The advancement of nuclear research reactors hinges on precise thermal-hydraulic analyses, especially when reactors undergo potential design modifications or power uprates. This study uses the computational fluid dynamics (CFD) tool, FLUENT, to analyze thermal-hydraulic behavior in the Replacement Research Reactor (RRR) and the Missouri University of Science and Technology Reactor (MSTR). The RRR model operates at 20 MW (MW) with flat plate fuel assemblies, while the MSTR explores a hypothetical power uprate from 0.2 to 2 MW using curved plate assemblies. Two CFD methods—realistic and porous media modeling—are applied for thermal-hydraulic analysis in RRR and MSTR. For RRR, realistic simulations at 5.08 m/s led to a 245 kPa pressure drop. In MSTR, simulations across 0.25–1.25 m/s velocities yielded maximum fuel and fluid temperatures of 323 K and 303 K, respectively, at 0.25 m/s and 2 MW power. The determined inertia resistance factors are 9.81 m−1 (RRR), 12.35 m−1 (MSTR), and viscous resistance factors are 1.98 x 107 m−2 (RRR), 683,060 m−2 (MSTR). This study validates porous media modeling as a computationally efficient approach for thermal-hydraulic analysis in nuclear reactors, effectively complementing realistic simulations for in-depth assessments.