MEEM 4200 Energy Conversions Michigan Tech University April 4, 2008 Jeff Katalenich

Transcription

1 MEEM 4200 Energy Conversions Michigan Tech University April 4, 2008 Jeff Katalenich

2 Half-lives and isotope decay N(t) = N 0 e- λ t t 1/2 = ln(2)/λ Fission of U U n 1 56 Ba Kr n MeV Enrichment of natural uranium 0.7% U-235 ~ 4% U-235 (commercial reactors) 0.7% U-235 > 90% U-235 (weapons grade)

3 - Sustaining a nuclear reaction - Transmutation of elements - Nuclear Reprocessing: - Methods and Considerations

4 - Kinetic energy of neutron striking U-235 is essential - Fission neutrons energy range: MeV [ 7 ] - Fast neutrons: > 0.1 MeV - Slow neutrons: < 1 ev - Thermal neutrons: ~ ev

5 U-235 captures thermal neutrons 10-5

6 Neutron moderators reduce neutron energies Good moderators have: 1) small nuclei 2) low probability of absorbing neutrons ex/ H, D, C, and Be Reactors have fuel surrounded by a moderator - coolant systems

7 U-235 isn t the only element capturing neutrons - Transmutation occurs mostly by neutron capture followed by beta and alpha decay - Fuel becomes contaminated with isotopes from Zn-66 to Es-255 U-235 not the only heat source U-235 reaction gets choked out Commercial fuel lasts about 1 year

8 License application to be submitted in June 2008 Hold 70,000 metric tons spent waste Projected cost of $77 billion Receive spent fuel starting in 2017 Cask Videos com/watch?v=1mht OW-OBO4 com/watch?v=t5xt sq-9vvo [3]

9 Spent fuel currently stored on site at reactors - fuel replaced annually - stays in cooling ponds while short-lived isotopes decay - can be put into dry cask storage Reprocessing is the separation of used nuclear fuel into different groups of elements PUREX Plutonium and Uranium Recovery by EXtraction

10 Proliferation Resistant: - Separates spent waste into 7 streams: 1) Iodine 5) Americium/Curium 2) Uranium 6) Cesium/Strontium 3) Neptunium/Plutonium 7) Mixed Fission Products 4) Technetium Yields and purities in each step sufficiently meet the needs of the AFCI: - Uranium and Np/Pu can be recycled into new fuel - Other waste streams can be siphoned into fuel, stored, or used for different applications including medicine, space exploration, and batteries

11 Betavoltaics (tritium) producing power on a microwatt scale Used for applications where battery replacement is difficult Need for higher capacity nuclear batteries - US soldiers in Iraq - Autonomous vehicles Higher capacity batteries realized using isotopes from spent fuel

12 Tc-99m used in million procedures per year Current US supply entirely from Canada - DOE IPDP Mo-99 initiative Mo-99 shipped to hospitals: decay rate of 1% per hour - Hospitals could produce their own Mo-99 [5] Tc-99m Generator Other medical isotopes available from spent fuel (directly separated or after neutron irradiation): Sm-153, Sr-90, Y-90, I-131

13 Long range missions soon an impossibility - Pu-238 stockpile diminishing [6] - Other radioisotopes must be utilized to continue missions - Using isotopes from spent fuel is the most economical method Radioisotope Thermoelectric Generators - Traditionally use Pu-238 for low dose characteristics GPHS RTG - Sr-90 and Cm-244 provide high power RTG s Center for Space Nuclear Research performing feasibility studies on radioisotope power for extraterrestrial UAV s and Lunar power modules

14 [1] Energy Information Administration. Annual Energy Outlook Jan < [2] U.S. Environmental Protection Agency. Global Greenhouse Gas Data Feb < [3] Office of Civilian Radioactive Waste Management. Yucca Mountain Repository. US Department of Energy Jan < doe.gov/ym_repository/index.shtml>. [4] Andrews, Anthony. Nuclear Fuel Reprocessing: U.S. Policy Development. CRS Report for Congress. 29 Nov [5] Brookhaven National Laboratory. The Technetium-99m Generator. 6 Feb < [6] Howe, Steven. CSNR Director. Interview. Feb [7] El-Wakil, M.M. Powerplant Technology. McGraw Hill Companies Inc., New York

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16 Go to: - search Cm click decay radiation - look for high intensities (5.76 MeV α at 23.6% and 5.8 MeV α at 76.4%) - take weighted average of primary decay energies - calculate power density using this value

17 Energies: % Intensity % Intensity Weighted Average: 5.76(.236) + 5.8(.764) = 5.79 MeV/decay Decay Constant = λ = ln(2)/(half life in seconds) Initial Activity = A(0) = [m 0 / molecular weight] * (λ)(n A ) / (3.7*10 10 ) (in Curies) m 0 = initial mass in grams N A = Avogadro's number = 6.022(10 23 ) A(t) = A(0) * e- λ t A sp = Specific Activity = A(t) / m(t) m(t) = mass at time t = m 0 *e -λ t Power Density (in W/g) = A sp * (3.7*10 10 ) * (MeV/decay) * (1.602*10-13 ) 3.7*1010 = conversion from Becquerel to Curies 1.602*10-13 = conversion from MeV to Joules

18 Current Energy Production (USA): 50% Coal 20% Nuclear 17% Natural Gas 7% Hydro 3% Oil 2% Landfill gas, geothermal, wood, wind, & solar 1% Other Industrial

19 Billion Kilowatt Hours Energy Information Administration - Annual Energy Outlook 2008 EIA projections suggest: 1) Modest growth of nuclear power 2) 75% of the increase in energy generation to be met by coal EPA Future Atmosphere Changes in Greenhouse Gas and Aerosol Concentrations [1] 75% of CO 2 emissions in the USA are from burning fossil fuels [2]

20 Carbon Dioxide Footprint: - Nuclear: 5 grams CO 2 / kwh - Coal Power Generation: > 1000 grams CO 2 / kwh - U.S. currently releases 6000 Tg CO 2 could be Tg by 2030 Nuclear and Renewable Energy Production: - To meet the 1000 billion kwh increase in 25 years it would take: 1) 114 nuclear reactors at 1GWe each -or- 2) 76 nuclear reactors at 1.5GWe each -or- 3) 325,700 wind turbines at 350kWe each -or- 4) 38,000 wind turbines at 3MWe each - Renewables appear more attractive to the public because of the issue of nuclear waste disposal

21 Political debates in Congress over Yucca Mountain - Nevada Senators are fighting the repository - Some suggest waste be stored on-site until better technology exists - UREX+ method demonstrated needs of Advanced Fuel Cycle Initiative 1977: Carter ends commercial reprocessing in the USA - AGNS Barnwell facility licensing frozen: $350 million investment 1981: Reagan lifted Carter s ban 1993: Clinton ended plutonium recycling for nuclear power and weapons production [4]

22 Quantify reprocessing aqueous waste Characteristics of an optimal new reactor fleet in the US Feasibility of a small reactor for hospitals Advanced, high powered nuclear batteries for armed forces and national security applications