Abstract: A method of declogging at least one filter of a plant for manufacturing uranium oxide from uranium hexafluoride, including separating, from the wall of the filter, uranium oxyfluoride particles deposited, by a stream of inert gas such as nitrogen, injected into the filter, in a counter-currentwise direction to the flow of hydrofluoric acid.

Abstract: A substance in a condensed state, for example a powdered solid, is in continuous movement in the longitudinal direction (6) of a furnace (4, 5). A reactive gas mixture is brought into contact with the substance in the condensed state. A plurality of samples of the gaseous mixture are removed at a plurality of reference points (14) spaced apart from one another along the longitudinal direction (6) of the furnace (4, 5); each of the gas samples is analyzed outside the furnace to determine the composition of the gas mixture and for each point (14), the extent of a chemical reaction between the condensed substance and the reactive gas mixture is deduced from the composition of the gas mixture at each of the reference points (14). In particular, the apparatus comprises a sampling and injection rod (10) introduced into the furnace (4, 5) and disposed in its longitudinal direction (6).