In the present studies, the thermal behaviour of NaUO2BO3 has been investigated. This compound is a potential product of interaction between the coolant (Na), control rods (B4C), and the oxide fuel, which could form under accidental conditions in sodium-cooled fast reactors. The thermal expansion, the heat capacity, and thermal diffusivity of NaUO2BO3 have been measured. The thermal conductivity of the material is derived from these results and presented here for the first time.

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Heat capacity, thermal expansion, and thermal diffusivity of NaUO2BO3

Physicochemical investigation and thermodynamics of oxide compounds of uranium and phase for immobilization of radionuclides

The standard enthalpy of formation of crystalline NaBUO 5 at 298.15 K (-2257.5 ′ 4.0 kJ/mol) was determined by reaction calorimetry. The heat capacity of the substance in the temperature range 10-300 K was studied by adiabatic vacuum calorimetry. The thermodynamic functions of the compound were calculated. The standard entropy and the Gibbs function of formation of sodium uranoborate at 298.15 K were found to be -452.7 ′ 2.1 J/(mol K) and -2122.5 ′ 4.5 kJ/mol, respectively. The standard thermodynamic functions of synthesis and thermal decomposition of sodium uranoborate were calculated and analyzed.

The thermodynamic properties of sodium uranoborate

Standard enthalpies of formation of uranovanadates of 3(4)d transition metals at 298.15 K were determined. The isobaric heat capacity of Co(VUO6)2 · 4H2O was measured. The standard Gibbs functions of formation of the compounds were calculated on the basis of these data using approximate methods of absolute entropy calculation. The thermochemical characteristics of the synthesis and dehydration of uranovanadates were considered.

Thermochemistry of AII(VUO6)2 .nH2O compounds (aII = Mn, Fe, Co, Ni, Cu, Zn, Cd)

The standard enthalpies of formartion of crystalline α-RbNbUO6, β-RbNbUO6, and RbNbUO6·H2O at 298.15 K were determined. The temperature dependence of the heat capacity of α-RbNbUO6, RbNbUO6·H2O, and β-RbNbUO6 was studied in the range 60-300 K. The thermodynamic functions and equilibrium constants of the reactions involved in synthesis of rubidium uranoniobates at various temperatures were calculated.

O. V. Feoktistova

Papers

The thermodynamic properties of sodium uranoborate

Thermochemistry of AII(VUO6)2 .nH2O compounds (aII = Mn, Fe, Co, Ni, Cu, Zn, Cd)

Thermodynamics of Rubidium Uranoniobate