Operational Reactor Safety
22.091 /22.903
Professor Andrew C. Kadak Professor of the Practice
Lecture 4
Fuel Depletion & Related Effects
Prof. Andrew C. Kadak, 2008 Page 1
Department of Nuclea r S c ien ce & Engineering
Topics to Be Covered
• Fuel “burnup”
• Transmutation
• Conversion/Breeding
• Samarium 149
• Xenon 135
• Operational Impacts
Prof. Andrew C. Kadak, 2008 Page 2
Department of Nuclea r S c ien ce & Engineering
Fuel Burnup
• Depletion Equation
• Definition of burnup
– t hermal energy output per mass of fuel
– M WD/MTHM
Prof. Andrew C. Kadak, 2008 Page 3
Department of Nuclea r S c ien ce & Engineering
Transmutation
• Equation for production of any nuclide
• Conversion versus Breeding
– Depending on core physics design of the reactor core
– Ș (eta)
• Number of neutrons produced/absorbed in fuel
• Conversion ratio
– r ate of creation of new fissile/destruction of existing fissile
Prof. Andrew C. Kadak, 2008 Page 4
Department of Nuclea r S c ien ce & Engineering
Prof. Andrew C. Kadak, 2008 Page 6
Department of Nuclea r S c ien ce & Engineering
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Breeding Ratios for Reactor Systems
Prof. Andrew C. Kadak, 2008 Page 7
Department of Nuclea r S c ien ce & Engineering
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Buildup of Plutonium with Burnup
Prof. Andrew C. Kadak, 2008 Page 8
Department of Nuclea r S c ien ce & Engineering
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Reactivity Penalty
Prof. Andrew C. Kadak, 2008 Page 9
Department of Nuclea r S c ien ce & Engineering
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Fission Products
• Fission Fragments Fission Products
– R ate of Creation - Ȗ Ȉ f ĭ
– Ȗ fission yield
• Fission Fragment Balance Equation
Department of Nuclea r S c ien ce & Engineering
Prof. Andrew C. Kadak, 2008 Page 10
Samarium Buildup
Prof. Andrew C. Kadak, 2008 Page 11
Department of Nuclea r S c ien ce & Engineering
Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .
Samarium Buildup
Prof. Andrew C. Kadak, 2008 Page 12
Department of Nuclea r S c ien ce & Engineering
Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .
Xenon Buildup
Prof. Andrew C. Kadak, 2008 Page 13
Department of Nuclea r S c ien ce & Engineering
Figures © Hemisphere. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse .
Fuel Depletion and Related EJerl/ 17 J
0.6
0.5
P O l S O N h l lG, bklk
0.4
0.3
0.2
0.1
0 10 D 0 40 50 60 70
TIME AFTER SHUTDOWN, h
FIGURE 6-8
Poisoning of "'Xe as a function of tims afler shutdown for a repre<nutive LWR fuel composition at vaHous neutron flux levels. Curve 1: & = 1 x 10" n/cm 2 • s; Cuwc 2: & = 5 X 10'° n/cm’-s; Curve 3: & = 1 x l0 ' 4 n/cm 2 - s; Curve 4: & = 5 x 10'° n/cm'-s.
Operational Impacts
• X enon Oscillations
• F uel Design for cycle length of core
• F uel management strategies
• P ower peaking limits
• P ower distribution control
Reactor Physics Calculations
• M ulti-Group Diffusion Equations
– M odel core – u sing fuel pin and assembly homogenization of materials and fuels with pins averaged horizontally but detailed axially
• R un Static calculation for core power and flux distribution
• F luxes used to perform depletion calculations as noted for a “time step”
• N ew material calculations used to produce new power and flux distribution for next “time step” – 1 month
• I ncorporate only significant isotopes – h igh absorption and/or fission cross sections ignoring short liv ed isotopes in decay chains. – u se lumping procedure
• N eed to consider early xenon and Samarium build up 50 hours/500 hours
• T rack key isotopes for all fuel assemblies for refueling management
Homework Assignment
• Chapter 6
– P roblems: 6.2, 6, 7, 9, 11, 15
Department of Nuclea r S c ien ce & Engineering
Prof. Andrew C. Kadak, 2008 Page 18
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22.091 Nuclear Reactor Safety
Spring 200 8
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