Pore growth in sintered UO2

The density of UO2 pellets decreases with sintering time during the sintering at 1500 C for 0.1 to 40 h in CO2 and H2-CO2 atmospheres. The density decrease is caused by pore growth. The microsctructure developed in CO2 atmosphere has many intragranular pores, which are mostly annihilated for further sintering, while intergranular pores grow significantly. The coalescence of intergranular pores occurs considerably even under negligible grain growth. In the unifrom grain structure developed in H2-CO2 atmosphere, the average pore size is proportional 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. (orig.)