RHEOLOGICAL ANALYSIS AND VIBRATIONAL SPECTROSCOPY FOR ENHANCED CONDITION MONITORING AND LIFETIME PREDITION OF CABLE MATERIALS

摘要

Cables deployed within nuclear power plants must be able to maintain their functionality throughout very long lifetimes even with high levels of cumulative radiation exposure. With requirements for qualified lifetimes being 60 years or more, large acceleration factors are often required for Arrhenius lifetime simulations. When comparing test data from accelerated aging studies to actual in-service conditions, it is important to ensure that the fundamental mechanisms of changes induced in the materials during the accelerated aging conditions are the same as those that would be experienced in service. Traditional room temperature mechanical characterization as well as rheological analysis, thermal analysis, and vibrational spectroscopy are used to characterize various cable materials under different thermal and radiation histories. From the combined data, clear mechanisms of the physical and chemical changes in each cable materials as well as relative rates of change can be determined. For thermoplastic compounds melt or solution viscosity measurements can provide rheological information about changes in polymer structure. These traditional viscosity measurements, however, are not possible on crosslinked materials. Dynamic Thermal Mechanical Analysis is be used to present a detailed picture of the structural changes which take place as a function of material as these materials are exposed to radiation and subsequent thermal aging. Changes in temperature dependent dynamic modulus and complex viscosity in various materials show that crosslinking is the dominating mechanism of chemical change in the cable materials studied.