NONMETALLIC MATERIALS FOR PLASMA FACING AND STRUCTURAL APPLICATIONS IN FUSION-REACTORS

In this article the properties of nonmetallic materials are reviewed with regard to potential applications in fusion reactors. Among the variety of materials carbon and carbides show the best potential for use. TiC and isotopically purified B4C are candidates for 1-2 mm thick protective coatings for the first wall. The plasma spray technique would provide the potential for in-situ repair of the coatings. In addition to the use on steel structures, the low activation of such coatings would well match with low activation V-alloys in later reactors. With regard to bulk materials the neutron damage behaviour of CFCs and of SiC/SiCs was reviewed and limits for plasma facing applications with regard to surface heat flux and neutron fluence are suggested. CFCs would reach the fluence goal for the ITER Physics Phase, but miss the fluence goal for the ITER Technology phase by a factor of two. SiC/SiCs which have been advocated as fusion reactor materials in the past few years, would reach the fluence goals for moderate heat flux components of ITER, but may be not yet be ready for use in ITER from a technology point of view. They miss the fluence goals for DEMO by a factor of about 3 and those of a prototype reactor by a factor of 10. With regard to structural applications of SiC/SiC, the use in receeded areas of the blanket with softer neutron spectrum would possibly allow operation to reasonable lifetimes of the component. Issues, as the poor hermeticity of SiC/SiC and the joining technology of ceramic components remain to be solved.