Oxygen activity changes in oxide fuels

The IAEA Advisory Group meeting is briefly reviewed and summary of the presentations is given made by thirteen scientists representing six countries and two international organizations. Data available for various oxide fuel materials were critically reviewed and a number of recommendations formulated for additional measurements and theoretical studies. These recommendations addressed the most serious gaps in present knowledge of oxygen activity - composition - temperature relationships for various fuel types, the influence of fission products and/or chemical interactions in these relationships, component redistribution under the influence of temperature gradients, and several important thermochemical/thermophysical properties. Although the primary emphasis was on mixed urania-plutonia solid solutions at typical fuel compositions and operating temperatures (1000-2250 K), specific recommendations were also developed for the higher temperatures appropriate to safety studies, for compositions that represent fast reactor blanket/breeder materials, and for certain alternative fuel types. Conditions for the required measurements were generally defined, but not experimental techniques. A general recommendation was also formulated that the IAEA should sponsor a basic thermodynamic data programme for multinary systems to support technological efforts aimed at understanding the thermodynamics of irradiated oxide fuel systems.