Vapour pressure measurements of uranium carbides up to 7000 K using laser pulse heating

The laser pulse heating technique, originally developed for equation-of-state studies on UO2 and the ternary fast breeder oxide fuel (U, Pu)O2, has now been extended by additional high speed diagnostics to measurements of advanced carbide fuels, starting with UC. Vaporization studies over uranium monocarbide were performed over the temperature range from 6000 K to 8000 K. Various interaction phenomena with the laser-induced gas jet, such as optical absorption, backscattering and radial flow, were studied at laser power densities of 107W/cm2. The average vapour pressure over the monocarbide at 6757 K was found to be 10.47 MPa. The final vapour pressure equation for the temperature range from the melting point at 2780 K, assuming a composition of UCsub(1.08), up to 7000 K, was determined to be: log p=8.622-(3.286x104/T)-0.715 log T where p is in megapascals and T is in kelvin. This yields a heat of evaporation within the measured range of temperature of ΔHsub(evap) = 141 kcal.mol-1 and entropy of evaporation of ΔSsub(evap) = 67 cal.mol-1.K-1. A spectral emissivity of 0.45 at the wavelength of 6540 A was measured at the melting point of UC at 2780 K. (author)