Thermodynamics and Phase Relationships for Plutonium Oxides

A compilation of available fundamental information concerning plutonium oxides. Methods of preparation, thermodynamic data, phase relationships, crystal structures, and some information on mixed oxide systems are considered. A bibliography is included. Methods of preparing PuO/sup 2/ by the peroxide and the oxalate processes and of lower oxides by thc reduction of PuO/sub 2/ are described and some chemical properties of plutonium oxides of interest in processing certain fuel elements are given. Thc fabrication of PuO/sub 2/ into discs is discussed. Measurements of heats of combustion a Pu, and Pu/sub 2/O/sub 3/ are described and the heats of formation of lower oxides and PuO/sub 2/ are given. Free energy data obtained by combining estimated entropies with the measured heats of formation are tabulated for the oxides. A tentative phase diagram for thc Pu-O system is presented which includes thc limiting solubility of oxygen in liquid plutonium, the ranges of stability of the three known oxide phases, hexagonal Pu/sub 2/O/sub 3/, a cubic oxide inaccurately designated as ''cubic Pu/sub 2/O/sub 3/'' and PuO/sub 2/, and some melting point data. (The crystal structures of the plutonium oxides have already been described in the literature and this will be reviewed. ) Crus tal structure data and methods of preparation for the PuO/sub 2/-UO/sub 2/, PuO/sub 2/-ThO/sub 2/, and PuO/sub 2/- CeO/sub 2/ solid solutions are described. (auth