Environmental Fatigue Analysis of the Feedwater Piping System of a BWR-5

The fatigue analyses are usually carried out with experimental data obtained in dry conditions. Nevertheless, a wet environment significantly affects the fatigue life of the elements exposed to these conditions. In this paper, the structural integrity of a feedwater piping system of a boiling water reactor (BWR-5), under wet environment fatigue conditions during 40 and 60 years of operation, was evaluated. A structural analysis of the piping system, between the feedwater nozzle and the adjacent piping support to the reactor pressure vessel, was done. The transient conditions, which are developed during the start-up and shut down, were taken into account. The fatigue analysis was developed in accordance with the Section III of the corresponding ASME Code. The environmental factors, which are related with the contact between the water and the internal surfaces of the piping system, were considered as penalty parameters. The procedure explained in the NUREG 6909 was followed. The results showed that the environmental conditions increased the cumulative usage factor, in comparison with those calculated in dry conditions.