Thermal Stratification in Steam Generator Feedwater Lines

In recent years cracks have been found in the inlet nozzles of feedwater lines of steam generators. These cracks occur as a result of material fatigue. Thermal stratification in the feedwater is probably one of the factors primarily responsible for the fatigue. This paper describes methods of calculating the stress intensity ranges occurring as a result of the stratification. In addition, a design modification (a diversion tank) is proposed which effectively prevents the occurrence of this load case.