Development of an insulator coating is the criti­cal feasibility issue for self-cooled Li blankets. A very limited number of ceramics are stable under long-term exposure to Li at high temperatures. The present candidates are Er2O3, Y2O3, and, under lim­ited conditions, AlN. In addition to concept verifica­tion studies using several physical coatings, chemical or reactive coatings have been explored as a potential means to cover large and complex surfaces.

Considering the very low tolerable crack fraction (<10~6), in situ healing and two-layer coating with metallic overlayer are promising candidates. Recent loop tests with high impurity control have demon­strated that a two-layer coating with a vanadium overlayer is stable in flowing lithium. Thus, verifica­tion of in situ coatings, including the healing function, and two-layer coatings for large and complex surfaces would be the next necessary step in development.

Er2O3 is also of interest as a candidate for the required tritium permeation barrier coating.43 Thus, collaborative effort to develop this material for appli­cation in fusion blankets, either for electrical insula­tion or for tritium permeation reduction, seems to be an efficient development strategy.

Studies on the effects of radiation on the coating (resistivity and mechanical properties) are limited and
further research is necessary. In particular, the perma­nent effects of radiation need to be assessed by con­trolled irradiation experiments. In addition to the use of fission neutrons and charged particles, the opportu­nity to use the International Thermonuclear Experi­mental Reactor-Test Blanket Module (ITER-TBM) and International Fusion Materials Irradiation Facility (IFMIF) is anticipated for integrated coating function tests and high fluence 14MeV neutron irradiation tests, respectively.