MICROSTRUCTURAL ANALYSIS AND MODELING OF INTERGRANULAR SWELLING OF ANIRRADIATED UO2 FUEL TREATED AT HIGH-TEMPERATURE

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