Thermophysical and thermochemical properties of U-23wt.%Pu-6wt.%Zr alloy fuel: Computational and high temperature mass spectrometric studies

Abstract Vaporisation studies were carried out over the liquid region of U-23wt.%Pu-6wt.%Zr (U0.65Pu0.21Zr0.14) alloy, which is proposed to be used as a fuel in future fast breeder test reactor, in the temperature range 1487–1641 K using Knudsen Effusion Mass Spectrometry (KEMS). Pu(g) was found to be the species observed in vapour phase over this alloy. Measurements on temperature dependence of partial pressures of Pu(g) yielded the pressure-temperature (p-T) relation: log(pPu(g)/Pa) = (−20336 ± 208)/T + (10.08 ± 0.13). Subsequently, the apparent enthalpy of vaporisation of Pu(g) at 1564 K was deduced by second law method. From the measured KEMS data, activity and activity coefficient data of Pu were derived. These data were also obtained by computation using known Gibbs energy functions of U-Pu-Zr ternary system using CALPHAD method. Vaporisation studies on this alloy have been carried out for the first time. Also, fractions of various phases present in U-19Pu-6Zr and U-23Pu-6Zr fuel compositions were calculated and a comparison is made between the phase fractions and overall thermal conductivity.