A first wall construction for a tokamak reactor is disclosed, comprising a series of hollow lobes, each having a pair of side wall portions with a curved end wall portion extending therebetween. Each lobe is adapted to withstand substantial pressure on the concave side of the curved end wall portion while withstanding substantial heat flux on the convex side. The curved end wall portion has a shape which is approximately cylindrical in curvature but differs from being circular in curvature by a substantial deviation, in that such curved end wall portion is flatter in curvature than a truly circular curvature by the amount of such deviation, such that the thermal stresses generated in the curved end wall portion by such heat flux are at least approximately balance or neutralized by the bending stresses generated in such curved end wall portion by such pressure. The curvature may correspond generally in shape to the flatter half of an ellipse. Each hollow lobe may comprise a generally plate-like member formed in one piece into such side wall portions and such curved end wall portion, or may be formed with a plurality of peripheral corrugations affording a flexible bellows action to relieve stresses in a direction transverse to such corrugations. The invention is applicable to other vessels subjected to similar pressure and thermal stresses.
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