Figure 4
shows the results of the first wall fatigue analysis in terms of
maximum permissible heat flux as a function of wall thickness.
For the vanadium alloy structure (Figure 4a), the maximum wall
thickness is in excess of 2 mm which allows erosion rates
(presently uncertain) to be more than 240m per year.
The SiC design does not perform as well as vanadium but
is acceptable. Figure 4b shows results for .5 mm and 1 mm CVD coating
thicknesses.
Erosion of SiC must be slower
than 130
m per year for this design (assuming .5 mm CVD).
The most damaging stresses for fatigue in the vanadium design were located on the plasma-facing surface. This is a result of the cycling between tensile stress when the plasma is off and large out-of-plane compressive stresses when the plasma is on. By contrast, the highest primary stresses are on the coolant channel surface. The SiC composite first wall had a more complex stress distribution due to the sacrificial layer. In general, the highest stresses were in the blanket-facing wall.