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NUCLEAR POWER

NUCLEAR POWER. APES 2009 CHAPTER 21. ISOTOPES. Isotopes- some atoms of the same element have different numbers of neutrons creating different mass numbers. EX: Uranium has 92 protons, & most uranium atoms contain 146 neutrons & have a mass number of 238… 92 + 146 = 238

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NUCLEAR POWER

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  1. NUCLEAR POWER APES 2009 CHAPTER 21

  2. ISOTOPES • Isotopes- some atoms of the same element have different numbers of neutrons creating different mass numbers. • EX: Uranium has 92 protons, & most uranium atoms contain 146 neutrons & have a mass number of 238… • 92 + 146 = 238 • How many neutrons does U-235 have?

  3. RADIOACTIVITY • Some isotopes are unstable and decay slowly, emitting particles & energy. • These are called radioactive atoms • Radioactive atoms eventually become stable and stop decaying.

  4. Radiation can come from • Alpha particles • Beta particles • Gamma rays- used in radiation therapy for cancer patients. • When alpha or beta particles are given off, the mass # & atomic # change creating a different element.

  5. Natural Radiation? • Natural sources of radiation… • Soil & rocks • Water • Air • Cosmic rays

  6. 2 radioactive isotopes of uranium are U-238 and • U-235 (know calculation!) • Both decay into stable form of lead. • The amount of time it takes for half of the atoms in a sample of a radioactive element to decay is called the isotope’s half-life. • Half-lives can be a few seconds or billions of years. • U-238 has half-life of 4.5 billion years. • U-235 has half-life of 700 million years.

  7. REACTIONS & REACTORS • Nuclear Fission- releasing energy by splitting the nucleus of an atom apart. • This energy can be used to create electricity.

  8. STEPS OF NUCLEAR FISSION • Neutron is fired into nucleus of U-235 atom. • Nucleus splits, forming two daughter nuclei • This reaction releases energy & several more neutrons. • This continuous action of neutrons splitting atomic nuclei is called a chain reaction.

  9. NUCLEAR REACTORS • Nuclear fuel is usually 97% U-238 and 3% • U-235. • U-238 is not fissionable so it is not part of the nuclear reaction (but can be used in plutonium reactors)

  10. NUCLEAR REACTORS • In the U.S., nuclear fission happens inside a nuclear reaction vessel • 20 m tall with walls that are 15-30 cm thick. • Large shield surrounds the vessel to contain any stray radioactive particles • The reactor is housed inside a concrete containment building.

  11. NUCLEAR REACTORS • Fuel rods are filled with pellets that contain the U-235. Positioned vertically in reactor so water can circulate betwn them.

  12. NUCLEAR REACTORS • Water is important because: • It absorbs heat & keeps core from melting. • It slows the movement of neutrons released during the chain reaction.

  13. NUCLEAR REACTORS • Speed of chain reactions is controlled by control rods made of cadmium, boron, etc. that absorb neutrons. • Raise control rods out of reactor= absorb fewer neutrons, speed up reaction, hotter water. • Lower control rods into reactor= absorb more neutrons, slow reaction, cool water

  14. NUCLEAR REACTORS • Hot water is passed to pipes where steam is created that turns turbines, creating electricity. • Water cooling system & control rods regulate heat. If they fail, it would cause a “nuclear meltdown” at the core.

  15. BREEDER REACTORS • U-238 is most plentiful, but non-fissionable. • Turn U-238 into plutonium-239 which is fissionable. • It creates more fuel than you start with. • Plutonium can be used to make atomic bombs as well as energy. • Breeder reactors not used in U.S. because of potential threat of nuclear terrorism.

  16. RADIATION & HEALTH • Radiation is unhealthy • Fast dividing skin cells & blood cells are particularly vulnerable • Large doses cause skin burns, anemia, death, miscarriage • Changes DNA leading to cancer & genetic mutations. • Can be passed on to offspring

  17. www.geology.fau.edu/course_info/fall02/ EVR3019/Nuclear_Waste.ppt

  18. RADIOACTIVE WASTE • HIGH LEVEL • Emit large amounts of radiation • Very dangerous & poisonous • Stored onsight in large containment vessels stored in water • Come from • Used uranium fuel rods • Control rods • Water used to cool & control chain reactions

  19. RADIOACTIVE WASTE • MEDIUM & LOW LEVEL • Not as radioactive • A lot more are produced vs. high level • Pose a greater risk because they are more prevalent & not as obvious • Clothing of nuclear power plant workers • Tailings from uranium mines • Hospital & laboratory waste

  20. WASTE DISPOSAL • Must be • stored in container that will last tens of thousands of years. • Stored in geologically stable area. No earthquakes! • Stored deep underground

  21. PROBLEMS WITH WASTE DISPOSAL • Most high level wastes sit in storage tanks outside nuclear power & weapons plants. Some have begun to leak contaminating groundwater. • Between 1940 & 1970, most medium & low level wastes were sealed in concrete & dropped into the ocean, exposing that environment to potential leaks. Now, it is put into landfills

  22. PROBLEMS WITH WASTE DISPOSAL • Send to Yucca Mountain in Nevada desert • 160 miles from Las Vegas • Underground storage chamber • Cost $50 billion • All high level waste would have to be containerized, and transported by train or truck to site across country • Many people oppose because they do not want radioactive waste transported thru their cities.

  23. Pros & Cons of Yucca Mountain • Desert- very little rain, reduce chance of corrosion • Secluded • Solid bedrock underneath- reduces chance of aquifer contamination • Has been geologically active- earthquakes • Cracks from slight earthquakes could allow water into tunnels, not to mention endanger the integrity of the storage casks • There is an aquifer underneath used for drinking & irrigating by desert population

  24. YuccaMountain www.geology.fau.edu/course_info/fall02/ EVR3019/Nuclear_Waste.ppt

  25. NUCLEAR MELTDOWN • Process by which nuclear chain reaction goes out of control & melts reactor core • Releases huge amounts of radiation into environment.

  26. Three Mile Island • March 29, 1979, a reactor near Harrisburg, PA lost coolant water because of mechanical and human errors and suffered a partial meltdown • 50,000 people evacuated & another 50,000 fled area • Unknown amounts of radioactive materials released • Partial cleanup & damages cost $1.2 billion • Released radiation increased cancer rates. www.bio.miami.edu/beck/esc101/Chapter14&15.ppt

  27. CHERNOBYL • Located in Ukraine • 1986 explosion killed 30 people immediately • 116,000 had to leave homes permanently • May cause 15,000 cases of cancer. • 62,000 sq mi contaminated • Cost $358 billion • Chernobyl was old & lacked safety equipment • Caused by human error

  28. CONS OF NUCLEAR POWER PROS OF NUCLEAR POWER • Potential accidents • Radioactive waste disposal expensive & difficult • Safety equipment expensive • High cost of building new plants • Uranium is nonrenewable • Use very little material to get a lot of energy. • Does not produce much air pollution

  29. Use of Nuclear Energy • U.S. phasing out • Some countries (France, Japan) investing increasingly • France 78% energy nuclear • U.S. currently ~7% of energy nuclear • No new U.S. power plants ordered since 1978 • North Korea is getting new plants from the US www.bio.miami.edu/beck/esc101/Chapter14&15.ppt

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