Method for determining gadolinia in uranium pellets cladded with zircaloy

Angra 2 Nuclear Power Plant, and maybe Angra 1 soon, uses Gadolinia (Gd2O3) in some positions of the reactor as 'burnable poison', i.e., neutron absorber, to meet the best performance in reactor core. The function of the burnable poison is to control core reactivity. It is designed to effectively reduce the initial high reactivity of a new core or after refuelling, and to burn out during irradiation inside reactor. Without it, a undesirable positive moderator coefficient would prevail under normal operating conditions during part of the first fuel cycle. In some pre-specified fuel assemblies, uranium oxide fuel pellets may contain Gadolinia from 0,0 w/o up to 8,0 w/o. The pellets are assembled into fuel rods and are cladded with Zircaloy. Each complete fuel rod may contain up to six different Gadolinia concentrations. To allow production at INB (Industrias Nucleares do Brasil S/A), quality control system requires a method to determine the presence, correct concentration and distribution of Gadolinia within a completed fuel rod assembly. This work presents a method which, by magnetic susceptibility analysis, determines Gadolinia presence and concentration, using an Eddy Current Test apparatus. (author)