VAPORIZATION THERMODYNAMICS OF URANIA-NEODYMIA MIXED OXIDES

Langmuir vaporization mass spectrometry and inductively-coupled-plasma mass spectrometry were used to investigate the thermodynamic function s of the solid solution UyNd1-yO2+/-x. The major metal-bearing vapor s pecies observed were UO2(g), UO3(g) and NdO(g). The system was treated as a pseudo-binary regular solution of urania and neodymia. The inter action parameter obtained from the ion-intensity-ratio method is -27 /- 4 kJ/mol. Extension of a defect-cluster oxygen potential model of t his mixed oxide to include vaporization was also investigated. Results obtained from the solution thermodynamics model agreed well with thos e from the defect equilibria model. Two numerical examples are present ed to demonstrate practical application of the results obtained.