A detailed RETRAN model of the secondary side of a Westinghouse model E steam generator has been developed to predict steam generator water level and primary side exit (cold-leg) temperature during startup testing and operational transients. These two parameters were identified as important in measuring the behavior of this steam generator RETRAN model. A nodalization study was performed to determine the minimum number of nodes (or control volumes) required in the secondary side to model the response of these two parameters for the transients of interest. The nodalization study began with a relatively detailed base model that represented each of the major secondary side regions. Included on the secondary side are the preheater region, upper and lower downcomer regions, primary steam separators, and leakage flow paths to account for the recirculation flow and flow branching. Eight modifications were developed from the base model to identify the sensitivity of various regions of the steam generator secondary side. Six transients were used as forcing functions to generate the response of the two steam generator parameters for each nodalization. The six transients represented a spectrum of secondary side initiated transients for which this model will be used. The impact on steam generator water level and cold-leg temperature due to a change in nodalization was evaluated for each transient. The nodalization study has identified the importance of the preheater region and the recirculation loop on the steam generator model performance. As long as secondary side water level remained above the tube bundle and below the steam dome, the two parameters of interest were insensitive to the nodalization of the upper tube bundle, lower downcomer, and steam dome regions.