Nuclear reactors are one of the major sources of energy production in the present age, which has unique characteristics. Accurate understanding of these features and full familiarity with them is essential for the accident-free operation of nuclear reactors. The UTRS-1J training reactor was set up by the Addis Knowledge base Company with the aim of training specialized manpower in the field of nuclear power plants in the training centers of the country's universities. In this research, the neutron calculations of the reactor core are based on changing the pitch of the fuel rod in each complex without changing the number of fuel arrays using the MCNPX code. Calculations are performed in the equilibrium cycle and factors such as the effective core rate and neutron flux in the thermal energy group are calculated. By changing the pitch of the fuel rod in the proposed models, parameters such as the pitch of the fuel assemblies and the active radius of the core are subject to changes. By examining the criticality level of the reactor core in each model using the KCODE critical source card, parameters such as critical water light height and soluble boric acid concentration were adjusted and the necessary conditions were provided for the fission chain reaction to continue in the reactors. Considering the reactors in operating conditions, the power distribution factor in the core of the reactor in the radial and axial directions has been calculated and reported using the MESH TALLY card. The results of calculations show that with the changes applied in the design parameters of the reactors, the amount of excess reactivity factor created in the core, which is the basis of deviation from the critical state, has a standard limit in all models and has the necessary conditions from the reactor safety point of view. The amount of axial flux has not changed significantly in the study models, but the radial flux profile has undergone fundamental changes due to the change the pitch o