Dilatometric study of a co-converted (U,Am)O2 powder

A possible option to reduce the radiotoxicity of nuclear waste is to transmute minor actinides and notably americium into lighter short-lived elements in fast neutron reactors of fourth generation. It consists in irradiating uranium-americium mixed-oxide compounds named AmBB (Americium-Bearing Blankets) and located at the reactor core periphery. Among the processes developed to fabricate AmBB, a chemical synthesis route was investigated. Dense samples were achieved using a simplified pelletizing-sintering process from oxalate co-converted powder. This work focuses on the identification and comprehension of the steps occurring during the sintering of these co-converted (U,Am)O2 powders. To discriminate the different phenomena observed by dilatometric measurements, different experimental techniques were performed. It allowed identifying that the sintering of the finest particles occurred in the [1000-1350 K] range while the elimination of porosity and sintering of (U,Am)O2 larger grains is realized in the [1400-1900 K] range with an apparent activation energy of 430 kJ.mol−1.