Methodology for Calculating the Hydrogen Isotope Inventory in Tritium Fuel Cycle Systems of the DEMO-FNS Tokamak

The applied technologies for handling tritium and the efficiency of its use in the fuel cycle of a fusion facility affect the start-up tritium inventory, the possibility of tritium self-sufficiency, etc. These parameters largely determine the cost of the facility, its efficiency, and safety during operation. Formation of the conceptual configuration of the fuel cycle, calculation of the tritium inventory in its systems, and determination of the scope for further development are important problems in facility design. In order to calculate the flows of fuel components and tritium inventory in the fuel cycle (FC) of a tokamak-based fusion neutron source, the FC-FNS code developed at the Kurchatov Institute has been used since 2013. It implements the possibility of calculating the number of hydrogen isotopes contained in different FC systems. The article describes the current state of research on modeling the flow of fuel components in FC systems of the tokamak with a tritium-breeding blanket, presents simplified schemes of FC systems, and describes the principles of their operation and the methodology for calculating the inventory of hydrogen isotopes in them. It is substantiated that the number of fuel components in the facility will be primarily determined by fuel cycle technologies, which, in turn, depend on plasma parameters and scenarios of facility operation. It is shown that, for the DEMO-FNS project with a fusion power of 40 MW, which corresponds to the combustion of 7 × 10^–5 g/s of tritium, the startup tritium inventory will be 400–430 g with a circulating fuel flow through the facility chamber of up to 0.1 g/s. Increasing fuel flows through the injection, hydrogen isotope separation, and some other DEMO-FNS systems, if convective edge-localized modes (ELMs) are taken into account, will lead to an increase in the operational tritium inventory in the fuel cycle up to 500 g. If there is a tritium-breeding blanket in the facility, tritium inventory in it (including the long-term storage) will be no more than 800 g.