Synthesis and characterization of nanocrystalline UO2 ceramics

High-performance ceramics with nanosized grains provide today the technical base for a large variety of improved applications in many technologies. This type of microstructure is of special interest as well in the nuclear field as it appears at the periphery of light water reactor (LWR) UO2 fuels at high burn-up (BU), where the material transforms spontaneously to a closed porous nanocrystalline nc-structure after surpassing a critical dose. The mechanical properties of this newly formed material are superior to those of the fresh fuel due to the nanostructure. Taking this into account, the aim of this work is to develop a fuel consisting of nc-UO2, which, besides the advantages of enhanced plasticity and faster creep, characteristic of the nc-state, which diminish the pellet clad interaction (PCI) stresses and cladding failure risks, has also the potentiality to develop closed porosity under irradiation, to largely retain fission gases. The study of its behaviour is therefore important, especially during accident conditions under which large amounts of radioactive fission products could be released into the reactor vessel, or to the exterior if the core containment breaks. Its potentiality for retention of fission gas and its improved mechanical properties and resistance to radiation-damage make so the nc-fuel material worthy of deep experimental analysis