Oxide fuels with controlled microstructure

The control of microstructural properties of UO2, UO2-Gd2O3, and UO2-PuO2 pellets for light water reactors and the relations of these properties to in-reactor performance aspects are discussed for four groups of properties: density/porosity, pore structure, grain structure, and oxide phase structure of the mixed oxides. According to theoretical modelling, in-reactor densification/swelling behavior mainly depends on the density and pore size distribution. The pore structure can be adapted to performance requirements by adequate methods during fuel production. The benefit of this approach has been proven by available operational experience and by postirradiation examinations. Tailoring of the grain structure allows the reduction of fission gas release and pellet/clad interaction, i.e., stress corrosion cracking of the zirconium alloy cladding. A safe and reliable operation is also attained with the mixed oxides by the control of the oxide phase structures, e.g., by avoiding thermal spiking