Fuel Cycle Subcommittee: Overview and Status

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Fuel Cycle SubcommitteeOverview and Status

• Fusion-Fission Hybrid Workshop
• Gaithersburg, MD
• September 30, 2009
• Robert N. Hill
• Department Head Nuclear Systems Analysis
• Nuclear Engineering Division
• Argonne National Laboratory

Work sponsored by U.S. Department of Energy
Office of Nuclear Energy, Science Technology
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Overview

• A wide variety of hybrid concepts are proposed
• Different fuel cycle missions are postulated
• Thus, it is important to provide a systematic and
  well defined framework to categorize
• Goals of different fuel cycle approaches
• Strategies employed to meet the fuel cycle goals
• This is a prerequisite for valid comparisons
• (e.g., a breeder compared to a minor actinide
  burner should have vastly different performance)

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Outline of Fuel Cycle Chapter

• 3.1 Fission Fuel Cycles
• 3.2 Fusion Fuel Cycles
• 3.3 Proposed Hybrid Fuel Cycles
• Limited input on 3.3 before workshop!
• Given that fusion-fission hybrids primarily
  conceived to deal with fission fuel cycle issues,
  the focus of this presentation will be on 3.1

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3.1 Fission Fuel Cycles

• Nuclear energy is a significant contributor to
  U.S. and international electricity production
• 16 world, 20 U.S., 78 France
• Given the concern over carbon emissions, there
  may be significant growth worldwide
• In the U.S., a once-through fuel cycle has been
  employed to-date
• Large quantities of spent fuel stored at reactor
  sites
• Final waste disposal is not secured
• With nuclear expansion, this is not a sustainable
  approach thus, advanced fuel cycles being
  explored two key goals
• Waste Management
• Resource Utilization

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AFCI is considering a variety of fuel cycle
options Closed fuel cycle with actinide
management
Energy Production Reactor
Extend Uranium Resources

• Spent nuclear fuel will be separated into re-
  useable and waste materials
• Residual waste will go to a geological repository
  
• Uranium recycled for resource extension
• Fuel fabricated from recycled actinides used in
  recycle reactor
• Fuel cycle closure with repeated use in recycle
  reactor

Recycle Used Uranium
Recycle Reactor
Recycle Fuel Fabrication
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Advanced Nuclear Fuel Cycle Potential Benefits

• Reduction in the volume of HLW that must be
  disposed in a deep geologic disposal facility as
  compared to the direct disposal of spent nuclear
  fuel
• Factor of 2-5 reduction in volume as compared to
  spent nuclear fuel
• Intermediate-level (GTCC) and low-level volumes
  could be large and disposal pathways would have
  to be developed
• Reduction in the amount of long-lived radioactive
  material (e.g., minor actinides) that must be
  isolated in a geologic disposal facility
  (reduction of source term)
• Potential for re-design of engineered barriers
• Advanced waste forms could result in improved
  performance and reduced uncertainty over the very
  long time periods
• Reduction in decay heat allowing for increased
  thermal management flexibility, potentially
  increasing emplacement density
• Increased loading density - better utilization of
  valuable repository space

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Waste Hazard and Risk Measures

• Radiotoxicity reflects the hazard of the source
  materials
• transuranics dominate after about a 100 years.
  The fission products contribution to the
  radiotoxicity is small after 100 years
• Radiotoxicity alone does not provide any
  indication of how a geologic repository may
  perform
• Engineered and natural barriers serve to isolate
  the wastes or control the release of
  radionuclides

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Transmutation for Improved Waste Management

• Long-term heat, radiotoxicity, and peak dose are
  all dominated by the Pu-241 to Am-241 to Np-237
  decay chain
• Thus, destruction of the transuranics (neptunium,
  plutonium, americium, and curium) is targeted to
  eliminate all problematic isotopes
• Some form of reprocessing is necessary to extract
  transuranic elements for consumption elsewhere
• The transuranic (TRU) inventory is reduced by
  fission
• Commonly referred to as actinide burning
• Transmutation by neutron irradiation
• Additional fission products are produced
• This requires the development of transmutation
  fuel forms
• Robust fast reactor fuel form high reliability
• Partial destruction each recycle high burnup
  goal
• In the interim, the TRU inventory is contained in
  the transmutation fuel cycle

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Reactor Types for Transmutation
SystemMinimization of Waste

• Conventional LWRs using LEU fuels produce TRU
• At current 50 GWd/MT burnup, 1.3 TRU content at
  discharge
• This corresponds to 250 kg/year for each GWe
  power
• For any fission energy system, 1 gram of
  actinides destroyed produces roughly 1 MWt-day of
  energy
• This implies 1.3/5 25 of the original LWR
  energy production is created in the destruction
  of the TRU content (significant capacity)
• Thus, efficient use of this energy is a key to
  both system economics and resource utilization
• However for uranium-based fuel, TRUs are also
  being produced
• This behavior is quantified by the conversion
  ratio (CR)

• Dictated primarily by the recycle fuel
  composition (U content)
• Fast system can be designed with CR ranging from
  gt1 (breeders) to ltlt1 (burners) for thermal
  reactors CR lt 0.7 is achievable with MOX

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Reactor Types for Transmutation
SystemMinimization of Waste (cont.)

• To assure no TRUs remain in waste, the LWR
  production rate must be balanced by destruction
  in the actinide burners (AB)

• For pure burner (CR0), 1 burner for every four
  LWRs
• For CR0.25, 1 burner for every three LWRs
• For CR1, all recycle reactors
• If only the minor actinides are to be consumed in
  the burner reactor, the initial production rate
  by LWRs is only 10 of the TRU content
• However, the plutonium must be consumed elsewhere
• Additional minor actinides are produced as the
  plutonium is consumed, particularly if a thermal
  spectrum is utilized

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Reactor Types for Transmutation
SystemMaximization of Energy

• The opposite trend is observed when the goal is
  to maximize the energy production for a fixed
  amount of resource materials

• For a given quantity of recovered TRU, the energy
  can be extended by recycling the material in a
  high CR system
• Thus, net resource utilization is vastly improved
  at high CR
• For once-through cycle, 7MT of uranium ore
  required to produce 1 MT of fuel to 5 burnup --
  .05/7 0.7 of the energy content
• With TRU recovery and recycle, burnup extended to
  .05 .013/(1-CR)
• Roughly 1 of energy content at low conversion
  ratio
• Limit of 100 utilization at CR1 where a make-up
  feed (e.g., depleted uranium or thorium) that
  contains fertile material is required

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3.2 Fusion Fuel Cycles

• Tritium needs to be produced to sustain the
  fusion cycle
• 14 MeV neutrons can be used to breed
• Typically employ Li-6 capture in fusion blanket
• For hybrid, fusion blanket must also be utilized
• Wide variety of technology options
• Homogeneous or heterogeneous with fission blanket
• Neutron balance is enhanced through subcritical
  multiplication in the fission blanket

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3.x.4 Proliferation Issues

• The proliferation risks associated with spent
  fuel reprocessing and recycle continue to be
  hotly debated
• At least partial separation is required
• Fission products are waste, actinides recycled
• This reduces the radiation barrier
• Safeguards employed for material accounting
• Physical protection provides additional barriers
• Technology misuse is another concern
• Enrichment technology may be an easier pathway
• Any neutron source can produce fissile material
• Fertile targets installed to capture neutrons
• This became an issue for ADS concepts

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3.3 Hybrid Fuel Cycles

• Waste management role
• Lack of criticality constraint allows operation
  on very low reactivity fuels and potentially very
  high burnup
• However, practical operation (e.g., large power
  swings) and material (e.g., radiation damage)
  challenges exist
• Some proposals
• Burn the entire TRU inventory
• Target a smaller fleet of minor actinide burners
• Sustain support of LWR power production or
  nuclear close-out scenarios (like ADS)
• Resource extension role proposals
• Breed fuel for use in fission fuel cycle
• Perform an extended in-situ breed and burn
• Similar challenges to the burner mode noted above

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Backup Slides
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Fast and Thermal Reactor Energy Spectra

• In LWR, most fissions occur in the 0.1 eV thermal
  peak
• In SFR, moderation is avoided no thermal
  neutrons

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Impact of Energy Spectrum on Fuel Cycle
(Transmutation) Performance

• Fissile isotopes are likely to fission in both
  thermal/fast spectrum
• Fission fraction is higher in fast spectrum
• Significant (up to 50) fission of fertile
  isotopes in fast spectrum
• Net result is more excess neutrons and less
  higher actinide generation in FR

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Equilibrium Composition in Fast and Thermal
Spectra

• Equilibrium higher actinide content much lower in
  fast spectrum system
• Generation of Pu-241 (key waste decay chain) is
  suppressed
• However, if starting from once-through LWR
  composition (e.g., burner reactor) the higher
  actinide content will be higher than the U-238
  equilibrium

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Fuel Cycle Implications

• The physics distinctions facilitate different
  fuel cycle strategies
• Thermal reactors are typically configured for
  once-through (open) fuel cycle
• They can operate on low enriched uranium (LEU)
• They require an external fissile feed (neutron
  balance)
• Higher actinides must be managed to allow recycle
• Separation of higher elements still a disposal
  issue
• Extended cooling time for curium decay
• Fast reactors are typically intended for closed
  fuel cycle with uranium conversion and resource
  extension
• Higher actinide generation is suppressed
• Neutron balance is favorable for recycled TRU
• No external fissile material is required
• Can enhance U-238 conversion for traditional
  breeding
• Can limit U-238 conversion for burning

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Advanced Nuclear Fuel Cycle Potential Benefits

• Cs/Sr (and decay products), Cm, and Pu dominate
  early decay heat
• Am dominates later decay heat
• Removal of decay heat producers would allow for
  increased utilization of repository space

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Aqueous Processing Potential Waste Streams and
Waste Forms
Cladding Zircaloy Hardware SS
Chopping
Metal Waste Form
Volox
Specialized Waste Forms
Gases I, HTO, Kr, Xe, CO2
Dissolu-tion
Metal Waste Form
UDS Pd, Ru, Rh, Mo, Tc, Zr, O
Tc
Metal Waste Form
Ion Exchange
UREX
U
Decay Storage Waste Form (glass or ceramic)
FPEX
Cs/Sr Cs, Sr, Ba, Rb
Metal Waste Form
TRUEX
TMFP Fe, S, Ru, Pd, Rh, Mo, Zr
Glass Waste Form
TALSPEAK
LNFP Ce, Ln, Pr, Nd, Y
Losses
TRU Pu, Am, Cm, Np
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Advanced Nuclear Fuel Cycle Waste Form
Development
Cs/Sr Glass
Glass Bonded Sodalite
Metallic Waste Form from Electro-Chemical
Processing
Lanthanide Borosilicate Glass
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Advanced Nuclear Fuel Cycle - Waste Management

• Waste management is an important factor in
  developing and implementing an advanced closed
  nuclear fuel cycle
• The waste management system is broader than
  disposal (processing, storage, transportation,
  disposal)
• Deep geologic disposal will still be required
• Disposal of low level and intermediate level
  (GTCC) wastes will be required
• Volumes potentially larger than once-through
• An advanced closed nuclear fuel cycle would allow
  for a re-optimization of the back-end of the
  current once-through fuel cycle, taking advantage
  of
• Minor actinide separation/transmutation
• Heat producing fission product (Cs/Sr) management
  (i.e., decay storage)
• Decisions must consider this entire system
• Regulatory, economic, risk/safety, environmental,
  other considerations

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Waste Management System for Advanced Fuel Cycle

• AFCI Integrated Waste Management Strategy
  establishes the framework for analyzing and
  optimizing the waste management system
• Emphasizes recycle and reuse, but based on
  economic recovery evaluation factoring in value
  of material and cost avoidance of disposal
• Considers need for industry to have a reliable
  system to routinely transport nuclear materials
  and dispose wastes
• Considers disposal options based on the risk of
  the waste streams and waste forms
• Rather than requiring all waste be disposed as
  HLW in a geologic repository
• Requires change to existing waste classification
  system embodied in current regulatory framework
• A key aspect is the inclusion of managed storage
  facilities where isotopic concentrations, and
  heat, are allowed to decay prior to storage
• Evaluation of alternatives and options are being
  performed under the context of the IWMS

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Integrated Waste Management Strategy Logic
Diagram