Multi-Scale Modeling of Interstitial Dislocation Loop Growth in Irradiated Materials
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Multi-Scale Modeling of Interstitial Dislocation Loop Growth in Irradiated Materials Bei Ye, Di Yun, Zeke Insepov, Jeffrey Rest Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439, U.S.A. ABSTRACT In order to reduce the inherent uncertainty in kinetic theory models and promote their transition to become predictive methodologies, a multi-scale modeling approach is proposed and demonstrated in this work. KiValues of key materials properties such as point defect (vacancy and interstitial) migration enthalpies, as well as kinetic factors, such as dimer formation and defect recombination coefficients and self-interstitial atom – interstitial loop reaction rates, were obtained by ab initio/molecular dynamics calculations. A rate theory model was used to interpret the evolution of dislocation loops in irradiated molybdenum. Calculations of the dose dependence of average loop diameter were performed and compared to experimental measurements obtained from irradiations with high-energy electrons. The comparison demonstrates reasonable agreement between model-predicted and experiment-measured data. INTRODUCTION The development of a predictive capability for damage produced by high-energy particle irradiation in nuclear materials is important for design of future nuclear reactors, as well as for establishing safety margins for fuel behavior. However, the typical meso and macro scale kinetic models, such as those embodied in rate-theory, phase-field theory and finite element methodologies, bear an inherent uncertainty due to the absence of experimental validation of key materials properties and proposed behavioral mechanisms that have been derived based on mean field, or continuum theories. As such, these models can serve as interpretative tools, but are short in predictive capability. In general, modeling of the irradiation behavior of nuclear materials has been accomplished using rate-theory type formulations [1,2]. In this approach, for example, the gain and loss of irradiation generated defects and impurities are tracked by various terms in the constitutive equations, each term being associated with an assumed behavioral mechanism. The analytic form of the terms representing the various physical processes are generally derived based on a continuum approach from mean field theory; they are defocused from the specific details and variations present at the atomistic level. Therefore questions are raised on the validity of such expressions to realistically describe the phenomena. Validation of specific assumed behavioral mechanisms is limited by the difficulty in performing realistic separate-effect experiments, or in extraction information from in-pile irradiation that by nature is highly multivariate. The lack of reliable values of materials properties and the difficulty in performing separate effect studies in irradiation environments have greatly plagued the effort to develop a predictive model for the analysis of the irradiation behavior of nuclear fuels. Activities of basic experimentation on the nature of ir
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