Effect of gamma radiation on sealing capacity characteristics of three commercially available nitrile rubber samples compared against an industrial seal used in AGR power plants

The maintenance of the Fuelling Machine operating in an AGR reactor consumes a large number of working hours and operational budget. As part of an optimisation programme research work is currently being carried out to investigate the degradation mechanism on the dynamic seal on one of these machines. The aim of this work is to understand seal behaviour under reactor working conditions in a bid to develop a mechanistic understanding of its long-term degradation and optimise the component’s maintenance schedule.

The deleterious operational conditions have been identified as; activation of the sealing face through compression, exposure to a low radiation dose and cycle exposure to pressurised carbon dioxide. This part of the work investigates the effect of radiation damage on the CO2 uptake and swelling behaviour, mechanical properties and physical and chemical structure of three commercially available nitrile rubber samples which are then compared against the characteristics for the chosen seal.

Exposure to radiation resulted in increased mechanical strength and resilience of the rubber as well as decreased CO2 loading capacity and swelling, further supporting the theory of cross-link formation. The seal was more resistant to the effects of radiation than the three nitrile rubber samples, however scanning electron microscopy identified the initiation and propagation of cracks without any external stress applied on the irradiated samples, the result of in-built stresses created during the manufacturing process. The next stage of this work will investigate the effect of the local environment on the radiation-induced changes in the sample’s ultimate sealing capacity.