The configurational entropy of defect complexes in UOsub(2 + x)

The configurational entropy for idealised models of the 2:1:2, 2:2:2, and 4:3:2 defect complexes and their mixtures in UOsub(2+x) was calculated by methods based on Mayer cluster theory. Comparison with measured thermodynamic properties suggested that a satisfactory model of the system must include both partial ionisation of the complexes to give free holes and the association equilibrium between smaller and larger complexes. Such a model based on a doubly ionised 2:2:2 and 4:3:2 complexes was moderately satisfactory in the range accessible to the present calculations. (author)