Experimental and analytical investigations to reduce MHD pressure drop for liquid LiPb fusion blanket systems: use of ODS-FeCrAl alloys with electrically insulating α-Al2O3 layer in optimal flow channel geometry

The magnetohydrodynamic (MHD) pressure drop in a liquid–metal breeder blanket of magnetic confinement fusion reactors was studied under conditions in which an α-Al₂O₃ layer functioned as an electrically insulating layer on flow channel walls. The α-Al₂O₃ layers had a compact microstructure and uniform thicknesses up to 3.2 μm, which were formed on oxide-dispersion-strengthened FeCrAl alloys SP10 (Fe-15Cr-7Al) and NF12 (Fe-12Cr-6Al) by the oxidation treatment in air atmosphere at 1273 K and 1373 K. The electrical conductivities of the α-Al₂O₃ layers were measured and formulated in the temperature range from 291 K to 1073 K. The electrical conductivity of the layer which was formed on SP10 at 1373 K was 9.4 × 10⁻⁹ S/m at 773 K. This value was lower than those of other oxides such as ZrO₂ and Er₂O₃. The MHD pressure drop in a rectangular flow channel with an α-Al₂O₃ layer was analytically obtained under the conditions of Re = 2.9 × 10⁴ and Ha = 5.9 × 10³. The α-Al₂O₃ layer can significantly reduce the MHD pressure drop. The aspect ratio of width to height of the rectangular channel was varied from 10⁻⁵ to 10⁵ under the magnetic field applied horizontally to the channel. The additional reduction of MHD pressure drop by 74 % can be achieved when the aspect ratio changes from 1 to 16 at the cross-sectional area of 2500 mm².