A new analytical model for predicting the radio-thermal oxidation kinetics and the lifetime of electric cable insulation in nuclear power plants. application to silane cross-linked polyethylene

Sarah Hettal, Sébastien Roland, Konsta Sipila, Harri Joki, Xavier Colin (Corresponding Author)

Research output: Contribution to journalArticleScientificpeer-review

Abstract

The radio-thermal oxidation of silane cross-linked polyethylene (Si-XLPE) was studied in air under different γ dose rates (6.0, 8.5, 77.8, and 400 Gy.h−1) at different temperatures (21, 47, and 86°C). The changes in the physico-chemical and mechanical properties of Si-XLPE throughout its exposure were determined by FTIR spectroscopy, differential scanning calorimetry (DSC), swelling measurements, rheometry in rubbery (DMTA) and in molten states, and uniaxial tensile testing. It was found that oxidation leads to the build-up of a wide variety of carbonyl and hydroxyl products (mostly carboxylic acids and hydroperoxides) and an efficient chain scission process that catastrophically reduces the concentration in elastically active chains and the elongation at break from the early periods of exposure. A new analytical model was derived from the current radio-thermal mechanistic scheme without making the usual assumption of thermal stability of hydroperoxides. After an initial period where the oxidation kinetics occurs with a constant rate, this model allows also predicting the auto-acceleration of the oxidation kinetics when the hydroperoxide concentration reaches a critical value of about 1.6 × 10−1 mol.L−1. Choosing this critical value as a structural end-of-life criterion allows a more direct assessment of the lifetime of Si-XLPE in the various radio-thermal environments under study, except at the highest temperature (i.e. 86°C) where the kinetic model can still be noticeably improved.

Original languageEnglish
Article number109492
JournalPolymer Degradation and Stability
Volume185
DOIs
Publication statusPublished - Mar 2021
MoE publication typeA1 Journal article-refereed

Keywords

  • Analytical kinetic model
  • Carbonyl build-up
  • Chain scissions
  • Hydroperoxide decomposition
  • Lifetime prediction
  • Radio-thermal oxidation
  • Silane cross-linked polyethylene
  • Structural end-of-life criterion

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