Thermal-hydraulic assessment of the Steam Generator mock-up for the EU DEMO WCLL using CFD co-simulation

The Primary Heat Transfer System (PHTS) of the EU DEMO Water-Cooled Lithium-Lead (WCLL) Breeding Blanket might rely on Once-Through Steam Generators (OTSGs) technology, widely used in fission industry. ENEA is currently developing the STEAM facility, in order to characterize the behaviour of the EU DEMO OTSG. To this aim, a dedicated OTSG mock-up is being designed. The present work describes the Computational Fluid Dynamics (CFD) approach used to investigate the flow field within the inlet and outlet regions of the OTSG mock-up in steady-state conditions. One of the key objectives of the analysis is to assess the mass flow distribution within the OTSG primary bundle, as uniform distribution is crucial for achieving the desired performance. To this aim, the computational approach employs reliable models such as RANS k-epsilon as well as a fluid-fluid co-simulation routine. The aim is to reach a satisfactory self-consistency of the flow distribution within the OTSG primary bundle without the discretization of the full geometry. The CFD analysis predicts a maximum absolute deviation from the average mass flow rate value lower than 2%. This predicted behaviour is compared against a benchmark simulation that discretizes the whole primary bundle. The comparison displays an acceptable compatibility and a significant reduction in the required computational resources thanks to the implementation of a co-simulation routine.