A simplified approach for the lifetime prediction of PE in nuclear environments

A simplified method is proposed to estimate the lifetime of thin samples of unstabilised and unfilled polyethylene (PE) exposed at low dose rates at room temperature in air. The point of departure is the observation that the ceiling lifetime is the lifetime due to thermal oxidation. Pure thermal oxidation predominates at very low dose rates (typically for (D) over bar < 1.6 x 10(-7) Gy s(-1)) and is characterised by very long lifetimes (typically of the order of 20 years at ambient temperature). Pure radio-oxidation predominates at high dose rates (typically for D > 5 x 10(-1) Gy s(-1)) and is characterised by a letal dose independent of dose rate, i.e. a lifetime proportional to the reciprocal dose rate: t(F) approximate to 1.6 x 10(5)(D) over bar -1. At intermediary dose rates (typically for 1.6 x 10-7 < D < 5 x 10-1 Gy s(-1)), a radiothermal oxidation proceeds. From a kinetic investigation, it is found that, in this latter domain, lifetime can be also estimated by a simple power law: (5)(D) over bar t(F) approximate to 2.3 x 10(5)(D) over bar (-1/2) (c) 2005 Elsevier B.V. All rights reserved.