This thesis work involves the use of the RELAP5-3D thermal hydraulic code to model flow for a typical pressurized water reactor (PWR). A model using several three-dimensional components was created to accurately predict complex accident scenarios with greater fidelity and detail than models consisting of only one-dimensional control volumes. In order to build this model, a one-dimensional model was first used as a reference and a foundation. The three-dimensional model was then constructed from this reference model using various techniques and methodologies. These are described in this thesis and represent best practices for similar work. Additionally, a tool was constructed to enhance the ease and accuracy of utilizing both Cartesian and cylindrical components. An overview of this tool is presented in this thesis, which includes verification and validation efforts as well as a discussion on its capabilities and use. After the three-dimensional model had been finalized, it was compared to its one dimensional analogue using a variety of metrics that demonstrate its consistency with the one dimensional reference. A detailed summary of this comparison is presented in this work. The final model was developed for use in Loss-of-Coolant Accident (LOCA) scenarios that simulate hypothesized situations relating to the Nuclear Regulatory Commission's (NRC's) Generic Safety Issue 191 (GSI-191). Thus, a standard of prudence was implemented (i.e. specifications) to ensure the model would be capable of accurately predicting phenomena associated with such scenarios.
