Shielding Design of ITER Pressure Suprression System

Pressure relief lines are installed to cope with the unexpected in-vessel pressurization due to LOCA in the vacuum vessel of ITER. Since neutrons stream through the line, it must be designed so that the activation of components in the line is low enough for the maintenance work. Several designs of the pressure relief lines were studied with a simple design code DUCT-III, and the reasonable condition for the duct size, number of bends and the lengths of the legs were estimated to suppress the activation of the rupture disc. On the other hand, neutron permeation from the first to the second or third leg through the duct shield may also enhance the activation. The permeation was studied by Monte Carlo calculations with MCNP code, and 0.15 m thick iron shield was estimated enough to suppress the permeating neutrons. In addition, the volume of the shield may be reduced by about 30% if the optimized iron shield structure having localized thickness against the intense permeation path is employed