[en] Faced with global crisis in the production of radioisotope ⁹⁹Mo, which product of decay, ⁹⁹mTc, is the tracer element most often used in nuclear medicine and accounts for about 80% of all diagnostic procedures in vivo, since September 2008 Brazil is developing the project called Brazilian Multipurpose Reactor (RMB). Within the Brazilian Nuclear Program (PNB) the construction of the RMB, is seen as a long term solution to meet all domestic demand relative to the supply of radioisotopes and radiopharmaceuticals. In the process to be studied to obtain ⁹⁹Mo from irradiated UA1_x-A1 LEU targets employing alkaline dissolution, processing time should be minimized, considering the short half life of ⁹⁹Mo and ⁹⁹mTc, about 66 h and 6 h, respectively. That makes dissolution time a significant factor in the development of the process. This paper presents the results of alkaline dissolution of scraps of Al, used to simulate the dissolution process of UA1_x-A1 targets. Al corresponds to about 79% of the total weight of the UA1_x-A1 target. The effect of NaOH concentration on dissolution time for the interval of 1 to 3.5 mol.L-1 was studied, keeping the molar ratio in 1Al:2.16NaOH and the initial temperature of 88 degree C. The influence of reagent composition over dissolution time was studied using three different solutions: a) 3 mol.L^-1 NaOH, b) 3 mol.L^-1 NaOH/NaNO₃ and c) 3 mol.L^-1 NaOH/NaNO₂, keeping the same molar ratio and temperature. The results showed that the dissolution time decreases with increasing NaOH concentration and the addition of NaNO₃ or NaNO₂ in the NaOH solution reduces both dissolution time and volume of gases released. (author)