Topic of the Special Session:

 

There has been a significant research effort in recent years addressing the influence of high temperature light water reactor (LWR) coolant environments on fatigue of pressure vessel and circuit materials. The response of these materials to cyclic loading resulting from plant transients is assessed on the basis of materials properties and design codes similar to the ASME III and XI design codes for fatigue endurance (commonly referred to as fatigue initiation) and fatigue crack growth respectively. These materials research activities have addressed both the effects on fatigue life, using conventional fatigue endurance testing methods, and fatigue crack growth using fracture mechanics specimens. As an example, for both ferritic and austenitic steels, significant effects of high temperature water on fatigue endurance have been observed under specific conditions.

 

The application of fatigue assessment procedures for nuclear components (e.g., USNRC Regulatory Guide 1.207) can result in predictions of very high cumulative fatigue usage factors for some plant components and transients which appear inconsistent with the relatively good performance of stainless steel components in operating reactors over several decades, revealing the existence of significant knowledge gaps.

 

The aims of this session are, among others:

 

1. To share views on international approaches for assessing Environmental Assisted Fatigue

 

2. To share understanding of gaps in assessment capabilities

 

3. To share ideas for improved understanding to the benefit of assessment capability