Use of On-Line Fatigue Monitoring of Nuclear Reactor Components as a Tool for Plant Life Extension

The application of an on-line fatigue monitoring system for tracking fatigue usage in operating power plants is described. The system, like several others which have been developed, uses the influence function approach, operates on a microcomputer, and determines component stresses using temperature, pressure, and flow rate data that are typically available from plant computers. Using plant-unique influence functions developed specifically for each component location, the system calculates stresses as a function of time and computes the fatigue usage. Stress values are calculated at time intervals defined by the user and the fatigue values are saved on files for use at a later time. The application of the GE Fatigue Monitoring System (GEFMS) to calculate fatigue usage in the feedwater nozzle of a GE Boiling Water Reactor is described in this paper. Stress predictions using GEFMS for a sample temperature transient show excellent agreement with results from finite element thermal and stress analysis performed on a mainframe computer. Fatigue usage calculations for a simulated 24-hr temperature record confirm that the system provides accurate results at a cost that is significantly lower than similar analysis done on mainframe computer systems. The system, which has been installed in a boiling water reactor plant, provides the technical basis to evaluate actual reactor conditions and justify plant life extension.