Characteristics and Sinterability of MOX Powder Prepared by the Microwave Heating Denitration Method

The characteristics and sinterability of UO₂-PuO₂ mixed oxide (MH-MOX) powder prepared by the microwave heating denitration method were measured and compared with those of UO₂ (ADU-UO₂) powder prepared by the ADU method. Furthermore, the degree of surface roughness and flowability of MH-MOX powder were evaluated and also compared with those of ADU-UO₂ powder. The degree of surface roughness of ADU-UO₂ powder calcined at temperatures >700°C significantly decreased, and its sintered density also dropped below 80% theoretical density. However, the degree of surface roughness and sinterability of MH-MOX powder calcined at 950°C were higher than those of ADU-UO₂ powder. These results could be understood using the concept of Hüttig and Tamman temperatures, which is commonly cited for ceramic materials. The flowabilities of MH-MOX and ADU-UO₂ powders decreased with an increase of compressibility, and they were categorized as non-free-flowing according to Carr's theory on powder flowability. It is, therefore, necessary for the mixed powder of MH-MOX powder, ADU-UO₂ powder, and dry recycled MOX scrap powder to be granulated to provide a free-flowing feed to the pelletizing press in the MOX pellet fabrication process.