Probabilistic evaluation of limiting conditions of operations outage times for diesel generators

This paper presents the results of two approaches for quantitative evaluation of Limiting Conditions of Operations for Outage Times for Diesel Generators. The first approach calculates the core damage frequency conditional on the state of the Emergency ac System (EAC). These conditional frequencies can be used to determine appropriate Allowable Outage Times (AOTs). Four representative EAC systems are analysed; one with four, two with three and one with two diesel generators. The results indicate that there is substantial variability of conditional core damage probabilities within the states of a given EAC system. The variability is attributed to asymmetries in the loads of various diesels of the EAC. The second approach calculates the average unavailability of various EAC configurations and the expected reactor shutdown time given that the AOTs are predetermined at a given level. Three typical configurations (1/2, 2/3 and 1/3) were analysed for various testing schemes, levels of diesel reliabilities, repair rates and AOTs