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

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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