A transient tritium permeation model is developed based on a simplified conceptual DT-fueled fusion reactor design. The major design features in the model are a solid breeder blanket, a low pressure purge gas in the blanket and a high pressure helium primary coolant. Tritium inventory in the breeder is due to diffusive hold-up and solubility effects. Diffusive hold-up is assumed to be the dominant factor in order to separate the solution for the breeder tritium concentration. The model was applied to the STARFIRE-Interim Reference Design, whose system parameters yielded a breeder tritium inventory on the order of grams. The breeder pellets (average radius, 10−3 cm) reach their steady-state tritium content in approximately 4 hours from startup, assuming continuous full power operation. Both the steady-state breeder tritium concentration and the time to reach that steady-state are proportional to the square of the pellet radius.