MEEM 4200 Energy Conversions Michigan Tech University ...-Nuclear Reprocessing: -Methods and...
Transcript of MEEM 4200 Energy Conversions Michigan Tech University ...-Nuclear Reprocessing: -Methods and...
MEEM 4200 Energy Conversions
Michigan Tech University
April 4, 2008
Jeff Katalenich
• Half-lives and isotope decayN(t) = N0e- λ t t1/2 = ln(2)/λ
• Fission of U-235
92U235 + 0n156Ba137 + 36Kr97 +20n1 + 196 MeV
• Enrichment of natural uranium0.7% U-235 ~ 4% U-235 (commercial reactors)
0.7% U-235 > 90% U-235 (weapons grade)
- Sustaining a nuclear reaction
- Transmutation of elements
- Nuclear Reprocessing:
- Methods and Considerations
- Kinetic energy of neutron striking
U-235 is essential
- Fission neutrons energy range: 0.075 – 17 MeV [ 7 ]
- Fast neutrons: > 0.1 MeV
- Slow neutrons: < 1 eV
- Thermal neutrons: ~ 0.025 eV
U-235 captures thermal neutrons
10-5
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
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
• 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
[3]
• Cask Videoshttp://www.youtube.com/watch?v=1mHtOW-OBO4
http://www.youtube.com/watch?v=T5XTsQ-9vvo
• 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
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
• 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
• Other medical isotopes available from spent fuel (directly separated or after neutron irradiation):
Sm-153, Sr-90, Y-90, I-131
• Tc-99m used in 20-25 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-99Tc-99m Generator
[5]
• 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
- 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
GPHS RTG
[1] Energy Information Administration. “Annual Energy Outlook 2008.” 2007. 28 Jan. 2008. <http://www.eia.doe.gov/oiaf/aeo/electricity.html>
[2] U.S. Environmental Protection Agency. “Global Greenhouse Gas Data.” 2008. 14 Feb. 2008. <http://www.epa.gov/climatechange/emissions/globalghg.html>
[3] Office of Civilian Radioactive Waste Management. “Yucca Mountain Repository.” US Department of Energy. 2007. 26 Jan. 2008. <http://www.ocrwm.doe.gov/ym_repository/index.shtml>.
[4] Andrews, Anthony. “Nuclear Fuel Reprocessing: U.S. Policy Development.” CRS Report for Congress. 29 Nov. 2006.
[5] Brookhaven National Laboratory. “The Technetium-99m Generator.” 6 Feb 2008. <http://www.bnl.gov/bnlweb/history/Tc-99m.asp>
[6] Howe, Steven. CSNR Director. Email Interview. Feb 2008.
[7] El-Wakil, M.M. Powerplant Technology. McGraw Hill Companies Inc., New York. 2002.
Go to: http://www.nndc.bnl.gov/chart/
- search Cm-244
- 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
Energies:
5.76 MeV @ 23.6% Intensity
5.8 MeV @ 76.4% 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) = [m0 / molecular weight] * (λ)(NA) / (3.7*1010) (in Curies)
m0 = initial mass in grams
NA = Avogadro's number = 6.022(1023)
A(t) = A(0) * e- λ t
Asp = Specific Activity = A(t) / m(t)
m(t) = mass at time t = m0*e -λ t
Power Density (in W/g) = Asp * (3.7*1010) * (MeV/decay) * (1.602*10-13)
3.7*1010 = conversion from Becquerel to Curies
1.602*10-13 = conversion from MeV to Joules
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
Billio
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Energy Information Administration - Annual Energy Outlook 2008
EPA – Future Atmosphere Changes in Greenhouse Gas and Aerosol Concentrations
• 75% of CO2 emissions in the USA are from burning fossil fuels
• EIA projections suggest:
1) Modest growth of nuclear power
2) 75% of the increase in energy generation to be met by coal
[1]
[2]
• Carbon Dioxide Footprint:
- Nuclear: 5 grams CO2 / kWh
- Coal Power Generation: > 1000 grams CO2 / kWh
- U.S. currently releases 6000 Tg CO2 – could be 7000+ 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
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]
• 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
• 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