Modelling end–OF–life of radiolytically and thermally aged cable insulations by non-destructive condition monitoring parameters

Abstract

Many United States nuclear power plants (NPPs) are seeking to renew life licenses to extend the operational life of the plant to an additional 20 or 40 years. Radiation and thermal degradation of insulation and jacket of cables, which are originally designed for 40 years in the second round of operation, is a critical issue which can impair the safe and reliable function of cables and ultimately the plant. The main criterion for assessing the end of life of these insulations is defined when the elongation at break (EAB) reaches 50% of its original value.In this work, a new model to estimate the end-of-life of insulation cables aged by radiation and thermal stressors is established. The model is based on correlating the effective activation energy corresponding to EAB changes to the effective activation energy corresponding to non-destructive examination condition monitoring, NDE-CM, parameters. This includes the correlation between the effective activation energy of EAB changes and the effective activation energy corresponding to CM parameters, water-uptake, Gel%, strength at break (SAB), oxidation index (OI), indenter modulus and density. The calculated effective activation energy of radiolytically aged cables is based on Time-Temperature dose-rate superposition and that of thermally aged cables is based on Time-Temperature superposition approach.The database of this model is based on cable polymer aging database (C-PAD) along with experimental results done in the university of Maryland (UMD) laboratory.The published experimental results of cable insulations aged by radiation stressor were used to validate the model. A good fit between the experimental and modeled results confirms the validity of the model.