Oxidation of Scrap Duplex Burnable Absorber Pellets

Duplex burnable absorber pellet has two distinct potions with different compositions. One is the annular outer portion composed of an enriched UO2-2%Er2O3 and the other is the cylindrical inner portion composed of a natural or depleted UO2-12%Gd2O3. A duplex structure consisting of different materials is advantageous over a structure using either a sintered (U,Gd)O2 or (U,Er)O2 material as a sintered burnable absorber pellet, because the duplex structure exhibits an improved nuclear performance in a nuclear reactor. Generally, about 10 % of pellet can not satisfy the specifications during a nuclear fuel pellet fabrication. In a commercial UO2 or burnable absorber pellet fabrication process, those scrap pellets are usually recycled as a U3O8 or M3O8 (M=U-Gd or U-Er) powder form though an oxidation at 350-550 .deg. C in air. However, in the case of a duplex burnable absorber pellet, a simple oxidation technique could not be used for a scrap recycling, because it is not helpful to mix the enriched uranium of the annular outer portion and the natural or depleted uranium of the cylindrical inner portion. Also it is undesirable to mix gadolinium and erbium. Thus, it is necessary to develop a new technique for recycling a scrap duplex burnable absorber pellet. In this study, the oxidation behavior of a scrap UO2- 12%Gd2O3/UO2-2%Er2O3 duplex pellet has been investigated and a promising method for dividing the recycled scrap powders has been proposed