Fabrication of CaO insulator coatings by MOCVD for application in vanadium/lithium blankets

The blanket system is one of the most important components in a fusion reactor because it has a major impact on both the economics and safety of fusion energy. The primary functions of the blanket in a deuterium/tritium-fueled fusion reactor are to convert the fusion energy into sensible heat and to breed tritium for the fuel cycle. The self-cooled liquid metal blanket concept requires an electrically insulating coating on the first-wall structural material to minimize the magnetohydrodynamic (MHD) pressure drop that occurs during the flow of liquid metal in a magnetic field. Calcium oxide is a possible coating material because it is an excellent electrical insulator and it has large negative free energy to prevent the attack from liquid lithium. In this paper, details are presented on the metallorganic chemical vapor deposition (MOCVD) method that was used to fabricate the CaO coating. The as-deposited CaO coating was annealed in calcium vapor to prevent coating spallation. Composition and phase analyses of the coating were performed by energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD). Scanning electron microscopy (SEM) showed that the coating did not crack after several thermal cycles from room temperature to 715 °C. The resistance of the coating was high enough for application as an insulating coating for the self-cooled lithium blanket in fusion systems. The information on Li compatibility is only preliminary and additional effort is needed to evaluate their long-term performance in fusion-relevant conditions.