The effect of pulse operation on tritium permeation and inventory in ITER's plasma-facing components

The estimation of tritium inventories and permeation fluxes to the coolant in the international Thermonuclear Experimental Reactor (ITER) is an import ant issue from the safety standpoint. Previous calculations have been perfo rmed neglecting ITER's pulse operation because it was assumed that during p lasma-off periods the processes become "frozen" until the plasma starts aga in. It is shown that this assumption may fail in certain cases, particularl y in the first wall of ITER, where a larger (by an order of magnitude) inve ntory and permeation flux to the coolant is obtained when pulse operation i s considered. The calculations are performed with the code TMAP4. The disco ntinuous nature of the plasma operation is mimicked by imposing on the plas ma-facing side a heat flux and a particle implantation flux in the form of a quadratic stepwise periodic function oscillating between zero (plasma off ) and a maximum value (plasma on).