Failure rate updates using condition-based prognostics in probabilistic safety assessments

Probabilistic safety assessment (PSA) performs a key role in the safety assessment of nuclear power plants. In this study, in order to further utilize PSA, a new methodology was developed by incorporating the idea of condition-based prognostics to analyze plant-specific aging effects. In conventional PSA, aging effects are usually excluded because they are considered in separate aging management programs. Although aging effects are reflected, their quantification is generally conducted using generic data. Condition-based prognostics utilizes plant-specific data from condition-monitoring systems and quantifies prediction uncertainties. As a case study, the initiating event frequency of a steam generator tube rupture was demonstrated to show the update process by reflecting crack observation in the steam generator tubes and the effects of its maintenance. Furthermore, the variation to the total core damage frequency was also calculated by considering the availability of safety systems according to maintenance status, which reverts a system to its original state before aging effects.