Lattice thermodynamic behavior in nuclear fuel ThO2 from first principles

Abstract

Using first-principle calculations and combining with the phonon Boltzmann transport equation, we have systematically investigated the lattice thermodynamic behavior in thorium dioxide (ThO2) and predicted the lattice thermal conductivity of thorium dioxide from 300 K up to 2000 K. According to the calculated phonon dispersion curves, phonon group velocity, relaxation time, Grüneisen parameters and weighted phase space, the contributions of acoustic and optical phonon branches to the lattice thermal conductivity are estimated. From further analyses, we know that although the phase space of three-phonon process (PW3) of acoustic phonon is large at low frequency, which is different from that of ordinary materials, the valley value appears at 3 THz, resulting in the whole thermal resistance is not too high. So acoustic phonon transports lead to the dominant contributions of the lattice thermal conductivity, while the contributions from optical components is small. Our analyses can make a significance to understand the thermodynamic behaviors of this new type of nuclear fuel dioxide at different temperatures. In addition, by means of the phonon mean-free path and nanowires width, we also studied the size dependence of the lattice thermal conductivity in ThO2.