EQUILIBRIUM OXYGEN PARTIAL PRFSSURE AND PHASE DIAGRAM OF THE URANIUM-OXYGEN SYSTEM IN THE COMPOSITION RANGE 2.61-e O/U < 2.67 BETWEEN 844 AND 1371 K

A. CANEIRO; J.P. ABRIATA

JOURNAL OF NUCLEAR MATERIALS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1984 vol. 126 p. 255 - 267

0022-3115

The equilibrium partial pressure of oxygen in the ura~um-oxygen system has been determined by a thermo~a~met~ctectique in the composition range 2.61 i O/U < 2.67 and for temperatures between 800 and 1400 K. The nature of theuranium-oxygen phase diagram in this composition and temperature range has been established from the results obtainedThe nearly stoichiometric phase U,Os * I has been confirmed to exist in the U-O system, together with a nonstoichiometricuo s 2, fx phase which is stable in the range 2.617 -z O/U -C 2.655. The high precision of the experimental set up has permittedthe determination of the narrow two phase region (U,O,_, + UsO,, +,) with small errors.A hysteresis has been observed in the Ro, versus O/U ratio. The corresponding metastable states could have been obtainedonly upon oxidation of the U s 0 2tfx phase. These metastable states have been observed to depend on sample morphology.The partial molar enthalpy and entropy of solution of oxygen in the UsO,, fx phase have also been evaluated.