Microstructural analysis and modelling of intergranular swelling of an irradiated UO2 fuel treated at high temperature

Unstressed samples of uranium oxide irradiated in pressurized water reactor (PWR) fuel to a burn-up of 25 GWd/tU were subjected to thermal treatment in a laboratory furnace at temperatures of 1130 degrees C and 1715 degrees C for durations varying between 5 min and 10 h. They were then examined and swelling was measured. Micrographic examination of the samples showed that the bubbles were lenticular in form and intergranular. The swelling measured can be explained by bubbles coalescence alone, and a model was therefore developed. This made it possible to establish an equation for the intergranular swelling of fuel after two operating cycles as a function of time and temperature. (C) 1998 Elsevier Science B.V. All rights reserved.