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Session 10 – nuclear power

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nuclear power

nuclear power

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  • 1. Session 10 – Nuclear Power T. Ferguson, University of
  • 2. Session 10 – Nuclear Power • Recall that nuclear supplies ~ 8 Quads to US annually (8% of total; 20% of electricity) • Terminology • Fuels, reserves, wastes • Energy Release, Efficiencies • Costs • Status and Policy T. Ferguson, University of
  • 3. Nuclear Power Basics • • • • • Nuclear vs. chemical energy All energy derives from nuclear! Resulting sum of Fission: Splitting heavy atoms products has slightly less mass than sum Fusion: Combining lighter atoms of original reactants Fissionable isotope captures neutron, yields: – – – – Unstable isotope Fragments with high kinetic energy Neutrons Beta, gamma, neutrino emissions • Moderator • Control Rods T. Ferguson, University of
  • 4. Terminology • • • • • • • • Nucleon Nuclide Radionuclide Isotope Alpha, Beta, Gamma Rays Fissionable Material Fertile Material Enrichment T. Ferguson, University of
  • 5. Radioactive Decay Fission might be best understood by first looking at how the most abundant, naturally occurring isotope of Uranium, U-238, decays: • First, elements with atomic number above Lead tend to decay • “Decay” implies transitioning to a stable element with smaller neutron-proton ratio • U-238 has 146 neutrons, for an n/p of 1.587 • This neutron ratio is the highest for any natural isotope U-238 decays by first emitting an alpha particle: 2n + 2p • An alpha particle is identical to the Helium nucleus • So U-238 loses 2n and 2p, reducing it to Thorium-234 • But Thorium is also unstable, and emits a Beta particle: nuclear electron • This, in effect, increases the proton count by 1, forcing the release of a neutron to keep the nucleon count constant T. Ferguson, University of So, Thorium-234 becomes Protactinium-234 (Z=91), which is also unstable . . . And eventually ends at Pb
  • 6. Radioactive Decay Radioactive Half-life: time for half of atoms to decay If N=number of atoms present, and N0 = number of atoms initially, and λ = decay rate constant, Then N = N0 e –λt Set N=0.5N0 to solve for T1/2 U-238 half-life is 4.5 E 9 years (age of universe) T. Ferguson, University of
  • 7. Radioactive Decay Radioactive Half-life: time for half of atoms to decay Radium: Discovered by Curies in 1898, T 1/2 of 1600 years, part of U-238 decay chain Decay rate of 1 gram of Radium is basis for unit of decay, the curie. So, the curie is a measure of the radioactivity of a material T. Ferguson, University of
  • 8. Radioactive Decay Derivation of curie: If N = N0 e –λt, then λ = 0.693/T1/2. Given T1/2 for Ra-226 = 1600 yrs, λ = 1.375 E -11 sec-1. To obtain the decay rate, we need the number of atoms in one gram of Ra-226 T. Ferguson, University of
  • 9. Radioactive Decay Ra-226 has atomic weight of about 226, so 1 kg-mol = 226 kg has Avogadro’s number of atoms (6.02 E 26), which becomes N0. 1 gram, therefore, contains 2.66 E 21 atoms, which is N The decay rate is λN = 3.66 E 10 disintegrations per second (almost 40 billion events per second) (The curie is formally 3.7 E 10 disintegrations/s) T. Ferguson, University of
  • 10. Nuclear Fission Energy (scattered) (absorption &) Uranium-235 + Neutrons Fission (absorption & capture) Radioactive fission products Neutrons (about 2.5) Uranium-235 T. Ferguson, University of Process repeats
  • 11. Nuclear Fission 1. Neutrons are the key ingredient Energy Uranium-235 + Neutrons 3. Critical: Steady rate of chain reaction Subcritical: Decreasing reaction rate Supercritical: Increasing reaction rate Fission Radioactive fission products 2. If at least one Neutrons of these results (about 2.5) in a second event, a self-sustaining fission chain reaction ensues Uranium-235 T. Ferguson, University of Process repeats
  • 12. Quote of the Week “If we have in the future an accident where the reactors go critical, I would only pray for MiamiDade County since there is no way to evacuate the population today compared with in 1972, when the reactors were originally permitted," the president Rhonda Roff of an environmental group called "Save It Now, Glades" told AFP. Comment from article from AFP on Florida’s electrical blackout of 2/26/08 <http://afp.google.com/article/ALeqM5hqzKZYV_FS7JoyYm90kopwwsSKBA> T. Ferguson, University of
  • 13. Nuclear Fission 1. Moderator Energy Uranium-235 + Neutrons Fission Radioactive fission products Neutrons (about 2.5) 2. Neutrons: W/O moderator: 2 MeV With moderator: 1/40 eV 3. Neutrons start with high energy, but are then thermalized by moderator T. Ferguson, University of Uranium-235 Process repeats
  • 14. Thermal Nuclear Fission vs. Fast Fission Energy Uranium-235 + Neutrons 1. U-235 only natural fuel that works with thermal neutrons 2. Probability of spontaneous fission of U-235 very, very small (1 per second, or 200 MeV=3.2E-11 J/s/kg) 3. Fission starts with absorption of neutron 4. Prob of absorption decreases with neutron energy (so moderator used in thermal reactors) 5. Fast fission reactors use other fuels able to fission with high energy neutrons T. Ferguson, University of Fission Radioactive fission products Neutrons (about 2.5) Uranium-235 Process repeats
  • 15. Thermal Fission T. Ferguson, University of From Wikipedia: http://upload.wikimedia.org/wikipedia/commons/7/72/Thermal_reactor_diagram.png Accessed 2/28/08
  • 16. Energy of Fission • Fission of U-235 releases about 200 MeV per atom (recall that 1 electron volt = 1.6 E -19 J, or 200 MeV = 3.2 E -11 Joules) • Compare to combustion of Carbon with Q=94E6 cal/kg-mol 4.1 eV per atom • 50 million times more energy on atom-atom basis • 2.5 million times more energy on weight basis • Instead of 3 million tons of coal per year for 1000 MW plant, nuclear fission would require 1.2 tons of U-235 T. Ferguson, University of
  • 17. PWR Fuel Assembly Sample PWR Fuel Assembly •Array of 14X14 rods •179 fuel rods •16 control rods - ganged •1 instrumentation rod •Assembly is 7” X 7”, 12 ft tall Fuel: U-235 enriched from natural concentration of 0.71% to a few % Fission of U-238 possible only with fast neutrons T. Ferguson, University of From http://www.mnf.co.jp/pages2/pwr2.htm. Accessed 2/28/08; and instructor notes
  • 18. The Uranium Fuel Cycle - Sources - T. Ferguson, University of Source: International Atomic Energy Agency
  • 19. Fuel Cycle Annual mass flows for 1000 MWe LWR Ore 86,000 tons Storage (US) Reprocessing (UK, France) T. Ferguson, University of UF6 gas 203 tons U3O8 solid 162 tons Spent Fuel 36 tons Enriched UF6 53 tons Reactor UO2 Fuel 36 tons Low Level Waste 50 tons Adapted from Tester, et al, Sustainable Energy. Figure 8.6
  • 20. Reactor Designs Designs Currently in Operation (Generation II) • PWR – Pressurized Water Reactor (Westinghouse) • BWR – Boiling Water Reactor (GE) • GCR – Gas Cooled Reactor • LMFBR – Liquid Metal Fast Breeder Reactor • PHWR – Pressurized Heavy Water Reactor • RBMK – Similar to BWR T. Ferguson, University of
  • 21. New Reactor Designs Designs Submitted in Recent Applications (Generation III and III+): – AP1000 (Westinghouse) – EPR (Areva) – ESBWR (GE) – ABWR (GE) – US-APWR (Mitsubishi) 1 T. Ferguson, University of (6 COLs)1 (3) (5) (1) (1) Combined Licenses, as of 10/21/08. Covers 25 new units
  • 22. New Reactor Locations, US T. Ferguson, University of Source: NRC
  • 23. T. Ferguson, University of
  • 24. Boiling Water Reactor Source: US NRC T. Ferguson, University of
  • 25. Pressurized Water Reactor T. Ferguson, University of
  • 26. Nuclear Power Performance • Water in liquid state limited to 705 °F • Reactors (PWR, BWR) limited to η<30% • (70% waste heat)/(30% useful) = 2 1/3 units of waste heat per useful unit - must be dissipated in condenser • Fossil Fuel: η=40%, or 1.5 units waste/useful • Hence, difference in cooling tower size T. Ferguson, University of
  • 27. Nuclear Power Performance US Reactors Operating: • Licensed 1968-74: 38 reactors, 6 closed • Licensed 1975-78: 23 reactors, 3 closed • Licensed 1979-96: 52 reactors, 0 closed • 104 reactors in operation • Only 1 reactor licensed since 1976 is permanently closed (TMI-II) T. Ferguson, University of Source: EIA
  • 28. Nuclear Power Performance US Nuclear Plant Capacity Factors • 1980: 56% • 1990: 66% • 2000: 88% • 2002: 90% • 2007: 91.8% • Capacity constant since 1990, but . . . • Energy produced increased by 33% T. Ferguson, University of Source: EIA
  • 29. Costs • Average Operating Expenses, 2001 – – – – Nuclear: Fossil: Hydro Other Fossil: 1.8 cents/kWh (1/4 is fuel) 2.3 cents (3/4 is fuel) 1.0 cents (no fuel cost) 5.0 cents (80% is fuel) • Fuel: $1787/kg UO2 (1/2007) – For 45,000 MWd/t burn-up: 360,000 kWh/kg, or $0.005/kWh • Capital: $1000/kW in Czech Republic $2500/kW in Japan (Compare to $1000-1500 for coal, $500-1000 for gas, and $1000-1500 for wind; 2005 numbers) T. Ferguson, University of Source: EIA, Electric Power Annual 2000; Australian Uranium Association
  • 30. Costs Cost Projections for 2010 with 10% discount rate (capital becomes 70% of energy cost): USA France Japan Canada Korea Czech Rep. Nuclear 4.65 c/kWh 3.93 6.86 3.71 3.38 3.17 Gas 3.65 4.42 6.91 4.12 2.71 3.71 Coal 4.90 4.30 6.38 4.36 4.94 5.46 US 2003 cents/kWh; 40 year lifetime; 85% capacity factor T. Ferguson, University of Source: OECD/IEA NEA 2005/Australian Uranium Association
  • 31. Major US Nuclear Plant Operators • • • • • Exelon Entergy Duke TVA NMC 17,000 MW 9,000 MW 7,000 MW 6,700 MW 1,689 MW 17% 9% 7% 7% 2% (figures are approximate) T. Ferguson, University of Sources: EIA, Wikipedia.org/wiki/nuclear_management_corporation (accessed 3/10/08)
  • 32. US Nuclear Power Policy Energy Policy Act of 2005 – Price-Anderson Act extended to 2026 ($10B) – Cost overrun support for up to 6 new plants – First 6000 MW: PTC of 1.8 cents/kWh Nuclear Power 2010 Program, of 2002 – Joint gov’t/industry effort to build adv. Plants – 3 consortia have received grants – Applications have been submitted T. Ferguson, University of Source: DOE
  • 33. US Nuclear Power Policy A Renaissance? After nearly 30 years, the first applications to the NRC for Combined Construction and Operating Licenses: – 9/2007: South Texas Project: GE ABWR’s – 11/2007: TVA in Alabama: Westinghouse AP1000 PWR’s – 5 18 other sites T. Ferguson, University of Source: NRC
  • 34. Global Nuclear Power Policy • • • • • • • • • • • • Canada: will maintain current fleet Mexico: Planning another 8 reactors UK: Undecided Russia: Planning another 27 reactors China: Planning another 25 India: Planning another 15 Pakistan: Planning another 2 Japan: Planning another 12 Norway/Sweden/Finland: maybe/no/yes Germany: Phase out by 2020 Italy: Shuttered; moratorium Brazil: Planning another 7 reactors T. Ferguson, University of Source: Wikipedia

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