Requirements of tritium breeding ratio for early fusion power reactors

Requirements of tritium breeding ratio and the initial inventory of tritium for early fusion power reactors were investigated with a calculation model. The results of calculated time-dependence of tritium inventory were examined, in particular from the following three points of view; the doubling time of tritium inventory in the storage system to provide the initial inventory of the next plant, the recovery time in which the tritium inventory in the storage system recovers to the initial value and the minimum tritium storage required during the operation. The following limits were adopted to evaluate the results, i.e., the doubling time shorter than 3 years, the recovery time shorter than 1 year and the minimum storage larger than the tritium for 50 days burn up. For a reference case, which assumes reasonable performance parameters of the fuel processing subsystems, the requirements for the tritium breeding ratio and the initial tritium inventory were estimated to be 1.10 and 27.6 kg, respectively. If a poor tritium processing system is assumed, the requirements become inevitably higher. On the other hand, mitigation of the requirements is not conspicuous even with a good processing system. The obtained results suggest that the high performance tritium processing is indispensable, but still insufficient for achievement of tritium self-sufficiency. From the point of view of tritium fuel supply, a blanket system with high tritium breeding ratio is also indispensable in early stage of fusion power reactor development, in order to introduce fusion reactors at a reasonable pace.