Modeling power non-recovery using the saphire risk assessment software

SAPHIRE (Systems Analysis Program for Hands-on Integrated Reliability Evaluation) is a software tool for performing probabilistic risk assessments. Within this tool, there exists the capability to create and quantify logic models depicting a nuclear power plant's response to an accident, including the potential for recovery of failed components. Specifically we discuss two methods of incorporating these "nonrecovery" basic events into the risk model via (1) the direct manipulation of the logic structure or (2) the application of "recovery" rules. Also presented are three methods of quantifying the nonrecovery probabilities, including general human reliability analysis, integration of the recovery times, and a "time series" Monte Carlo simulation approach. The results of our analysis show that introducing offsite power recovery events into the model is relatively simple. But, determining the appropriate probabilities (conditional upon specific accident sequences) is generally a non-trivial process. With the aid of time-based recovery modules in SAPHIRE, the determination of applicable nonrecovery probabilities becomes a manageable process.