Fabrication Aspects and Performance Characterization of α-Al2O3/ALPO4 Based Sandwich Configuration Flow Channel Inserts and Coatings for High Temperature Liquid Metal Applications

Liquid metals (LMs) exhibit several key characteristics justifying their utilization as coolants/breeders for nuclear fusion reactors and advanced fission reactors. In a fusion reactor, LMs confront a large flow retarding MHD force, imposing significant demands on pumping power and designs of ancillary systems. Corrosion of structural materials and coolant chemistry control are vital issues common to both fusion and fission reactors employing liquid lead (Pb) and its alloys. To address these concerns, technological solutions such as Flow Channel Inserts and corrosion resistant coatings are being investigated to provide a chemical/electrical isolation between LM and structural material. In this study, three prototype geometries (circular, square and 90 bend) of steel-insulator-steel FCIs are fabricated and an electrical insulation characterization is performed over a temperature range of 100C - 600C. Welding trials and pressure tests are performed to validate the electrical and mechanical integrity over typical fusion reactor operational regime. This paper presents detailed fabrication aspects along with quantitative estimations of insulation filling density, electrical insulation performance and, for the first time, a systematic study of insulation degradation owing to combined effects of TIG welding, pressure and machining operations. Critical details derived from metallurgical examinations and destructive tests are also presented. From implementation perspective towards LFRs, a feasibility assessment of a-Al2O3/AlPO4 thin film coating deposition on planar and non-planar substrates is performed followed by its mechanical characterizations. Detailed metallurgical analyses are presented to assess Pb ingress after 700 hour exposure to molten Pb alloy.