NERI PROJECT REVIEW

NERI PROJECT REVIEW

NERI 08-041Performance of Actinide-Containing

Fuel Matrices Under Extreme Radiation and Temperature Environments

University of IllinoisBrent J. Heuser

Panel No. 1 Session 7

04/21/23 NERI PROJECT NO. 08-041 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.

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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

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 Structure—anions red, cations white

CeO2Tm=2673 Ka=5.4114 A

UO2Tm=3138 Ka=5.466 A

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Molecular Beam EpitaxyR-plane sapphire + CeO2 or UO2Lattice mismatch: CeO2 <2% UO2 <1%

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XRD Analysis of MBE CeO2 film

CM2 TP2

TP1

Forelinepump

FV1 FV2

GV1

GV2Sample Trans. Arm

PrimaryChamber

Load-lock

S1 S2 S3

CG1

IG1

CM1

ThicknessMonitor

O2AirAr1 Ar2

CG2 IG2

VV1

VV2

MassSpec.

SV5

SV2 SV3SV1

MFC2

SV6SV4

MFC1

TCG

TP—turbo pumpGV—gate valveFV—foreline valveVV—vent valveSV—solenoid valveRV—relief valve

CG—convectron gaugeIG—ion gaugeTCG—thermocouple gaugePG—Pirani gaugeCM—capacitance manometerMFC—mass flow controllerS—sputter gun

SPUTTER DEPOSITION FACILITY SCHEMATIC

CM3

RV

PG

APC

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Magnetron Sputtering System at Illinois

Targets: depleted U; Ce; NdPower Supply: 2 DC; 1 RFGas Supply: O2: 0 to 10 sccm Ar: 1 to 100 sccmMax. Ts=850 C

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MBE—2302 RGS—3

MBE vs. Reactive Gas Sputtering (RGS)Comparison of SIMS Positive Ion Collection

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Berg Model for Reactive Gas SputteringThin 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

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 CeO2360 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 RT

1.8 MeV Kr

=6 A5/eV

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Radiation-Enhanced Diffusion in CeO21.8 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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Interatomic Interaction Potential

Molecular Dynamics

Develop w/DFT Existing

DFT

short time scales [ps]displacement cascades kMC

Em

long time scalesdiffusive motion

rate catalog

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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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-UU-OO-O all Morelon potential in UO2

plusU-O Born-Mayer-Huggins covalent bondingO-O Born-Mayer + polynomial + 1/r6

U-U pure Coulombic

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Histogram of displacement lengthsof 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 atomsThis 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 HeterogeneousXe Bubble Re-solution in UO2

Huang et al., to be submitted 9/2009

Two temperature model couplingelectronic and phonon (atom) contributions based on sputteringyield benchmarks.

dE/dx=55.4 keV/nm

dE/dx=47.0 keV/nm

dE/dx=32.8 keV/nm

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 ffcomplete bubble destruction never observed

13 11

6 2

079 Xe atoms

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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

1/20081/2009

1/20094/2009

CB

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

Computational studies of transport phenomena

10/2008 1/2011(2) O

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: 4 UG, 8 Grad, 2 post-doct.Georgia: 5 GradMichigan: 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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