Metallography of thoria-based fuel materials

Thoria and mixed thoria-urania fuel pellets were used to power the light-water breeder reactor (LWBR) installed at Shippingport, Pennsylvania, and a compilation of this technology was recently authorized for public consumption. Metallography using light, electron, and X-ray sources played a substantial part in understanding the behavior of the fuel in the powder and pellet forms, in both the unirradiated and irradiated conditions. Sinterability was determined by the shapes of comminuted starting powder particles. Reactor fuel pellet processing changes were instituted because of the metallographic data generated, especially when contaminants were found to have a disproportionate effect on properties due to concentration at key locations such as surfaces and grain boundary tri-junction