[en] An Electric Power Research Institute (EPRI)-sponsored study to identify availability limiting factors in plant having nuclear steam supply systems supplied by Babcock and Wilcox (B and W) is described. Oconee Nuclear Unit 1, owned and operated by Duke Power Company, was the reference study plant. The study was conducted by a team from B and W representing the nuclear steam system supplier and from Duke representing the owner/operator and architect-engineer. The operation and maintenance data were assigned to one of 48 systems/components; refueling data were assigned to one of 17 work events. Limiting factors for operation, maintenance, and refueling were calculated. The formula used for calculating the limiting factor for operation considered the number of events, the loss of power, and the time to repair. The latter included indirectly related time, such as access times, acceptance times, delays, etc. Approximate formulas were also developed to calculate limiting factors for maintenance and for refueling. Each of the systems/components was ranked according to its calculated importance. Discussions were included for each system, refueling work event, and each of the 17 key valves