[en] A device is described for flame fluorination of mixed uranium and plutonium oxides consisting of a duplex cylindrical vessel with a conic bottom provided with an inlet and a discharge for the coolant, and of metalloceramic filters. The cooling space is formed between the inner wall of the reactor vessel and the external wall of the built-in internals. THe device is capable of withdrawing such reaction heat that the temperature of the wall of the combustion chamber is in the region of 500 degC; it is further able to withdraw very quickly heat from the reaction gases, this below the temperature of 300 degC with end cooling to a temperature of around 100 degC. The built-in internals substantially reduce the length of the device. Another advantage is the common space for trapping incombustible residues from the combustion area and from the metalloceramic filters. A schematic diagram is provided. (J.B.)