Assessment of alkali metal coolants for the ITER blanket

Abstract

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 safety of fusion energy. The primary functions of the blanket in a deuterium-tritium-fueled fusion reactor are to convert the fusion energy into sensible heat and to breed tritium for the fuel cycle. The Blanket Comparison 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 International Thermonuclear Experimental Reactor requirements for a self-cooled blanket that uses liquid Li and for indirectly cooled blankets that use other alkali metals such as NaK. The paper addresses the thermodynamics of interactions between the liquid metals (e.g. Li and NaK) and structural materials (e.g. V-base alloys), together with associated corrosion and compatibility issues. Available experimental data are used to assess the long-term performance of the first wall in a liquid metal environment. Other key issues include development of electrically insulating coatings for the first-wall structural material to minimize magnetohydrodynamic (MHD) pressure drop, and tritium permeation and inventory in self-cooled and indirectly cooled blankets. Acceptable types of coating (based on their chemical compatibility and physical properties) are identified, and surface modifications to achieve these coatings on the first wall are discussed. The assessment examines the extent of our knowledge on the performance of structural materials in liquid metals and identifies needed research and development in several areas to establish performance envelopes for the first wall in a liquid metal environment.