A new methodology for the accurate and efficient determination of steady-state thermal-hydraulic parameters for prismatic high-temperature gas reactors is developed. Whole-core steady-state temperature, pressure, and mass flow distributions are determined for the conceptual MHTGR-350 [Modular High Temperature Gas Reactor] reactor design and also for a range of values of the important parameters. Full-core three-dimensional heat conduction calculations are performed at the individual fuel pin and lattice assembly block levels. A simplified one-dimensional fluid model is developed to predict convective heat removal rates from solid core nodes. Downstream fluid properties are determined by performing a channel energy balance along the axial node length. To establish flow distribution, channel exit pressures are compared, and inlet mass flows are adjusted until a uniform outlet pressure is reached. Bypass gaps between assembly blocks as well as coolant channels are modeled. Finite volume discretization of energy and momentum conservation equations are formulated and explicitly integrated in time. Iterations are performed until all local core temperatures stabilize and global convective heat removal matches heat generation.

Whole-core steady-state, thermal-hydraulic results are presented for various axial power and uniform radial power configurations. For all cases, peak temperatures were below expected normal operational limits for TRISO fuels. Bottom-peaked axial power shapes had the highest peak temperatures but the lowest average temperatures. Different reactor designs with increased core inlet temperatures, reduced flow rates, or higher-power-density fuels could however challenge temperature limits. Partial assembly hydrodynamic and temperature results compared favorably with those available in the literature for similar analyses.