The grain-size effect on thermal conductivity of uranium dioxide

K. Shrestha,M. Sessim,K. Gofryk,J. Lian,D. Antonio,M. R. Tonks,T. Yao

doi:10.1063/1.5116372

Abstract

We have investigated the grain-boundary scattering effect on the thermal transport behavior of uranium dioxide (UO2). The polycrystalline samples having different grain-sizes (0.125, 1.8, and 7.2μm) have been prepared by a spark plasma sintering technique and characterized by x-ray powder diffraction, scanning electron microscope, and Raman spectroscopy. The thermal transport properties (the thermal conductivity and thermoelectric power) have been measured in the temperature range of 2–300 K, and the results were analyzed in terms of various physical parameters contributing to thermal conductivity in these materials in relation to grain-size. We show that thermal conductivity decreases systematically with lowering grain-size in the temperatures below 30 K, where the boundary scattering dominates the thermal transport. At higher temperatures, more scattering processes are involved in the heat transport in these materials, making the analysis difficult. We determined the grain-boundary Kapitza resistance that would result in the observed increase in thermal conductivity with grain-size and compared the value with Kapitza resistances calculated for UO2 using molecular dynamics from the literature.

Highlights

Uranium dioxide is one of the most studied actinide materials, as it is used as the primary fuel in the commercial nuclear reactors.[1,2,3] There are around 500 active nuclear reactors, producing more than 15% of the total electricity worldwide
The samples have been characterized by x-ray powder diffraction (XRD), scanning electron microscope (SEM), and Raman spectroscopy
By performing low-temperature thermal conductivity measurements, we have studied the grain-boundary scattering related to grain-size and its impact on the thermal conductivity in these materials

Summary

INTRODUCTION

Uranium dioxide is one of the most studied actinide materials, as it is used as the primary fuel in the commercial nuclear reactors.[1,2,3] There are around 500 active nuclear reactors, producing more than 15% of the total electricity worldwide. The heat transport mechanism, i.e., thermal conductivity, of the fuel material is an important parameter for fuel performance, regarding its efficiency and safety. Umklapp phononphonon scattering dominates the thermal conductivity at high temperature, while the point-defect and boundary scattering govern the heat transport at intermediate and low temperatures, respectively. In the case of UO2, most of the studies on thermal properties are focused on the high-temperature range (where nuclear reactors operate) to better. In order to better understand mechanisms that govern heat transport in this important technological material and to accurately model this compound at all relevant temperatures, the effects of various scattering mechanisms must be quantified. We have carried out systematic studies on the grain-size effect on thermal conductivity of UO2 by performing measurements at low temperatures to study different scattering mechanisms, focusing on grain boundary scattering. The grain-boundary scattering has been assessed in these materials using molecular dynamic simulations at higher temperatures

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION