Results of R&D for lithium/vanadium breeding blanket design

The self-cooled lithium/vanadium blanket concept has several attractive features for fusion power systems, including reduced activation, resistance to radiation damage, accommodation of high heat loads and operating to temperatures of 650–700°C. The primary issue associated with the lithium/vanadium concept is the potentially high MHD pressure drop experienced by the lithium as it flows through the high magnetic field of the tokamak. The solution to this issue is to apply a thin insulating coating to the inside of the vanadium alloy to prevent the generation of eddy currents within the structures that are responsible for the high MHD forces and pressure drop. This paper presents the progress in the development of an insulator coating that is capable of operating in the severe fusion environment, progress in the fabrication development of vanadium alloys, and a summary of MHD testing. A large number of small scale tests of vanadium alloy specimens coated with CaO and A1N have been conducted in liquid lithium to determine the resistivity and stability of the coating. In-situ measurements in lithium have determined that CaO coatings, ∼5 μm thick, have resistivity times thickness values (p*t) exceeding 106 Ω cm2. These results have been used to identify fabrication procedures for coating a large vanadium alloy (V–4Cr–4Ti) test section that was tested in the ALEX (Argonne Liquid metal Experiment) facility. Similar test sections have been produced in both Russia and the USA.