Heat removal and heat conduction analyses were performed to determine the heat flux limits for a number of possible structural material/coolant combinations: SS316/H2O (5 and 14 MPa), HT-9/H2O (14 MPa), V-4Cr-4Ti/H2O (14 MPa), HT-9/He (15 MPa), and V-4Cr-4Ti/He (15 MPa). A common first-wall design geometry, similar to that of ITER, was used. With H2O coolant and steel, the ASME stress criteria were the most limiting, which constrained the surface heat flux to 0.46 MW/m2 (5 MPa) and 0.41 MW/m2 (14 MPa) for SS316 and to 1.1 MW/m2 for HT-9/H2O (14 MPa). The maximum Be temperature was most limiting for V-4Cr-4Ti/H2O (14 MPa), constraining the heat flux to 1.73 MW/m2. For this first wall geometry, which was optimized for H2O, the He-cooled designs were limited by the 2% pumping power constraint to less than 0.5 MW/m2.

The sensitivity of heat flux limits to maximum allowable material temperatures and to parameters of the model was evaluated.