Re-sintering behavior of UO2+5wt%CeO2 sintered pellet

UO2+5wt%CeO2 sintered pellets were fabricated following oxidative sintering process at 1300∼1600 .deg. C in oxidizing atmosphere for 5h, then reduced them at 800∼1450 .deg. C in 7H2+93N2 for 2h. The sintered pellets were re-sintered at 1700 .deg. C in reducing atmosphere for 24h to check the thermal stability of the pellets. The density of the re-sintered pellets was decreased as the reducing temperature was low in oxidative sintering process. The density of pellet, of which O/M ratio was 2.116, was decreased up to 1.4% and the grain size was increased from about 7μm to 30μm after re-sintering. The density difference re-sintered in helium atmosphere was less than the case re-sintered in reducing atmosphere. While in case of the pellets which were re-sintered at 1600 .deg. C in CO2 for 24h and then reduced at 1200 .deg. C in 7H2+93N2, the density decreased and the grain grew up to 24μm but the average pore size decreased a little. The density decrease after re-sintering is thought mainly due to the increase of lattice parameter, that occurs by the reduction of hyperstoichiometric U0.924Ce0.076O2+x to hypostoichiometric U0.924Ce0.076O2-x, and not due to the solarization