Study on Thermal Performance of Binary Composite Material with Microscopic Configuration

Abstract

To improve the thermal performance of composite materials, different approaches are being researched to fabricate composite materials and evaluate their performance. Many studies have shown that the thermal performance of composites is effectively improved when binary materials exist in interconnected structures. However, very few studies have explored the thermal performance characteristics of composites with respect to the arrangement of microstructures or suggested guidelines for improving thermal performance. This study aims to investigate the thermal performance characteristics based on the microscopic configuration via numerical calculations and design a numerical model to confirm the behavior of microstructure under thermal expansion. Through the development of this model, guidelines about the microscopic configuration of binary material are suggested herein for improving the thermal performance of composites. This study focuses on a composite nuclear fuel, namely, a UO2–Mo microcell pellet. The microstructure placement is analyzed for the creation of a numerical calculation model of the UO2–Mo microcell pellets having a complex microstructure arrangement of the binary metal molybdenum (Mo). In addition, the boundary conditions and governing equations applicable to the numerical calculation of the thermal performance characteristics are considered, and the geometry is modeled to simplify the thermal performance analysis with respect to the microstructure arrangement. The results of the designed numerical calculation model are compared with the measured thermal performance. Based on the designed model, the characteristics of thermal performance according to the microstructure arrangement are identified. For the same binary material content, the thermal performance is effectively improved when the microstructures are aligned with the heat-transfer direction, leading to an increase in thermal conductivity as the vertical microstructure length decreases in the direction of heat transfer. In addition, it is predicted that a good interface of the fabricated sample can be achieved through analysis, assuming that there are a few contact thermal resistances between the interfaces. The improved thermal performance of the UO2–Mo 5 vol% microcell pellets is expected to reduce the maximum temperature by 26% over that of a UO2 pellet. The thermal gradients of the pellets are mitigated through reduction in the maximum temperature, which in turn reduces the stress gradient. Finally, the thermal expansion behavior of the composite material is investigated in a design having a sandwich configuration of binary materials, considering the thermal performance characteristics. Thus, in this model study, a numerical calculation model of a nuclear fuel composite having a simplified microstructure was developed to investigate its thermal performance characteristics. Similarly, it will be possible to develop a numerical calculation model for other types of composite materials to investigate their thermal performance.