Thermal Conductivity and Kapitza Resistance of Ceramic Composites

Advanced ceramic composites are actively investigated for use in various fields of the technology sector including nuclear fuel. Conventional uranium dioxide (UO2) nuclear fuel has low thermal conductivity resulting in a limited lifetime within a nuclear reactor. Novel ceramic composites with higher thermal conductivity can be engineered for use as nuclear fuel to increase efficiency and accident tolerance. In this study, the role of microstructure and composition on thermal conductivity of several ceramic composites will be investigated. First, the thermal conductivity of three-phase ceramic composites consisting of aluminum oxide (Al2O3), magnesium aluminum spinel (MgAl2O4), and cubic 8 mol% yttria stabilized zirconia (8YSZ) is measured experimentally and modeled via OOF2 and MOOSE finite element analyses for two distinct grain sizes. A difference between experimental and calculated results is observed at low temperatures and is attributed to the Kapitza resistance of interfaces and grain boundaries within the material. It is hypothesized that the presence of heterointerfaces, or grain boundaries between different materials, increases the overall Kapitza resistance of composite materials. Next, the same three-phase composite system is shown to validate the 3 method for thermal conductivity measurements of bulk ceramic samples at low temperatures when compared to values obtained via laser flash analysis. Then, several uranium containing composites are explored. The effect of microstructure on thermal conductivity is investigated for unique accident tolerant fuel forms containing various compositions of UN and U3Si2. Finally, phase field modeling of hyperstoichiometric UO2+x simulates the influence of oxygen nonstoichiometry on the degradation of thermal conductivity in UO2+x and U4O9 binary-phase composites