Characterisation and fabrication of zirconia and thoria based ceramics for nuclear applications

The reduction of the long term radiotoxicity of nuclear waste during disposal is the aim of the research called “Partitioning & Transmutation of minor actinides (MAs)”, which also requires the development of inert ceramic support materials. Moreover, after separation, if the transmutation is not available, the actinides can be conditioned into stable dedicated solid matrices (Partitioning & Conditioning strategy). Yttrium-stabilized zirconia and thoria are discussed in the international nuclear community as candidates for the fixation of long-lived actinides as target material for transmutation and as stable materials for long-term final disposal.The aims of the following work are twofold: determine the impact of the addition of actinides, simulated by cerium on the properties of the matrices and study the possibility of synthesising homogeneous ceramics using simple fabrication routes. Within this framework, (Zr,Y)O2-x - CeO2 and ThO2 - CeO2 powders with variable ceria contents (from 0 to 100%) were synthesised by a co-precipitation method of nitrate solution. The influence of ceria concentration on the powder' properties, such as thermal behaviour and the evolution of material crystallisation during annealing, was investigated in detail by thermogravimetry (TG) coupled with differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Both systems crystallise at high temperature in a stable solid solution, fcc, fluorite type structure and follow the Vegard’s law for the complete range of ceria. For both systems a critical concentration of 20 mol% has been established. For ceria concentrations lower than 20%, the properties of the system are mainly controlled by the matrix. Pellets with different ceria concentrations were compacted from these powders by using different technological cycles. In order to obtain materials with reliable properties, the technological parameters of each chosen fabrication route, have been optimised. By employing mild wet methods (calcination at 600°C, wet-grinding in ...