ASSESSMENT OF ALKALI-METAL COOLANTS FOR THE ITER BLANKET

The blanket system is one of the most important components of a fusion reactor becuase it has a major impact on both the economics and safet y of fusion energy. The primary functions of the blanket in a deuteriu m-tritium-fueled fusion reactor are to convert the fusion energy into sensible heat and to breed tritium for the fuel cycle. The Blanket Com parison and Selection Study, conducted earlier, described the overall comparative performance of various blanket concepts, including liquid metal, molten salt, water, and helium. This paper discusses the Intern ational Thermonuclear Experimental Reactor requirements for a self-coo led blanket that uses liquid Li and for indirectly cooled blankets tha t use other alkali metals such as NaK. The paper addresses the thermod ynamics of interactions between the liquid metals (e.g. Li and NaK) an d structural materials (e.g. V-base alloys), together with associated corrosion and compatibility issues. Available experimental data are us ed to assess the long-term performance of the first wall in a liquid m etal environment. Other key issues include development of electrically insulating coatings for the first-wall structural material to minimiz e magnetohydrodynamic (MHD) pressure drop, and tritium permeation and inventory in self-cooled and indirectly cooled blankets. Acceptable ty pes of coating (based on their chemical compatibility and physical pro perties) are identified, and surface modifications to achieve these co atings on the first wall are discussed. The assessment examines the ex tent of our knowledge on the performance of structural materials in li quid metals and identifies needed research and development in several areas to establish performance envelopes for the first wall in a liqui d metal environment.