A method for correlating natural aging data and its application to insulation aging in nuclear power plants

A mathematical model has been developed to compare the aging of polymers in a nuclear reactor environment with that under accelerated laboratory conditions typical of those used in qualification. The aging stresses under consideration include temperature and gamma-radiation intensity. The proposed method is based on the hypothesis that several measurable properties of a polymer are continuous functions of time, with time shifted in a fixed manner according to the imposed stresses. A major feature of the model is that other than smoothness, no attributes of the functions connecting properties with aging time have to be assumed. While available data from naturally aged specimens are spotty, preliminary results indicate that the method does work