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This report presents requirements for advanced simulation of nuclear reactor and chemical processing plants that are of interest to the Global Nuclear Energy Partnership (GNEP) initiative. Justification for advanced simulation and some examples of grand challenges that will benefit from it are provided. An integrated software tool that has its main components, whenever possible based on first principles, is proposed as possible future approach for dealing with the complex problems linked to the simulation of nuclear reactor and chemical processing plants. The main benefits that are associated with a better integrated simulation have been identified as: a reduction of design margins, a decrease of the number of experiments in support of the design process, a shortening of the developmental design cycle, and a better understanding of the physical phenomena and the related underlying fundamental processes. For each component of the proposed integrated software tool, background information, functional requirements, current tools and approach, and proposed future approaches have been provided. Whenever possible, current uncertainties have been quoted and existing limitations have been presented. Desired target accuracies with associated benefits to the different aspects of the nuclear reactor and chemical processing plants were also given. In many cases the possible gains associated with a better simulation have been identified, quantified, and translated into economical benefits. Results reported in the AFCI series of technical memoranda frequently are preliminary in nature and subject to revision. Consequently, they should not be quoted or referenced without the author's permission
Dense nano‐sized UO2+x pellets are synthesized by spark plasma sintering with controlled stoichiometries (UO2.03 and UO2.11) and grain sizes (~100 nm), and subsequently isothermally annealed to study their effects on grain growth kinetics and microstructure stability. The grain growth kinetics is determined and analyzed focusing on the interaction between grain boundary migration, pore growth, and coalescence. Grains grow much bigger in nano‐sized UO2.11 than UO2.03 upon thermal annealing, consistent with the fact that hyper‐stoichiometric UO2+x is beneficial for sintering due to enhanced U ion diffusion from excessive O ion interstitials. The activation energies of the grain growth for UO2.03 and UO2.11 are determined as ~1.0 and ~2.0 eV, respectively. As compared with the micrometer‐sized UO2 in which volumetric diffusion dominates the grain coarsening with an activation energy of ~3.0 eV, the enhanced grain growth kinetics in nano‐sized UO2+x suggests that grain boundary diffusion controls grain growth. The higher activation energy of more hyper‐stoichiometric nano‐sized UO2.11 may be attributed to the excessive O interstitials pinning grain boundary migration.
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