PREDICTING STEAM GENERATOR AUXILIARY FEEDWATER NOZZLE THERMAL STRATIFICATION TRANSIENTS AND FATIGUE EFFECTS IN COMPLEX SYSTEMS

摘要

External thermocouple measurements on auxiliary feedwater piping revealed thermal transient cycles that warranted evaluation and monitoring. Development of a fatigue monitoring system for the associated steam generator auxiliary feedwater nozzles required consideration of a number of complex factors. The thermal transients measured on the external surface often indicated the presence of thermal stratification cycling of the contained fluids. The characteristics of the transients were influenced by complex combinations of the thermal hydraulic influence of four interacting systems. The transient characteristics were found to be very sensitive to small changes in the system parameters. This paper describes methods used to simulate these complex system characteristics and obtain reasonable predictions of local thermal transient characteristics that correlate with the measured data. The predicted transient loads are used to calculate the related stress and fatigue impact in the nozzles.