Comprehensive Comparison of Nuclear Materials in BNPP Fuel Assemblies

There is an obvious effort to increase the burnup of used fuel assemblies in the Bushehr WWER-1000 Nuclear Power Plant (BNPP) in order to improve fuel utilization. The outcomes of this research could result in an increase in the BNPP reactor cycle length, which would lead to improved fuel consumption. Considering the lack of uranium resources and the planning to use new types of fuel in the BNPP, the use of integrated burnable absorber (IBA) materials is of great importance. An analysis of the performance of various IBAs, including Gd₂O₃-UO₂, Er₂O₃-UO₂, and Dy₂O₃-UO₂, as well as the standard (proposed by the designer) burnable absorber (BA) (CrB₂Al) in the BNPP, and their impact on fuel neutronic characteristics has been performed. Five fuel assemblies: one without a BA fuel rod and four each containing standard BA gadolinia, erbia, and dysprosia fuel pins were investigated. The neutronic properties of BAs were evaluated by the infinite multiplication factor, reactivity swing, and power peaking factor dependence on fuel burnup. Gadolinia, with a concentration of 5%, has the greatest effect on initial reactivity with 10 893 pcm and the lowest effect on the reactivity swing with 0.277 Δk among the other BAs, which leads to selecting the most appropriate BA for improving reactor core stabilities and enhancing operational safety. The gadolinium IBA extends the cycle burnup by about 1 GWd/tonne U compared to the standard BA. At the beginning of the cycle, erbium has a more uniform power distribution than the standard BA; however, at the end of the cycle, gadolinia has a more uniform power distribution.