b'Variationally ConsistentNovel modeling methodology increases understanding of mechanical Contact Dynamics for Generalcontact dynamics and predicts grid-to-rod fretting wear.Nuclear Fuel Modeling M echanical contact is a pervasive physical phenomenon that entails modeling and numerical challenges. Traditional approaches employ discretized points and surfaces to enforce contact constraints (i.e., strong enforcement). More advanced and recently developed approaches, such as the mortar finite element, enforce those constraints on segments in dynamically-computed lower dimensional domains. This work developed the stabilization of mortar contact constraints for dynamic applicationsapplications in which inertia PROJECT NUMBER:and vibrations or impacts are of relevancein MOOSE. A comparative study was 21P1062-016 completed between a mortar approach and a point-to-surface approach to contact TOTAL APPROVED AMOUNT:dynamics, which stressed the numerical convergence and accuracy gains obtained by $125,000 over 1 year the extension of mortar constraints to dynamic problems. PRINCIPAL INVESTIGATOR:In the context of mortar-based contact dynamics formulations, small wear depths Antonio Martin Recuero in the constraint equations were considered, which enables wear in nuclear reactor systems to be studied, such as grid-to-rod fretting. Existing creep, fission gas CO-INVESTIGATOR: release, burnup, swelling, thermal expansion, and fuel relocation models in the Alexander Lindsay, INL nuclear fuel performance code BISON were used to run fuel-cladding-spacer grid setups in which dynamic excitations lead to wear on the claddings outer surface. This methodology allows for the study of grid-to-rod fretting wear by employing a consistent formulation in contact dynamics natively in a nuclear fuel performance code. Various geometries of spacer grid and the influence of fuel-cladding contact were considered. Grid-to-rod fretting wear results were consistent with experimental results and allowed to gain insight into single fuel rods configurations natively in a MOOSE application. Particularly, the additional stiffness provided by fuel-cladding contact was shown to generate higher normal contact pressure values that are conducive to increased wear generation. Using conformal geometry for spacer grids reduced and spatially homogenized overall wear throughout the contact interface. These findings are consistent with laboratory experiments reported in the literature. 46'