The RETRAN code was developed in recognition of the need for utilities with a small analysis staff to be able to perform best-estimate analyses of operational transients. It provided General Public Utilities with a powerful tool for independent analysis of dynamic plant performance. Previously, all such best-estimate analyses were rarely performed, and only vendors, consultants, and large utilities had the required capability. The use of RETRAN by our own staff on our in-house computer has allowed us to establish our own schedules for a variety of analysis applications. In addition, the general nature of RETRAN allowed for the analysis of many different events with only minor changes to the model and for the modeling of both pressurized water reactor and boiling water reactor plants with the same code. To date, RETRAN has been successfully used to predict plant performance for the purposes of design optimization, short-term operational support, in-house support of licensing, and operator training activities. Plant procedures and postulated transient scenarios have been verified using RETRAN. Inferences have been made regarding the behavior of unrecorded plant parameters using the recorded parameters and iteratively varying the unknowns until a consistent simulation was obtained. This approach is presently being refined with the use of RETRAN control system models to preclude the need for iterative analyses. Our activities with RETRAN have given us confidence in the ability of the code to provide accurate thermal-hydraulic simulations, including simulations that require thermal-hydraulic and control system coupling. The importance of benchmarking against actual plant data as a means of providing confidence in the code and the particular plant models cannot be overemphasized. The control system models in RETRAN have been shown to provide a great deal of flexibility in displaying results in terms familiar to operations personnel and as a general means of problem solving. We anticipate an increased usage of RETRAN for operator training and procedure development. We also plan to conduct analyses of expected plant performance during different modes of operation such as startups and load changes. It is further anticipated that RETRAN will be used to provide prepredictions of plant performance during the Three Mile Island Unit 1 startup testing program. Future applications will include analyses in support of fuel reloads and plant modifications.