Considerations on fatigue stress range calculations in nuclear power plants using on-line monitoring systems and the ASME Code

Nuclear power plants are generally designed and inspected according to the ASME Code. This code indicates stress intensity (SINT) as the parameter to be used in the stress analysis of components. One of the particularities of SINT is that it always takes positive values, independently of the nature of the stress (tensile or compressive). This circumstance is relevant in the Fatigue Monitoring Systems used in nuclear power plants, due to the manner in which the different variable stresses are combined in order to obtain the final total stress range. This paper describes some situations derived from the application of the ASME Code, shows different ways of dealing with them and illustrates their influence on the evaluation of the fatigue usage factor through a case study.