[en] A fault tree analysis is reported of an auxiliary feedwater system intended for Westinghouse 4-loop reactors. The analysis is structured to find the comparative reliability of design variants and the comparative importance of failure modes, rather than to generate an absolute risk assessment. Many insights useful in design and operation are obtained. An auxiliary feedwater system (AFS) was chosen for study for two reasons, a recent study identified the AFS as particularly critical to PWR (Pressurized Water Reactor) safety, and several PWR power plant projects being designed by Bechtel could benefit from the deisgn insights that might arise. 7 refs