Thermophysical properties of U3Si5 to 1773 K

Abstract

a b s t r a c tPossible use of U 3 Si 5 as a nuclear reactor fuel requires knowledge of its thermophysical properties as a function of temperature. While limited data is available for U-Si compounds containing higher uranium densities, no investigations of U 3 Si 5 have been presented in the literature to date. High purity U 3 Si 5 was fabricated to facilitate a set of experiments to determine the coefficient of thermal expansion, heat capacity, thermal diffusivity, and thermal conductivity from room temperature to 1773 K. Each measurement on nearly stoichiometric U 3 Si 5 showed the existence of a phase transformation at 723 K, which is not consistent with the most recently published phase diagram.

Thermophysical properties of U3Si2 to 1773 K

“…The Debye-like lattice contribution is typically saturated to the Dulong-Petit value (124.71 J mol À1 K À1 ) above the Debye temperature, which is unknown for U 3 Si 2 . Based on other U-Si binary compound Debye temperature values [13,21], it is estimated that U 3 Si 2 has an approximate Debye temperature of 200 K, which is below the temperature range investigated in this study. Contributions to the heat capacity from the dilational term are approximated using the well-known formula C d ¼ a ) - [16], and ( ) - [17].…”

“…The authors acknowledge that many of the U-Si XRD peaks are convoluted making identification and quantitative analysis of secondary U-Si phases difficult. Characteristic peaks for UO 2 were included as this phase is typical of oxidized U-Si compounds [12,13]. These specimens exhibited no evidence of UO 2 presence.…”

Structural stability and fission product behaviour in U3Si

“…Economically, the higher density fuels exhibit improved uranium loading allowing manufacturers to sell the assemblies at a premium. More importantly, the safety characteristics of such fuels can be improved markedly over conventional UO 2 pellets held within a Zr-alloy cladding (materials can be chosen with better oxidation resistance [1] or lower susceptibility for degradation due to hydrogen pick-up [2][3][4], for example), and the enrichment of the fuel can be reduced owing to the greater 235 U density.…”

Investigation of thermal transport in composites and ion beam irradiated materials for nuclear energy applications

“…U 3 Si 2 is considered as an alternative fuel to UO 2 due to its higher uranium atom density and thermal conductivity. 79 Unlike previously discussed cases, the conductivity of this material is determined by electron transport. Point defects and extended defects do not typically have a strong impact on electronic thermal conductivity, unless the material is cooled to cryogenic temperatures.…”