Wirbelschicht-Apparat

1,100,311. Nuclear fuel. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. 14 April, 1965 [22 April, 1964], No. 16663/64. Heading G6C. [Also in Division B2] A method of coating, e.g. with carbon, nuclear fuel particles by pyrolysis of process gas containing the coating material, resides in treating the particles in a heated fluidized bed apparatus whilst process gas and inert fluidizing gas are introduced into the base of the bed via a parallel sided mixing zone constituted by a parallel walled portion at the base of the bed. A test using uranium dicarbide particles is described. Suitable apparatus comprises an outer heater tube 1 of graphite within which is located a graphite reactor tube 2 connected with a graphite nozzle portion 3 which includes a parallel walled portion 6 and receives a gas injection assembly 9. The portion 6 is preferably fitted with a replaceable graphite sleeve 8. In use particles are fed into the reaction tube 2 and are fluidized by a gas stream admitted through the gas injection assembly 9. Tube 1 is heated by electric means and the coating agent, a gas or a vapour, is injected into the reaction zone. The gas injection assembly 9 is water cooled to minimize deposition of coating material thereon. The parallel walled portion 6 is said to improve the uniformity of temperature distribution throughout the bed of particles and the effect of particle density on the average temperature of the particles is said to be lessened by it, as compared with devices not having such a portion.