A MOLECULAR-DYNAMICS STUDY OF THE THERMAL-CONDUCTIVITY OF CAF2 AND UO2

Previous experimental work has revealed an anomalous increase of thermal conductivity lambda in solid UO2 above about 2000 K, which has been attributed to the effect of electronic excitations. The present molecular dynamics simulations of UO2 and the closely related material CaF2 are designed to test this explanation by providing quantitative results for the temperature dependence of lambda in the absence of electronic excitations. The simulation results for lambda, obtained by the Green-Kubo technique, are in fair agreement with the (limited) experimental results for CaF2. For UO2, close agreement with experiment exists for T < 2000 K, but there is a large discrepancy for higher temperatures. This confirms the existence of an additional heat conduction mechanism in UO2 at high temperatures.