Vanadium alloys for fusion reactor first wall application

The first wall of a tokamak-type of fusion reactor separates the blanket/coolant from the plasma, provides for mechanical stability of the torus, and maintains a vacuum in the plasma chamber. Current tokamak designs require the first wall to withstand a neutron flux of 0.4 to 1.2 x 1019 neutrons m-2 s-1, with 20% of the neutrons having an energy of 14.1 MeV. In addition to the high displacement damage, fusion neutrons will produce 20 to 30 times more helium and hydrogen in the wall than a reactor like EBR-II. Recently, the need for the first wall to demonstrate a low residual activity created a renewed interest in the refractory metal vanadium. Compared to the austenitic and ferritic stainless steels, vanadium and its alloys also provide lower thermal stresses for given flux, good strength at elevated temperatures, excellent compatibility with Li (a proposed coolant/blanket material), and lower nuclear heating, helium generation, and void-swelling rates. Major concerns regarding the use of vanadium alloys for a first wall include: cost, reactivity with light elements (C,N,O,H) as well as various coolant/blanket materials, and resistance to radiation damage. These latter two areas will be reviewed in this paper