A two–dimensional ring model is developed with SAM to model the core of the High Temperature Test Facility (HTTF) at the system level. The ring model simplifies the complex structure of the HTTF core by converting the hexagonal rows of heaters and flow channels into layers of concentric annular rings. The ring model is first compared against a three–dimensional (3D)–one–dimensional (1D) model where the solid structures are fully resolved in three dimensions while the fluid structures are modeled as 1D flows. Comparison between the 3D–1D and the ring models shows that the latter can predict major parameters reasonably well under steady–state normal operating conditions, but the heater temperatures are under predicted. Adjustment is made to the effective thermal conductivity of the ceramic core of the ring model to improve the heater temperature predictions. The ring model is also used to simulate a transient pressurized conduction cooldown condition and is benchmarked with the experimental data from the HTTF Test PG–27. Good agreement is obtained between the experimental data and the predictions by the ring model.