Reconciliation of fatigue usage factors for class-1 components considering plant operation history

The evaluation of metal fatigue for the period of extended operation requires a time-limited aging analysis (TLAA) and is an important task for Nuclear Power Station. Both cumulative usage factors of components and the actual numbers of design transient cycles have to be reviewed. The factors of environment are also imposed on metal fatigue by NRC as a multiplier. In reviewing the cycles of a generic BWR pressure vessel design transients, the number of cycles of some design transients have no sufficient margin for current license basis even for period of extended operation. The operating margins of technical specification, operating cycles of design transients and cumulative usage factors of components, are subjected to severe challenge under the review of license renewal. The objective of this study aims to relieve such limits by using design transients reconciliation based on existing plant operating history. The predicted fatigue usage factors of Feed water nozzle of the reactor vessel are shown as an example using the adjusting cycles of design transients.