Tritium saturation in plasma-facing materials surfaces

Plasma-facing components in the International Thermonuclear Experimental Re actor (ITER) will experience, high heat loads and intense plasma fluxes of order 10(20)-10(23) particles/m(2)s. Experiments on Be and W, two of the ma terials considered for use in ITER, have revealed that a tritium saturation phenomenon can take place under these conditions in which damage to the su rface results that enhances the return of implanted tritium to the plasma a nd inhibits uptake of tritium. This phenomenon is important because it impl ies that tritium inventories due to implantation in these plasma-facing mat erials will probably be lower than was previously estimated using classical recombination-limited release at the plasma surface. Similarly, permeation through these components to the coolant streams should be re duced. In thi s paper we discuss evidences for the existence of this phenomenon, describe techniques for modeling it, and present results of the application of such modeling to prior experiments. (C) 1998 Elsevier Science B.V. All rights r eserved.