[en] Radioisotopes play an important role in the peaceful uses of nuclear energy. Radionuclides in nuclear medicine can be used for diagnosis and therapy. The ^9Tc, daughter of ⁹⁹Mo is most often used in nuclear medicine as tracer element because of its favorable nuclear properties, accounting for about 80% of all diagnostic procedures in vivo. Nowadays, the supply of this important isotope is deficient, due to the shutdown of the reactors in Canada and Belgium, the world's largest producers. Aiming to resolve the dependency of Brazil with respect to the supply of ⁹⁹Mo was created the Brazilian Multipurpose Reactor project (RMB), started in 2008, having as main objective to produce about 1000 Ci/week of ⁹⁹Mo. This study is part of the project to obtain ⁹⁹Mo by alkaline dissolution of UA1_x-A1 targets. Al, which corresponds to 79% of the total mass, was used to simulate the targets. The reagent used in the dissolution was a 3 mol.L^-1 NaOH/NaNO₃ solution and initial temperature of 88 degree influence of the reagent on the dissolution time, related to the molar ratio 1Al:1.66NaOH:1.66NaNO₃, for a range of over 5 to 50%, and the influence of the amount of mass in a range from 16 to 48 g of Al were studied. It was observed that the dissolution time. (author)