The RETRAN-01 system thermal-hydraulics analysis code has been used to simulate the Peach Bottom Unit 2 boiling water reactor (BWR) turbine trip tests. Since these studies have been performed, a second version of the code, RETRAN-02, has been developed and released. The RETRAN-02 code has a number of physical models that did not exist in RETRAN-01. These include slip between phases, subcooled voiding, special steam separator, one-dimensional kinetics, and iterative numerics models. The new models that exist in RETRAN-02 allow a more realistic modeling of the physical phenomena that occur, in particular, in a BWR. The effect of these new models is studied through the analysis of one of the Peach Bottom turbine trip tests. Each model’s effect is easily observed since the models are applied one at a time. It was demonstrated that if the same options are used in both RETRAN-01 and RETRAN-02, essentially the same results are obtained. This is important because of the large amount of validation that has been performed with RETRAN-01. The results using the new models demonstrate that they are capable of more realistically describing the physical phenomena that occur during a turbine trip in a BWR.