EQUILIBRIUM OXYGEN PARTIAL-PRESSURE AND PHASE-DIAGRAM OF THE URANIUM OXYGEN SYSTEM IN THE COMPOSITION RANGE 2.61-LESS-THAN-O U-LESS-THAN-2.67 BETWEEN 844-K AND 1371-K

The equilibrium partial pressure of oxygen has been determined in the composition range 2. 61 less than O/U less than 2. 67. The nearly stoichiometric phase U//3O//8// plus or minus //z has been confirmed together with a nonstoichiometric U//8O//2//1// plus or minus //x phase which is stable in the range 2. 617 less than O/U less than 2. 655. Hysteresis has been observed in the P//O//2 versus O/U ratio. The partial molar enthalpy and entropy of solution of oxygen in the U//8O//2//1// plus or minus //x phase have also been evaluated.