Amir Karimi Jafari - Department of Faculty of Engineering Science and Research branch, Islamic Azad University Tehran – Iran

numerous burnable-absorber (BA) types have been used in commercial nuclear fuel assembly designs to suppress initial reactivity. In this study, presents results of calculations for PWR 17 17 fuel assembly with natural gadolinium and erbium content by using the DRAGON code simulation. These BAs characteristics are varied in number of gadolinia rods in fuel assembly. The effect of gadolinium on kinf values at the first burnup steps is larger than erbium, this effect decreases quickly in case of gadolinium. This is because gadolinium is burnt very quickly in relative to erbium