2017 | AFC ACCOMPLISHMENTS 146 U3Si2 is considered as a new fuel for the existing Light Water Reactor (LWR) fleet. While nuclear fuel operates at high to very high temperatures, measurements of thermal conductivity and other materials properties lack sensitivity to temperature variations and to material variations at reactor temperatures, especially those related to heat transport, scattering interactions, and electronic correlations.These variations need to be characterized as they will afford the highest predictive capability in modeling and offer best assurances for validation and verification at all temperatures. Project Description: Nearly 20% of the world’s electricity today is generated by nuclear energy. Since the thermal properties, especially thermal conductivity, of the fuel governs the conversion of heat produced from fission events into electricity; it is an important parameter in reactor design and safety. Therefore detailed understanding of electronic properties and the way the nuclear materials transport heat are of paramount interest of nuclear energy research and one of the Department of Energy (DOE) missions. Thermal and transport properties of U3Si2 Principal Investigator: Krzysztof Gofryk Collaborators: D. Antonio, K. Shrestha, C. Papesch,Y. Zhang, J. Harp, and Jon Carmack Uranium-silicon compounds have been extensively investigated for use as nuclear fuels in new generation reactors. In particular, U3Si2 has become a material of interest for its potential as an accident tolerant fuel used in commercial LWR. Several factors make U3Si2 appealing, including a higher uranium density than UO2 (currently the most commonly used commercial fuel).An improved thermal conductivity over the comparatively poor UO2 is also of particular note, as better thermal properties can contribute to smaller temperature gradients during reactor start up, which could reduce cracking of fuel pellets.A higher thermal conductivity is also beneficial during some accident scenarios.Although much effort has been dedicated to studying the thermo- physical properties of U3Si2 at high temperatures, there is only limited data available at lower temperatures. The operating temperatures in nuclear reactors are high (~1000 K), however, many important physical characteristics such as the effect of electronic correlations and/or impact of defects and other degrees of freedom on the electrical and heat transport in nuclear materials are all emphasized at moderate or low temperatures.Therefore, in order to better understand the nature of the 5felectrons and mechanisms that govern electrical and heat transport in this important technological material, and to accurately model this compound at all relevant temperatures, these effects must be quantified. Accomplishments: In order to understand the electronic and thermal properties we have studied U3Si2 by means of the heat capacity, electrical resistivity, Seebeck and Hall effects, and thermal conductivity. Polycrystalline samples of U3Si2 were prepared by arc-melting stoichiometric amounts of elemental U and Si. The arc-melted ingots were then comminuted into powder, pressed and sintered into pellets. Samples for this work were sectioned from these pellets. Powder diffraction confirmed that the structure was tetragonal (space group P4/mbm) with lattice parameters similar to those previously reported in literature.A sketch of the crystal structure of U3Si2 is shown in the inset of Figure 1.The thermal conductivity, resistivity, Hall effect, and heat capacity measurements were done in a DynaCool Quantum Design Physical Property Measurement System.All the results obtained, especially small magnetoresistivity, large low-temperature heat capacity, and characteristic dependence of the Seebeck coefficient, point to delocalized nature of 5f-electrons in Understanding of thermal and electrical transport of nuclear materials