Abstract: Nowadays, reducing fuel consumption, fuel cost, and fuel waste is obtained by increasing the burnup and reactor cycle length as essential goals in nuclear power plants. Due to the scarcity of Iran’s uranium resources and the plan for using new types of fuel in the Water–Water Energetic Reactors (WWER-1000) at Bushehr Nuclear Power Plant (BNPP), utilizing Integral Burnable Absorbers (IBAs) is of great importance. In the present study, a neutronic evaluation has been conducted to investigate the variations of infinite multiplication factor versus burnup, reactivity swing, and power distribution in various IBAs, including Gd2O3-UO2, Er2O3-UO2, and Dy2O3-UO2. The results were compared with the standard burnable absorber in the BNPP reactor core (CrB2Al). It can be concluded that gadolinium IBA, with a concentration of 5%, has the greatest effect on the initial reactivity and reduces the reactivity swing by 19% compared to the CrB2Al BA. In addition, by using coaxial gadolinium-erbium IBA pins, as well as optimizing the neutronic condition, the reactor cycle length increased by
