FUEL CONSTITUENT REDISTRIBUTION DURING THE EARLY STAGES OF U-PU-ZR IRRADIATION

Irradiation and fission-related phenomena in metallic fuels based on the U- Pu-Zr system result in fuel restructuring in the forms of fuel swelling (Xe/Kr bubble growth) and constituent redistribution. An experiment designed to analyze the early development of these phenomena and the correlative behavior between them has recently been completed. Fuel porosity development was traced carefully as a function of fuel burnup. The results indicated that the porosity distributions would lead to significant changes in fuel operating temperature. Concurrent observations concerning composition redistribution indicated that the porosity development preceded significant constituent redistribution. The zirconium redistribution had been theorized to be related to the position of phase boundaries at specific locations within the thermal gradients existing in the fuel. The restructuring phenomena were analyzed in terms of how they may affect the existence of specific phases and, therefore, atomic migration.