Fluidized bed furnace and method of emptying the same

A fluidized bed furnace for coating fuel particles for nuclear reactors, particularly high temperature reactors, can be emptied without cooling down the reaction tube by substituting an inert gas for the coating gas and then lowering the inner tube through which this gas is fed so as to clear a passage in the surrounding outer gas feed tube through which the kernels may fall down to a diverting device in the intermediate space between the inner and outer tubes that guides the kernels to a discharge tube. The reaction tube is emptied by lowering the feed gas pressure by cutting off the carrier gas flow and regulating the escape of the inert gas through an overflow pipe. After the reactor is emptied, the flow of carrier gas can be restored and the overflow pipe shut, so that the reactor can be refilled, after which the flow of coating gas is restored and another coating operation can begin without delay