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Nuclear Power: Promise and Problems

Nuclear Power: Promise and Problems. Chapter 13 Environmental Science. Rancho Seco Nuclear Plant in California decommisioned in 1989 now serves as a nature park. I’ve done many triathlons in the cooling pond near these towers… At the annual Tri-4-FUN. Look out for toxic fish??.

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Nuclear Power: Promise and Problems

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  1. Nuclear Power: Promise and Problems Chapter 13 Environmental Science

  2. Rancho Seco Nuclear Plant in California decommisioned in 1989 now serves as a nature park I’ve done many triathlons in the cooling pond near these towers… At the annual Tri-4-FUN Look out for toxic fish??

  3. Nuclear Power: Dream or Delusion? Nuclear Power in the US (pg. 343) Peak orders in 70’s, no new ones in US since early 90’s

  4. Nuclear Power Works byMass converting to Energy • Fission: a large atom of one element splitting into two smaller (different) elements & releasing free neutrons causing a chain reaction • A tiny amount of mass is lost, and that is converted into energy E = mc2 • Fuel Uranium-235 (235U),only 0.7%of ore • 99.3% U ore is Uranium-238 isotope • Enrichment: isolating isotopes, creating higher concentration of Uranium-235 up to 4% • U is only naturally fissionable substance used for chain reactions

  5. Half-life is the time is takes for ½ of a particular radioisotope to decay • U-238 is 4.5 billions years (99.3% of U in nature) • U-235 is 700 millions year (0.7% in nature) • Therefore if starting with 1 kg of U after 4.5 bil years only ½ kg of U is left, after 9 bil years on ¼ kg of U is left and after 13.5 bil years (3 half lives) only 1/8 kg of U is left

  6. Fission Reactions Pg. 346

  7. How Nuclear Power Works • Neutron (neutral particle) hits nucleus at right speed to cause fission & Energy release • Fission reaction gives off more neutrons, if these neutrons are slowed down, they can strike another Uranium-235 atom causing fission (chain-reaction) again & again • Moderator: slows down the neutron (very pure water-light water reactors used in US)

  8. Control Rods: absorb neutrons. These are inserted and withdrawn to start and control the chain reaction. Pellets of enriched uranium dioxide are loaded in to metal tubes to achieve the proper geometric pattern Water: Moderator And Coolant.

  9. Fuel Cycle

  10. Nuclear Reactor Summary Uranium Ore (rock) mined  purified to UO2  enriched (further isolated) from 0.7% U-235 to 4% U-235 (this is the technology limiting step for developing countries)  U pellets loaded in fuel rods  packaged into a geometric pattern of rods to form reactor core to allow chain reactions  Moderator-coolant fluid (light water H2O or heavy water D2O) used to slow down neutrons to keep chain reaction going  Control rods (made of Ag, Cd, others) control the flux of neutrons to speed up or slow down chain reactions in the core  “spent” fuel rods are no longer useful once too many non-fissionable daughter products build up in fuel rod  France and others now recycle these through additional enrichment

  11. Nuclear Reactor Summary Part 2 Heat from fission chain reaction used to boil water coolant  pressure of steam used to drive turbogenerators (opposite of a fan) to produce electricity In US, a double heating loop is used…moderator coolant heats up under pressure with no steam  heating other water that does boil to move turbogenerator Benefit of safety: isolates the hazardous materials including moderator coolant from rest of power plant Drawback: Loss of Coolant Accident (LOCA) like 3 mile Island when reactor vessel breaks, loss of water coolant leads to overheating and meltdown (hot enough to melt material in core)  thick concrete is secondary protection

  12. US Pressurized nuclear power plant. (pg. 348)

  13. Nuclear: • 30 tons • Uranium • No CO2 • low levels of • radioactive • waste gases • 240 tons • radioactive • waste • Minor- • Catastrophic • Emissions • Risky • investment • Why Coal: • 3 million tons • of coal • Mining issues • 7 million tons • CO2 • 300,000 tons • Sulfur dioxide • 600,000 tons • flyash waste • Acid rain • Fatalities to • workers often • But coal plants are less risky investment

  14. Nuclear Trends • Nuclear plants create 19% of our electricity in US • France (most in world) creates 79% of electricity from Nuclear • Nuclear power plants are risky investment and coal plants are much safer investment with more government subsidies to support them • Regulated and monitored in US by Nuclear Regulatory Commission

  15. Electromagnetic Spectrum

  16. U decay series…multiple radioactive decays • Most decays have gamma radiation as well

  17. Hazards and Costs • Emissions (radioisotopes: unstable) • Biological effects of ionizing radiation = causes chemical changes in DNA leading possibly to cancer (tumors)

  18. What to do with the waste?Nobody wants it…do you? • Radioactive waste • During radioactive decays, radiation particles are emitted such as gamma, beta and alpha particles from highest to lowest energy • Spent fuel rods still have other types of radioisotopes remaining as waste • radioactivity material is considered “SAFE” after 10 half lives • Battle between DOE & Proposed storage sites: • Short term: 10 years, loss of 97% radioactivity • Swimming pool, dry storage (decommissioning) • Skull Valley Goshute Reservation in Utah? • Long term: 100,000 years • Yucca Mountain in Nevada? • WIPP Waste Isolation Pilot Plant in New Mexico

  19. Accidents • Worst = Chernobyl in 1986: • Disabled safety system, withdrew control rods, shut off steam’s flow, decreased water level Re-inserted control rods too late, not enough to stop reactions, steam explosion blew up reactor and fire radioactive particles spread for thousands of miles (400 times the radiation fall out of bombs of Hiroshima and Nagasaki) • 2 killed due to explosion, 28 workers died soon after, 4000 confirmed cases of cancer and 1000’s more deaths expected from radiation exposure http://birdhouse.org/blog/wp-content/uploads/2007/12/chernobyl.jpg www.ens-newswire.com

  20. Other Prominent Disasters • 3 Mile Island, Pennsylvania 1979 Loss of coolant resulted in partial meltdown the reactor Steam generator shut down, pressure valve opened and stayed open (water drained) System said there was water in container, at one point emergency cooling system shut down $30 million to settle claims though never admited to any radiation caused illnesses • Tokaimura Japan 1999 3 workers added too much nitric acid manually with buckets to uranium causing nuclear fission to begin  emitted high levels of gamma rays and neutrons (luckily only trace radioactive gases escaped)  two of the workers died of radiation poisoning

  21. Safety • Active: operator-controlled, external power, electrical signals. • Passive: involves engineering devices and structures that make it virtually impossible for the reactor to go beyond acceptable levels of power, temperature and radioactive emissions • ALWRs: cold-water reservoir, conduct heat from nuclear decay outwards,

  22. Issues with Nuclear • Slower growth of electrical demand • Safety is expensive! • Public opinion of waste • If problems do occur, very expensive to company • Deregulation of electric industry • Short-lifetime of power plants (embrittlement, corrosion, then decommission)

  23. Other reactor types • Breeder • Uranium 238 absorbs extra neutron, creating plutonium which is also fissionable • Very efficient, more severe if accidents occur, potential to convert to weapons • Fusion • Two atoms join to make a larger atom • Used in sun, hydrogen bomb • Uses Deuterium (2H-used to make heavy water) • Energy Consumer • How to contain reaction?

  24. The future? Opposition • Distrust • Management/regulation of technology • Lax safety, cover-ups • High construction cost • Accidents that have occurred • Disposal of nuclear waste • Issue with coal’s price

  25. The future? Adaptations • Reactor safety issues addressed • Manufacturing philosophy changed • Licensing and monitoring- streamlined • Where to put new reactors • Waste dilemma solved • Political leadership needs to do these things

  26. Rocky Flats • Outside of Denver • Made plutonium triggers for weapons • Questionable safety • Leaks? • Higher cancer rate • Clean up ended in 2003

  27. Nuclear Quiz - 25 points 1. a) Describe nuclear fission of U-235 and b) how is so much raw energy produced through this process (not the electricity part). • Describe the process of electricity production (secondary production) using nuclear power. Use the following terms at a minimum: moderator-coolant fluid, control rods, fuel rods, turbogenerator. • Thorium-234 has a half life of 24 days. If 20 grams of Th-234 decays for 72 days, how much radioactive Th-234 will remain? • Name the location of 2 nuclear power disaster events (not nuclear bomb usage). List year as well to recapture 2 points lost earlier.

  28. The Induced Fission Reaction of U-235 (it is fissionable)

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