Special blanket design in the NB region of ITER

The paper explains the evolution of the ITER blanket design in the Neutral Beam (NB) region and the compromise among the requirements of many interacting components, such as the blanket with the first wall, the vacuum vessel and its penetrations, the NB system, the coolant manifolds and the toroidal field coils. At first a design constrained by the square shape of the blanket modules is presented, as was adopted in ITER 2001. Then, a new design is described with three special modules around the NB penetration and regular modules elsewhere. The acceptance of more complex design in a few modules improves significantly the configuration of the blanket, the strength of the module attachment and the maintenance of the machine