Cable Aging Monitoring with Differential Scanning Calorimetry (DSC) in Nuclear Power Plants

As a requirement for plant life extension for more than 40 years, additional Cable Aging Management Program (CAMP) has to be implemented in Nuclear Power Plant Krško. Samples of cables are selected based on nuclear safety and electrical equipment criticality for inspection and testing, to check functionality and prevent unexpected failure during normal operation. Different onsite testing equipment and methods are implemented to find harsh environment due to temperature, radiation, humidity and chemical effects that could affect insulation lifetime. Infrared thermography is used for determining and evaluating temperature hot spots. The article presents a development of laboratory testing of cable insulation using Differential Scanning Calorimetry (DSC). Thirty-six samples of different nuclear qualified cables made of most frequently used materials, ethylene propylene rubber (EPR) and cross linked polyethylene (XLPE) – all with chlorosulfonated polyethylene (CSPE) jacket, were tested. Samples were 35 years old and additionally temperature aged in several steps with an intention to get acceptance criteria. Similar tests were conducted in two testing laboratories. The results showed an evident decrease in oxidation stability of the inner EPR insulation; the onset temperature of oxidation processes has been shifted from 238 °C (unaged samples) to 175 °C (most aged samples). A decrease in oxidation stability was also observed for XPLE insulation; the onset oxidation temperature decreased from 266 °C for unaged samples to 213 °C (most aged samples). For the jacket material CSPE used as the insulation protection nearly no changes were observed