant on Long Island, NY With little electricity produced, this plant was closed because of concerns about whether surrounding areas could be evacuated in case of an accident. The plant is now being dismantled

  8. Global Picture • Nuclear power plants generates about 16% of the world’s electricity • France and Japan remain fully committed to pushing forward with nuclear programs • France now produces 78% of its energy with nuclear power with plans to push it to 80% • As of 2005, the U.S. had 103 nuclear plants operating, producing 20% of U.S. electricity

  9. Nuclear share of electrical power generation In 2005, those countries lacking fossil fuel reserves tended to bet he most eager to use nuclear power (Source: Date from International Atomic Energy Agency)

  10. 13.2 How Nuclear Power works

  11. Objective • Control nuclear reactions so that energy is released gradually as heat • Heat is used to boil water and produce steam, which then drives conventional turbogenerators

  12. From Mass to Energy • Differs from generating electricity using fossil fuels • Fossil fuels – chemical reactions remain unchanged at the atomic level • Nuclear energy involves changes at the atomic level through fission or fusion

  13. Nuclear Energy Fission Fusion Two small atoms combine to form a larger atoms of a different element • A large atoms of one element is split to produce two smaller atoms of different elements • In both fission and fusion, the mass of the product(s) is less than the mass of the starting material, and the lost mass is converted to energy in accordance with the law of mass energy equivalence (E = mc2)

  14. Nuclear Energy • The amount of energy released by the mass-to-energy conversion is tremendous • The sudden fission or fusion of a mere 1 kg of material releases the explosive energy of a nuclear bomb • Controlled fission releases the energy gradually as heat

  15. Nuclear Fission Splitting of certain large atoms into smaller atoms

  16. Nuclear Fusion Fusing together of small atoms to form a larger atoms

  17. The Fuel for Nuclear Power Plants • All current nuclear power plants employ the fission of uranium 235 (U-235) • The element Uranium occurs naturally in various minerals in Earth’s crusts

  18. Uranium • Exists as two isotopes • Isotope – any given element that contains different numbers of neutrons, but the same number of protons and electrons • U-238 • U-235 • The numbers (238, and 235) is called the mass number of the element. It is the sum of the number of neutrons and the number of protons in the nucleus of the atoms • U-235 will readily undergo fission, but U-238 will not

  19. Fission • It takes a neutron hitting the nucleus at jus the right speed to cause U-235 to undergo fission • The fission reaction gives off several more neutrons and releases a great deal of energy • Chain reaction occurs when the neutrons cause other fissions, which release more neutrons, which causes other fissions • Fission products: • Radioactive by-products, heat, neutrons

  20. Chain Reaction

  21. Nuclear Fuel • To make nuclear “fuel” uranium ore is mined, purified into uranium dioxide (UO2) and enriched • 99.3% of uranium found in nature is U-238 • Enrichment involves separating U-235 from U-238 to produce a material containing higher concentrations of U-235

  22. Nuclear Bomb • When U-235 is highly enriched, the spontaneous fission of an atom can trigger a chain reaction • A nuclear bomb is the result of an uncontrolled fission of a high grade U-235

  23. Nuclear Reactor • Designed to sustain a continuous chain reaction but not allow it to amplify into a nuclear explosion • Uranium is enriched to 4% U-235 • This prevents nuclear explosion • Consists primarily of an array of fuel and control rods • Generates an enormous amount of heat

  24. Moderator • Chain reaction can be sustained in a reactor only if a sufficient mass of enriched uranium is arranged into a geometric pattern and is surrounded with a material called a moderator • Moderator slows down neutrons that produce fission so they are traveling at the right speed to trigger another fission.

  25. Fuel Rods • Enriched UO2 is made into pellets that are loaded into long metal tubes • Loaded tubes are called fuel elements or fuel rods • Over time daughter products that also absorb neutrons accumulate in the fuel rods and slow down the rate of fission and heat production • The highly reactive spent fuel elements are removed and replaced with new ones

  26. Control Rods • Chain reaction in the reactor core is controlled by rods of neutron-absorbing material (typically cadmium) called control rods • Chain reaction is started and controlled by withdrawing and inserting the control rods as necessary

  27. Nuclear Reactor In the core of a nuclear reactor, a large mass of uranium is created by placing uranium in adjacent tubes, called fuel elements. The rate of the chain reaction is moderated by inserting or removing rods of neutron-absorbing material between the fuel elements

  28. Nuclear Reactor The fuel and rods are surrounded by the moderator fluid, near-pure water

  29. Nuclear Power Plant • Heat from the reactor is used to boil water and provide steam for driving conventional turbogenerators

  30. LOCA • If the reactor vessel should break, the sudden loss of water from around the reactor, called a “loss-of-coolant)accident” (LOCA) could result in the core’s overheating, resulting in a meltdown

  31. Warm-Up • What is the difference between fusion and fission? • What isotope of uranium is used in fission reactions? • What are the products of fission?

  32. Comparing Nuclear Power with Coal Power Fuel Needed - Nuclear Fuel Needed - Coal Coal plant consumes 2 – 3 million tons of coal Obtained through strip mining Acid mine drainage, erosion Obtained through deep mining Human costs in the form of accidental deaths and impaired health • Requires 1.5 tons of raw material • Mining causes much less harm to humans and environment • Fission of about 1 pound of uranium fuel releases the energy equivalent to burning 50 tons of coal • About 60 tons of uranium is sufficient to run for as long as two years

  33. Comparing Nuclear Power with Coal CO2 Emissions – Nuclear CO2 Emissions – Coal Emits more than 10 million tons of CO2 into th4e atmosphere Since coal pants also need to be constructed, coal and waste ash, the extra fossil fuel consumption can apply to coal • Does not emit ANY CO2 into the atmosphere while producing energy • However, fossil fuels are used in the mining and enriching of uranium, construction of plants, the decommissioning of the plant after it is shut down and the transportation and storage of waste

  34. Comparing Nuclear Power to Coal SO2 and other Emissions – Nuclear SO2 and other Emissions – Coal Emits more than 300,000 tons of SO2, particulates, and other pollutants Leads to acid rain and health-threatening air pollution • Produces no acid-forming pollutants or particulates

  35. Comparing Nuclear Energy with Coal Radioactivity - Nuclear Radioactivity - Coal Releases 100 x more radioactivity than a nuclear power plant because of the natural presence of radioactive compounds in coal Uranium, thorium • Releases low levels of radioactive waste gases

  36. Comparing Nuclear Energy with Coal Solid Wastes - Nuclear Solid Wastes - Coal Produces about 600,000 tons of ash requiring land disposal. • Produces about 250 tons of highly radioactive wastes • Requiring safe storage and ultimate safe disposal • Safe disposal is an unresolved problem

  37. Comparing Nuclear Energy with Coal Accidents – Nuclear Accidents – Coal Worst case scenario Fatalities to workers and a destructive fire • Range from minor emissions of radioactivity to catastrophic releases that can lead to widespread radiation sickness, death, cancer, widespread and long lasting environmental contamination

  38. 12.3 The hazards and costs of nuclear power facilities

  39. Radioactive Emissions • When an element undergoes fission, the split “halves” are atoms of lighter elements • These are the DIRECT products of fission • Typically unstable isotopes of their respective elements • Unstable isotopes are called radioisotopes • Radioisotopes become stable by spontaneously ejecting subatomic particles (alpha/beta particles and neutrons), high energy radiation (gamma rays and X rays) or both

  40. Radioactive Emissions • Radioactivity is measured in curies • The particles and radiation emitted from radioisotopes are called radioactive emissions • Many materials in and around the reactor may be converted to unstable isotopes and become radioactive by absorbing neutrons from the fission process • These indirect products (unstable isotopes) of fission, along with the direct products (spent fuel) are the radioactive wastes of nuclear power

  41. Biological Effects of Radioactive Emissions • Radioactive emissions can penetrate biological tissue and damage it • Radiation displaces electrons from molecules leaving behind charged particles, or ions • Therefore emissions are called ionizing radiation • Ionizing radiation can break chemical bonds or change the structure of the molecule and inhibit its function

  42. Biological Effects of Radioactive Emissions • High Doses • Prevent cell division • In medical applications – chemotherapy • However, if whole body is exposed, a general blockage of cell division occurs that prevents the normal replacement or repair of blood, skin, and other tissues • “radiation sickness” • May lead to death a few days, or months after exposure • Very high levels can cause immediate death

  43. Biological Effects of Radiation Exposure • Low Dose • Damages DNA • Cells with damaged DNA may then begin growing out of control • Forms malignant tumors or leukemia • If damaged DNA is a sex cell, it can result in birth defects • Other effects include weakening of the immune system, mental retardation, and the development of cataracts • Low level effects may go unseen until many years after the even

  44. Exposure to Radiation • Health effects are directly related to exposure • Evidence for this hypothesis comes from studies of patients with various illnesses who were exposed to high levels of X rays in the 1930s • People in these groups developed higher-than-normal rates of cancer and leukemia • There is no agreement among health care agencies as to what a safe level of exposure is

  45. Sources of Radiation • Background exposure • Uranium and radon gas that occurs naturally in the Earth’s crust • Medical and dental X rays • Cosmic radiation from outer space