Microstructure Changes in a high burn up Spent Fuel (57,900 MWd/tU)

In the nuclear industry, an increase in the burn up and the residence time of fuels is being considered because of the advantages in the fuel cycle cost and the spent fuel management. But, it leads to structural changes in an outer zone (rim) of a UO2 pellet within a few hundreds of micrometers in thickness. Despite its thin layer, this rim would determine the thermal behavior of a fuel. Therefore, to identify a rim zone effect, the microstructures such as the pores, the grains and the UO2 lattice size have been investigated by many researchers. In this study, the microstructure changes in the rim of a UO2 spent fuel, the corrosion layer of a Zry-4 cladding and the interface between a fuel and a cladding were investigated by a micro-XRD and a SEM