Application of Non-Destructive Condition Monitoring Techniques on Irradiated Low Voltage Unshielded Nuclear Power Cables

In this paper, the effect of radiation stress on the overall degradation of jacket and insulation of low voltage unshielded power cable used in nuclear power plants is discussed. The XLPE insulated and CSPE jacketed cable samples were exposed to a total dose of 400 kGy γ-irradiation with 0.5 kGy/h dose-rate. Dielectric spectroscopy; complex permittivity, and extended voltage response; namely slopes of decay and return voltages were used to study the effect of the irradiation on the cable with an aim to establish the application of these techniques for a non-destructive condition monitoring of the unshielded cables. Shore D hardness was also used to investigate the mechanical characteristic of the cable. It was observed that the radiation stress affected the electrical and mechanical properties of the cable polymeric components i.e. insulation and jacket. The imaginary part of permittivity at low frequency; 100 Hz, the slope of return voltage, and hardness showed a significant increase with absorbed dose showing the effect of irradiation on the jacket and insulating material, as well. A strong correlation was observed between the imaginary part of permittivity at 100 Hz, slopes of return voltage, and hardness. The results show the dielectric measurement techniques are potential non-destructive condition monitoring methods for the unshielded low voltage nuclear power plant power cables for on-site diagnosis.