Thermal conductivity of actinide compounds

Abstract

Thorium is beginning to attract attention because of its potential use as a nuclear fuel. It is not easy to carry out experiments because of its radioactive nature, and therefore theoretical works are highly appreciated. Thorium contains only a small number of the 5f states. It is generally accepted that these states are itinerant, that they form a chemical bond, and their nature does not need to be corrected with the Hubbard model. On the other hand, there is a well-known problem with the description of the 6p1/2 states when the spin-orbit coupling is added as the perturbation to a scalar-relativistic calculation. Electronic, elastic, and phonon properties are analyzed in terms of the importance of the spin-orbit coupling acting on the 6p, 6d, and 5f states. The same properties are analyzed for thorium monocarbide, and a difference caused by adding a carbon atom into the structure is discussed. Detailed analysis of the thermal conductivity (both phonon and electronic contributions) is also included. The extra attention is paid to the thermal conductivity of ThC explaining why the optical phonon modes account only for approximately 6 % of the phonon thermal conductivity. The existence of grain boundary and point defects on the phonon thermal conductivity is also discussed.