The complex hydrodynamic phenomena of a Pebble Bed Modular Reactor (PBMR) are partly attributed to interconnecting flow paths. Modelling the hydrodynamic phenomena provides insight to the reactor over a wide range of operating conditions. The Systems Computational Fluid Dynamics (SCFD) approach combines the advantage of conventional Computational Fluid Dynamics (CFD) modelling in simulating the detailed flow interaction to the more robust solver applied in Flownex thermal-hydraulics software. Although this approach is inherently geometry-dependent, its application in a large network or complex model has seen a reduction in computational speed compared to the conventional CFD modelling approach, without compromising the integrity of the result. This expedites the design-analysis cycle and allows testing of a combination of design changes.Copyright © 2008 by Pebble Bed Modular Reactor (Pty) Ltd.