Tritium inventory issues for future reactors: choices, parameters, limits

The tritium inventory of an experimental fusion reactor or power plant is determined by a broad range of factors, including plasma physics parameters, machine operating scenario, the design and material selections for components (principally plasma facing components (PFCs) and elements of the fuel cycle), and system integration choices. The influences that these factors exert on tritium inventory, and the options available to designers to minimise tritium inventories in the plant as a whole, and especially in vulnerable systems, will be discussed in the paper. For power reactors, the potential trade-offs between plant availability and the minimisation of tritium inventory will be more critical than in experimental machines. The requirement to meet overall site release limits dictates that tritium inventories of larger machines now in detailed design (ITER) and conceptual (DEMO) phases cannot be permitted to scale linearly as a function of time-averaged fusion power from present generation machines. This necessitates the development of robust low-inventory processes, a concentrated effort on inventory segregation, the capability to follow inventory transfers between systems, and implementation of defence in depth measures such as multiple containments and engineered safety barriers throughout the plant. The progress which has been made on these topics in the last few years is reviewed and areas where additional work is necessary are identified. (C) 1999 Elsevier Science S.A. All rights reserved.