The results of determination of activation energies (EA) of polymeric cable insulations obtained by conventional methods (usually based on the evaluation of changes of mechanical
properties of insulations after their ageing in thermal chamber at different temperatures) have been compared with results
obtained by methods employing the differential scanning calorimetry (DSC). Three DSC methods have been tested: the method
according the ASTM E 698; measuring of DSC characteristics in the isothermal mode at several different temperatures; and the
method based on evaluation of DSC characteristics of insulations after their thermal ageing in thermal chamber. The last method
— which can be called as a modified conventional method, because instead of mechanical properties, the DSC characteristics
are determined — has been found as most acceptable and giving similar values of EA as the other conventional methods.
Degradation of polymeric materials used in nuclear power plants (NPP), especially polymeric cable insulation materials, in
the course of their service can be monitored by measuring their properties by DSC, mainly oxidative induction time — OIT.
The studied materials were in-laboratory aged by applying main stressors that act in NPP — ionising radiation and temperature.
The dependence of OIT on radiation and thermal degradation of polymeric material was determined. The OIT values have been
compared to elongation at break as a property that directly reflects the functionality of the studied material. The comparison
of monitored OIT of real cable samples taken from NPP with dependencies on how the OIT values change with the elongation at
break, makes possible to establish the extent of cable degradation. This method can be considered as a suitable and effective
technique for lifetime assessment not only of cable insulations but also of many other plastics.