AP1000 Plant Availability Analysis in Accordance With the EUR Available to Purchase

As part of the European Passive Pressurized Water reactor (EPP) Program, AP1000 plant availability analyses and studies were performed to show compliance with the European Utility Requirements (EUR) goal of an overall plant availability greater than 90%. The EUR annual Design Availability Factor averaged over a 20-year period is defined as a function of the reference duration and number of a pre-defined set of normal outages (e.g., regular refueling and maintenance, 10 years in-service inspection, turbine overhaul) as well as a function of expected forced outages. Reference duration for the regular outages has been evaluated on a deterministic basis using current experience tailored for the AP1000 18 month fuel cycle. Provision for special work has been addressed, also in a deterministic fashion, by assuming a steam generator replacement. Estimation of the annual forced outage has been addressed in a two-fold probabilistic fashion: the expected unavailability due to generic balance of plant and support systems have been derived on a system-level basis from historic operational data, relying on AP600 based information and on updated European operating plant historical information provided by European utilities participating in the EPP Program. Such system-specific analyses also addressed the evolution from the AP600 to the AP1000 design as well as EPP-specific issues (such as the increased Reactor Coolant Pumps (RCP) unavailability due to continuous use of a variable speed driver on a 50 Hz grid). A selected set of AP1000 front end systems have then been analyzed with a fully probabilistic approach by means of Fault Tree Analysis (FTA) and Reliability Block Diagram (RBD) techniques, using reliability data (i.e., failure rates and Mean Time To Repair (MTTR)) for basic components. Again, the evolution of the design from the AP600 and the previous EPP availability analysis has been factored into these studies. The result of the evaluation leads to an overall AP1000 Annual Design Availability of 93.7% averaged over a 20-year period. This exceeds the 90% EUR availability goal.