NERI PROJECT REVIEW

1
NERI PROJECT REVIEW

• NERI 08-041
• Performance of Actinide-Containing Fuel Matrices
  Under Extreme Radiation and Temperature
  Environments
• University of Illinois
• Brent J. Heuser
• Panel No. 1 Session 7

2
Project Objectives

• Establish UO2 thin film growth capability with
  controlled microstructure, stoichiometry, and
  actinide surrogate concentrations.
• Determine transport properties of actinide
  surrogates and implanted volatile fission gases
  under conditions that mimic the fission process
  in nuclear reactors.
• Investigate affect of microstructure,
  stoichiometry, and impurity concentration of
  transport properties.
• Develop and apply predictive computational models
  of transport mechanisms at an atomistic level.

3
Project Work Scope

• Task 1construction of dedicated UO2 thin film
  growth facility grow CeO2 surrogate films in the
  interim.
• Task 2perform transport studies of actinide
  surrogate and fission gases.
• Task 3develop computational tools for predictive
  modeling.
• Task 4apply computational models to
  actinide/fission gas transport.

4
Project Participants

• Lead Organization University of Illinois
• PI Brent J. Heuser
• CoPIs J. Stubbins, R. Averback. P. Bellon, J.
  Eckstein
• Collaborating Organizations
• Georgia Institute of Technology/CoPIs C. Deo, M.
  Li
• University of Michigan/CoPI L. Wang
• South Carolina State University/CoPI M. Danjaji

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Organizational Roles

• University of Illinois
• Provide thin film samples study transport
  phenomena develop computational tools for
  predictive transport studies based on MC, MD,
  kMC.
• Georgia Institute of Technology
• Perform first-principles and kMC computations of
  transport phenomena develop digital
  microstructure.
• University of Michigan
• Perform in situ studies of actinide/fission gas
  transport.
• South Carolina State University
• Participate in experimental studies performed at
  Illinois via student/faculty exchange.

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Task 1 (Film Growth) Progress

• Design and construction of dedicated thin film
  growth facility at Illinois complete.
• Commissioning of facility underway.
• MBE capability for CeO2 surrogate thin films with
  actinide surrogates established.

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Crystal Structure
Fluorite Structureanions red, cations white
CeO2 Tm2673 K a5.4114 A UO2 Tm3138 K a5.466 A
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Molecular Beam Epitaxy
R-plane sapphire CeO2 or UO2 Lattice mismatch
CeO2 lt2 UO2 lt1
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XRD Analysis of MBE CeO2 film
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(No Transcript)
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Magnetron Sputtering System at Illinois
Targets depleted U Ce Nd Power Supply 2 DC
1 RF Gas Supply O2 0 to 10 sccm
Ar 1 to 100 sccm Max. Ts850 C
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MBE vs. Reactive Gas Sputtering (RGS)Comparison
of SIMS Positive Ion Collection
MBE2302
RGS3
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Berg Model for Reactive Gas Sputtering Thin Solid
Films, 476 (2005) 215
metal mode
poison mode
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Poison vs. Metal Modes in Reactive Gas Sputtering
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Poison vs. Metal Sputtering Modes
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XRD Analysis of Sputtered CeO2 film
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Control of RGS Film Microstructure
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Task 1 Planned Activities

• Thin film growth facility finishedcurrently
  growing CeO2 films for benchmarking,
  commissioning.
• UO2 films in the next few months.
• UO2 films with controlled microstructure,
  actinide surrogate concentration, stoichiometry.
• CeO2 films via MBE with actinide surrogates to
  continue.
• Additional implantation of UO2 and CeO2 films
  w/Xe.

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Task 1 Issues or Concerns

• Shutter design of source flange somewhat
  problematic and may require periodic (quarterly)
  adjustment.
• Debris build up will require the system to be
  opened occasionally (quarterly).
• Do not control MBE systemcan expect 1 to 4
  samples per month.

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Task 2 (Experimental Transport Studies) Progress

• Performed RED measurements of cation sublattice
  in CeO2 with a La marker layer.
• Performed low-energy Xe implantations in CeO2 at
  two concentrations for fission gas bubble
  dissolution experiments.
• Irradiated Xe-implanted CeO2 samples with Kr.
• Developed TEM specimen preparation techniques.
• Performed ex situ TEM analysis of irradiated CeO2
  and Xe-implanted CeO2.
• Performed in situ TEM analysis of Xe-implanted
  CeO2.
• Performed EXAFS measurements of Xe implanted
  (unirradiated) CeO2.

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Experimental Facilities at Illinois

• Microanalytical AES, SIMS, RBS, XRD/XRR, TEM,
  SEM, AFM.
• Implantation tandem van de Graaff (0.5-2.3 MeV
  H, He, Xe, Kr, Ne 100 nA)

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SIMS of Irradiated Single Crystal CeO2 360 A
thickness w/1 ML La at centerline 1.8 MeV Kr 1
ion/A2 at RT
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La Depth ProfilesRT Irradiation 1.8 MeV Kr
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Mixing Parameter Analysis in CeO2 at RT1.8 MeV Kr
x6 A5/eV
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Radiation-Enhanced Diffusion in CeO21.8 MeV Kr
at dose of 1 ion/Å2
Dth2.64x10-16 exp(-0.154 eV/kT)
cm2/sec DRED5.25x10-16 exp(-0.091 eV/kT)
cm2/sec
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Task 2 Planned Activities

• RED investigation of anion sublattice with O-18
  in CeO2 and UO2.
• Further RED investigations on cation sublattice
  in UO2 and CeO2.
• Implementation of model based on kinetic rate
  equations for RED.
• EXAFS, SAXS, SIMS studies of precipitation of
  actinide surrogates and Xe.
• Further in situ and ex situ TEM analysis of
  actinide surrogate precipitation and Xe bubble
  formation/dissolution.

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Task 2 Issues or Concerns

• Availability of ANL in situ TEM facilitySaclay
  facility available for use via P. Bellon.
• Supply of samples to L. Wang (U. Mich) delayedXe
  implanted samples, other samples within next
  month.

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Task 3/4 (Development/Application of
Computational Tools for Predictive Modeling)
Progress

• Development of combined MC-MD approach to model
  UO2 at Illinois complete.
• Study of Xe bubble homogeneous re-solution in UO2
  via MC-MD complete.
• Study of Xe bubble heterogeneous re-solution in
  UO2 via MD complete.
• Development of DFT-kMC capability for UO2 at
  Georgia Institute of Technology complete.
• Initial studies of oxygen transport in UO2 using
  DFT-kMC complete.
• Development of geometric computational methods
  for polycrystalline media based on constrained
  Voronoi tessellation (digital microstructure)
  complete.

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Computational Method
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MC-MD Study of Homogeneous Xe Bubble Re-solution
in UO2
Xe recoil spectrum from MC.
Homogeneous re-solution Interaction of
fission fragment with fission gas atoms in
bubble via energetic collisions (ballistic
ejection). Heterogeneous re-solutions
Interaction of displacement cascade with entire
bubble.
Schwen et al., J. Nuclear Materials, 392 (2009)
35.
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MC-MD Study of Homogeneous Xe Bubble Re-solution
in UO2
Computational Details MC BCM, ZBL potential,
based TRIM algorithm to treat arbitrary
geometries and irradiation conditions (not fixed
layer geo.). MD LAMMPS code Long range
Coulomb U-O treated PPPM method.
Rigid-ion potential U-U U-O O-O all
Morelon potential in UO2 plus U-O
Born-Mayer-Huggins covalent bonding O-O
Born-Mayer polynomial 1/r6 U-U pure
Coulombic
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MC-MD Study of Homogeneous Xe Bubble Re-solution
in UO2
Histogram of displacement lengths of Xe atoms
from bubble center.
Probability of Xe atoms leaving Bubble vs. Xe
PKA energy.
Re-solution parameter 3x10-6 s-1 Xe knock-outs
per Xe gas atoms This result is factor of 50
lower than analytical work of Nelson.
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Channeling
Xe atom displacement histograms
MCMD
MC
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MD Simulations of Heterogeneous Xe Bubble
Re-solution in UO2
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Two temperature model coupling electronic and
phonon (atom) contributions based on
sputtering yield benchmarks.
dE/dx55.4 keV/nm
6
2
Conclusions No Xe re-solution dE/dxlt34 keV/nm
(ff 18-22 keV/nm) ff cross section for
interaction w/bubble 5 nm2 1-5 ff-bubble
interactions per ff complete bubble destruction
never observed
dE/dx47.0 keV/nm
dE/dx32.8 keV/nm
79 Xe atoms
0
Huang et al., to be submitted 9/2009
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DFT-kMC Simulations of Oxygen Diffusion in UO2x
Buckingham Potential for UO2
DFT LDAU for UO2
di-interstitial mechanism
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Task 3 Planned Activities

• Further MC-MD studies of Xe bubble behavior
  coupling of computational studies to experimental
  investigations (EXAFS, SAXS, in situ TEM) of
  bubble behavior in UO2.
• Further DFT and kMC studies of transport
  phenomena in UO2 coupling of computational
  studies to experimental investigations (RED) of
  transport behavior in UO2.
• Application of geometric methods of
  microstructure to polycrystalline UO2 in MC and
  MD coupling of MC polycrystalline models to RED
  in polycrystalline UO2.

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Task 3 Issues or Concerns

• None.

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Project Milestones Schedule
Note 1 Enter C if milestone has been
completed O if milestone is on schedule for
completion or, B if milestone is behind
schedule for completion.
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Year 1 Planned Vs. Actual Costs
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Year 2 Planned Vs. Actual Costs
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Year 3 Planned Vs. Anticipated Costs
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Project AccomplishmentsTo Date

• Dedicated thin film growth facility completed.
• Commissioning nearly completed.
• Control of microstructure (via Ts), stoichiometry
  (via O2 pressure) and actinide concentration (via
  gun power level) demonstrated.
• RED on cation sublattice in CeO2 measured up to
  1208 K.
• Initial in situ TEM analysis of Xe bubble
  resolution in CeO2 performed.
• Initial EXAFS measurements of Xe bubble
  resolution in CeO2 performed.
• Computational tools in place initial set of
  studies (Xe bubble resolution, oxygen diffusion,
  microstructure modeling via inverse MC) complete.

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Project AccomplishmentsAnticipated

• Demonstrate of UO2 thin film growth with
  controlled stoichiometry, microstructure,
  actinide surrogate concentration.
• RED measurements on cation and anion sublattices
  in UO2 under different bombardment conditions (T,
  dose, E).
• Measurements of Xe and actinide surrogate
  precipitation behavior in UO2 under different
  bombardment conditions.
• Determination of synergistic effect of UO2
  microstructure, bombardment conditions, impurity
  concentrations.
• Further kMC and MD simulations of transport
  behavior.

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RD Programs Benefits

• Project addresses the nuclear fuel cycle by
  investigating materials aspects of actinide
  incorporation into UO2 matrices.
• Project will provide
• Measurements of actinide and fission gas
  transport properties in UO2.
• Computational tools for predictive modeling of
  transport properties.
• Successful completion of this project will
  facilitate an improved understanding of fuel
  behavior within a closed fuel cycle.

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Programmatic Contributions

• Contribution to NERI Program objectives
• Project helps close the fuel cycle by providing
  data and predictive modeling capabilities that
  promote better understanding of UO2 containing
  actinides.
• Project will advance the state of nuclear
  technology in the U.S. by 1) aiding in the
  reduction of waste disposition time scales and 2)
  increasing fuel efficiency via recovery of major
  actinide energy content.
• Project addresses nuclear science and engineering
  infrastructure through the training of young
  researches
• Illinois 4 UG, 8 Grad, 2 post-doct.
• Georgia 5 Grad
• Michigan 1 Grad, 1 post-doct.
• And the development of capabilities at Illinois
  and Georgia Tech.

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Commercialization Potential

• Potential exists through Hitachi GE Nuclear.

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Potential Future RD Efforts

• A dedicated UO2 thin film growth facility at
  Illinois represents a unique capability we
  anticipate studies beyond the current NERI grant
  within the AFCI.
• Development of computational tools at Illinois
  and Georgia Institute of Technology offers
  potential for further synergistic efforts of
  collaboration between the two institutions within
  the AFCI.