The radial and axial power distribution in power reactors are determined mainly by the patterns of the fuel assembly and the burnable absorber at the beginning of cycle. In Advanced Pressurized Water Reactor (APWR), gadolinium burnable absorber is used to decrease the relative power of fresh fuel assemblies. In this paper, the effect of the axial distribution of gadolinium (Gd) on the power of the APWR assembly is studied. Three models of APWR assemblies are simulated using MCNP6 code. In the first model, UO2 fuel is distributed uniformly in all the fuel rods. In the other two models some of the UO2 fuel rods are replaced by UO2-Gd2O3 rods in part length distribution. Two gadolinium concentrations 6% and 10% are used. The main neutronic parameters are estimated for the three models: the multiplication factor (K-infinity) as a function of burnup (GWd/MTU), the radial and axial power distributions. The results show that the distribution of the gadolinium absorber in the central region of fuel rod (part-length absorber) leads to flattening of axial power, which means additional axial power distribution control.
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