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The sintering kinetics of non-stoichiometric uranium dioxide powders have been studied in the temperature range 700 to 950° C. The results of the relative linear shrinkage during the stepwise heating of samples, were analysed as a function of sintering temperature and time. It has been shown that it is impossible to explain the exceptionally large shrinkage of UO2+xcompacts in the temperature range 0.3 to 0.4 Tm by means of a single sintering mechanism.

This paper is devoted to a study of the sintering of two Y2O3 powders in the temperature range where only minor densification occurs. Two powders have been examined; one powder, Y2O3-A, was obtained by decomposition of hydroxide, because earlier examinations showed [11] that use of this powder resulted in the highest densities of samples in the sintering temperature range from 1300 to 1900° C. The second powder, Y2O3-D, was purchased externally. In order to ensure that the pores in the Y2O3-A compacts closed as late as possible, the heating rates up to the appropriate temperatures (1000 to 1400° C) were varied in the range 0.013 to 6° C sec-1. The results obtained show that the heating rate in this temperature range, for the powder obtained by decomposition of hydroxide, is of primary importance in the densification of the material, and that cessation of shrinkage was not observed in the period of 240 min.