Abstract
Plasma surface interactions in fusion tokamak reactors involve an inherently multiscale, highly non-equilibrium set of phenomena, for which current models are insufficient to predict the divertor response to and feedback on the plasma. This presentation highlights the latest developments of Xolotl, a spatially­-dependent reaction-diffusion cluster dynamics code. It will first focus on initial benchmarking against molecular dynamics simulations to then dive into the bubble bursting model for helium release from over-pressurized bubbles in tungsten. Xolotl is part of a code­ coupling effort to model both plasma and material simultaneously, incorporating simulations of: the edge plasma in steady­ state conditions; the effect of the sheath at shallow magnetic angles; migration and redeposition of impurities eroded from the surface; and the response of the wall surface to plasma conditions. Benchmarking against linear plasma device experiments as well as preliminary ITER predictions will be presented. Finally, Xolotl is also able to simulate xenon-irradiated UO2 fuel and we developed a hybrid code that is coupled with the phase-field approach to model the different stages of fission gas release. The fission gas production, diffusion through grains, clustering, and re-solution are included in Xolotl, while intergranular gas bubble growth and interconnection are included using the phase-field method in the MARMOT mesoscale fuel performance code. The codes exchange information at every time step: MARMOT passes the grain boundary (GB) locations to Xolotl, and Xolotl passes fission gas rates at GB surfaces to MARMOT. A short overview of other material applications will conclude the presentation.

Bio
Sophie Blondel is a research scientist in the Wirth Research Group at University of Tennessee. She received her BSc from Ecole Polytechnique (France) and her MS from Université Paris Diderot (France), both in physics. After finishing her PhD in particle physics in 2013 from Université Paris-Sud (France), she started at ORNL as a postdoctoral research associate to work on code development for Xolotl within a DOE SciDAC project. She has since become the lead developer for Xolotl and joined the Nuclear Engineering department at the University of Tennessee. She was a visiting academic fellow at Université Sorbonne Paris Nord in April 2022. Blondel's research focuses on developing continuum scale models for irradiated materials and implementing them for high performance computing applications.