Lattice Calculations and Power Distribution for Nigeria Research Reactor-1 (NIRR-1) using Serpent Code

Abstract

Nigerian Research Reactor (NIRR-1) is a tank-in-pool Miniature Neutron Source (MNRS) reactor type that originally uses 90.3% enriched UAl₄-Al which is a highly enriched uranium fuel as the source of neutron. The recent conversion of this reactor core to low-enriched uranium with 13% enriched UO₂ may significantly affect many neutronics behavior in the core and hence power output. Hence, the need to investigate the likely changes in the neutronic parameters that the fuel replacement may cause. This study investigates the static neutronic behavior in the reactor core lattice arrangement and reactor power distribution using “Serpent” Monte Carlo reactor Physics burnup simulation code module computations which include multi-group diffusion and flux-power reactivity equation for k_eff eigenvalue and diffusion solution respectively were carried out to determine the effect of lattice geometry and mesh on the power distribution in the core. The result shows that the power distribution is slightly affected by the macroscopic group constant, heat transfer, fluid temperature, coolant density and fission reaction stability. The computational results of power distribution in arrayed fuel core and power distribution per neutron energy generated in the reactor indicate a uniform distribution. The result is important in determining the effect of fuel change and core configuration and in the overall operational safety of the reactor.