METHOD AND DEVICE FOR PRODUCING PELLETIZED FUEL FOR FUEL ELEMENTS Russian patent published in 2003 - IPC

FIELD: nuclear power engineering; production of pelletized uranium dioxide fuel. SUBSTANCE: method includes preparation of molding powder from uranium dioxide UO₂ enriched by uranium 235 to 5%. Then this powder is stepwise mixed up with binder in the form of zinc stearate {Zn(C₁₇H₃₅COO)₂ and with powdered uranium dioxide U₃O₈ and compressed with lubricant in the form of zinc stearate in matrix introduced in powder. Binder is thermally extracted, Pelletized fuel is sintered in gaseous reducing medium. Pelletized fuel is subjected to wet grinding in skive, dried out, and given quality inspection, defective pellets being culled. Source uranium dioxide powder used for the purpose includes fine fractions up to 0.071 mm in the amount of maximum 0.1 mass percent. Zinc stearate powder is pre-rubbed through screen having mesh aperture size of 0.04-0.1 mm. Biconical mixing container is filled with source powder in the amount of maximum 70 volume percent. Uranium dioxide is mixed up with zinc stearate concurrently with pelletizing uranium dioxide and oxide particles from dendrite to spherical structure. In the process number of revolutions of biconical mixing container in two planes about its axis and perpendicular to the latter in vertical direction within one revolution cycle is maximum 70 to 1, respectively. Device implementing proposed method has removable biconical mixing containers of mixing unit made of stainless steel with polished inner surface. Angles at cone vortexes do not exceed 54 deg. Unit for pressing pelletized fuel has its cylindrical part of bottom punch and bottom part of die contacting the latter assembled by sliding fit. Length of cylindrical working part of bottom punch amounts to minimum six diameters of cylindrical working part of bottom punch. EFFECT: enhanced yield, quality of pelletized fuel, and wear resistance of pressing tools. 2 cl, 3 dwg