Marius Stan

Computational Physics Group

Los Alamos National Laboratory

Atomistic and Continuum Simulations of Phase Stability of Alloys - Advanced Models and Simulations of Nuclear Fuel Materials

UNCLASSIFIED

Characterization of Advanced Materials under Extreme Environments for the Next Generation Energy Systems Workshop

Brookhaven National Laboratory, Sept. 25-26, 2009

Outline

• Multi-scale methods and simulations can qualitatively predict phase stability of alloys…

• …and nuclear fuel performance

• In the future, experiment, theory and computation will work hand in hand to create materials with spectacular properties.

1M. Stan, J. Nucl. Eng. Techn., 41 (2009) 39-52.2M. Stan, et al., J. Alloys Comp., 444–445 (2007) 415–423

Multi-scale theoretical and computational methods1

Phase Stability of Pu-Ga Alloys Will -Pu decompose into -Pu and Pu3Ga, at room temperature and 1 atm.?

N. T. Chebotarev, E. S. Smotriskaya, M. A. Adrianov, and O. E. Kostyuk, in Plutonium 1975 and Other Actinides, Proc. of the Fifth International Conference on Plutonium and Other Actinides, Baden Baden, Germany, September 10-13, 1975, Edited by North-Holland Publishing Company, New York, 1976, p.37-45.

F. H. Ellinger, C. C. Land, and V. O. Strebing, The Plutonium-Gallium System, J. Nucl. Mat., 12 (1964) p. 226.

No, δ-phase will not decompose at room temp. Yes, δ-phase will (eventually) decompose at room temp.

• Ga atoms

• Molecular Dynamics simulationsMolecular Dynamics simulations11

• MEAM potentialMEAM potential22

Melting of gallium at 1 atm.

Liquid Liquid Solid (A11)

1Courtesy of S. M. Valone 2M.I. Baskes et al., Phys. Rev. B, 66 (2002), p. 104–107.

• Distorted- Pu• Interstitial Pu• Initial atomInitial atom

(010) view direction

Radiation damage in plutonium at 1 atm.

• Molecular Dynamics simulationsMolecular Dynamics simulations11

• Distorted Distorted -Pu structure at 300 K-Pu structure at 300 K

• MEAM potentialMEAM potential22

1S. M. Valone et al., J. Nucl. Mater., 324 (2004) 41-512M. I. Baskes, Phys. Rev. B 62, 15532 (2000).

Multi-scale method for alloys1

1M. I. Baskes and M. Stan, Metall. Mater. Trans. 34A (2003) 435-39. 2M. I. Baskes, et al. JOM, 55 (2003) 41-50.3 N. T. Chebotarev, et al. Proc. Fifth International Conf. on Plutonium and Other Actinides, Baden Baden, Germany, Sept. 10-13, 1975, North-Holland Publishing, NY, 1976, p.37-45.

Phase diagram

Free energy of all phases

Chemical potentials

PTGaPuGaPu xn

xPTGxPT

,,, )(

),,(),,(

Thermodynamic equilibrium

),,(),,(

),,(),,(

xPTxPT

xPTxPT

GaGa

PuPu

Electronic Structure

Atomistic

PredictedPu-Ga diagram.2

Experimental Pu-Ga diagram.3

''

),,'(),,(),,(2

T

T

ref

refref

ref

dTT

xPTH

T

xPTG

T

xPTG

Irradiation Effects on Fission Reactor Materials

1From Donald R. Olander, "Fundamental Aspects of Nuclear Reactor Fuel Elements," TID-26711-P1, Technical Information Service, U.S. Department of Commerce, Springfield, Virginia.

Fuel restructuring, changes in chemistry1

Issues: • Fission products accumulation, gas bubbles formation• Formation of dislocations, cracks.• Localized melting, phase transformations• Fuel-cladding chemical Interactions

Consequences: • Fuel and clad swelling, deformation• Loss of mechanical integrity• Decrease in heat release, overheating.• Fuel element replacement.

grain boundary (GB)

Xe

1M. Stan, et al., J. Alloys Comp., 444–445 (2007) 415–423.2P. Cristea et al., J. Optoelectr. Adv. Mater, 9 (2007) 1750-1756.3Courtesy of John Wills

Understand and control atomic-scale phenomena: defect formation and fission products migration

Schematic representation of grain boundary defect formation from MD3.

To meso-scale

- GB structure, orientation, and energy- FPs mobility at GBsand in the bulk- Nucleation sites- Free energy model

From ES

• Defect formation time = ps• Recombination time = 1-10 ps• Defects (clusters) size 1-10 nm.

- Defect formation energy- Diffusion energy barriers

To experiment

- Chemical potentials- Nucleation sites

From experiment

- Grain size, orientation- FPs diffusivity (bulk)

• Fission products (FP) migrate in the grain and at the grain boundary (GB). • At high doses (burnup) point defects interact and form clusters1-2

• Point defect and clusters are nucleation centers for FP gas bubbles and cracks.

Understand and control meso-scale phenomena: microstructure evolution

1M. Stan, J. Nucl. Eng. Technology, 41 (2009) 39-52.2S.Y. Hu et al., J. Nucl. Mater. 392 (2009) 292–300.3I. Zacharie et. al.,  J. Nucl. Mater. 255 (1998), 92-104.

Phase Field simulation using empirical free energy model2

10m10m

Experiment: Irradiated UO2 in PWR3

• Fission products migrate in the nuclear fuel and form gas bubbles. • The gas bubbles can lead to formation of “tunnels” (channels) that release the gas into the gap (fuel-clad) region.• Radiation induced changes in microstructure decrease the effective thermal conductivity1.

• Nucleation times = ps• Coalescence times = µs• Size distributions of gas bubbles 1nm-10µm.

From atomistic To continuum

- GB structure, orientation, and energy- FPs mobility at GBsand in the bulk- Nucleation sites- Free energy model

From experiment

- Grain size, orientation- FPs diffusivity (bulk)

To experiment

- Pore distribution- FPs distribution

-Thermal cond. model- Thermal exp. model-Crack nucleation andevolution model

Understand and control continuum phenomena : heat and chemical transport

1J. C. Ramirez et al, J. Nucl. Mater, 359 (2006) 174-184.2B. Mihaila et al., J. Nucl. Mater (2009) in press.

Radial profile of properties2

• Finite Element Method (FEM) simulations of coupled heat transport, oxygen diffusion and thermal expansion in a UO2 fuel element with steel clad are show that including the dependence of thermal conductivity on defects and local oxygen content can lead to changes in the predicted centerline temperature and displacements of 5% or more1,2. Following a power excursion of 1 ms: •Thermal time to steady state = seconds• Displacement time to steady state = seconds• Composition time to steady state = weeks!

To reactor level

To experiment

- Temp. distribution- Chemical speciesdistribution (O, FPs).

- Centerline temp.- Fuel pin deformation

From meso-scale

From experiment

-Crack distribution-Burnup effects

-Thermal cond. model- Thermal exp. model-Crack nucleation andevolution model

The Future: Institutes for Materials Discovery and Design (IMDD)

The institutes will integrate experiment, theory, and computation. The scientists will be trained in all areas and experts in one of them1,2.

• State of the art laboratories for small-scale experiments

• A computational materials science hub for model development and small-scale simulations

• Meeting rooms equipped with visualization capabilities for discussions

• Offices for staff, guest scientists and students

IMDDComputational Materials Science Hub

Meeting/Visualizationrooms

Laboratories

Offices

1M. Stan and S. Yip, white paper DOE workshop on Advanced Modeling and Simulation for Nuclear Fission Energy Systems, Washington DC, May 11-2, 2009: https://www.cels.anl.gov/events/workshops/extremecomputing/nuclearenergy/agenda.php.1M. Stan, Materials Today , Nov. (2009) accepted.

• Experimental and computational data

• Models (mathematical)• Simulations (pictures,

movies)• Fully searchable

International knowledge base for fuels and materials

Meetings of potential interest

• Materials Models and Simulations for Nuclear Fuels Workshop, Albuquerque, NM, Oct. 19-21, 2009. See: http://inside.mines.edu/~tsemi/MMSNF8.html

• From Basic Concepts to Real Materials Conference, Santa Barbara, CA, Nov. 2-6, 2009. See: http://www.kitp.ucsb.edu/activities/auto/?id=982.

• The Nuclear Materials Congress, Karlsruhe, Germany, 4-8 October 2010,Contact: Marius Stan, mastan@lanl.gov.