Melting of Stoichiometric and Hyperstoichiometric Uranium Dioxide

Abstract The solid–liquid transition in stoichiometric and hyperstoichiometric UO 2 was investigated by means of advanced techniques. Laser heating enabling fast melting and freezing processes was used under container-less conditions and buffer gas pressures up to 250 MPa, making non-congruent evaporation ineffective. Pulse thermograms of UO 2+ x with 0 ⩽  x  ⩽ 0.21 were recorded with fast pyrometers and interpreted with computer simulations. In addition, a novel method for identification of phase transitions was implemented, based on the detection of surface reflectivity variations. The melting line of UO 2.00 was for the first time determined at pressures between 10 and 250 MPa, and the melting temperature of the stoichiometric oxide was measured to be 3147 ± 20 K, in fair agreement to previous measurements reported in the literature. The liquidus and solidus lines of UO 2+ x differ from the currently recommended data, which substantially underrate the effect of oxygen on melting.

[1]  Christine Guéneau,et al.  Thermodynamic assessment of the uranium–oxygen system , 2002 .

[2]  M. J. Bannister,et al.  Melting temperatures in the system uranium — Uranium dioxide☆ , 1967 .

[3]  W. E. Baily,et al.  The solid-liquid phase diagram for the UO2-PuO2 system☆ , 1967 .

[4]  Theodore M. Besmann,et al.  Chemical thermodynamic representation of , 1985 .

[5]  J. Pelsmaekers,et al.  On the phase limits of U4O9 , 1970 .

[6]  D. Manara,et al.  Solidus and liquidus of UO2+x from high-pressure melting experiments , 2003 .

[7]  C. Ronchi,et al.  Equation of State of Uranium Dioxide , 2004 .

[8]  W. Breitung.  Oxygen self and chemical diffusion coefficients in UO2±x , 1978 .

[9]  R. E. Latta,et al.  Determination of solidus-liquidus temperatures in the uo2 + x system (−0.50 , 1970 .

[10]  A. J. Walter,et al.  Equilibrium pressures and phase relations in the uranium oxide system , 1961 .

[11]  Saito Yasutoshi.  Nonstoichiometry in uranium dioxide , 1974 .

[12]  K. Wagner,et al.  Bestimmung der optischen konstanten von geschmolzenen kernbrennstoffen , 1984 .

[13]  J. K. Fink,et al.  Thermophysical properties of uranium dioxide , 2000 .

[14]  C. Ronchi,et al.  Thermal Conductivity of Uranium Dioxide up to 2900 K from Simultaneous Measurement of the Heat Capacity and Thermal Diffusivity. , 1999 .

[15]  Toshimichi Tachibana,et al.  Determination of Melting Point of Mixed-Oxide Fuel Irradiated in Fast Breeder Reactor , 1985 .

[16]  A. Nakamura,et al.  Thermodynamic study of UO2 +x by solid state emf technique , 1987 .

[17]  B. Schaner.  Metallographic determination of the UO2-U409 phase diagram , 1960 .

[18]  M. Hoch,et al.  The system U-UO3: Phase diagram and oxygen potential , 1986 .

[19]  Y. Kim.  Evolution of Near-Surface Elemental Composition Profile and Its Effect on Thermal Diffusivity , 2002 .

[20]  B. Cheynet,et al.  Progress in the thermodynamic modelling of the O–U binary system , 2002 .

[21]  G. Petot-ervas,et al.  Chemical diffusion in uranium dioxide: influence of defect interactions , 2004 .