A best-estimate methodology for analysis of an anticipated transient without scram (ATWS) in a pressurized water reactor (PWR) is applied to the simulation of the passive response to postulated ATWS scenarios of the José Cabrera (Zorita) nuclear power plant (NPP) owned and operated by Union Fenosa, which is the only Westinghouse PWR with a single coolant loop. A justification of the calculation hypotheses is included. The results of the specific studies are evaluated, and the conclusion is that the intrinsic safety margins of the original design of the plant guarantees the integrity of the fuel, primary circuit, and containment, without the need to incorporate an automatic ATWS mitigation system. Finally, a suitable plant-specific prototype emergency operating procedure is designed that is substantially different from the previous Zorita NPP procedure and from the generic procedure applicable to multiloop plants. This procedure is validated by simulating the operator-plant interface by means of a validation matrix including the scenarios presenting the most adverse dynamic modes foreseeable.