Physics-based model of the degradation of cable insulation subject to radiation and heat

Cable insulations in nuclear power plants (NPPs) are susceptible to degradation due to heat and radiation. Elongation at break (EAB) is one of the mechanical properties that provide a metric for the degree of degradation. An EAB model has been extensively discussed by many researchers and organizations, including Sandia National Laboratories, Harwell Laboratory, International Electrotechnical Commission (IEC), International Atomic Energy Agency (IAEA), and Japan Nuclear Energy Safety Organization (JNES). The model is empirically based on Arrhenius equation. A newly proposed method models one EAB curve as a function of time by a combination of two phases: the incubation phase whose drop-off rate is insignificant, and the degradation phase in which the drop-off rate is quantified. The two phases are of physical significance. When the parameters of the model are anchored to specific materials, the EAB curves corresponding to different ageing temperatures and dose rates can be quantitatively predicted as a function of time. Ethylene Propylene Rubber (EPR) is a widely-used material for cable insulation. Experimental data of EPR subject to heat and radiation is used to validate this newly proposed model. The derived physics-based equations in this research pertinently fit experimental data.