Maximum implementation capacity of commercial fusion reactors based on bree
ding and supply of tritium has been investigated. The implementation capaci
ty of fusion power reactors depends upon the net tritium breeding gain and
a requirement of the initial supply of tritium for a steady commercial oper
ation. In the reference case, the maximum implementation capacity is 7 GWe
in 10 years after the year of fusion introduction, 118 GWe in 20 years and
488 GWe in 25 years. It is mainly limited by the industrial construction ca
pacity after 25 years. The maximum implementation capacity is largely depen
ds on the preparation interval of operation as well as the tritium breeding
performance. It means that subsequent reactors must start operation as soo
n as possible not to leave produced tritium. The requirement to the tritium
breeding for a satisfactory implementation effusion power plants is also d
iscussed. In the case that fusion implementation is similar to the increase
of fission reactors in last 40 years, tritium breeding ratio of 1.08 will
be required for the early plants. On the other hand, tritium breeding ratio
of 1.02 is sufficient when fusion plants are widely deployed.