ABSTRACT

The enthalpies of formation of cubic urania thoria (c-ThxU1 xO2+y) and urania zirconia (c-ZrxU1 xO2, x less than 0.3) solid solutions at 25 C from end-member binary oxides (c-UO2, and c-ThO2 or m-ZrO2) have been measured by high temperature oxide melt solution calorimetry. The enthalpies of mixing for both systems are zero within experimental error. The interaction parameters for binary solid solutions MO2 M0O2 (M, M0 = U, Th, Ce, Zr, and Hf), fitted by regular and subregular thermodynamic models using both calorimetric and computational data, increase linearly with the corresponding volume mismatch. Cubic UO2 ZrO2 appears to be an exception to this correlation and shows a zero heat of mixing despite large size mismatch, suggestive of some short-range ordering and/or incipient phase separation to mitigate the strain. The incorporation of ZrO2 into UO2 stabilizes the system and makes it a potential candidate for immobilization and disposal of nuclear waste.

Compounds

#	Formula	Name
1	O2Th	thorium dioxide
2	O2U	uranium dioxide
3	O3U	uranium(VI) oxide
4	O2Zr	zirconium oxide

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Constraint	Phase	Method	#Points
POMD	1 2 3	Mass density, kg/m3 ; Crystal	Mole fraction - 1; Crystal Mole fraction - 3; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	X-ray diffraction	6
POMD	1 2 3	Excess molar enthalpy (molar enthalpy of mixing), kJ/mol ; Crystal	Mole fraction - 1; Crystal Mole fraction - 3; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	Calvet calorimetry	6
POMD	4 2	Mass density, kg/m3 ; Crystal	Mole fraction - 4; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	X-ray diffraction	3
POMD	4 2	Excess molar enthalpy (molar enthalpy of mixing), kJ/mol ; Crystal	Mole fraction - 4; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	Calvet calorimetry	3
POMD	1 2	Mass density, kg/m3 ; Crystal	Mole fraction - 1; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	X-ray diffraction	3
POMD	1 2	Excess molar enthalpy (molar enthalpy of mixing), kJ/mol ; Crystal	Mole fraction - 1; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal	Crystal	Calvet calorimetry	3

Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Thermochemistry of UO2 - ThO2 and UO2 - ZrO2 fluorite solid solutions

Zhang, L.[Lei], Shelyug, A.[Anna], Navrotsky, A.[Alexandra]

ABSTRACT