Studies on sintering kinetics of ThO2-UO2 pellets using master sintering curve approach

Three different compositions of thoria-urania pellets, namely, ThO2-4%UO2, ThO2-10%UO2 and ThO2-20%UO2 (all compositions are in wt% containing natural uranium) were fabricated by Coated Agglomerate Pelletization (CAP) process. The compositions studied in the current paper are the proposed fuels for the forthcoming Indian Advanced Heavy water Reactor (AHWR) and its variant based on low enriched uranium. Sintering kinetics of ThO2-x%UO2 (x = 4, 10, 20) green pellets, thus fabricated, were evaluated using constant heating rate experiments in a vertical dilatometer. Activation energies of sintering (Q) were estimated using Arrhenius plot as proposed by Wang and Raj. Master Sintering Curves (MSC) for the above three compositions were constructed using shrinkage data. A FORTRAN program, employing optimization based numerical algorithm for fitting relative density vs. work of sintering data with sigmoid function, was used for this purpose. The apparent activation energies, evaluated using MSC principle, appear to be consistent with the values obtained by Arrhenius plot.