Computer simulation of defects formation and equilibrium in non-stoichiometric uranium dioxide

Abstract Formation and stability of different types of clusters in hyperstoichiometric UO 2+ x , including Willis’s 2:2:2 interstitial dimers as well as cuboctahedral tetra- and pentamers are investigated under static and dynamic conditions based on a partly-ionic model. A ‘Free Hopping Approximation’ for small polarons is proposed and implemented in a molecular dynamic simulation computer code. Lattice parameter and other equilibrium properties of UO 2+ x are calculated and compared with existing experimental data in a wide range of temperature and stoichiometry.

[1]  Ranninger.  Spectral properties of small-polaron systems. , 1993, Physical review. B, Condensed matter.

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

[3]  John H. Harding,et al.  The calculation of defect parameters in UO2 , 1986 .

[4]  C. Catlow,et al.  Fission gas diffusion in uranium dioxide , 1978, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[5]  C. Catlow,et al.  Point defect and electronic properties of uranium dioxide , 1977, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[6]  B. Willis,et al.  A neutron diffraction study of anion clusters in nonstoichiometric uranium dioxide , 1990 .

[7]  J. Harding,et al.  Small-polaron hopping in Mott-insulating UO2 , 1994 .

[8]  B. Willis,et al.  Refinement of the structure of β-U4O9 , 2004 .

[9]  N. F. Mott,et al.  Conduction in polar crystals. I. Electrolytic conduction in solid salts , 1938 .

[10]  H. Ullmann,et al.  Investigation of the oxygen activity of oxide fuels and fuel-fission product systems by solid electrolyte techniques. Part I: Qualification and limitations of the method , 1983 .

[11]  K. Idemitsu,et al.  Evaluation of thermal conductivity of hypostoichiometric (U, Pu)O2−x solid solution by molecular dynamics simulation at temperatures up to 2000 K , 2006 .

[12]  C. Ronchi,et al.  An efficient method for computation of long-ranged Coulomb forces in computer simulation of ionic fluids , 2003 .

[13]  B. Belbeoch,et al.  Changements de structure de l'oxyde U4O9 , 1967 .

[14]  Michel Freyss,et al.  Point defects in uranium dioxide: Ab initio pseudopotential approach in the generalized gradient approximation , 2005 .

[15]  Claudio Ronchi,et al.  Molecular dynamics simulation of premelting and melting phase transitions in stoichiometric uranium dioxide. , 2007, The Journal of chemical physics.

[16]  D. J. M. Bevan,et al.  The crystal structure of -U4O9-y , 1986 .

[17]  S. Vogel,et al.  Kinetics of precipitation of U4O9 from hyperstoichiometric UO2+x , 2007 .

[18]  F. Grønvold,et al.  High-temperature X-ray study of uranium oxides in the UO2U3O8 region , 1955 .

[19]  B. Willis.  Positions of the Oxygen Atoms in UO2.13 , 1963, Nature.

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

[21]  C. Ronchi,et al.  Electron diffraction of U4O9 , 1968 .

[22]  C. Alcock,et al.  Thermodynamic Properties of Individual Substances , 1994 .

[23]  G. C. Allen,et al.  Ordered defects in the oxides of uranium , 1986, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.