Microstructure of as atomized and annealed U-Mo7 particles: A SEM/EBSD study of grain growth

International audienceSignificant progresses in the performances under in-pile irradiation of particular U-Mo based fuels have been observed in last fifteen years. A last issue has still to be tackled for use as a LEU fuel in the high power research reactors the U-Mo recrystallization and its associated swelling at high burn-up have to be controlled or delayed. One way to mitigate this problem would be to optimise the initial microstructure of U-Mo atomised particle, by homogenizing Mo concentration and increasing grain size. This paper mainly focuses on U-Mo grain growth. Based on samples prepared in the frame of KOMO-5 and EMPIrE tests, a methodological work based on the use of EBSD is presented. In particular, surface preparation procedures are proposed for powders and rods, this last one being most likely readily applicable for plate analysis. As-atomised microstructures are analysed in details and subsequently compared to those obtained on particles annealed at 1000 DC under various conditions. It is found that 1 hour annealing under vacuum is a good compromise to meet the development goals, provided that few impurity precipitates are present within U-Mo particles, since they can impact grain growth