Improvement of electrical insulation performance of silicone rubber cables due to exposure to heat and radiation
Yoshimichi Ohki, Naoshi Hirai, Yasuhiro Tanaka
Abstract
Abstract Thermal treatments, with and without co‐irradiation with gamma rays, were given to safety‐related cables insulated with silicone rubber for nuclear power plants (NPPs). To examine the effects of the above treatments on the insulation properties of the cables, DC voltages were applied to them and the induced changes in leakage current were measured by the current integration method. As a result, it has become clear that the leakage current is the largest in the pristine untreated cable. In addition, almost no leakage current flows in the cables heated at 200°C or 290°C for several hundred hours. The leakage current remains small when the co‐irradiation with gamma rays was given at 100°C or 200°C for relatively long periods exceeding 1000 h. The reason for these results seems to be that the silicone rubber insulation becomes hardened as a result of the thermal or concurrent treatment, and the transport of ionic carriers becomes difficult. The above results indicate experimentally that the degradation is not a matter of great concern for the insulation performance of silicone‐rubber‐insulated safety‐related cables in NPPs.