The Massachusetts Institute of Technology Research Reactor (MITR) is evaluating a transitional core conversion strategy for converting from high-enrichment uranium (HEU) to low-enrichment uranium (LEU) fuel. The objective of this study is to analyze steady-state operational safety margins and loss of primary flow (LOF) accidents for the postulated HEU-LEU transitional core configurations. The thermal-hydraulic calculation was performed using the RELAP5 MOD 3.3 code based on 7.40-MW reactor power, which is the limiting safety system settings of the current licensed reactor power of 6 MW. A lumped average and a single hot channel were modeled in each core configuration with radial peaking factors of 2.0 and 1.76 for HEU and LEU fuel elements, respectively. Four natural convection valves and two antisiphon valves were modeled for natural convective heat removal during the LOF transient. Two different hot-channel configurations and full- and side-channel geometries were evaluated because the unique design of the MITR fuel element can form these two types of geometries. RELAP5 calculation results suggest that the transitional core conversion strategy is feasible and that sufficient thermal-hydraulic safety margins can be maintained.