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

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