An alternate pump trip criterion is described that meets the intent of the U.S. Nuclear Regulatory Commission pump trip requirement [i.e., to minimize primary system mass loss during a small-break loss-of-coolant accident (SBLOCA)] while providing the operators with a valuable tool to differentiate between various generic types of off-nominal transient conditions (heatup, cooldown, and loss-of-coolant accident) and to determine the efficacy of the recovery from these transients. The technique also provides a reliable measure of primary system mass inventory during heatup and cooldown transients and in the early phases of an SBLOCA. This method was developed by examining pump response to a variety of transients conducted in the Loss-of-Flow Test (LOFT) Facility. To explain the data, a mathematical model was developed based on one-dimensional pump theory. The response of the LOFT pumps was extended to full-scale commercial pressurized water reactor (PWR) pump response by examining general centrifugal pump behavior and by calculating PWR response to an SBLOCA. The results of the study indicate that the PWR pump behavior can be expected to be similar to that measured in LOFT and that the pump model can be used to gain valuable information on the status of a PWR during off-nominal transient conditions.