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Other Conventional Power: Nuclear Power

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  1. Other Conventional Power:Nuclear Power

  2. Housekeeping Mid-term • Tuesday 2/8 • Can have one page worth of notes • Cover sheet with useful data/formulae included • AY wrote a summary of the first half / assignment keys 2&3 posted Assignment 4 • Would be good to have worked through prior to mid term • As discussed, HW4 due MONDAY 2/7 @ 5:00 (1700) • Key will be posted at that time (therefore will take no late work) • AY will be available Monday afternoon 1200 – 1700, Tuesday morning 1000-1200

  3. US Net Generation (GWHr) Conventional Renewables Hydroelectric 247,510 Pumped Storage -6,896 Wind 34,450 Solar (Th and PV) 612 Wood 39,014 Other Biomass 16,525 Geothermal 14,637 Total Renewables 105,238 Coal 2,016,456 Natural Gas 896,590 Other Gases 13,453 Petroleum 65,739 Nuclear 806,425 All Sources 4,156,745

  4. Nuclear Intro Fundamental concept highlighted by Einstein in 1905 E = mc2 Energy in matter as “binding energy” • Makes mass of heavy isotopes smaller than sum of nucleons • Find released energy by calculating “mass anomaly” The possibility of harvesting nuclear energy recognized in the 1930s Drivers: • Obtaining large amounts of energy from small amounts of matter • No CO2 emissions (but yes, radiological waste produced)

  5. Early discoveries Bequerel 1896: photographic plates “exposed” by Uranium salts • Identifies radioactivity (similar to “cathode rays”) Marie and Pierre Curie: Active principle stronger than Uranium • 1898 – Polonium • 1902 – Radium (100 mg from 1000 kg ore…) Ernst Rutherford: Radioactivity follows zero order kinetics (half life of radioactive materials…)

  6. Early Discoveries Irene and Frederic Joliot-Curie, 1932: Discovery of neutron Also identified ca. 3 neutrons per 235U fission later Hahn, Strassman and Meitner, 1938: Artificial fission demonstrated (bombarding U with neutrons led to formation of Ba) Fermi and Szilard 1942: Self sustaining nuclear chain reaction (part of Manhattan Project) Nuclear power plants developed for naval propulsion and energy production in 1950s

  7. Nuclear Power Pioneers World’s first nuclear-powered electric generating plant was constructed by Soviet Union in 1954 – 5 MW First US PWR was constructed and placed in service by Westinghouse at Pennsylvania in 1957 – 4 MW First US BWR was constructed and placed in service by GE at California in 1957 – 5 MW Most nuclear plants are light water reactors • Pressurized Water Reactor (PWR) – Most Common • Boiling Water Reactor (BWR)

  8. HISTORICAL PERSPECTIVE US Nuclear plant orders placed annually 1979: Three Mile Island #2

  9. Historical Perspective: Decline Factors Expansion in US halted in 1970s Drivers • Overbuilt generation and cheap coal/natural gas • Reduction in load growth rate • Popular objection to nuclear power • Media: “The China Syndrome” • Reinforced by: Three Mile Island / Chernobyl (different perceptions for high-consequence, low risk events vs. chronic risk) • Inherited secretive culture of nuclear energy industry due to association with nuclear weapons programs • Industry downplayed issues with disposal of high level waste

  10. HISTORICAL PERSPECTIVE There are 439 nuclear plants in the world 103 of them in 31 US states



  13. U.S. Nuclear Plant Capacity Factors http://www.nei.org/

  14. How it works Element’s chemical nature determined by the number of electrons In a neutral atom, the number of electrons is equal to the number of protons in the nucleus The repelling positive charge of protons is overcome by “residual nuclear force” from neutrons -Like electrostatic force, but much stronger and shorter range of action Energy gain due to residual nuclear force interaction leads to mass anomaly

  15. BACKGROUND The number of protons in a nucleus determines the elements (atomic number, Z) The number of neutrons determines the isotope Sum of number of protons and neutrons is the “mass number” (A) • Example • Uranium nucleus has 92 protons • If it has 143 neutrons, it is Uranium-235 ( ) • If it has 146 neutrons, it is Uranium-238 ( )

  16. BACKGROUND 103 named elements in about 1000 isotopes There are 4 more un-named known elements Of all identified isotopes, 279 are stable There are 14 known isotopes of uranium More than one combination of p and n can be stable Sn has 10 stable isotopes (!) Not all Z can make a stable isotope Tc has no stable isotopes…

  17. Fission Unstable nuclei will eventually decay But the half life may be longer than the age of the solar system… 113Cd half-life is 7.7 x 1015 years Decay always leads to a more stable isotope and involves emission of disintegration product(s) Ex: (a is a 4He nucleus)

  18. Emitted particles from nuclear decay Alpha particle: Helium nucleus emitted Beta particle: electron emitted Gamma ray: high energy photon Neutron Daughter nuclei: large fragments carrying the remainder of mass

  19. Transmutation You can artificially convert nuclei by bombarding them with • Neutrons • Protons • Helium nuclei If you use photons you can change the “nuclear angular momentum” which may cause nucleus to fall apart

  20. Nuclear reactions A chemical reaction is a reaction which involves electrons Nuclear reaction is a reaction which involves the nucleus of an atom Nuclear reaction produces more energy per atom than chemical reactions Because nuclear forces holding the nucleus together are much stronger than the electrostatic forces that are holding electrons

  21. Artificial Fission In 1938 Hahn and Strassman in Berlin bombarded a Uranium-235 target with neutrons and demonstrated nuclear fission for the first time

  22. NUCLEAR FISSION Enormous amounts of energy released as heat Notice the 3 neutrons released Carry some of the excess energy If you can use neutron to start new nuclear reaction, we have the chain reaction At a certain capture level we get a self-sustaining chain reaction Neutrons that have too much energy (are too fast) cannot be captured Neutrons for reactions need to be slowed (concept of “moderator” invented by Fermi)

  23. Neutron Energy and Moderator 1 barn = 10-28 m2

  24. Criticality Basic concept relates to ability to have reaction at steady state If a general example reaction is 235U + 0n → 141Ba + 92Kr + 3 0n (+ DH) One of the terms in “reaction rate” should be neutron concentration… r=k[235U][0n]

  25. Criticality Sub-critical: • fewer neutrons produced than consumed • reaction dampened Critical: • as many free neutrons produced as consumed • reaction at steady state Super-critical: • more free neutrons produced than consumed • reaction accelerating

  26. Criticality Time dependence of flux for a source-free multiplying medium

  27. Nuclear Fuel Bohr found that nuclear fission was more likely to occur in 235U than in 238U Natural uranium is 0.7% 235U and 99.3% 238U • Separation difficult The process of “enrichment” was developed to increase concentration of 235U in the mixture Other common nuclear fuels: 239PU and 232Th

  28. World reserves: 3.1 million tU Open-pit mining: 30% Underground mining: 38% (55% in 1990) In situ leaching (ISL): 21% Mining Processes

  29. Milling – Uranium Extraction • Grinding (~100 microns) • Acid (H2SO4) or alkaline (Na2CO3 / NaHCO3) leach • Solid / liquid separation of slurry • Purification (simple or extensive) • Precipitation – diuranate salt (e.g. Na2U2O7) • Drying Uranium oxide concentrate (UOC) (predominantly U3O8)

  30. Milling – Uranium Conversion • Dissolving of U3O8 in HNO3 • Calcination (strong heating) → UO3 • Reduction with H2 → UO2 • Hydrofluorination (HF) → UF4 • Fluorination (F2) → UF6 • In most cases, end-use requires conversion to UF6 for enrichment • Certain reactors (CANDU) can use “natural” UO2

  31. Enrichment Natural uranium: 235U: 0.7%, 238U: 99.3% Reactor-grade: 235U increased to 3-5% • Necessary to sustain fission chain reaction Enrichment Methods • Thermal diffusion (primitive, uses Soret/thermophoretic effect) • Ion/cyclotron resonance (“Caultron” – still used in France) • Gas diffusion (GD, nearly obsolete, uses membranes/ Graham’s Law) • High-speed gas centrifugation (GC, current technology) • 5% of power requirements for GD • Laser technology (in development, Separation of Ions by Laser Excitation - SILEX) • Proposed as ca. 1% of GD Afterward, UF6 converted back to UO2 for mechanical processing (fuel rods)

  32. Nuclear Fuel Cycle • Uranium Mining and Milling • Conversion to UF6 • Enrichment • Fuel Fabrication • Power Reactors • Waste repository

  33. Nuclear Fuel Cycle with Reprocessing

  34. FUEL Fissile material made into pellets by sintering Oxide – Most reactors use oxide (UO2) fuel elements due to high melting point (melting point of UO2 is 2800oC) • “UOX” – Uranium oxide • “MOX” – Mixed Oxide (Pu and U oxides mixed together) Metal – Some reactors use metal/metal alloy fuel elements • Safer due to strongly negative “temperature factor” • E.g., UZrH alloy used in OSU’s TRIGA reactor “Ceramic” – Non oxide materials like Nitrides and carbides • Even higher melting point • Better thermal conductivity

  35. FUEL Cm sized pellets are arranged in zirconium alloy tubes to form fuel rods Pellets are 1 cm in diameter and 1.5 cm long Rods arranged in core

  36. Nuclear fuel costs

  37. U.S. Electricity Production Costs 1995-2008, In 2008 cents per kilowatt-hour Production Costs = Operations and Maintenance Costs + Fuel Costs. Production costs do not include indirect costs and are based on FERC Form 1 filings submitted by regulated utilities. Production costs are modeled for utilities that are not regulated. Source: Ventyx Velocity Suite Updated: 5/09

  38. Fuel breeding 232Th + 0n → 233Th → 233Pa + b → 233U + b 238U + 0n → 239U → 239Np + b → 239Pu + b 232Th and 238U are “fertile” nuclei (can be transmuted to “fissile” nuclei using neutrons) Fast breeder reactor that creates more fuel than it burns can be designed… 200x 238U and 400x 232Th in earth’s crust than 235U.

  39. Nuclear Power Plants use Rankine Cycle


  41. The Core Reactor core is the portion of the nuclear reactor which contains the nuclear fuel where the nuclear reaction takes place The main function of a core is to create an environment which establishes and maintains the nuclear chain reaction It provides a means for controlling the neutron population and removing the energy released within the core


  43. MODERATOR Newly released neutrons after a nuclear fission move at 300,000 km/sec “Fast neutrons” Think of the energy contained as kinetic energy E=hn=1/2mv2 Slow moving neutrons are much more likely to be absorbed by uranium atoms to cause fission than fast moving neutrons Moderator is a material which slows down the released neutrons from the fission process

  44. MODERATOR Neutrons must be slowed down or “moderated” to speeds of a few km/sec “epi-thermal neutrons” • This is necessary to cause further fission and continue the chain reaction

  45. Common Moderators • Water - H2O • Light water reactor • Not efficient – it slows neutrons and absorbs them • Heavy water (D2O) • Heavy water reactor • Efficient – slows neutrons and bounces them back • CANDU (Canada Deuterium Uranium) reactor can use natural/low enriched Uranium! • Graphite • RBMK design • Efficient, but graphite (carbon) can burn…


  47. Control Rods • Too many neutrons could lead to runaway reaction (not a good thing) • Number of neutrons in reactor controlled by absorbing some • Made of neutron-absorbing material • Cadmium • Hafnium • Boron Rods inserted or withdrawn from the core to control rate of reaction