A prediction of the thermal conductivity of UO2 vapor

An important aspect of Liquid-Metal Fast Breeder Reactor (LMFBR) safety analysis is an accurate description of the transport phenomena of the various reactor materials during a hypothetical core-disruptive accident. For the case of an accident sequence leading to fuel vaporization, the problem of energy losses by conduction, radiation, and latent heat and mass losses by condensation of the fuel vapor in the presence of cold structure and/or coolant is of particular interest since such losses will determine, to a large extent, the energetics of the fuel vapor expansion process following pin failure. In this paper, a theoretical estimate of the thermal conductivity of UO2 vapor is determined, based upon kinetic theory for a multicomponent gas. Results indicate that at elevated temperatures, the conductivity is a strong function of temperature due to thermal dissociation of the UO2 molecule, where the species concentrations are taken from calculations presented elsewhere. At 5000 K the thermal conductivity is 2.2x10-3 cal/cm-sec K, which is relatively high; thus, it should be considered in analyses of fuel vapor phenomenon. The functional relationship between conductivity and temperature can be approximated as: lambdasub(t) = exp[-39.66+1.891(-2)T-3.561(-6)T2+2.242(-10)T3], for 3000 K<=T<=5500 K. (Auth.)