This webinar demonstrates how Flownex and Ansys SpaceClaim can be used together to streamline the setup of prismatic block fuel reactor models for nuclear simulations. By using Python scripts in SpaceClaim, key reactor geometry parameters are automatically extracted from CAD models and written directly into Flownex, reducing manual input and minimizing potential errors. The completed reactor model is then used to simulate a depressurized loss of forced cooling (DLOFC) accident, where a pipe rupture causes coolant loss and reactor temperature changes over several days. Results show how Flownex captures complex thermal-hydraulic and neutronic behavior, including pressure blowdown, fuel temperature evolution, decay heat effects, and xenon-induced recriticality. The presentation highlights Flownex's capability to efficiently model advanced reactor designs, accident scenarios, and long-duration transient analyses for nuclear safety evaluations.