Oxidation is the dominating degradation process in most polymers during long term use in nuclear power plant (NPP) applications. Under radiation, oxygen diffusion is known to be detrimental for poly-mers at room temperature and it is accelerated by increased temperature. Diffusion limited oxidation (DLO) has an effect to the heterogeneous oxidation behavior of polymers. [1]. During normal service of NPPs the temperature within the containment can be tens of degrees beyond room temperature. Also radiation levels can vary, depending on e.g. the reactor design, typically being less than 10 Gy/h during normal service [2].

The long-term performance of polymeric materials is obviously best assessed by exposure of test specimens to natural ageing conditions followed by examination of their performance characteristics in terms of changes in physical properties. The testing conditions can be either in-door or out-door envi-ronments, and the first signs of degradation are often detected by testing mechanical properties such as tensile strength and elongation-at-break [3]. Although natural ageing is the most reliable

exposure method for examining long-term performance, its use is restricted due to the extremely long exposure times required to achieve service lifetimes. In order to decrease the testing time significantly, and thereby achieve more rapid prediction of long-term behaviour of polymeric materials, artificial ac-celerated test methods involving harsher environments are used [4]. However, the accelerated ageing conditions cause at least two kinds of problems. Firstly, the chemistry of degradation can be markedly affected when the conditions of artificial ageing are too harsh. One consequence of this is a poor cor-relation with the changes that occur during natural ageing, resulting in misleading performance data. Secondly, all factors used in artificial ageing to induce chemical degradation and obtain observable physical changes must be accelerated to the same degree. However, neither the factors responsible for the ultimate degradation of a more or less complex polymeric system, nor the effects of their inter-relation are known. Consequently, it is essential that the analytical tools used to follow the ageing are capable of detecting and identifying differences between the employed accelerated tests and the natu-ral ageing already at an early stage of degradation. Moreover, sensitive tools can limit the need for high acceleration factors in artificial ageing.

During accelerated ageing DLO effects may cause heterogeneous oxidation of the polymer which usu-ally does not occur to the same extent under normal service conditions at NPP. Combined to DLO ef-fects, understanding the combined effects of ionizing radiation and temperature is essential when evaluating the lifetime of polymeric components during normal service life or in Design Based Accident (DBA) situations.

In order to study the oxygen containing degradation products on the surface compared to the bulk ma-terial a surface sensitive analytical instrument, Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), was applied on EPDM samples. The aim is ultimately to evaluate the possibility to use ToF-SIMS in oxidation profile measurements. For comparisons this study includes differential scanning DSC, and Fourier transform infrared Spectroscopy (FTIR) as well as tensile testing.