A flow channel insert (FCI) is the key element of the DCLL blanket concept. The FCI serves as electrical and thermal insulator to reduce the MHD pressure dropand to decouple the temperature-limitedferritic structure from the flowing hot lead-lithium(PbLi) alloy.The main focus of the paperis on numerical computationsto simulateMHD flows in the first experiments on PbLi flows in a stainless steel rectangular duct with a foam-based silicon carbide (SiC)FCI. A single uninterrupted long-term (~6500 hrs) test has recently been performed on a CVD coated FCI sample in the flowing PbLi in a magnetic field up to 1.5 T at the PbLi temperature of 300°C in the MaPLE loop at UCLA. An unexpectedly high MHD pressure drop measured in this experiment suggests that a PbLi ingress into the FCI occurred in the course of the experiment, resulting in degradation of electroinsulating FCI properties. The ingress through the protective CVD layer was further confirmed by the post-experimental microscopic analysis of the FCI. The numerical modeling included 2D and 3D computations using HIMAG, COMSOL and a UCLA research code to address important flow features associated with the FCI finite length, fringing magnetic field, rounded FCI corners and also to predict changes in the MHD pressure drop in the unwanted event of a PbLi ingress.Two physical/mathematical models have been proposed and 3D and 2D computations performed to explain theexperimental results. Although the computations do confirm that the SiC FCI can significantly reduce the MHD pressure drop, these first testing resultsthat yet don't match the theoretical predictions, suggestthat more work on the FCI development and testing is still needed, first of all to ensure that the FCI can withstand PbLi ingress in a long run.