A numerical analysis of the purge flow in sphere-pac solid breeder has been carried out using the modified Darcy equations. The results show that: (1) the tritium accumulation in the purge and permeation through the wall is not a concern, (2) pressure drop expressions for fully developed flow are applicable in evaluating the pressure drop in a developing flow regime because of the very short entry length and (3) the pressure drop for low porosity (~20%) and high flow rate considered in conceptual reactor designs can be unacceptably high.