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Abstract

This paper investigates the evolution of electrical and physico-chemical properties of low-voltage power cables for nuclear application subjected to both temperature and radiation aging. Electrical response is evaluated by the means of the dielectric spectroscopy technique while the physico-chemical and mechanical changes are analysed at different structural scales by five complementary techniques (FTIR spectroscopy, DSC, OIT, swelling measurement and micro-indentation). All these techniques are shown to be appropriate for the evaluation of the radiochemical aging development on LV cables, suggesting the effectiveness of dielectric spectroscopy as a non-destructive technique for on-site cable diagnosis.

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... As showed and widely known in literature [5][6][7][8], aging can significantly change the physical-chemical properties of organic species, including polymers. ...
... This process yields to the formation of higher dipolar oxygen-bonded chains, whose electrical response (dipolar polarization) is placed in the highest frequency range here considered. For this reason, this frequency range is usually reported as sensitive to degradation [6][7][8]. Among the high frequencies of the analyzed spectra, 100 kHz showed in literature to be representative of this frequency range and highly related to both the dipolar polarization and the aging of the polymer [4,5,7]. ...
... Previous studies [8] showed that during aging the primary antioxidant can move from the inner part of the polymer to the outer part changing its shape into needles (polymorphism of the antioxidant). Oxidation, indeed, occurs primarily in the outer layers of the polymer due to the interaction of the surface with the environment; this activates the antioxidants which act like an oxygen-proof layer, localizing the degradation only in the outer layer of the polymer. ...
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This paper investigates the evolution of electrical properties with aging for two XLPE based materials having different chemical compositions. It is shown that aging and material composition can significantly affect the electrical response, suggesting the suitability of dielectric spectroscopy for polymer diagnostics. Furthermore, the dielectric response is correlated with the evolution of mechanical properties, in particular elongation at break (EaB), in order to evaluate the possible scaling-up of the current cable qualification standard.
... To do so, a correlation among these various properties was performed. In particular, a relationship between the high frequency dielectric response and the total esters absorbance peaks obtained by the FT-IR spectra is possible and was shown to be consistent in previous works [12,27]. Unfortunately, since the material analyzed here shows no ester peak in the base material (lack of external antioxidants, e.g., phenol-based molecules), the total absorbance peak ( Figure 4) is almost zero and the dielectric losses (Figure 1d) in the high frequency region show very little variation with aging (inside the same order of magnitude) until the last aging period (1500 h) in air. ...
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This paper focuses on the electrical and mechanical properties of irradiated and thermally-stressed NPP cables used for instrumentation and control (I&C). These cables show some noteworthy changes after few years of uncontrolled environment conditions due to a phenomenon called post-irradiation effect. Strong post-irradiation effects, e.g. reduction of mechanical properties, raise of crosslinking and oxidation grade, were found on XLPE cable insulation years after irradiation. These degradation mechanisms can be correlated with electrical measurements in which imaginary permittivity values raise, in particular at low-frequencies where interfacial phenomena take place. This behavior can be linked to the increase of interfacial area between amorphous and crystalline region of polymer, supporting the evidence that post-irradiation effects can lead to polymer crosslinking during a storage period even at room temperature.
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Aging of nuclear power plant cables: in search of non-destructive diagnostic quantities
  • L Verardi
L. Verardi, "Aging of nuclear power plant cables: in search of non-destructive diagnostic quantities", PhD Thesis, University of Bologna, 2014.
Thermal analysis of polymers
  • J D Menczel
  • R B Prime
J.D. Menczel, R.B. Prime, "Thermal analysis of polymers", Wiley, 2009.
Characterization of polymer materials using FT-IR and DSC techniques
  • P Pagès
P. Pagès, Characterization of polymer materials using FT-IR and DSC techniques. Universidade da Coruña, 2005.
Investigation on Thermal Degradation Phenomena on Low Density Polyethylene (LDPE) through Dielectric Spectroscopy
  • S V Suraci
  • D Fabiani
  • L Mazzocchetti
  • V Maceratesi
  • S Merighi
S.V. Suraci, D. Fabiani, L. Mazzocchetti, V. Maceratesi, S. Merighi, "Investigation on Thermal Degradation Phenomena on Low Density Polyethylene (LDPE) through Dielectric Spectroscopy", IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP, 2018, pp. 434 -437.