Development of Automated Cycle Counting Algorithms for APR1400 Fatigue Monitoring System

Effect of light water reactor environments on fatigue behavior in the reactor coolant system structural materials has been an issue for decades among nuclear industries and safety regulators, particularly for the design of long-life nuclear power plants including APR1400. In 2007, U.S.NRC issued Regulatory Guide 1.207 for use in the design analyses of new reactors, incorporating the fatigue life reduction of pressure boundary components due to the effects of the plant environment. The environmental fatigue is considered as a safety issue, and thus the highest quality standard issue for new plant design. APR1400 Fatigue Monitoring System (FMS) is being developed to evaluate actual loads and fatigue usages in critical components over the plant lifetime. The automated cycle counting system (ACCS) is one of the APR1400 FMS main modules used to count the occurrences of design basis events for calculation of accumulated usage factor of plant components. The purpose of this paper is to introduce the ACCS algorithms developed by KEPCO E&C, which are effective for evaluation of the integrity of APR1400 NSSS components. The APR1400 FMS ACCS algorithms are being developed to effectively count the occurrence of design basis set of transients. The process of verification and validation for event counting logic using actual and virtual plant operation data will enhance the credibility of the ACCS in calculating the CBF usage of selectively monitored components of APR1400 plants.