[en] The Nuclear Fuel Centre of IPEN / CNEN - SP develops and manufactures dispersion fuel with high uranium concentration. It meets the demand of the IEA-R1 reactor and future research reactors to be constructed in Brazil. The fuel uses uranium silicide (U₃Si₂) dispersed in aluminum. For producing the fuel, the process of uranium hexafluoride (UF₆) conversion consist in obtaining U₃Si₂ and / or U₃O₈ through the preparation of intermediate compounds, among them ammonium uranyl carbonate - AUC, ammonium diuranate - DUA and uranium tetrafluoride - UF₄. This work describes a procedure for preparing uranium tetrafluoride via a dry route, using as raw material the filtrate generated when ammonium uranyl carbonate is routinely produced. The filtrate consists mainly of a solution containing high concentrations of ammonium (NH⁴⁺), fluoride (F^-), carbonate (CO^3-) and low concentrations of uranium. The procedure consists in recovering NH^4F and uranium, as UF₄, through the crystallization of ammonium bifluoride (NH₄HF₂) and, in a later step, the addition of UO₂, occurring fluoridation and decomposition. The UF₄ obtained is further diluted in the UF₄ produced routinely at IPEN / CNEN-SP by a wet route process. (author)