Technical Influence of High Burnup UOX and MOX Water Reactor Fuel on Spent Fuel Management (IAEA Consultancy)

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Technical Influence of High Burnup UOX and MOX
Water Reactor Fuel on Spent Fuel Management(IAEA
Consultancy)

• R.E. Einziger (USNRC) and Z Lovasic (IAEA)
• Presented at
• International Conference on Management of Spent
  Fuel from Nuclear Power Reactors
• May 31 - June 4, 2010
• Vienna, Austria

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Main Contributors

• W. Goll (AREVA NP GmbH, Germany) - Chair
• A. Kumar (Bhabha Atomic Research Centre,
• India)
• S. Kusuno (Institute of Applied Energy, Japan)
• N. Tikhonov (Federal State Unitary Enterprise
• Leading Institute, Russian Federation)
• P. Cook (British Nuclear Group, United Kingdom)
• J. Kessler (Electric Power Research Institute,
  United States of America)
• R. Einziger (NRC, United States of America).

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Purpose of the Work

• Compile data on high burnup UOX and MOX fuels
• Evaluate Potential Influence of high burnup UOX
  and MOX on spent fuel management
• Make countries aware of the technical
  ramifications of the fuel changes for the
  back-end of the fuel cycle.

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Assumptions in the Study

• Only MOX and UOX were evaluated.
• Only zirconium alloy clad oxide fuels have been
  considered.
• Issues will be identified in general. Solutions
  will not be pursued.

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UOX Fuel

• The uranium is enriched up to 5 in PWR and BWR
  fuel and natural to slightly enriched in HWR
  fuel.
• Most fuel rods are filled with helium gas
• The PWR Zircaloy-4 was metallurgically treated in
  such a way as to form circumferential hydrides
  during irradiation, while the BWR Zircaloy-2 had
  a random grain texture.

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The major differences between the high and low
burnup LWR fuel

• Fissile content is higher
• Fission product content is higher,
• Fission gas pressure is higher,
• Cladding mechanical properties are different,
• Fuel rim effect is greater.

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MOX Fuel and UOX Fuel Comparison

• Pellet and rod design of MOX fuels is generally
  similar to UO2 fuels
• Increased MOX internal rod pressure
• The mechanical design of MOX fuel assemblies is
  similar
• Some MOX assembly designs include additional
  water rods to improve moderation
• Rod placement in assembly

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Fuel Characteristics not Considered in Evaluation

• Unimportant
• Cladding oxidation
• CRUD
• Pellet- cladding gap
• Fuel rod bowing
• Minor influence
• Pellet fracturing
• Fuel oxidation

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What was considered in the investigation

• Neutronics
• Fission gas release
• Mechanical Properties of the Cladding
• Pellet Rim

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Where high burnup affects the backend fuel cycle?
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Wet Storage Possible impacts of HBU UOX and MOX
fuels

• Upgrade of the pool facility with respect to heat
  removal, pool cleanup systems
• Regulatory issues.
• Criticality - additional neutron poison material
  in the pool water or in storage racks

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Dry Storage and Transportation Possible impacts
of HBU UOX and MOX fuels

• Redesign of the cask heat removal and shielding
  systems,
• Decrease in the number of spent fuel assemblies
  that can be placed into a single transport
  /storage cask,
• Increased decay time in the pool prior to
  placement in dry storage,
• Redesign of the structural support for the spent
  fuel assemblies.
• Lower maximum fuel temperature for MOX fuel

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Reprocessing Possible impacts of HBU UOX and
MOX fuels

• Redesign of some systems may be required.
• Recalibration of radiometric instrumentation
• Higher discharges into environment and HLW stream
• Reprocessed MOX additional challenges due to
  lower Pu solubility

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Repository Possible impacts of HBU UOX and MOX
fuels

• Higher source terms of the radionuclides
• potentially higher release to the groundwater,
• additional shielding during spent fuel transfer
  from the transportation cask.
• Higher temperatures
• Smaller waste containers,
• longer decay times at the surface prior to
  loading
• Repository space may have to be increased or
  decreased depending if combined with reprocessing

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REPU and MOX Fabrication Possible impacts of HBU
UOX and MOX fuels

• Different isotopic concentration in recycled
  fuel (less Pu-239, more Pu-238 and 240)
• Increased enrichment of REPU or an increased
  amount of plutonium in MOX fuel is required to
  meet the same burnup target,
• Increases in shielding may be required for REPU
  and MOX fuel fabrication operations.

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Non-proliferation Possible impacts of HBU UOX
and MOX fuel

• High burnup UOX, REPU, and MOX fuels tend to be
  more proliferation-resistant, because of the
  higher specific activity of each of these fuel
  types and because of less favourable fuel
  isotopics for proliferation (less Pu-239 and more
  Pu-240 and Pu-238).

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Conclusions

• Experience has indicated the safe feasibility of
  using high burnup UOX and MOX fuels in the
  reactor,
• It still appears that longer cycles, higher
  radiation and heat load may enhance some
  characteristics of SNF that could require
  additional attention and specific investigation
  in SNF management.