Grain size control Of UO2 pellets by adding heat-treated U3O8 particles to UO2 powder

A method of controlling the grain size of UO2 pellets was investigated by adding heat-treated U3O8 particles to UO2 powder. The recycled U3O8 powder, which was made by oxidizing defective UO2 pellets in air, was heat-treated at 1200-1500 degreesC in air and then divided into individual crystals. The U3O8 seed - product - consists of one or several crystals. The U3O8 seed was added to UO2 powder, and the powder mixture was pressed and then sintered at 1700 degreesC in hydrogen gas. The grain size of seeded UO2 pellets is dependent on the amount and size of the U3O8 seed. A seeded UO2 pellet can have a grain size of 14 mum, while a conventional UO2 pellet has a grain size of 8 mum. A mechanism for grain growth in seeded UO2 is proposed and discussed. (C) 2003 Elsevier Science B.V. All rights reserved.