Fatigue Monitoring of BWR Feedwater Nozzles

Implementing a stress based fatigue monitoring system, including all six stress terms per NB-3200 methodology, can help to reduce conservatism associated with design basis fatigue calculations. The boiling water reactor (BWR) feedwater nozzle is a perfect example of a location that has been analyzed in detail, but can still have many conservative assumptions in the design basis fatigue calculations or when using a single stress term Green’s function. The BWR feedwater nozzle is also typically subjected to operational changes such as transient ramp time and cycle count changes. Some important differences between the simplified single stress term methodology and the advanced six stress term methodology will be briefly outlined. Furthermore, a stress based fatigue monitoring system can automatically take into account operational changes that might affect fatigue calculations. This paper will explore the implementation and benefits for using a stress based fatigue monitoring system to monitor locations associated with a BWR feedwater nozzle.