Abstract: A fluidized bed furnace for coating fuel particles for nuclear reactors, ticularly 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.

Abstract: For certain related dimensions of features of a nozzle feeding a fluidized bed reactor from below, it has been found that a central flow of a coating gas is squeezed down in diameter in passing through a constriction at the nozzle end by the action of the surrounding dilution gas flow, without the setting up of turbulence such as might have been expected, which would cause deposits from the decomposition of the coating gas at the constriction. The spacing between the mouth of the central tube that feeds the coating gas and the constriction at the end of the nozzle should be in the range of 20 to 70 mm, the diameter of the constriction aperture should be in the range from 3 to 10 mm and the diameter of the central channel should be greater than the constriction aperture diameter but not more than 3.5 times the latter diameter. For coating particles having a density of about 10 g/m.sup.3 and a diameter of about 200 .mu.m , the constriction aperture diameter should not exceed 7 mm.

Abstract: A fluidized bed furnace employed for depositing pyrolytic carbon or silicon carbide on nuclear fuel particles is supplied with an inert dilution gas and a decomposable coating gas. These are supplied by means of a gas injector having at least three pipes 4 for coating gas extending within a surrounding duct for a stream of dilution gas 6. This leads to a partition 2 at the base of the bed, having at least three apertures 3 for through passage of the gases.

Abstract: The reaction gas throughout of the supply duct feeding gas to the bottom of a fluidized bed reactor of the kind shown in U.S. Pat. No. 4,153,004, issued May 8, 1979, is increased by providing the reaction gas supply tube in the form of a bundle of tubes of small cross-section of about 2 mm diameter. Subdivision of the supply tube into hexagonal ducts in honeycomb arrangement maximizes the useful cross-sectional area of the supply tube. With the smaller elemental tube diameters, a higher rate of flow is maintainable without loss of laminar flow behavior, which behavior is maintained in the jet issuing from the subdivided reaction gas supply duct as it flows towards the constricted entrance into the fluidized bed container while being surrounded by a sheath of inert carrier gas supplied by an annular duct surrounding the reaction gas tube.

Abstract: In a fluidized bed reactor total gas feed is through a constricted opening at the bottom of the reactor. A carrier gas supply duct communicates with said bottom. A reaction gas supply tube, disposed within said duct, has an outlet spaced from said bottom and is comprised of a bundle of tubes arranged to dispense an annular stream.

Abstract: An inner tube through which the coating gas is supplied terminates short of he end of the outer tube which forms an annular channel around the inner tube for supply of the carrier gas, so that a chamber is formed between the ends of these channels and the connection of the outer tube to the bottom of the heated reaction container. A constriction is provided where the outer tube joins the reaction container with its aperture aligned with the common axis of the two gas supply tubes. The position of the end of the inner tube is adjustable to suit the particular gas feed rate. The inner tube never reaches the temperature at which the coating gas decomposes. The upper portion of the outer tube, particularly at the constriction, is at or above that temperature, but the flow of carrier gas along the hot surfaces prevents the deposit of a coating on these surfaces.