b'High-fidelity multiscaleParticle-based methods for high-fidelity predictive model developmentmodeling of fuel fragmentation, relocation, and dispersal for accelerated fuelphenomena accelerate nuclear fuels qualification.qualification using finiteR eactor vendors seek economic benefits associated with increasing nuclear fuel service lifetime in the existing fleet of light water reactors to overcome element-informed discretethe downturn in economic viability associated with their aging. However, the 20% proposed increase of the fuel discharge burnup from the current regulatory element modeling limit represents a major safety concern, which still needs to be addressed. This originates from the formation of high burnup structures in conjunction with a loss of coolant accident that can lead to a phenomenon known as fuel fragmentation, relocation, and dispersal (FFRD), which adversely impacts fuel performance. In addition, FFRD increases the potential of primary system contamination and radiation exposure resulting from relocating fuel escaping the fuel pin and getting PROJECT NUMBER:dispersed into the primary coolant system. The fuel performance code BISON, 22P1074-009FP developed at INL, has been used in a limited capacity to explore fuel performance during FFRD. To date, no model exists to predict the relocation and dispersal of fuel TOTAL APPROVED AMOUNT:particles under realistic scenarios. Developing this capability will aid industry to $125,000 over 1 year cultivate risk mitigation strategies for FFRD. PRINCIPAL INVESTIGATOR:In this project, a multiscale framework integrating particle-based and mesh-based Kyle Gamble methods was developed to model FFRD during a simulated loss of coolant accident. CO-INVESTIGATORS: In this multistage scheme, BISON was used to simulate experimentally observed Ahmed Hamed, INL scenarios leading to FFRD up to the condition prior to fuel relocation and furnished Yidong Xia, INLthe results to INLs discrete element method software Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) improved for general granular and granular heat transfer simulations, called LIGGGHTS-INL. In this later stage, the effect of fuel particle size and distribution, the ballooned and ruptured cladding geometries, and internal pressure on the dynamics of fuel relocation and dispersal was investigated. The analysis demonstrated the strong correlations between the considered parameters and the fuel missing length. Interestingly, high internal pressure was shown to prevent fuel axial relocation prior to cladding rupture. Contrarily, pressure played no role afterward. Furthermore, finer particles, which correspond to higher burnup level, were found more prone to axial relocation and less sensitive to the cladding burst opening shape. The results also emphasize the importance of accounting for fuel particle size distribution, shape, surface roughness and spatial arrangement for a reliable prediction of the fuel behavior during FFRD. For example, using rim structure where fine particles are found at the radial outer edge of the fuel pin predicted a layer-by-layer fuel dispersal behavior that is more consistent with a one-dimensional mass flow pattern preserving the axisymmetry. Completely different dynamics were observed for particle random packing. 60'