For many nuclear power plants worldwide the operation period will be extended from 40 to 60 years in the coming years. As the operation period increases the importance of knowledge of ageing mechanisms like fatigue increases. Knowlegde of the influence of the environment is crucial, since environmental fatigue is a relatively new development which is a modification to the existing assessment method and has to be projected to 60 years as well.

This paper contains the results of a literature survey of environmentally assisted fatigue in nuclear power plants. It describes the current status and developments in the world. The main regulatory rules, guidelines and methods from the US, Germany, Japan, Finland and France are presented.

At this moment different approaches for incorporating the effect of the coolant water environment exist, although the general trend is towards a more uniform approach worldwide. The most common approach is the incorporation of an environmental fatigue correction factor (Fen) in the fatigue derivation of the cumulative usage factor. The Fen formulas and the S-N fatigue curves differ but the general equations are:

Fen=Nair/Nwater

and

CUF=ΣUpartial*Fenpartial

Alternatives like using fatigue curves including the environmental effects, using threshold criteria and calculation of an allowable Fen based on testing, are described.

Research and material tests are still on-going and subject of international development. An overview of the current international state-of-the-art is presented.

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