PORE GROWTH IN SINTERED UO2

The density of UO2 pellets decreases with sintering time during the si ntering at 1500-degrees-C for 0.1 to 40 h in CO2 and H-2-CO2 atmospher es. The density decrease is caused by pore growth. The microstructure developed in CO2 atmosphere has many intragranular pores, which are mo stly annihilated for further sintering, while intergranular pores grow significantly. The coalescence of intergranular pores occurs consider ably even under negligible grain growth. In the uniform grain structur e developed in H-2-CO2 atmosphere, the average pore size is proportion al to the grain size as long as grain growth proceeds. The mechanisms of pore growth are discussed on the basis of the pore coalescence due to grain growth and the interlinkage of pores.