Gamma-Ray Irradiation Induced Variation in Thermal Conductivity of Polyethylene/Nano-Silica/Micro-Boron Nitride Composite as Potential Cable Insulation

Polyethylene (PE) has been widely used as cable insulation in nuclear power plant (NPP), where the material is inevitably exposed to severe working conditions like high energy irradiation (gamma-ray) and high temperature, which in turn influence the insulation performance and safe operation of the cable system. For the safe use of the material, the improvements on radiation resistance and thermal conductivity of PE become important issues. In this work, the thermal conductivity as well as the insulation property of PE was modified by adding nano-silica (SiO 2 ) and micro-boron nitride (BN) to form the micro/nanocomposite. A cobalt-60 gamma source was employed to irradiate the sample, and the total irradiation dose was accumulated up to 1000 kGy. Material structure characterization method such as Fourier Transform Infrared Spectrum (FTIR), differential scanning calorimetry (DSC) and gel content extraction were performed to assist the analysis of radiation induced variation in thermal conductivity of PE based composite. The test results showed the decrease in thermal conductivity with the total irradiation dose, which was ascribed to the change in both chemical and physical structures. It is suggested that the thermal conductivity is dependent upon the lattice vibration in the composite, which is destroyed by the gamma-ray irradiation induced chemical reactions.