Effect of thermal ageing on creep and oxidation behaviour of Type 316H stainless steel

The UK has unique experience in operating high temperature civil nuclear power systems, known as advanced gas cooled reactors (AGRs). One of the primary challenges for extending the lifetime of the AGR power stations is to understand the interaction that occurs between the AGR CO2 environment and creep-fatigue cracking behaviour. This is one of the life limiting degradation mechanisms for steel components within the reactor pressure vessel. This paper addresses the effect of thermal aging on material internal state that controls both the creep deformation and oxidation behaviour of Type 316H stainless steels when they are exposed at a simulated AGR environment. Experimental results from creep tests are discussed with respect to a multi-scale self-consistent model, while experimental results from oxidation tests are considered with respect to the application of measured short term data to predict the long term oxidation behaviour. Finally, the interaction between oxidation and creep and its impact on high temperature structural integrity of AGR nuclear systems are discussed.