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GECH119 Nuclear Power

GECH119 Nuclear Power. Dr. Ralph C. Gatrone Virginia State University Department of Chemistry and Physics. Nuclear Power Chapter Objectives. A Tragedy Historical Perspective The nucleus of the atom Unstable nuclei and radioactivity Kinetics of Decay Applications and nuclear weapons

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GECH119 Nuclear Power

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  1. GECH119Nuclear Power Dr. Ralph C. Gatrone Virginia State University Department of Chemistry and Physics

  2. Nuclear PowerChapter Objectives • A Tragedy • Historical Perspective • The nucleus of the atom • Unstable nuclei and radioactivity • Kinetics of Decay • Applications and nuclear weapons • Fission and the Generation of Electricity • Fusion • Waste Disposal • The Future

  3. Assignment • Read Chapter 12 in Investigating Chemistry: A Forensic Science Perspective • For future tests and quizzes you should be able to do problems: 1 – 32 in Chapters12.

  4. Tragedy in the Ukraine • April 26, 1986 at 1:24 AM • Two explosions were heard in reactor 4 • Power rose to 120X normal • Hot pieces of the core flew through the plant • Hours later • Several workers climbed onto the roof • Peered into the hole in the roof • All died that night

  5. Historical Perspective • 1895 – Wilhelm Roentgen • Discovered X-rays • 1901 Nobel Prize • 1895 – Henri Becquerel • Studying uranium • Photographic plate wrapped in dark paper; stored in dark near U • Developed to see shape of U metal • U-rays • Limited study to uranium salts • 1903 Nobel Prize (with Curies)

  6. Historical Perspective • 1898 – Marie Curie • PhD thesis with Pierre Curie • Investigated radiation (U-rays) • Th radioactive like U • Discovered Po – million times more radioactive than U • Discovered Ra – 2.5 million times more radioactive than U • Received the 1903 and 1911 Nobel Prizes

  7. Historical Perspective • Pierre Curie • Studied radiation released • Identified positive and negative particles, neutral rays • Named by Rutherford • Alpha, beta, gamma radiation • Received the 1903 Nobel prize • Killed in 1906 in accident • Stepped in front of a cart

  8. Historical Perspective • Irene and Frederick Joliet-Curie • Bombarded Al with alpha particles • Produced a radioactive P isotope • Natural P is not radioactive • Received the 1935 Nobel Prize • Detected neutrons in fission • Detected large energy release • Enrico Fermi • Bombarded Uranium with neutrons • Reported that he produced the trans-uranium elements • Received the 1939 Nobel Prize

  9. Historical Perspective • Lise Meitner • Working with Otto Hahn and Fritz Strassmann • Suggested they look at trans-U products • Discovered that Ba was produced • U to Ba? From fission • 1945 Nobel Prize awarded to Hahn and Strassmann • Meitner never received Noble • Died in 1968

  10. Historical Perspective • Enrico Fermi • University of Chicago • Built first nuclear reactor • Sustained nuclear chain reaction • Led to establishment of Manhattan Project

  11. Manhattan Project -Trinity

  12. Historical Perspective • Frederick Joliot Curie • Built ZOE in 1948 • First peacetime nuclear reactor • Used to generate electricity

  13. ZOE • Reactor generated electricity • Operated from 1948 – 1976 • 80% of French electricity produced by nuclear • Proposed use of Th so that there are no by-product waste product to worry about

  14. The Nucleus – A Review • Atoms are very small • Number of Cu atoms in diameter of a penny • If the size of a golf ball, • would line up from NY to LA • Nucleus is even smaller • If atom were size of a football field • Nucleus would the eye on the Franklin dime

  15. The Nucleus • Recall • Atom • Mostly empty space • Small nucleus containing most of the mass • Protons: mass = 1amu, charge = +1 • Neutrons: mass = 1amu, charge = 0 • Electrons • Located in orbitals surrounding nucleus • Mass is nearly 0, charge = -1

  16. The Nucleus • Protons • Number of protons is given by the atomic number • Atomic number determines the identity of the element • Neutrons • Number of neutrons is given by • Mass number – atomic number • Protons + neutrons – protons = neutrons • Elements with differing numbers of neutrons are isotopes

  17. Isotopes • Hydrogen • Hydrogen-1: 1 proton and 1 electron • Hydrogen-2: 1 proton, 1 electron, 1 neutron • Deuterium, heavy hydrogen • Hydrogen-3: 1 proton, 1 electron, 2 neutrons • Tritium • Isotope is radioactive • Most elements have isotopes • Some isotopes are radioactive

  18. Radioactivity • Nuclear property • Related to ratio of protons and neutrons • 1:1 for light elements is stable • C-12: 6 protons and 6 neutrons • Other ratios are not necessarily stable • C-13: 6 protons and 7 neutrons - stable • C-14: 6 protons and 8 neutrons – radioactive • Heavier elements • more neutrons than protons – stable • Fe-56: 26 protons and 30 neutrons – stable • Pb-206: 82 protons and 124 neutrons - stable

  19. Radioactivity • Spontaneous • Release of energy • Release of particles • Radiation • Force (weak nuclear) • Poorly understood

  20. Radioactivity • Unstable nucleus • Decays • Ejects particle • Ejects energy • Electromagnetic • Alpha particles • Beta particles • Gamma radiation • Fission

  21. Alpha Particles • 2 protons + 2 neutrons • He nucleus • Mass = 4 amu • Charge is positive 2 • Slow moving • Can’t penetrate a piece of paper • Damaging to chemicals during collisions

  22. Radon Gas • Rn (MN = 222, AN = 86) • Releases He+2 (MN = 4, AN = 2) • During process: • Atomic number decreases by 2 (86 to 84) • Mass number decreases by 4 (222 to 218) • Atomic number 82 is polonium • Rn decays into Po

  23. Beta Particles • Beta particles are electrons • Mass = 0 • Charge = -1 • Occurs when a neutron in the nucleus splits • Forms a proton and an electron • Electron is released from nucleus • Higher energy • Can penetrate skin

  24. Beta Decay • Pb (MN = 214, AN = 82) • Releases an Beta particle (electron) • Neutron split into proton and electron • Nucleus has 1 more proton • AN = 83, MN = 214 (electron has no mass) • Pb becomes Bi (MN = 214, AN = 83)

  25. Gamma Radiation • Excess energy in nucleus • Released as gamma ray • Photon, light, high energy • Able to Penetrate concrete • Most health hazards are due to gamma rays

  26. Other Transformations • Positron emission • Positive charge, no mass • Occurs when proton becomes a neutron • Na-22 (AN = 11) does this • Na-22 (MN = 22, one less proton, AN = 10) • Na became Ne

  27. Other Transformations • Electron Capture • Inner electron is captured by nucleus • Combines with proton to form neutron • One less proton, AN changes • Sn (MN108, AN 30) + electron = In (108, 21) • Fission • Nucleus splits into two smaller nuclei • Can be induced by collisions with other particles

  28. Nuclear Decay • Frequently occurs in series • Rn-222 decayed to Po-218 (alpha particle) • Po-218 decays to Pb-214 (alpha particle) • Pb-214 decays to Bi-214 (beta particle) • Bi-214 decays to Po-214 (beta particle) • Decay series • Unstable nuclei continue to decay • Until stable nuclei form

  29. Health Aspect • Radioactive nuclide (element) • If ingested, nuclide decays in body to other nuclides that may also decay • Damage continues • Rn-222 gas – breathe into lungs • Decays to Po-214 (solid) attached to lung • Alpha particles damage leads to lung cancer • 5,000 to 20,000 deaths due to Rn exposure • Rn present in soil rich in U-238 • Eastern US has serious problem with Rn exposure

  30. Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (pico curies per liter) (red zones)

  31. How Long Are Nuclides Radioactive? • What is the rate of decay? • Rate of anything – measured using kinetics • Radioactive decay follows predictable pattern • The half-life • Half-life = time for ½ of mass to decay • Rn-222 = 3.82 days • H-3 (T) = 12.26 years • C-14 = 5730 years • U-235 = 700,000,000 years • U-238 = 4,510,000,000 years • Pu-239 = 24,110 years

  32. Half-Life • Definition: time for ½ of mass to decay • Assume 100 grams • 1 half-life = 50 grams • 2 half-life = 25 grams • 3 half-life = 12.5 grams • 4 half-life = 6.25 grams • 5 half-life = 3.125 grams • And so on

  33. Short Review • Nuclei can be unstable • Alpha and beta particles are released • Gamma radiation is released • Particles are very energetic • Decay occurs in series • Health hazards due to radiation released during decay series • Half-lives vary for nuclides • Short – microseconds • Long – trillions of years

  34. Applications of Radioactivity • Leak detection • Ir-192 (t1/2 = 73.8 d) • Releases gamma radiation • Penetrates faults in pipe • Film detects gamma ray • Smoke Detectors • Am-241 (t1/2 = 432.2 years) • Alpha particles ionize air • Smoke blocks ion current sets off detector • Alpha particles cannot penetrate smoke particle

  35. Applications of Radioactivity • Medical • Tracers for imaging • See Table 14.5 in text • Short half-lives • Eliminated easily • Non-reactive chemically • Therapy • Ir-192, Ra-226, Co-60, Au-198, P-32 • Some risk due to exposure • Value of test vs risk of exposure

  36. Applications of RadioactivityCarbon Dating • N-14 in atmosphere • Neutron bombardment • C-14 produced when N-14 releases positron • Amount of C-14 is nearly constant • Correction necessary for objects older than 20,000 years • C-14 is exchanged during life processes • Death causes the cessation of this exchange • Amount therefore decays • Measure amount of C-14 left in object • Calculate age based on half-life

  37. Nuclear Fission • Nucleus splits in two smaller nuclei • U-235 splits into Br-87 + La-146 + 3 n0 • Neutrons can start another fission • Chain reaction can start • Amount of energy released given by • E = mc2 • Energy is enormous • Need substantial amount of U-235 • Natural U is largely the 238 isotope • U-235 is < 1% of a Uranium sample

  38. Fission • Critical • Enough neutrons to sustain chain reaction • Nuclear power plants • Subcritical • Insufficient number of neutrons to sustain the chain reaction • Normal situation for radioactive elements • Supercritical • More neutrons present, reaction is out-of-control • Occurs in when nuclear weapons are released

  39. Nuclear Power PlantsUse of Critical Neutrons • Conventional Reactors • Fuel: U-235 enriched fuel rod • Controlled fission • Neutrons are slowed by water moderator • Neutrons are captured by U-235 nuclei • Boron control rods used to moderate number of neutrons produced • Boron absorbs neutrons • Reactor has 100,000 kg of U-235 • Generates heat • Heat is used to generate steam • Steam moves a turbine to generate electricity

  40. A Nuclear Power Plant

  41. Nuclear Power Plant • Breeder Reactor • Fuel: U-238 • Pu-239 generates neutrons • U-238 absorbs neutrons • U-239 generates Pu-239 (breeds) • Pu-239 primary nuclear material in fission weapons • Heat generates steam • Steam drives a turbine, generates electricity

  42. Case Against Nuclear Power • Safety • Chernobyl – radiation release, many health problems • Three Mile Island – loss of coolant, release, no health problems (probably good luck) • Dresden – radioactive I release • Lucens – mountain containing the reactor was sealed permanently • Idaho Falls, explosion killed 3 • Windscale – graphite core caught fire, release of radioactive Iodine, banned milk production for 60 days

  43. Case Against Nuclear Power • Spent fuel rods • What do we do with them? • Currently stored in swimming pools on site • Nuclear Waste • Here today, here tomorrow • Long lived isotopes • Sr-90 • Cs-137 • I-131

  44. Fusion • D + T fuses into He • Similar to reaction on Sun • Compress nuclei close together to overcome normal repulsion of nuclei • Current status • Can produce electricity • Requires more energy than we get

  45. Fusion – the challenges • T > millions of degrees • Keep vessel from melting • Investigating • Lasers to hold fusing nuclei • High magnetic fields • Electricity has been produced • Cost is greater than amount generated

  46. Nuclear Waste • What do we do with it? • Pu – vitrified • Mixed with silicon and boron • Heated to form glass • Put in carbon-steel tubes • Buried in Yucca Mountain, NV • Question: how can we guarantee Pu-239 for 10 half lives (250,000 years)?

  47. C.U.R.E. • Clean Use of Reactor Energy • Convert waste nuclides into new fuel rods • Use to generate electricy • Reprocess • Reuse • Eventually no mass left, complete conversion to energy • Under study

  48. Political questions • Burial of Waste • Not in my backyard • Fuel rods are stored • No new reactors since 1978 • No new refineries for oil • Few new oil reserves being tapped

  49. The Case for Nuclear Power • Energy Resources • Petroleum – 39.5% • Coal – 24.2% • Natural Gas – 22.1% • Hydroelectric – 6.9% • Nuclear – 6.3%

  50. The Case for Nuclear Power • France – 79% • Belgium – 60% • Sweden – 42% • Switzerland – 39% • Spain – 37% • Japan – 34% • UK – 21% • US – 19% (US is largest producer in world)

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