The projects of a new generation of nuclear plants with improved yield and drastical reduction of waste production make necessary the development of materials able to withstand high temperature (1000-1200°C) in normal conditions. New materials such as the refractory transition metal carbides are then considered. These materials have a ceramic-like, brittle behaviour. Their mechanical properties might be improved by decreasing the particles size at a nanometer level. The behaviour under irradiation of such nano-sized materials have then to be compared with classical micro-sized ones. High density, nano-sized materials have been obtained by two different sintering techniques. In order to simulate neutron irradiation, the samples were irradiated with low energy heavy ions. Consequently, the damaged material has a low thickness (100-200 nm), requiring surface analysis methods. Here, the grazing incidence X-ray diffraction method is used. From a Rietveld analysis of the diffraction patterns, the micro-sized materials show a linear volume swelling in the range 20-40 dpa in the Zr sublattice. Nano- and micro-sized materials both show high internal distortions.