AREVA Fatigue Concept: A New Method for Fast Fatigue Evaluation

Within the AREVA Fatigue Concept (AFC) a new method for fast fatigue evaluation for highly loaded nuclear power plant components was developed. This method uses FAMOS (FAtigue MOnitoring System) measured data from the outside surface of a pipe and can evaluate a fatigue level for the component for the thermal event plug flow. The measuring location of FAMOS is chosen close to a fatigue relevant component and the points of interest are at the inner surface of the component. The calculated inner wall temperature time history will be transferred to the inner surface of the component. The thermal load cycles are well known after that step and the stress time history and also the strain rates would be calculated with the Green’s function approach. Unit transients will be used to calculate principle stresses and shear stresses in all fatigue relevant locations within the monitored component. Pressure cycles will also be evaluated with the Green’s function approach. After the calculation of the equivalent stresses the mechanical load cycles can be classified by the use of the rainflow algorithm. Comparisons (Miner’s rule) with the fatigue curve results in fatigue levels for all relevant locations within a component. In the current approach, the conservatism will be reduced with this method, and an enveloping fatigue level can still be calculated. In another words, for highly loaded components, using the current methodology can provide a more realistic stress calculation and enveloping fatigue level calculation. Depending on the number of load cycles, the new and more stringent requirements can be complied.