Further Development of a Thermal-Hydraulics Two-Phase Flow Tool

The numerical simulation tool TWOPORFLOW is under development at the Institute for Neutron Physics and Reactor Technology (INR) of the Karlsruhe Institute of Technology (KIT). TWOPORFLOW is a thermal-hydraulics code that is able to simulate single- and two-phase flow in a structured or unstructured porous medium using a flexible 3-D Cartesian geometry. It has the capability to simulate simple 1-D geometries (like heated pipes), fuel assemblies resolving the sub-channel flow between rods or a whole nuclear core using a coarse mesh. The code uses six conservation equations in order to describe the coupled flow of steam and liquid. Several closure correlations are implemented to model the heat transfer between solid and coolant, phase change, wall friction as well as the liquid-vapor momentum coupling. Originally, TWOPORFLOW was used to calculate the flow and heat transfer in micro-channel heat exchangers. The main purpose of this work is the extension, improvement and validation of TWOPORFLOW in order to simulate the thermal-hydraulic behavior of Boiling Water Reactor (BWR) cores. For that aim, the code needs some additional empirical models. In particular, a turbulent lateral mixing model, and a void drift model have been implemented, tested and validated, adopting relevant tests found in the literature. Regarding reactor conditions, the BFBT critical power bundle experiments were selected for the validation.