Direct denitration using microwaves (MWD) is an interesting alternative conversion method to obtain uranium dioxide powders from nitric solutions of uranium, since it has many attractive features. However, as other methods, traditional MWD includes a milling step of the powders, which is a disadvantage from the operative and economical point of view. In this paper, the denitration process was studied by depressing the pressure inside the vessel where the solution is denitrated. Intermediate and final products were characterized. It was demonstrated that when working pressure ranges between 520 and 970 hPa during denitration, high density UO2 pellets can be obtained without resorting to a milling step.