The contribution of tritium fuel system construction and operation to the global COE and the life-cycle GHG emissions is analysed using PEC reactor system design code for both magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. This contribution is less than a few percents in the present model, but the CO2 emissions from the ICF fuel system are rather higher than those from MCF, because of the DT pellet fabrication processes.