Zirconium carbide is a refractory material, with a very high melting temperature, good thermochemical stability, high hardness, a rather low cross section for thermal neutrons capture and a high retention rate of the nuclear fission products. These properties are critical for the use of ZrC thin films for nuclear fuel encapsulation applications in very high temperature gas cooled nuclear reactors using tri-structural isotropic coated particles (TRISO). There are many unknowns regarding such complex and demanding applications. The investigations to solve them were hampered by the lack of suitable quality ZrC films. We obtained using the pulsed laser deposition technique some of the best quality ZrC films reported so far: nanohardness higher than 40 GPa, density above 97% of the bulk value, surface roughness below 1 nm (rms), good crystallinity and oxygen content below 1.5%. These ZrC films are ideal to perform investigations about the diffusion coefficients of Pd and Ag, chemical interactions with nuclear fission products, the energetics of defects formation, diffusion and clustering during irradiation, the influence of defects and understoichiometry (loss of C) on the microstructure, thermochemical and mechanical properties, the interaction with H and Xe. Three groups from the University of Florida, University of Nevada Las Vegas and CEA Orsay will join forces with us to tackle these complex and multidisciplinary problems.


Fig. 1 TEM micrographs showing the structure of TiN/ZrC multilayer structure	Fig. 2 Cross-sectional TEM image of the area of a TiN/ZrC multilayer sample after 100-pass wear test from diamond-tipped nanoindenter at 18.2 Gpa