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The need for extending lifetimes of nuclear power plants and an increased interest in passive safety systems in Generation III+ and small modular reactors has brought a new focus in probabilistic risk assessment (PRA) to the treatment of passive systems, structures and components (SSCs).Although previously thought to play a lesser role in determining plant risk, research and industry experience have shown that degradation mechanisms of passive SSCs increase in importance with extended operating lifetimes.The case study analyzed in this research involves an accident scenario, in which steam generator tubes degraded by stress corrosion cracking rupture due to depressurization following a steam line break resulting from flow-accelerated corrosion.This study was performed by developing a state-dependent risk model.The model has the capability of using traditional PRA tools such as event trees and fault trees to determine a state-dependent core damage frequency.Unlike traditional PRA, which emphasizes active components, this methodology was used with a mechanistic aging model of a passive component.In addition, the model considers the effectiveness of the surveillance program and may be further developed to account for the possibility of component rejuvenation.Thus, the model allows for a time-dependent assessment of plant aging on risk.The application of the model to the Zion Nuclear Power Station has indicated that the maximum core damage frequency over the plant lifetime for a steam line break-This research is being performed using funding received from the DOE Office of
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