TRITIUM HYDROGEN BARRIER DEVELOPMENT

A review of the hydrogen permeation barriers which can be applied to t he structural metals used in fusion power plants is presented. Both im planted and chemically available hydrogen isotopes must be controlled in fusion plants. The need for permeation barriers appears strongest i n Pb-17Li blanket designs, although barriers are also necessary for ot her blanket and coolant systems. Barriers which provide greater than a 1000- fold reduction in the permeation of structural metals are desir ed. In laboratory experiments, aluminide and titanium ceramic coatings provide permeation reduction factors (PRFs) of 1000 to over 100 000 w ith a wide range of scatter. The rate-controlling mechanism for hydrog en permeation through these barriers may be related to the number and type of defects in the barriers. Although these barriers appear robust and resistant to liquid metal corrosion, irradiation tests which simu late blanket environments result in very low PRFs in comparison with l aboratory experiments, i.e. less than 150. It is anticipated from fund amental research activities that the radiation- and electric-field-ind uced enhancement of hydrogen diffusion in oxides may contribute to the lower PRFs during in-reactor experiments.