Aging Mechanisms and Nondestructive Aging Indicator of Filled Cross-Linked Polyethylene (XLPE) Exposed to Simultaneous Thermal and Gamma Radiation
Aging mechanisms and a nondestructive aging indicator of filled cross-linked polyethylene (XLPE) cable insulation material used in nuclear power plants (NPPs) are studied. Using various material characterization techniques, likely candidates and functions for the main additives in a commercial filled-XLPE insulation material have been identified. These include a mixture of brominated components such as decabromodiphenyl ether and Sb2O3 as flame retardants, ZnS as white pigment and polymerized 1,2-dihydro-2,2,4-trimethylquinoline as antioxidant. Gas chromatography-mass spectrometry, differential scanning calorimetry, oxidation induction time and measurements of dielectric loss tangent are utilized to monitor property changes as a function of thermal and radiation exposure of the cable material. The level of antioxidant decreases with aging by volatilization and chemical reaction with free radicals. Thermal aging at 90 ℃ for 25 days or less causes no observable change to the cross-linked polymer structure. Gamma radiation causes damage to crystalline polymer regions and introduces defects. Dielectric loss tangent is shown to be an effective and reliable nondestructive indicator of the aging severity of the filled-XLPE insulation material.
KeywordsFilled cross-linked polyethylene Aging mechanisms Gas chromatography-mass spectrometry Differential scanning calorimetry Oxidation induction time Dielectric loss tangent
This research is being performed using funding received from the DOE Office of Nuclear Energy’s Nuclear Energy University Programs under contract number DENE0008269 and the DOE Office of Nuclear Energy’s Light Water Reactor Sustainability Program. Exposure experiments were conducted at Pacific Northwest National Laboratory which is operated by Battelle for the US DOE under contract DE-AC05-76RL01830.
- 1.Electric Power Research Institute (EPRI), Low-Voltage Environmentally-Qualified Cable License Renewal Industry Report; Revision 1. TR-103841 (1994)Google Scholar
- 2.N. Bowler and S. Liu, Aging Mechanisms and Monitoring of Cable Polymers. Int. J. Prognostics Health Manage., ISSN 2153-2648, pp. 1–12, 2015Google Scholar
- 3.L.S. Fifield, S. Liu, N. Bowler, Simultaneous Thermal and Gamma Radiation Aging of Cable Polymers. IEEE Conference on Electrical Insulation and Dielectric Phenomena, Toronto, Canada, October 16–19, 2016Google Scholar
- 4.M. Sheridan, The Vanderbilt Rubber Handbook (R.T. Vanderbilt Company Inc, Norwalk, CT, 2010), p. 431Google Scholar
- 5.M. Ash, Handbook of Green Chemicals, p. 22, Synapse Info Resources, 2004Google Scholar