This International Standard describes the ceramographic preparation of uranium dioxide (UO2) sintered pellets for qualitative and quantitative microstructure examinations. These examinations may be carried out before and after thermal or chemical etching. They enable * — observations of fissures, inter- or intra-granular pores and inclusions, * — measurement of pore and grain size and measurement of pore and grain size distributions. The measurement of average grain size may be carried out using a classical counting method as described in ISO 2624 or ASTM E112, i.e. intercept procedure, comparison with standard grids or reference photographs. The measurement of pore-size distributions is usually carried out by an automatic image analyser. If the grain-size distributions are also measured with an image analyser, it is recommended that thermal etching be used to reveal the grain structure uniformly throughout the whole sample.