Fabrication of UO 2 pellets by gel pelletization technique without addition of carbon as pore former

Abstract

High density UO 2 pellets for pressurised heavy water reactor fuel were fabricated by a gel pelletization technique from soft UO 2 microspheres prepared by an internal gelation process. Chemical and heat treatment parameters were determined for obtaining soft UO 2 microspheres with optimum properties required for making defect-free, high density, UO 2 pellets. Investigations reveal that a high uranium concentration in the feed broth during the preparation of UO 3 gel particles, conversion to UO 2 via U 3O 8, and optimized calcination and reduction temperatures, result in UO 2 microspheres suitable for obtaining good quality green compacts. Green pellets were densified by low temperature sintering in a C0 2 atmosphere at 1200°C to obtain high density UO 2+ x pellets and reduced at 800°C to UO 2.00 in Ar + 8%H 2 Resulting pellets were free from open porosity and black berry structure.