Evaluation of Thermally Aged and Gamma-Irradiated Nuclear Cables using Electrical Diagnostic Tests

Electrical cables are essential within nuclear power plants (NPPs) to support power, control, and instrumentation systems. Given the importance of these systems in servicing NPPs, prevention and detection of electrical cable failure is a vital part of aging management programs. As such, nondestructive examination (NDE) techniques are commonly used to evaluate the degradation of electrical cables. Common offline electrical NDE techniques for condition monitoring (CM) may include lowfrequency dielectric spectroscopy (LFDS), time domain reflectometry (TDR), frequency domain reflectometry (FDR), and time domain dielectric spectroscopy (TDDS). However, there is no single NDE method to comprehensively evaluate cable condition and, in many cases, a combination of local and global tests is required. In this work, we evaluate the sequentially applied thermal and gamma radiation aging of electrical cable insulation using electrical diagnostic test methods to better understand damage detection in cables using a combination approach. Gamma radiation aging was performed on cross-linked polyethylene (XLPE) polymer cable insulation material commonly used in NPPs. Long “30-foot” cable mandrels of XLPE were irradiated at room temperature, using Co-60 gamma-rays, to intervals of 100 kGy each, for a combined total dose of 500 kGy. Post irradiation electrical testing was performed on these cables. Preliminary results of the electrical diagnostics indicate trends with increasing aging conditions in the XLPE cable insulation samples. The results of this study advance electrical-based diagnostic techniques for condition monitoring of electrical cables in NPPs, providing plant operators with more complete information to support repair, mitigation, or replacement decisions.