Post-irradiation degradation of low voltage cables in nuclear power plants: Insights from X-ray microtomography and comsol multiphysics

Abstract

Medium and low voltage cables constitute a critical component of nuclear power plants worldwide. Consequently, monitoring these cables to assess their aging process and reliability is essential. Several parameters can influence the dielectric loss process in these cables, including electrical, thermal and mechanical resistances, as well as daily radiation doses, all of which can contribute to insulation breakdown over time. This study employed electrical experiments and gamma irradiation from a Cobalt-60 source to simulate the aging of materials used in the nuclear industry and other radiation-exposed environments. Electric current peaks were applied at an output voltage of 60 kV and a current amplitude of 250 A. Next, the sample was exposed to a radiation dose of 300 kGy. To assess the structure of the aluminum stranded cable, X-ray microcomputed tomography (microCT) analyses were conducted at three experimental stages: before exposure to any mechanical or electrical stress, post-electrical test and after radiation exposure. The results showed detectable changes in both the cable core and its coating, evidencing a direct correlation between increased radiation exposure and a higher likelihood of dielectric breakdown. Additionally, a reduction in energy transmission capacity was observed. Using COMSOL Multiphysics software, samples with and without anomalies were compared. The results exhibited significant variations in volumetric power density and the electric field. Furthermore, a decrease in electromagnetic energy transmission efficiency was observed, along with an increase in the electric field within the cable.