High-Fidelity Monte Carlo Modelling of the HTGR Fuel Cycle for Fuel Utilization Optimization and Nuclear Safety Assurance

This paper presents a numerical study of fuel cycle performance and time–space characteristics of a research-scale high temperature gas-cooled reactor (HTGR) using high-fidelity Monte Carlo simulations with continuous-energy and double-heterogeneity modeling. Three core geometries (V1, V2, V3) and three fuel enrichment levels (5%, 8%, 12%) were analyzed with axial batch refueling strategies. Results show a strong dependence of fuel utilization on geometry and enrichment. The V2 configuration achieves the best performance, with sub-cycle lengths up to 550 days and fuel utilization over 91% at 12% enrichment. V1 and V3 yield shorter cycles but maintain stable power and temperature profiles. In all cases, fuel temperature remained below 1200 K, ensuring a wide safety margin. The similarity of power distributions for different enrichments indicates that a single core design can accommodate various fuel types without compromising safety. These findings support the selection of V2 as a reference configuration for a future HTGR research reactor.