Simple models for radial transport in the bulk plasma, for hydrogen recycling in a poloidal divertor and for the scrape-off layer as a link between these two regions are combined and used to study hydrogen refuelling and helium pumping in a thermonuclear tokamak reactor. It is shown that the helium pumping requirements impose restrictions on the hydrogen refuelling depth and the minimum hydrogen flux to be pumped together with helium. Pellet refuelling with penetration of only a fraction of the minor radius seems to be adequate for INTOR.