Chemical diffusion coefficient of oxygen in thoria-urania mixed oxide

The chemical diffusion coefficients of oxygen (D tilde) in sintered samples of (Thsub(1-y)Usub(y))Osub(2+x) (y=0.2 and 0.4) were measured by means of thermogravimetry in the temperature range 1282<=T<=1373 K. The defect diffusion coefficients (Dsub(d)) were also calculated from the chemical diffusion coefficients obtained in this study. The activation energies of D tilde or Dsub(d) for the two samples (Thsub(1-y)Usub(y))Osub(2+x) with y=0.2 and 0.4 were observed to be nearly the same, irrespective of the y value. These activation energies also nearly coincided with those of UOsub(2+x) reported previously, suggesting the presence of a similar diffusion mechanism to that found in UOsub(2+x). The magnitude of both diffusion coefficients D tilde and Dsub(d) of (Thsub(1-y)Usub(y))Osub(2+x) with y value was considered to be due to the increase of both the vibrational frequency of lattice and the entropy change of migration produced by the substitution of a U ion for a Th ion. (orig.)