Density measurements as a condition monitoring approach for following the aging of nuclear power plant cable materials

Monitoring changes in material density has been suggested as a potentially useful condition monitoring (CM) method for following the aging of cable ja cket and insulation materials in nuclear power plants. In this study, we co mpare density measurements and ultimate tensile elongation results versus a ging time for most of the important generic types of commercial nuclear pow er plant cable materials. Aging conditions, which include thermal-only, as well as combined radiation plus thermal, were chosen such that potentially anomalous effects caused by diffusion-limited oxidation (DLO) are unimporta nt. The results show that easily measurable density increases occur in most important cable materials. For some materials and environments, the densit y change occurs at a fairly constant rate throughout the mechanical propert y lifetime. For cases involving so-called induction-time behavior, density increases are slow to moderate until after the induction time, at which poi nt they begin to increase dramatically. In other instances, density increas es rapidly at first, then slows down. The results offer strong evidence tha t density measurements, which reflect property changes under both radiation and thermal conditions, could represent a very useful CM approach. (C) 199 9 Elsevier Science Ltd. Ail rights reserved.