Thermodynamic assessment of the Th–U–Pu system

AbstractThermodynamic assessments of the Th–U and Th–Pu binary systems are performed in this study according to CALPHAD method and together with the data on the U–Pu system, which has been already published in the literature, the Th–U–Pu ternary system is determined. All available experimental data from the literature were used for the binary system assessments and based on them the Gibbs energy properties of the unknown phases have been optimized. For the excess Gibbs energy of the liquid phase the ionic liquid model has been used, whereas for solid solutions the Redlich–Kister description was selected. In case of the Th–U and Th–Pu binary systems a very good agreement between the assessment and the experimental equilibrium data has been achieved, with 80% of equilibrium data reproduced within ±20K

Determination of oxygen stoichiometry of oxide fuel during high temperature vapour pressure measurement

AbstractThis study presents an original approach of oxygen stoichiometry determination during high temperature (>2000K) measurements of vapour pressure using the Knudsen effusion mass spectrometry technique. The method has been developed taking into account the vapour pressure measurements of series of (U1-x,Pux)O2-δ samples with x(Pu)=0.25, 0.5, 0.75 together with pure UO2-δ and PuO2-δ end-members coupled with equilibrium calculations based on thermodynamic assessment of the U–Pu–O system. The presented method consists of two steps; in the first step the oxygen potential of the oxide phase is determined based on the measured partial vapour pressures of UO(g), UO2(g), PuO(g) and PuO2(g) gaseous species and during the second step the thus determined oxygen potential is linked with the matching oxygen stoichiometry of the sample. From the obtained results it has been demonstrated that it is possible to accurately estimate the oxygen stoichiometry of the mixed oxide fuel samples knowing the description of the oxygen potential of the corresponding end-members only

Thermal properties of minor actinide targets

The thermal properties of minor actinide targets for the management of high level and long lived radioactive waste are investigated. The microstructure, thermal diffusivity and specific heat of (Pu,Am)O2, (Zr,Pu,Am)O2, (Zr,Y,Am)O2, (Zr,Y,Pu,Am)O2 and CERMETS with Mo matrix are characterised in order to assess the safety limits of these materials

Excess heat capacity of the (Li1?xCax)F1+x liquid solution determined by differential scanning calorimetry and drop calorimetry

The work presents the measured heat capacity of the (Li1?xCax)F1+x liquid solution. Four samples with different compositions have been prepared and measured using a Differential Scanning Calorimeter. Since this technique was newly adopted for measuring encapsulated fluoride samples, some modifications were introduced in the standard configuration of the instrument and they are described in this work as well. For comparison one of the analysed composition (xCaF2xCaF2 = 0.5) was also measured using drop calorimetry, which has been previously used for similar studies. The reliability of the results obtained was confirmed by the good agreement between the two techniques. Moreover, the excess heat capacity of the (Li1?xCax)F1+x liquid solution was derived and a strong deviation from the ideal behaviour was observed.RST/Radiation, Science and TechnologyApplied Science