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
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.
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Project Work Scope
Task 1—construction of dedicated UO2
thin film growth facility; grow CeO2
surrogate films in the interim.
 Task 2—perform transport studies of
actinide surrogate and fission gases.
 Task 3—develop computational tools for
predictive modeling.
 Task 4—apply computational models to
actinide/fission gas transport.

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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


Georgia Institute of Technology


Perform first-principles and kMC computations of
transport phenomena; develop digital microstructure.
University of Michigan


Provide thin film samples; study transport phenomena;
develop computational tools for predictive transport
studies based on MC, MD, kMC.
Perform in situ studies of actinide/fission gas transport.
South Carolina State University

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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 Structure—anions red, cations white
CeO2
Tm=2673 K
a=5.4114 A
UO2
Tm=3138 K
a=5.466 A
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Molecular Beam Epitaxy
R-plane sapphire + CeO2 or UO2
Lattice mismatch: CeO2 <2%
UO2 <1%
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XRD Analysis of MBE CeO2 film
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SPUTTER DEPOSITION FACILITY SCHEMATIC
Ar1
O2
Ar2
Air
Foreline
pump
MFC1
MFC2
FV1
VV1
SV4
SV6
FV2
TP1
PG
TCG
Mass
Spec.
GV1
APC
RV
CG1
CM2
TP2
VV2
IG1
CM1
GV2
CM3
Primary
Chamber
Thickness
Monitor
Loadlock
CG2
SV5
S1
SV1
S2
SV2
S3
SV3
TP—turbo pump
GV—gate valve
FV—foreline valve
VV—vent valve
SV—solenoid valve
RV—relief valve
Sample
Trans.
Arm
IG2
CG—convectron gauge
IG—ion gauge
TCG—thermocouple gauge
PG—Pirani gauge
CM—capacitance manometer
MFC—mass flow controller
S—sputter gun
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. Ts=850 C
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MBE vs. Reactive Gas Sputtering (RGS)
Comparison of SIMS Positive Ion Collection
MBE—2302
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RGS—3
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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 finished—currently
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 system—can expect 1
to 4 samples per month.
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Task 2 (Experimental Transport Studies) Progress



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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 Profiles
RT Irradiation 1.8 MeV Kr
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Mixing Parameter Analysis in CeO2 at RT
1.8 MeV Kr
x=6 A5/eV
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Radiation-Enhanced Diffusion in CeO2
1.8 MeV Kr at dose of 1 ion/Å2
Dth=2.64x10-16 exp(-0.154 eV/kT) [cm2/sec]
DRED=5.25x10-16 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 facility—
Saclay facility available for use via P.
Bellon.
 Supply of samples to L. Wang (U. Mich)
delayed—Xe 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
Develop w/DFT
Interatomic Interaction Potential
Molecular Dynamics
short time scales [ps]
displacement cascades
Existing
DFT
Em
rate catalog
kMC
long time scales
diffusive motion
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MC-MD Study of Homogeneous Xe Bubble Resolution 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 Resolution 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 Resolution 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
MC+MD
MC
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MD Simulations of Heterogeneous
Xe Bubble Re-solution in UO2
13
11
Two temperature model coupling
electronic and phonon (atom)
contributions based on sputtering
yield benchmarks.
dE/dx=55.4 keV/nm
6
2
Conclusions
No Xe re-solution dE/dx<34 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/dx=47.0 keV/nm
dE/dx=32.8 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
UO2+x
Buckingham Potential for UO2
DFT LDA+U 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
Milestone Description
Planned
Start Date
Planned
Completion Date
Status1
Constr. of thin film growth facility;
Commissioning of facility
1/2008
1/2009
1/2009
4/2009
C
B
Establish MBE capability for CeO2
films
4/2008
9/2008
C
Experimental studies of transport
phenomena in CeO2
9/2008
1/2010
O
Experimental studies of transport
phenomena in UO2
4/2009
1/2011(2)
B
Development of computational
tools—MC, MD, kMC, DFT
1/2008
9/2008
C
1/2011(2)
O
Computational studies of transport 10/2008
phenomena
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 Accomplishments—To 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 Accomplishments—Anticipated





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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R&D 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:
Georgia:
Michigan:
4 UG, 8 Grad, 2 post-doct.
5 Grad
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 R&D 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.

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