Effects of Granulation Process Parameters on Properties of MOX Fuel Powder

On the purpose of reducing dust dispersion, improving the flowability of MOX mixed powder and decreasing the production scrap rate, the Al2O3 powder is used to study the influence rule of rolling pressure, granulation cycles, roll gap, and spheroidization time on the MOX fuel powder's bulk packing density and granulation rate. The dry-granulation integrated technology of MOX fuel powder is systematically studied through metallographic microscopy, scanning electron microscopy and screening analysis methods. The results show that with the rolling pressure increases from 2 kN?cm-1 to 18 kN?cm-1, the loose density of the powder gradually increases from 0.752±0.002 g?cm-3 to 0.813±0.002 g?cm-3, and the granulation rate shows a trend of increasing first and then decreasing, with a peak of 87.5±0.3 wt.%. The number of crack defects inside the particles increases significantly when the pressure exceeds 10 kN?cm-1. When the number of granulation times increased from 1 to 6 times, the loose density of the powder continued to rise, but the granulation rate showed the characteristics of rising first and stabilizing. The experimental data showes that after 4 times of granulations, the proportion of powders above 150 mesh reachs 84.1±0.15 wt.%, but after 6 times of granulations, it only rise to 84.5±0.12 wt.%, indicating that the granulation process tend to be stable after 4 times of granulation. The increase of the roll gap causes the loose density to rise first and then fall, with a peak value of 0.738±0.002 g?cm-3, meanwhile, the granulation rate continues to decline. As the mixing spheroidization time extends, the loose density of the powder gradually increases and tends to be stable, the powder particles shape also change from irregular to spherical. To sum up, the pherical particles with high loose density (0.815±0.004 g?cm-3) can be stably obtained when the dry granulation process parameters are comprehensively regulated: the rolling pressure should be ≤10 kN?cm-1 to suppress particle cracks; the effective granulation rate saturates at 4 times; the roll gap size is best to be within 1 mm-2 mm; the optimal spheroidization time is 2 hours. It can effectively improving the compression and filling performance of MOX fuel powder, and providing a key technical support for the engineering application of MOX fuel.