Insight into Thermal Aging of Jacket-Bonded Ethylene-Propylene Rubber Cable Insulation

摘要

Electrical cables are integral to nuclear power plant operation and control during power generation, during planned outages, and during design basis events. Polymeric insulation and jacketing used in cable construction does age over time as a function of environmental stresses including heat, moisture, and radiation. Degradation of polymer mechanical properties can lead to breaks in the insulation and consequent electrical shorting. The tensile elongation at break (EAB) has therefore developed as a metric of cable health for elastomeric cable insulation. A conservative estimate of the ability of a cable to perform its safety-related function in the case of a design basis event such as a loss of coolant accident is associated with an EAB value of 50%. The lifetime curve then of cables thus maps exposure over time from initial EAB values of ~300% to approximate end of remaining useful life at 50%. A condition monitoring program for installed cables may correlate non-destructively measured key indicators of aging with corresponding EAB values to place snapshots of cable health on the cable lifetime curve for predictive value. A cable far from the end of its remaining useful life may safely be retained. A cable status corresponding to further along its lifetime curve may need to be scheduled for evaluation more frequently or even scheduled for immediate replacement prior to functional failure.