Browsing by Author "Rest, J."

Now showing 1 - 5 of 5
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    A New Multiscale Approach to Nuclear Fuel Simulations: Atomistic Validation of Kinetic Method
    (Transactions of the American Nuclear Society, 2010) Insepov, Z.; Rest, J.; Hofman, G. L.; Yacout, A.; Norman, G. E.; Starikov, S. A.; Stegailov, V. V.
    A key issue for fuel behavior codes is their sensitivity to values of various materials properties, many of which have large uncertainties or have not been measured. Kinetic mesoscale models, such as those developed at Argonne National Laboratory within the past decade, are directly comparable to data obtained from in-reactor experiments. In the present paper, a new multiscale concept is proposed that consists of using atomistic simulation methods to verify the kinetic approach. The new concept includes kinetic rate-equations for radiation damage, energetics and kinetics of defects, and gas/defect-driven swelling of fuels as a function of temperature and burnup. The quantum and classical atomistic simulation methods are applied to increase our understanding of radiation damage and defect formation and growth processes and to calculate the probabilities of elemental processes and reactions that are applicable to irradiated nuclear materials.
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    A multiscale method for the analysis of defect behavior in Mo during electron irradiation
    (Computational Materials Science, 2014-10-31) Rest, J.; Ye, B.; Yun, D.; Insepov, Z.; Rest, J.
    Abstract In order to overcome a lack of experimental information on values for key materials properties and kinetic coefficients, a multiscale modeling approach is applied to defect behavior in irradiated Mo where key materials properties, such as point defect (vacancy and interstitial) migration enthalpies as well as kinetic factors such as dimer formation, defect recombination, and self interstitial–interstitial loop interaction coefficients, are obtained by molecular dynamics calculations and implemented into rate-theory simulations of defect behavior. The multiscale methodology is validated against interstitial loop growth data obtained from electron irradiation of pure Mo. It is shown that the observed linear behavior of the loop diameter vs. the square root of irradiation time is a direct consequence of the 1D migration of self-interstitial atoms.
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    Radiation-induced damage and evolution of defects in Mo
    (Physical Review B, 2011) Starikov, S. V.; Insepov, Z.; Rest, J.; Kuksin, A. Y.; Norman, G. E.; Stegailov, V. V.; Yanilkin, A. V.
    The formation of defects in bcc Mo lattice as a result of 50-keV Xe bombardment is studied via atomistic simulation with an interatomic potential developed using the force-matching ab initio based approach. The defect evolution in the cascade is described. Diffusion and interaction of interstitials and vacancies are analyzed. Only small interstitial atom clusters form directly in the cascade. Larger clusters grow only via aggregation at temperatures up to 2000 K. Stable forms of clusters demonstrate one-dimensional diffusion with a very high diffusion coefficient and escape quickly to the open surface. Point vacancies have much lower diffusivity and do not aggregate. The possibility of a large prismatic vacancy loop formation near the impact surface as a result of fast recrystallization is revealed. The mobility of the vacancy dislocation loop segments is high, however, the motion of the entire loops is strongly hindered by neighbor point defects. This paper explains the existence of the large prismatic vacancy loops and the absence of the interstitial loops in the recent experiments with ion irradiation of Mo foils.
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    Simulation of ion implantation into nuclear materials and comparison with experiment
    (American Institute of Physics, 2011-06) Insepov, Z.; Yun, D.; Ye, B.; Rest, J.; Starikov, S.; Yacout, A. M.
    Radiation defects generated in Mo formed by sub-MeV Xe ion implantations were studied by atomistic molecular dynamics based on interatomic potential matched to density functional calculations. The results of the simulations were qualitatively compared with defect distributions in CeO2 and CeLaO2 crystals used as surrogate materials for UO2 obtained from experiments by implantation of these ions at a dose of 1×1017 ions/cm2 at several temperatures. A combination of in situ Transmission Electron Microscopy (TEM) and ex situ TEM experiments was used to study the evolution of defect clusters during implantation of Xe and Kr ions at energies of 150-700 keV, depending on the experimental conditions. The simulation and irradiation were performed on thin-film, single-crystal materials. The formation of defects, dislocation loops, and precipitates was studied by simulation and compared to experiment. Various sets of quantitative experimental results were obtained to characterize the dose and temperature effects of irradiation. These experimental results include size distributions of dislocation loops, voids, and gas bubble structures created by irradiation.
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    Simulation of Ion Irradiation of Nuclear Materials and Comparison with Experiment
    (arXiv preprint arXiv:1203.0327, 2012) Insepov, Z.; Kuksin, A.; Rest, J.; Starikov, S.; Yanilkin, A.; Yacout, A. M.; Yun, D.
    Radiation defects generated in various nuclear materials such as Mo and CeO2, used as a surrogate material for UO2, formed by sub-MeV Xe and Kr ion implantations were studied via TRIM and MD codes. Calculated results were compared with defect distributions in CeO2 crystals obtained from experiments by implantation of these ions at the doses of 11017 ions/cm2 at several temperatures. A combination of in situ TEM (Transmission Electron Microscopy) and ex situ TEM experiments on Mo were used to study the evolution of defect clusters during implantation of Xe and Kr ions at energies of 150-700 keV, depending on the experimental conditions. The simulation and irradiation were performed on thin film single crystal materials. The formation of defects, dislocations, and solid-state precipitates were studied by simulation and compared to experiment. Void and bubble formation rates are estimated based on a new mesoscale approach that combines experiment with the kinetic models validated by atomistic and Ab-initio simulations. Various sets of quantitative experimental results were obtained to characterize the dose and temperature effects of irradiation. These experimental results include size distributions of dislocation loops, voids and gas bubble structures created by irradiation.