Numerical modeling of first experiments on PbLi MHD flows in a rectangular duct with foam-based SiC flow channel insert

• Numerical studies were performed as a pre-experimental analysis to the experiment on MHD PbLi flows in a rectangular duct with a flow channel insert (FCI).
• Dynamic testing of foam-based SiC foam-based CVD coated FCI has been performed using MaPLE facility at UCLA.
• Two physical models were proposed to explain the experimental results and 3D and 2D computations performed using COMSOL, HIMAG and UCLA codes.
• The obtained results suggest that more work on FCI development, fabrication and testing has to be done to assure good hermetic properties before the implementation in a fusion device.

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 drop and to decouple the temperature-limited ferritic structure from the flowing hot lead-lithium (PbLi) alloy. The main focus of the paper is on numerical computations to simulate MHD 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 h) 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 using 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 the experimental results. Although the computations do confirm that the SiC FCI can significantly reduce the MHD pressure drop, these first testing results that yet do not match the theoretical predictions, suggest that 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.