The goal of the work is to investigate the abilities of the realizable k- and the k- turbulence models to predict phenomena expected in the lower plenum of the prismatic gas cooled reactor by benchmarking them against one another as well as verifying them against available experimental data . Simulations were performed with CD-Adapcos Star-CCM+ computational fluid dynamics (CFD) code utilizing the steady state approximation of the realizable k- turbulence model and the unsteady RANS approximations of the shear stress transport (SST) k- turbulence model. The unsteady results were averaged over a period of time corresponding to one full fluctuation cycle of the phenomena present with the lowest frequency. A case with a single jet of Reynolds number 12,700 was simulated as well as a case with dual jets of Reynolds numbers 6,300 and 12,700. Impingement of the jets occurred on the lower plane of the setup as occurs in the lower plenum. A two-layer shear driven  y+ wall treatment was used to satisfy the boundary layer profile. A mesh of 8.6 million polyhedral cells was generated to capture critical flow characteristics within the domain. Polyhedral cells were chosen for this application because they provided a better quality mesh and reduced the total number of cells necessary to achieve accurate results . The simulations carried out were defined as having reached a converged solution when all residuals reduced to less than 105. The simulations of the flow in the rod bundle were successful in providing insight into locations of some key recirculation zones and the dependence they have on inlet conditions. The comparison between numerical and experimental results showed similar key flow patterns as well as aided in possible points of focus for future investigation. The information obtained and conclusions drawn will be critical in future numerical benchmarks in this area of research.