A comparative study of the performance and economics of advanced and conventional structural materials in fusion systems

The impact of the neutron wall load as well as the lifetime and operating temperature of the structural material on tokamak reactor economics was investigated and a comparative study of stainless steel and vanadium alloys was performed. In order to limit the fractional increase in the cost of energy due to the plant downtime, t, for replacement of the structural material to delta, the structure lifetime, T, must be greater than t/delta where T and t are in years. Economically attractive tokamak reactors produce a neutron wall load of 3-4 MW/m2 for 3000 MW thermal power. The cost of energy is optimized by an operating temperature of the structural material in the wall/blanket in the range 475-5000C for stainless steel and 620-6600C for vanadium alloys. The gain in electric power due to higher operating temperatures is not sufficient to offset the penalty in the capital cost associated with the use of vanadium alloys as compared to stainless steel. Therefore, the vanadium alloy must exhibit a significant lifetime advantage over stainless steel to be economically competitive. The magnitude of this advantage is particularly sensitive to the plant downtime and the reference lifetime of stainless steel as well as the extent to which the refractory alloy has to be used in the heat transport system. (orig.)