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2. Materials Ageing – Mechanical Fatigue

The primary purpose of this synthesis report is to deliver a coherent and comprehensive review of research into mechanical fatigue performed during Euratom Framework Programmes 4, 5, 6 and 7, linking the research to the related projects, reports, materials and components. In this context, the synthesis report gives consideration both to fatigue endurance and fatigue crack growth.

To ensure a consistent treatment of a given ageing mechanism as well as across different ageing mechanisms, consideration is given to the research outputs from Euratom projects that fulfil certain criteria, as follows:

  • Sufficiently detailed information exists regarding materials and conditions of experiments or simulations;
  • The materials in the experiments or simulations correspond to those used in operating European nuclear power plants (NPPs);
  • The conditions investigated correspond to the operating conditions of European NPPs.

Given that mechanical fatigue is well-investigated and relatively well-understood, research into this particular ageing mechanism is largely absent in Euratom FP6 and FP7. Instead, it is apparent that the focus during these more recent Framework Programmes has been on thermal fatigue, which is not considered in this synthesis report. Further, while there has been some very limited research into mechanical fatigue during Euratom FP6 and FP7, the focus has been on characterising the behaviour of materials intended for Gen IV reactor systems, such as ferritic/martensitic steels (T91/P91) or oxide dispersion-strengthened (ODS) steels.

In the context of the aforementioned criteria, the majority of potentially relevant Euratom FP6 and FP7 projects (such as RAPHAEL, ARCHER, GETMAT, HELIMNET and MATTER) dealt with new materials, mainly ODS steels and P91 (a steel commonly used in fossil fired plants), which are not used in operating European NPPs. Similarly, other potentially relevant projects, such as NULIFE, were concerned entirely with thermal fatigue. Thus, in view of the limited research into mechanical fatigue undertaken during Euratom FP6 and FP7, this synthesis report also takes into consideration the Framework Programmes of the European Coal and Steel Community (now RFCS) as well as materials technology and standardisation projects of EC RTD FP4 and FP5. Where appropriate, reference is also made to external reports coming from international research programmes.