Basic concept of JA DEMO fuel cycle

Abstract In the JA DEMO, the deuterium-tritium (DT) fuel will be supplied by a combination of gas puff, pellet injection and neutral beam injection. Since the combustion rate of fuel in the JA DEMO is approximately 1.7 %, it is necessary to establish the closed deuterium-tritium fuel cycle in the facility for fuel recycling. The fuel cycle for DEMO inevitably differs from that for ITER. Compared to the ITER fuel cycle, which requires high flexibility for fuel supply based on the requirements of plasma experiments, the flexibility required for the fuel cycle decreases in the DEMO reactor. The flow in the fuel cycle becomes steadier. Therefore, the fuel cycle of the DEMO shifts to the continuous processing system. In addition, considering the tritium breeding in the blanket, the fuel cycle must be established so that tritium in the DEMO facility can be balanced. The process components of the fuel cycle that process a large amount of tritium-containing gas are provided with multiple barriers that confine tritium, and the detritiation system processes the confined tritium. The confinement of tritium in the DEMO facility according to nuclear safety regulations is an important safety issue. As a result, the fuel cycle becomes a complex chemical plant. Assuming safety requirements, it is necessary to consider the reduction of the tritium inventory as much as possible at the design stage of the DEMO fuel cycle. The tritium inventory in the fuel cycle is closely related to the requirements to pellet manufacturing and hydrogen isotope separation, and the reduction of the requirements to the hydrogen isotope separation is the major issue in the fuel cycle. For this purpose, it is necessary to minimize the D/T separation based on the concept of direct fuel cycle with the D/T mixture. For the possible shortage in the preparation of the initial loading tritium for the DEMO reactor, it is necessary to design the fuel cycle through dynamic numerical simulation so that the fuel cycle can be started with the minimum initial loading tritium. In the system design of the fuel cycle, it is necessary to support various operation modes from the startup of DT operation to steady operation. The requirements to design the JA DEMO fuel cycle are being investigated in the JA DEMO design activity.