Pronghorn was originally developed for simulation of the gas-cooled pebble-bed VHTR concept. The current capabilities of Pronghorn include transient and steady coupled porous fluid flow and solid-state heat conduction coupled with a standard multi-group diffusion model (i.e., fixed-source, criticality, and time-dependent), provided by MAMMOTH and Rattlesnake, and BISON’s nuclear fuels performance capability. Future capabilities will include a more advanced multi-phase flow type of model (to study thermal boundary layer effects) and a thermal radiation transport model. The physics can be solved in three-dimensional Cartesian coordinates and two-dimensional cylindrical (r-z) coordinates, with precursor and adiabatic thermal feedback models. This code has been validated against the PBMR400 benchmark problem. Using Pronghorn, rod ejection simulations have been conducted for thermal-fluids/neutronics for both pebble-bed and prismatic gas-cooled reactors and simple thermal-neutronics coupled LWR benchmark problems.