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Brian Wirth1

1, University of Tennessee, Knoxville, Knoxville, Tennessee, United States

The behavior of xenon (Xe) in nuclear fuel is of critical importance to nuclear fuel performance, because the diffusion and precipitation of Xe in fission gas bubbles influences both the amount of fuel swelling and the quantity of fission gas released to the fuel rod plenum. Despite decades of investigation, significant uncertainties exist regarding the underlying mechanisms controlling Xe diffusion, precipitation and release that impact predictions of fission gas swelling and release during both normal operation and transient conditions in accidents. Despite being a key determinant of fission gas effects, which control fuel performance, accurate physically-based models of intra-granular bubble evolution are still lacking in current models. This presentation will first introduce a multiscale modeling approach to simulate the behaviour of fission gas and intra-granular fission gas bubble populations. We will then review the current status of understanding of Xe diffusion mechanisms, and our recent results to investigate the re-solution behaviour of fission gas bubbles as a function of bubble size and xenon concentration (pressure), and finally show initial results of our cluster dynamics model for xenon bubble density. Our approach to multiscale modeling is based on an information-passing paradigm, which allows us to attack the complex fission gas behavior problem from both a “bottom-up” atomistic-based approach, as well as from a “top-down” continuum perspective that focuses on kinetic models of intra-granular gas bubble evolution. Simultaneously attacking such complex and inter-related diffusion and gas bubble evolution processes from both an atomistic and a continuum approach will minimize the risk of using just a single approach and further the prospects for scale bridging, or multiscale integration. The presentation will conclude by benchmarking our continuum clusters dynamics bubble evolution model to available experimental data on intra-granular bubble size and density as a function of temperature and burnup.

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