To model the fuel supply in nuclear fusion reactors with D-T burning plasmas, the relationship among the D/T fuel ratio, tritium consumption, and reactor output power is analyzed numerically using the TOTAL (toroidal transport analysis linkage) simulation code. In the case that a deuterium-rich pellet is employed, the amount of tritium to be injected to the reactor as the fuel can be reduced compared with the case when the D to T ratio is the same. The fusion output power can be adjusted by controlling the D/T ratio while the electron density is fixed. This control method of the output power by D/T ratio scan can save the tritium consumption compared with that by the density scan, especially in the cases with lower fusion output power.