Parametric study of the computational model on fuel and fission products characteristics analysis of HTR-PM equilibrium core

Fission products (FPs) release from TRISO-coated particles in Pebble Bed High-Temperature Gas-Cooled reactors (PB-HTGRs) is a critical safety concern, influenced by various input parameters. This study examines the impact of neutron cross-sections, grid resolution, and tracer pebble distribution on fuel behavior, radionuclide inventory, and release rates in the HTR-PM equilibrium core using FIRCS computational framework. A preliminary multi-region strategy has also been proposed to address in-core temperature variations for doppler broadened cross-sections. The results show that FPs concentration and release rates (CRR) generally decrease with increasing cross-section temperatures. The multi-region approach produced CRR values similar to those at high cross-section temperatures. Additionally, cumulative burnup and particle failure fraction (PFF) for average fuel decrease with increasing cross-section temperatures, and the multi-region approaches yield the highest average fuel burnup. Beginning-of-life (BOL) cross-sections significantly underestimate ²³⁵U depletion (by a factor of 2.21) and overestimate discharge burnup (by ∼20 %) compared to burnup-dependent cross-sections. Coarser grids over predict FPs release rates but improve computational efficiency, highlighting a trade-off. Similarly, tracer pebble distribution has a significant effect on release rate variability, but both grid resolution and tracer distribution show minimal sensitivity to discharged fuel actinide concentrations and fuel behavior. This comprehensive analysis highlights the importance of selecting appropriate cross-section libraries, grid resolutions, the proposed multi-region strategy, and tracer pebble distributions for accurate PB–HTGR modeling. The findings provide valuable insights into radionuclide behavior and fuel performance, supporting the development of safer and more optimized PB-HTGR designs.