Aging has become a more important consideration since nuclear power plants have been in operation for decades. However, the current probabilistic risk assessment (PRA) and generation risk assessment (GRA) models are based on the assumption of constant failure rate. The consistent treatment of the dynamics of the evolution of aging and maintenance is critical to system reliability. The entry-time approach to dynamic reliability is based upon computational solution of the Chapman-Kolmogorov (generalized state-transition) equations underlying a certain class of marked point processes. Previous work has verified a particular finite-difference approach to computational solution of these equations. The objective of this work is to illustrate the potential application of the entry-time approach to PRA and GRA regarding maintenance or replacement of major systems within a plant. Results are presented in the form of plots, with replacement/maintenance period as a parameter, of associated risks and probabilities. Further recommendations for application of the entry-time approach to dynamic PRA/GRA are given at the end of the article.

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