Comment by DennisP

Some tokamaks do. MIT's ARC, for example, uses jointed superconducting tapes that let the reactor be opened up to replace the inner wall. That's done annually, and the wall is 3D-printed. Surrounding the inner wall is molten FLiBe salt, which acts as coolant, neutron absorber, and breeding blanket. Commonwealth Fusion is attempting to commercialize the design.