Within the framework of activities on a pilot industrial hybrid reactor (pilot hybrid plant-PHP) development, the DEMO–FNS fusion neutron source is being designed in Russia. Russian fusion and fission community considers it as the main facility developing prospective nuclear technologies, which should update the results of the ITER researches in the field of physics and control of burning plasma. Progress in the development of the plant and simulations of the fusion fuel cycle allows starting the engineering design of basic fuel cycle systems. In this paper, we consider the new prospective of technological solutions for the tokamak fuel cycle. The possibility of their integration and the analysis of the technology readiness level for them in the Russian Federation are addressed as well. The code simulating the hydrogen isotope flows in a tokamak was significantly upgraded for evaluation of the specific technological solutions as well as for combined modeling of the fuel circulation in the core and divertor plasmas allowing for the pumping, processing, and fuel isotope content control in the plasma. The article describes the core and divertor plasma model used for the calculations and shows the D/T fuel throughput values, which should be provided by the fuel injection systems (NBI and pellets). The dependencies of the HFS and LFS pellet injection frequency necessary for the main plasma supply and ELM control are found for different core and divertor plasma parameters. For the DEMO–FNS core plasma, an operating window has been found in terms of fueling control parameters. It was shown that D and T throughputs of 40–50 Pa·m3 s−1 should be provided by the fuel injection systems (NBI and pellets) to maintain the fusion power up to 40 MW. For the DEMO–FNS core plasma, an operating window defined by the particle confinement times and fuel injection throughputs has been found.