Reliable simulation of graphite-moderated pebble bed reactors requires validation against integral experiments. This work validates the SCALE development version (SCALE 7.0 Beta 12) against the HTR-PROTEUS benchmark suite from the International Handbook of Evaluated Reactor Physics Benchmark Experiments (IRPhE). Eleven critical configurations were analyzed, including hexagonal close-packed (HCP), columnar hexagonal point-on-point (CHPOP), and nominally random pebble-bed arrangements, with variations in moderator-to-fuel ratio and simulated water-ingress conditions. Criticality calculations were performed with SCALE’s Shift Monte Carlo code using multiple nuclear data libraries in both continuous-energy and multigroup modes and with explicit pebble modeling. Recent Shift enhancements in the mesh acceleration for such stochastic geometries made the simulations efficient. In addition to criticality, the effective delayed neutron fraction and selected control rod worths were evaluated. Nuclear data sensitivity and uncertainty analyses were also performed. The calculations reproduced the main benchmark trends, with both ENDF/B-VIII.0 and the preliminary SCALE-processed ENDF/B-VIII.1 continuous-energy libraries yielding smaller criticality biases than ENDF/B-VII.1. For ENDF/B-VII.1 and ENDF/B-VIII.0, the propagated nuclear-data-induced uncertainty in 𝑘eff remained near 0.7%. The ENDF/B-VIII.1 analysis was limited to the continuous-energy 𝑘eff comparison. Overall, these results support the use of SCALE for high-fidelity analysis of graphite-moderated pebble bed reactor systems.
