Origin of Low Thermal Conductivity in Nuclear Fuels

TL;DR

This study uses a new many-body method to analyze the lattice dynamics of UO2 and PuO2, revealing that only certain acoustic phonons effectively conduct heat, while optical modes do not due to anharmonicity, informing potential improvements.

Contribution

Introduces a novel many-body approach to understand phonon contributions to thermal conductivity in nuclear fuels UO2 and PuO2.

Findings

Longitudinal acoustic phonons are primary heat carriers.

Optical phonons with large velocities do not contribute to heat transfer.

Strategies for enhancing thermal conductivity are discussed.

Abstract

Using a novel many-body approach, we report lattice dynamical properties of UO2 and PuO2 and uncover various contributions to their thermal conductivities. Via calculated Grueneisen constants, we show that only longitudinal acoustic modes having large phonon group velocities are efficient heat carriers. Despite the fact that some optical modes also show their velocities which are extremely large, they do not participate in the heat transfer due to their unusual anharmonicity. Ways to improve thermal conductivity in these materials are discussed.